Big Chemical Encyclopedia

Chemical substances, components, reactions, process design ...

Articles Figures Tables About

SURFACTANT FREE

The concentration of free surfactant, counterions, and micelles as a function of overall surfactant concentration is shown in Fig. XIII-13. Above the CMC, the concentration of free surfactant is essentially constant while the counterion concentration increases and... [Pg.481]

Anionic Surfactants. PVP also interacts with anionic detergents, another class of large anions (108). This interaction has generated considerable interest because addition of PVP results in the formation of micelles at lower concentration than the critical micelle concentration (CMC) of the free surfactant the mechanism is described as a "necklace" of hemimicelles along the polymer chain, the hemimicelles being surrounded to some extent with PVP (109). The effective lowering of the CMC increases the surfactant s apparent activity at interfaces. PVP will increase foaming of anionic surfactants for this reason. [Pg.532]

Beyond the CMC, surfactants which are added to the solution thus form micelles which are in equilibrium with the free surfactants. This explains why Xi and level off at that concentration. Note that even though it is called critical, the CMC is not related to a phase transition. Therefore, it is not defined unambiguously. In the simulations, some authors identify it with the concentration where more than half of the surfactants are assembled into aggregates [114] others determine the intersection point of linear fits to the low concentration and the high concentration regime, either plotting the free surfactant concentration vs the total surfactant concentration [115], or plotting the surfactant chemical potential vs ln( ) [119]. [Pg.652]

Guillaume et al. [69] presented a high performance liquid chromatographic method for an association study of miconazole and other imidazole derivatives in surfactant micellar using a hydrophilic reagent, Montanox DF 80. The thermodynamic results obtained showed that imidazole association in the surfactant micelles was effective over a concentration of surfactant equal to 0.4 pM. In addition, an enthalpy-entropy compensation study revealed that the type of interaction between the solute and the RP-18 stationary phase was independent of the molecular structure. The thermodynamic variations observed were considered the result of equilibrium displacement between the solute and free ethanol (respectively free surfactant) and its clusters (respective to micelles) created in the mobile phase. [Pg.49]

Surfactant head groups. The remarkable fact remains that this charge neutralization allows aggregation to take place at free surfactant concentrations orders of magnitude below the cmc, dependent on the polyion charge density. [Pg.238]

M.P. Aronson The Role of Free Surfactant in Destabilizing Oil-in-Water Emulsions. Langmuir 5, 494 (1989). [Pg.50]

The situation is complicated by the fact that the cmc value determined in the pure surfactant solution generally differs from that fomid in the presence of biopolymer. This is mainly because the surfactant-biopolymer interactions can shift the equilibrium between free surfactant molecules and their micelles, leading to a change in the effective cmc of surfactant molecules in the biopolymer system (Kelley and McClements, 2003 McClements, 2000 Thongngam and McClements, 2005). [Pg.179]

Mixed micelles, comprising both polymerized and free surfactants, are formed once the critical association concentration (CAC) of the free am-phiphiles is reached. The CAC is typically much smaller than the CMC for the formation of free micelles. As the fraction of unpolymerized surfactants within the mixed micelles grows, their structure approaches that of free micelles. [Pg.25]

The basis for the phase-separation model (Mukerjee, 1967) assumes that the occurrence of thf phase change happens at the CMC. This model uses the chemical potentials of the free surfactant ii the aqueous phaseassociated surfactant in the micellar pha 0,Gu,... [Pg.263]

Miniemulsion polymerization involves the use of an effective surfactant/costabi-lizer system to produce very small (0.01-0.5 micron) monomer droplets. The droplet surface area in these systems is very large, and most of the surfactant is adsorbed at the droplet surfaces. Particle nucleation is primarily via radical (primary or oligomeric) entry into monomer droplets, since little surfactant is present in the form of micelles, or as free surfactant available to stabilize particles formed in the continuous phase. The reaction then proceeds by polymerization of the monomer in these small droplets hence there may be no true Interval II. [Pg.20]

Electrophoretic Mobility (I0 5cm2s lv 1) Free Surfactant Concentration (I0 4N) pH Primary Recovery (%)... [Pg.281]

In emulsion systems, an equilibrium between surfactant associated with the particles and free surfactant is considered to exist—i.e.,... [Pg.212]

