Influence of Functional Components On the Film Formation of Colloidal Dispersions
A number of colloidal dispersions were synthesized to advance knowledge and gain understanding regarding interactions between individual components and for elucidation of complex processes governing their film formation. These studies show that for methyl methacrylate/n-butyl acrylate (MMA/nBA) colloidal dispersions, the presence of functional components significantly affects film formation. The incorporation of polyvinyl alcohol (PVOH) into pMMA/nBA colloidal dispersions creates competing environments between the copolymer particle surfaces, aqueous phases, and dispersing agents which results in migration with self-induced stratification occurring during coalescence. pMMA/nBA/PVOH films stratify to form sodium dodecyl sulfate (SDS) rich film-air (F-A) interfaces, and the -SO 3- moieties exhibit preferential parallel orientation with respect to the surface. At the same time, the bulk of the film is dominated by intramolecular hydrogen bonding between the PVOH phase and the copolymer matrix. This behavior is attributed to significant interactions between PVOH and pMMA/nBA resulting in limited mobility of PVOH. Also, colloidal dispersions of poly(methyl methacrylate/n-butyl acrylate) in the presence of methylene bisacrylamide (MBA), n-(hydroxyl methyl)-acrylamide (HAM), and methacrylic acid (MA) crosslinkers have significant influence on the mobility of individual components and their stratification during and after coalescence. Utilizing thermomechanical and spectroscopic analytical tools, these studies show that physical and/or chemical crosslinking, which is a function of temperature, significantly alters interactions among the film components. While the presence of physical crosslinks significantly affects the mechanical strength of polymer networks at lower temperatures while chemical crosslinks are effective at elevated temperatures. Furthermore, the degree of crosslinking also influences stratification of selected components. These studies also examine the role of nano-SiO2 particles during colloidal synthesis of poly(methyl methacrylate/n-butyl acrylate) (pMMA/nBA) and their effect on the polydispersity index (PDI). Due to the presence of defects on the surface of SiO2 nanoparticles, these entities are capable of controlling the propagation of free radicals. In contrast to previous assessments that SiO2 nanoparticles serve as a loci of polymerization, SiO2 nanoparticles adsorb on the exterior of surfactant micelles where they couple with carbon based propagating radicals in the oil phase and the hydroxyl radicals produced in the aqueous phase. The control of carbon based radicals as well as the trapping of highly reactive hydroxyl radicals is shown to lower the PDI of pMMA/nBA from 15 to 93%, depending upon the initiator as well as reaction conditions. Finally, the creation of bioactive surfaces has garnered much interest due to potential applications in the medical industry. Many well-known methods used for the creation of bioactive surfaces utilize post modification techniques. With this in mind, we focused on the creation of bioactive surfaces with stimuli-responsive character without the need for further modification. These studies explored the concept of controlling inter/intramolecular interactions of multicomponent systems during the film formation process to create tailor-made surfaces of colloidal films. By utilizing the ionization of aspartic acid (Asp) by controlling the pH of poly-(methyl methacrylate/n-butyl acrylate) (pMMA/nBA) colloidal dispersions, bioactive surfaces could not only be created but also controlled. At acidic pHs, a surfactant rich layer could be observed at the film-air interface, while at basic pHs bioactive Asp islands were observed.