Synthetic Bilayer Wetting on SiO2 Surfaces

Abstract

Wetting on SiO2/Si wafers in the presence of dioctadecyldimethylammonium bromide (DODAB) bilayer vesicles is determined as a function of DODAB concentration and time of interaction between surface and vesicles. In 10 mM TRIS buffer at pH 7.4, the dynamic contact angle (θ) displays a maximum at an intermediate DODAB concentration (C) that corresponds to a minimum of contact angle hysteresis and is consistent with optimization of bilayer deposition. In pure water, θ is smaller than the contact angle for the bare surface consistently with adhesion of collapsed vesicles that carry water. In buffer, angles are larger than those for the bare surface, suggesting bilayer deposition under water and its conversion to a monolayer as the bilayer-bearing surface recedes into air. At a given C, θ against the interaction time (t) has an inverted-bell shape, indicating first vesicle adhesion, then bilayer deposition (at intermediate times), and finally further vesicle adhesion onto the deposited bilayer. Two major wettability parameters characterize bilayer deposition on the solid surface: minimization of contact angle hysteresis and maximization of the measured contact angle. Determination of dynamic contact angles is proposed as a quick and efficient technique to distinguish between vesicle adhesion and bilayer deposition on solid surfaces in general.