Search

Statistical and block copolymers of n‐hexyl isocyanate (HIC) and 2‐chloroethyl isocyanate (ClEtIC) were synthesized via cοοrdination polymerization employing the half‐titanocene complex [(η5‐C5H5)((S)‐2‐Bu‐O)TiCl2] as initiator. The complex, bearing a chiral substituent, led to optically active products, as confirmed by circular dichroism measurements. The molecular characterization of all products was carried out by NMR and IR spectroscopy and size exclusion chromatography (SEC), while their thermal stability was investigated through differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and differential thermogravimetry (DTG). The reactivity ratios of the two monomers were determined using various graphical methods, as well as the COPOINT program, according to the terminal copolymerization model. Structural parameters, such as the dyad monomer sequences and the mean sequence lengths were calculated as well. In addition, the kinetics of the thermal degradation of the statistical copolymers was studied, and the activation energies of the thermal degradation were calculated employing the Kissinger, Ozawa–Flynn–Wall (OFW), and Kissinger–Akahira–Sunose (KAS) methods. The block copolymers were synthesized by sequential addition of monomers starting from the polymerization of HIC. Well‐defined products were obtained in a controlled way as revealed by SEC, IR, and NMR measurements. [ABSTRACT FROM AUTHOR]

The rapid and painless dressing change is a global challenge in wound management due to the traditional ways of dressing change often cause secondary damage on newly formed skin tissue. Recently, researchers have shown great interest in the development of on‐demand dissolvable hydrogel dressings that can be rapidly and safely dissolved under specific stimuli. These hydrogel dressings possess multifunctional properties, including injectability, self‐healing capacity, anti‐inflammation, antioxidation, and angiogenesis capabilities, which have successfully promoted healing for various types of wounds. In this review, we summarize current methods for fabricating on‐demand dissolvable hydrogels dressings, which include two strategies: (1) chemical stimuli, involving the introduction of external dissolving agents; (2) physical stimuli, where stimuli are applied without the use of dissolving agents. These approaches can decrease the density of cross‐links, resulting in the dissolution of hydrogel dressings. The advantages and drawbacks of these on‐demand dissolvable hydrogels dressings for promoting wound healing are discussed and addressed. The development and challenges for the clinical application of on‐demand dissolvable hydrogel dressings are prospected. [ABSTRACT FROM AUTHOR]

Traditional living/controlled cationic polymerization provides a simple synthetic route for the preparation of various polymers with set molecular weight, narrow molecular weight distribution, and clear structure. Nowadays, under the requirements of sustainable development, it is very important to explore the green chemical technology in depth. This review offers an overview of initiation systems, reaction media, polymerization techniques, and monomers, with the aim of summarizing environmentally friendly methods utilized in the field of cationic polymerization over the past 15 years. It covers a variety of directions from traditional initiation systems to green initiators, from corrosive solvents to environmentally friendly solvents, from drop initiation to external stimulation initiation, from petroleum fractionated monomers to bio‐based monomers. These methods and Techniques aim to develop advanced high‐quality polymer products using cationic polymerization, and achieving efficient energy savings and reducing emissions. The ongoing exploration of green‐controlled cationic polymerization holds promise for opening up new avenues and novel technology for high‐performance polyolefin materials. [ABSTRACT FROM AUTHOR]

Fused deposition modeling (FDM), an advanced 3D printing method, is a rapidly growing technology for realizing geometrically complex parts. FDM utilizes a thermoplastic feedstock that is heated and extruded through a nozzle to build up layers of material following toolpaths prescribed by three‐dimensional (3D) data. However, the rapid thermal cycles that the material undergoes during this process limit the formation, growth, and entanglement of the molecular chains in the material. Herein, we have proposed a novel laser‐assisted fused deposition modeling (LAFDM) process for the improvement in printed part properties such as bond width and tensile strength. The LAFDM system was developed consisting of an infrared CO2 laser, coupled with an industrial FDM printer. Using an adapted tensile testing method, the bond strength between deposited layers of acrylonitrile butadiene styrene (ABS) in 3D‐printed structures was assessed. Thermogravimetric analysis was used to monitor the thermal stability of the polymer to detect alterations to the chemical composition of the material as a result of the processing conditions. A 9.5% increase in the average bond tensile strength for the LAFDM‐printed specimen was observed compared to that of the non‐laser‐assisted FDM‐printed specimen. The improvement to the bond strengths was achieved without compromising the thermal stability of the polymer. [ABSTRACT FROM AUTHOR]

In the rapidly advancing era of intelligent technologies, the development of advanced materials characterized by high performance and functionality is considered a crucial aspect. A series of high‐performance functional polymers known as cis/trans‐tetraphenylethene‐containing poly (p‐phenylene terephthalamide) (cis/trans‐TPE‐PPTA), has been developed. These polymers exhibited typical aggregation‐induced emission (AIE) characteristics along with exceptional electrical and mechanical properties. It has been observed that addition ratios of cis/trans‐TPE‐2NH2 as the comonomer significantly influenced the properties of the cis/trans‐TPE‐PPTA paper. Specifically, when compared with pure poly (p‐phenylene terephthalamide) (PPTA), the homogeneous trans‐TPE‐PPTA paper at 10% trans‐TPE‐2NH2 addition ratio, fabricated using a hot‐pressing method, demonstrated significantly improved overall performance, including a substantial increase in tensile strength (97.4%) and dielectric strength (41.5%), as well as other favorable properties. This enhancement suggests promising prospects for numerous applications. [ABSTRACT FROM AUTHOR]

Polymer agglomeration is a useful way to enlarge the particle size of polybutadiene latex (PBL). However, the agglomeration process is very complex and is affected by many factors. Therefore, it is difficult to predict the mean particle size and distribution of agglomerated PBL. This study proposed a novel simulation method based on the artificial neural network (ANN) model. Firstly, the influence of agglomeration conditions on the particle size of agglomerated PBL were investigated, including the particle size of pre‐agglomerate PBL, the amount, the α‐methacrylic acid (α‐MAA) content, the solid content and the particle size of agglomerating agent. It is found that these factors have a close nonlinear relationship with the mean particle size and polydispersion index (PDI) of agglomerated PBL. Then, a model containing 236 data points was built using ANN including these properties as input with mean particle size and PDI of agglomerated PBL as output. The coefficient of determination (R2) values predicted by ANN for training, validation, test and total data are 0.9879, 0.9964, 0.9930, and 0.9902, respectively. It indicates that there is a good agreement between experimental data and predicted results by ANN. This study demonstrates that a simple machine learning method has good performance in predicting the particle size of agglomerated PBL, which further improves the development efficiency of PBL polymer agglomeration. [ABSTRACT FROM AUTHOR]

