Modification of flow through silica micro-capillaries via polymer brushes

Polymer brushes were synthesized on the interior of silica micro-capillaries to study the influence of brushes on solvent flow through a confined space. The synthesis of several polymer brush coatings were performed in fused silica micro-capillary tubing by atom transfer radical polymerization using the “grafting from” approach. The hydrophilic and hydrophobic nature of the polymer coatings led to flow in micro-capillaries that could be manipulated and controlled in a passive fashion without an external stimulus. Backpressure measurements were performed to study how polymer brushes might alter the flow of solvents. An analogous study involved capillaries functionalized with small molecule silanes. Preferential flow experiments were designed to measure the preferred path an aqueous solvent would take when comparing two capillaries containing polymer coatings of different surface energies. Aqueous flow preferred the hydrophilic, higher surface energy coated capillary when comparing capillaries of a similar internal diameter. When the difference in internal size became too large, the surface energy effect mitigated.

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► A variety of polymer brushes were prepared on the interior surface of silica capillaries.
► Backpressure measurements and preferential flow experiments were used to assess the influence of polymer brush coatings on aqueous flow.
► The results from the polymer-brush modified capillaries were compared to capillaries modified with low molecular weight silanes.
► Aqueous flow shows a preference for capillaries coated with hydrophilic brushes or silanes when comparing capillaries of the same interior diameter of 75 microns.
► If the capillary interior diameter is significantly greater (250 microns), the bias effect of surface coatings is minimized.