Date of Award
Fall 2017
Project Type
Dissertation
Program or Major
Materials Science
Degree Name
Doctor of Philosophy
First Advisor
John G Tsavalas
Second Advisor
Erik B Berda
Third Advisor
Gonghu Li
Abstract
Complex morphological structures of composite latex particles are designed so as to affect the physical properties of the final product those particles are applied in. This complex structure between multiple polymer phases is formed through the competition of polymerization reaction kinetics and the polymer phase separation process (when the two phases are incompatible) occurring simultaneously during the emulsion polymerization. Different reaction conditions and post-reaction processes will lead to various particle composite structures. The purpose of this thesis has been to investigate these dynamic processes within latex particles during emulsion polymerization and determine some of the key relevant parameters influencing the mechanism polymerization induced phase separation, specifically in an emulsion environment. Carefully designed matrixes were developed to obtain quantitative assessment of the degree of phase mixing, as a function of both reaction chemistry and process conditions, to build an understanding of the connection between particle morphology development, chemical composition, as well as reaction conditions. The overall message in this study was to explore how far polymer chains from each composition in the particles could diffuse over the reaction timeframe, given a preference for phase separation. Their diffusion sets how far they can translate, while the Gibbs free energy of mixing and the miscibility gap influences how early and fast they can rearrange into a second phase starting the separation process. This combination is critical to understanding particle morphology development, and those factors are dynamically changing throughout the course of the reaction. Once domains of a second phase are formed, phase separation then proceeds further by Ostwald ripening toward the equilibrium morphology.
We also considered the challenges associated with special interactions and functional comonomers, such as carboxylic acids or divinyl crosslinkers, which can influence the interactions between polymer chains and thus make the unraveling of these mechanistic pathways even more complicated. These types of functional comonomers are widely used in both laboratory and industrial copolymerization reactions, as a small molar fraction can have dramatic impact on polymer properties. One key portion of this study that will be discussed is the relationship between the network microstructures developed from hydrogen bonding interactions versus that of covalently crosslinked copolymers, the role combined roles of intermolecular and intramolecular networking, and the impact of those networks on the polymer’s effective glass transition temperature (Tg). That effective Tg directly impacts the chain’s ability to diffuse, which then is critical to the ability for the system to phase separate, or not.
Different categories of water exist in colloidal particles due to various bonding conditions. This is a well-known phenomenon in bulk polymeric films, often called ‘water whitening’, yet our group was the first to report the heterogenous structure of water domains within such confined dimensions as 100nm colloidal polymer particles. At the time, our whole approach was novel (as applied to polymer colloids), and after some reflection we felt the approach could indeed apply, but would need to be carefully updated with more appropriate constraints. In this thesis, the result of our recent efforts to modify and improve that approach to investigate water distribution within colloidal nanoparticles is discussed. Aside from applying new boundary conditions to the thermal gravimetric analysis (TGA) peak deconvolution, we introduce a new FTIR characterization study as a function of water content, including a 2D-correlation analysis, to assist in the interpretation of the TGA water loss profiles. With combination of those two characterization techniques, a new water-domain model was also built to determinate the water loss mechanism within nanoparticles. Experimental results from TGA analysis were in good agreement with those theoretical expectations.
Recommended Citation
ZHANG, PEI, "EXPLORATION OF FACTORS INFLUENCING POLYMERIZATION INDUCED PHASE SEPARATION IN SEEDED EMULSION POLYMERIZATION" (2017). Doctoral Dissertations. 2289.
https://scholars.unh.edu/dissertation/2289