Liquid-crystalline structures, effect

Finally, we should mention that the asymmetry of molecular shape, polyphilic effects and conformational constraints are the dominant factors in the stabilization of polar ordering in achiral mesogens. The examples presented above are, therefore, highly significant. They show that many liquid crystalline structures are intrinsically polar and may be effectively stabilized by suitable design of the mesogenic molecules. 

The recent studies on the structure and properties of polypeptide liquid crystals, which are formed in solution as well as in the solid state, are reviewed in this article. Especially the cholesteric pitch and the cholesteric sense (right-handed or left-handed), which are characteristic factors of cholesteric liquid crystals, are discussed in detail in relation to the effects of temperature, concentration, and solvent. Further cholesteric liquid crystalline structure retained in cast fdms and thermotropic mesomorphic state in some copolypeptides are also discussed. 

Effect of Liquid-Crystalline Structures on Lubrication of Aluminum Surfaces... 

Kunieda, H., Umizu, G., and Aramaki, K. (2000) Effect of mixing oils on the hexagonal liquid crystalline structures. 

Polymers with fixed liquid crystalline structure — if the polymerization temperature was below the glass ti ansition temperature ( ) of the polymer. These polymers exhibit a liquid crystalline structure in the solid glassy phase because the structure of the ordered monomer phase was "frozen in" by polymerization. By heating the polymer these frozen structures were irreversibly lost above the Tq An additional effect was observed starting from... 

The above method of stabilization (referred to as electrostatic stabilization) can be produced by the use of ionic surfactants (of the anionic, cationic, or zwitterionic type). However, for a number of reasons this method of stabilization is not ideal for personal care formulations. First, the stabilization is influenced by the presence of electrolytes in the system, which reduces repulsion and may cause instability. In addition, many ionic surfactants cause skin irritation as a result of their penetration and interaction with the stratum corneum (4). The latter is the main barrier to water loss and it consists of lipids that are organized in a bilayer structure (liquid crystalline), which at high water content is transparent and soft (5). Surfactants that interact with the lipid bilayer and reduce its liquid-like nature (by disrupting the liquid crystalline structure) may cause crystallization of the lipids, and this has a drastic effect on the appearance and smoothness of the skin ( dry skin feeling). 

One of the earliest methods for reducing coalescence is to use mixed surfactant films. These will increase the Gibbs elasticity and/or interfacial viscosity. Both effects reduce film fluctuations and, hence, reduce coalescence. In addition, mixed surfactant films are usually more condensed and hence diffusion of the surfactant molecules from the interface is greatly hindered. An alternative explanation for enhanced stability using surfactant mixture was introduced by Friberg and coworkers [67] who considered the formation of a three-dimensional association structure (liquid crystals) at the oil/water interface. These liquid crystalline structures prevent coalescence since one has to remove several surfactant layers before droplet-droplet contact may occur. 

Table 8.2 summarizes the possible effects of the different liquid crystalline structures on the photopolymerization reaction, as well as on the morphology and final properties of the obtained UV-cured systems this issues will be discussed in the followings. 

Lin QH, Yee AF, Sue HJ, Earls JD, Hefiier RE (1997) Evolution of structtue and properties of a liquid crystalline epoxy during curing. J Polym Sci Polym Phys 35 2363-2378 Liu JP, Wang CC, Campbell GA, Earls JD, Priester RD (1997) Effects of liquid crystalline structure formation on the curing kinetics of an epoxy resin. J Poljm Sci Poljm Chem... 

Iwanaga T, Suzuki M and Kunieda H. 1998. Effect of added salts or polyols on the liquid crystalline structures of polyoxyethylene-type nonionic surfactants. Langmuir 5775-5781. 

Kunieda H, Umizu G and Yamaguchi Y. 1999. Mixing effect of polyoxyethylene-type nonionic surfactants on the liquid crystalline structures. Journal of CoUoid and Interface Science 88-96. 

Around the turn of the last century, chemists were reluctant to accept the idea of rubber, starch, and cotton as long, linear chains connected by covalent bonds. A popular alternative was the idea of an associated colloidal structure. As a matter of fact, some small molecules do exhibit such behavior. Soap molecules will associate into complex liquid crystalline structures and are used as the basis for the formation of mesoscopic solids. Other surfactant molecules such as the phospholipids present in the wall of many living cells will form micelles and vesicles. However, the effective molecular weight of such structures varies with concentration and temperature, whereas the molecular weights of true polymers with covalent links do not. 

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