Effects of surfactants

Surfactants are very often added to biological samples to prevent the formation of aggregates. Surfactants also prevent target molecules to stick to the solid walls of the microsystem. 

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The energetics and kinetics of film formation appear to be especially important when two or more solutes are present, since now the matter of monolayer penetration or complex formation enters the picture (see Section IV-7). Schul-man and co-workers [77, 78], in particular, noted that especially stable emulsions result when the adsorbed film of surfactant material forms strong penetration complexes with a species present in the oil phase. The stabilizing effect of such mixed films may lie in their slow desorption or elevated viscosity. The dynamic effects of surfactant transport have been investigated by Shah and coworkers [22] who show the correlation between micellar lifetime and droplet size. More stable micelles are unable to rapidly transport surfactant from the bulk to the surface, and hence they support emulsions containing larger droplets. 

Breslow studied the dimerisation of cyclopentadiene and the reaction between substituted maleimides and 9-(hydroxymethyl)anthracene in alcohol-water mixtures. He successfully correlated the rate constant with the solubility of the starting materials for each Diels-Alder reaction. From these relations he estimated the change in solvent accessible surface between initial state and activated complex " . Again, Breslow completely neglects hydrogen bonding interactions, but since he only studied alcohol-water mixtures, the enforced hydrophobic interactions will dominate the behaviour. Recently, also Diels-Alder reactions in dilute salt solutions in aqueous ethanol have been studied and minor rate increases have been observed Lubineau has demonstrated that addition of sugars can induce an extra acceleration of the aqueous Diels-Alder reaction . Also the effect of surfactants on Diels-Alder reactions has been studied. This topic will be extensively reviewed in Chapter 4. 

Effects of Surfactants on Solutions. A surfactant changes the properties of a solvent ia which it is dissolved to a much greater extent than is expected from its concentration effects. This marked effect is the result of adsorption at the solution s iaterfaces, orientation of the adsorbed surfactant ions or molecules, micelle formation ia the bulk of the solution, and orientation of the surfactant ions or molecules ia the micelles, which are caused by the amphipathic stmcture of a surfactant molecule. The magnitude of these effects depends to a large extent on the solubiUty balance of the molecule. An efficient surfactant is usually relatively iasoluble as iadividual ions or molecules ia the bulk of a solution, eg, 10 to mol/L. 

Fig. 5. Effect of surfactant type on surface resistivity, (a) Concentration of surface-active compound in low density polyethylene (LDPE) requked to achieve 10 Q/sq surface resistivity and (b) effect on surface resistivity of an acrylic polymer. Concentration of surface-active compound is 0.3%.

Use of Surfa.cta.nts, Although the use of steam to improve dewatering is consistently beneficial, the effects of surfactants on residual moisture are highly inconsistent. Additions of anionic, nonionic, or sometimes cationic surfactants of a few hundredths weight percent of the slurry, 0.02—0.5 kg/1 of soHds (50), are as effective as viscosity reduction in removing water from a number of filter cakes, including froth-floated coal, metal sulfide concentrates, and fine iron ores (Table 2). A few studies have used both steam and a surfactant on coal and iron ore and found that the effects are additive, giving twice the moisture reduction of either treatment alone (44—46,49). 

Table 2. Effect of Surfactants on Residual Moisture in Filter Cakes...

CMC), reverses the effect that the surfactant has on contact angle at lower concentrations, and at or above the CMC there is no further lowering of surface tension. At the higher concentrations, the surfactant loses some of its beneficial effect on dewateriag, as shown ia Figure 5. The beneficial effects of surfactants on dewateriag are most pronounced ia cakes that have been partially deslimed or ia cakes of partially hydrophobic particles (eg, flotation concentrates) that are adsorbed onto each other. Surfactants at or above CMC have Httle practical effect on extremely fine cakes, where pores are small and the cake has no further opportunity to consoHdate. A number of filter cakes do not respond to surfactant addition at any level. 

Fig. 5. Effect of surfactant concentration on moisture content of <500 fim coal filter cake (51). Poiat A represents 2ero surfactant concentration Poiat B,...

An evaluation of the retardation effects of surfactants on the steady velocity of a single drop (or bubble) under the influence of gravity has been made by Levich (L3) and extended recently by Newman (Nl). A further generalization to the domain of flow around an ensemble of many drops or bubbles in the presence of surfactants has been completed most recently by Waslo and Gal-Or (Wl). The terminal velocity of the ensemble is expressed in terms of the dispersed-phase holdup fraction and reduces to Levich s solution for a single particle when approaches zero. The basic theoretical principles governing these retardation effects will be demonstrated here for the case of a single drop or bubble. Thermodynamically, this is a case where coupling effects between the diffusion of surfactants (first-order tensorial transfer) and viscous flow (second-order tensorial transfer) takes place. Subject to the Curie principle, it demonstrates that this retardation effect occurs on a nonisotropic interface. Therefore, it is necessary to express the concentration of surfactants T, as it varies from point to point on the interface, in terms of the coordinates of the interface, i.e.,... 

Electrochemical analytical techniques are a class of titration methods which in turn can be subdivided into potentiometric titrations using ion-selective electrodes and polarographic methods. Polarographic methods are based on the suppression of the overpotential associated with oxygen or other species in the polarographic cell caused by surfactants or on the effect of surfactants on the capacitance of the electrode. One example of this latter case is the method based on the interference of anionic surfactants with cationic surfactants, or vice versa, on the capacitance of a mercury drop electrode. This interference can be used in the one-phase titration of sulfates without indicator to determine the endpoint... 

