We have used light scattering to determine the interaction potential between the surfactant coated water droplets in an oil continuous microemulsion system. The forward extrapolated zero angle scattering intensities at various water volume fractions were analyzed in terms of the Carnahan–Starling hard-sphere model modified for two-body attractive interactions. It was found that interparticle attractive interaction due to the overlapping of the surfactant tails could explain the observed phase behavior with respect to changes in the carbon chain length of the oil phase, as well as the existence of the lower critical point. It is further found that the optically determined potential is consistent with the microscopic results obtained with small angle neutron scattering experiments.
Light scattering has been used to study phase separation near the critical point in a binary mixture of methanol and cyclohexane. The intensity measurements are in conformity with the spinodal decomposition theory of Cahn. Measurements were also made of the spectral width of the scattered light in the phase separation process.
We have observed in a three-component oil-continuous microemulsion a new percolation phenomenon. The system of interest consists of anionic surfactant-coated water droplets dispersed in oil. The percolation limit ${\ensuremath{\varphi}}_{p}$ is found to be strongly temperature dependent, while the structure of the microemulsion remains constant. We have proposed a surfactant anion hopping model with a temperature-dependent hopping range. Percolation occurs when the effective droplet volume, as defined by the hopping range, exceeds the hard-sphere close-packing limit of 0.65.
We report rheological, microscopic, and calorimetric studies of the crystallization of long chain n-paraffins and their mixtures from model waxy oils and the effect of microcrystalline poly(ethylene-butene) (PEB) random copolymers. Optical micrographs and differential scanning calorimetry (DSC) reveal that the crystals formed from decane solutions of binary mixtures of C36 + C32 and of C32 + C28 are of mixed composition, whereas solutions of C28 + C24, C36 + C28, C32 + C24, and C36 + C24 form separate crystal phases. There is no miscibility when the difference in carbon number between two long chain n-paraffins Δnc > 4. These findings agree with Kravchenko's prediction for crystallization of molten binary n-alkane mixtures. However, the crystallization of long chain n-paraffins from decane solution gives a stable crystal structure directly, while from the melt it tends to pass through a metastable rotator phase. Since PEB can either self-assemble into a needlelike structure or cocrystallize with long chain n-paraffins to form small thin sheets in decane, mixtures of wax and PEB formed quite complex shapes such as rodlike or shuttle-like structures, particularly for the longer paraffin chains. These structures reduce the yield stress of the cold model waxy oil as compared with the platelike crystals formed in the absence of PEB. PEB10, which has an average of 10 ethyl side groups per 100 carbon atoms in the polymer backbone, is more effective in reducing the yield stress than PEB7.5 except for the mixture C36 + C28. All the other mixtures of paraffins with PEBs show intermediate rheological properties between those of the single paraffin components.
ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTStudy of Schultz distribution to model polydispersity of microemulsion dropletsMichael Kotlarchyk, Richard B. Stephens, and John S. HuangCite this: J. Phys. Chem. 1988, 92, 6, 1533–1538Publication Date (Print):March 1, 1988Publication History Published online1 May 2002Published inissue 1 March 1988https://pubs.acs.org/doi/10.1021/j100317a032https://doi.org/10.1021/j100317a032research-articleACS PublicationsRequest reuse permissionsArticle Views1654Altmetric-Citations128LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access options Get e-Alerts
The crystallization of long-chain n-paraffins and their binary mixtures from model waxy oils with decane as the solvent has been studied as a function of cooling rates by rheology, optical microscopy, and differential scanning calorimetry (DSC). The yield stresses of the gels formed upon cooling solutions of n-hexatriacontane (C36) and n-dotriacontane (C32) in decane increase with faster cooling rate, while for n-octacosane (C28) they decrease. DSC shows that the pure C28 wax precipitated from solution comprises multiple metastable phases as has been shown previously by X-ray scattering. Crystallization of C36 + C32 mixtures gives solid solutions with the yield stresses increasing with cooling rate, similar to the behavior of the pure component waxes. C36 and C28 crystallize separately from their mixed solution as observed by DSC. Addition of microcrystalline poly(ethylene butene) (PEB) wax crystal modifiers to single or mixed solutions greatly reduces the gel yield stress. The PEBs reduce crystal sizes and change morphologies significantly. DSC thermograms on the separated crystals show that the co-crystallization of PEB with C28 creates additional trapped metastable solid phases that appear between 51 and 73 °C. The magnitude and breadth of the peaks depend on the cooling rate as would be expected for the kinetic trapping of metastable phases.
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