Juan J. De Pablo, University of Wisconsin-Madison, DMR 0520527

1. Reversible Control of Ordering Transitions at Aqueous/Liquid Crystal Interfaces Using Functional Amphiphilic Polymers Juan J. De Pablo, University of Wisconsin-Madison, DMR 0520527 Materials and interfaces with properties governed by weak intramolecular interactions form the basis of systems designed to sense, respond to, or report on changes in their environments. For example, polymers, surfaces, and fluids that respond to changes in temperature, pH, ionic strength, light, or electric fields have been exploited to develop sensors, actuators, and myriad other “smart” materials. Here, we report the design of a functional amphiphilic polymer that assembles at interfaces between a nematic liquid crystal and immiscible aqueous solutions and triggers ordering transitions in the liquid crystal. We demonstrate further that appropriately designed polymer-functionalized aqueous/liquid crystal interfaces respond reversibly to changes in the pH of aqueous phases in ways that couple the order of the liquid crystals to changes in the physico-chemical properties of their aqueous environments. The results of this investigation suggest principles and approaches that could be used to tailor the interfacial properties of liquid crystalline systems and design fluid interfaces that respond actively or reversibly to a broad range of environmental stimuli. Michael I. Kinsinger, Bin Sun, Nicholas L. Abbott and David M. Lynn, “Reversible Control of Ordering Transitions at Aqueous/Liquid Crystal Interfaces Using Functional Amphiphilic Polymers” Advanced Materials (Cover Article), in press, 2008. Figure Caption: A) Polarized light micrographs of polymer-functionalized PBS/5CB interfaces contacted alternately with PBS at pH 5.0 and PBS at pH 9.0. These experiments were conducted using a flow cell and interfaces prepared as described in the text. Variation in the interference colors across some grids likely results from variations in the thickness of the 5CB hosted in the pores of the TEM grid. B) Control experiment conducted using PBS/5CB interfaces not functionalized with polymer 1. C) Average gray-scale intensity of polarized light micrographs acquired after each exposure of the aqueous/liquid crystal interface to PBS at pH 5.0 or 9.0 for 10 cycles (see text). D) Average gray-scale intensity of polarized light micrographs acquired every second during exposure of the aqueous/liquid crystal interface to PBS at pH 5.0 or 9.0 for two cycles (arrows indicate times at which the pH of the buffer was changed). For the plots in C) and D), average gray-scale intensities of ~100 correspond to planar/tilted orientations of 5CB, and intensities of ~20 correspond to homeotropic orientations This work was supported by the National Science Foundation through the University of Wisconsin Materials Research Science and Engineering Center, DMR-0520527.