Mixing with Other Amphiphiles

These examples and investigations on azobenzene moieties in polymers show that the photochromic behavior is mainly Gontrolled by the free volume distribution around the chromophore. Tb obtain LBK films in which azobenzene moieties can undergo photoisomerization, therefore, the free volume around the azobenzene chromophore must be controlled precisely to allow for the molecular rearrangement inherent in the reversible tran to cis photo-isomerization. This is possible by (1) mixing with other amphiphiles, (2) adjusting the architecture of the amphiphile, or (3) attaching the chromophore to a polymer either by coulomb interaction or covalently. 

A mixture that is stable in the cis-form was achieved by mixing an ionic azobenzene amphiphile having a long spacer between the head group and the 

10 Schematic representation of the molecular packing arrangement in the nrth monolayer of an ionic azobenzene amphiphile and an oppositely charged spacer amphiphile (reproduced with permission from reference 50 Copyright (1995) American Chemical Society). 

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Crowns have also been used in concert with other amphiphiles to form mixed bilayers. An example is the mixture of amphiphilic crown and amphiphilic ammonium salt (16) blended to form a mixed bilayer. Circular dichroism (CD) was used to detect the... 

The suppression of C60 crystallite formation in mixed LB films was attempted by mixing C60 and amphiphilic electron donor compounds [259]. Observation of the C60 LB film transferred horizontally by TEM clearly showed 10-40-nm-size crystallites. The diffraction pattern gave an fee lattice with unit cell length 1.410 nm. Examination of the mixed films with arachidic acid by TEM showed extensive crystallite formation. Mixed LB films of three different amphiphilic derivatives of electron donors with C60 were examined. One particular derivative showed very little formation of C60 crystallites when LB films were formed from monolayers of it mixed with C60 in a 1 2 ratio, while two others reduced C60 crystallite formation but did not eliminate it. 

The extensive studies of the behavior of mixed monolayers or bilayers of di-acetylenic lipids and other amphiphiles parallel to some degree the studies of dienoyl-substituted amphiphiles. Since the dienoyl lipids do not contain a rigid diacetylenic group in the middle of the hydrophobic chains, they tend to be miscible with other lipids over a wide range of temperatures and compositions. In order to decrease the lipid miscibility of certain dienoyl amphiphiles, Ringsdorf and coworkers utilized the well-known insolubility of hydrocarbons and fluorocarbons. Thus two amphiphiles were prepared, one with hydrocarbon chains and the other with fluorocarbon chains, in order to reduce their ability to mix with one another in the bilayer. Of course it is necessary to demonstrate that the lipids form a mixed lipid bilayer rather than independent structures. Elbert et al. used freeze fracture electron microscopy to demonstrate that a molar mixture of 95% DM PC and 5% of a fluorinated amphiphile formed phase-separated mixed bilayers [39]. Electron micrographs showed extensive regions of the ripple phase (Pb phase) of the DM PC and occasional smooth patches that were attributed to the fluorinated lipid. In some instances it is possible to... 

These statements lead to the conclusion that the limiting proportion of 1 gram of Na cholate associated to 1 gram of lecithin is simply imposed by the size of a certain form of mixed micelle which can remain in equilibrium with an excess of Na cholate in micellar solution. Thus, it clearly appears that association is governed by the necessity of securing the proper hydrophilic-lipophilic balance of the mixture of two components. Here, as in the case of other amphiphilic substances, by the progressive increase in proportion of the more hydrophilic amphiphile. the association can reach complete micellar dispersion in water. 

Low molecular mass surfactants are not needed in an ice cream mix to stabilize the fat emulsion, due to an excess of protein and other amphiphilic molecules in solution. If a mix is homogenized without added surfactants, both the whey proteins and the caseins will form this new fat globule membrane, with the caseins contributing most of the adsorbed protein... 

Surfactants. Surfactants and other amphiphilic compounds are very versatile materials when mixed with water and/or nonpolar compounds. For this reason, many different ways have been proposed to use surfactants to modify underground flow patterns in various types of EOR. One of these proposals, coprecipitation of a cationic and an anionic surfactant to clog cracks or pores in highly permeable rock zones, might prove useful for gas flooding (K. L. Stellner, J. C. Amente,... 

Lyotropic liquid crystals are principally systems that are made up of amphiphiles and suitable solvents or liquids. In essence an amphiphilic molecule has a dichotomous structure which has two halves that have vastly different physical properties, in particular their ability to mix with various liquids. For example, a dichotomous material may be made up of a fluorinated part and a hydrocarbon part. In a fluorinated solvent environment the fluorinated part of the material will mix with the solvent whereas the hydrocarbon part will be rejected. This leads to microphase separation of the two systems, i.e., the hydrocarbon parts of the amphiphile stick together and the fluorinated parts and the fluorinated liquid stick together. The reverse is the case when mixing with a hydrocarbon solvent. When such systems have no bend or splay curvature, i.e., they have zero curvature, lamellar sheets can be formed. In the case of hydrocarbon/fluorocarbon systems, a mesophase is formed where there are sheets of fluorocarbon species separated from other such sheets by sheets of hydrocarbon. This phase is called the La phase. In the La phase the molecules are orientationally ordered but positionally disordered, and as a consequence the amphiphiles are arranged perpendicular to the lamellae. The La phase of lyotropics is therefore equivalent to the smectic A phase of thermotropic liquid crystals. 

Selecting a suitable surfactant is a crucial step for the preparation of microemnlsions, because formulation of a microemulsion requires the use of moderate to high concentration of surfactant. Surfactants are those compounds, which lower the interfacial tension between two liquids or between a liquid and a solid. Surfactants are usually amphiphilic compounds, that is, the molecule of a surfactant has two parts one part is soluble in polar solvents, which is hydrophilic, and the other part is insoluble in the polar solvent, which is hydrophobic. - The polar part of the surfactant molecule is referred as head, and the nonpolar part of the molecule is referred as tail. This amphiphilic nature confers unique capabilities to the surfactant molecules tendency to adsorb at the surfaces and interfaces, which causes the decrease of the surface tension, and also formation of the aggregates inside the solutions, resulting in the formation of the microemulsions. - - Surfactants will diffuse in water and adsorb at interfaces between air and water or at the interface between oil and water, in the case where water is mixed with oil. Surfactant in solution below its... 

Add some hydrophilic substance to a glass of water, and it will merely mix with the water, just like sugar. In other words, it will be dissolved. On the other hand, a hydrophobic substance cannot be dissolved, it will separate out from the water, just like oil. However, there is a more complex amphiphilic kind of molecule each molecule contains both a hydrophilic and a hydrophobic part. What happens to them in water ... 

Kunieda and coworkers investigated diverse colloidal systems including spherical and elongated micelles, and liquid-crystalline systems on the basis of polymer or other amphiphilic molecules mixed with water [4, 10, 18, 23, 24]. 

The use of more complex systems such as ternary blends allows the functionalization of the surfaces with varies chemical functionalities. For instance a PS matrix was mixed with two block copolymers, a hydrophobic (PS-b-P5FS) and an amphiphilic polystyrene-b-poly[poly(ethylene glycol) methyl ether methacrylate] (PS-6-P(PEGMA)) copolymer [96], The chemical distribution of the resultant surface pattern implies an enrichment of the holes in the amphiphilic copolymer with an external surface mainly functionalized in the fluorinated copolymer with low surface energy (Scheme lO.lg). Other ternary blends combining incompatible copolymers and homopolymers have been reported leading to more complex topographies and chemical distributions [148],... 

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