Gelatin‐methacryloyl (GelMA) hydrogel has gained huge success in the last decades thanks to its versatilities in many applications. Notably, one of them is 3D bioprinting, as GelMA physical‐mechanical properties and biocompatibility of uncured formulation perfectly suit the requirements of a bioink. Nevertheless, before the photopolymerization, the hydrogel shows weak mechanical properties and long recovery time after stress application, which results in the inability to obtain complex and self‐standing forms due to structure collapse. In this work, Carbopol ETD 2020 NF, dissolved in cell culture medium, was used as supporting bath to optimize GelMA bioprinting and overcome its stability limitations. The achieved results demonstrated the possibility of printing shapes containing hollows with lumens or non‐planar surfaces, also by using nozzles with larger inner diameter, which reduced cell death during printing process, but were usually avoid because of low resolution. Moreover, constructs' extraction was easier when Carbopol solution was prepared in culture medium rather than in water, reducing sample handling. In conclusion, thanks to this supporting bath, it was possible to print cellularized scaffold, with channels that were then seeded, obtaining inner structure. Further, this Carbopol formulation could be considered an eligible candidate as a supporting bath to obtain GelMA 3D self‐standing‐shaped and vascularized scaffold. [ABSTRACT FROM AUTHOR]

To improve the therapeutic efficiency of paclitaxel (PTX) and reduce its toxicity to normal tissues, a novel hydroxypropyl‐β‐cyclodextrin (HP‐β‐CD) derivative has been designed and developed. The polymer (bio‐HP‐β‐CD(NAC)‐PLA) is synthesized by modifying HP‐β‐CD with polylactic acid, cysteine, and biotin. Using bio‐HP‐β‐CD(NAC)‐PLA as the carrier, a PTX‐loaded nanoparticulate system is developed by a modified emulsion solvent evaporation method. The optimized drug‐loaded nanoparticles are obtained with a mean diameter of 162.4 nm and drug loading of 16.1%. In vitro drug release study exhibits that PTX is released in a redox‐dependent manner. Cellular uptake study suggests that the bio‐HP‐β‐CD(NAC)‐PLA nanoparticles can be specifically taken up by MCF‐7 cells via the biotin receptor‐mediated endocytosis. In vitro and in vivo anticancer efficacy evaluations demonstrate the superior antitumor activity and negligible toxicity of the PTX‐loaded nanoparticles. It can be concluded that the proposed polymer bio‐HP‐β‐CD(NAC)‐PLA offers a promising drug delivery system for targeted delivery and controlled release of PTX. [ABSTRACT FROM AUTHOR]

Block polyethers comprised of poly(propylene oxide) (PPO) and poly(ethylene oxide) (PEG or PEO) segments form the basis of ABA‐type PEO‐b‐PPO‐b‐PEO poloxamer materials. The inverse architecture with an internal hydrophilic PEO segment flanked by hydrophobic blocks can be difficult to prepare with control of architecture by use of traditional anionic polymerization. These oxyanionic polymerizations are plagued by chain‐transfer‐to‐monomer side reactions that occur with substituted epoxides such as propylene oxide (PO). Herein, we report a new method for the preparation of block polymers through a controlled polymerization involving a N‐Al Lewis adduct catalyst and an aluminum alkoxide macroinitiator. The Lewis pair catalyst was able to chain‐extend commercial PEO macroinitiators to prepare di‐, tri‐, and pentablock polyethers with low dispersity and reasonable monomer tolerance. Chain extension was confirmed using size exclusion chromatography and diffusion ordered nuclear magnetic resonance spectroscopy. The resulting block polymers were additionally analyzed with small‐angle X‐ray scattering to correlate the morphology to molecular architecture. [ABSTRACT FROM AUTHOR]

With the development of heat and creep‐resistant UHMWPE fiber via UV crosslinking, its structure‐properties evolution during processing needs attention. The structures of UHMWPE fiber in different forms, the pre‐oriented yarn (POY), the full stretch yarn (FDY) and UV crosslinked FDY (UVFDY), obtained from our pilot line were systematically studied with differential scanning calorimetry (DSC), wide‐angle X‐ray diffraction (WAXD), small‐angle X‐ray scattering (SAXS), and solid‐state 13C NMR. Additionally, the heat and creep resistance of UVFDY were evaluated by the temperature at break (Tb), glass transition temperature (Tg), time at break (tb) for a given aging temperature, and creep elongation (Lc). The results demonstrated that UVFDY possessed high gel content (89.0%), high crystallinity (84.2%), and high orientation (91.7%). These characteristics caused UVFDY not only with excellent mechanical properties but also process extraordinary heat and creep resistance, especially for its much higher Tb (220 °C), Tg (−75.7 °C) and tb (20 h) while lower Lc (7.8%), comparing with FDY (Tb = 158 °C, Tg = −86.8 °C, tb = 1.3 h and Lc = 38.2%). This work provides insights into the structure‐properties relationship of UVFDY, which will aid in the development of UV crosslinked UHMWPE fiber with better heat and creep resistance. [ABSTRACT FROM AUTHOR]

High‐performance fibers are used in fire‐protective garments due to their exceptional thermal stability and mechanical performance. However, these garments suffer from a reduction in their performance over their lifetime. The purpose of this study was to investigate the hydrothermal aging of 15 yarns contained in eight fabrics made of different fiber blends. The accelerated hydrothermal aging was performed via immersion in reverse osmosis (RO) and acidic water at temperatures between 40 °C and 90 °C for up to 1200 h. The resulting mechanical, chemical, and physicochemical changes in the yarns and fabrics were assessed. The result showed a large drop in the breaking force of yarns made from para‐aramid/polybenzimidazole (PBI) fiber blends in all aging water conditions. For the other fabrics, aging in acidic water and a jar with the PBI‐containing fabrics generally caused a larger decrease in strength compared to aging in RO water in a separate jar. The results also showed that a change in crystallinity rather than in chemical structure appeared to be the cause for the changes in tensile strength after hydrothermal aging. The findings of this study will contribute to identifying strategies to improve the long‐term performance of fire‐protective fabrics. [ABSTRACT FROM AUTHOR]

