Lyotropic

A unique but widely studied polymeric LB system are the polyglutamates or hairy rod polymers. These polymers have a hydrophilic rod of helical polyglutamate with hydrophobic alkyl side chains. Their rigidity and amphiphilic-ity imparts order (lyotropic and thermotropic) in LB films and they take on a F-type stmcture such as that illustrated in Fig. XV-16 [182]. These LB films are useful for waveguides, photoresists, and chemical sensors. LB films of these polymers are very thermally stable, as was indicated by the lack of interdiffusion up to 414 K shown by neutron reflectivity of alternating hydrogenated and deuterated layers [183]. AFM measurements have shown that these films take on different stmctures if directly deposited onto silicon or onto LB films of cadmium arachidate [184]. 

Lyotropic liquid crystals are discussed in section C2.3 and section C2.6 of tliis encyclopedia and will not be considered furtlier here. 

Alexandridis P, Olsson U and Lindman B 1997 Structural polymorphism of amphiphilic copolymers Six lyotropic liquid crystalline and two solution phases in a poly(oxybutylene)-poly(oxyethylene)-water-xylene system Langmuir 23-34... 

Lyophobic colloids Lyotropic liquid crystals Lyotropic mesophases Lyotropic polymers Lyral [31906-04-4]... 

Hydrophobic Interaction Chromatography. Hydrophobic interactions of solutes with a stationary phase result in thek adsorption on neutral or mildly hydrophobic stationary phases. The solutes are adsorbed at a high salt concentration, and then desorbed in order of increasing surface hydrophobicity, in a decreasing kosmotrope gradient. This characteristic follows the order of the lyotropic series for the anions ... 

Fig. 13. Preferential iateraction parameter vs lyotropic number for lysozyme on (° ) bovine semm albumin and ( ) Toyopead.

Rigid-rod polymers are often Hquid crystalline polymers classified as lyotropic, such as the aramids Nomex and Kevlar, or thermotropic Hquid crystalline polymers, such as Vectran. 

Liquid crystals may be divided into two broad categories, thermotropic and lyotropic, according to the principal means of breaking down the complete order of the soHd state. Thermotropic Hquid crystals result from the melting of mesogenic soHds due to an increase in temperature. Both pure substances and mixtures form thermotropic Hquid crystals. In order for a mixture to be a thermotropic Hquid crystal, the different components must be completely miscible. Table 1 contains a few examples of the many Hquid crystal forming compounds (2). Much more is known about calamitic (rod-Hke) Hquid crystals then discotic (disk-like) Hquid crystals, since the latter were discovered only recendy. Therefore, most of this section deals exclusively with calamities, with brief coverage of discotics at the end. 

Some molecules ia a solvent form phases with orientational and/or positional order. In these systems, the transition from one phase to another can occur due to a change of concentration, so they are given the name lyotropic Hquid crystals. Of course temperature can also cause phase transitions ia these systems, so this aspect of thermotropic Hquid crystals is shared by lyotropics. The real distinctiveness of lyotropic Hquid crystals is the fact that at least two very different species of molecules must be present for these stmctures to form. 

Amphiphilic Molecules. In just about all cases of lyotropic Hquid crystals, the important component of the system is a molecule with two very different parts, one that is hydrophobic and one that is hydrophilic. These molecules are called amphiphilic because when possible they migrate to the iaterface between a polar and nonpolar Hquid. Soaps such as sodium laurate and phosphoHpids such as a-cephalin [5681-36-7] (phosphatidylethanolamine) (2) are important examples of amphiphilic molecules which form Hquid crystal phases (see Lecithin Soap). 

Fig. 13. Lyotropic liquid crystal structures (a) micelle formed by a typical soap (b) vesicle formed by a typical phospholipid.

E. J. Ambrose, iu S. Eriberg, ed., lyotropic Eiquid Cystals, American Chemical Society, Washiagton, D.C., 1976, Chapt. 10. 

Similady, hquid-crystal polymers exhibit considerable order in the hquid state, either in solution (lyotropic) or melt (thermotropic). When crystallized from solution or melt, they have a high degree of extended-chain crystallinity, and thus have superior mechanical properties. Kevlar (Du Pont) is an aromatic polyamide (atamid) with the repeating unit designated as (2). It is spun into... 

Licjuid Crystals. Ferroelectric Hquid crystals have been appHed to LCD (Uquid crystal display) because of their quick response (239). Ferroelectric Hquid crystals have chiral components in their molecules, some of which are derived from amino acids (240). Concentrated solutions (10—30%) of a-helix poly(amino acid)s show a lyotropic cholesteric Hquid crystalline phase, and poly(glutamic acid ester) films display a thermotropic phase (241). Their practical appHcations have not been deterrnined. 

Many cellulose derivatives form Hquid crystalline phases, both in solution (lyotropic mesophases) and in the melt (thermotropic mesophases). The first report (96) showed that aqueous solutions of 30% hydroxypropylceUulose [9004-64-2] (HPC) form lyotropic mesophases that display iridescent colors characteristic of the chiral nematic (cholesteric) state. The field has grown rapidly and has been reviewed from different perspectives (97—101). 

P. Kekicheff, H. K. Christenson. Forces measured in a swollen smectic lyotropic lamellar mesophase confined between solid surfaces. Phys Rev Lett (55 2823-2826, 1989. 

T. K. Attwood, J. E. Lydon, C. Hall, G. L. Tiddy. The distinction between chromonic and amphiphilic lyotropic mesophases. Liquid Cryst 7 657-668,1990. 

L. Paz, J. M. Di Meglio, M. Dvolaitzky, R. Ober, C. Taupin. Highly curved defects in lyotropic (nonionic) lamellar phases. Origin and role in hydration processes. J Phys Chem 55 3415-3418, 1984. 

M. Allain, P. Oswald, J. M. di Meglio. Structural defects and phase transition in a lyotropic system optical birefringence and order parameter measurements. Mol Cry St Liq Cryst 7625 161-169, 1988. 

P. Sakya, J. M. Seddon, V. Vill. Thermotropic and lyotropic phase behavior of monoalkyl glycosides. Liq Cryst 25 409- 24, 1997. 

L. Sallen, P. Sotta, P. Oswald. Pretransitional effects near the hexagonal-micellar phase transition of the CnEOA/HoO lyotropic mixture. J Phys Chem 707 4875-4881, 1997. 

Lymph-gefass, n. lymphatic vessel, -korper-chen, n. lymph corpuscle, leucocyte, lyo-pbil, a. lyophile, lyophil(ic). -phob, a. lyophobe, lyophobic. -trop, a. lyotrope, lyotropic. 

The order of cations and anions regarding these structure breaking and making properties is related to their position in the lyotropic or Hofmeister series, such as... 

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