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An original design strategy for the preparation of thermosetting resins with both super-high-frequency low dielectric constant (k) and low dielectric loss (f) as well as high glass transition temperature (Tg) values is presented. The key to this design strategy is incorporating a bulky group and reactive furan ring to increase the free volume and the cross-linking density, respectively. The formed multistructural networks (relatively dense near furan rings and relatively loose near bulky groups) are beneficial not only for lowering kvalues but also for maintaining high Tgs of main-chain benzoxazine copolymers. More importantly, the optimized copolymers possess low fvalues (≤0.008) under 5 and 10 GHz, satisfying the requirement of super-high-frequency communications. The correlations between the free volume and thermal and dielectric properties are also discussed to understand the synergistic mechanism. The work opens a new route for the structural design and preparation of super-high-frequency low dielectric functional polymeric materials.

The toughness of composite materials is size dependent below a critical load transfer length (lT). Fiber-reinforced viscoelastic polymers are uniquely suited to study the size-limited regime because the lTof these soft composites can be as high as several centimeters, in contrast to traditional composites where lTis extremely small, allowing a large window for macroscale characterization. In this work, we elucidate the parameters that influence the toughness of soft composites when failure is governed by a fiber pullout-induced matrix-fracture mechanism. We ultimately demonstrate three important points: (1) fiber-reinforced viscoelastic polymers can possess high toughness, even at dimensions well below lT, (2) significant toughness amplification occurs due to the presence of fibers, even when the fracture process consists solely of matrix rupture, and (3) the composite toughness in the fiber pullout region can be predicted from easily attainable component parameters.

Hydrogels usually are fabricated by using monomers or preexisting polymers in precursor solutions. Here, a polyelectrolyte complex biohydrogel (Bio‐PEC hydrogel) made from a precursor dough, by kneading, annealing, and crosslinking the dough of two oppositely charged polysaccharides, cationic chitosan quaternary ammonium salt (HACC) and anionic sodium hyaluronate (HA), photoinitiator (α‐ketoglutaric acid), crosslinker glycidyl methacrylate (GMA), and water of very small quantity is reported. Controlled kneading and annealing homogenized the dough with respect to transforming randomly distributed, individual polymer chains into tightly wound double‐stranded structures, which, upon UV irradiation, covalently sparsely crosslinked into a highly entangled network and subsequently, upon fully swollen in water, results in Bio‐PEC hydrogel, HACC/HA, exhibiting near‐perfect elasticity, high tensile strength, and high swelling resistance. Via the same kneading and annealing, tetracarboxyphenylporphyrin iron (Fe‐TCPP) metal nanoclusters are incorporated into HACC/HA to obtain photocatalytic, antibacterial, and biocompatible Bio‐PEC hydrogel composite, Fe‐TCPP@HACC/HA. Using SD rat models, the efficacy of Fe‐TCPP@HACC/HA in inhibiting Escherichia coli(E. coli) growth in vitro and the ability to promote wound healing and scar‐free skin regeneration in vivo, or its high potential as a wound dressing material for biomedical applications are demonstrated. This work demonstrates an approach to high tensile strength, toughness, and high swelling resistance polyelectrolyte complex biohydrogel (Bio‐PEC hydrogel) via the controlled kneading and annealing homogenized formation of tightly wound double‐stranded structures and sparsely covalently crosslinked into a highly entangled network. Tetracarboxyphenylporphyrin iron (Fe‐TCPP) is incorporated into Bio‐PEC hydrogel, showing favourable antibacterial activity and promoting wound healing and skin regeneration.

