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Constructing the spatio-selective crystalline structures has been an effective strategy to diversify the functions and applications of polymers. However, it is still challenging to program the crystalline heterogeneity into commercialized polymers and realize associate functions by a simple yet generalizable method. Herein, we propose a facile approach to fabricate multifunctional materials by programming the spatial distribution of crystal size in semicrystalline polymers. Various crystal size patterns in both plane and depth directions are introduced by the photothermal effect of printed ink and subsequent crystallization at different temperatures, which can be reprogrammed by repeated melting and crystallization. These obtained materials with well-defined crystal size heterogeneities exhibit diverse and regulable optics, mechanical and swelling properties, as manifested in applications including rewritable polymer paper, programmed mechanics, and advanced morphing devices. The light-induced crystal size heterogeneity of polymers has provided insights into developing advanced multifunctional materials.

Stereocomplex (SC) crystallization between polymer enantiomers has opened a promising avenue for preparing high-performance materials. However, high-crystallinity SCs are difficult to achieve for high-molecular-weight (HMW) enantiomeric blends of chiral polymers [e.g., poly(lactic acid)]. Despite extensive studies, why HMW enantiomeric blends have difficulty in SC crystallization has not been clarified. Herein, we chose the HMW poly(l-lactic acid)/poly(d-lactic acid) (PLLA/PDLA) 1/1 blend as the model system and demonstrated the crucial role of chain entanglement in regulating SC crystallization. PLLA/PDLA blends with various entanglement degrees were prepared by freeze-drying. We observed that disentangling promoted not only the crystallization rate but also the crystallinity of SCs in both the nonisothermal and isothermal processes. The less-entangled samples crystallized exclusively as the high-crystallinity SCs at different temperatures, in contrast to the predominant homocrystallization that occurred in the common entangled samples. This study provides deep insight into the SC crystallization mechanism of polymers and paves the way for future research attempting to prepare SC materials.

Smart hydrogels have attracted widespread attention and have displayed comprehensive applications in many fields. The development of a novel type of bilayer hydrogel with synergistic function of anisotropic deformation and photochromic property is extremely challenging. Many previous researches have focused on multiple response hydrogels. However, it hardly achieves the synergy of deformation and color-changing through a method with the advantages of simplicity, stability, practicality, and precise control. Herein, a near-infrared light (NIR) photothermal thermoresponsive graphene oxide/poly(N-isopropylacrylamide-β-cyclodextrin) (PNIPAM-β-CD/GO) hydrogel layer and a reversible photochromic ammonium molybdate tetrahydrate/poly(N-isopropylacrylamide-co-β-cyclodextrin) (PNIPAM-β-CD/Mo7) hydrogel layer were combined to obtain a bilayer hydrogel through the host–guest interactions between β-CD and the isopropyl group of NIPAM, exhibiting integrate anisotropic shape deformation and reversible photochromic behaviors. The designed actuators can undergo complex deformation owing to volume shrinkage caused by the photothermal effect under NIR of the PNIPAM-β-CD/GO layer, while the PNIPAM-β-CD/Mo7 hydrogel layer shows the characteristics of quickly color changing within 5 s when irradiated by a UV light source. The multiple responsiveness of hydrogels on temperature, NIR irradiation, and UV irradiation displays valuable advantages in multifunctional smart materials, such as intelligent soft robots.

Thermoresponsive polymers that exhibit a cloud point temperature (Tcp) are an important class of stimuli-responsive polymers that have great potential for biomedical applications. Precise tuning of the Tcp is of fundamental importance for designing thermoresponsive polymers. However, tuning the Tcp generally requires sophisticated control over the chemical and assembled structures of thermoresponsive polymers. Here, we report a simple yet effective method to tune the Tcp of thermoresponsive polymers only by mixing and varying the mixing ratios of amphiphilic copolymer pair that contains l- and d-configured hydrophobic blocks in a dilute solution. Stereocomplex (SC) crystallization of the l- and d-configured blocks led to form core–shell micelles with a larger size, a bigger core, and a higher aggregation number, which facilitated the intermicellar aggregation upon heating due to improved intermicellar attractions. SC crystallization of the hydrophobic blocks improved the separation efficacy of the thermor...

