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Architecturally hindered crystallization of bottlebrush graft copolymers offers a reaction- and solvent-free pathway for creating injectable elastomers with tissue-mimetic softness. Currently, injectable materials involve solvents and chemical reactions, leading to uncontrolled swelling, leaching of unreacted moieties, and side reactions with tissue. To address this issue, bottlebrush copolymers with a poly(ethylene glycol) (PEG) amorphous block and crystallizable poly(lactic acid) (PLA) grafted chains (A- g -B) were synthesized, with grafted chains of controlled length arranged along the backbone at controlled spacing. The densely grafted PEG brush is leveraged to architecturally control both the rate and degree of crystallization of PLA grafts, offering tunability of mechanical properties as a function of architecture and time in a single-component solvent-free system covering a broad range of aggregation states comprising fluid-, paste-, and elastomer-like behaviors with modulus ranging from 1 to 50 kPa. The PLA- g -PEG pastes are particularly interesting, as they combine solvent-free injectability and time-controlled formation of shape-persistent elastomers at constant temperature. This molecular paste platform may advance reconstructive surgery, drug depots, and tissue engineering.

Silicones find use in a myriad of applications from sealants and adhesives to cooking utensils and medical implants. However, state-of-the-art silicone parts fall short in terms of shape complexity and reprocessability. Advances in three-dimensional printing and the discovery of vitrimers have recently opened opportunities for shaping and recycling of silicone objects. Here, we report the 3D printing via direct ink writing of silicone vitrimers into complex-shaped parts with high strength and room-temperature reprocessability. The reprocessing properties of the printed objects result from the adaptive nature of the silicone vitrimer, which can deform under stress without losing its network connectivity. Rheological and mechanical experiments reveal that printable inks can be tuned to generate strong parts with high creep resistance and room-temperature reprocessability, two properties that are usually challenging to reconcile in vitrimers. By combining printability, high strength, and room-temperature reprocessability, the reported silicone vitrimers represent an attractive sustainable alternative to currently available elastomers in a broad range of established and prospective applications.

Mechanochromic materials exhibit color changes upon external mechanical stimuli, finding wide-ranging applications in colorimetric sensing, display technology, and anticounterfeiting measures. Many of these materials rely on fluorescence properties and therefore necessitate external optical or electrical excitation. However, for broader applicability, the detection of color changes by the naked eye only or without complicated detection instrumentation is highly desirable. Photonic crystals offer a promising avenue for attaining such performances. In this work, we present elastomeric distributed Bragg reflectors (DBRs) characterized by a series of photonic bandgaps exhibiting mechanochromic response from the near-infrared to the visible wavelengths. To achieve this, we engineered alternating thin films of a thermoplastic fluoropolymer and a styrene-butadiene copolymer using different elastomeric substrates to attain different behaviors. The reported system demonstrates a reversible and instantaneous shift of the photonic bandgaps in response to 100% strain in multiple deformation cycles. Comparing the DBR stress-strain response with the optical strain response confirms a mechanochromic sensitivity of ∼1.7-6.9 nm/% and ∼80 nm/MPa, with an optical Poisson's ratio in the range 0.3-0.7. All these properties are spectrally dependent, as demonstrated by exploiting the properties of different diffraction order photonic band gaps.

Stretchable electronics has received major attention in recent years due to the prospects of integrating electronics onto and into the human body. While many studies investigate how different conductive fillers perform in stretchable composites, the effect of different elastomers on composite performance, and the related fundamental understanding of what is causing the performance differences, is poorly understood. Here, we perform a systematic investigation of the elastomer influence on the electromechanical performance of gold nanowire-based stretchable conductors based on five chemically different elastomers of similar Young's modulus. The choice of elastomer has a huge impact on the electromechanical performance of the conductors under cyclic strain, as some composites perform well, while others fail rapidly at 100% strain cycling. The lack of macroscopic crack formation in the failing composites indicates that the key aspect for good electromechanical performance is not homogeneous films on the macroscale but rather beneficial interactions on the nanoscale. Based on the comprehensive characterization, we propose a failure mechanism related to the mechanical properties of the elastomers. By improving our understanding of elastomer influence on the mechanisms of electrical failure, we can move toward rational material design, which could greatly benefit the field of stretchable electronics.

Continuous pulse wave detection can be used for monitoring and diagnosing cardiovascular diseases, and research on pulse sensing based on piezoelectric thin films is one of the hot spots. Usually, piezoelectric thin films do not come into direct contact with the skin and need to be connected through a layer of an elastic medium. Most views think that the main function of this layer of elastic medium is to increase the adhesion between the sensor component and the skin, but there is little discussion about the impact of the elastic medium on pulse vibration transmission. Here, we conducted a detailed study on the effects of Young's modulus and the thickness of elastic media on pulse sensing signals. The results show that the waveform amplitude of the piezoelectric sensing signal decreases with the increase of Young's modulus and thickness of the elastic medium. Then, we constructed a theoretical model of the influence of elastic media on pulse wave propagation. The amplitude of the pulse wave signal detected by the optimized sensor was increased to 480%. Our research shows that by regulating Young's modulus and thickness of elastic media, pulse wave signals can undergo a similar amplification effect, which has an important theoretical reference value for achieving ambulatory blood pressure monitoring based on high-quality pulse waves.

Magnetorheological elastomer thin films (MREFs) exhibit remarkable deformability and an adjustable modulus under magnetic fields, rendering them promising in fields such as robotics, flexible sensors, and biomedical engineering. Here, we fabricated MREF by introducing magnetostrictive particles (MSPs) and evaluated the magneto-mechanical coupling effect on the enhancement of sensitivity. The saturation magnetization ( M s ) in a parallel anisotropic TbDyFe-PDMS MREF was 5.8 emu/g, and the initial tensile modulus was 55% greater than that of an Iso MREF. We propose a nonlinear magnetorheological formula on the magnetostriction effect, incorporating magnetic dipole interactions and the nonlinear prestress of magnetic particles. This formula highlights the complex nonlinear relationship between the external magnetic field ( H ) and the key parameters that affect the enhanced MR effect of MSPs-MREF, such as saturation magnetization, remanence ( M r ), magnetostriction constant ( λ s ) and stress deviator in ferromagnetic particles ( S ed ) in the magnetic chain structure. Furthermore, we validate the influence of the key parameters of the rectified magnetorheological formula on a nonlinear magneto-mechanical behavior of MSPs-MREF in PDMS-based MSPs-MREF models by using finite-element simulations. Finally, we developed a biosensor based on MSPs-MREF to detect human serum albumin at low concentrations in human urine samples. There is a 4-fold increase in sensitivity, a lower detection of limit (0.442 μg/mL), and a faster response time (15 min) than traditional biosensors, which in the future might provide an effective way of detecting biomolecules of low concentrations.