Micellar Liquid Chromatography (MLC) uses surfactant solutions as mobile phases for reversed phase liquid chromatography. The two main properties of surfactant molecules, as related to chromatography, are micelle formation and adsorption at interfaces. The micelles play the role of the organic modifier, so their influence on retention has been extensively studied (1). At surfactant concentrations above the critical micellar concentration (CMC), micelles are present and the amount of free surfactant is essentially... [Pg.130]

Additive effects Low amounts of methanol have little effect on the free surfactant concentration (Table I). Nevertheless, the adsorbed amount of surfactant is decreased by 5% v/v methanol. The decreasing is slight (8%) with ODS Hypersil and the two surfactants and with SAS Hypersil and CTAB, but it can reach 30% in the case of SDS on SAS Hypersil (Table IV). [Pg.134]

The surfactants only slightly affect polystyrene incorporation up to the surfactant concentration where surfactant adsorption on the particles is maximal,54,76 that is 0.02 mol kg 1. At higher surfactant concentrations the amount of free surfactant that is surfactants not adsorbed on the particles... [Pg.495]

Enhanced oil recovery always deals with two or more fluids. By implication these fluids are conjugate phases in equilibrium with each other, although Chapter 6 shows that nonequilibrium mixing can sometimes be important when surfactants are used. When one considers the role of the critical micelle concentration (CMC) in CO2 mobility control, it is the CMC of the aqueous phase saturated with CO2 that is important. As illustrated in Figure 10, this CMC may be much lower than the CMC of C02 free surfactant solutions (R. S. Schechter, University of Texas, personal communication, October 26, 1987). [Pg.31]

In this paper, the results on solution and Interfaclal properties of a cationic celluloslcs polymer with hydrophobic groups are presented. Interaction of such polymers with added surfactants can be even more complex than that of "unmodified" polymers. In the past we have reported the results of Interactions of unmodified cationic polymer with various surfactants Investigated using such techniques as surface tension, preclpltatlon-redlssolutlon, viscosity, solubilization, fluorescence, electroklnetlc measurements, SANS,etc.(15-17). Briefly, these results showed that as the concentration of the surfactant Is Increased at constant polymer level significant binding of the surfactant to the polymer occurred leading to marked Increases In the surface activity and viscosity. These systems were able to solubilize water Insoluble materials at surfactant concentrations well below the CMC of polymer-free surfactant solutions. Excess surfactant beyond that required to form stoichiometric complex was found to solubilize this Insoluble complex and Information on the structure of these solubilized systems has been presented. [Pg.298]

The presence of free surfactant is not preferred in some applications of polymer emulsions. It may, for instance, result in water sensitivity of dried latex coatings or... [Pg.288]

In view of the foregoing discussion, it is not surprising that many emulsion polymerizations can be carried out without the addition of free surfactants. This is accomplished by use of ionic initiators, like the widely used persulfates, with the additional assistance of copoly merizable surfactants, if these are needed. It should be realized, however, that emulsion polymerization itself generates surfactants, and the process cannot therefore be entirely surfactant free. [Pg.289]


See other pages where SURFACTANT FREE is mentioned: [Pg.495]    [Pg.2038]    [Pg.651]    [Pg.217]    [Pg.22]    [Pg.225]    [Pg.225]    [Pg.228]    [Pg.231]    [Pg.232]    [Pg.237]    [Pg.240]    [Pg.204]    [Pg.475]    [Pg.96]    [Pg.281]    [Pg.281]    [Pg.233]    [Pg.35]    [Pg.702]    [Pg.81]    [Pg.84]    [Pg.108]    [Pg.108]    [Pg.135]    [Pg.496]    [Pg.1796]    [Pg.391]   
See also in sourсe #XX -- [ Pg.54 ]




SEARCH



Emulsion polymerization surfactant-free

Emulsion polymerization surfactant-free system

Free energy binary surfactant systems

Free energy single surfactant systems

Free energy surfactant systems

Free energy surfactants transferred from

Free surfactant concentration

Permeability Measurements High-phospholipid in Surfactant-free Solutions

Surfactant adsorption surface free energy

Surfactant-free dispersions

Surfactant-free emulsion

© 2024 chempedia.info