Animal tests were commonly used in the past, also according to the Draize protocol [357,372]. However, such tests have been questioned for several reasons. In addition to the public concern about animal welfare, animal tests are conducted under conditions and at concentrations quite different from those that occur in practice, as in the case of eye irritancy. The effects of surfactants on the skin cannot be compared when the results have been obtained through different protocols and even results obtained by the same method are not comparable if conditions differ. 

The effect of surfactant structures and properties on emulsion polymerization have been investigated by numerous authors [82-89]. Efforts were made to study the effects of surfactants with different molecular weights on the rate of polymerization [82], swelling and solubilization effects [83], effects of alkyl chain length of homologous series on the rate of polymerization, particle size... 

Hetsroni G, Zakin JL, Lin Z, Mosyak A, Pancallo EA, Rozenblit R (2001) The effect of surfactants on bubble grows, wall thermal patterns and heat transfer in pool boiling. Int J Heat Mass Transfer 44 485-497... 

Marches JR, NJ Russel, GF White, WA House (1991) Effects of surfactant adsorption and biodegradability on the distribution of bacteria between sediments and water in a freshwater microcosm. Appl Environ Microbiol 57 2507-2513. 

Adverse effect of surfactants on bacterial adhesion to surfaces in the matrix... 

Experiments have been conducted in a contaminated aquifer to examine the effect of Triton X-100 on increasing the release of TCE from sediments (Sahoo et al. 1998). The increase was rather modest (ca. 30%), and is consistent with the limited effect of surfactants in increasing the availability of PAHs, which has been discussed in Part 2 of this chapter. 

The effectiveness of surfactants in overcoming the hydrophobic effect of magnesium stearate may not be a result solely of an increase in the wetting properties of the bulk phase. Compared to putting the surfactant in the dosage form, Botzolakis [71] and Wang and Chowhan [135] found that adding an equivalent amount of surfactant to the dissolution medium was not effective. The possible impact of the surfactant at... 

JR Crison, ND Weiner, GL Amidon. Dissolution media for in vitro testing of water-insoluble drugs Effect of surfactant purity on in vitro dissolution of carbama-zepine in aqueous solutions of sodium lauryl sulfate. J Pharm Sci 86 384-388, 1997. 

In this section the laboratory measurements of CC -foam mobility are presented along with the description of the experimental procedure, the apparatus, and the evaluation of the mobility. The mobility results are shown in the order of the effects of surfactant concentration, CC -foam fraction, and rock permeability. The preparation of the surfactant solution is briefly mentioned in the Effect of Surfactant Concentrations section. A zwitteronic surfactant Varion CAS (ZS) from Sherex (23) and an anionic surfactant Enordet X2001 (AEGS) from Shell were used for this experimental study. 

The Effect of Surfactant Concentrations, The effect of surfactant concentrations on CC -foam mobility is plotted on a log-log scale in Figure 3. The presented data points are the average mobility values obtained from a superficial velocity range of 2-10 ft/day, with the CC -foam fraction was kept constant around 80%. With Berea sandstone, ZS and AEGS surfactants were used. The measured average permeability of the Berea sandstone with 1% brine was 305 md. With Baker dolomite, AEGS was used to make comparison with Berea sandstone. The permeability of the Baker dolomite was 6.09 md measured with 1% brine solution. 

Lee J, Kentish S, Ashokkumar M (2005) Effect of surfactants on the rate of growth of an air bubble by rectified diffusion. J Phys Chem B 109 14595-14598... 

The proposed mechanism of effect of surfactant and ultrasound is reported in Fig. 7.5. The long chain surfactant molecules attach to surface of nanoparticles due to physical adsorption. Only thin layer is adsorbed onto the CaC03 nanoparticles. Due to presence of ultrasound and use of surfactant will control the nucleation. Surfactant keeps the particles away from each other by preventing flocculation due to change in surface tension of reaction mass. The concentration of additives was changed from 0.2 to 1.0 g/L. Addition of 0.2 g/L tripolyphosphate shows the increase in the rate of precipitation which is determined from the Ca(OH)2 consumption. Polyacrylic acid shows the least rate of precipitation (0.115 mol/1), which... 

Table 7.2 Effect of surfactant and ultrasound on structure of nano CaC03 particles (crystallite size, particle size distribution) [43]...

Sonawane S, Khanna P, Meshram S, Mahajan C, Deosarkar M, Gumfekar S (2009) Effect of surfactant on synthesis of calcium carbonate nanoparticles using sonochemical carbonization. Int J Chem Reactor Eng (Be press) 7 A(47) l-15, www.bepress.com/ijcre/vol7/47... 

Figure 17.2 Effects of surface tension and surfactant on alveolar stability, (a) Effect of surface tension. According to the law of LaPlace (P = 1ST/r), if two alveoli have the same surface tension (ST), the alveolus with the smaller radius (r), and therefore a greater collapsing pressure (P), would tend to empty into the alveolus with the larger radius, (b) Effect of surfactant. Surfactant decreases the surface tension and thus the collapsing pressure in smaller alveoli to a greater extent than it does in larger alveoli. As a result, the collapsing pressures in all alveoli are equal. This prevents alveolar collapse and promotes alveolar stability.

Table 10.20 Effect of surfactant addition on AOX values after chlorite bleaching of synthetic fibres [224]...

Effects of Surfactant on High-phospholipid Membrane Permeability and Retention... 

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