Preparing an autonomous self-healing supramolecular elastomer with sunlight degradability is still a challenging task in related fields. In this work, we report a supramolecular elastomer by using the classic host–guest complexation of visible-light-photolabile picolinium-containing adamantanes (Ad) and β-cyclodextrin nanogels (β-CD). The as-synthesized elastomer possesses merits of high mechanical strength, excellent stretchability (>1500% strain), efficient self-healing (>85% at 60 min), ultrastability against electrolytes, and photodegradation properties, implying versatile applications in flexible and stretchable electronics. As proofs-of-concept, self-healable strain and pressure sensors using conductive elastomers are first fabricated, which feature exceptionally high sensitivity (e.g., 0.1% in capacitance at 0.2 kPa) and fast response to detect human body motions. A degradable and flexible supercapacitor is also fabricated using the conductive elastomer as the flexible matrix. Remarkably, both the elastomer and this supercapacitor can be degraded upon the exposure to sunlight irradiation in 48 h at very mild conditions. Therefore, it is anticipated that such a novel strategy and the as-prepared supramolecular elastomer can inspire further applications in the multidisciplinary fields of materials science, electronics, etc. [ABSTRACT FROM AUTHOR]

Block copolymers of polyisoprene and polystyrene are key materials for polymer nanostructures as well as for several commercially established thermoplastic elastomers. In a combined experimental and kinetic Monte Carlo simulation study, the direct (i.e., statistical) living anionic copolymerization of a mixture of isoprene (I) and 4-methylstyrene (4MS) in nonpolar media was investigated on a fundamental level. In situ ¹H NMR spectroscopy enabled to directly monitor gradient formation during the copolymerization and to determine the nature of the gradient. In addition, a precise comparison with the established copolymerization of isoprene and styrene (I/S) was possible. Statistical copolymerization in both systems leads to tapered block copolymers due to an extremely slow crossover from isoprene to the styrenic monomer. For the system I/4MS the determination of the reactivity ratios shows highly disparate values with rI = 25.4 and r4MS = 0.007, resulting in a steep gradient of the comonomer composition. The rate constants determined from online NMR studies were used for a kinetic Monte Carlo simulation, revealing structural details, such as the distribution of the homopolymer sequences for both blocks, which are a consequence of the peculiar kinetics of the diene/styrene systems. DFT calculations were used to compare the established copolymerization of isoprene and styrene with the isoprene/4-methylstyrene system. A variety of gradient copolymers differing in molecular weight and monomer feed composition were synthesized, confirming strong microphase segregation as a consequence of the blocklike structure. The one-pot synthesis of such tapered block copolymers, avoiding high vacuum or break-seal techniques, is a key advantage for the preparation of ultrahigh molecular weight block copolymers (Mn > 1.2 x 106 g/mol) in one synthetic step. These materials show microphase-segregated bulk structures like diblock copolymers prepared by sequential block copolymer synthesis. Because of the living nature of the tapered block copolymer structures, a vast variety of complex structures are accessible by the addition of further monomers or monomer mixtures in subsequent steps. [ABSTRACT FROM AUTHOR]

We present and discuss a sensitive spectroscopic means of detecting and quantifying network defects within a series of polysiloxane elastomers through a novel application of 19F solution state nuclear magnetic resonance (NMR). Polysiloxanes are the most utilized non-carbon polymeric material today. Their final network structure is complex, hierarchical, and often ill-defined due to modification. Characterization of these materials with respect to starting and age-dependent network structure is obfuscated by the intractable nature of polysiloxane network elastomers. We report a synthetic strategy for selectively tagging chain-end silanols with an organofluorine compound, which may then be conveniently and quantitatively measured as a function of structure and environment by means of 19F NMR. This study represents a new and sensitive means of directly quantifying aspects of network architecture in polysiloxane materials and has the potential to be a powerful new tool for the spectroscopic assessment of structural dynamic response in polysiloxane networks. [ABSTRACT FROM AUTHOR]

This work studied a flexible and stretchable magnetoactive elastomer (MAE) film consisting of carbonyl iron (CI) particles and polydimethylsiloxane (PDMS) elastomer matrix. The deformation of the MAE film was investigated using digital image correlation (DIC) and laser Doppler velocimetry (LDV) methods. The MAE film with free boundary is highly wrinkled under a magnetic field generated by an electromagnet with the current of 0.65 A. While in fixed boundary condition, the maximum deformation appears at the center point, and the maximum displacement reaches 0.63 mm when the current is 3 A. The finite element method (FEM) results demonstrate that the maximum internal stress and strain are 33 kPa and 2.3%, respectively. The FEM results are in good agreement with the DIC and LDV tests. With the exceptional magnetic controllability, the MAE film can find extensive applications in intelligent control systems, acoustic absorption devices, and haptics. [ABSTRACT FROM AUTHOR]

Inspired by unparalleled adhesion of mussels, bioinspired poly(dopamine) (PDA) has been used to functionalize the surface of aluminum oxide (Al2O3) nanoparticles aiming at improving the thermal conductivity of silicone rubber (SR). The successful and effective preparation of PDA modified Al2O3 nanoparticles (Al2O3–PDA) was confirmed by XPS, HR-TEM, and XRD. The PDA coating on the Al2O3 nanoparticles improved its interfacial interaction between polymeric matrix and facilitated the uniform-dispersion of filler, leading to the 30 vol % Al2O3–PDA/SR composite that exhibited a high thermal conductivity (0.585 W/((m·K))), which was almost 400% of pure silicone rubber (0.147 W/(m·K)). In addition, the 30 vol % Al2O3–PDA/SR composite displayed a relatively low dielectric constant (4.06 at 1 kHz), which was a bit higher than that of pure SR (2.59 at 1 kHz), a big advantage for the electronic or electrical engineering application. With advantages of efficient, easy handling, controllable, and eco-friendly, this modification method provides a new universal route to improve the thermal conductivity of composites. [ABSTRACT FROM AUTHOR]

A promising way to induce shape transformation in soft materials is via spatial variation in the orientation of the alignment of liquid crystalline elastomers (LCEs). Here, we improve the nascent thermomechanial shape transformation in main-chain LCEs prepared via aza-Michael addition reactions. Specifically, increasing the alkyl length in the n-alkylamine chain extender effectively reduces the actuation temperature by destabilizing the nematic phase as well as reduces the glass transition temperature (Tg) by increasing the free volume. In addition, incorporating a hydroxyl end-group in the amine chain extender (i.e., n-alkanolamine) increases the actuation strain and improves the film quality by preventing side-chain aggregates of n-alkylamine-functionalized LCEs. Interestingly, uniaxially aligned n-alkanolamine-functionalized LCEs exhibit an unprecedentedly large elongation and an enhanced toughness even along the loading direction likely due to hydrogen bonding between chains. Thus, our study highlights that the choice of amine chain extender during LCEs synthesis can be an efficient strategy to tailor the properties as well as to provide a new functionality in the LCEs which may expand their range of applications in shape morphing devices, smart coatings, and dynamic substrates. [ABSTRACT FROM AUTHOR]

