Fluid-holding time parameter and fluid holding capability of polymeric materials

The fluid holding capability of polymeric materials was semiquantitatively characterized with a new parameter called the fluid holding time (FHT). FHT measures the time it takes a continuous film to recede down the side of a Wilhelmy plate, which varies on different surfaces with the same degree of wettability. Both pure water and an artificial tear fluid (i.e., protein/sa lt solution) were used to systematically wet uncoated and plasma polymer co ated polymeric plates. The FHT was calculated from Wilhelmy force loop plot s in the event that a continuous water or aqueous film adhered to a polymer ic surface. Such events are easily verified by consecutive wetting. Dynamic Wilhelmy force measurement is probably the most sensitive technique for mo nitoring wettability and surface configuration change, two important phenom enological factors that affect the FHT. The FHT measured by the Wilhelmy ba lance method can be effectively used to compare the liquid holding capabili ties of different surfaces. The value of the FHT depends on experimental pa rameters and thus cannot be used in an absolute sense. In general, spontane ous wetting is the most favorable condition for producing continuous aqueou s films on unperturbable surfaces. However, moderately hydrophilic and poss ibly even some hydrophobic surfaces perturbable by water were found to be c apable of holding continuous films of water.