Liquid crystalline polymers are attractive materials for untethered miniature soft robots. When they contain azo dyes, they acquire light-responsive actuation properties. However, the manipulation of such photoresponsive polymers at the micrometer scale remains largely unexplored. Here, we report uni-and bidirectional rotation and speed control of polymerized azo-containing chiral liquid crystalline photonic microparticles powered by light. We first study the rotation of these polymer particles in an optical trap experimentally and theoretically. The micro-sized polymer particles respond to the handedness of a circularly polarized trapping laser due to their chirality and exhibit uni-and bidirectional rotation depending on their alignment within the optical tweezers. The attained optical torque causes the particles to spin with a rotation rate of several hertz. The angular speed can be controlled by small structural changes, induced by UV light absorption. After switching off the UV illumination, the particle recovers its rotation speed. Our results provide evidence of uni-and bidirectional motion and speed control in light-responsive polymer particles and offer a new way to devise light-controlled rotary microengines at the micrometer scale.Received: ((will be filled in by the editorial staff))Revised: ((will be filled in by the editorial staff))
Forward osmosis (FO), using the osmotic pressure difference over a membrane to remove water, can treat highly foul streams and can reach high concentration factors. In this work, electrospun TFC membranes with a very porous open support (porosity: 82.3%; mean flow pore size: 2.9 µm), a dense PA-separating layer (thickness: 0.63 µm) covalently attached to the support and, at 0.29 g/L, having a very low specific reverse salt flux (4 to 12 times lower than commercial membranes) are developed, and their FO performance for the concentration of apple juice, manure and whey is evaluated. Apple juice is a low-fouling feed. Manure concentration fouls the membrane, but this results in only a small decrease in overall water flux. Whey concentration results in instantaneous, very severe fouling and flux decline (especially at high DS concentrations) due to protein salting-out effects in the boundary layer of the membrane, causing a high drag force resulting in lower water flux. For all streams, concentration factors of approximately two can be obtained, which is realistic for industrial applications.
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