Polymer surface modification by adsorption from supercritical fluids

In this thesis, we develop a novel and simple approach to modify polymer surfaces by adsorbing functionalized polymers from supercritical fluids to get desirable properties. One example described in the thesis uses a photoactive block copolymer poly(styrene-b-tert-butylacrylate) (P(S- b-tBA)) to modify a polystyrene (PS) substrate. Supercritical fluid coating yields a surface bilayer structure with the low surface tension tert-butyl acrylate block residing at the polymer-air interface and the high surface tension PS block entangled with the PS substrate. A surface functionalized with carboxylic acid groups is subsequently formed and/or patterned by exposing the surface to UV radiation in the presence of a photo acid generator or by exposure to an acid such as trifluoroacetic acid. The part of surface covered by carboxylic acid groups is hydrophilic and reactive whereas the original surface is hydrophobic and inert. The surface patterned with tert-butyl regions and carboxylic acid regions is used as a template for selective electroless nickel deposition. The surface fully covered by carboxylic acid groups is conjugated with adhesion ligand, YRGDS, to improve surface biocompatibility. Another example is the use of poly(dimethyl siloxane) (PDMS) based antimicrobial polymers to coat both hydrophobic and hydrophilic cloth fibers to make the fibers have biological welfare. The antibacterial ability of the coated fibers is evaluated by standard methods.; The success of each research aspect is confirmed and characterized by a number of techniques, including XPS, contact angle, AVM, and ellipsometry. It is shown that the supercritical fluid coating method is a general, inexpensive, and environmental friendly approach for successful surface modification. Properties of polymer surfaces are easily controlled by functional groups in modifying polymers and the modified surfaces have many new applications.