Structural transitions in a monolayer of fluorinated amphiphile molecules

Abstract

We present results of an extensive x-ray diffraction study of a monolayer of C10F21CH2COOH spread on water (pH2) at 19.1 °C. Lever-rule analysis of the in-plane scattering is used to show that there is a coexistence region between ordered condensed islands and a dilute disordered phase. The coexistence region is found to be bounded by molecular areas of 29 Å2 and 2000±600 Å2, in agreement with the pressure-area isotherm. The molecular tilt of the ordered phase remains unchanged from closest packing (near collapse of the monolayer) throughout the coexistence region, and has a value of 2±3 degrees with respect to the normal to the liquid surface. These results are contrasted with those for hydrocarbon monolayers in which the onset of order in the coexistence region is close to the condensed phase boundary, and the ordered phase is compressible with a continuously variable tilt angle ranging from 30 to 0 deg at closest packing. The differences are attributed to the enhanced chain stiffness of the fluorinated chain. To illustrate this interpretation, preliminary scattering results are presented for a monolayer of C8F17(CH2)4COOH on water, which has some of the features of the aliphatic lipid monolayers. Recent molecular dynamics simulations have been found to reproduce all the important qualitative features of these systems [S. Shin, N. Collazo, and S. A. Rice, J. Chem. Phys. 96, xxxx (1992)].

Stratified Dipole‐Arrays Model Accounting for Bulk Properties Specific to Perfluoroalkyl Compounds

“…In addition, the limiting molecular area, that is, the cross-sectional area of a straight molecule is 0.482 (n = 3) and 0.402 nm 2 (n = 5) per molecule, which is much larger than the theoretical cross section of 0.296 nm 2 per molecule. [1,[18][19][20] In this manner, a short R f group has poor aggregation and apparent hydrophilic properties; these are supported by IR spectroscopy data discussed below.…”

Understanding and control of nucleation, growth, habit, dissolution and structure of two- and three-dimensional crystals using `tailor-made' auxiliaries

“…<80%, so that the monolayer surface pressure is very low) was shown to be a widespread phenomenon. This was demonstrated for a variety of amphiphiles, such as long fluorocarbon chain a-amino acids (Jacquemain et al, 1990) and carboxylic acids (Durra et al, 1987;Barton et al, 1988Barton et al, , 1992, hydrocarbon chain alcohols, amides, carboxylic acids and their cadmium or calcium salts (BiShm et al, 1994). Indeed the GID spectrum of the cadmium arachidate monolayer gave direct evidence of an ordered counterionic cadmium layer bound to the carboxylate head group.…”

Reflection–absorption FT-IR spectroscopy of pentadecanoic acid at the air/water interface

“…More extensive studies by Lundquist [13] and Peterson and colleagues [14][15][16][17] have revealed a complex polymorphism for monolayers of fatty acids and Peterson has produced a generic phase diagram in which the phase boundaries change systematically with acyl chain length. Structural studies by, for example, grazing incidence synchrotron X-ray diffraction, have revealed details of the molecular structures of some of these phases [17][18][19][20][21][22][23]. In Fig.…”