Non-equilibrium adsorbed polymer layers via hydrogen bonding

The layer-by-layer or self-assembly (SA) technique, based on the electrosta tic interaction between oppositely charged layers, provides a simple and el egant way of producing multilayer structures from a variety of materials. M ultilayers are normally employed because one layer is usually too thin for any device application. We show that considerably thicker layers may be obt ained if the adsorption process is non-self-limiting, unlike the case of me chanisms entirely based on electrostatic attraction. This was obtained in s pontaneously adsorbed layers of polyaniline (PANi), poly(o-methoxyaniline) (POMA) and tetrahydrothiophenium polyphenylenevinylidene, a PPV precursor. The non-self-limiting adsorption is attributed to H-bonding which is more e ffective for uncharged polymers. It is also shown that the adsorption proce ss is only non-self-limiting under appropriate experimental conditions, sin ce adsorption must be performed under a non-equilibrium condition. Producin g thicker layers via the non-self-limiting adsorption procedure may have im portant implications in device applications, but for that one needs to over come the drawback caused by aggregation that affects film quality. For PANi and POMA, we have also demonstrated that multilayers can still be produced from uncharged polymers, simply by protonating them in an acid solution, a nd then alternating one of them with a polyanion.