Surfactant layers at water surfaces

Abstract

This review hies to summarize the progress that has been achieved in understanding surfactant monolayers, concentrating on fatty acids and phospholipids and trying to generalize the results. It is shown that surfactant monolayers exist in a variety of phases that are distinguished by internal and external order and a coupling or decoupling of various degrees of freedom. The interface also orients dipolar molecular moieties resulting in long range electrostatic repulsion. This causes peculiar shapes and superlattices of domains of coexisting phases.These features could be explored by introducing new experimental techniques, predominantly optical microscopies and surface x-ray scattering. These techniques are discussed together with other conventional and new ones to demonstrate which type of information could be derived. Also summarized is the status of theoretical description and simulations in relation to the experimental results.It appears that there are even more interesting open questions to be solved than have been addressed until now. An outlook from a very personal perspective is given to point into directions which may gain increasing interest in the near future.

Molecular mechanisms of phosphatidylcholine monolayer solidification due to hydroxyl radicals

“…The domains were chiral (the mirror images cannot be superimposed), a result of the fact that L-α-DPPC itself is chiral. 4 The predominant domain shape was reminiscent of a bean, but multilobed shapes could also be observed.…”

“…Furthermore, isotherms demonstrated that the minimum molecular area attainable in the liquid-condensed phase was decreased. X-ray diffraction showed that at Deleted: [22] Deleted: [4] Page 29 of 32 Soft Matter this minimum molecular area the alkyl chains had a lower tilt angle than sterically possible for the large DPPC head group. IRRAS experiments indicated a cleavage of the head group.…”

“…The effect of molecular shape is especially clear in the condensed phase, when the molecules are laterally compressed, and the fatty acid tails are in an all-trans conformation. [4][5] Then, the crystallographic phase of the tails is strongly influenced by the constraints imposed by the head group. Phosphatidylcholines (PC), which constitute 10-20 % of membranes have a large head group.…”

“…This phosphocholine was chosen because its fluid and condensed phase are well characterized, both on thermodynamic and a molecular level 4 . Specifically, we have generated Thermodynamic data about the effect of ROS on the phase behaviour of DPPC monolayers are obtained with isotherms.…”

Dynamic Properties of Supercritical C14TEMPO Monolayers at the Air/Water Interface

“…2 Not surprisingly, Langmuir monolayers have been the subject of intense investigations. [3][4][5][6][7] Their structure and phase behavior have been studied using X-ray diffraction techniques, 5,8 Brewster angle microscopy (BAM), 9,10 epifluorescence microscopy, and other methods. 3,4,7 These investigations concerned primarily the condensed phases of the phospholipid and long chain fatty acid monolayers.…”