Design of the polymer networks with tunable mechanical properties and multishape memory effects (multi-SMEs) is highly desired in the engineering applications. Herein, we report on the stereocomplexed and homochiral polyurethane (PU) elastomers with tunable multi-SMEs by cross-linking the triblock prepolymers bearing the poly(l-lactic acid) (PLLA) and poly(d-lactic acid) (PDLA) enantiomeric segments. The homochiral PU is nearly amorphous, yet the stereocomplexed PU becomes highly crystalline due to the stereocomplexation of enantiomeric segments. Moreover, the two distinct thermal (glass, melting) transitions of PLLA (or PDLA) segments in PUs are integrated to realize the thermally induced triple- and quadruple-SMEs. Control over the enantiomeric segmental ratios allows the feasible manipulation of crystallizability, mechanical and thermal properties, and multi-SMEs of PUs.

End functionalization of homopolymers by noncovalent binding units is a straightforward approach to prepare supramolecular polymers with a broad application scope as stimuli-responsive functional m...

End functionalization is an effective avenue to develop polymers with specific functions. Microphase separation between the polymer segment and the end group can lead to end-functionalized polymers organizing into ordered structures; this behavior is more significant for crystallizable end-functionalized polymers. However, the role of polymer crystallization in the ordering organization of end-functionalized polymers remains unclear. Herein, we synthesized end-functionalized poly(e-caprolactone) (PCL) with the liquid crystalline (LC) 4-hexyloxy-4′-cyanobiphenyl terminal, denoted LC-PCL. We demonstrated that the structural organization of LC-PCL was governed by the polymer composition and PCL crystallization. LC-PCL with a short PCL block organized in a smectic-like bilayer structure. LC-PCL with a medium PCL block length assembled in multilayers comprised of alternating PCL lamellae and LC layer; however, the formation of the LC layer was prohibited when the crystallization of PCL was fast. LC-PCL with a long PCL block only formed PCL lamellae, similar to conventional semicrystalline polymers. This study provides deep insight into the hierarchical structural organization of semicrystalline end-functionalized polymers.

End-functionalization of oligomers with multiple H-bonding units is a feasible method to prepare supramolecular polymers. Competitive crystallization of H-bonding units and oligomeric blocks can drive supramolecular polymers to form long-range ordered structures. Herein, we report the controlled synthesis, competitive crystallization kinetics, and crystallization-driven structural organization of thymine-monofunctionalized supramolecular poly(L-lactide) (PLLA-Thy). PLLA-Thy having a well-defined end-functionality and controlled molecular weight was synthesized by ring-opening polymerization using hydroxyl-functionalized thymine as the initiator. PLLA-Thy exhibits the double-crystalline nature, in which the PLLA block and the thymine terminal have a similar crystallization temperature (Tc) and melting point (Tm). The crystallizability of the thymine unit was depressed in PLLA-Thy with a long PLLA block. The thymine terminal and PLLA block revealed the competitive and coincident crystallization kinetics in PLLA-Thy with a medium thymine fraction, depending on Tc. Prompt crystallization of the thymine unit drove the lamellar organization of PLLA-Thy in a long range; the subsequent crystallization of the PLLA block segregated between thymine layers depressed the regularity of the lamellar ordering of PLLA-Thy. This work provides important insights into the multi-step crystallization and crystallization-induced structural organization of semicrystalline supramolecular polymers.

