The interaction of fumed silica A-300 (S-BET = 297 m(2) g(-1)) with bovine serum albumin (prepared by different methods), ovalbumin, human hemoglobin, and gelatin as a function of pH, salinity, and concentrations of components inaqueous medium was studied by adsorption and photon correlation spectroscopy (PCS) methods. Comparison of equilibrium (incubation time t(i) approximate to 1 h) adsorption of proteins on A-300, minute (t(i) approximate to 1 min) flocculation rate, and the particle size distributions measured by the PCs method shows different rearrangement of particle swarms depending on pH, salinity, and concentration of proteins, especially at pH close to IEP of silica or proteins. The electrokinetic mobility of protein/silica swarms is greater than that of individual components at pH far from the IEP of proteins. Changes in the Gibbs free energy (DeltaG) on protein adsorption depend on pH (-DeltaG is minimal at pH 2, close to the IEP of silica, and maximal at pH between the IEP of protein and silica), concentration (-DeltaG is maximal at C-p between 1 and 6 mg/ml), type of proteins, and their preparation technique. (C) 2003 Elsevier Science (USA). All rights reserved.