Surfactants microstructure

Figure 13.6 Changes in surfactant microstructures with changing shape parameters (reproduced by permission of The Royal Society of Chemistry).

J. R. Bellare, Cryo-electron and optical microscopy of surfactant microstructures. Doctoral Dissertation, University of Minnesota, 1988. 

In several systems, interfacial water, which is associated with the hydrophilic surfaces (polar groups and counterions) of surfactant microstructures, is present. This kind of water is also called bound water, hydration shell, hydration water, solvent shell [182], or vicinal water [171]. This water can be operationally defined as water detected by a certain technique as it had been influenced by the surface of the substrate in contact with the water [177]. The presence of the microstructure surface may alter the thermodynamic properties (such as melting point, melting enthalpy and entropy, and heat capacity) and the spectroscopic properties (such as IR absorption frequencies and band shapes) of water [61,214]. The chemical potential of bound water is different from that of bulk water [216]. Properties of bound water (viscosity, density, fl-eezing point, etc.) adsorbed on different surfaces of adsorbents differ from those of bulk water [216-223]. 

Neutron-scattering experiments demonstrated that the electrostriction effects are small in the secondary hydration shell of ions and beyond [275], This conclusion probably holds for the hydration layer on the hydrophilic surfaces of surfactant microstructures. 

Barnes and co-workers have studied mixed-monolayer systems [278,281,283,284] and found some striking nonidealities. Mixed films of octadecanol and cholesterol, for example, show little evaporation resistance if only 10% cholesterol is present [278] apparently due to an uneven granular microstructure in films with cholesterol [284]. Another study of cellulose decanoate films showed no correlation between holes in the monolayer and permeation rate [285]. Polymerized surfactants make relatively poor water evaporation retarders when compared to octadecanol [286]. There are problems in obtaining reproducible values for r [287] due to impurities in the monolayer material or in the spreading solvent. 

D. M. Anderson. A new technique for studying microstructures NMR band-shapes of polymerized surfactants and counterions in microstructures described by minimal surfaces. J Physique Colloque 57 1-18, 1990. 

S. T. Hyde. Microstructure of bicontinuous surfactant aggregates. J Phys Chem 95 1458-1464, 1989. 

R. G. Larson. Monte Carlo simulations of microstructural transitions in surfactant systems. J Chem Phys 96 7904-7918, 1992. 

The cobalt, nickel, and copper bis(2-ethylhexyl) phosphate surfactants dissolved in n-heptane lead to quasi-one-dimensional association microstructures, i.e., rodlike reversed micelles that increase in size via water solubilization [111],... 

While the order parameters derived from the self-diffusion data provide quantitative estimates of the distribution of water among the competing chemical equilibria for the various pseudophase microstructures, the onset of electrical percolation, the onset of water self-diffusion increase, and the onset of surfactant self-diffusion increase provide experimental markers of the continuous transitions discussed here. The formation of irregular bicontinuous microstructures of low mean curvature occurs after the onset of conductivity increase and coincides with the onset of increase in surfactant self-diffusion. This onset of surfactant diffusion increase is not observed in the acrylamide-driven percolation. This combination of conductivity and self-diffusion yields the possibility of mapping pseudophase transitions within isotropic microemulsions domains. 

Foam generated in porous media consists of a gas (or a liquid) dispersed in a second interconnected wetting liquid phase, usually an aqueous surfactant solution (1). Figure 1 shows a micrograph of foam flowing in a two-dimensional etched-glass porous medium micromodel (replicated from a Kuparuk sandstone, Prudhoe Bay, Alaska (2)). Observe that the dispersion microstructure is not that of bulk foam. Rather discontinuous... 

The procedure consists of three steps. The first step is to identify all the desired product quality factors or attributes for the new product. Then what follows is the selection of the appropriate product form and microstructure, a stable surfactant system with the right performance based on phase behavior, and the appropriate active ingredients in order to realize those quality factors previously identified. Finally the process flowsheet will be created with the equipment units and process operating conditions determined. 

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