Semicrystalline polymers can crystallize in the unique crystalline polymorph and show different phase behaviors under the high-pressure CO2 treatment. Understanding such unique crystallization and phase transition behavior is of fundamental importance for the CO2-assisited processing of semicrystalline polymers. Herein, we investigated the polymorphic crystalline structure, phase transition, and structure-property relationships of poly(L-lactic acid) (PLLA) treated by CO2 at different pressures (1–13 MPa) and crystallization temperatures (Tc’s, 10–110 °C). PLLA crystallized in the PLLA/CO2 complex crystals under 7–13 MPa CO2 at Tc ≤ 50 °C but the common a crystals under the high-pressure CO2 at Tc ≥ 70 °C. Solid-state nuclear magnetic resonance analysis indicated that the PLLA/CO2 complex crystals possessed weaker interactions between the PLLA chains than the common a crystals. The PLLA/CO2 complex crystals were metastable and transformed into the thermally stable a crystals via the solid-to-solid route during heating or annealing at the temperature above 50 °C. The complex crystals of PLLA produced at low Tc was more ductile than the a crystals due to the lower crystallinity and the plasticizing effect of CO2.

Crystallization in confined environments usually induces polymers showing complicated crystallization kinetics and unusual crystalline structure. Beyond the typical confined polymer systems, pre-existing crystals can also exert confinement effects on the subsequent crystallization of polymorphic or multi-component polymers; this, however, is not well understood at present. Herein, poly(L-lactic acid)/poly(D-lactic acid) (PLLA/PDLA, abbreviated as L/D) asymmetric blends with various PDLA fractions (f D = 0.02–0.5) are chosen as a model system and the effects of pre-existing stereocomplexes (SCs) on the crystallization kinetics and polymorphic structure are investigated. It is found that unusual β-form homocrystals (HCs) of poly(lactic acid) can be formed in an asymmetric L/D blend, which are strongly influenced by the molecular weights (MWs) of the used polymers, L/D mixing ratio, thermal treatment temperature (T max) and crystallization temperature (T c). The formation of β-HCs is preferred in asymmetric L/D blends with low and medium MWs, medium f D (0.1–0.2), medium T max (170–200°C), and low T c (70–110°C). The metastable β-HCs reorganize into the more stable α-HCs via melt recrystallization in the heating process. It is proposed that the β-HC formation stems from the constraining effects of pre-existing SCs; this constraining effect is governed by the content of pre-existing unmelted SCs in the thermally treated samples.

The stability and rheology of water-in-oil-in-water (W/O/W) emulsions stabilized by ABIL EM 90 (water-in-oil) and fatty alkoxy ethylene ether-AEO9 (oil-in-water) were investigated. The addition of ...

Stress-free two-way shape memory polymers (2W-SMPs) capable of reversible shifting between two distinct shapes are versatile platforms for the development of future smart devices. However, it is challenging to prepare stress-free 2W-SMPs with good actuation performance and shape programmability from single-component semicrystalline polymers. Herein, we demonstrate a straightforward and universal strategy for preparing 2W-SMPs through self-nucleated crystallization (SNC) of semicrystalline polymers. SNC enables the formation of two types of crystals in the 2W-SMPs, annealed and primary crystals, which function as the skeleton phase and actuation phase, respectively. We achieved a high reversible actuation strain of 17.6% and a good reprogrammability of the SNC-treated polymer networks. Complex shape transformations were obtained, and smart devices were fabricated from the SNC-treated networks by using a locally designed folding and kirigami structure. The SNC strategy provides a generalized approach to improve the 2W-shape memory behavior of semicrystalline polymers.

The dispersed phase of the water-in-oil-in-water emulsion system appears to be useful as a novel drug-delivery system in pharmaceuticals, food, and cosmetics applications. Until recently, achieving...

Switching temperature (Tsw) is a key parameter governing the service condition of shape memory polymers (SMPs). However, tuning Tsw of SMPs often requires sophisticated synthesis or intricate proce...