Bacterial infections are common during skin wound healing, which can interrupt the healing process, delay wound healing and seriously affect the quality of life. Long‐term antibiotic treatment may lead to the development of drug resistance. Traditional bandages, sponges, films, and textiles are commonly single‐functional, and usually fail to satisfy the complicated needs of wound healing process. In recent years, antibacterial hydrogel dressings have received extensive attention for treatment of infected and chronic wounds, which can serve as biocompatible, multifunctional platforms for both promoting tissue regeneration and inhibiting bacterial infection. Cationic polymers with inherent antibacterial properties have been used as the hydrogel backbone, and metal ions and metal nanoparticles can be loaded in the hydrogels to enhance the antibacterial effects. Besides, various drugs and bioactive factors have been incorporated to provide the hydrogel with anti‐inflammatory and antioxidant activities in complicated environment of chronic wound healing. Additionally, the tissue adhesion of hydrogel dressings can have advantages in fixing the dressings at wound sites and promoting the dressing‐tissue interactions. In this review, we focus on the designing strategies for tissue‐adhesive, antibacterial, naturally‐derived polymer hydrogels for treating infected and chronic wounds. The typical tissue adhesion mechanisms and antibacterial mechanisms of the hydrogel dressings are summarized. Finally, the prospects and challenges in the further development of multi‐functional hydrogels to treat infected and chronic wounds are proposed. [ABSTRACT FROM AUTHOR]

This paper presents a systematic review of the literature on the melt memory effects observed in polymers, an area that has engendered considerable debate for over 50 years. Recent advances in experimental techniques have provided fresh insights into how a polymer's thermal history influences its recrystallization behavior. It has been observed that given other conditions unchanged, the crystallization temperature during recrystallization decreases with an increase in the melt temperature Ts above the melting point Tm until a critical melt temperature is attained. This phenomenon also extends to the half‐time of crystallization and the secondary structures, such as lamellar thickness, of semi‐crystalline polymers. Despite these findings, a comprehensive constitutive model that encapsulates polymer melt memory effects remains elusive. Cutting‐edge instrumentation, including in situ small and wide‐angle X‐ray scattering, temperature‐controlled Fourier transform infrared spectroscopy, and flash differential scanning calorimetry, have posed significant challenges to the traditional nucleation and growth models established in the 1970s. These models are foundational to our understanding of polymer crystallization, which is an integral part of polymer processing and production. In this review, the historical contours of this discourse are traced, with an examination of both the recent experimental breakthroughs and theoretical advancements pertinent to polymer melt memory effects. This paper delves into the prevailing theories of polymer nucleation and crystallization and engages with theoretical discussions and numerical simulations that attempt to elucidate and rationalize these melt memory phenomena. [ABSTRACT FROM AUTHOR]

The preparation of four types of epoxidized iron‐based comb butadiene‐isoprene rubber (EBIR) with different epoxidation degrees (4.7%, 6.4%, 10.2%, and 12.3%) was investigated for the first time in this study. The modification involved the use of hydrogen peroxide and formic acid as raw materials for the epoxidation process. Following this, silica/EBIR composites were prepared by mixing EBIR with silica nanoparticles, without the use of a silane coupling agent (SCA). The objective was to investigate the influence of the epoxidation degree on the structure and properties of the resulting silica/EBIR nanocomposites. The results indicated that the introduction of epoxy groups had a positive effect on the interfacial interaction between the rubber and filler, leading to improved dispersion of the silica nanoparticles in the rubber matrix. Consequently, the tensile properties, wet skid resistance, and abrasion resistance of the silica/EBIR composites were found to be superior to those of the un‐epoxidized silica/BIR composites. Furthermore, comparing the silica/EBIR‐12.3 nanocomposites with silica/BIR‐Si69 nanocomposites, it was revealed that silica/EBIR‐12.3 showed a 69.4% enhancement in wet skid resistance and an 8.0% reduction in rolling resistance. These findings demonstrate the potential of silica/EBIR composites for high‐performance tire tread rubber applications, offering environmental benefits and improved properties. [ABSTRACT FROM AUTHOR]

We explore the crystal structure and ionic conductivity of unfilled and cellulose nanowhisker‐filled polymer electrolytes, based on high molecular weight PEO and LiClO4 at a concentration EO:Li = 6:1 (EO = ether oxygen). At this concentration, the polymer electrolyte forms crystalline PEO6 (PEOy—the crystal structure co‐crystallizes "y" PEO ether oxygens to one Li‐anion pair). While the diffraction patterns for PEO3 and PEO6 with LiClO4 are available, their structures are not. Thus, we optimize these structures using density functional theory and show agreement between simulated and experimental diffraction patterns. The PEO6 crystal shows insufficient Li‐ion conductivity due to a lack of percolated conduction paths, and the crystal structure is unstable following 2 months after annealing. Cellulose nanowhiskers, with their patterned surface OH groups, extend the length of PEO6 tunnels, stabilize these tunnels for as long as a year, and result in the percolation of crystals. Although the EO:Li = 6:1 stoichiometry should not favor PEO3 formation, we observe this crystal phase in some unfilled samples. But, with the addition of nanowhiskers, the patterned surface templates PEO6 formation rather than PEO3. Despite these advantages, nanowhiskers do not improve ionic conductivity as hypothesized. The tools developed in this work allow further mechanistic exploration of conduction through crystalline domains. [ABSTRACT FROM AUTHOR]

Microgels have a wide range of applications, from catalysis to biomedical applications such as drug delivery in dispersion, or as surface‐attached materials to improve the biocompatibility of implants or as anti‐fouling coatings. The first aim of this work is to understand the morphology of the supramacromolecular, tannic acid (TA) crosslinked microgels using two‐dimensional 1H NMR spectroscopy, and relaxometry. The second aim is to study the volume phase transition (VPT) of TA‐crosslinked microgels with different crosslinker densities in dispersion using NMR. In this context, 1H high‐resolution NMR spectroscopy is used in combination with the two‐state model and the Boltzmann sigmoidal function to determine thermodynamic quantities of the VPT, such as temperature (Tt), width of transition (ΔTt), and change in entropy (ΔS). Third, surface‐deposited microgels are characterized in terms of their VPT using a quartz crystal microbalance (QCM‐D) to study the properties of these microgels for applications where they are used as coatings. Finally, the Tt of microgels supramolecular crosslinked with TA are compared with microgels covalently crosslinked with N,N′‐methylenebisacrylamide (BIS) in dispersion, using NMR, and deposited on a surface, using QCM‐D. For this purpose temperature‐responsive poly(N‐vinylcaprolactam) and poly(N‐isopropylacrylamide) microgels crosslinked with the plant‐derived polyphenol TA or BIS are used. [ABSTRACT FROM AUTHOR]

Many countries have recently banned the production and importation of petrochemical plastic microbeads for use as exfoliating agents in personal care products. Plastic particles in products of this nature are too small to be retrieved during wastewater treatment and they accumulate in the environment, negatively impacting living organisms and ecosystems. Sustainable alternatives that offer comparable mechanical properties to synthetic plastic microbeads could be developed using biowaste material. Brewer's spent grain (BSG), the primary residue of the brewery industry, is shown herein to be a promising starting material in the development of biodegradable, nontoxic microbeads. After dilute acid hydrolysis, pretreated lignocellulosic pulp from BSG is solubilized using an aqueous system of NaOH and ZnO. Solid microbeads may then be formed by dropping the resulting solution into an acid bath, filtering, and drying. The conditions of each step required optimization to successfully produce spherical microbeads with a mean diameter as small as 1.25 mm, a homogeneous size distribution, and an average hardness of 199 MPa. The beads also demonstrated superior cleansing abilities to commercially available natural exfoliating particles. BSG microbeads are therefore a promising option for use as a physical exfoliating agent in various personal hygiene products. [ABSTRACT FROM AUTHOR]

