STATISTICAL PROPERTIES OF SURFACES COVERED BY DEPOSITED PARTICLES

The statistical properties of surfaces covered by irreversibly adsorbe d colloidal particles are studied as a function of the Peclet number ( or equivalently as a function of their rescaled radius R). More preci sely, the radial distribution function g(r) is determined as a functio n of the coverage theta for five systems corresponding to different va lues of R. Also measured is the reduced variance sigma(2)/[n] of the number n of adsorbed particles on surfaces of given area out of the ad sorption plane. Finally, the evolution of [n] with the concentration o f particles in solution during the deposition process is determined fo r the different systems. This allows us to obtain information on the a vailable surface function Phi. All these parameters are compared to th eir expected behavior according to the random sequential adsorption (R SA) model and to the ballistic model (BM). It is found that the radial distribution function of the system of particles characterized by R< 1 is well predicted by the RSA model whereas for R>3 the BM can serve as a good first approximation. On the other hand, one finds surprisin gly that the available surface function Phi and the reduced variance s igma(2)/[n] vary with the coverage theta in a similar way for all the systems over the range of value of R investigated. Their behavior cor responds, in first approximation, to the expectations from the BM. In particular, the reduced variance sigma(2)/[n] exhibits a horizontal ta ngent at low coverage whereas the RSA model predicts an initial slope of -4. This result is the more intriguing that sigma(2)/[n] is directl y related to the radial distribution function g(r), which does vary wi th R. Finally, higher order moments of the distribution of the number of particles n adsorbed on our surfaces are also determined as a func tion of the coverage. They behave, within experimental errors, like th ose of a Gaussian distribution as predicted by the central limit theor em. (C) 1995 American Institute of Physics.