Homodisperse colloids

Penners, N.H.G. (1985) The preparation and stability of homodisperse colloidal hematite (a-Pe203). Ph.D. Thesis Wageningen, The Netherlands, 97 p. 

Penners, N.H.G. Koopal, L.K. (1986) Preparation and optical properties of homodisperse hematite hydrosols. Colloids Surfaces 19 337-349... 

So far, only a limited number of full dielectric relaxation spectra for well defined systems are available. Apart from the technical problems involved in the measurements (sec. 4.5e) there is the colloidal problem of synthesizing sufficiently concentrated sols with homodisperse spherical particles, preferably having different radii but fixed surface properties. Latices are popular objects because the particles are easily made homodisperse and spherical. Nevertheless they are somewhat suspect because there may be hairs on the surface, drastically affecting lateral hydrodynamic motion close to the surface. Moreover, changing the radius requires new syntheses and it is difficult to guarantee exact reproducibility of the surface structure. Inorganic particles do not have these drawbacks but it is not so ea to synthesize these as perfect spheres. 

Figure 4.39 gives another example, taken from Nature. The Corynebacterium considered here has more or less spherical, homodisperse cells, with diameters of 1.1 and 0.8 pm for the longer and shorter axis. Such cells are fascinating model colloids. The relaxation frequency, Ae and AK behave as expected for colloidal particles with a finite conduction behind the shear plane, which, in this case, is caused by the ions in the cell wall. As in the previous example, the data were analyzed with (4.8.30 and 31(, using (4.6.56] for Du. The three curves, drawn through the measuring points, refer to this interpretation with the values of indicated. The conductivity of the cell wall exceeds that of the bulk... 

Penners, N.H.G.. Koopal. L.K., and Lyklema. J.. Interfaciai electrochemistry of haematite (a-FcjOj) Homodisperse and heterodisperse sols. Colloids Sutf.. 21.457,1986. Shchukaiev. A.. Boily, J.-E, and Fehny. A.R., XPS of fast-frozen hematite colloids in NaCl aqueous solutions I. Evidence for the formation of multiple layers of hydrated sodium and chloride ions induced by the 001) basal plane, J. Phys. Chem. C, 111, 18307. 2007. 

Penners, N. H. G., and L. K. Koopal (1986), Preparation and Optical Properties of Homodisperse Hematite Hydrosols, Colloids Surf. 19, 337-349. 

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