With the development of high power‐density electronic devices on smaller scales and emerging new energy vehicles, high thermal conductive materials have attracted more attention for better thermal management to adapt to various applications. By combining both the advantages of polymer materials and thermally conductive fillers, thermal conductive polymer composite materials are widely used in packaging and the protection of electronic devices for their mechanical robustness, high thermal conductivity, excellent insulation properties, heat resistance, and chemical resistance. In this review, first, the basic theory of heat conduction of polymer composites is discussed. Second, according to the classification of the composition of the thermal conductive polymer, the filled thermal conductive material is emphatically introduced. In this paper, the construction process of a thermal conductive network of polymer and composites is discussed from the perspective of processing. The simple construction of a thermal conductive network includes core‐shell structure, external force orientation, electrostatic spinning, electrostatic spraying, induced orientation, and vacuum‐assisted filtration. The three‐dimensional thermal conductivity network can be constructed using self‐assembly and template methods. From the above processing methods, this paper analyzes how to effectively improve thermal conductivity and achieve the goal of high thermal conductivity and excellent mechanical properties under low filling. After that, the contribution of filler and polymer modification to thermal conductivity is explained in detail. Finally, the future research direction of functionalization is prospected. [ABSTRACT FROM AUTHOR]

Herein, we demonstrate that blending an organic dye (guest/filler), with a vinyl polymer (host template), is an inexpensive and simple approach for the fabrication of multifunctional photonic materials which could display an enhancement in the desirable properties of the constituent materials and, at the same time provide novel synergistic properties for the guest-host system. A new guest-host nanocomposite system comprising Phenol Red dye and poly (vinyl alcohol) as guest and host template, respectively, which exhibits tunable optical characteristics and saturable absorption behavior, is introduced. The dependence of local electronic environment provided by the polymer template and the interactions of the polymer molecules with the encapsulated guest molecules on the observed optical/nonlinear absorption behavior is discussed. An understanding of the tunability of the optical/ photophysical processes, with respect to the filler content, as discussed herein could help in the design of improved optical materials for several photonic device applications like organic light emitting diodes and saturable absorbers. [ABSTRACT FROM AUTHOR]

The dissociation of polaron pairs into free charge carriers in organic bulk heterojunction solar cells is a fundamental step in generating photocurrent and is still in debate. In this study, we propose two simple criteria that can be used to test the validity of any polaron pair dissociation model for polymer-fullerene bulk heterojunction solar cells. The first criterion states that the ratio of the bimolecular recombination current density to the maximum photocurrent density should increase as a function of applied voltage. The second criterion states that the ratio of the bimolecular recombination current density to the maximum photocurrent density at short circuit should not be larger than 1. We apply these criteria to test the validity of the widely used Onsager-Braun model by using the experimental current-voltage data of poly[2-methoxy-5-(3'-7'-dimethyloctyloxy)-p-phenylene vinylene] (OC1C10-PPV) and [6,6]-phenyl C61-butyric acid methylester (PCBM) based solar cells. We find that our numerical analysis is not suitable to employ these criteria. Our analytical analysis, on the other hand, clearly demonstrates that the Onsager-Braun model simply cannot fulfill the first criteria. The reason is because the polaron pair dissociation given by the Onsager- Braun model is too strongly influenced by the electric field (i.e., decreases too rapidly as the electric field decreases). The analysis provides a further evidence against the widely used Onsager- Braun model. The proposed criteria can help us to determine the correct model for polaron pair dissociation by serving as a guideline on how strongly the electric field is allowed to influence the polaron pair dissociation. [ABSTRACT FROM AUTHOR]

In this report, an attempt has been made to investigate the morphological evolution of nanoscale surface ripples on aliphatic (polypropylene, PP) and aromatic (polyethylene terephthalate, PET) polymeric substrates irradiated with 50 keV Ar+ ions. The specimens were sputtered at off normal incidence of 30° with 5 x 1016 Ar+ cm-2. The topographical features and structural behavior of the specimens were studied using Atomic Force Microscopy (AFM) and UV-Visible spectroscopy techniques, respectively. The Stopping and Range of Ions in Matter simulations were performed to calculate sputtering yield of irradiated PP and PET polymers. Sputtering yield of carbon atoms has been found to be smaller for PP (0.40) as compared to PET (0.73), which is attributed to the different structures of two polymers. AFM analysis demonstrates the evolution of ripple like features with amplitude (2.50 nm) and wavelength (690 nm) on PET while that of lower amplitude (1.50 nm) and higher wavelength (980 nm) on PP specimen. The disorder parameter (Urbach energy) has been found to increase significantly from 0.30 eV to 1.67 eV in case of PP as compared to a lesser increase from 0.35 eV to 0.72 eV in case of PET as revealed by UV-Visible characterization. A mutual correlation between ion beam sputtering induced topographical variations with that of enhancement in the disorder parameter of the specimens has been discussed. [ABSTRACT FROM AUTHOR]

The forced translocation of homopolymers through αβα sandwich-like compound channels was investigated by Monte Carlo simulation. The interaction between polymer and part α is strongly attractive, whereas that between polymer and part β is purely repulsive. Simulation results show that the translocation is influenced obviously by the length of part β (Lβ) and the starting position of part β (Lα1). For small Lβ, the translocation is mainly governed by the escaping process, and polymer is trapped near the exit of the channel. However, the translocation time can be tuned by varying Lα1 and the fastest translocation can be achieved at relatively large Lα1. Whereas for large Lβ and small Lα1, the translocation is mainly controlled by the filling process. It is difficult for polymer to enter the channel, and polymer is trapped at the first αβ interface. Finally, the dynamics for the filling process and the escaping process are discussed from the view of free-energy landscape, respectively. [ABSTRACT FROM AUTHOR]

Reconfigurable metamaterials have great potential to alleviate complications involved in using passive metamaterials to realize emerging electromagnetic functions, such as dynamical filtering, sensing, and cloaking. This paper presents a new type of tunable meta-atoms in the X-band frequency range (8-12 GHz) toward reconfigurable metamaterials. The meta-atom is made of all flexible materials compliant to the surface of an interaction object. It uses a liquid metal-based split-ring resonator as its core constituent embedded in a highly flexible elastomer. We demonstrate that simple mechanical stretching of the meta-atom can lead to the great flexibility in reconfiguring its resonance frequency continuously over more than 70% of the X-band frequency range. The presented meta-atom technique provides a simple approach to dynamically tune response characteristics of metamaterials over a broad frequency range. [ABSTRACT FROM AUTHOR]

