ISSN:
1089-7690
Source:
AIP Digital Archive
Topics:
Physics
,
Chemistry and Pharmacology
Notes:
The liquid crystalline phase diagrams for aqueous solutions of the homologous series of surfactants CF3(CF2)nCO−2Cs+ (n=5–8) have been determined. They all exhibit the classical isotropic (I)-to-discotic nematic (ND) and ND-to-smectic lamellar (L) sequences of transitions with increasing concentration, as previously established for the n=6 system [N. Boden, S. A. Corne, and K. W. Jolley, J. Phys. Chem. 91, 4092 (1987)]. The effect of increasing n is to displace the transitions to higher temperatures. The behavior of all of the surfactant systems can be represented on a universal phase diagram. Both the I-to-ND and the ND-to-L transitions at corresponding concentrations are found to occur when the axial ratio of the disklike micelles attains a singular value in each case, irrespective of the value of n. The form of the experimental phase diagrams can be qualitatively understood in terms of a simple "zeroth'' order theory which uses the results of Onsager's theory [L. Onsager, Ann. NY Acad. Sci. 51, 627 (1949)] applied to disks to find the critical axial ratios in the coexisting isotropic and nematic phases and, separately, a dilute solution, self-assembly theory of disklike micelles [W. E. McMullen, A. Ben-Shaul, and W. M. Gelbart, J. Colloid Interface Sci. 98, 523 (1984)] to determine the temperatures at which these axial ratios are achieved at each concentration. The same treatment is also shown to account for the experimental phase behavior of mixed-chain-length systems. © 1995 American Institute of Physics.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1063/1.470553
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