Mixed Langmuir monolayers made from single-chain perfluoroalkylated amphiphiles

Surface pressure (pi)-area (A), surface potential (DeltaV)-area, and dipole moment (mu (perpendicular to))-area isotherms were obtained for Langmuir m onolayers made from (perfluorooctyl) pentylphosphocholine (F8C5PC), (perflu orooctyl) pentanol (F8C5OH), and their combinations. Monolayers were spread on a 0.15 M NaCl subphase. Surface potentials were analyzed using the thre e-layer model proposed by Demchak and Fort. The contributions of the CF3 om ega -group and the phosphocholine (PC) headgroup to the vertical component of the dipole moment mu (perpendicular to) were estimated to be -2.5 and 3. 3 D, respectively. The miscibility of F8C5PC and F8C5OH in the mixed monola yers was examined by plotting the variation of the molecular area, surface potential, and dipole moment as a function of the F8C5OH molar fraction, us ing the additivity rule. Negative deviations to the linearity of the molecu lar area were observed at various surface pressures (5, 15, 25, and 35 mN m (-1)), showing partial miscibility with attractive interaction between the monolayers components. Assuming a regular surface mixture, the Joos equatio n, which was used to describe the collapse pressure of mixed monolayers wit h miscible components, allowed calculation of the interaction parameter (xi = -0.52) and the interaction energy (210 J/mol) between the two fluorinate d amphiphiles.