The cover image is based on the Research Article Biosourced spherical microbeads from brewer's spent grain for sustainable personal hygiene products by Amy McMackin et al., https://doi.org/10.1002/pol.20230613 Microbeads used in personal hygiene products have conventionally been crafted from synthetic plastics offering precise control over hardness and shape. However, the disposable nature of these products has linked synthetic plastic microbeads to pollution in marine environments. In this study, we present a sustainable alternative by using brewer's spent grain as our starting material. Through solubilization and regeneration, we transform this brewery residue into spherical lignocellulosic microbeads. Beyond mitigating the environmental impact associated with exfoliating microbeads in personal care items, this method introduces an innovative valorization strategy for brewer's spent grain. Image design by Amy McMackin via Canva.com. [ABSTRACT FROM AUTHOR]

This article aims to describe the implementation, evaluation, and outcomes associated with a science, technology, engineering, and mathematics (STEM) research fellow experience at an historically Black college and university (HBCU) funded by the National Science Foundation. This experience, Polymer Research, was part of a multipronged approach for infusing polymers into the General and Physical Chemistry curricula. After briefly reviewing the literature on broadening participation in STEM and undergraduate research experiences, the authors provide a description of the context, evaluation, and project outcomes and conclude with a discussion on project impact and the role of HBCUs in training and graduating underrepresented students in STEM. [ABSTRACT FROM AUTHOR]

Using dissipative particle dynamics simulations the aggregation of nanoparticles on single and two-component bilayers is investigated. For a uniform bilayer the aggregation of nanoparticles depends strongly on the location of the particles in the bilayer; particles residing on the bilayer exterior cluster strongly under the influence of bilayer-mediated interactions, whereas the interaction between the particles in the bilayer interior is significantly weaker leading to more loosely bound, dynamic aggregates. The aggregation of nanoparticles on two-component bilayers composed of immiscible components changes due to competition between nanoparticle clustering and their adsorption on the boundary between the bilayer components. This reduces the size of the nanoparticle clusters formed on the bilayer exterior, with the clusters adhering onto the boundary between the bilayer components. Due to their weaker attraction nanoparticles in the interior of a mixed bilayer no longer aggregate and instead form strings along the boundary between the two bilayer components. Nanoparticles with an affinity to one bilayer component nucleate small domains of their favoured component around themselves. For asymmetric mixtures this leads to a notable change in the aggregation behaviour of the nanoparticles. [ABSTRACT FROM AUTHOR]

Bidisperse melts of linear, entangled polymer chains were studied using dissipative particle dynamics. The entanglement constraints were mimicked with our newly developed slip-spring approach. The compositions cover blends with short matrix chains, slightly above the molecular entanglement weight as well as blends were both chain lengths exhibit distinct entangled dynamics at various weight fractions. The Struglinsky-Graessley parameter Gr, which is the ratio between the relaxation time of the long chains due to pure reptation and the relaxation time of the tube caused by constraint release, ranges between values high above and below unity. We compare our slip-spring model with simulations that use conventional generic polymer models where bond crossings are prevented by excluded-volume interactions and find fairly good agreement in terms of the mean squared displacement. However, the slip-spring approach requires only a fraction of the computational time, making large scale systems feasible. The dynamical interference of the two different chain lengths is discussed in terms of reptation and constraint release dynamics. For bidisperse melt compositions with Gr < 1.0 the relaxation time of the long chain component is not affected by constraint release. However, for compositions where constraint release is supposed to contribute significantly to the relaxation mechanism (Gr > 1.0), we find strong evidence that the long chains reptate inside a dilated tube whose diameter increases with an exponent of 1/2 towards lower weight fraction of the long chains. Furthermore we observe a linear relation between the relaxation time and weight fraction. Therefore, based on the relaxation times, our results support the validity of the tube dilation model as proposed by Doi et al. [Macromolecules 20, 1900-1906 (1987)]. [ABSTRACT FROM AUTHOR]

In this work, a graphene based strain sensor has been reported for explosive vapour detection applications by exploiting the piezoresistive property of graphene. Instead of silicon based cantilevers, a low cost polymeric micro-cantilever platform has been used to fabricate this strain sensor by embedding the graphene nanoplatelet layer inside the beam. The fabricated devices were characterized for their mechanical and electromechanical behaviour. This device shows a very high gauge factor which is around ~144. Also the resonant frequency of these cantilevers is high enough such that the measurements are not affected by environmental noise. These devices have been used in this work for reliable detection of explosive vapours such as 2,4,6-Trinitrotoluene down to parts-per-billion concentrations in ambient conditions. [ABSTRACT FROM AUTHOR]

tandard models explaining the spin coating of polymer solutions generally fail to describe the early stages of film formation, when hydrodynamic forces control the solution behavior. Using in situ light scattering alongside theoretical and semi-empirical models, it is shown that inertial forces (which initially cause a vertical gradient in the radial solvent velocity within the film) play a significant role in the rate of thinning of the solution. The development of thickness as a function of time of a solute-free liquid (toluene) and a blend of polystyrene and poly(methyl methacrylate) cast from toluene were fitted to different models as a function of toluene partial pressure. In the case of the formation of the polymer blend film, a concentration-dependent (Huggins) viscosity formula was used to account for changes in viscosity during spin coating. A semi-empirical model is introduced, which permits calculation of the solvent evaporation rate and the temporal evolution of the solute volume fraction and solution viscosity. [ABSTRACT FROM AUTHOR]

Mechanical characterization is important for understanding small-scale systems and developing devices, particularly at the interface of biology, medicine, and nanotechnology. Yet, monitoring sub-surface forces is challenging with current technologies like atomic force microscopes (AFMs) or optical tweezers due to their probe sizes and sophisticated feedback mechanisms. An alternative transducer design relying on the indentation mechanics of a compressible thin polymer would be an ideal system for more compact and versatile probes, facilitating measurements in situ or in vivo. However, application-specific tuning of a polymer's mechanical properties can be burdensome via experimental optimization. Therefore, efficient transducer design requires a fundamental understanding of how synthetic parameters such as the molecular weight and grafting density influence the bulk material properties that determine the force response. In this work, we apply molecular-level polymer scaling laws to a first order elastic foundation model, relating the conformational state of individual polymer chains to the macroscopic compression of thin film systems. A parameter sweep analysis was conducted to observe predicted model trends under various system conditions and to understand how nano-structural elements influence the material stiffness. We validate the model by comparing predicted force profiles to experimental AFM curves for a real polymer system and show that it has reasonable predictive power for initial estimates of the force response, displaying excellent agreement with experimental force curves. We also present an analysis of the force sensitivity of an example transducer system to demonstrate identification of synthetic protocols based on desired mechanical properties. These results highlight the usefulness of this simple model as an aid for the design of a new class of compact and tunable nanomechanical force transducers. [ABSTRACT FROM AUTHOR]