The growing urgence of information protection promotes continuously the development of information-encryption technique. To date, hydrogels have become an emerging candidate for advanced information-encryption materials, because of their unique stimulus responsiveness. However, current methods to design multi-level information-encrypted hydrogels usually need sophisticated chemistry or experimental setup. Herein, a novel strategy is reported to fabricate hydrogels with multi-level information encryption/decryption functions through spatially programming the polymorphic crystal phases. As homocrystalline and stereocomplex crystal phases in fluorescent hydrogels have different solvent stabilities, the transparency and fluorescence of the hydrogels can be regulated, thereby enabling the multi-level encryption/decryption processes. Moreover, the structural origins behind these processes are discussed. It is believe that this work will inspire future research on developing advanced information-encryption materials upon programming the polymer crystal structure.

Constructing noncovalent interactions has been a benign method to tune the stimuli responsivity and assembled structure of polymers in solution; this is essential for controlling the functions and properties of stimuli-responsive materials. Herein, we demonstrate a novel supramolecular strategy to manipulate the cloud point (

A graphene oxide/poly(N-isopropylacrylamide-co-β-cyclodextrin) (GO/poly(NIPAM-co-β-CD)) hydrogel has been synthesized through host-guest interaction between β-cyclodextrin (β-CD) and the isopropyl group of N-isopropylacrylamide (NIPAM). The product exhibits rapid responses to the stimuli of temperature and near-infrared (NIR) irradiation, self-healing properties, and excellent mechanical properties. The host-guest interaction serves as the main physical cross-linker, while a hydrogen bond between the hydroxyl group of β-CD, GO sheets and amide group of NIPAM acts as a secondary cross-linker. The volume phase transition temperature and NIR response rate of such a hydrogel are controlled by its contents of β-CD and GO. The obtained hydrogels showing excellent properties might be applied in remote contactless control devices in advanced smart technologies. Based on the excellent characteristics of the hydrogels, remote light-controlled switches have been designed, and more applications will be explored, such as intelligent light-controlled drivers and soft robots.

Block copolymers of poly(N-isopropylacrylamide) (PNIPAM) with both a hydrophobic segment and a hydrophilic terminal group in the same chain were synthesized by reversible addition-fragmentation chain-transfer (RAFT) polymerization. One is a diblock copolymer with only hydrophobic poly (stearyl methacrylate) (PSMA) segment, while the other is a triblock copolymer with both a PSMA segment and a hydrophilic terminal group. Uniform spherical micelles were obtained. The triblock copolymer micelles showed a distinct evolution, first becoming small, then becoming larger, and finally becoming stable. The transition process was fast and reversible with temperature. Although the hydrophobic PSMA chain segment lowered the lower critical solution temperature of the diblock copolymer micelles, that of the triblock copolymer micelles was almost as high as that of the PNIPAM homopolymer. In the triblock copolymer, hydrophobic chains and hydrophilic segments co-existed, and their opposing effects partially canceled. The hydrophilic terminal group on the triblock copolymer made a great difference.

Stereocomplex (SC) crystallization has been an effective way to improve the physical performance of polymer materials. However, SC crystallization of stereocomplexable polymer blends with complemen...

Semicrystalline polymers generally undergo polymorphic crystal transition and lamellae structural changes during stretching deformation. Such stretch-induced multilevel microstructural evolutions a...

NiCo-based layered double hydroxides (NiCo-LDHs) have plenty of superior properties as electrode materials of supercapacitors, while the poor cycle performance heavily limits their application. An effective strategy to tackle this issue is to dope inactive Al that could stabilize the metallic layers to form ternary hydroxides. However, the desired ternary electrodes with appropriate content of Al3+ can hardly be prepared by conventional electrodeposition due to the great difference in solubility product constants (K sp) of corresponding hydroxides, where the non-electroactive Al(OH)3 (K sp = 1.3 × 10‒33) are preferentially deposited than the hydroxides of nickel and cobalt (K sp = 2.0 × 10‒15, 1.6 × 10‒15). Here, we propose a novel electrodeposition method assisted by F‒ to control Al3+ content in NiCoAl-LDHs. By adjusting the concentration of F‒ in the electrolyte, Al3+ content, as well as the morphology and electrochemical performance of the electrodes, could be manipulated. With the optimum ratio of F− to Al3+, the as-obtained electrode shows high specific capacitance along with a long lifespan (54.1%, 10000 cycles). An asymmetric supercapacitor is assembled using active carbon as the negative electrodes, which displays the maximal energy density of 35.5 Wh kg−1 at the power density of 477.3 W kg−1, with a long lifespan (75%, 10000 cycles).

