NEUTRON REFLECTIVITY OF AN ADSORBED WATER-SOLUBLE BLOCK-COPOLYMER AT THE AIR WATER INTERFACE - THE EFFECTS OF PH AND IONIC-STRENGTH/

We describe the effects of pH and added electrolyte on the structure o f layers of poly(2-(dimethylamino)ethyl methacrylate-block-methyl meth acrylate) copolymer (poly(DMAEMA-b-MMA)) (70 mol % DMAEMA, M-n = 10 00 0) adsorbed at the air/water interface. Previously, we had shown by me ans of neutron reflection measurements that at a pH of 7.5 there is a surface phase transition from a layer about 20 Angstrom thick to one a bout 40 Angstrom thick and that the adsorbed layer at the higher conce ntration has a cross sectional structure resembling that expected for a micelle. The present work shows that the ''micellar'' structure is p romoted by any changes in the solution that enhance the surface covera ge but is inhibited by an increase in the fractional charge on the pol yelectrolyte part of the copolymer. Some surprising lack of correlatio n between surface tension and surface coverages is also observed, whic h may be related to this unusual surface structure.