Use of Atomic Force Microscopy to Study a Molecular Micelle as an Anionic Polymer for Polyelectrolyte Multilayer Deposition on Polymeric Substrates
Polyelectrolyte multilayers (PEMs) have been used as stationary phases for various chiral and achiral separations in open-tubular electrochromatagraphy (OT-CEC). However, the physical characteristics of PEMs are not well understood. The production of PEM coatings involves flowing alternating rinses of positive and negative charged polyelectrolytes onto a surface. Although PEMs are typically deposited on fused silica capillaries, there is growing interest to use this approach in conjunction with microchip devices to enhance separation characteristics. Since microchips are fabricated using polymeric substrates, the deposition of PEMs on these substrates needs to be examined.
The study reported in this thesis uses atomic force microscopy (AFM) to examine the thickness and integrity of PEMs deposited on polycarbonate (PC), poly(methylmethacrylate) (PMMA), oxidized poly(dimethylsiloxane) (PDMS) and a glass wafer as a control. Poly(diallyldimethylammonium chloride) (PDADMAC) and a molecular micelle, poly(sodium N-undecylenyl- L-leucyl-alanate) (poly-L-SULA), were the polyions used in this study. The PEMs flowed through a microfluidic network defined by PDMS channels in contact with the polymer surface. Since salt is used in OT-CEC to increase the surface area in which analytes can interact, the effect of varying the salt concentration of the PDADMAC on the polymeric substrates was investigated, as well as the overall heights and integrity of the PEMs on the various substrates. Inconsistency of the PEM heights within a single system was observed and is most likely the result of roughness or defects within the substrates, leading to incomplete surface coverage. Preliminary data suggest that PDADMAC/SULA coating may prove to be beneficial in achieving microchip separations at NaCl concentrations of 0.1M and lower since higher concentrations lead to the collapse of the PEM assembly.
Advisor:Steve Watkins; Steve Soper; Robert Cook; Isiah Warner
School:Louisiana State University in Shreveport
School Location:USA - Louisiana
Source Type:Master's Thesis
Date of Publication:09/05/2006