Off-campus UMass Amherst users: To download campus access dissertations, please use the following link to log into our proxy server with your UMass Amherst user name and password.

Non-UMass Amherst users: Please talk to your librarian about requesting this dissertation through interlibrary loan.

Dissertations that have an embargo placed on them will not be available to anyone until the embargo expires.

Date of Award

9-2010

Document Type

Campus Access

Degree Name

Doctor of Philosophy (PhD)

Degree Program

Polymer Science and Engineering

First Advisor

Thomas P. Russell

Second Advisor

Paul M. Lahti

Third Advisor

Samuel P. Gido

Subject Categories

Materials Science and Engineering | Nanoscience and Nanotechnology | Polymer Chemistry

Abstract

One of the current challenges in materials science is establishing a simple way to generate an ultradense arrays of addressable nanoscopic elements on macroscopic scales. The addressability of nanomaterials is essential for many applications, ranging from high-density magnetic storage to high-density, ultrahigh resolution displays to photovoltaics. Among the strategies available, "photocombing" has been proposed as a promising route to create long-range ordered nanostructures in self-assembled block copolymers (BCPs) over macroscopic distances through a photocontrollable ordering transition. In this process, bands of light act as a "comb" to sweep across BCP thin films unidirectionally, reversibly bringing the BCPs through an ordering transition, like the disorder-to-order transition (DOT) and the order-to-order transition (OOT). Thus, defects are "combed" out, forming arrays of highly ordered BCP microdomains on a macroscopic length scale. It is similar in principle to the classic zone refining method, which is used to produce large single crystals of metals and semiconductors.

In this dissertation, I will focus on three systems to investigate photocombing. System I is the supramolecular assembly of poly(2-vinylpyridine)-block-poly(n-butyl methacrylate) and polystyrene-block-poly(2-vinylpyridine) di-BCPs with azobenzene-containing 2-(4-hydroxyphenylazo)benzoic acid chromophores. In these systems, an ordering transition from lamellae to hexagonally packed cylinders was observed after one hour of UV radiation at 150 °C. System II is the deuterated polystyrene-block-poly(n-butyl methacrylate) BCPs with photoisomerizable azobenzene functionalities. They exhibit an entropy-driven lower DOT, the characteristic of "compressibility", similar to their parent BCPs. System III is anthracene-functionalized tri-BCPs containing deuterated polystyrene (d 8 -PS) and poly(methyl methacrylate) (PMMA) blocks, as well as a small middle block of poly(2-hydroxyethyl methacrylates) that is randomly functionalized by anthracene. Under UV exposure, the junction between d8 -PS and PMMA blocks in the tri-BCPs is joined together through anthracene photodimers, thereby resulting in a significantly increase in the total molecular weight of the tri-BCPs. As a consequence, the tri-BCPs undergo an ordering transition from a disordered state to an ordered state, when it is phase-mixed but close to the boundary of the ordering transition.

Share

COinS