Flow rate roll coating

Ribbing evenly spaced lines down the web web speed too fast/viscosity too high/ web coat too thin/flow rate too low/too little vacuum/(air entrainment] /Ca too high/channel divergence angle too small/Re too small. Forward roll coaters are... 

Figure 13.4 View through the glass roll of the coating bead as the flow rate is reduced. The roll speed was fixed capillary number (Ca) = 0.12 and no vacuum was applied to the upstream free surface. The cylinder was moving from bottom to top in each photograph. As the film thickness falls, the upstream free surface moves towards the feed slot and becomes three-dimensional. As the flow rate is decreased even further, the V pattern grows until the coating bead breaks. Reproduced from ref. 9 with the permission of Elsevier, 2014.

The cytoplasmic domain of P-selectin contains signals that mediate its rapid en-docytosis in clathrin-coated pits. Interactions of the cytoplasmic domain of P-selectin with these structures were found to enhance its adhesive function under flow [47]. Transfected CHO cells were prepared that express wild-type P-selectin or P-selectin constructs with substitutions or deletions in the cytoplasmic domain that either increase or decrease its internalization rate. Under flow, neutrophils tether equivalently to all constructs when expressed at matched densities. However, neutrophils roll on the internalization-competent constructs with greater adhesive strength, at slower velocities, and with more uniform motion. Confocal immunofluorescence microscopy demonstrates colocalization of a-adaptin, a component of clathrin-coated pits, with wild-type P-selectin but not with internalization-defective P-selectin lacking the cytoplasmic domain. Thus, interactions of P-selectin with clathrin-coated pits provide an alternative to cytoskeletal interactions to enhance adhesive function. The association of P-selectin with clathrin-coated pits may delay dissociation of P-selectin-PSGL-1 bonds and/or prevent forced extraction of P-selectin from the membrane. 

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