ABSTRACT
Experimental . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 501
Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 501
Adsorption . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 501
Electrophoresis and Swarm Size
Distribution (SSD) . . . . . . . . . . . . . . . . . . . . . . . 504
Potentiometric Titration . . . . . . . . . . . . . . . . . . . . 505
Adsorption of Metal Ions . . . . . . . . . . . . . . . . . . . 505
1H NMR Spectroscopy . . . . . . . . . . . . . . . . . . . . 505
Infrared Spectroscopy . . . . . . . . . . . . . . . . . . . . . 506
Results and Discussion . . . . . . . . . . . . . . . . . . . . . . 506
Polymer Adsorption . . . . . . . . . . . . . . . . . . . . . . . 514
Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 527
Acknowledgment . . . . . . . . . . . . . . . . . . . . . . . . . . . 529
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 529
Fumed silicas synthesized under varied conditions were studied by means of adsorption, 1H NMR, photon cor-
relation spectroscopy, and electrokinetic methods. Prepared silicas possess different specific surface area
(SAr ¼ 85-512 m2/g), structures of primary particles and their swarms, concentrations of silanols (COH ¼ 1.9-5.2 mmol/m2), and weakly (Cw,105 ¼ 0.4-2.4 wt%) and strongly (Cw,900 ¼ 0.4-2.2 wt%) bound waters. There is correlation between the specific surface area (S) of fumed silica and the flow velocity
vf (S ln vf at vf , 25-30 m/s). Decrease in the amounts of hydrogen/oxygen in the flame and elevating synthesis temperature or flame turbulence enhance the size of primary particles, which become slightly micropous
on addition of hydrogen reacting at the flame periphery. Dividing of the flow in the burner to several smaller
flows reducing the turbulence without changes in other synthesis conditions significantly enhances the specific
surface area. The concentration of silanols increases with growing primary particle size, and the hydrophilicity
(Cw,105þ Cw,900) decreases at oxygen deficiency on the synthesis. The impact of polymers on the suspension and dried powder characteristics depends on the adsorption mechanism and conformation of polymer molecules
(globular or unfolded) due to strong or weak intramolecular interactions. Globular proteins interacting with
silica through the flocculation mechanism have a weaker effect on the textural characteristics of powders pre-
pared by drying of the suspensions but strongly impact the aqueous suspension shifting the swarm size distri-
bution toward larger sizes in comparison with poly(vinyl pyrrolidone), PVP, adsorbed in the unfolded state
and giving nearly monomodal particle size distribution. Ionogenic surfactant 1,2-ethylene-bis-(N-dimethyl car-
bodecyloxymethyl) ammonium dichloride at CAet , 0.01 wt. % and ethanol at CEtOH ¼ 10-50 wt. % impact the swarm size distributions of silicas dependent nonlinearly on the concentrations and pH. Adsorbed metal ions
have an influence on the surface charge density and the electrophoretic mobility of fumed silica particles
increasing with concentration.
