Making van der Waals Films on Fibers

The liquid layer coating a solid fiber drawn at constant velocity V 0 out of a bath of liquid is all the thicker since V 0 is large. We discuss in this letter the limit of very low capillary numbers: if the liquid wets the fiber, the thickness e of the liquid layer should not depend any longer on V 0 below a critical value of the velocity ( V 0 < Ṽ 0 ) and should be equal to a 2/3 b 1/3 , where a is a microscopic length related to the wetting interactions (which are supposed to be van der Waals ones) and b is the radius of the fiber. This thickness is in the 100 Å range. Then, a new experiment is presented: it consists of making such very thin films of dodecane on polymeric fibers and measuring their average thicknesses by gas chromatrography titrations. The results are promising: this technique could be an interesting alternative for detecting or measuring very thin films on curved surfaces for which more usual methods like ellipsometry are not suited.