Short(Perfluoroalkyl) Alkyl Diblocks studied by Axisymmetric Drop Shape Analysis-Based Surface Balance and Molecular Dynamics Simulations

F. SARMIENTO; A. PIÑEIRO; G. PRIETO; J. RUSO; P. VERDES; E. BLANCO; P. TOIMIL; P. MESSINA

Nueva York

Simposio; 13th ICSCS/ 83rd CSS Symposium; 2009

New York University

comprehensive study of semifluorinated alkane CnF2n+ 1CmH2m+ 1 (FnHm diblocks, with n = 6, 8 and m = 10, 14, 16,18,20) films on the water/air interface is performed using an axisymmetric drop shape analysis (ADSA)-based surface balance. In contrast with previous data obtained by using a Langmuir film balance (LBF),high surface pressure values (> 1)were found for-SO mN m F6H16 films at molecular areas of about 26 Á2. Similarly, high collapse pressures were detected for the rest of the diblocks investigated, including the short F6Hl0. A definitive phase transition, was found for each of the three shortest diblocks before film collapse during surface compression. It was observed by molecular dynamics sirnulations that both F6Hl Oand F6H16 are stable on the liquid/air interface and that the compression of the films may induce the formation of multilayers with separated fluorinated/hydrogenated pseudo-phases on the surface of the liquid. Although it has already been stated that ADA balances could be better suited than LFBsfor the study of closely packed films, it is demonstrated here for the first time that, in addition to the serious discrepancies in collapse pressures between the two techniques, ADSA balances are certainly able to detect transitions that are not seen with classical Langmuir balances.