Surface adsorption alcohols

If the dependence on temperature as well as on composition is known for a solution, enthalpies and entropies of adsorption may be calculated from the appropriate thermodynamic relationships [82]. Neam and Spaull [147] have, for example, calculated the enthalpies of surface adsorption for a series of straight-chain alcohols. They find an increment in enthalpy of about 1.96 kJ/mol per CH2 group. 

The Effect of Alkyl Alcohols on the Surface Adsorption and Micellization of Fluorocarbon and Hydrocarbon Surfactants... 

In order to elucidate the effect of alkyl alcohol on the surface adsorption of CyFNa and C,oSNa, it is useful to calculate the surface molecular interaction parameters of the binary surface active mixtures (y8,) according to the equation at constant surface tension and constant ionic strength (13,14,10) ... 

The effect of alkyl alcohol on the surface adsorption and micellization of FC surfactant is noticeably different from HC surfactant. The molecular interactions between ROH and C7pNa in the surface layer are shown to be weaker (Smaler l jl-value) as compared with ROH-C, SNa system. 

Present investigation was undertaken to elucidate the relationships between the nonaethoxylated fatty alcohols with different distributions of hydrocarbon chain lengths and surface adsorption,... 

The regular solution theory may be applied to surface adsorption and micelle formation of mixed nonaethoxylated fatty alcohols with Gaussian distribution In hydrophobic chain length. Such a system can be treated as an Ideal mixture,... 

A number of contradictory views have been published concerning the structure of adsorbed alcohols and the nature of adsorption sites (for review see ref. 69). Experimental evidence from IR investigations has shown that, on alumina, alcohols form several surface complexes of very different chemical natures (e.g. refs. 31, 32, 117, 133—137) (i) alcohol molecules weakly bonded to the surface, very probably by hydrogen bonds (I) (such complexes are sometimes denoted as physically sorbed alcohols) (ii) surface alkoxides (alcoholates) (II) (iii) surface carboxy-lates (III). Less certain is the existence of species with partial double bonds or of ketone-like species. The formation of the various surface complexes is dependent on the structure of the alcohol. For examples, weakly bonded species (I) have been found with all alcohols, alkoxides (II) mostly with primary alcohols, sometimes also with secondary alcohols, but have never been reported for tertiary alcohols. 

Proteins contain a variety of functional groups that can bind them to mineral surfaces carbonyl, alcoholic, carboxylic acid, and amine. Studies have shown that protein adsorption to clays is rapid at a pH below the isoelectric point of the protein (e.g., McLaren, 1954 Armstrong and Chesters, 1964). Conversely, then, protein should be extracted by a solvent system with a pH above the protein s isoelectric point. There are also hydrophobic regions on some proteins that create the possibility for hydrophobic interactions between the sorbed protein and the mineral surface (Quiquampoix, 2000). 

Ohtani B., Iwai K., Nishimoto S., Sato T. (1993) Effect of Surface Adsorptions of Alifatic Alcohols and Silver Ions on the Photocatalytic Activity of Ti02 Suspended in Aqueous Solutions, J. Phys. Chem., 97(4), 920-926. 

The surface adsorption approach has been used to make a DPI device. First, a fatty acid or fatty alcohol derivative or a poloxamer is dissolved or dispersed in a solvent in which drugs and carriers are insoluble. The preferred solvent is n-hexane or... 

The influence of the surface layer on response time must also be considered. In a study of the sorption of alcohol vapours by a ZnO surface, Martin observed both a fast and a slow response time which he attributed to surface adsorption and bulk adsorption respectively (32). The fast response had a time constant of less than 100 s and was thought to be due to attachment of molecules to the top of the ZnO layer. A slower response to the alcohols ranging in time constant values from 240 to 750 s was attributed to diffusion of molecules into the bulk of the ZnO followed by adsorption. It was found that smaller molecules exhibited longer response times, which indicated that their smaller size allowed them to diffuse further into the ZnO or into smaller pores. This behaviour is quite analogous to that observed in chromatographic applications. To prevent slow response times, then, sensor surface coatings should be kept thin, and films with small pores should be avoided. 

Other similar cases exist, such as direct electro-oxidation of alcohols such as methanol and formic acid in low-temperature fuel cells. In these cases, an alternative to the BV formulation that accounts for the limiting adsorption and charge transfer steps is appropriate. Two common models for a surface adsorption limited reaction are the Langmuir and Temkin kinetics. In the simpler Langmuir model, the surface adsorption rate constant is independent of surface coverage. In the Temkin model, the adsorption rate constant is modeled as a function of the surface coverage of adsorbed species. In both models, a two-step reaction mechanism is assumed [6] ... 

We have considered the surface tension behavior of several types of systems, and now it is desirable to discuss in slightly more detail the very important case of aqueous mixtures. If the surface tensions of the separate pure liquids differ appreciably, as in the case of alcohol-water mixtures, then the addition of small amounts of the second component generally results in a marked decrease in surface tension from that of the pure water. The case of ethanol and water is shown in Fig. III-9c. As seen in Section III-5, this effect may be accounted for in terms of selective adsorption of the alcohol at the interface. Dilute aqueous solutions of organic substances can be treated with a semiempirical equation attributed to von Szyszkowski [89,90]... 

Most LB-forming amphiphiles have hydrophobic tails, leaving a very hydrophobic surface. In order to introduce polarity to the final surface, one needs to incorporate bipolar components that would not normally form LB films on their own. Berg and co-workers have partly surmounted this problem with two- and three-component mixtures of fatty acids, amines, and bipolar alcohols [175, 176]. Interestingly, the type of deposition depends on the contact angle of the substrate, and, thus, when relatively polar monolayers are formed, they are deposited as Z-type multilayers. Phase-separated LB films of hydrocarbon-fluorocarbon mixtures provide selective adsorption sites for macromolecules, due to the formation of a step site at the domain boundary [177]. 

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