Impact of Some Organics on Structural and Adsorptive Characteristics of Fumed Silica in Different Media

Pristine fumed silica and powders with dried residuals of centrifuged aqueous suspensions of fumed silica, silica/PVP, or silica/protein were studied using nitrogen adsorption and IR spectroscopy methods. The aqueous suspensions of silica with added polymers, surfactant, or ethanol were investigated by means of photon correlation spectroscopy, 1H NMR, and adsorption methods. The impact of polymers on the suspension and dried powder characteristics depends on the adsorption mechanism and the conformation of polymer molecules (globular or unfolded) due to strong or weak intramolecular interactions. Globular proteins interacting with silica through the flocculation mechanism affect the textural characteristics of dried powders more weakly than do unfolded proteins but strongly impact the aqueous suspension, thus shifting the swarm size distribution toward larger sizes compared to the size distribution of poly(vinylpyrrolidone), PVP. PVP is adsorbed in the unfolded state and gives a nearly monomodal particle size distribution (PSD). The ionogenic surfactant 1,2-ethylene-bis(N-dimethyl carbodecyloxymethyl)ammonium dichloride at C Aet < 0.01 wt % and ethanol at C EtOH = 10−50 wt % impacts the silica's PSD-dependent nonlinearly on the concentrations and pH.