Hydrophobic surfaces, surfactant

Alvarez-Cohen et al. [91] explicitly showed that microbial transformation rates of trichloroethylene (TCE) were proportional to the aqueous TCE concentrations and independent from zeolite-sorbed TCE concentrations. Apparently in contrast to these findings, Crocker et al. [92] reported on the direct bioavailability of naphthalene sorbed to hexadecyltrimethylammonium (HDTMA)-modified smectite clay to Pseudomonas putida 17848, but not to Alcaligenes sp. strain NP-Alk. It should be noted that sorption to the hexadecyl chains of HDTMA resembles more the solubilisation by a surfactant than adsorption to a solid surface. Possibly, hydrophobic surface structures of strain 17848 allowed the close contact with HDTMA, thereby facilitating the uptake of naphthalene by a lipophilic pathway. 

Hydrophobic polar surfaces, adsorption of ionic surfactants on, 24 140-141 Hydrophobic precipitated silica, 22 399 Hydrophobic solvents, 16 413 Hydrophobic surfaces, 1 584-585... 

Physical properties of the protein structure should be considered in designing strategies to achieve stable formulations because they can often yield clues about which solution environment would be appropriate for stabilization. For example, the insulin molecule is known to self-associate via a nonspecific hydrophobic mechanism66 Stabilizers tested include phenol derivatives, nonionic and ionic surfactants, polypropylene glycol, glycerol, and carbohydrates. The choice of using stabilizers that are amphiphilic in nature to minimize interactions where protein hydrophobic surfaces instigate the instability is founded upon the hydro-phobic effect.19 It has already been mentioned that hydrophobic surfaces prefer... 

Contact angle measurements indicated that conditioning with increasing amount of polymer before conditioning with surfactant resulted in reduced surface hydrophobicity. Preconditioning with surfactant resulted in a hydrophobic surface which was not affected by subsequent polymer additions. 

The weak surfactant solution forms bubbles on agitation in the aqueous phase, which are stabilized as microscopic spheres from coalescing into large bubbles by the orientation of insoluble surfactant across the air/ liquid interface and by adhering to the hydrophobic surface created on the cement particle by the adsorbed surfactant. This is shown diagrammatically in Fig. 3.15 [16]. 

There are numerous studies on the spreading of trisiloxane surfactants on hydrophobic surfaces (for two comprehensive reviews, see [21,22]), but the... 

Wu Y, Rosen MJ (2002) Superspreading of trisiloxane surfactant mixtures on hydrophobic surfaces 2. Interaction and spreading of aqueous trisiloxane surfactant -n-alkyl pyrrolidinone mixtures in contact with polyethylene. Langmuir 18 2205-2215... 

Zhu S, Miller WG, Scriven LE, Davis HT (1994) Superspreading of water-silicone surfactant on hydrophobic surfaces. Colloids Surf A 90 63-78... 

On hydrophobic surfaces, similar effects probably occur and can explain the difference in adsorption of an anionic surfactant in the absence and presence of a nonionic surfactant above the CMC on carbon (78) ... 

Our aim, however, is to find a model that is as simple as possible and yet makes it possible to estimate adsorption from surfactant mixtures within experimental error in the type of systems investigated by us, i.e. adsorption at coverages approaching monolayers on essentially hydrophobic surfaces, the surfactants adsorbing with their... 

A w Y O represents the molar free energy of replacing direct surface/water contacts by surface/surfactant contacts. The surfactants adsorb with their hydrocarbon tail directed towards a hydrophobic surface and hence we expect this term to be independent of the surfactant type and to cause a decrease in the free energy of adsorption. 

Thus, there is a simple way to predict the surfactant composition on a hydrophobic surface for a mixed surfactant system. The... 

Micellar catalysis is a broad field (Fendler and Fendler, 1975 Rathman, 1996 Rispens and Engberts, 2001), and caution is needed when using this term. In fact, whereas the broad term catalysis is justihed when referring to an increase of the velocity of reachon, this does not always mean that the velocity constant is increased (namely that there is a decrease of the specific activation energy). Rather, the velocity effect can be due to a concentration effect operated by the surface of the micelles. This is also the case for the autocatalytic self-reproduction of micelles discussed in the previous chapter, where the lipophilic precursor of the surfactant is concentrated on the hydrophobic surface of the fatty acid micelles (Bachmann et al., 1992), a feature that has given rise to some controversy (Mavelli and Luisi, 1996 Buhse etal, 1991 1998 Mavelli, 2004). 

To rate the wetting tendency of surfactants for hydrophobic surfaces. A graphitic powder, for example, with its low heat of wetting in water, yields much higher heat effects if immersed in solutions of surface active agents. Heats of dilution and of demicellization can be taken into account, if desired, to arrive directly at energies of interaction. 

The crystal structure of talc, illustrated in Figure 4, consists of repeating layers of a sandwich of bmcite [1317-43-7], Mg(OH)2, between sheets of silica [7631-86-9], SiOj. The layers of silica are not strongly bonded to each other (except for van der Waals forces) and thus it is easy to fracture talc along this surface, which corresponds to delamination. This surface is covalent and hydrophobic. If talc is fractured across the bmcite layer, the surfaces generated are ionic and hydrophilic in nature. Thus talc has a natural balance of hydrophilic and hydrophobic surfaces, giving it surfactant properties and consequendy the name soapstone which is used in many parts of the wodd. 

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