Date

2017

Document Type

Dissertation

Degree

Doctor of Philosophy

Department

Chemical Engineering

First Adviser

Pearson, Raymond A.

Other advisers/committee members

Gilchrist, James F.; Daniels, Eric S.; Dittanet, Peerapan

Abstract

This dissertation contains two portions: modification of latex particle surfaces with polymerizable surfactants during emulsion polymerization for latex and coating application; synthesis of latex particles of multilayer morphology for epoxy toughening applications. The main focus of first portion of this dissertation research is to evaluate improvements in poly (n-butyl methacrylate) – PBMA - latex and film properties resulting from the use of a polymerizable surfactant HITENOL KH-10 compared with its non-polymerizable control LA-12 during the latex synthesis via emulsion polymerization, and to investigate the underlying mechanism of those improvements. Latexes prepared with KH-10 exhibited 240% higher stability against CaCl2 addition, and resulted in films with suppressed water-sensitivity and surfactant migration. Mechanism accounting for these improvements of the PBMA latex and film properties is a significant difference in surfactant distribution/incorporation into different loci in latex system (including in aqueous phase, on latex particle surfaces and inside latex particles) between KH-10 and LA-12. 66% of KH-10 was anchored on latex particles surfaces compared with only 21% for LA-12. Further study found the increase of surface-anchored polymerizable surfactants causes a 300% increase of particle coalescence enthalpy during film formation, increasing the energy barrier for dried particles to heal and form a coherent film. The second portion of this dissertation research focuses on development of a novel emulsion polymerization technique for synthesizing silica/PBA/PMMA multilayer core-shell composite latex particles with single cores of silica nanoparticles (avg. diam. 22 nm), because these multilayer particles were proposed to be promising toughening agents for epoxy. Colloidal silica nanoparticles were surface-treated with silane (3-methacryloxypropyl trimethoxysilane) before sequential emulsion polymerization of n-butyl acrylate (BA) and methyl methacrylate (MMA). Precise control of a series of parameters including surfactant concentration and monomer feed rate is critical for successful synthesis of multilayer particles with single silica cores. Synthesized multilayer nanoparticles were extracted from latex and utilized as epoxy toughening agents for diglycidyl ether of bisphenol A (DGEBA) compared with two other toughening agents—commercial core-shell poly(styrene-butadiene) rubber (CSR) particles and hybrid toughening agents containing mixture of CSR and silica nanoparticles. Multilayer particles exceeded the other two in toughening ability at low volume fractions in epoxy (<2.5%) but exhibited a decreasing toughening ability as volume fraction increased, a trend contrary to the other two. Particle dispersion morphology and fracture surface morphology were investigated by transmission electron microscopy (TEM) and scanning electron microscopy (SEM). It was observed that multilayer particles formed small clusters throughout the matrix for all volume fractions studied (1.25% - 7.5%), while CSR and silica nanoparticles were uniformly and individually dispersed inside epoxy matrix. SEM images of fracture surfaces showed that matrix void growth might be the primary toughening mechanism for multilayer-particle-toughened epoxy but void growth became less prominent as volume fraction of particles increased, corresponding to the trend that epoxy toughness decreased as volume fraction of multilayer particles increased.

Available for download on Friday, June 01, 2018

Share

COinS