Functionalization of silica micro-capillaries and silica nanoparticles via polymer brushes

Polymer brushes were synthesized on the interior of micro-capillaries to study the influence of brushes on solvent flow through a confined space. The synthesis of several polymer brush coatings was performed in fused silica micro-capillary tubing by atom transfer radical polymerization using the "grafting from" approach. Characterization of the polymer coatings inside of the capillaries was challenging due to inaccessibility of the sample geometry. Fluorescence spectroscopy was used as a technique to verify that covalently-attached polymer brushes were present. Capillary rise measurements demonstrated that the Zisman critical surface energy changes as the polymer coatings were modified from either a hydrophilic or a hydrophobic surface. The hydrophilic and hydrophobic nature of polymers leads to flow in micro-capillaries that can be manipulated and controlled in a passive fashion without external stimulus.;Backpressure measurements were performed to show how selective solvents can be used to alter the backpressure required for flow. The measurements were used to correlate the flow of good/bad solvents with different polymer coatings; we speculate how these solvents alter brush conformation as an explanation for differentiated backpressure measurements. An analogous study involved capillaries functionalized with small molecule silanes which supported the hypothesis that the polymer brush is in an extended (solvated) state in good solvent and in a collapsed stated in bad solvent.;Preferential flow experiments were designed to measure the preferred path an aqueous solvent would take when comparing two capillaries containing polymer coatings of different surface energies. Water flow preferred the hydrophilic, higher surface energy coated capillary when comparing capillaries of the same internal diameter. When the difference in internal size became too large, the surface energy effect was overwhelmed and the aqueous solvent flowed down the larger, hydrophobic capillary.;The second portion of this dissertation describes the in situ formation of functionalized silica nanoparticles. The reactive stabilizers used in the study were [3-(2-bromoisobutyryl)propyl]triethoxysilane and [3-(2-bromoisobutyryl)propyl]ethoxydimethylsilane. Both stabilizers have an ATRP initiator at the non-condensable end yielding an initiator-immobilized silica nanoparticle. With the initiator-functionalized silica nanoparticles, ATRP synthesis was performed with styrene, tert-butyl acrylate and methyl acrylate. The size of these functionalized silica nanoparticles was controlled by varying the reactive stabilizer concentration and the time of addition.;This work was extended by using preformed polymer chains as the reactive stabilizer. The polymer chain contained a monoethoxysilane-functional group which condensed to form hybrid polymer/silica nanoparticles. The relationships among the molecular weight, time of addition and concentration of the polymeric stabilizer to the nature of the resulting nanoparticle were studied. The large polymer reactive stabilizers did not afford the control in particle size observed with the small molecule reactive stabilizers.