Title

Design, Synthesis, and Film Formation of Stimuli-Responsive Colloidal Dispersions Containing Phospholipids

Date of Award

2005

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Polymers and High Performance Materials

First Advisor

Marek W. Urban

Advisor Department

Polymers and High Performance Materials

Abstract

These studies were undertaken to further understand the design of colloidal dispersions containing bio-active phospholipids (PL) as stabilizing agents and their stimuli-responsive behaviors during film formation. Methyl methacrylate (MMA) and n-butyl acrylate (nBA) dispersions were synthesized using anionic surfactants and PL, and the surface-responsiveness of coalesced films was monitored at the film-air (F-A) and film-substrate (F-S) interfaces after exposure to temperature, UV, pH, ionic strength, and enzymatic stimuli. Using spectroscopic molecular-level probes such as attenuated total reflectance (ATR) and internal reflection IR imaging (IRIRI), these studies show that structural features of PL and surfactants significantly affect stimuli-responsiveness of polymeric films. MMA/nBA homopolymer, blend, copolymer, and core-shell particle coalescence studies indicated that controlled permeability is influenced by particle composition and sodium dioctyl sulfosuccinate (SDOSS) mobility to the F-A interface is enhanced in response to temperature. Utilization of hydrogenated soybean phosphocholine (HSPC) as a co-surfactant with SDOSS resulted in bimodal p-MMA/nBA colloidal particles, and experiments showed that ionic interactions with HSPC inhibit SDOSS mobility. However, the controlled release of individual species is detected in the presence of Ca 2+ ionic strength stimuli. Utilizing 1,2-bis(10,12-tricosadiynoyl)- sn -glycero-3-phosphocholine (DCPC), cocklebur-shape particle morphologies were obtained and using transmission electron microscopy (TEM), self-assembled tubules were detected at particle interfaces, but not in the presence of Ca 2+ . At altered concentration levels of DCPC, surface localized ionic clusters (SLICs) composed of SDOSS and DCPC form at the F-A and F-S interfaces in response to temperature and ionic strength stimuli. Micelle formation of 1-myristoyl-2-hydroxy-sn -glycero-phosphocholine (MHPC) stabilizes unimodal p-MMA/nBA colloidal particles. Elevated temperatures and K + ionic stimuli generate SLICs in the form of lipid rafts at F-A interfaces, and IRIRI and atomic force microscopy (AFM) experiments revealed that the rafts consist of crystalline SDOSS and MHPC domains. In contrast, 1,2-dilauroyl- sn -glycero-3-phosphocholine (DLPC) assembles liposomes during colloidal dispersion synthesis. TEM data illustrated that hollow p-MMA/nBA particles form, capable of releasing DLPC during coalescence in response to temperature, pH, ionic strength, and enzymatic changes, and lipid raft formation may be systematically controlled at the F-A and F-S interfaces.