We analyze the universal size characteristics of flexible ring polymers in solutions in presence of structural obstacles (impurities) in d dimensions. One encounters such situations when considering polymers in gels, colloidal solutions, intra- and extracellular environments. A special case of extended impurities correlated on large distances r according to a power law ~r-a is considered. Applying the direct polymer renormalization scheme, we evaluate the estimates for averaged gyraion radius and spanning radius of typical ring polymer conformation up to the first order of double ε = 4 - d, δ = 4 - a expansion. Our results quantitatively reveal an extent of the effective size and anisotropy of closed ring macromolecules in disordered environment. In particular, he size ratio of ring and open (linear) polymers of the same molecular weight grows when increasing he strength of disorder according to >/ > 1/2 (1 + 13/48 δ). [ABSTRACT FROM AUTHOR]

This work formulates, at a molecular level, a phenomenological theoretical description of the brittle-ductile transition (BDT) in tensile extension, exhibited by all polymeric glasses of high molecular weight (MW). The starting point is our perception of a polymer glass (under large deformation) as a structural hybrid, consisting of a primary structure due to the van der Waals bonding and a chain network whose junctions are made of pairs of hairpins and function like chemical crosslinks due to the intermolecular uncrossability. During extension, load-earing strands (LBSs) emerge between the junctions in the affinely strained chain network. Above the BDT, i.e., at "warmer" temperatures where the glass is less vitreous, the influence of the chain network reaches out everywhere by activating all segments populated transversely between LBSs, starting from those adjacent to LBSs. It is the chain network that drives the primary structure to undergo yielding and plastic flow. Below the BDT, the glassy state is too vitreous to yield before the chain network suffers a structural breakdown. Thus, brittle failure becomes inevitable. For any given polymer glass of high MW, there is one temperature TBD or a very narrow range of temperature where the yielding of the glass barely takes place as the chain network also reaches the point of a structural failure. This is the point of the BDT. A theoretical analysis of the available experimental data reveals that (a) chain pullout occurs at the BDT when the chain tension builds up to reach a critical value fcp during tensile extension; (b) the limiting value of fcp, extrapolated to far below the glass transition temperature Tg, is of a universal magnitude around 0.2-0.3 nN, for all eight polymers examined in this work; (c) pressurization, which is known [K. Matsushige, S. V. Radcliffe, and E. Baer, J. Appl. Polym. Sci. 20, 1853 (1976)] to make brittle polystyrene (PS) and poly(methyl methacrylate) (PMMA) ductile at room temperature, can cause fcp to rise above its ambient value, reaching 0.6 nN at 0.8 kbar. Our theoretical description identifies the areal density ψ of LBSs in the chain network as the key structural parameter to depict the characteristics of the BDT for all polymer glasses made of flexible (Gaussian) linear chains. In particular, it explains the surprising linear correlation between the tensile stress σBD at the BDT and ψ. Moreover, the theoretical picture elucidates how and why each of the following four factors can change the coordinates (σBD,TBD) of the BDT: (i) mechanical "rejuvenation" (i.e., large deformation below Tg), (ii) physical aging, (iii) melt stretching, and (iv) pressurization. Finally, two methods are put forward to delineate the degree of vitrification among various polymer glasses. First, we plot the distance of the BDT from Tg, i.e., Tg/TBD as a function of ψ to demonstrate that different classes of polymer glasses with varying degree of vitrification show different functional dependence of Tg/TBD on ψ. Second, we plot the tensile yield stress σY as a function Tg/T to show that bisphenol-A polycarbonate (bpA-PC) is less vitreous than PS and PMMA whose σY is considerably higher and shows much stronger dependence on Tg/T than that of bpA-PC. [ABSTRACT FROM AUTHOR]

We studied the effect of elongational flow on structure and kinetics of phase separation in immiscible blends using molecular dynamics simulations. Two different blend systems have been investigated—binary blend of polymers and binary mixture of molecular fluids. The interaction potential parameters in both material systems were chosen to ensure complete phase-separation in equilibrium. We found that elongational flow, beyond a certain rate, significantly alters the steady state morphology in such immiscible mixtures. For the case of polymer blends, perpendicular lamellar morphology was formed under elongation rates (˙ε) from 0.05 to 0.5 MD units possibly due to the interplay of two opposing phenomena—domain deformation/rupture under elongation and aggregation of like-domains due to favorable energetic interactions. The elongation timescale at the critical rate of transition from phase-separated to the lamellar structure (˙ε = 0.05) was found to be comparable to the estimated polymer relaxation time, suggesting a cross-over to the elongation/rupture-dominant regime. Under strong elongational flow rate, ˙ε > 0.5, the formation of disordered morphology was seen in polymer blend systems. The kinetics of phase separation was monitored by calculating domain size as a function of time for various elongational flow rates. The domain growth along the vorticity-axis was shown to follow a power law, Rz(t) ∼ t α. A growth exponent, α of 1/3 for the polymer blend and 0.5–0.6 for the fluid molecular mixture was found under elongation rates from 0.005 to 0.1. The higher growth exponent in the fluid mixture is a result of its faster diffusion time scale compared to that of polymer chains. The steady state end-to-end distance of polymer chains and viscosity of the polymer blend were examined and found to depend on the steady state morphology and elongation rate. [ABSTRACT FROM AUTHOR]

Velocity relaxation of a spherically symmetric polymer, immersed in a viscous incompressible fluid, and after a sudden small impulse or a sudden twist from a state of rest, is studied on the basis of the linearized Navier-Stokes equations with an added Darcy type drag term. Explicit expressions for the translational and rotational velocity relaxation functions of the polymer and for the flow pattern of the fluid are derived for a uniform permeable sphere. Surprisingly, it is found that the added mass vanishes. For fairly large values of the ratio of sphere radius to the screening length characterizing the permeability, the velocity relaxation functions in the short and intermediate time regime differ significantly from that of a sphere with no-slip boundary condition. At long times, both relaxation functions show universal power law behavior. [ABSTRACT FROM AUTHOR]