Amorphous and melted components can segregate into the interlamellar or interspherulitic regions of polymer crystals in their blends/mixtures; this phase behavior strongly influences the physical properties and functions of materials. However, it is experimentally difficult to evaluate the spatial distributions of the other components in polymer crystals. Herein, we use a small-molecule liquid crystal (LC) as a probe and find that it forms different solid phases when mixed with the semicrystalline polymer poly(l-lactic acid) (PLLA). The LC can form the metastable phase at the lower PLLA crystallization temperature but the stable phase at the higher PLLA crystallization temperature in the PLLA/LC mixture. The formation of LC metastable and stable phases is attributed to the segregation of the LC material in the interlamellar and interspherulitic regions of polymer crystals, respectively. This study provides a potential way to evaluate the spatial segregation in the crystallization-induced microphase separation of polymer blends/mixtures.

The widespread application of thermo-responsive hydrogels requires materials with robust mechanical properties and tunable responsiveness. Herein, we report robust thermo-responsive physical hydrogels with a tunable network structure and responsiveness by controlling the manner of crystallization of hydrophobic blocks. Biocompatible, stereocomplexable poly(l-lactic acid) (PLLA) and poly(d-lactic acid) (PDLA) were introduced into thermo-responsive poly(N-isopropylacrylamide) (PNIPAM) to obtain the enantiomeric grafted copolymers PNIPAM-g-PLLA and PNIPAM-g-PDLA and their corresponding hydrogels. The hydrophobic PLLA/PDLA domains served as physical crosslinking junctions in the hydrogels. The crystalline structure of the hydrogels can be facilely tuned by varying the ratio of PLLA/PDLA enantiomeric blocks. Stereocomplex (SC) crystallization between PLLA and PDLA facilitates the formation of H-bonded hydrophobic domains with denser chain packing, which endows the racemic hydrogels with a stronger network structure, higher mechanical strength, and better solvent resistance compared to enantiopure examples. The hydrogels exhibit good thermo-sensitivity in water; the stronger racemic hydrogel network restricts volume shrinkage and water desorption at high temperatures, enabling the facile control of thermo-responsiveness. The crystallization-tuned thermo-responsiveness of racemic and enantiopure hydrogels also allows for the design of assembled bilayer hydrogels capable of thermally triggered reversible shape morphing.

Interaction between networks has been proven to be of importance for mechanical property enhancement of double-network (DN) hydrogels. In this work, inter-network ionically cross-linked hybrid DN hydrogels have been prepared using poly(sodium 2-acrylamide-2-methylpropanesulfonate) (PNaAMPS) as the first network, and a co-polymer of a cationic monomer and acrylamide (AM) as the second network. Ionic complexes were formed between the two oppositely charged networks after dialyzing the hydrogels in water. Near the ion-balance point, hybrid DN hydrogels with enhanced strengths were achieved compared to the unmodified PNaAMPS/polyacrylamide (PAM) DN hydrogel. Synchrotron radiation small-angle X-ray scattering (SAXS) analyses were performed on the DN hydrogels. It was found that large and compact cross-linked domains were formed in the hybrid DN hydrogels, especially near the ion-balance point, as demonstrated by the SAXS results. These large and compact cross-linked domains, which indicate enhanced interactions between networks containing ionic bonds besides physical entanglements, dissipate additional concentrated stress, resulting in high strength of the hybrid DN hydrogels.

