Titration, soaps

Table 1. Comparison of polymer latexes obtained by emulsion polymerization of 1,4-DVB and S [79], Experimental conditions temperature = 50 °C volume ratio water to monomer = 6.25, SDS concentration = 0.02 M, PPS concentration = 0.01 M. Particle diameters were measured by soap titration and by electron microscopy.

The authors appreciate the discussions with Prof. I. M. Krieger of Case Western Reserve University and his allocation of laboratory space and TEM facilities. The authors also thank Ms. L. Bender for synthesizing many of the latexes, Dr. K. J. Abbey for performing the soap titrations, and Mr. R. M. Holsworth for taking the SEM photomicrographs. 

Measurement of characteristics of the emulsion droplets in concentrated media is indeed a difficult task. Some indirect methods have been used. The interfacial area and therefore the droplet size were determined by measuring the critical micelle concentration of miniemulsions [43]. Erdem et al. determined droplet sizes of concentrated miniemulsions via soap titration, which could be confirmed by CHDF measurements [44]. Droplet sizes without diluting the system can much better be estimated by small angle neutron scattering (SANS) measurements [23]. 

Our understanding of miniemulsion stability is limited by the practical difficulties encountered when attempting to measure and characterize a distribution of droplets. In fact, most of the well-known, established techniques used in the literature to characterize distributions of polymer particles in water are quite invasive and generally rely upon sample dilution (as in dynamic and static laser light scattering), and/or shear (as in capillary hydrodynamic fractionation), both of which are very likely to alter or destroy the sensitive equihbrium upon which a miniemulsion is based. Good results have been obtained by indirect techniques that do not need dilution, such as soap titration [125], SANS measurements[126] or turbidity and surface tension measurements [127]. Nevertheless, a substantial amount of experimental evidence has been collected, that has enabled us to estabhsh the effects of different amounts of surfactant and costabihzer, or different costabilizer structures, on stabihty. 

In this paper, a means is demonstrated for experimentally determining the percent of monomer conversion at which soap micelles disappear from the system during emulsion polymerization. By applying the mathematics and latex particle surface area which a soap molecule will occupy, developed for the soap titration particle size measurement procedure, the average particle size of the finished latex can be calculated. In fact, under some circumstances It might even be feasible to adjust monomer content. 

Surface tension measurement. Adsorption titration, also called soap titration, (2.3) was carried out by the drop volume method at different polymer concentrations. The equivalent concentration of salt was held constant. The amount of emulsifier necessary to reach the critical micelle concentration (CMC) in the latex was determined by each titration. The total weight of emulsifier present in the latex is the weight of emulsifier in the water plus the weight of emulsifier adsorbed. The linear plot of emulsifier concentration (total amount of emulsifier corresponding to the end-point of each titration) versus polymer concentration gives the CMC as the intercept and the slope determines the amount of emulsifier adsorbed on the polymer surface in equilibrium with emulsifier in solution at the CMC (E ). 

Figure 14. Dp measured by analytical centrifuge. Em determined by soap titration. Estimation of Am from these data.

Unless stated otherwise, the agglomeration experiments were carried out in a temperature chamber at 40°C and 32.5% TS using 0.1% PEO/TS. Samples were collected at fixed intervals, and the reaction was terminated by adding the samples to sufficient potassium oleate solution to decrease the surface tension of the latex to about 40 dyne/cm or by diluting with water to about 6% TS. The particle surface (2) was then determined by soap titration so that rate constant (fc ) and stability factor could be calculated from Equations 3, 4, and 5. 

Erdem B, Sully Y, Sudol ED, et al. (2000) Determination of miniemulsion droplet size via soap titration. Langmuir 16 4890-4895... 

When conversion is determined gravimetrically. Interval I may be completed before the first sample is taken. When rates of emulsion polymerization are discussed it is the constant rate fi-equently observed during Interval II which is meant. Most commonly, practically all the emulsifier is adsorbed on the surface of the latex particles at the end of Interval I then the surface concentration of adsorbed emulsifier decreases as the latex particles grow. Soap titration [67], in which the volume of a standard emulsifier solution required to reduce the surface tension of the latex to the value characterizing the presence of micellar soap is determined can be used to determine the final surface concentration of emulsifier. The surface-average particle size can be calculated from a knowledge of the amount of surfactant adsorbed at this point and the area occupied at the interface by a surfactant molecule in a saturated monolayer. This area should... 

It represents the diameter of a sphere having the same surface area as the particle. This average is of interest in l x technology since it can be easily obtained soap titration. The weight average is ddined as ... 

The result of these investigations leaves the following view of adsorption of ionic surfactants onto hydrophobic surfaces. Measured adsorption isotherms (Langmuir type) and comparisons between particle sizes as measured by soap titration and... 

A special case of using surface tension for the determination of surfactant concentration is the soap titration method (1). Here, the particle dispersion is subjected to measurements of surface tension under the addition of surfactant solution. Knowing the total particle surface area and the surface tension as a function of the total amount of added surfactant, it is possible to directly calculate the adsorption isotherm. The soap titration rests on the assumption that equal surface tension corresponds to equal surfactant activity (concentration) in the solution, and hence equal values of surfactant adsorption on the particle surface. 

Figure 22.4. In the soap titration method, the surface tension is determined with added surfactant for various batches of dispersions, with solid contents p. (b) Plots of VCo/ Kot versus p according to the soap titration method, rendering the F(y) and C(y) from the slope and intercept, respectively, according to equation (22.11)...

Soap Titration The fact that sufficient soap solution has to be added to precipitate all the hardness causing ions from a hard water sample before lather is formed is utilized in the determination of hardness. A. suitable aliquot of the hard water sample is taken in a stoppered flask and after successive additions of a soap solution (previously standardised by titration against standard hard water) from a burette, the mixture is vigorously shaken. The stage where the lather formed persists for 2-3 minutes is taken as the end-point of the titration. The hardness of the water sample is equivalent to the volume of the soap solution used minus lather factor (volume of soap solution used to produce lather with a volume of distilled water equal to the aliquot of the hard water sample). 

The surface characterization of a polymer particle involves investigating the adsorption of ions and amphiphilic molecules (emulsifiers, oligomers), determining the number of covalently bonded functional groups and acquiring information on the structure of the interfadal layer (swollen state or hairy layers ). Presently this task can not be solved satisfactorily. The main methods used are titrimetric analyses on purified dispersions, soap titration and electrokinetics. 

The soap titration is usually carried out at a series of solids contents (for example,... 

Fig. 3 -10 Soap titration. Determination of the emulsifier coverage of the polymer particles.

The soap titration technique is strictly only applicable for dispersions which contain one type of emulsifier. However, many polymer dispersions are stabilized by a combination of emulsifiers, often both ionic and non-ionic types. One approach in such cases is to perform the study with the emulsifier mixture, though there is the problem of exchange processes occurring on the particle surfaces if one of the emulsifiers is preferentially adsorbed. The results may also be affected by adsorbed amphiphilic oligomers generated during the emulsion polymerization. 

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