Confinement and flow of microscopic defects in layered liquids.

摘要

The term layered liquid applies to a broad range of materials containing anisotropic molecules that arrange themselves in parallel stacks. Examples are concentrated surfactant solutions, block copolymers, bio-membranes, liquid crystalline polymers, and liquid crystals. Due to the solid-like nature of these materials, microscopic defects form when their parallel layer structure is disturbed by external forces, surface interactions, or geometrical confinement. Unlike in solid crystals, defects formed here can flow and we show that the presence of defects changes the flow characteristics of these materials.; In this work, we first introduce three different methods for using surface treatments to control the size and ordering of a particular class of defects known as focal conics: within closed PDMS microchannels, on PDMS surfaces covered with nanoscale cracks, and within ordered microcavities formed in PDMS films. We then examine the flow behavior of these defects in microchannels, using both surface tension differences and pressure gradients to drive the flow.; A microfluidic network is designed and developed to enable more precise control over the pressure driven flow. Driving flow within this microfluidic network enables simultaneous visualization of the defect texture evolution and measurement of the pressure gradient-flow rate relationship.; Our measurements show that the flow properties of layered liquids under confinement are different from their bulk, possibly due to the interaction of defects with each other and with the flow itself.