Lamellar structure, inhibition

Inhibits the formation of a lamellar structure with the common straight-chain surfactants. 

Some interesting simulations have been used to investigate crystallization and deposition processes, in order to obtain a fundamental understanding of how these processes can be inhibited. The inhibition of formation of waxes (mixtures of normal alkanes that form lamellar structures) was examined.302 Gas hydrate formation has been investigated, and it was demonstrated that inhibition of methane hydrate by a octomer of polyvinylpyrrolidone was able to be simulated,302 and simulations were used to assist in developing a new class of inhibitors of gas-hydrate formation.303... 

Under defined conditions, the toughness is also driven by the content and spatial distribution of the -nucleating agent. The increase in fracture resistance is more pronounced in PP homopolymers than in random or rubber-modified copolymers. In the case of sequential copolymers, the molecular architecture inhibits a maximization of the amount of the /1-phase in heterophasic systems, the rubber phase mainly controls the fracture behavior. The performance of -nucleated grades has been explained in terms of smaller spherulitic size, lower packing density and favorable lamellar arrangement of the /3-modification (towards the cross-hatched structure of the non-nucleated resin) which induce a higher mobility of both crystalline and amorphous phases. 

The mechanism by means of which hydrotropes operate in surfactant solutions was elucidated by Friberg and coworkers (1970, 1971 Cox, 1981), who showed that it is due to the inhibition of the formation of surfactant liquid-crystalline phases by the hydrotrope. Since they have structures similar to those of surfactants, hydrotropes can form mixed micellar structures with surfactants. However, since their hydrophilic heads are large and their hydrophobic groups are small (their V)/ Icdo ratio [Chapter 3, Section II] is liquid-crystalline structures and thus inhibit the formation of the latter. This destruction or inhibition of the liquid-crystalline phase increases the solubility of the surfactant in the aqueous phase and the capacity of its micellar solution to solubilize material. Hydrotropic action occurs at concentrations at which the hydrotrope self-associates to form these mixed structures with the surfactant (Gonzalez, 2000). 

Smectic phases are characterized by a layered structure, in which a two-dimensional fluid order prevails. In Fig. 3.4a, a schematic picture of the skeleton structure of a smectic phase is shown. The two-dimensional fluid layers are stacked upon each other with the periodicity distance d, causing a one-dimensional positional order along the direction of the layer normal k. In the case of the lyotropic lamellar L phase one smectic layer is usually referred to as a lamella. The lamella can be separated into two parts, as shown in Fig. 3.4b. The first part is a surfactant bilayer, in which the molecules are on the average oriented perpendicular to the layer plane. For conventional lyotropic mixtures polar solvents are used, which cause the hydrophobic chains to point towards the middle of the bilayers. This arrangement can be inverted by using apolar solvents, i.e. alkyls. If the surfactant molecules are interdigitated to some degree, the term partial bilayer is used. The second part of the lamella is a layer of solvent molecules, in which the molecules are believed to solely possess a fluid-like order. The solvent layers separate the surfactant bilayers from each other and should thus inhibit the transfer of information from one surfactant layer to the next. Consequently, the lamellar L phase is the only fluid. 

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