Chain-end modification of low molar mass polybutadienes allowed the formation of thermoreversible networks based on the Diels-Alder chemistry. Furan telechelic polybutadienes with various chain length were first synthesized. Addition of a bis-maleimide (BM) compound to the liquid polymer led to the formation of elastomeric networks. Properties of this material were highly affected by the chain length of the polymer precursor and the cross-linking density, monitored by changing the quantity of the BM compound. Finally, the capacity of recycling of the rubber was shown by remolding the used material over five cycles without mechanical properties loss. [ABSTRACT FROM AUTHOR]

Chemically cross-linked elastomers are an important class of polymeric materials with excellent temperature and solvent resistance. However, nearly all elastomers are petroleum-derived and persist in the environment or in landfills long after they are discarded; this work strives to address these issues by demonstrating the synthesis of renewable, enzymatically hydrolyzable, and mechanically competitive polyester elastomers. The elastomers described were synthesized using a novel bis(β-lactone) cross-linker and star-shaped, hydroxylterminated poly(γ-methyl-ε-caprolactone). Using model compounds, we determined that the bis(β-lactone) cross-linker undergoes acyl bond cleavage to afford β-hydroxyesters at the junctions. The mechanical properties of the cross-linked materials were tunable and competitive with a commodity rubber band. Furthermore, the elastomers demonstrated high thermal stability and a low glass transition (-50 °C), indicating a wide range of use temperatures. The polyester networks were also subjected to enzymatic hydrolysis experiments to investigate the potential for these materials to biodegrade in natural environments. We found that they readily hydrolyzed at neutral pH and environmentally relevant temperatures (2-40 °C); complete hydrolysis was achieved in all cases at temperature-dependent rates. The results presented in this work exemplify the development of high performance yet sustainable alternatives to conventional elastomers. [ABSTRACT FROM AUTHOR]

Using a combination of the scaling analysis and molecular dynamics simulations, we study relationship between mechanical properties of networks of graft polymers and their molecular architecture. The elastic response of such networks can be described by replacing the brushlike strands with wormlike strands characterized by the effective Kuhn length which is controlled by the degree of polymerization of the side chains nsc and their grafting density 1/ng. In the framework of this approach we have established relationships between the network structural shear modulus G, strands extension ratio β, and architectural triplet [nsc, ng, nx], where nx is the degree of polymerization of the backbone strand between cross-links. Analysis of the simulation data shows that G could increase with β (G ∝ β), which reflects the "golden rule" of elastomers: softer materials are more deformable. However, networks of graft polymers can also break this rule and demonstrate an increase of the modulus G with decreasing extension ratio β such as G ∝ β-2. This can be achieved by changing the grafting density of the side chains 1/ng and keeping nx and nsc constant. This peculiar mechanical response of graft polymer networks is in agreement with experimental studies of poly(dimethylsiloxane) graft polymer elastomers. [ABSTRACT FROM AUTHOR]

We present a novel infrared thermography technique to investigate the dependence of heat capacity on deformation in cross-linked polymers. This phenomenon is directly related with the longstanding question of whether or not there is an energetic contribution to the stress in deformed polymers and, in general, to the nonisothermal, viscoelastic behavior of polymer materials. By tracking the temperature evolution of samples heated by a laser, we are able to measure heat capacity changes relative to the equilibrium value in an elastomer subjected to uniaxial extension. We find that the heat capacity increases with elongation in lightly cross-linked cis-1,4-polyisoprene. Remarkably, the onset of heat capacity dependence on deformation is observed at strains similar to those required to achieve finite extensibility. The deviation from the equilibrium value of heat capacity is consistent with an independent set of experiments comparing anisotropy in thermal diffusivity from forced Rayleigh scattering and thermal conductivity from steady-state infrared thermography. Finally, we propose a straightforward thermodynamic analysis of the results based on classical rubber elasticity. [ABSTRACT FROM AUTHOR]

Polymeric surface grafting offers a tunable way to control the interfacial interactions between a material's surface and its environment. The ability to tailor the surface properties of poly(dimethylsiloxane) elastomer (PDMSe) substrates with functional chemistry, wettability, and roughness can enhance the fields of biofouling, microfluidics, and medical implants. We developed a reversible addition-fragmentation chain transfer (RAFT) polymerization technique to synthesize a host of copolymers composed of acrylamide, acrylic acid, hydroxyethyl methacrylate, and (3-acrylamidopropyl)trimethylammonium chloride with targetable molecular weight from ~5 to 80 kg/mol and low dispersity of Đ ≤ 1.13. This RAFT strategy was used in conjunction with photografting to chemically engineer the surface of PDMSe with hydrophilic, hydrophobic, and anionic groups. Varying grafting time and copolymer composition allowed for targetable molecular weight, chemical functionality, and water contact angles ranging from 112° to 14°. These new material surfaces will be evaluated for their antifouling and fouling release potential. [ABSTRACT FROM AUTHOR]

Diels-Alder chemistry has been used for the thermoreversible cross-linking of furan-functionalized ethylene/propylene (EPM) and ethylene/vinyl acetate (EVM) rubbers. Both furan-functionalized elastomers were successfully cross-linked with bismaleimide to yield products with a similar cross-link density. NMR relaxometry and SAXS measurements both show that the apolar EPM-g-furan precursor contains phase-separated polar clusters and that cross-linking with polar bismaleimide occurs in these clusters. The heterogeneously cross-linked network of EPM-g-furan contrasts with the homogeneous network in the polar EVM-g-furan. The heterogeneous character of the cross-links in EPM-g-furan results in a relatively high Young's modulus, whereas the more uniform cross-linking in EVM-g-furan results in a higher tensile strength and elongation at break. [ABSTRACT FROM AUTHOR]

Synthetic polymers are all around us in the 21st century, ranging from commodity items made from poly(ethylene) and poly(vinyl chloride) to high-tech materials for aerospace, electronics, and medicine. Yet polymer chemistry is often neglected in formal chemical education. Once students recognize the many ways in which polymers are part of their everyday lives, they are motivated to learn about how polymers are made, their unique thermal, mechanical, and optical properties, and how plastics, fibers, elastomers, and adhesives all are possible because of long-chain molecules. Recognizing the importance of synthetic polymers as well as biopolymers, supramolecular structures, and nanoscale materials, the American Chemical Society (ACS) Committee on Professional Training now requires teaching of at least two of these topics in chemistry courses for ACS-certified undergraduate degrees. This special issue of the Journal is a contributed collection of papers describing how polymers are being taught in general, foundational, and advanced chemistry courses and also in high schools, workshops, and demonstrations for the public. The papers in general do not describe complete courses; instead, they describe modules and experiments that could be implemented at different educational levels and in different environments. The papers are sources of ideas of how instructors can incorporate polymer chemistry into their own courses. [ABSTRACT FROM AUTHOR]

