Temperature Dependence of the Lateral Diffusion of Acridine Orange at Water/Hydrocarbon Interfaces

The temperature dependence was investigated for the lateral diffusion of acridine orange at the interface of water and an octadecylsiloxane (C 18 ) monolayer on silica and at the interface of water and liquid n -dodecane. Fluorescence recovery after pattern photobleaching was used to measure the lateral diffusion coefficient. The data revealed very different activation parameters for lateral diffusion at the two interfaces. For the water/dodecane interface, the activation enthalpy for lateral diffusion is consistent with stronger ordering of water at the interface compared to bulk water. For the water/C 18 interface, a large entropic barrier is observed, indicating that the path for diffusion is restricted by high-energy adsorption sites. Further, the activation enthalpy is 5-fold lower than that of the water/dodecane case, indicating that transport to the unfavorable sites is not rate-limiting.