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Permeative flows, known for the explanation of the anomalous viscosity (10^5 Poise) in cholesterics at low shear rates, are still under debate due to the difficulty of experiments. Here we use the Surface Force Balance, in which uniform domains with regular circular defects are formed, to probe the forces generated by compression in the direction of the helical axis. At the quasi-static speed of the surface approach, the measured forces are shown to be elastic (not dissipative), arising from the twist elastic deformation when the planar anchoring at the walls is strong. A mechanism involving frictional surface torque under strong planar surface anchoring will be proposed. The results indicate that the strong resistance to flow observed, previously interpreted as an enormous apparent viscosity, may in fact originate from the intrinsic non-linear increase of elasticity when the molecules are rotated away from equilibrium. The system is found to store energy (the force is reversible), without dissipation, as long as the applied stress is below the threshold for nucleating new defects. Our study underpins the importance of boundary conditions that may dramatically change the rheology of other viscoelastic materials and sheds light on the rational design of strain-stiffening materials, nanomotors, and artificial muscles involving helical architectures.

The stick-slip phenomenon widely exists in contact mechanics, from the macroscale to the nanoscale. During cholesteric-nematic unwinding by external fields, there is controversy regarding the role of planar surface anchoring, which may induce discontinuous stick-slip behaviors despite the well-known continuous transitions observed in past experiments. Here, we observe three regimes, namely constrained, stick-slip, and sliding-slip, under mechanical winding with different anchoring conditions, and measure the responded forces by the Surface Force Balance. These behaviors result from a balance of cholesteric elastic torque and surface torque, reminiscent of the slip morphology on frictional substrates [T. G. Sano et al., Phys. Rev. Lett. 118, 178001 (2017)], and provide evidence of dynamics in static rotational friction.

Air contaminants emitted from animal buildings may harm the environment and public health. A windbreak wall with slightly acidic electrolyzed water (SAEW) sprayed downwind of the exhaust fans offers a potential approach for the removal of some of these air contaminants, including ammonia and airborne culturable bacteria (CB). This study was conducted to investigate the removal efficiency of ammonia and airborne CB by a proof-of-concept windbreak wall with SAEW spray for a layer breeding house. A windbreak wall with spraying system was placed downwind of an exhaust fan. Tap water and SAEW, a novel environment-friendly disinfectant, were used in the spraying system. Separate sampling manifolds for ammonia and airborne CB were placed at the inlet and the outlet of the windbreak wall, respectively, for ammonia and CB sampling. The windbreak wall with water spray and 70 mg L -1 (available chlorine concentration) SAEW spray both significantly reduced ammonia emissions from the house though the removal was small. The 70 mg L -1 SAEW spray showed a numerically higher ammonia removal efficiency (13.2%) than water spray (8.8%), but no significant difference was found (p = 0.13). The windbreak wall with 70 mg L -1 and 100 mg L -1 SAEW spray both significantly and moderately reduced airborne CB emission from the layer breeding house (p