Polymer-matrix nanocomposites based on Poly(lactic-co-glycolic) acid (PLGA) and Graphene platelets (GNPs) were studied. GNPs, nanomaterials with a 2D flat surface, were chosen with or without chemical modification in PLGA/GNP nanocomposites and their microstructure, thermal property, and their compatibility as scaffolds for cell growth were investigated. PLGA/GNP nanocomposites (0, 1, and 5wt.% of GNPs) were prepared using a solution based technique. Transmission electron microscopy, X-ray diffraction, Differential scanning calorimeter, and Thermogravimetric analyzer were used to analyze morphology and thermal properties. This work demonstrated the role of GNPs flat surface to provide a favorable platform resulting in an enhanced PLGA crystallization. Functionalized GNPs suppress both the thermal stability and the crystallization of PLGA. Finally, to determine the potential usefulness of these scaffolds for biomedical applications, mammalian cells were cultured on various PLGA/GNP nanocomposites (0, 1, and 5wt.% GNPs). 1wt.% PLGA/GNP nanocomposites showed better biocompatibility for cell growth with/without graphenes functionalization compared to pure PLGA and 5wt.% PLGA/GNP. The function of GNPs in PLGA/GNPs (1wt.%) composites is to provide a stage for PLGA crystallization where cell growth is favored. These results provide strong evidence for a new class of materials that could be important for biomedical applications. [ABSTRACT FROM AUTHOR]

To investigate the mechanism of structural changes of water and polymer networks with drying and swelling, we measured the Raman spectra of a physically cross-linked poly(vinyl alcohol) (PVA) hydrogel synthesized using the freezing–thawing method. The results show that the vibrational frequencies of the O–H and C–H stretching modes decrease with dehydration. The frequency shifts observed are attributed to reduction of free water inside the polymer network. The C–H bonds elongate as the water density decreases, and the average length of the O–H bonds increases with increasing proportion of bound water to the total amount of water. On the basis of the dependence of the frequency shifts on the PVA concentration of the original solution, it was found that the structure of the polymer network in the reswollen hydrogel becomes inhomogeneous due to shrinkage of the polymer network with drying. Furthermore, to investigate the effects of the crosslinking structure on the drying process, these results were compared with those of a chemically cross-linked PVA hydrogel synthesized using glutaraldehyde as a cross-linker. The result shows that the vibrational frequency of the O–H stretching mode for the chemically cross-linked hydrogel increases with dehydration, whereas that of the C–H stretching mode decreases. The opposite trend observed in the O–H stretching mode between the physically and chemically crosslinked hydrogels is due to the difference in the shrinkage rate of the polymer network. Because the rate of shrinking is slow compared with that of dehydration in the chemically cross-linked hydrogel, water density in the polymer network decreases. For the physically cross-linked hydrogel, the polymer network structure can be easily shrunken, and the average strength of hydrogen bonds increases with dehydration. The results show that the structures of the polymer network and water change with the gel preparation process, cross-linking method, and drying and reswelling processes. The structure of the polymer network and the behavior of water accommodated in the network are important factors governing the chemical and physical properties of gel materials. [ABSTRACT FROM AUTHOR]

Between 20 and 90 MHz frequency-dependent shear viscosities of the polystyrene-cyclohexane mixture of critical composition have been measured at polymer molar weight Mw = 30 000. The viscosity data reveal dispersion, in conformity with relaxation characteristics in the non-critical background contributions to the ultrasonic attenuation, i.e., in the longitudinal viscosity of the critical system. The dispersion behavior is discussed with a view to its effect on the critical dynamics of the liquid near its consolute point. Attention is especially given to the relaxation rates of fluctuations of that system. The data as resulting from ultrasonic attenuation spectroscopy on the one hand and from quasi-elastic light scattering and viscosity measurements on the other hand differ near the critical temperature. It is concluded that likely an additional dispersion exists in the shear viscosity at frequencies below the presently available frequency range of measurement. [ABSTRACT FROM AUTHOR]

Aimed to optimize the ratio accuracy/computational cost, in this work we study the performance of three different theoretical methodologies in the calculation of the optical bandgap for a test set made of a number of poly(aryl-ethynylene)s related polymers. Infinite, ideal polymer chains were first optimized by means of periodic calculations. Different length oligomers were afterward generated by direct replication of the corresponding periodic structure and their optical bandgaps were calculated by means of different time dependent-density functional theory (TD-DFT) methodologies. These results were fitted to an exponential function for each oligomer family in order to get a theoretical estimation of the optical bandgap for each polymer to be compared to the experimental reported values. The best result was obtained for TD-M06-2X yielding an average deviation of 3.4% with respect to the experimental values. [ABSTRACT FROM AUTHOR]

Porous coordination polymers (PCPs) with soft frameworks show a gate phenomenon consisting of an abrupt structural transition induced by adsorption of guest molecules. To understand the dependence of the gating behavior on the host framework structure, we conduct grand canonical Monte Carlo simulations and a free-energy analysis of a simplified model of a stacked-layer PCP. The interlayer width of the rigid layers composing the simplified model can be changed by guest adsorption and by varying the initial interlayer width h0, which is controlled by the length of pillars between the layers. We introduce three types of gating behavior, one-step gating, filling and gating, and double gating, which depend on three parameters: the initial interlayer width h0; the interaction parameter εss, which determines the host–guest framework interaction as well as the inter-framework interaction; and the elastic modulus of the framework, which depends on the stiffness of the pillars. We show that the one-step gating and the filling and gating behaviors depend strongly on h0 rather than on εss, and thus a transformation from filling and gating to double gating can be achieved by reducing the stiffness of the host framework. This study should be a guideline for controlling the gating pressure of PCPs by modifying their chemical components. [ABSTRACT FROM AUTHOR]

For a double-ring polymer in solution we evaluate the mean-square radius of gyration and the diffusion coefficient through simulation of off-lattice self-avoiding double polygons consisting of cylindrical segments with radius rex of unit length. Here, a self-avoiding double polygon consists of twin self-avoiding polygons which are connected by a cylindrical segment. We show numerically that several statistical and dynamical properties of double-ring polymers in solution depend on the linking number of the constituent twin ring polymers. The ratio of the mean-square radius of gyration of self-avoiding double polygons with zero linking number to that of no topological constraint is larger than 1, in particular, when the radius of cylindrical segments rex is small. However, the ratio is almost constant with respect to the number of vertices, N, and does not depend on N. The large-N behavior of topological swelling is thus quite different from the case of knotted random polygons. [ABSTRACT FROM AUTHOR]

