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| - Adsorption at a Carbon Black Microparticle Surface in Aqueous Colloids Probed byOptical Second-Harmonic Generation
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| - The surface properties of carbon black microparticles in aqueous solution are characterized through adsorptionof a hydrophobic ion (malachite green) monitored by optical second-harmonic generation (SHG). Carbonblack particle surfaces with 14 different O/C ratios (from 0.028 to 0.270) have been examined. The adsorptionisotherm of MG on the surface of carbon black particles weighing as little as 0.010 g can be measured usingSHG measured during continuous titration of the MG molecule into the solution. The SHG data allowsdetermination of the adsorption free energy and reveals coherent interference between the SH fields from thesurface-adsorbed MG molecules and the carbon black particle. The change in the coherent interference impliesa change of adsorption orientation of MG on surfaces with different O/C ratios. There is strong correlationfound between the observed adsorption characteristics and the O/C ratio of the surfaces. Furthermore, MGadsorption isotherms of surfaces with higher O/C ratios appear similar to the ones of surfaces preadsorbedwith surfactants that can increase surface hydrophilicity and dispersion in aqueous solution. All observationsindicate that particle surfaces with higher O/C ratios appear more hydrophilic. This study demonstrates onceagain the many advantages of SHG as an effective surface analytical technique of colloidal particles.
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