XC. <i>A problem in viscosity: The thickness of liquid films formed on solid surfaces under dynamic conditions</i>

Abstract

Summary The problem of determining the thickness of the liquid layer coating a solid body drawn out of a liquid is discussed theoretically and practically. It is shown that if the solid is a flat slab of infinite width, the forces determining the thickness are those of gravity (g) and viscosity (η) , and that the relation between thickness (t), density (ρ), and velocity of drawing v 0 is t 2 = 2v 0 η/ρg If the solid is a fine wire of radius r, surface tension is dominant and gravity negligible; If γ is the surface tension, the relation must be of the form t / r f(ηv / γ). It is found empirically that f(νv / γ) is of the form 4·8 γv / γ in c.g.s, units. These results apply to suspensions if (1) the diameter of the suspended particles is not greater than t, (2) the effect of the particles in increasing ν is taken into account. There is no evidence of any special cohesion between solids and liquids wetted by them other than that which prevents slipping at the interface.