The adsorption of oleate on apatite was studied at pH values from 6 to 9.8 and oleate concentrations from 2 X 10"5 6to 3 X 10~4 mol Lr1. Diffuse reflectance infrared Fourier transform spectroscopy has been found to be superior to the transmission infrared technique for detecting adsorbed oleate species. Confusion in previous studies is clarified and a better understanding of the adsorption mechanism obtained. Chemisorbed oleate corresponds to a single peak at 1550 cm"1 and probably comprises one oleate ion bonding with one lattice calcium ion on the surface. Surface calcium oleate precipitate showing peaks at 1574 and 1538 cm-1 has a structure similar to that of bulk calcium oleate and probably adsorbs through ion-dipole interaction and hydrocarbon chain association. Oleic acid dimer and monomer adsorb via hydrocarbon chain association onto underlying chemisorbed oleate and correspond to a sharp peak at 1713 cm'1 and a shoulder at 1732 cm"1, respectively. Chemisorption of oleate on apatite occurred under all conditions studied and was accompanied by physical adsorption of calcium oleate precipitate and/or oleic acid monomer and/or oleic acid dimer, depending on the pH and concentration of the solution.
Polystyrene latices containing particles which have a very narrow distribution of sizes can be prepared. In addition, by variation of preparative conditions, a range of latices can be prepared, so although each has a narrow size range, the radii can be varied from 25 nm to 2 pm. In these systems, by working at very low electrolyte conditions, the particles can be made to form an ordered array. From the latter, Bragg diffraction peaks can be observed by using a conventional light-scattering apparatus and the data used to determine the radius of the latex particles. With larger particle radii, 50-200 nm, diffraction studies can be made by reflection techniques which provide structural information on the type of ordering in the array and also allow an estimate to be made of the particle radius. With particle radii greater than 500 nm, particulate monolayers can be formed at the air-water interface from which diffraction patterns can be obtained by transmission of a well-collimated light beam. This technique also leads directly to a determination of the particle size.
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