Bimolecular film

K.Okuyama, "Formation of Bimolecular Films and Crystal Structure" in "Reactivity in Molecular Crystals", Ed. Ohashi, Y. Kodansha VCH, (1993) pp. 299. 

Such cases have been occasionally reported, but appear to the author to be not established. The polymolecular films of Harkins and Morgan (Proc. Nat. Acad. Set., II, 637 (1925)) were with substances which spread very badly and are almost certainly largely present as aggregates precipitated on the surface, not spread at all Lyons and Rideal, and Schulman and Ridcal (Proc. Roy. Soc. A, 124, 344 (1929) 130, 284 (1931)) described bimolecular films of fatty acids on alkaline solutions, but Adam and Miller (ibid., 142, 401 (1933)) found these to consist of mixtures of collapsed small aggregates, very thick, and monomolecular films. 

Bimolecular Film A membrane that separates two aqueous phases and is composed of polar organic molecules such as surfactants or lipids that are oriented with their hydrocarbon groups together and their polar groups facing the respective aqueous phases. See also Black Lipid Membrane. 

Black Lipid Membrane A bimolecular film in which the molecules comprising the membrane film are lipid molecules. The term black refers to the fact that these films appear black when illuminated (no apparent interference colors). See also Bimolecular Film, Black Film. 

Hemimicelle An aggregate of adsorbed surfactant molecules that may form beyond monolayer coverage, the enhanced adsorption being due to hydrophobic interactions between surfactant tails. Hemimicelles have the form of surface aggregates or of a second adsorption layer with reversed orientation, somewhat like a bimolecular film. 

Colloidal liquid aphrons are a kind of emulsion in which micrometre-size dispersed droplets have an unusually thick stabilizing film and exist clustered together as opposed to either separated, nearly spherical droplets. The stabilizing aqueous film, sometimes called a soapy shell, is thought to have inner and outer surfactant monolayers. Taking this a step further, vesicles are droplets characterized by the presence at their surface of a lipid bimolecular film (bilayer) or series of concentric bilayers. A vesicle can be single or multilamellar and stabilized by natural or synthetic surfactants. Vesicles made from lipid or fat (e.g. phospholipid) bilayers are called liposomes (or, sometimes,/jofyso/wes). 

The structure and appearance of the so-called microfoams, also termed colloidal gas aphrons, is somewhat different from conventional foams. Microfoams consist of very small foam bubbles (microbubbles) created by dispersing gas into surfactant solution under conditions of very high shear such that very small gas bubbles are created, each surrounded by a bimolecular film of stabilizing surfactant molecules [94-97] (see Section 8.3). 

A vesicle is a droplet characterized by the presence at its surface of a lipid bimolecular film (bilayer) or series of concentric bilayets. A vesicle can be single or multilamellar and stabilized by natural or synthetic surfactants. Multilamellar vesicles are also termed liposomes. 

The question still remains open whether in this bimolecular film the two mono-... 

To the question of how the phosphatide molecules are orientated in the coacervate/aqueous medium boundary one is inclined to answer that the polar portion of the molecule will indeed be directed towards the aqueous medium, and consequently the non-polar portion towards the coacervatc side. In that case the bimolecular film is set on the two outer sides with polar groups. 

There are however indications which make one doubt whether the assumed orientation is really correct. If one assumes the opposite orientation then the polar portions would be adjacent to one another in the bimolecular film whereby the electrical dipoles can form precisely a favourable salt pattern. For a detailed elaboration of this idea see ... 

Lagaly, G. 1976. Kink-block and gauche-block structures of bimolecular films. Angewandte Chemie International Edition 15 575-586. 

FIGURE 6 Confonnation of alkyl chains in a bimolecular film (a) aU-trans confonnation with an isolated kink and (b) nucleation of kink-block defects. (Based on Ref. 31.)... 

Like alkylpyridinium derivatives, dialkyldimethylammonium derivatives show basal spacings that increase linearly with alkyl-chain length from 4 nm (n = 14) to 5 nm (n = 18). (Fig. 20). The slope Ad/An = 0.180 nm indicates that the alkylammonium ions form bilayers with the chains tilted 45° to the layer [42]. The tetrahedral orientation of ammonium C-N bonds causes the alkyl chains in all-trans conformations to form a V (Fig. 21a), and space filling in mono-or bimolecular films subsequently would be poor. Transformation of two trans bonds into two gauche bonds (Fig. 21b) brings the alkyl chains in parallel orientation (Fig. 21c). This configuration is adopted by dialkyldimethylammonium ions... 

In aqueous equilibrium solutions, interlamellar alkylammonium ions and al-kylamine molecules aggregate as bimolecular films with the all-trans alkyl chains perpendicular to the layers (Fig. 22) [42], The basal spacings decrease when ethanol (10-15%, v/v) is added to the surfactant solution. Ethanol addition reduces the amount of intercalated alkylamine. Alkylammonium ions with 8-14 carbon atoms form bilayers and are tilted to the layer at angles of 55°. Furthermore, the basal spacings correspond to those of gauche block structures. The longer chain cations form monolayers. 

By swelling organic kanemites in alkanols and alkylamines, intralamellar bimolecular films can be prepared with different combinations of alkanol or al-kylamine molecules and organic cations this has been observed for the corresponding montmorillonite derivatives [18]. 

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