Monodisperse sulfur sols

Chiu G, Meehan EJ. 1977. Monodisperse sulfur sols from the air oxidation of hydrogen sulfide solutions. Journal of Colloid and Interface Science 62 1-7. 

Another colloidal system with light scattering characteristics that have been widely studied is the so-called monodisperse sulfur sol. Although not actually monodisperse, the particle size distribution in this preparation is narrow enough to make it an ideal system for the study of optical phenomena. 

Formulate a generalization correlating the observed number of green bands in the HOTS for this system with the approximate particle size. Briefly describe how this information could be used to grow a monodisperse sulfur sol with a dimension that corresponds aproximately to a predetermined size. 

Autoxidation of aqueous H2S solutions results in elemental sulfur, sulfite, thiosulfate, and eventually sulfate. However, under certain conditions monodispersed sulfur sols with particle diameters of between 0.2 and 1.2 /um are obtained [48]. For example, a solution of H2S of concentration 46 mmol 1 in pure H2O exposed to air at 25 °C became turbid after an induction period of ca. 8 h and then showed briUiant higher-order Tyndall spectra. A solution saturated in H2S exhibited a pH value of 4.1 and was rapidly oxidized in an atmosphere of pure O2. At pH values >8 no elemental sulfur was formed (clear colorless solution), in the range pH=7-8 yellow solutions were obtained (polysulfide anions), while at pH<7 turbid solutions were produced but the induction period was as longer as lower the pH value [48] ... 

Comprehensive and detailed description of monodisperse systems is given in review articles [13-15], book contributions [16-19] and references therein. As with the La Mer s monodisperse sulfur sols, the fundamental requirement for the preparation of monodispersed particles is the control of kinetics of the generation of species that serve as precursors for the formation... 

Kenyon, A. S., and V. K. LaMer Light Scattering Properties of Monodispersed Sulfur Sols. I. Monochromatic Ultraviolet Angular Scattering. II. Effect of the Complex Index of Refraction Upon Transmittance. J. Colloid Sci. 4, 163—184 (1949). 

In the remainder of this section we see how the theoretical calculations of Mie account for the observed spectrum of colloidal gold. In the next section we consider the inverse problem for a simpler system how to interpret the experimental spectrum of sulfur sols in terms of the size and concentration of the particles. Both of these example systems consist of relatively monodisperse particles. Polydispersity complicates the spectrum of a colloid since the same x value will occur at different X values for spheres of different radii according to Equations (99M101). 

Od n has shown that Raffo sols can be separated into fractions of differing particle size by fractional precipitation with increasing concentrations of NaCl. As larger the particles as less NaCl is needed for precipitation [38]. Under special conditions monodispersed Raffo sols of particle size between 0.1 and 1.0 can be prepared directly from very dilute aqueous thiosulfate and sulfuric acid or hydrochloric acid without fractionation. These sols are characterized by higher order Tyndall spectra [39]. 

To obtain a monodispersed sol it is necessary to add the water to the organic sulfur solution and not the other way round. The observed particle size, derived from higher order Tyndall spectra, ranges from 0.20 to 0.45 jum if the initial sulfur concentration in ethanol is between 0.25 and 2.9 mg 1 [8]. 

---