An easy-to-implement science outreach demonstration featuring a mechanically and photochemically color-changing polymer is described. The active polymeric material is a filled poly-(dimethylsiloxane) (PDMS) elastomer that is covalently functionalized with spiropyran (SP), which is both a photochemical and mechano-chemical switch. The material can be reversibly changed from colorless to dark purple by exposing it to light from a blue laser pointer or providing a mechanical stimulus such as hitting the polymer with a hammer or dragging a blunt object across the surface. The keynote demonstration is a PDMS chemical-drawing board that allows children literally to "write without ink" using a laser pointer or a blunt stylus. Collectively, these demonstrations are suitable for various student groups and encompass concepts in polymer and materials chemistry, photochemistry, and mechanochemistry. This demonstration has been successfully employed dozens of times in multiple universities across North America. [ABSTRACT FROM AUTHOR]

Triclosan (TCS), a broad-spectrum antimicrobial, is used in commercial toothpastes with reported dental benefits. Our studies on 22 popular manual toothbrushes in the U.S. showed that common toothbrush head components can accumulate substantial amounts of TCS after brushing with TCS-formulated toothpastes (TCS-TPs). After simulated 3-month brushing with a commercial best-selling TCS-TP, over one third of the adults' toothbrushes showed a cumulative TCS uptake of 21-37.5 mg, equivalent to 712.5 doses of the TCS used per brushing. Similar results were observed on children's toothbrushes with small pea-size heads. Elastomer components were found to be the main contributor while both nylon bristles and elastomers could act as absorptive sinks for TCS during brushing. Studies on six different TCS-TPs containing 0.3 wt% TCS showed similar profiles of TCS accumulation. The absorbed TCS was gradually released into toothpaste slurries after switching to TCS-free alternatives. Release of TCS, which typically measured at a fraction (<75%) of the standard dose using the TCS-TPs, continued for over 2 weeks and occurred most rapidly in peroxide-containing °whitening" toothpastes, followed by alkaline and surfactant-rich toothpastes. The accumulating effect was not exclusive to TCS but was commonly observed on several chemicals identified in TCS-TPs and a range of regular toothpastes. [ABSTRACT FROM AUTHOR]

Poly(dimethylsiloxane) (PDMS) is a commonly used elastomer for fabricating microfluidic devices, but it has previously been shown to absorb hydrophobic molecules. Although this has been demonstrated for molecules such as estrogen and Nile Red, the absorption of small hydrophobic molecules in PDMS specifically used to treat cancer and its subsequent impact on cytotoxicity measurements and assays have not been investigated. This is critical for the development of microfluidic chemosensitivity and resistance assay (CSRA) platforms that have shown potential to help guide clinical therapy selection and which rely on the accuracy of the readout involving interactions between patient-derived cells and cancer drugs. It is thus important to address the issue of drug absorption into device material. We investigated drug absorption into microfluidic devices by treating multiple myeloma (MM) tumor cells with two MM drugs (bortezomib (BTZ) and carfilzomib (CFZ)) in devices fabricated using three different materials (polystyrene (PS), cyclo-olefin polymer (COP), and PDMS). Half-maximal inhibitory concentrations (IC50) were obtained for each drug--material combination, and an increase in IC50 of ~4.3x was observed in PDMS devices compared to both thermoplastic devices. Additionally, each MM drug was exposed to polymer samples, and samples were analyzed using time-of-flight secondary ion mass spectrometry (ToF-SIMS) to characterize adsorption and absorption of the drugs into each material. ToF-SIMS data showed the bias observed in IC50 values found in PDMS devices was directly related to the absorption of drug during dose--response experiments. Specifically, BTZ and CFZ absorption in both PS and COP were all in the range of ~100-300 nm, whereas BTZ and CFZ absorption in PDMS was ~5.0 and ~3.5 μm, respectively. These results highlight the biases that exist in PDMS devices and the importance of material selection in microfluidic device design, especially in applications involving drug cytotoxicity and hydrophobic molecules. [ABSTRACT FROM AUTHOR]

Self-assembly of colloidal nanospheres combined with various nanofabrication techniques produces an ever-increasing range of two-dimensional (2D) ordered nanostructures, although the pattern periodicity is typically bound to the original interparticle spacing. Deformable soft lithography using controlled deformation of elastomeric substrates and subsequent contact printing transfer offer a versatile method to systematically control the lattice spacing and arrangements of the 2D nanosphere array. However, the anisotropic nature of uniaxial and biaxial stretching as well as the strain limit of solvent swelling makes it difficult to create well-separated, ordered 2D nanosphere arrays with large-area hexagonal arrangements. In this paper, we report a simple, facile approach to fabricate such arrays of polystyrene nanospheres using a custom-made radial stretching apparatus. The maximum stretchability and spatial uniformity of the poly(dimethylsiloxane) (PDMS) elastomeric substrate is systematically investigated. A pitch increase as large as 213% is demonstrated using a single stretching-and-transfer process, which is at least 3 times larger than the maximum pitch increase achievable using a single swelling-and-transfer process. Unlike the colloidal arrays generated by the uniaxial and biaxial stretching, the isotropic expansion of radial stretching allows the hexagonal array to retain its original structure across the entire substrate. Upon radial strain applied to the PDMS sheet, the nanosphere array with modified pitch is transferred to a variety of target substrates, exhibiting different optical behaviors and serving as an etch mask or a template for molding. [ABSTRACT FROM AUTHOR]

Elastomeric polyurea is an important polymer for impact mitigation, but viscoelasticity, nonlinearity, pressure-effects, and the onset of the glass transition complicate analyses of experimental measurements. Consequently, development efforts rely on modeling, which in turn requires accurate potential functions. To address this issue, we measured the glass transition, Tg, of polyurea at pressures up to 6 GPa in a diamond anvil cell. In this method, Tg is determined as the lowest temperature at which the pressure is hydrostatic. From the pressure dependence of Tg, in combination with equation of state measurements at pressures up to 1 GPa, the density scaling exponent for the polyurea was obtained. The value 2.39 ± 0.06 is in accord with previous determinations based on lower pressure experiments; thus, density scaling remains valid for density changes as large as 50%. The scaling exponent reflects the steepness of the intermolecular repulsive potential and should serve as a guide to the choice of potential parameters for simulations of the high strain rate, high pressure dynamics of the material. [ABSTRACT FROM AUTHOR]

This work aimed at preparing supertough PA6 blends with only a small amount of elastomer. The PA6/SEBS-g-MA/PP blends were obtained by melt extrusion, in which the core-shell particles (PP as core and SEBS-g-MA as shell) could be formed in situ in PA6 matrix. The morphology of PA6 blends was explained by both the thermodynamic factor (interfacial tension and spreading coefficient) and the kinetic factor (viscosity ratio). By adjusting the loading of PP and SEBS-g-MA, the core-shell particles with suitable size could be obtained, and the notched impact strength of the PA6 blends could be significantly improved. The effects of the loading of PP and SEBS-g-MA on tensile properties were also studied. Consequently, PA6 blends with high tensile strength and excellent impact strength could be obtained by loading only a small amount of SEBS-g-MA. [ABSTRACT FROM AUTHOR]

