Polyelectrolytes tethered to a similarly charged surface

Conformations of weakly charged quenched polyelectrolyte chains tethered to a similarly charged planar surface are analyzed on the basis of a combinat ion of scaling, analytical, and numerical self-consistent field (SCF) appro aches. Scaling theory predicts universal power law dependences of the large -scale conformational properties (like the end-to-end distance) of grafted chains on the overall surface charge per unit area. The SCF approach allows analysis of the detailed conformational structure of grafted polyions as a function of the distribution of immobilized charges between the surface an d grafted chains. The analytical solution is only available in the limiting cases of sparse grafting of polyions to the charged plane and sufficiently dense grafting of polyions to a neutral surface. In the intermediate case when both interchain interactions and interaction of grafted chains with th e surface are important, only numerical solutions can be obtained. We consi der various ways to distribute the charges between the surface and the brus h chains while keeping the sum of the two contributions constant. Upon incr easing the charge on the surface, by concomitant reduction of the grafting density of the tethered chains we found: (i) an increase in height of the p olymer layer; (ii) the development of a depletion zone of end points near t he surface; and (iii) a sharpening of the end-point distribution with the p eak shifting away from the surface. In the appropriate limiting cases excel lent agreement of analytical SCF predictions is obtained with the numerical results. (C) 2001 American Institute of Physics.