Epoxy polymers represent a recently emerged class of thermoset shape memory polymers with superior thermo-mechanical endurance and excellent processability.

We demonstrate that stronger and more robust nacre-like laminated GO (graphene oxide)/SF (silk fibroin) nanocomposite membranes can be obtained by selectively tailoring the interfacial interactions between "bricks"-GO sheets and "mortar"-silk interlayers via controlled water vapor annealing. This facial annealing process relaxes the secondary structure of silk backbones confined between flexible GO sheets. The increased mobility leads to a significant increase in ultimate strength (by up to 41%), Young's modulus (up to 75%) and toughness (up to 45%). We suggest that local silk recrystallization is initiated in the proximity to GO surface by the hydrophobic surface regions serving as nucleation sites for β-sheet domains formation and followed by SF assembly into nanofibrils. Strong hydrophobic-hydrophobic interactions between GO layers with SF nanofibrils result in enhanced shear strength of layered packing. This work presented here not only gives a better understanding of SF and GO interfacial interactions, but also provides insight on how to enhance the mechanical properties for the nacre-mimic nanocomposites by focusing on adjusting the delicate interactions between heterogeneous "brick" and adaptive "mortar" components with water/temperature annealing routines.

Silk protein is a promising natural material applied in various fields, but the application of silk protein-based hydrogel is quite limited because of its long gelation time and poor mechanical properties. Here, we present a facile way to prepare strong silk protein hydrogels simply by adding surfactant into silk fibroin aqueous solution and incubating at 60 °C. The resulting silk protein hydrogels demonstrate fairly good mechanical properties; for example, the silk protein hydrogel made by adding sodium dodecyl sulfate (SDS) has the compressive and tensile moduli of 3.0 and 3.3 MPa, respectively, which are close to some tissues in the body, such as cartilages, tendons, and ligaments. The effect of different types of surfactant on the formation of strong silk protein hydrogel, and the possible reason for the improvement of the mechanical properties of the hydrogel are also discussed. In addition, we show that such a strong silk protein hydrogel maintains good biocompatibility when adding a proper amount of surfactant. Finally, we use a Fe3O4-loaded silk protein hydrogel as an example to demonstrate its application in the catalytic field. All these results imply that such a natural, sustainable, strong, and biocompatible protein-based hydrogel holds great promise as a multifunctional material in various applications.

The extraordinary comprehensive mechanical properties of animal silk (especially spider and silkworm silk) have led to extensive research on the underlying mechanisms involved. Herein, we selected various regenerated silk fibroin (RSF) fibers by choosing different postdraw conditions in a wet-spinning process developed in this laboratory to study their structure−property relationship. We use synchrotron radiation infrared and X-ray diffraction techniques to monitor the structural differences in these RSF fibers and correlate them with their mechanical properties. The results show that with the increase of post draw-down ratio, the β-sheet content, crystallinity, and molecular orientation in these RSF fibers increase while the crystalline size decreases. The relationship between structural changes and the draw-down ratio reflects the corresponding variation in mechanical properties, namely, an increase in breaking stress with a decline in breaking strain in relation to increases in draw-down ratio. Therefore, these results provide solid and direct evidence on the evolution of structure during the artificial spinning process and on how structure determines the final mechanical performance of silk fibers. We believe this study provides a good background on the relationship between microscopic structure and macroscopic properties in polymer science and may prove useful in the production of high performance materials, not only for silk fibers but also for other natural and synthetic polymeric materials.

The mystery of the structural–mechanical relationship in mulberry and non-mulberry silkworm silks was explored using synchrotron radiation techniques.

Tough RSF–CNT hybrid fibers with a breaking energy beyond 130 MJ m−3 were successfully obtained by using cheap regenerated silkworm protein and commercially available functionalized CNTs, with simplified industrial wet-spinning apparatus.

The effect of organo-nanoclay (Nanomer I30E) on the cure mechanism and kinetics of epoxy nanocomposites based on Epon 828 and Epicure 3046 was studied by means of dynamic differential scanning calorimetry (DSC) at four heating rates (2.5, 5, 10, and 20°C•min Ϫ1 ) and by Fourier transform infrared (FT-IR) spectroscopy. The DSC cure data for epoxy-amine mixtures with and without nanoclay was modeled by means of different approaches; the Kissinger and isoconversional models were used to calculate the kinetics parameters while the Avrami model was utilized to compare the cure behavior of the two systems. The Nanomer I30E was shown to initiate rapid homopolymerization of the Epon 828 resin at temperatures above 180°C. For the epoxy-amine mixtures, the presence of nanoclay had little effect on the cure kinetics in the early stages (i.e., at lower temperatures), and the apparent activation energy was around 60 kJ•mol Ϫ1 . However, in the later stages, the apparent activation energy increased significantly in the absence of nanoclay, but did not do so when it was present. The presence of nanoclay also lowered the final glass transition temperature by about 4°C.

Spatially heterogeneous distribution of active components is key to the diverse shape-morphing behaviors of biological species and their associated functions. Artificial morphing materials employing similar strategies have widened the design space for advanced functional devices. Typically, the spatial heterogeneity is introduced during the material synthesis/fabrication step and cannot be altered afterward. An approach that allows spatio-selective programming of crystallinity in a shape-memory polymer (SMP) by a digital photothermal effect is reported. The light-patternable crystallinity affects greatly the shape morphing behavior. Consequently, a pre-stretched 2D film with spatial heterogeneity in crystallinity can morph with time into designable 3D permanent shapes, achieving the 4D transformation. This approach utilizes a reprocessible thermoplastic SMP (polylactide) and the programming relies on a physical phase transformation (crystallization) instead of chemical heterogeneity. This allows repeated erasing and reprogramming using the same material, suggesting a versatile and sustainable means for manufacturing advanced morphing devices.