Polymer bilayer formation due to specific interactions between β-cyclodextrin and adamantane: A surface force study

• The purposes of this study are to utilize the interactions between an adamantane end-capped poly-(ethylene oxide) (PEO) and a cationic polymer of β-cyclodextrin to build polymer bilayers on negatively charged surfaces, and to investigate the interactions between such layers. The association of this system in solution has been studied by rheology, light scattering, and fluorescence measurements. It was found that the adamantane-terminated PEO (PEO-Ad) mixed with the β-cyclodextrin polymer gives complexes where the interpolymer links are formed by specific inclusion of the adamantane groups in the β-cyclodextrin cavities. This results in a higher viscosity of the solution and growth of intermolecular clusters. The interactions between surfaces coated with a cationized β-cyclodextrin polymer across a water solution containing PEO-Ad polymers were studied by employing the interferometric surface force apparatus (SFA). In the first step, the interaction between mica surfaces coated with the cationized β-cyclodextrin polymer in pure water was investigated. It was found that the β-cyclodextrin polymer adsorbs onto mica and almost neutralizes the surface charge. The adsorbed layers of the β-cyclodextrin polymer are rather compact, with a layer thickness of about 60Å(30Å per surface). Upon separation, a very weak attractive force is observed. The β-cyclodextrin solution was then diluted by pure water by a factor of 3000 and a PEO-Ad polymer was introduced into the solution. Two different architectures of the PEO-Ad polymer were investigated: a four-arm structure and a linear structure. After the adsorption of the PEO polymer onto the β-cyclodextrin layer reached equilibrium, the forces were measured again. It was found that the weak repulsive longrange force had disappeared and an attractive force caused the surfaces to jump into contact, and that the compressed layer thickness had increased. The attractive force is interpreted as being due to a specific recognition between the hydrophobic adamantane groups on the PEO-Ad polymer and the hydrophobic cavity in the β-cyclodextrin molecules. Furthermore, the attractive force observed on separation has increased significantly, which is a further indication of a specific interaction between the β-cyclodextrin polymer and the adamantane groups

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