Application of Brewster angle microscopy and fractal analysis in investigations of compressibility of Langmuir monolayers

Abstract

The aim of this study was to investigate the connection between the lipid/amphiphile monolayer structure at the interface and its macroscopic/rheological properties, in particular, to establish the link between the fractality of the monolayer structure and its compressibility modulus. To that purpose we have used fractal analysis of images obtained by Brewster angle microscopy to infer the fractal dimension of the monolayer structure and relate its change to the corresponding changes in compressibility derived from a simultaneously measured π-A isotherm. The results of the study confirmed the starting assumption based on theoretical considerations that the fractal dimension of an amphiphilic monolayer and its compressibility should be correlated. We have shown that there exists a strong correlation between the fractal dimension and the corresponding compressibility modulus of different amphiphilic materials. Thus, confirming the link between the short ordered structure on the molecular level and the macroscopic property-compressibility of the monolayer. The established correlation between the fractal dynamics and compressibility modulus of the monolayer enabled identification of onset of percolation-a second-order phase transition that is otherwise not easy and unambiguously detectable. We have found that the signature of percolation in a monolayer, regardless of its composition, is the occurrence of a sharp increase (a jump) of compressibility modulus (at macroscopic level) at the characteristic value of the corresponding fractal dimension D = 1.89. This is the result of the abrupt establishment of a connected structure on the molecular level, consequently involving a change in the elastic properties of the monolayer on a macroscopic scale. The results of this investigation provide means for unambiguous identification of the onset of percolation in the Langmuir layer and should facilitate a more efficient application of the percolation theory in further study of processes and structures at the interface during the monolayer compression.

Evaluation of the Structure–Activity Relationship of Rifabutin and Analogs: A Drug–Membrane Study

“…[17,[31][32][33][34] According to the C À1 s values obtained for EPC monolayers, described in previous works, the CHOL molecules, as expected, decrease the fluidity of the EPC monolayer. [15,35,36] The collapse pressure of 46 mN m À1 obtained for EPC:CHOL (4:1) ( Table 1) is slightly lower than that reported for pure EPC (% 50 mN m À1 ). [15] The isotherms of EPC:CHOL in the presence of the antimycobacterial compounds have different shapes to that of EPC:CHOL.…”

“…The morphology of the EPC monolayer is described in the literature in terms of the formation of noncircular-shaped domains at low pressures and a homogenous condensed phase for pressures above 25 mN m À1 . [35] On the other hand, the monolayers of CHOL are characterized by the appearance of small brighter spots on a fluid background. [45,46] It is well-known that CHOL molecules can undergo tight packing with phosphatidylcholines, which results in the formation of domains in the membranes and liquid-ordered phases in artificial systems.…”

Solvent-dependent properties of poly(vinylidene fluoride) monolayers at the air–water interface

“…This phase transition took place because the domains were brought into contact. 35,40 We infer that PVDF molecules in the PVDF Langmuir lms of two kinds occupy the area with different molecular conformations. Therefore, changing solvent properties is effective to modulate molecular aggregation of PVDF at the air-water interface.…”

“…2b(I). 40 The BAM images show that PVDF molecules do not form a gas analogous phase. The PVDF molecules exist as multilayers in the domains at the air-water interface.…”

Self-assembly and molecular packing in cholesteryl esters at interfaces

“…It will be interesting to investigate it by a GIXD study. Fractal analysis of the BAM images 24 may also reveal a correlation between the domain size and the ordered/lessordered phase. Recently, there have been some simulation studies on the domain formation in biomimetric membranes.…”