Interaction of hydrophobized filaments in aqueous electrolyte solutions

The apparatus developed earlier to measure dispersion forces has been applied in the measurement of the forces of attraction between hydrophobic (θ ≈ 100°) silica filaments immersed in water and the disjoining pressure before the samples are brought into contact, as a function of the distance separating the filaments, H (for gaps H=20 to 60 nm). The attraction forces and disjoining pressure exceeded by one to two orders of magnitude the dispersion forces, and decayed exponentially as the distance increased. The decay length was 12 to 13 nm — considerably larger than for the structural repulsive forces in thin interlayers of polar liquids adjoining lyophilic surfaces.

The result for gaps H<20 nm (the decay length equal to about 3 nm) is in qualitative agreement with the works of Israelachvili, Pashley and Claesson.

The attractive forces decayed still more slowly as the distance increased after the samples' contact position was reached. The presence of hysteresis of forces allows a conclusion to be drawn on the formation of a vapour-gas bubble when the samples are brought into contact. This confirms the Schchukin-Yushchenko statement.