Contact line motion of polymer solution inside capillary

In this research we investigated the contact line motion of polyacrylamide solutions in glycerin inside glass capillaries. Three different molecular weights of 100,000 (100 k), 610,000 (610 k) and 5,000,000 g/mole (5 M) were used. It was hypothesized that the depletion of large polymers from the contact line region by migration strongly affects the contact line speed and experiments were carried out to confirm whether this hypothesis is applied to the present system. The experimental results for large molecular weight polymers (5 M) are consistent with the migration theory while those for small molecular weight polymers (100 k) do not show the migration effect. The 610 k polymers show either 5 M or 100 k behavior depending on concentration and contact line speed. These experimental observations are consistent with the migration theory. The positive first normal stress difference (N-1) of 100 k polymer solutions also affects the contact line speed. N-1 of 5 M polyacrylamide solutions does not appear to strongly affect the contact line motion, which also supports the polymer depletion near the contact line due to the migration. The result of the present experimental research independently supports the previous reports on the contact line motions of polymer solutions using the drop spreading method and the theoretical analysis (Han and Kim, 2013, 2014). (C) 2015 Elsevier B.V. All rights reserved.