Acrylic acid-modified polyhedral oligomeric silsesquioxane (AC-POSS) was synthesized by the reaction between the amine groups in polyhedral oligomeric silsesquioxane (POSS) and acrylic acid, which could dissolve in water and can be easily purified. Free-radical copolymerization was applied to synthesize azobenzene liquid crystalline polymer silsesquioxane (LCP-POSS) with different proportions of AC-POSS and liquid crystalline monomers. The trans-isomers of azobenzene moieties in LCP-POSS were gradually transformed to cis-isomers with increasing ultraviolet irradiation time. The photoisomerization reaction of liquid crystalline polymer (LCP) and LCP-POSS showed the first-order dynamic reaction. Compared with the LCP, the photoisomerization rate constant of LCP-POSS was decreased due to the space steric hindrance of the POSS as a rigid segment. The phase transition temperature of liquid crystalline in LCP-POSS increased with increasing POSS content, and the liquid crystalline texture in LCP-POSS became smaller under the polarized light. With further increasing the POSS content (>50 wt%) in LCP-POSS, the ordered structure of the liquid crystalline phase was gradually affected, resulting in one-way liquid crystal (LC) phase behavior. The synthesized LCP-POSS has LC properties, light-responsive properties, and thermal stability. When the POSS is introduced into the LC material, the phase state of the LC material will become more abundant and the LC phase will become more stable. The significance of this study is to develop and extend its applications as stimuli-responsive materials and devices.

The human body is composed of composite structures made of water-rich hydrophilic domains and hydrophobic barriers. Combining hydrogels with elastomers results in similar synthetic biomaterials applicable to fields ranging from stretchable electronics to actuators. Here, we report a method to combine hydrogels with elastomers via a glass fiber fabric interphase. The interphase plays two roles: it enables chemically different materials to be robustly bound without chemical treatment while also dramatically improving the mechanical properties of the composite. Maximum interfacial adhesion energies of ∼1,000 N m−1between the hydrogel and fabric and ∼360 N m−1between the elastomer and fabric approach adhesion values of chemically bound soft materials. The composite tearing toughness (143 kJ m−2) vastly exceeds that of all neat components. In these materials, Young's modulus is high (∼1.2 GPa), while bending modulus is low (∼7 MPa), resulting in structures that can serve as actuators through controlled solvent exposure.

Ligaments are unique wet biological tissues with high tensile modulus and fracture stress, combined with high bending flexibility. Developing synthetic materials with these properties is a significant challenge. Hydrogel composites made from high stiffness fabrics is a strategy to develop such unique materials; however, the ability to produce these materials has proven difficult, since common hydrogels swell in water and interact poorly with solid components, limiting the transfer of force from the fabric to the hydrogel matrix. In this work, for the first time, we successfully produce extraordinarily tough hydrogel composites by strategically selecting a recently developed tough hydrogel that de-swells in water. The new composites, consisting of polyampholyte hydrogels and glass fiber woven fabrics, exhibit extremely high effective toughness (250 000 J m−2), high tear strength (∼65 N mm−1), high tensile modulus (606 MPa), and low bending modulus (4.7 MPa). Even though these composites are composed of water-containing, biocompatible materials, their mechanical properties are comparable to high toughness Kevlar/polyurethane blends and fiber-reinforced polymers. Importantly, the mechanical properties of these composites greatly outperform the properties of either individual component. A mechanism is proposed based on established fabric tearing theory, which will enable the development of a new generation of mechanically robust composites based on fabrics. These results will be important towards developing soft biological prosthetics, and more generally for commercial applications such as tear-resistant gloves and bulletproof vests.

An upper estimate for fiber/matrix modulus ratio in traditional fiber reinforced polymer (FRP) composites is 100. Matrices made from tough elastic gels can have modulus approaching kilopascals and increase this ratio to 107. We study how this extremely high modulus ratio affects the mechanical behavior of such fiber reinforced “soft” composites (FRSCs). We focus on unidirectional FRSCs with parallel fibers perfectly bonded to a soft elastic matrix. We show such composites exhibit the Mullins effect typically observed in rubbers and double network (DN) gels. We quantify size effect on mechanical properties by studying unidirectional composites consisting of finite lengthfibers. We determine the stress concentration factors (SCFs) for a cluster of fiber breaks in this geometry and show that there is a transition from equal load sharing (ELS) to local load sharing (LLS). We also determine the mean strength and work of extension assuming fibers obey Weibull statistics. We discuss the application of fracture mechanics to this emerging class of composites. We highlight similarities and differences between FRSCs and DN gels.