Reinforcement, recycling, and functional applications are three important issues in elastomer science and engineering. It is of great importance, but rarely achievable, to integrate these properties into elastomers. Herein, we report a simple way to prepare covalently cross-linked yet recyclable, robust, and macroscopically responsive elastomer vitrimers by engineering exchangeable bonds into rubber-carbon nanodot (CD) interphase using CD as high-functionality cross-linker. The cross-linked rubbers can rearrange the network topology through transesterification reactions in the interphase, conferring the materials the ability to be recycled, reshaped, and welded. The relatively short chains bridging adjacent CD are highly stretched and preferentially rupture to dissipate energy under external force, resulting in remarkable improvements on the mechanical properties. Moreover, the malleable and welding properties allow the samples to access reconfigurable/multiple shape memory effects. [ABSTRACT FROM AUTHOR]

Cellulose, especially cellulose nanocrystal and cellulose nanofibril, has captured much attention as a bio-based candidate for the reinforcement of elastomers, but data in the use of regenerated cellulose (RC) from alkaline-urea-aqueous system as reinforcing agent remain scarce. In this contribution, fully bio-based hybrids were produced by flocculating a mixture of natural rubber (NR) latex and cellulose alkaline-urea-aqueous solution, during which NR latex particles were demulsificated to form the polymeric matrix while the porous honeycomb-like RC phase was also generated due to the coagulant-induced gelation, indicating that both the matrix and the filler were synchronously in situ formed by the bottom-up route. RC possesses a unique honeycomb-like structure which apparently could induce extensive physical entanglements, making the filler tightly interlocked with the matrix and therefore favoring the stress transfer. Predictably, RC, without any chemical modification, could endow NR with a pronounced reinforcement. Overall, this work provides (i) a unique inspiration for reinforcing NR with honeycomb-like cellulose and (ii) a better understanding of how could RC truly reinforce NR composites. [ABSTRACT FROM AUTHOR]

Large aspect ratio Ba0.85Ca0.15Zr0.1Ti0.9O3 (BZCT) nanofibers mat was prepared using the electro-spinning technique. Crystal structure analysis confirmed the existence of MPB between tetragonal and rhombohedra phases. The morphology study suggested the formation of discrete nanofibers having a diameter 80-250 nm. Dielectric studies were performed on sintered nanofibers and Curie temperature (TC) was measured at -108 °C, which showed a significantly improved TC than that for bulk BCZT particles. The sintered fibers mat was used for fabricating a flexible nanogenerator using room temperature vulcanized silicone elastomer. The open circuit peak voltage was measured ranging from 5.0 to 17.5 V. Peak voltage and power output were found at -2.68 V and -2.95 μW, respectively, under periodic tapping. The developed BCZT nanofibers mat-based nanogenerator may be applied in wireless microelectronics, energy harvesting devices, and self-powered sensors for structural health monitoring applications. [ABSTRACT FROM AUTHOR]

Advanced applications, involving high risk mechanical systems, require the in-service deformation level to be verified in order to assess their safety and reliability, providing information for repairing or replacing interventions. In the present work, a self-diagnostic poly(dimethylsiloxane) (PDMS) elastomer containing a supramolecular detection probe is proposed, enabling the strain intensity in the polymeric matrix to be identified by fluorescence detection. Turn-on fluorescence represents an efficient, sensitive, simple, and real time diagnostic tool to quantitatively detect high-strain regions for the mechanical monitoring of structural elements. The supramolecular complex--cross-linking the polymer's chains--provides fluorescence response induced by strain even if present in a very low amount (10-6 mol kg-1), completely preserving the mechanical characteristics of the matrix. The developed PDMS material is mechanically tested, and the observed fluorescence field is correlated with that obtained by theoretical and numerical simulations as well as by contactless measurements performed via the digital image correlation (DIC) technique. [ABSTRACT FROM AUTHOR]

Filled elastomers acquire their mechanical strength through fillers forming spanning branched networks throughout the rubber matrix. Here we study one reversibly breakable filler aggregate-to-filler aggregate contact within a network branch and its contribution to dissipative loss using molecular dynamics simulations. Our model system consists of a pair of spherical silica particles embedded in cis-1,4-polyisoprene. Variable chemical options include silanes attached to the particle surfaces at varying density and surface distribution and cross-links between polymer chains as well as chemical bonding of the polymer chains to the silica particles via silanes. We validate key properties of the pure polymer, including density, thermal expansion, and characteristic ratio as well as the dependence of the polymer network density on sulfur content. On the basis of force-vs-inter particle separation curves for cyclic loading, we obtain the energy dissipation in the contact depending on the aforementioned chemical parameters and temperature. We track the segmental relaxation peak in our model system along the temperature axis while moving the filler particle relative to one another at different speeds. From this we are able to show that the peaks in the loss-vs-temperature diagram correspond to the experimental segment relaxation in pure polyisoprene at the attendant frequencies. This in turn allows to relate the high frequency results of our atomistic simulations to the technically relevant frequency range. Finally, we investigate the structure and mobility of the polymer in the vicinity of the particles. [ABSTRACT FROM AUTHOR]

We extend the model proposed by Merabia et al. [2008] regarding reinforcement mechanisms of filled elastomers. This model is based on the presence of glassy layers around filler particles which may bridge neighboring particles. The model was solved by Merabia et al. for spherical particles only and for a single dispersion state. However, experiments show that mechanical properties depend crucially on the complex shape of fillers as well as on their spatial distribution. We consider extensively both aspects in this article. We show that the distribution state of the fillers is key for controlling the reinforcement at high temperature. For a given distribution state, we show a strong effect of filler morphology on reinforcement. Distances between fillers are smaller with fractal aggregates, which leads to stronger reinforcement. Our model opens the path for the development of systems with tailored properties by tuning the filler distribution state and morphology. [ABSTRACT FROM AUTHOR]

Engineering reversible cross-links between nanoparticles and polymer matrix is a promising avenue to reinforce the mechanical properties of elastomers and in particular soft hydrogels. In this work, we study a model system of composite hydrogel reinforced with cellulose nanofibrils (CNFs), where the integration of reversible hydrogen bonds into a lightly covalently cross-linked polyacrylamide (PAAm) matrix. This approach yields the dual cross-linked networks with synergistically improved strength, modulus, and toughness. The reversible nature of the hydrogen-bonded cross-links manifests a strong strain rate (ἑ) dependent dynamics properties. The CNF-PAAm interaction among physically adsorbed chains on the surface of CNF is examined as a function of CNF fraction by sum frequency generation spectroscopy. The results indicate a decrease of the number of free -OH groups on the CNF surface. Moreover, the deformation-resting experiments show a unique interface stiffening mechanism where the polymer chains desorbed from the CNF surface under oscillatory shear become entangled during resting time. The bending micromechanics test reveals that the CNF interfacial slip imparts the capability to strengthen the composites during deformation. The fibril pull-out process activates a series of dissipation mechanisms that increase the crack propagation resistance. These findings advance our understanding the role of interfacial layer in microscopic reinforcement mechanism and provide a constitutive foundation for exploring the deformation behaviors of the cellulosic hydrogels. [ABSTRACT FROM AUTHOR]

