Title page for ETD etd-05092001-140133


Type of Document Master's Thesis
Author Farmer, Catherine Elizabeth
Author's Email Address cafarmer@vt.edu
URN etd-05092001-140133
Title Surface Characterization of Siloxane, Silsesquioxane, and Maleic Anhydride Containing Polymers at Air/Liquid Interfaces
Degree Master of Science
Department Chemistry
Advisory Committee
Advisor Name Title
Esker, Alan R. Committee Chair
Anderson, Mark R. Committee Member
Morris, John R. Committee Member
Keywords
  • polyvinylacetate
  • polydimethylsiloxane
  • poly(1-alkene-alt-maleic anhydride)
  • polyhedral oligomeric silsesquioxane
  • Langmuir-Blodgett
Date of Defense 2001-05-03
Availability unrestricted
Abstract
SURFACE CHARACTERIZATION OF SILOXANE, SILSESQUIOXANE, AND MALEIC ANHYDRIDE CONTAINING POLYMERS AT AIR/LIQUID INTERFACES

by

Catherine E. Farmer

(Abstract)

Langmuir-monolayer formation at the air/water interface (A/W) can be achieved by spreading amphiphilic molecules on a liquid subphase and compressing them into an ordered arrangement. The use of the Langmuir-Blodgett technique (LB) to prepare ultra thin films on solid surfaces from monolayers at A/W has considerable utility for studying surface interactions. In particular, the phase behavior of polyhedral oligomeric silsesquioxanes (POSS) was examined using a combination of LB and Brewster angle microscopy (BAM).

Polymer fillers have been shown to reduce the cost and often improve the properties of high performance polymer composites. The utility of POSS as a potential nanofiller in blends with polymers such as poly(dimethylsiloxane) (PDMS) and poly(vinylacetate) (PVAc) was explored using surface pressure-area per monomer isotherms (P-A) and BAM. Substantial morphological differences are seen between polymer blends with heptasubstituted trisilanol-POSS and fully condensed octasubstituted-POSS due to differences in subphase affinity.

Several poly(1-alkene-alt-maleic anhydride) (PXcMA) polymers were studied at both the gas/liquid interface as Langmuir films and at the gas/solid interface as Langmuir-Blodgett thin films on silicon substrates. A 0.01 M HCl solution (pH~2) was used during film deposition to ensure the carboxylic acids were fully protonated. The PXcMA polymers included X=1-hexene, 1-octene, 1-decene, and 1-octadecene (represented as PHcMA, POcMA, PDcMA, and PODcMA respectively). The P-A isotherms of these polymers were consistent with those obtained previously.1

Tensiometry was used to determine the critical micelle concentrations (c.m.c.) of variable molar mass poly(dimethylsiloxane-b-(3-cyanopropyl)methylsiloxane-b-dimethylsiloxane) (PDMS-PCPMS-PDMS) triblock copolymers and a poly(dimethylsiloxane-b-2-ethyl-2-oxazoline) diblock copolymer. Dynamic light scattering (DLS) corroborated interfacial tension results. The polymers exhibited well-defined temperature-independent c.m.c.'s. These measurements ensured that the synthesis of cobalt nanoparticles for biocompatible magnetic fluids occurred above the c.m.c.

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