Polyelectrolyte multilayer formation on protein layer supports

Polyelectrolyte multilayers (PEMs) have been intensively studied as a straightforward means to modify surfaces for a variety of applications. Their study using advanced tools of interfacial science has underpinned their potential as surface coatings, however, this degree of characterisation is greater for PEMs on solid substrates. The formation of multilayers on soft/deformable interfaces is not so heavily studied, and to a great extent the formation characteristics are simply assumed. In this work, we have studied comparatively the formation of a polyelectrolyte multilayer on both a solid support and upon a pre-adsorbed layer of a protein (β-lactoglobulin – BLG). The study of a protein support for PEMs is a useful intermediate step between a solid support and truly deformable interfaces (such as the air-water or oil-water interface). Our investigation has revealed that, compared to build-up on a solid support, a polyelectrolyte multilayer formed from polydiallyldimethylammonium chloride (PDADMAC) and poly(sodium styrene sulfonate) (PSS) on a pre-adsorbed layer of BLG displays more regular growth from the very first layer, with overall higher mass deposited. The protein-supported film also displays more regular outer layer effects (in this case mechanical properties), at an earlier stage of build-up. For applications that require relatively thin PEMs, the use of a soft cushion support as an initial layer may produce better coatings.