화학공학소재연구정보센터
Journal of Colloid and Interface Science, Vol.392, 369-375, 2013
Thermodynamics of hydrophobic interaction between silica surfaces coated with octadecyltrichlorosilane
Surface force measurements conducted with thiolated gold surfaces showed previously that hydrophobic interaction entails a decrease in excess film entropy, suggesting that hydrophobic force originates from changes in the structure of the medium (water) confined between hydrophobic surfaces [1]. As a follow-up work, surface force measurements have been conducted in the present work using an atomic force microscope (AFM) with silica surfaces coated with octadecyltrichlorosilane (OTS) at temperatures in the range of 10-40 degrees C. A thermodynamic analysis of the results show that both the excess film entropy (Delta S-f) and excess film enthalpy (Delta H-f) decrease with decreasing thickness of the water films between the hydrophobic surfaces. It has been found also that vertical bar Delta H-f vertical bar > vertical bar T Delta S-f vertical bar which represents a necessary condition for the excess free energy change (Delta G(f)) to be negative and hence the hydrophobic interaction be attractive. Thus, the results obtained with both the thiolated and silylated surfaces show that hydrophobic forces originate from the structural changes in the medium. It is believed that the water molecules in the thin liquid films (TLFs) of water form clusters as a means to reduce the free energy when they cannot form H-bonds to neighboring hydrophobic surfaces. (c) 2012 Elsevier Inc. All rights reserved.