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Local structure of liquid crystal molecules anchored on polarized domains
Scope and goals of research project:
This research is aimed at correlating how polarizable molecules, in particular classes of molecules that comprise liquid crystalline material, interact with a polar surface as it relates to crystallinity and structural phases. For the design of nanoscale opto-electronic devices including chemical sensing surfaces, a detailed understanding of how this surface could serve as a support for these molecules is paramount. This research direction is a fundamental study of new routes to self-assembly using atomically smooth, polarized domains to act as the anchors for polarized or polarizable molecules.
We are proposing to use a patterned piezoelectric surface composed of discrete, polarized regions that will serve to attract, to anchor, and to influence the alignment mechanism in both the polar (surface tilt) and azimuthal (in plane) orientations for liquid crystalline domains. Once attached, intermolecular forces, in particular non-covalent bonding, can serve to guide monolayer ordering and subsequent growth of multilayers emanating from these locally polarized domains. The presence of the permanent dipole moment as well as other polarization directions, allow for an external field, like a surface polarization, to tether and to dictate the alignment of this molecule. Of particular interest will be the study of ferroelectric and chiral liquid crystal molecules. We will study their surface bound behavior, and especially how the chiral centers dictate intermolecular interactions, and how highly functionalized nanoscale structures can be engineered. The chiral nature of the molecules will enable the creation of chiral, ordered domains, which can then offer stereoselectivity for potential chemical sensing applications analogous to surfaces used in enantioselective heterogeneous catalytic systems.
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| Figure 1: |
Example of competing forces in determining overlayer stucture measured by low temperature (4K) STM. Carbon disulfide (CS2), a quadrupolar molecule, deposited on Au(111) forms an ordered monolayer but intermolecular forces disrupt the registry with the underlying metal lattice.
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| Figure 2: |
Scanning probe microscopy will be used to address the monolayer structural phases that form on the polarized domains. Crystalline ordering at various surface coverages and temperature regimes will be determined by the competition between electrostatic anchoring (polar molecules-red dipoles) and intermolecular forces (blue dashes).
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