Entrainment and alignment of fibers by dip coating*

Withdrawing an object from a liquid bath leads to coating a thin film on its surface. When particles are dispersed in the liquid, and under the right operating conditions, the particles can be entrained in the coating film and deposited on the surface of the substrate. Whereas recent studies have considered the conditions for entrainment and the resulting coating film for spherical particles, the situation with anisotropic particles remains more elusive. Here, we experimentally investigate the dip coating process when rigid cylindrical fibers are dispersed in the liquid phase. Fibers differ from spherical particles since they have two lengthscales and may align on the substrate. Our experiments provide the condition for fiber entrainment in the coating film and characterize how the substrate geometry plays an important role in this process. We further characterize the alignment of the deposited fibers on different substrates and under different operating conditions. This deposition mechanism can be leveraged for applications where deposition and alignment of fibers are important, such as smart textiles.