Ultra-thin films of polyvinyl alcohol on hydrophobic surfaces: Preparation, properties, chemistry, and applications
Abstract (Summary)A new approach to surface modification of materials has been formulated and explored in great detail. It was shown that polyvinyl alcohol (PVOH) quickly and irreversibly adsorbs to hydrophobic surfaces producing smooth, continuous, hydrophilic, robust films in the thickness range of tens of angstroms. Surfaces of all hydrophobic materials studied could be successfully turned hydrophilic by this adsorption, which is performed from dilute aqueous solutions of PVOH. The ultra-thin films of adsorbed PVOH were studied by means of contact angle, ellipsometry, XPS, AFM, FT-IR, and DSC. Adsorption conditions, such as time, polymer concentration and molecular weight, temperature, salt type and concentration, and polymer composition all have an effect on the properties of the adsorbed film. The unique character of PVOH irreversible adsorption among other water-soluble polymers is explained by polymer crystallization that occurs concurrently with adsorption. Crystallinity within adsorbed films is demonstrated by the means of FT-IR and DSC. Chemical properties of adsorbed PVOH were studied, and a number of synthetic procedures were developed for further modification of PVOH ultra-thin films. Cross-linking of adsorbed PVOH imparted great stability in hot water. PVOH in the ultra-thin films was successfully converted into a variety of polyvinyl esters and urethanes; polyethylene glycol was grafted "to" and "from" these films. Prospective applications of PVOH adsorption and its ultra-thin films were studied. Improved adhesion in glued joints of polyethylene was demonstrated when PVOH was pre-adsorbed on PE before applying adhesive. PVOH adsorption and subsequent PEG grafting significantly reduced protein adsorption on a hydrophobic surface. A possibility to create defined features on PVOH surface by chemical patterning was demonstrated. A novel design of vapor sensing devices based on the adsorbed and modified PVOH was proposed and studied in detail. It was shown that remarkable reproducibility in PVOH adsorption on surface acoustic wave devices can be achieved and that further chemistry of the adsorbed films permits the preparation of sensitive and selective vapor sensors.
School Location:USA - Massachusetts
Source Type:Master's Thesis
Date of Publication:01/01/2004