IRREVERSIBLE ADSORPTION FROM CONCENTRATED POLYMER-SOLUTIONS

We study the adsorption of concentrated Poly(dimethylsiloxane) (PDMS) solutions in Dichloromethane on porous silica. We vary the polymerization index N and the chain volume fraction-PHI from the overlap concentration to the melt. The adsorption of PDMS on silica by hydrogen bonding is very strong and a large amount of polymer remains bound to the surface after the washing of the silica with a good solvent of the chains. We measure this quantity-GAMMA by small angle neutron scattering. If there is no chain desorption, GAMMA-represents the weight of polymer attached to the solid in the initial solution, which varies as the product N(1/2)PHI(7/8) according to a recent prediction. This relation of proportionality indeed interprets our experimental results. When the size of the chains is comparable to the pore diameter (either 500, 1 200 or 3 000 angstrom depending on the samples) we observe confinement effects which lower the adsorbed amount.