The swelling equilibrium of N-isopropylacrylamide (NIPA) gel was studied as a function of temperature in aqueous solutions of surfactants: sodium dodecyl sulfate (SDS, anionic), dodecyltrimethylammonium chloride (DTAC, cationic), and nonaoxyethylene dodecyl ether (NODE, nonionic). In pure water the gel showed a discontinuous volume phase transition at 33.6 °C with a volume change of Vlwau«n/ VcoiiapMd = 8. With the addition of SDS, the transition temperature as well as the volume change at the transition increased. At 3.47 X 10~2 M of SDS concentration, the transition temperature became 88 °C and the volume ratio increased to V.^n-V V^n.p^= 32. A similar but less drastic change was observed when DTAC was used. In contrast, NODE induced little change in both the temperature and temperature phase transition for the concentration range studied (<6.94 X 10-2 M). In order to understand these effects of ionic surfactants, the association and dissociation of SDS with the gel or homopolymer of NIPA were investigated in an aqueous system. The amount of free SDS ions was measured at different temperatures by a conductometric method. An increase in the transition temperature was brought about by SDS binding to the gel or polymer whereupon the bound SDS was completely dissociated by cooling. The association and dissociation of SDS were reversible and, respectively, occurred in the temperature ranges above and below 30 °C. Thus, the ionic surfactant molecules convert the gel into an ionic gel due to binding through the hydrophobic interaction. The obtained experimental results have been qualitatively discussed in terms of the classical Flory-Huggins theory with modifications to account for the free energy of association of surfactant molecules with the gel network or polymer and surfactant self-association.
SynopsisThe aim of this study was to investigate the effect of iron oxide application on improving the volume of eyelashes. Iron oxide, having a negative surface charge in its natural form, was coated with commercial cationic polymers to increase its adhesion. The iron oxides coated with different types and concentrations of these polymers were incorporated into a basic mascara formula to test their volume effects by means of the weight difference of eyelashes. The results indicated that the type and concentration of coating materials affect the surface zeta potential and particle cluster size of iron oxides. The type of cationic polymer, especially, was shown to modify both factors of iron oxide. The obtained results also suggested that the volume effect of mascara increases with a higher positive surface zeta potential and a smaller particle cluster size of the coated iron oxides.J. Cosmet. Sci., 60, 627-636 (November/December 2009) Study and description of hydrogels and organogels as vehicles for cosmetic active ingredients Synopsis Cellulite, a clinical syndrome mainly affecting women, involves specific changes in conjunctive dermic and subcutaneous tissue, leading to vascular and hypertrophic alterations in adipose tissues and the consequent alteration of tissue structure. This paper describes the design of hydrogels and pluronic-lecithin organogels elaborated as vehicles of Aloe vera (Aloe vera linné) and Hydrocotyle asiatica (Centella asiatica) for the treatment of cellulite.The objective of this work was to carry out a complete evaluation of the proposed formulae through the study of the organoleptic and rheological properties of the formulae. Our work revealed that, in appearance, hydrogels show better organoleptic characteristics than organogels. On the other hand, from a rheological point of view, both hydrogels and organogels display a plastic behavior. However, the main difference between the two is that the more complex internal structure of the organogel bestows it with more viscosity. Finally, in vitro tests with Franz-type diffusion cells revealed that the release of cosmetic active principle from the tested excipients was appropriate, both in terms of magnitude and velocity.J. Cosmet. Sci., 60, 637-648 (November/December 2009) Changes in structure and geometric properties of human hair by aging SynopsisTo clarify hair changes by aging, the effect of age on hair properties was investigated from macro-to microscopic viewpoints. Sensory hair luster tests were performed on 230 Japanese females from 10 to 70 year of age, revealing that hair luster decreases with age. The age dependence of the hair diameter and the ellipticity of the hair cross section could not explain luster reduction by aging. It has been determined that an irregular increase in fiber curvature occurs with age and is a cause of luster reduction with aging. A detailed structural analysis by synchrotron radiation microbeam X-ray diffraction revealed that the inhomogeneity in the lateral distribution of the hair microstructure increas...
It has been reported that various age-dependent changes of whole hair shaft, such as diameter, density, elasticity, etc., occur in the age range of 40s and 50s. In this study, it was revealed that cuticle becomes more fragile and the hair surface properties deteriorate in the same age range.
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