Polyelectrolyte Multilayer Coatings

Layer-by-layer electrostatic assembly of polyelectrolyte multilayers (PEMs) has emerged as an important new type of molecular-level processing scheme for fabricating functionally active heterostructure thin film coatings and devices. This facile technique has been used to prepare a wide array of functional nanoscale structures, including biomimetic organic/inorganic nanocomposites, drug delivery vehicles, microporous membranes and various functionally active biomaterials. PEM assembly is a surface deposition process involving the sequential adsorption of polyanions and polycations. The properties of the resulting films can be controllably altered through choice of polyelectrolyte components, deposition conditions (e.g., pH and salt content) and post-fabrication crosslinking.

Research in our group explores the properties of PEMs incorporating weak polyelectrolytes, such as poly(acrylic acid) (PAA) and poly(allylamine hydrochloride) (PAH). For this PEM system, the bilayer thickness and degree of hydration is strongly dependent on the pH of the deposition bath, qualitatively captured by our free energy model of the multilayer assembly process. For PAA/PAH multilayers built under certain pH conditions and subsequently exposed to a low pH rinse, a microporous/nanoporous film morphology is produced, which has found application in the preparation of anti-fogging, superhydrophobic and controlled release coatings. To further extend controlled release applications to biologically derived pharmaceutics (i.e., peptides and proteins), we have developed a photo-crosslinkable PAA derivative, poly(acrylic acid -ran- vinyl benzyl acrylate), PAA r VBA, and prepared PEM films of this material with PAH. The selective inclusion of PAArVBA during PEM assembly enables control over the vertical placement of crosslinking functionality and, combined with 2-D photomasking, provides 3-D patterning capability, useful for the fabrication of diagnostic arrays, biosensors, and drug delivery devices.