We report on the synthesis and properties of cholesteric liquid crystalline random terpolymers with comblike architecture as a modular platform for preparation of stimuli-responsive photonic elastomers. Ring-opening metathesis of norbornene monomers bearing n-alkyloxy cholesteryl (Ch9), n-alkoxy cyanobiphenyl (CB6 or CB12), and poly(ethylene glycol) (PEG) side chains is efficient and quantitatively yields low polydispersity random terpolymers. This terpolymer scaffold self-assembles to form cholesteric mesophases (N*) in which microphase-segregated domains of PEG side chains are randomly embedded. The cholesteric mesophase provides a 1D photonic band gap structure at optical wavelengths, which is maintained during chemical cross-linking of the norbornene backbone to form elastomers. The presence of cyanobiphenyl mesogens leads to an increase in the helical pitch of the cholesteric mesophase, resulting in a red-shift of the reflectivity relative to the pure cholesteric mesophase. By contrast, the presence of PEG blue-shifts the reflectivity, such that the overall optical properties can be readily tailored by the composition of the terpolymer. Furthermore, the mechanical properties of the materials are enhanced by the presence of the microphase-separated PEG domains which act as physical cross-links and also provide plasticization of the system. The terpolymers described here provide a modular and versatile platform for the realization of photopatternable materials that exhibit shape memory and thermochromic properties. [ABSTRACT FROM AUTHOR]

Vistamaxx performance polymer which is one type of propylene-based elastomer acting as the flexibilizer for toughening the homopolypropylene (HPP) was studied using X-ray scattering at wide, small and ultrasmall angle regimes and dynamic mechanical analysis techniques. The well-overlapped scattering curves at wide angle and ultrasmall angle indicate the unaffected structure on the atomic scale and hundreds of nanometer scale for all the compounds. The different scattering intensity at the moderate scattering vector indicates the existence of heterogeneities induced by the flexibilizer on the nanometer scale from 20 to 100 nm. The flexibilizer exfoliated the lamellae from the periodic stacks in HPP. The heterogeneities could be ascribed to the phase-separated flexibilizer and the exfoliated lamellae. The phase-separated flexibilizer domains block the formation of the complete crystalline skeleton that lowers the storage modulus of the compounds compared with the pure HPP. [ABSTRACT FROM AUTHOR]

Sustainable elastomers have undergone explosive growth in recent years, partly due to the resurgence of biobased materials prepared from renewable natural resources. However, mounting challenges still prevail: How can the chemical compositions and macromolecular architectures of sustainable polymers be controlled and broadened? How can their processability and recyclability be enabled? How can they compete with petroleum-based counterparts in both cost and performance? Molecular-biomass-derived polymers, such as polymyrcene, polymenthide, and poly(ε-decalactone), have been employed for constructing thermoplastic elastomers (TPEs). Plant oils are widely used for fabricating thermoset elastomers. We use abundant biomass, such as plant oils, cellulose, rosin acids, and lignin, to develop elastomers covering a wide range of structure-property relationships in the hope of delivering better performance. In this Account, recent progress in preparing monomers and TPEs from biomass is first reviewed. ABA triblock copolymer TPEs were obtained with a soft middle block containing a soybean-oil-based monomer and hard outer blocks containing styrene. In addition, a combination of biobased monomers from rosin acids and soybean oil was formulated to prepare triblock copolymer TPEs. Together with the above-mentioned approaches based on block copolymers, multigraft copolymers with a soft backbone and rigid side chains are recognized as the first-generation and second-generation TPEs, respectively. It has been recently demonstrated that multigraft copolymers with a rigid backbone and elastic side chains can also be used as a novel architecture of TPEs. Natural polymers, such as cellulose and lignin, are utilized as a stiff, macromolecular backbone. Cellulose/lignin graft copolymers with side chains containing a copolymer of methyl methacrylate and butyl acrylate exhibited excellent elastic properties. Cellulose graft copolymers with biomass-derived polymers as side chains were further explored to enhance the overall sustainability. Isoprene polymers were grafted from a cellulosic backbone to afford Cell-g-polyisoprene copolymers. Via cross-linking of these graft copolymers, human-skin-mimic elastomers and high resilient elastomers with a well-defined network structure were achieved. The mechanical properties of these resilient elastomers could be finely controlled by tuning the cellulose content. As isoprene can be produced by engineering of microorganisms, these elastomers could be a renewable alternative to petroleum products. In summary, triblock copolymer and graft copolymer TPEs with biomass components, skin-mimic elastomers, high resilient biobased elastomers, and engineering of macromolecular architectures for elastomers are discussed. These approaches and design provide us knowledge on the potential to make sustainable elastomers for various applications to compete with petroleum-based counterparts. [ABSTRACT FROM AUTHOR]

Hydrogels are supramolecular assemblies with both solute transport properties like liquids and mechanical properties like elastomers. To date, every type of biomolecules except ribonucleic acid (RNA), is capable of forming a hydrogel. Here, we report an RNA that forms a hydrogel by self-assembly. This RNA is originally identified by systematic evolution of ligands by exponential enrichment (SELEX) to enhance the activity of a-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors as a potential RNA drug for the treatment of cognitive disorders. The RNA hydrogel exhibits an elastic modulus plateau on the order of 10² Pa and shows dynamic RNA chain interactions with relaxation behaviors similar to living wormlike micellar solutions. Small-angle X-ray scattering and cryogenic electron microscopy characterization support the RNA network structures. By sequence mutation and rheological measurements, we reveal two key sequence motifs in the RNA responsible for intermolecular recognition and the formation of a polymer network by self-assembly. [ABSTRACT FROM AUTHOR]

Living cells sense the physical and chemical nature of their micro/nano environment with exquisite sensitivity. In this context, there is a growing need to functionalize soft materials with micro/nanoscale biochemical patterns for applications in mechanobiology. This, however, is still an engineering challenge. Here a new method is proposed, where submicronic protein-patterns are first formed on glass and are then printed on to an elastomer. The degree of transfer is shown to be governed mainly by hydrophobic interactions and to be influenced by grafting an appropriate fluorophore onto the core protein of interest. The transfer mechanism is probed by measuring the forces of adhesion/cohesion using atomic force microscopy. The transfer of functional arrays of dots with size down to about 400 nm, on elastomers with stiffness ranging from 3 kPa to 7 MPa, is demonstrated. Pilot studies on adhesion of T lymphocytes on such soft patterned substrates are reported. [ABSTRACT FROM AUTHOR]

