Reversible formation of plastic two-dimensional lipid crystals

Influence of temperature and alkyl chain length on phase behavior in Langmuir monolayers of some oxyethylenated nonionic surfactants

“…On further compression, the monolayer undergoes a transition between the LE and the liquid condensed (LC) phases, showing a cusp followed by a plateau region in the π-A isotherm. By the use of microscopic techniques such as fluorescence microscopy (FM) [7,8] and Brewster angle microscopy (BAM) [9,10], one can readily visualize an exciting variety of structures, such as hexagonal [11,12], cardioidal [13], circular [14][15][16], striplike [17,18], needlelike [19,20], and spiral structures, in the monolayers of chiral [21][22][23] as well as nonchiral [17,18] amphiphiles at the air-water interface, which are not common in three-dimensional systems. The equilibrium shapes of these structures are governed by the competition between the line tension, which tends to make the domain circular, and the long-range dipolar-repulsive interactions between the molecules, which tends to stabilize elongated structures by maximizing the intermolecular distance, representing a delicate balance between the favorable van der Waals interactions of the hydrophobic alkyl chains and the opposing repulsive interactions between the head groups [21][22][23].…”

Two-dimensional facets in Langmuir monolayers of 1-O-hexadecyl-rac-glycerol at the air–water interface

“…Depending on the subphase temperature, the surface pressure, the subphase composition, and the structure of the amphiphile, Langmuir monolayers can exist in a wide variety of 2-D states such as gaseous (G), liquid expanded (LE), and liquid condensed (LC) phases at the air-water interface [15][16][17][18][19][20][21][22][23][24][25].…”

“…The LC phase that exists after the appearance of the conspicuous cusp point in the π -A isotherm during the LE-LC coexistence state can show an exciting variety of shapes such as circular [15,16], dendrites [17][18][19], needle-like [20,21] or spiral domains in both chiral [22,23], and nonchiral [24,25] amphiphiles at the air-water interface. The shape and texture of the domain is governed by a number of factors, such as the line tension of the interface, the subphase temperature, film composition, and the orientation of the molecules.…”

“…From similar analysis McConnell et al [31] reported that within a single domain the effect of electrostatic repulsive interactions maximize the average distance between the molecules showing strip-like or spiral structures. Opposite to this tendency is the effect of the line tension of the LE-LC interface, which tends to minimize the interfacial area of the domains showing large compact disk-like structures at the air-water interface [22,23]. In the case of chiral phospholipid monolayers McConnell and Möhwald and their co-workers have shown that the width of the spiral domain is thermodynamically controlled by the delicate balance between the dipolar repulsions and line tension along the boundaries between the two phases [22,23,32].…”

“…Opposite to this tendency is the effect of the line tension of the LE-LC interface, which tends to minimize the interfacial area of the domains showing large compact disk-like structures at the air-water interface [22,23]. In the case of chiral phospholipid monolayers McConnell and Möhwald and their co-workers have shown that the width of the spiral domain is thermodynamically controlled by the delicate balance between the dipolar repulsions and line tension along the boundaries between the two phases [22,23,32]. These studies elegantly addressed the situation in equilibrium taking into consideration the effect of cholesterol, pH, and the ionic strength of the subphase, and ascribed the observed findings to long range electrostatic repulsive interactions between the dipoles carried by the molecules.…”