Doctoral Dissertations

Date of Award

8-2016

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Chemistry

Major Professor

Bin Zhao

Committee Members

Brian Long, John Bartmess, Hong Guo

Abstract

This dissertation describes the synthesis of polymer brush-grafted nanoparticles (hairy NPs) and an analysis of their behavior or utility in multiple areas. The hairy NPs were synthesized from silica NPs functionalized with initiating moieties by surface-initiated atom transfer radical polymerization. A brief introduction to hairy NPs, with a focus on the synthesis and behavior of stimuli-responsive polymer brush-grafted particles, is given in Chapter 1 to provide context for this work.

Chapters 2 and 3 present the synthesis of thermosensitive diblock copolymer brush-grafted nanoparticles designed as hairy NP analogues in place of thermosensitive block copolymers micelles for the construction of hybrid, physical hydrogels. Chapter 2 details a series of hairy NPs with a thermosensitive poly(methoxydi(ethylene glycol) methacrylate) (PDEGMMA) inner block and a charge-bearing, poly(DEGMMA-co-2-(methacryloyloxy)ethyltrimethylammonium iodide) (PDEGMMA-co-TMAEMA-I) outer block. These hairy particles underwent a reversible, cooling-induced gelation at moderate concentrations in water, based on the packing of hairy NPs due to the LCST-driven increase in brush volume fraction upon cooling. Another series of thermosensitive hairy NPs was made with brushes composed of P(TMAEMA-I)-b-PDEGMMA, which exhibited a heating-induced reversible gelation at concentrations as low as 3 wt % in water, due to the association of PDEGMMA outer blocks at temperatures above their LCST. The inner hydrophilic polyelectrolyte block served to bridge these domains and NPs to form a three-dimensional gel network.

Chapter 4 details the use of NPs grafted with oil-soluble poly(lauryl mathacrylate) as lubricant additives. These hairy NPs showed superior stability in a poly(alphaolefin) (PAO) base lubricating oil, and the addition of 1.0 wt % hairy NPs to PAO yielded significant reductions in both friction and material wear. These gains were attributed to the formation of a load-bearing tribofilm at the rubbing interface. Chapter 5 explores the brush microphase separation of poly(n-butyl acrylate)-b-polystyrene (PnBA-b-PS) brush-grafted particles with PnBA as inner block. From TEM analysis, there appeared an evolution of phase morphology from a stripe-like nanostructure to a more uniform layered structure with increasing PS molecular weight, in qualitative agreement with simulation studies. Chapter 6 includes a look back on this dissertation work in its entirety and possible future work.

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