Polymerization in Confined Geometries

Abstract

The work presented in this PhD thesis is centered on nanometer-sized pores. Two detailed objectives include: 1) investigating the confinement effect on "grafting from" polymerization carried out directly inside the pore, and 2) using porous silicon as a novel platform for controlled motion of liquid drops moving along wettability gradients created on the pores. In chapter 2 we investigate the confinement effect of the pore (< 50 nm) on the polymerization of poly methyl methacryrlate (PMMA) in porous silicon. Porous silicon has the unique quality of acting as a replacement for the conventional organic matrix used in matrix assited laser desorption ionization (MALDI). To this end, porous silicon not only acts as the substrate in which the polymerization takes place, but also serves as an in situ platform for the direct molecular weight analysis of the pore-grown polymer. We also report on the efficiency of porous silicon to produce MALDI spectra of PMMA as compared to MALDI spectra obtained using a conventional organic matrix.

Chapter 3 focuses upon the use of an alternative substrate, anodic aluminum oxide (AAO), for the in-pore polymerization of PMMA. AAO is attractive for its homogeneous pore distribution and commercial availability. Although AAO does not serve as an organic matrix replacement for MALDI like porous silicon, a procedure for the ex situ characterization of the pore grown PMMA via MALDI is discussed.

In chapter 4 we report on the motion of water droplets on porous and flat silicon surfaces decorated with molecular gradients comprising semifluorinated (SF) organosilanes. SF molecular gradients deposited on flat silica substrates facilitate faster motion of water droplets relative to the specimens covered with an analogous hydrocarbon gradient. Further increase in the drop speed is achieved by advancing it along porous substrates coated with the SF wettability gradients. The results of our experiments are in quantitative agreement with a simple scaling theory that describes the faster liquid motion in terms of reduced friction at the liquid/substrate interface.