Behavior of 10-(perfluorohexyl)-decanol, a partially fluorinated analog of hexadecanol, at the air-water interface

Abstract

10-(Perfluorohexyl)-decanol is a partially fluorinated analog of hexadecanol, an important detergent alcohol. With a melting point of T = 48.82 °C and a melting enthalpy of ΔH = 53.96 J/g, the intermolecular interactions of the fluorinated alcohol are weaker compared to hexadecanol (T = 52.67 °C, ΔH = 244.41 J/g). The behavior of this fluorinated alcohol at the air-water interface was studied on five different subphases, namely, water, NaCl (150 mM), CaCl2 (2 mM), HCl (pH = 2.0), and urea (0.5 M). Similar to other partially fluorinated amphiphiles, the compression isotherms of the fluorinated alcohol on all subphases are more expanded compared to the hydrocarbon alcohol with a limiting area of 32-36 Å2 per molecule and a temperature-dependent phase transition at 5.6-8.2 mN/m (37 °C, compression rate of 10 mm/min). The dependence of the compression isotherms of 10-(perfluorohexyl)-decanol on subphase composition and temperature follows the trends reported for tetra- and hexadecanol. In particular, a shift to smaller molecular areas with increasing temperatures was observed on all five subphases. The shift to smaller molecular areas on urea indicates that in the case of 10-(perfluorohexyl)-decanol the effect is largely due to a loss of material from the air-water interface during compression of the monolayers. However, a squeezing-out of water molecules from the hydration sphere of the polar headgroup may still occur but can not be unambiguously proven. © 2002 Elsevier Science B.V. All rights reserved.