Photonic Properties of Self -Assembled Organic Materials: Supramolecular Films, and Nanoribbon -Templated Gels and Polymers
Li, Leiming
This item is only available for download by members of the University of Illinois community. Students, faculty, and staff at the U of I may log in with your NetID and password to view the item. If you are trying to access an Illinois-restricted dissertation or thesis, you can request a copy through your library's Inter-Library Loan office or purchase a copy directly from ProQuest.
Permalink
https://hdl.handle.net/2142/82713
Description
Title
Photonic Properties of Self -Assembled Organic Materials: Supramolecular Films, and Nanoribbon -Templated Gels and Polymers
Author(s)
Li, Leiming
Issue Date
2002
Doctoral Committee Chair(s)
Stupp, Samuel I.
Department of Study
Materials Science and Engineering
Discipline
Materials Science and Engineering
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Engineering, Materials Science
Language
eng
Abstract
Photonic properties were studied in two self-assembled systems: supramolecular rodcoil self-assemblies, and materials templated with dendron rodcoil (DRC) nanoribbons. A rodcoil molecule contains covalently connected rod-like and coil-like segments. The aggregation of rodcoils forms supramolecular polar layered structures with infinitymm symmetry. Nonlinear optical properties of these materials are determined by their molecular characteristics. Several sets of architecturally similar but chemically different rodcoils were studied, and their nonlinear susceptibility was found strongly influenced by molecular hyperpolarizability and layer spacing of the supramolecular materials formed by these molecules. The macroscopic polarization of these materials is relatively low, possibly caused by polydomain structures. To improve the polarization, glass substrates were patterned with periodic arrays of squares with lateral dimensions of 7 and 17mum, created by focused ion beams. The average molecular tilt angle was found smaller in the films on patterned substrates, suggesting that substrate micropatterning enhances overall polarization in these supramolecular films. DRC molecules contain covalently connected dendritic, rod-like, and coil-like segments, and form gels with certain monomers and solvents like styrene or 2-ethylhexyl methacrylate (EHMA). Gelation is triggered by the self-assembly of DRC molecules into a network of ribbon-like nanostructures that are 10nm wide, 2nm thick, and up to 10mum long. DRC nanoribbons improve chain orientation in stretched DRC-polystyrene samples polymerized from DRC-styrene gels, compared with pure polystyrene stretched to the same extent. Linear-shape dyes show significantly larger emission polarization when incorporated in stretched DRC-polystyrene than in stretched pure polystyrene. When subject to a DC electric field, DRC-EHMA gels undergo electrophoresis, creating solid films consisting mostly of oriented DRC nanoribbons. The poled nanoribbon film shows uniform birefringence, and the nanoribbons are oriented along the poling field, suggested by TEM studies of ultramicrotomed samples. DRC gelation process disperses inorganic nanocrystals like ZnO, forming a stable nanocrystal-nanoribbon hybrid material. Similar electrophoresis occurs to the gel containing ZnO, orienting both nanoribbons and ZnO nanocrystals along the poling field. The poled DRC-ZnO film generates ultraviolet lasing emissions, with greatly lowered threshold compared with pure ZnO nanocrystals.
Use this login method if you
don't
have an
@illinois.edu
email address.
(Oops, I do have one)
IDEALS migrated to a new platform on June 23, 2022. If you created
your account prior to this date, you will have to reset your password
using the forgot-password link below.
