Isodispersed

Before the number of doublets, triplets, etc., becomes too laige, one can write for the rate of coagulation at the primary minimum of isodispersed sols... 

Equation (7) is valid for agglomerates formed by approximately isodisperse, convex, and monosized particles. With the third moment M30 of the number density distribution n x) and a shape factor /q, a formula can be derived which is valid for distributions of similar, approximately isometric, and convex particles ... 

Figure 2.10. Dispersion of a dye, injected as a sample zone (Sy = 25 jiL) into A, straight tube By coiled tube C, knitted tube and D, a SBSR reactor. The reactor volumes (Vr = 160 iL) and pumping rates (Q = 0.75 mL/min) were identical in all experiments. The same piece of Microline tubing (L = 80 cm, 0.5 mm inside diameter) was used in experiments Ay By and C. (The injected dye was bromthymol blue, carrier stream 0.1 M borax and wavelength 620 nm, cf. Chapter 6.) The SBSR reactor was made of 0.86 mm inside diameter tube filled with 0.6-mm glass beads. Note that the isodispersion points on the peaks were recorded with microreactors made of identical length and diameter, but different geometry.

Zone penetration is an ideal tool for measuring selectivity coefficients, since the method allows readouts to be taken (1) at that vertical slice of the composite zone where the dispersion coefficients are equal (Da = Db at point M Fig. 2.26, bottom) and (2) at the peak maximum of the pure A component. The concentrations within such a composite zone and position of the point M at a time tM are readily established by an experiment where zone A is first injected alone and peak A is recorded by a detector of choice. (If chemical reactions are involved, like a reaction with a suitable reagent for colorimetric detection, a suitable manifold and colorimetric detector are used—cf. Section 4.5.2). Next, zone B is injected alone and peak B is recorded. Provided that the same solution of analyte is injected in both runs A and B, and that the detector responds linearly to the injected species, this experiment yields, (a) the isodispersion point M within the time concentration rnatrix, which is identified via time delay tM, and (b) the peak height Ha for the response of the pure species A at the time Im, because it equals the horizontal distance between point M and the baseline (Fig. 2.26). 

Figure 3.10. Residence time distribution curves in a coiled tube computed with the aid of Speberg s model [3.3]. (a) For = 0 the familiar Taylor s solution is obtained. When the function E is included, then RTD curves showing isodispersion points are obtained for both mixing cup detector b) and area average (across the flow) detector (c).

In the course of the years, several types of models have been proposed and worked out. In the early years (1940-1970) a microemulsion structure was postulated, e.g., that of isodispersed droplets of oil in water or water in oil, and the free energy of such a system was formulated from known or estimated interfacial tension and bending free energy of the monolayer as related to the overall composition of the system. 

Another beautiful example of isodispersed sols is formed by the sulphur sols prepared by La Mer and Barnes They mixed veiy dilute solutions of sodium thiosulphate and hydrochloric acid During about one hour sulphur was formed as was... 

The dimensions of the particles and their isodispersity have been detertnined by optical methods for which wc refer to chapter III, 2, p 97 ... 

Of course, this instability is especially related to isodispersed sols, and for hctcro-dispersed hoh the normal growth of the larger particles at the cost of the smaller ones will be the main cause of ageing. 

In nearly all problems of this kind it would be an advantage to have isodispersed sols at one s disposal (see 2 c, p. 66) Unfortunately, isodispersed sols are very exceptional and can only be obtained by very special methods of preparation In practice one has mo ly to deal with strongly heterodispersed or polydtspersed sols. 

There arc two different ways of preparing isodispersed systems The first is sorting out the particles of one size out of a heterodispersed system. The second is preparing the sol in such a way, that all particles grow to exactly the same size. The first way has been followed by j RRiN in preparing the suspensions of mastix or gamboge on... 

Starting with an isodispersed sol with tiq particles, each of volume Vi, the scattered light will be given by (see chapter III)... 

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