In this work, three different polyether-modified siloxanes (PMS1, PMS2, and PMS3) were applied to stabilize water-in-oil emulsions, and sodium caseinate (SC) was used to establish water-in-oil-in-water (W/O/W) emulsions. Here, PMS polymers were modified by Isolan GPS and SC by Tween 80. The impact of modifications on the physical stability and controlled release of W/O/W emulsions were investigated. It was found that the storage stability and control release of double emulsions were dependent on the types of PMS used, percent of Isolan GPS, and Tween 80. When PMS1 and PMS2 were combined with low percent of Isolan GPS and Tween 80, the dispersed droplet sizes were reduced, lower percent in the gravitational sedimentation were achieved than using PMS3 emulsions. The controlled releases of Mg2+ from W/O/W emulsions by using PMS3 were slower than using other PMS. PMS3 had a strong influence in controlling the release of Mg2+ from the double emulsions.

Poly(ethylene glycol)-b-poly(ε-caprolactone) diblock copolymers (PEG-b-PCL) with predesigned hydrophilic/hydrophobic block length ratios have been synthesized and self-assembled to form micelles, then used to emulsify medium-chain triglycerides with an aqueous phase. The morphologies and sizes of PEG-b-PCL copolymer micelles have been characterized by transmission electron microscopy and dynamic light scattering. Interfacial tension testing between micellar dispersions and oil, combined with water contact angle measurements, have been performed to assess the ability of these micelles to adjust interfacial tension and micellar hydrophobicity, respectively. Relationship between the wettability of PEG-b-PCL copolymer micelles and their emulsification properties has been proved through phase diagram, optical microscopic observation, droplet sizes evolution and phase separation behavior of Pickering emulsion samples. Results show that both oil-in-water and water-in-oil Pickering emulsions, as well as water-in-oil-in-water (W/O/W) double-Pickering emulsions, may be controllably prepared through one-step homogenization. Double microstructure of W/O/W Pickering emulsion has proved to be extremely stable during long-term storage.

Polymorphic crystalline structure has been a key factor determining the mechanical property and degradation behavior of biodegradable polymers. Herein, we report on the polymorphic crystalline structure, phase transition, and their effects on the mechanical property and degradation behavior of poly(p-dioxanone) (PPDO), a typical biodegradable and bioabsorbable semicrystalline polymer for biomedical applications. Both the polymorphic crystalline structure and crystallization kinetics of PPDO depend on crystallization temperature (Tc) drastically. Melting enthalpy and degree of crystallinity of PPDO first decrease and then increase with increasing Tc. PPDO forms a new mesomorphic polymorph (denoted as the α′-form) during crystallization at low Tc (≤10 °C), in contrast to the common α crystals generated at high Tc (≥60 °C). The α′ crystals have weaker interchain interactions and a shorter long period than the common α crystals, indicating the looser chain packing of α′ crystals. The α′ crystals are metastabl...

Stereocomplexation of complementary chiral blocks has been a feasible way to prepare thermoresponsive physical gels (or thermogels). Understanding the thermoresponsive phase behavior of stereocomplexable amphiphilic copolymers in water is essential to prepare thermogels with tunable physical properties. Herein, we use an enantiomeric mixture of the poly(D-lactic acid) (PDLA)/poly(ethylene glycol) (PEG) diblock copolymer and the poly(L-lactic acid) (PLLA)/PEG triblock copolymer as a stereocomplexable system and report a novel thermogel that exhibits unique gel–sol–gel multiple transitions upon heating. The thermally-induced phase transition of the PEG–PDLA/PLLA–PEG–PLLA thermogel was governed by the copolymer composition and the stereocomplexation of PLLA/PDLA segments. The molecular motion of PEG segments enhances during the gel–sol transition but slows down in the subsequent sol–gel transition. The gel–sol and sol–gel transitions that occurred at low and high temperatures are driven by the increased mobility of PEG segments and micelles and the promoted PLLA/PDLA stereocomplexation, respectively. PEG–PDLA/PLLA–PEG–PLLA gels can be used to capsulate and release a hydrophobic drug; the drug release rate increases as the content of hydrophilic blocks increases.