Using fast lattice Monte Carlo (FLMC) simulations [Q. Wang, Soft Matter 5, 4564 (2009)] and the corresponding lattice self-consistent field (LSCF) calculations, we studied a model system of grafted homopolymers, in both the brush and mushroom regimes, in an explicit solvent compressed by an impenetrable surface. Direct comparisons between FLMC and LSCF results, both of which are based on the same Hamiltonian (thus without any parameter-fitting between them), unambiguously and quantitatively reveal the fluctuations/correlations neglected by the latter. We studied both the structure (including the canonical-ensemble averages of the height and the mean-square end-to-end distances of grafted polymers) and thermodynamics (including the ensemble-averaged reduced energy density and the related internal energy per chain, the differences in the Helmholtz free energy and entropy per chain from the uncompressed state, and the pressure due to compression) of the system. In particular, we generalized the method for calculating pressure in lattice Monte Carlo simulations proposed by Dickman [J. Chem. Phys. 87, 2246 (1987)], and combined it with the Wang-Landau– Optimized Ensemble sampling [S. Trebst, D. A. Huse, and M. Troyer, Phys. Rev. E 70, 046701 (2004)] to efficiently and accurately calculate the free energy difference and the pressure due to compression. While we mainly examined the effects of the degree of compression, the distance between the nearest-neighbor grafting points, the reduced number of chains grafted at each grafting point, and the system fluctuations/correlations in an athermal solvent, the θ-solvent is also considered in some cases. [ABSTRACT FROM AUTHOR]

We present results of molecular dynamics simulations for coarse-grained polymer brushes in a wide temperature range to investigate the factors that affect the glass transition in these systems. We focus on the influences of free surface, polymer-substrate interaction strength, grafting density, and chain length not only on the change of glass transition temperature Tg, but also the fragility D of the glass former. It is found that the confinement can enhance the dependence of the Tg on the cooling rate as compared to the bulk melt. Our layer-resolved analysis demonstrates that it is possible to control the glass transition temperature Tg of polymer brushes by tuning the polymer-substrate interaction strength, the grafting density, and the chain length. Moreover, we find quantitative differences in the influence range of the substrate and the free surface on the density and dynamics. This stresses the importance of long range cooperative motion in glass formers near the glass transition temperature. Furthermore, the string-like cooperative motion analysis demonstrates that there exists a close relation among glass transition temperature Tg, fragility D, and string length 〈S〉. The polymer brushes that possess larger string length 〈S〉 tend to have relatively higher Tg and smaller D. Our results suggest that confining a fragile glass former through forming polymer brushes changes not only the glass transition temperature Tg, but also the very nature of relaxation process. [ABSTRACT FROM AUTHOR]

A merged vector grating, which is holographically fabricated in an anisotropic medium by irradiation with interference light with intensity modulation and polarization modulation, was designed to detect the polarization of light. The merged vector grating is recorded by the interference of two elliptically polarized beams with equal intensities, parallel azimuths, equal ellipticities, and different directions of rotation. We clarified theoretically that the Stokes parameters of the incident light beam are described by the diffraction efficiency of the merged vector grating. Also, to apply this property to formation of a polarimeter without any moving parts or mechanisms, two merged vector gratings with different grating vectors were recorded in a photocrosslinkable polymer liquid crystal film by angle-multiplexed holography. By investigation of the diffraction properties of the gratings obtained, we demonstrated the applicability of the merged vector gratings for use in polarimetry. [ABSTRACT FROM AUTHOR]

Photorefractive grating formation dynamics in long-timescale writing and the effects of periodic writing through the control of writing beam irradiation or electric field application were investigated using typical photorefractive polymers. Both dark current and writing beam irradiation affected grating formation dynamics. Dark current in polymers changed the effective trap density over time through deep trap filling and/or detrapping and thus affected grating formation considerably. The writing beam irradiation also affected grating development in the presence of an electric field owing to the accumulation of filled deep traps. However, grating development recovered after the elimination of the electric field freed up the filled deep traps. [ABSTRACT FROM AUTHOR]

We developed a phenomenological theory to describe the aligning field of polymer networks in polymer stabilized liquid crystals where sub-micron size polymer networks are phase separated from the liquid crystal in dispersion. The polymer networks are anisotropic and anchor the liquid crystals in their longitudinal direction. They inhibit the liquid crystals reorientation when external stimuli, such as electric field and temperature, are applied and reduce the relaxation time from distorted states. We model the effects produced by the polymer networks as an effective aligning field. We calculate the effective field as a function of the polymer network volume fraction and the lateral size of the network. The theory is compared with experimental results and good agreements were obtained. It is very useful in predicting how much polymer networks change the driving voltage and response time of liquid crystal devices. [ABSTRACT FROM AUTHOR]

Tailorable anisotropic intrinsic and scale-dependent properties of carbon nanotubes (CNTs) make them attractive elements in next-generation advanced materials. However, in order to model and predict the behavior of CNTs in macroscopic architectures, mechanical constitutive relations must be evaluated. This study presents the full stiffness tensor for aligned CNT-reinforced polymers as a function of the CNT packing (up to ∼20 vol. %), revealing noticeable anisotropy. Finite element models reveal that the usually neglected CNT waviness dictates the degree of anisotropy and packing dependence of the mechanical behavior, rather than any of the usually cited aggregation or polymer interphase mechanisms. Combined with extensive morphology characterization, this work enables the evaluation of structure-property relations for such materials, enabling design of aligned CNT material architectures. [ABSTRACT FROM AUTHOR]

A large variety of composites for electrical applications are developed worldwide on a daily basis. Most of these materials are made from carbonaceous fillers dispersed in polymers. The optimization of the formulations is complex and depends on parameters that are difficult to identify ab initio. The results might also be very sensitive to the processing conditions. There is therefore a need for a fast and accurate method to measure the electrical properties of samples with unfamiliar geometric features and without altering their shape. A four point probes method is incremented that fulfills all the above mentioned requirements. An analytical model is proposed that extends Uhlirs theory and permits to quickly determine the resistivity distribution. Experimental and theoretical approaches were performed to validate the method. An example is proposed with the measurement of samples initially designed for fuel cell-bipolar plates-application. [ABSTRACT FROM AUTHOR]

A Monte Carlo (MC) study is made of the persistence length q and the binary cluster integral β (or the excluded-volume strength B) for polyelectrolytes by the use of the discrete Kratky-Porod wormlike chain with hard-core-effective Debye-Hückel electrostatic pair potentials. The quantity q is determined from the initial decay rate of the bond correlation function after preliminary confirmation of the validity of this procedure using the chain with Lennard-Jones pair potentials. The quantity B is determined from the mean-square radius of gyration along with q by the use of the quasi-two-parameter (QTP) excluded-volume theory. They are evaluated for two model cases of polyelectrolytes, sodium hyaluronate as an example of semiflexible polymers and poly(sodium 4-styrenesulfonate) as a typical example of flexible polymers, both in aqueous sodium chloride. The behavior of MC data so obtained for q and B as functions of added salt concentration c is examined in detail, comparing them with the Odijk-Skolnick-Fixman theory of q and the Fixman-Skolnick (FS) theory of B and also with literature experimental data. In particular, the MC values of B are in almost complete agreement with the FS theory for large c, although the latter still overestimates B somewhat for small c. The values of B themselves and also the validity of the QTP theory in general are discussed in comparison with the case of nonionic polymers. [ABSTRACT FROM AUTHOR]