Surfactant surface area, determination

Adsorption of ionic, nonionic and polymeric surfactant on the agrochemical solid gives valuable information on the magnitude and strength of the interaction between the molecules and the substrate as well as the orientation of the molecules. The latter is important in determining colloid stability. Adsorption isotherms are fairly simple to determine, but require careful experimental techniques. A representative sample of the solid with known surface area A per unit mass must be available. The surface area is usually determined using gas adsorption. N2 is usually used as the adsorbate, but for materials with relativdy low surface area, such as those encountered with most agrochemical solids, it is preferable to use Kr as the adsorbate. The surface area is obtained from the amount of gas adsorbed at various relative pressures by application of the BET equation [96]. However, the surface area determined by gas adsorption may not represent the true surface area of the solid in suspension (the so-called wet surface). In this case it is preferable to use dye adsorption to measure the surface area [99]. 

The ratio E/ps, calculated for different phases below the bifurcation, is shown in Fig. 15. In the special case of the C phase the surface intersects itself therefore, in the computation of S/p we have subtracted the volume occupied along the lines of intersection, since it would be counted twice otherwise. The surface area per volume is an increasing function of the surfactant volume fraction and it determines the sequence of phases. Moreover, we have found that the effect of broadening of the interface on the value S/p in different phases is different, and we have a quantitative... 

The number of polymer particles is the prime determinant of the rate and degree of polymerization since it appears as the first power in both Eqs. 4-5 and 4-7. The formation (and stabilization) of polymer particles by both micellar nucleation and homogeneous nucleation involves the adsorption of surfactant from the micelles, solution, and monomer droplets. The number of polymer particles that can be stabilized is dependent on the total surface area of surfactant present in the system asS, where as is the interfacial surface area occupied by a surfactant molecule and S is the total concentration of surfactant in the system (micelles, solution, monomer droplets). However, N is also directly dependent on the rate of radical generation. The quantitative dependence of N on asS and R,- has been derived as... 

Derivation of the Gibbs adsorption isotherm. Determination of the adsorption of surfactants at liquid interfaces. Laboratory project to determine the surface area of the common adsorbent, powdered activated charcoal. 

Specific surface area (SBet), total pore volume (V), determined by the BJH method and pore diameter (0) of products obtained from different synthesis conditions (decane/surfactant... 

The size of the monomer droplets plays the key role in determining the locus of particle nucleation in emulsion and miniemulsion polymerizations. The competitive position of monomer droplets for capture of free radicals during miniemulsion polymerization is enhanced by both the increase in total droplet surface area and the decrease in the available surfactant for micelle formation or stabilization of precursors in homogeneous nucleation. 

If the number of PAA blocking segments is limited and the surface area that can be blocked by all these segments being less than the working surface area of colloidal particle, a decrease in the quantum yield at the initial part of kinetic dependence will occur to a certain (pst. The value of stationary state of the working surface not blocked by PAA. This agrees with experimental data. Naturally, the fraction of the surface area blocked by the polymer surfactant, and hence the value cps/cpo depend on the nature of the surfactant used. 

Micelles are formed in order to protect the hydrophobic regions of the amphiphilic surfactant from the aqueous solution. The surface area S occupied by the surfactant molecule can be determined by ... 

The geometric model of a micelle used above depends only on the volume of the droplet determined by water molecules and the surface area of the droplet determined by the surfactant molecules. As a result, when a reactant is dissolved inside the droplet, it could affect the overall size of the droplet and the relationship... 

Results from the determination of the specific surface area of a foam from 0.5% sulphonole solution (commercial surfactant - dodecyl benzene sulphonate) [Pg.365]

Hence, the rate of decrease in specific surface area can be determined if the values of adsorption, foam expansion ratio and rate of increase in bulk surfactant concentration in the foam liquid are known. 

Fig. 6.1 depicts the experimental time dependence of foam expansion ratio, surfactant concentration in the flowing out solution as well as the rate of internal foam collapse. Within the whole time interval the rate of diminishing of specific foam surface area for a sulphonol foam is less than that for a NP20 foam, though the difference is not significant. Probably this is related to the fact that in the initial stage of internal foam collapse the rate deF/dx is determined by the gas mass-transfer that does not depend considerably on the surfactant kind. 

Si was nonporous (0.05 m /g). After partial removal of the template, the surface area increases to 140 m /g. The bands around 3000 and 1500 cm assigned to the stretching and bending vibrations of C-H of the surfactants are observed in the IR spectrum, indicating that some surfactant was still present and the extraction was uncompleted. Even in the elementary analysis the component of the element N decreased from 1.02% to 0.77%. If HCI/EtOH extraction is complete, the BET surface area may be more than 140 m /g. A particle size determination by TEM shows an average diameter of 2 um, indicating that the high surface area cannot be attributed to the size of small, dense spherical particles. 

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