Stereocomplex (SC) crystallites, formed between poly(l-lactide) (PLLA) and poly(d-lactide), exhibit great potential to substantially enhance crystallization rate of PLLA-based materials as an eco-friendly nucleating agent. However, the nucleation efficiency of the SC crystallites is still far below an expected level, mostly on account of their strong aggregation tendency in PLLA/PDLA melts. Herein, taking PLLA/poly(ethylene-methyl acrylate-glycidyl methacrylate) (E-MA-GMA) blends as an example, we report a unique and facile strategy to control the dispersion and distribution of SC crystallites within the PLLA matrix by using elastomeric E-MA-GMA as carrier for the incorporation of PDLA. To do this, PDLA was first blended with E-MA-GMA or chemically grafted onto the E-MA-GMA. During subsequent melt-blending of PLLA and the E-MA-GMA/PDLA master batch, the PDLA chain clusters predispersed in the E-MA-GMA phase can gradually migrate into PLLA matrix and then collaborate with the matrix chains to form large amounts of tiny and well-dispersed SC crystallites. Compared with the SC-crystallite agglomerates formed by the direct melt-blending of PLLA and PDLA components, such tiny SC crystallites are much more effective in accelerating PLLA matrix crystallization. More interestingly, when PDLA chains are grafted onto the EMA-GMA, the formed SC crystallites tend to preferentially distribute at the blend interface and thus induce not only optimal nucleation efficiency but also superior impact toughness because these interface-localized SC crystallites can also serve as bridges to enhance interface adhesion. This work could open a new avenue in designing heat-resistant and supertough PLLA blends via controllable construction of SC crystallites. [ABSTRACT FROM AUTHOR]

Non-isocyanate polyurethane (NIPU) was synthesized via cyclic carbonate aminolysis using poly(ethylene oxide) (PEO)- and poly(tetramethylene oxide) (PTMO)-based soft segments, divinylbenzene dicyclocarbonate as hard segment, and diamine–diamide (DDA) chain extender. Characterization of the resulting segmented polyhydroxyurethanes (PHUs) reveals that the use of amide-based DDA chain extender leads to unprecedented improvements in nanophase separation and thermal and mechanical properties over segmented PHUs without DDA chain extender. With PEO-based soft segments, previously known to yield only phase-mixed PHUs, use of DDA chain extender yields nanophase-separated PHUs above a certain hard-segment content, as characterized by small-angle X-ray scattering. With PTMO-based soft segments, previously known to yield nanophase-separated PHUs with broad interphase, use of DDA chain extender produces nanophase-separated PHUs with sharp domain interphase, leading to wide, relatively temperature-independent rubbery plateau regions and much improved thermal properties with flow temperature as high as 200 °C. The PTMO-based PHUs with 19–34 wt % hard-segment content exhibit tunable mechanical properties with Young’s modulus ranging from 6.6 to 43.2 MPa and tensile strength from 2.4 to 6.7 MPa, with ∼300% elongation at break. Cyclic tensile testing shows that these PHUs exhibit elastomeric recovery with attributes very similar to conventional, isocyanate-based thermoplastic polyurethane elastomers. [ABSTRACT FROM AUTHOR]

Approaches for the synthesis and processing of responsive materials that combine robust mechanical properties and the ability to undergo shape change in response to a stimulus are of intense interest. Here, we report an approach to integrate these properties by synthesizing liquid crystal elastomers (LCEs) that can be aligned and subsequently crystallized. We polymerize LCEs in the isotropic and nematic states and characterize the resulting actuation and mechanical properties. After polymerization, each of these materials can be reversibly crystallized. By crystallizing LCEs, we demonstrate stiffer and tougher shape changing materials. Notably, crystallized samples exhibit moduli 2 orders of magnitude higher and toughness 5 times higher than nematic elastomers. Heating melts the crystallinity and then induces shape change via melting of the liquid crystalline phase. These LCEs are capable of high load bearing during actuation, up to 1.3 MPa, and high work capacity, up to 730 kJ/m3. These aligned and crystallized LCEs offer promising benefits as dynamic smart materials with robust mechanical properties. [ABSTRACT FROM AUTHOR]

We report the synthesis of a new bio- and photodegradable ABA triblock copolymer that combines the high modulus of biodegradable poly(lactic acid) (PLA) with a novel photodegradable polybutadiene (PB). First, the central block was made by ring-opening metathesis polymerization (ROMP) of a mixture of 1,5-cyclooctadiene and an unsaturated cyclic ketone in the presence of cis-1,4-butenediol. The resulting hydroxyl-functionalized telechelic PB macroinitiator was then chain-extended by DBU-catalyzed ring-opening polymerization (ROP) of lactide. Using this combination of ROMP and ROP, the molecular weights of the A and B blocks were varied, and the resulting copolymers formed robust films with rubbery plateau moduli ranging from 180 to 1600 MPa as measured by dynamic mechanical analysis (DMA). Thermal analysis revealed that the polymers were thermally stable up to 273 °C and exhibited glass transition temperatures at −111 and 55 °C. Accelerated UV weathering was performed on thin polymer films with concentrations of the photodegradable monomer in the PB backbone ranging from 0 to 9 mol %. The degradation occurred through Norrish photocleavage and was tracked by IR spectroscopy, size exclusion chromatography, and DMA until complete mechanical loss. [ABSTRACT FROM AUTHOR]

A low-cost and scalable method is developed for producing large-area elastomer surfaces having ordered nanostructures with a variety of lattice features controllable to nanometer precision. The method adopts the known technique of molding a PDMS precursor film with a close-packed monolayer of monodisperse submicron polystyrene beads on water to form an inverse-opal dimple lattice with the dimple size controlled by the bead selection and the dimple depth by the molding condition. The subsequent novel precision engineering of the inverse-opal lattice comprises trimming the PDMS precursor by a combination of polymer curing temperature/time and polymer dissolution parameters. The resultant ordered surface nanostructures, fabricated with an increasing degree of trimming, include (a) submicron hemispherical dimples with nanothin interdimple rims and walls; (b) nanocones with variable degrees of tip-sharpness by trimming off the top part of the nanothin interdimple walls; and (c) soup-plate-like submicron shallow dimples with interdimple rims and walls by anisotropically trimming off the nanocones and forming close-packed shallow dimples. As exemplars of industrial relevance of these lattice features, tunable Young's modulus and wettability are demonstrated. [ABSTRACT FROM AUTHOR]

Although research on expandable graphite (EG) has achieved great progress, its practical application is restricted due to high sulfur content and serious pollution during production. Herein, low-sulfur EG was prepared through a two-step intercalation method using environmentally friendly hydrogen peroxide as an oxidant. By optimizing reaction parameters and process, the as-prepared EG exhibits low sulfur content (1.85 wt %) and high exfoliation volume (282 mL g-1). Moreover, when 30 wt % EG is mixed with ethylene-vinyl acetate copolymer (EVM) matrix, the obtained EG/EVM composite exhibits a high limited oxygen index (LOI) of 30.4%, showing its excellent flame retardancy. Furthermore, for the compatibility between EG and EVM to be improved, poly(vinyl acetate) (PVAc) was grafted to EG by in situ radical polymerization. The EG-g-PVAc/EVM composite shows high flame resistant performance with improved control of fly ash. Therefore, this easily prepared EG can be broadly applied in environmentally friendly polymeric flame-resistance field. [ABSTRACT FROM AUTHOR]

