Design of Collective Motions from Synthetic Molecular Switches, Rotors, and Motors

Precise control over molecular movement is of fundamental and practical importance in physics, biology, and chemistry. At nanoscale, the peculiar functioning principles and the synthesis of individual molecular actuators and machines has been the subject of intense investigations and debates over the past 60 years. In this review, we focus on the design of collective motions that are achieved by integrating, in space and time, several or many of these individual mechanical units together. In particular, we provide an in-depth look at the intermolecular couplings used to physically connect a number of artificial mechanically active molecular units such as photochromic molecular switches, nanomachines based on mechanical bonds, molecular rotors, and light-powered rotary motors. We highlight the various functioning principles that can lead to their collective motion at various length scales. We also emphasize how their synchronized, or desynchronized, mechanical behavior can lead to emerging functional properties and to their implementation into new active devices and materials.

Photoresponsive polymers with multi-azobenzene groups

Photoresponsive polymers with multi-azobenzene groups are reviewed and their potential applications in photoactuation, photo-patterning, and photoinduced birefringence are introduced.

Effects of UV irradiation and condensation on poly(ether-ether-ketone)/carbon fiber composites from nano- to macro-scale

Durability and damage mechanism of carbon fiber–reinforced poly(ether-ether-ketone) composites (T300/PEEK) have been investigated under ultraviolet (UV) and water condensation conditions for 1560 h. The tensile modulus decreased by 5.4% after 1560 h of exposure, while no significant changes were found in tensile strength. The microhardness and elastic modulus of the resin measured by atomic force microscope–based nanoindentation were found to be dramatically increased after 240 h treatment and then decreased after longer treatment. The thermal decomposition temperature decreased from 549° to 522° after 840 h of exposure due to the formation of side chains and low molecular products induced by UV. The damage of resin was attributed to chain scission and recombined cross-linking by UV irradiation and hydrolytic deterioration by hydrothermal conditioning, where the decomposition led to the formation of carbonyl groups and hydroxyl groups, as well as the reduction of ether groups determined by Fourier transform infrared spectroscope. Scanning electron microscopy analysis on tensile fractures near the exposed surface indicated fiber/matrix debonding. The resin on the surface degraded rapidly, and its roughness increased continuously from 30.8 ± 4.1 nm to 88.8 ± 6.8 nm after 840 h of degradation, with the formation of microholes and microcracks. A degradation mechanism was proposed, and the accelerated weather aging affected only the surface region of T300/PEEK.