Surface Properties of Hydrophilic Polymers

Abstract

Polymers based entirely or substantially on hydrophilic monomers have achieved importance in recent years largely because of their ability to absorb water and form (in the case of cross linked polymer) soft, elastic gels (‘hydrogels'). The surface properties of this group of materials are important in both the dehydrated and hydrated state and yet no thorough-going study has been previously made of this aspect of these polymers. The surface properties in the dehydrated state govern such important aspects of manufacturing technology as particle fusion and adhesion (to the mould surface). In the hydrated state the surface properties govern inter alia the bio-compatibility of the polymer. Since hydrogels are important in such diverse biomedical fields as artificial liver support systems and contact lenses this represents an important field of knowledge. In order to determine the surface energy of the hydrophilic polymers a series of samples was prepared and the surface energy of each sample was determined by means of wetting experiments. These measurements were performed on both hydrated and dehydrated samples but only the surface energy of the dehydrated samples could be calculated. The problems were too great to allow unambiguous values for the hydrated samples to be determined, although a method for determining only the polar component of the surface energy was used with the hydrated samples and provided useful results. These experimental results were compared with results obtained by two different predictive methods, Parachor and CED, each of which used different parameters to estimate the surface energy of a copolymer. The predictive method which best matched the experimental results was extended to predict the surface energy of hydrated samples. Since surface energy controls both the rate of fusion of particles and the degree of mould adhesion seen with the polymer an attempt was made to use the experimental surface energy results to illuminate these two areas which had been found to be a problem with hydrophilic polymers. Modification of the base polymer was also carried out in an attempt to lower the surface energy, modify some aspects of biocompatibility and to impart antibacterial properties to the polymer.