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Microdevices for the Demonstration of Active Transport through Liquid Crystalline Membranes

Stephen M. Martin and T. Alan Hatton. Department of Chemical Engineering, Massachusetts Institute of Technology, 77 Massachusetts Ave, 66-321, Cambridge, MA 02139

The physical properties of thermotropic liquid crystalline (LC) materials can vary significantly across phase boundaries (e.g. crystalline/nematic, nematic/isotropic.) Thus, the solubility and transport properties of a thermotropic LC can be altered in specific regions of the material through the application of external stimuli resulting in a phase change. If a spatially-controlled phase transformation, such as the nematic-isotropic transition, is induced in a sequence across the bulk of a LC sample then, in theory, a minor dissolved component can be forced across the sample. This ‘active transport' of the minor component is analogous to the zone-refining technique used to purify metals. Using this technique, the transport of a solute across a LC membrane could occur in the absence of an externally applied concentration gradient.

The development of a proof-of-concept device to examine the feasibility of such a technique led to the examination microdevices as test-beds for membrane materials. Using a variety of microfabrication and rapid-prototyping techniques, several test devices were developed. In addition, techniques were developed to control the phase transitions of a LC material in the devices through the variation of temperature gradients. The sequestration of LC material to form a ‘membrane' between two separate sections of the device has also been demonstrated.

We anticipate that these devices could prove valuable in the characterization of transport through a variety of membrane materials, and could also find specific applications in microdevices (e.g. sensors). Further, the development of LC supported membranes allows the introduction of a variety of organic functionalities to perform specific separations, including the potential for enantio-selective separations.



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