It is still a huge challenge to implement multiple energy dissipation mechanisms into polymers toward strong yet tough elastomers. Here, we describe a biomimetic design for diene-rubber by incorporating carbon nanodots (CDs) into a chemically cross-linked network. The high-functionality CDs serve as both physical and chemical cross-linkers, which give rise to a covalent network that interlinks multiple chains with nonuniform lengths, and interfacial hydrogen bonds. Upon stretching, the hydrogen bonds preferentially detach, leading to the orientation of short covalent bridging, which contributes the forward onset of strain-induced crystallization. The subsequent rupture of short covalent bridging, together with the successive detachment of hydrogen bonds result in further orientation of hidden length, which enhances the crystallinity. Consequently, the samples exhibit an integrated improvement of strength and toughness, and intact stretchability. We envisage that this strategy may provide a new avenue to implement biomimetic design for high-performance elastomers through multiple energy dissipation mechanisms. [ABSTRACT FROM AUTHOR]

We have found extremely low efficiency of the elastomeric properties for SEBS (polystyrene-block-poly(ethylene-co-butylene)-block-polystyrene) triblock copolymers having short polystyrene (PS) block chains. Since the SEBS specimens form spherical PS microdomains embedded in the matrix of the rubbery poly(ethylene-co-butylene) (PEB) chains, they exhibit elastomeric properties (thermoplastic elastomer film). However, it was found that the stress was dramatically decreased with time when the specimens were stretched and fixed at strain of 4.0. Furthermore, they showed macroscopic fracture with very short-term duration (400 s to 2 h). To reveal the reason for such low efficiency, we conducted time-resolved two-dimensional small-angle X-ray scattering (2d-SAXS) measurements for the SEBS triblock copolymer films under stretched state at strain of 4.0. Upon stretching, the strain-induced deformation (not fracture) of glassy microdomains was observed. In addition, the deformation of glassy microdomains was found to proceed as time elapsed. Since this deformation of the glassy PS microdomains is considered to result in such the low efficiency of the elastomeric properties, characteristic times related to the deformation and the stress relaxation were evaluated from the change in strain of the glassy microdomains and from the stress relaxation curves, respectively. Then, good agreements of the characteristic times were found, and therefore it was concluded that the deformation of the glassy microdomains has a strong correlation with the stress relaxation and therefore with the fracture of the elastomeric film specimen. [ABSTRACT FROM AUTHOR]

Drug delivery systems based on porous soft biomaterials have been widely reported because of stimuli-responsive drug release and their inherent reservoirs for drug storage. Especially, magnetic-responsive porous soft biomaterials achieve rapid and real-time control of drug release due to the magnetic field-triggered large deformation. However, the drug release profiles of these materials are difficult to predict and repeat, which restrict them from releasing drugs in the required dosage. Here, we report a soft capsule based on a flexible hard-magnetic elastomer foam (HEF) for magnetically controlled on-demand drug delivery. The HEF capsule contains an inner HEF and an outer elastomer shell. The HEF exhibits low elastic modulus (10 kPa) and highly interconnected pores (81% interconnected pores). Benefitting from the novel precompressed magnetization, the compressive deformation of HEF reaches 66%. Thus, an adjustable drug release rate ranging from 0.02 to 1.7 mL/min in the HEF capsule is achieved. The deformation-triggered drug release profiles of the HEF capsule under the magnetic field are accurately predicted, allowing 85% accuracy in drug dosage regulation and more than 90% maximum cumulative drug release. Especially, the HEF capsule is proven capable of acting as a soft robot to perform magnetically driven drug delivery in a human stomach model. HEF can potentially serve as a soft robot for biomedical applications in the human body.

In this work, isocyanate-free formulations for poly(propylene glycol) polyurethane elastomers are studied. These formulations are based on poly(propylene glycol) end-capped by CO 2 -sourced cyclic carbonate (bisCC PPG) macromonomers able to react with amines leading to poly(hydroxyurethane)s. In order to obtain covalent networks, two curing approaches are studied. First, the direct thermally activated cross-linking of bisCC PPG with a mixture of various aliphatic or aromatic diamines and a triamine is investigated, and in particular the nature of the diamine on the mechanical properties. In the second approach, UV-activated formulations are developed by reacting bisCC PPG with allylamine followed by the addition of a trithiol by photoactivated thiol-ene reaction. The swelling tests show that both systems provide highly cross-linked polymer networks and complementary characterizations highlighted excellent mechanical properties. Thanks to the fast curing and adapted viscosity of the developed photoactive formulation, the latter was found suitable for use as a photoresin for 3D printing as demonstrated by printing a vaginal ring by a nozzle-based photoprinter.

Current methods for making and disposing synthetic polymers have been widely pursued and are largely unsustainable. As a part of the solution, the reversible nature of dynamic covalent bonds emerges as an extraordinarily diverse and valuable feature in the development of exotic molecules and extended structures. With these bonds, it should be possible to construct recyclable and mechanically interlocked molecular structures using relatively simple precursors with preorganized geometries. A new helicide-based elastomer network is developed here with self-healing, recycling, and degradation features using a similar concept. The best self-healing performance (100%) was noted over 10-20 min, with various H 2 O, HCl, and NaOH solutions that delivered mechanical properties in the 1-1.4 MPa range. For hydrolytic degradation, the parameters are defined based on the type of binding, the pH of the solutions, and the copolymer network, which endowed a degradation time of approximately 4-11 h for each prepared sample. However, due to the reversible nature of the dynamic bonds, the material showed good recyclable mechanical properties compared to the pristine samples after five consecutive cycles, which meet the requirements of recyclable materials and recyclable packaging.

Liquid crystal elastomers (LCEs) have been optimized by combining cross-linkers and dynamic bonds to achieve a reversible actuation behavior comparable to living skeletal muscles. In this study, one unique type of segment with 2-fold dynamic properties was introduced into LCEs, which offered not only dynamic diselenide covalent bonds for thermo-/photoplasticity but also H-bond arrays for dynamic cross-linking and mechanical robustness. Besides self-healing, self-welding, and recyclability, the LCEs were reprogrammable with elevated temperature or intensive visible light irradiation. The resultant LCEs gave an actuation blocking stress of 1.96 MPa and an elastic modulus of 14.4 MPa at 80 °C. The actuation work capacity reached 135.2 kJ m -3 . When incorporating the Joule electrode or photothermal materials, the LCEs could be programmed as the electricity-driven and photothermal artificial muscles and thereby promised the application both as a biomimetic artificial hand and as an energy collector from sunlight. Thus, the 2-fold dynamic LCEs offered the pathway of enabling the reversible actuation behavior comparable to living skeletal muscles and promising applications in sustainable actuators, artificial muscles, and soft robots.