Although the elastocaloric effect was found in natural rubber as early as 160 years ago, commercial elastocaloric refrigeration based on polymer elastomers has stagnated owing to their deficient elastocaloric effects and large extension ratios. Herein, we demonstrate that polymer elastomers with uniform molecular chain-lengths exhibit enormous elastocaloric effects through reversible conformational changes. An adiabatic temperature change of −15.3 K and an isothermal entropy change of 145 J kg−1 K−1, obtained from poly(styrene-b-ethylene-co-butylene-b-styrene) near room temperature, exceed those of previously reported elastocaloric polymers. A rotary-motion cooling device is tailored to high-strains characteristics of rubbers, which effectively discharges the cooling energy of polymer elastomers. Our work provides a strategy for the enhancement of elastocaloric effects and could promote the commercialization of solid-state cooling devices based on polymer elastomers.

No abstract

Compared to polyvinylidene fluoride (PVDF) and its copolymers, castor-oil-derived nylon-11 has been less explored over the past decades, despite its excellent piezoelectric properties at elevated temperatures. To utilize nylon-11 for future sensor or vibrational energy harvesting devices, it is important to control the formation of the electroactive δ′ crystal phase. In this work, nylon-11 films were first fabricated by solution-casting and were then uniaxially stretched at different stretching ratios (SR) and temperatures (Ts) to obtain a series of stretched films. The combination of two-dimensional wide-angle X-ray diffraction (2D-WAXD) and differential scanning calorimetry (DSC) techniques showed that the fraction of the δ′ crystal phase increased with the stretching ratio and acquired a maximum at a Ts of 80 °C. Further, it was found that the ferroelectric and piezoelectric properties of the fabricated nylon-11 films could be correlated well with their crystalline structure. Consequently, the stretched nylon-11 film stretched at an SR of 300% and a Ts of 80 °C showed maximum remanent polarization and a remarkable piezoelectric coefficient of 7.2 pC/N. A simple piezoelectric device with such a nylon-11 film was made into a simple piezoelectric device, which could generate an output voltage of 1.5 V and a current of 11 nA, respectively.

No abstract

Stiffness and actomyosin contractility are intrinsic mechanical properties of animal cells required for the shaping of tissues. However, whether tissue stem cells (SCs) and progenitors located within SC niche have different mechanical properties that modulate their size and function remains unclear. Here, we show that hair follicle SCs in the bulge are stiff with high actomyosin contractility and resistant to size change, whereas hair germ (HG) progenitors are soft and periodically enlarge and contract during quiescence. During activation of hair follicle growth, HGs reduce contraction and more frequently enlarge, a process that is associated with weakening of the actomyosin network, nuclear YAP accumulation, and cell cycle reentry. Induction of miR-205 , a novel regulator of the actomyosin cytoskeleton, reduces actomyosin contractility and activates hair regeneration in young and old mice. This study reveals the control of tissue SC size and activities by spatiotemporally compartmentalized mechanical properties and demonstrates the possibility to stimulate tissue regeneration by fine-tuning cell mechanics.

The materials with low dielectric constant and low dielectric loss are vital for high integration degree of the circuit board. Although many polymers like epoxy resin exhibit excellent comprehensive performance, their dielectric constant is unable to satisfy high electronic packaging application. In this work, we present a simple grafting strategy via reaction between the hollow glass microsphere and polyhedral oligomeric silsesquioxane followed by blending epoxy resin to fabricate epoxy resin hollow glass microspheres composite materials. The superior heat resistance of hollow glass microspheres (HGM) can improve the thermal performance of composites. Due to the addition of Ge‐POSS, P‐HGM exhibited a good interfacial compatibility with epoxy resin matrix and forms an interfacial adhesion region. With the P‐HGM loading of 20 wt%, the fabricated composite materials exhibited the low dielectric constant of 2.59 and low dielectric loss of 0.0145. At the same time, the tensile strength, impact strength and flexural strength were 42.15 MPa, 24.33 kJ/m2 and 90.82 MPa, respectively, which demonstrated that the epoxy resin hollow glass microspheres composite materials processed superb mechanical behavior. It suggests that this method is a promising potential for fabricating low dielectric composite materials.

Polymers with both high dielectric breakdown strength and high dielectric constant are vital for large numbers of applications. However, most polymer or polymer composites suffer from the problem of deteriorated...

Stiffness and actomyosin contractility are intrinsic mechanical properties of animal cells required for the shaping of tissues. However, whether tissue stem cells (SCs) and progenitors located within SC niche have different mechanical properties that govern their size and functions remains unclear. We show that hair follicle SCs in the bulge are stiff with high actomyosin contractility and resistant to size change, whereas hair germ (HG) progenitors are soft and periodically enlarge and contract during quiescence. During activation, HGs reduce contraction and more frequently enlarge, a process that is associated with weakening of the actomyosin network, nuclear YAP accumulation and cell cycle re-entry. Induction of miR-205, a novel regulator of the actomyosin cytoskeleton, reduces actin contractility, decreases the stiffness of the bulge and HG, and activates hair regeneration in young and old mice. This study reveals the control of tissue SC size and activities by spatiotemporally compartmentalized mechanical properties and demonstrates the possibility to stimulate tissue regeneration by fine-tuning cell mechanics.