Micelle wetness

The model has been successfully used to describe wetting behavior of the microemulsion at the oil-water interface [12,18-20], to investigate a few ordered phases such as lamellar, double diamond, simple cubic, hexagonal, or crystals of spherical micelles [21,22], and to study the mixtures containing surfactant in confined geometry [23]. 

Clearly Fig. 7 must actually have a maximum at high asymmetry since this corresponds to negligible anchor block size and therefore to no adsorption (ct = 0). The lattice theory of Evers et al. predicts this quantitatively [78] and is, on preliminary examination, also able to explain some aspects of these data. From these data, the deviation from power law behavior occurs at a number density of chains where the number of segments in the PVP blocks are insufficient to cover the surface completely, making the idea of a continuous wetting anchor layer untenable. Discontinuous adsorbed layers and surface micelles have been studied theoretically but to date have not been directly observed experimentally [79]. 

Schulze [51] described an extensive study on C12-C14 ether carboxylic acid sodium salt (4.5 mol EO) in terms of surface tension, critical micelle concentration (CMC), wetting, detergency, foam, hardness stability, and lime soap dispersing properties. He found good detergent effect compared to the etho-xylated C16-C18 fatty alcohol (25 mol EO) independent of CaCl2 concentration, there was excellent soil suspending power, low surface tension, and fewer Ca deposits than with alkylbenzenesulfonate. 

The basic mechanism for surfactants to enhance solubility and dissolution is the ability of surface-active molecules to aggregate and form micelles [35], While the mathematical models used to describe surfactant-enhanced dissolution may differ, they all incorporate micellar transport. The basic assumption underlying micelle-facilitated transport is that no enhanced dissolution takes place below the critical micelle concentration of the surfactant solution. This assumption is debatable, since surfactant molecules below the critical micelle concentration may improve the wetting of solids by reducing the surface energy. 

These rate effects are consistent with a wet micellar surface and the water molecules associated with the micelle seem to have reactivities which... 

The rate of attack of water upon the tri-/>-anisylmethyl cation is unaffected by binding of this cation to anionic micelles of sodium dodecyl sulfate (SDS) (Bunton and Huang, 1972) and equilibrium constants for aldehyde hydration are only slightly reduced by binding to micelles (Albrizzio and Cordes, 1979). These observations are also consistent with substrate binding at a wet micellar surface rather than in the interior of the micelle. 

First, micelles have very loose, mobile, structures and there are considerable entropy costs in a concerted reaction. These costs are much less serious in enzymic systems where conformation at the active site is tailor-made to fit the transition state. Secondly, the sites of micellar reactions are very wet and omnipresent water molecules are available to transfer protons. 

Solubilization o-f dissolved organic molecules into micelles is important in detergency (2), emulsion polymerization (65). and micellar—enhanced ultra-fiItration (3), Just to name a -few applications. Solubilization also indirectly a-f-fects many other operations because it o-ften a-f-fects monomer—micelle equilibrium, in-fluencing sur-factant adsorption, wetting, etc. when solubi 1 izable, non—sur-factant species are present in solution. 

Test Methods. Surface tension (y) measurements were taken by Wil-helmy method (25+0.1°C). Critical micelle concentrations (cmc) were obtained from Y logC curves. Contact angle. Type GI, Japan. Wetting test. Canvas disk method, CIS,HG-2-380-66. Foam test, Ross-Miles lather method. Emulslbillty was determined by mixing 20 ml of 2.5%... 

Surfactants Soluble compounds which possess groups of opposite polarity and solubilizing tendencies. They can form oriented monolayers at phase interfaces, form micelles, and possess detergency, foaming, wetting, emulsifying, and dispersing properties. 

Polysorbate 80 is widely used as a nonionic surfactant in liquid pharmaceutical products such as inhalation, suspension, and nasal suspension products, due to its properties of solubilization, reduction of surface and interfacial tension, and wetting. Direct analysis of Polysorbate 80 is quite time consuming. Size-exclusion chromatography (SEC) has been reported [5] in which a mobile phase contained the surfactant at concentrations above the critical micelle concentration. Polysorbate 80 appeared as a very broad peak and coeluted with other peaks, which makes quantification in Nasonex impossible. 

Alternatively, the Rh/15-catalysed hydroformylation of 1-tetradecene may proceed in wet micelles 478 (which are water-permeated micelles) or in reversed micelles155,389,406 with solubilisation of an aqueous microdroplet of the Rh/15 catalyst in the organic bulk phase [cf. Figure 4 (A)]. 

This experiment introduces the use of a probe molecule to explore the microenvironment within a micelle. The results in this case show the environment to be quite wet, but this observation alone does not tell us where either the benzene or the water is. Any one of the... 

Two new chapters have been added which explore—via micelles and related structures and metal surfaces under ultra-high vacuum—both "wet" and "dry" facets of colloids and surfaces. Although neither of these areas is new, both are experiencing an upsurge of activity as new instrumentation is developed and new applications are found. 

The solubility of the sodium salt of (meta-sulfonatophenyl)diphenylphos-phine, TPPMS in water is approximately 12 g/L at room temperature.5 It dissolves slightly in cold ethanol, but is soluble at elevated temperatures. It is virtually insoluble in acetone and aliphatic, aromatic, or chlorinated hydrocarbons, but is soluble at room temperature in tetrahydrofuran. The compound crystallizes with two waters of crystallizations however, the anhydrous form can also be obtained.3 Dry TPPMS is stable to air but is oxidized rapidly when wet, especially in basic aqueous solutions. It is a highly surfactant compound and forms aggregates and micelles in neutral aqueous... 

The adsorption of block copolymers from a selective solvent was considered by Ligoure (1991). He predicted the existence of surface micelles (see Fig. 3.22) in the case when the block interacting unfavourably with the solvent only partially wets the surface. The model predicts a critical surface micellar concentration (csmc) that differs from the bulk cmc. When the contact angle, which characterizes the interfacial interactions between the copolymer, adsorbing surface, and solvent is lower than some universal value, surface micelles were predicted to appear at a lower copolymer concentration than bulk ones. Experimental results on surfaces are discussed in Section 3.8.4. 

Figure 3. SANS intensity for wet pellets of whole casein micelles made with (a) 96% D20,4% H20 (b) 74% D20, 26% H20 (c) 41% D20, 59% H20. Casein concn. approx. 250 mg/ml. Calculated intensities for models with subunits in close packing are (—) for 74% D20 and Nl=2, N2=l, N3=2, D=168 A.

There are mainly three reasons that surfactants are used in formulation (1) to increase wetting of drugs, which in turn increase the dissolution (2) to prevent drug precipitation from formulation and (3) to increase solubilization through micellization. 

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