Fluidity of the interfacial

Role of the Fluidity of the Interfacial Region in Water-in-Oil Microemulsions... 

The behavior of water in oil microemulsions has been studied using different techniques light scattering, electrical conductivity, viscosity, transient electrical birefringence, ultrasonic absorption. All these experiments lead us to propose a picture of the microemulsions structure which assignes an important role to the fluidity of the interfacial region. 

The preceding analysis assigns an important role to the interaction between droplets or equivalently the fluidity of the interfacial region in the microemulsions structure. 

In most of the emulsions, surfactants alone are not able to sufficiently reduce the interfacial tension between oil and water. Cosurfactants further reduce the interfacial tension and increase the fluidity of the interfacial film. The use of cosurfactants imparts sufficient flexibility to the interfacial film to take up different curvatures, which may be required to form microemulsion over a wide range of proportions of the components. The main role of cosurfactant is to destroy liquid crystalline or gel structures that form in place of a microemulsion phase. Typically used cosurfactants are short chain alcohols (C3-C8), glycols such as propylene glycol, medium chain alcohols, amines, or acids. - Cosurfactants are mainly used in microemulsion formulation for the following reasons ... 

By analyzing the fast portion of the anisotropy decay it is possible to obtain information about the microviscosity at the location of the probe, and for molecules incorporated at the interface the fluidity of the interfacial layer itself will influence the anisotropy relaxation rate [75]. Another way to obtain information on the water pool microviscosity is given by the application of 8-aniIino-l-naphthalenesulfonic acid (ANS) or Auramin O [76]. For these molecules the quantum yield of fluorescence increases with the microviscosity of the environment. 

The results from a test may also be used as an indication of the caking characteristics of the coal when it is burned as a fuel. The volume increase can be associated with the plastic properties of coal coals that do not exhibit plastic properties when heated do not show free swelling. It is believed that gas formed by thermal decomposition while the coal is in a plastic or semifluid condition is responsible for the swelling. The amount of swelling depends on the fluidity of the plastic coal, the thickness of bubble walls formed by the gas, and interfacial tension between the fluid and solid particles in the coal. When these factors cause more gas to be trapped, greater swelling of the coal occurs. 

They reduce the interfacial tension and increase the fluidity of the interface. 

The nature of the volume increase is associated with the plastic properties of coal (Loison et al., 1963) and, as might be anticipated, coals which do not exhibit plastic properties when heated do not, therefore, exhibit free swelling. Although this relationship between free swelling and plastic properties may be quite complex, it is presumed that when the coal is in a plastic (or semiflnid) condition the gas bubbles formed as a part of the thermal decomposition process within the flnid material cause the swelling phenomenon which, in turn, is influenced by the thickness of the bubble walls, the fluidity of the coal, and the interfacial tension between the fluid material and the solid particles that are presumed to be present under the test conditions. 

It is believed that the thin TLCP-rich skin layer or interlayer may be responsible for a pluglike flow (i.e., a continuous velocity profile), due to a composition-dependent interfacial slippage [9], and, therefore, for the improved fluidity of this binary system. 

Important factors when considering the enhanced hydrolysis at interfaces are the substrate environment in the monolayer and the need to transfer a substrate molecule from this monolayer to the active site. Interfacial disorder may provide an important parameter that facilitates such transfer of substrate to the active site. Phospholipase activity is enhanced under conditions that affect phospholipid fluidity, packing density of the phospholipids, and polymorphism of the aggregate. A highly ordered structure seen with phosphatidylcholine either above or below the transition temperature tends to give low rates of hydrolysis. Discontinuities in such ordered structures occur at temperatures close to the transition temperatures and the presence of other lipids such as anionic lipids or non-bilayer-forming phospholipids promote catalysis by perturbing the interface. 

The influence of adsorbed proteins on interfacial viscosity is relevant to the fluidity of biological membranes. An unusual effect is observed when lipid molecules are incorporated into protein monolayers, first reported by Schulman and Rideal As the mixed film is compressed, T] increases normally but then goes through a maximum, thereafter decreasing sharply with further increase of 11(6). Evidently, above a certain surface density, lipid molecules disrupt interactions between protein chains. The... 

In microemulsions, the alcohols are distributed between the oil-water interfaces and the oil phase of the microemulsions, with increases in chain length favoring binding at the oil-water interface. Results of these and other studies [35-37] suggest that the presence of sufficient cosurfactant can improve interfacial fluidity and facilitate electron transfer at electrodes. 

In summary, we suggest that both the degree of interfacial fluidity and the polymer layer thickness play key roles in determining the lubrication performance of surface-bound brushlike polymers in general and of PLL-g-PEG in particular. Both solvent quality and the nature of the counterface can influence these parameters. 

---