Soft-Material-Based Devices and Technologies

Soft matter systems have length scales ranging from several nanometres to a few microns and slow time scales due to large sizes. These systems are termed soft due to their sensitivity to external perturbations as compared to pure molecular materials. Colloidal dispersion, polymers, membranes, and biological macromolecules are typical soft matter systems. Soft matter systems in equilibrium have been studied in great details. These systems can be easily driven out of equilibrium by external perturbations, like shear, temperature gradient, tuning electric and magnetic fields and applying pressure, and so on. The simplest non-equilibrium state of a system is steady state. This means that there is a time-independent current in the system. Example of typical non-equilibrium steady-state phenomenon includes phase transitions like shear-banding, lane formation, glass and gel formation, homogeneous and heterogeneous crystal nucleation and cluster formation, tracer diffusion in polymeric membrane under external force. We have investigated a couple of classes of soft matter systems in non-equilibrium situation: (1) steady-state behaviour of systems with temperature-sensitive interactions in the presence of temperature gradient and (2) motion of particles driven through a polymeric network. These systems in non-equilibrium situations may be helpful for various technological purposes. We observe long-ranged crystalline order in cold region in thermo-sensitive ligand capped noble metal nanoparticles in the presence of temperature difference. The aggregated order particles may be useful for sensory applications. We also study thermo-responsive colloids that show change in diameter with temperature. We observe long-range order in hot region as well as in cold region in the presence of temperature gradient in this system beyond a certain diameter ratio. It can be helpful in designing structures at high temperature. In other class of problem, we explore different parameters of polymer network to reduce respiratory droplet permeation through a face mask. We observe that the efficiency of the face mask depends on composition of polymer, interaction strength of tracer and the network, the polymeric network rigidity, and the thickness of the confinement. Our results may be helpful in designing breathable face mask with better efficiency. Finally, we study a model system to control binary mixture separation through membrane using reverse osmosis technique. We observe performance of RO membrane in terms of permeation, solute rejection, and fouling can be controlled with changing relative interaction of membrane material with mixture. Our results may be useful for designing reverse osmosis membrane with better permeation, selectivity, and less fouling for longer use.