Poly(vinyl alcohol) (PVA) hydrogel tube was prepared (sub-millimeter inner diameter) from PVA-dimethylsulfoxide/water solution by repetitive cooling method. The inner surface of the PVA hydrogel tube was chemically modified with poly(acrylic acid) (PAA). Slip of water in intact and modified PVA hydrogel tubes was studied. The slip was inferred by observing the motion of micron-sized spherical monodispersed polystyrene particles suspended in the flowing water by using an optical microscope from very low to medium flow rate. The particle velocity was measured by both particle tracking (PT) and particle image deformation (PID) method and the slip velocity was estimated by extrapolating the experimental data of the velocity profiles on the gel surfaces. Microscopic measurements reveal that the slip velocities on the hydrogel surfaces depended on the chemical nature and the surface roughness of the hydrogel surfaces, and were proportional to flow rate. Slip velocity of modified PVA hydrogel tube was higher than that of intact PVA hydrogel tube.

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