ELECTROSTATIC DEPOSITION OF POLYIONIC MONOLAYERS ON CHARGED SURFACES

We explored molecular films of polyionic materials built by electrosta tic deposition on a charged surface. Formation of self-assembled monol ayers is monitored for poly(styrenesulfonate) (PSS) adsorbed on charge d surfaces of amine-terminated self-assembled monolayer (SAM) and poly (allylamine) In both cases, polyions are adsorbed on oppositely-charge d surfaces. Observations of PSS monolayers at various stages of electr ostatic deposition reveal inhomogeneous self-assembly at the earliest stages of deposition. During the first several minutes of deposition, negatively-charged PSS macromolecules tend to adsorb on selected defec t sites of positively-charged SAM (scratches, microparticles, and edge s) and form islands composed of PSS coils. At this stage, electrostati c adsorption of PSS chains is predominant and equilibration of the sur face structure is not achieved by the slow surface diffusion mechanism . Only longer deposition times (>10 min) result in an equilibration of polymer layers and formation of a homogeneous thin PSS layer composed of highly flattened macromolecular chains. The monolayer thickness is between 1.0 and 1.5 nm, with a microroughness of about 0.2 nm. Self-a ssembly of a second PAA layer on top of a PSS monolayer follows simila r tendencies, resulting in the formation of homogeneous PAA/PSS bilaye rs with an overall thickness of 1.7-2.5 nm.