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Center research is organized
into three major project areas: Molecular/Macroscopic,
Interfaces, and Polymers and Gels,
each of which combines molecular modeling and design, synthesis,
physical studies, and applications development into an integrated,
multidisciplinary, collaborative research effort.
Molecular/Macroscopic
- This project has three main themes: discovery of new LC structural paradigms;
understanding the molecular origins of the macroscopic characteristics
of LC systems; and the synthesis and physical evaluation of new materials
designed to exhibit chosen features of FLC molecular organization. The
focus is on the development of computer-based methods to relate macroscopic
LC properties to molecular structure, and their use to generate new LC
materials for EO and NLO.
- Chiral Smectics from
Achiral Molecules - Our recent discovery of the spontaneous formation
of macroscopic chiral domains in smectic phases composed of achiral
bow-shaped molecules has dramatically broadened the scope of our research
on chiral/polar smectics. These materials exhibit several completely
new phases of matter, and are (based on recent history) quite likely
to have more surprises in store. We are actively exploring this new
structural paradigm, pursuing the design of achiral bow-shaped molecules
exhibiting a ferroelectric ground state (the materials synthesized
to date have an antiferroelectric ground state), and investigating
an alternative route to the creation of achiral ferroelectrics, via
the molecular engineering of synclinic and anticlinic layer interfaces
in hydrogen-bonded bilayer smectics. We are also moving to exploit the
obvious latent EO and NLO applications potential of these novel polar
smectics.
- FLC NLO - A key
research opportunity for FLCs is their potential use as the nonlinear
optical (NLO) ultra-fast (> 10 GHz) integrated Electronic Electro-Optic
(EEO) modulators needed for ultra-fast optical switching in telecommunications
and computing. LCs enable integration of EEO thin films on semiconductor
chips, in a process easily adaptable to large scale manufacturing. Our
efforts will focus on the two critical materials issues in this application:
(1) Obtaining adequately large EEO second-order susceptibility coefficients
(r > 50 pm/V); and (2) Optical quality. The former goal is being
addressed both empirically and by employing LC design tools for pre-synthesis
assessment of the orientational ordering of FLC molecules containing
carefully chosen, highly-nonlinear chromophores suitable for use in
EEO with 1.3 micron light. The latter goal is being addressed by developing
a better understanding of FLC alignment.
- Computational Tools for
LC Materials Design and Discovery - The microscopic behavior of
LC systems remains poorly understood at a fundamental level, as does
the emergence of macroscopic properties from their collective behavior.
Center research focuses on the application of computer simulation and
statistical mechanics to the development of a molecular-level understanding
of self-organization in liquid crystalline materials, and on the creation
of calculational tools for the directed design and pre-synthesis prediction
of LC properties from chemical structure. This broad-based research
effort requires an equally broad range of calculational approaches (a
modeling hierarchy), including computationally inexpensive, single-molecule
mean-field theory based methods, intermediate-scale pair or cluster
approximations, and exploratory large-scale atomistic simulations. We
have applied this hierarchical strategy in the creation of predictive
mean-field models of FLC polarization and other properties, and in pioneering
large-scale simulation studies of LC microphysics. We are pursuing the
wider application of mean-field theory and large-scale simulation to
the calculation of critical materials properties of LCs and to a baseline
microscopic characterization of LC phases. We plan to extend our computational
capabilities through the creation of intermediate-scale calculational
approaches, including cluster simulation methods for modeling small
numbers of molecules with appropriately designed mean-field boundary
conditions, and application of liquid-state theory and density functional
theory to the calculation of LC thermodynamics and phase behavior.
Interfaces-
The situation with regard to understanding the LC-solid interface is analogous
to that of surface chemistry: If the structure of the solid surface underlying
an LC sample is not known at the molecular level, then a deep understanding
and, ultimately, control of LC alignment cannot be achieved. A principal
goal of the Interfaces project, therefore, is to develop solid surfaces
that can be structurally characterized at the molecular level, and then
to probe LC-solid interfacial structure and interactions. This demands
novel methods for LC interfacial structuring and control, which we will
pursue by using new techniques of fabrication and manipulation of Self-Assembled
Monolayers (SAMs) developed with NSF MRG support. Particular emphasis
will be placed on relating the bulk alignment characteristics of SAMs
and adsorbed LC monolayers to their structure; on the development of mesogenic
SAMs; on the role of chirality in surface structure; and on the creation
and evaluation of novel interface structures for SSFLC devices.
Polymers and Gels
- Hybrid LC-polymer materials significantly broaden the science and applicability
of LCs, enabling new alignment mechanisms, a myriad of novel structural,
EO, and NLO effects in LC-organic or inorganic composites, glass formation,
unique polymerization conditions and polymer morphology, and unusual phase
behavior. We are exploring the organization of monomers and polymers in
LC phases, and studying the effect of LC ordering on polymerization, pursuing
the discovery of monomer-structure-dependent nanosegregation made with
NSF MRG support. Systems to be studied include acrylate-based FLC-polymer
gels, and siloxane and ADMET polymerized side- and main-chain FLC polymers.
Emphasis will be placed on creating glassy LCs for NLO applications, probing
the structure of LC gels, and developing gels that combine mechanical
rigidity with low switching viscosity.
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