Wetting dynamics of polydimethylsiloxane mixtures on a poly(ethylene terephthalate) fiber

HYPOTHESIS: The wetting dynamics of liquids with identical surface tensions are mostly controlled by their viscosities. We therefore hypothesized that the wetting dynamics of one- (pure liquid) and two-component (mixture) polydimethylsiloxane (PDMS) on a poly(ethylene terephthalate) (PET) fiber with similar surface tensions and viscosities should be controlled by the same underlying physical mechanisms. EXPERIMENTS: We studied the capillary rise of PDMS liquids on a PET fiber. We compared the different contact angle relaxations and characterized the transitions between the molecular-kinetic theory (MKT) and hydrodynamic approach (HD) for the PDMS mixtures and the pure liquids as a function of their viscosities. FINDINGS: Compared to the pure PDMS liquid with a viscosity of 20 mm2/s that presents a contact angle relaxation following a t-1/2 scale law in agreement with HD, the PDMS mixture with a higher viscosity (27.4 mm2/s) shows a t-1 behavior predicted by the MKT. Moreover, the transition between MKT and HD appears in a regime with higher viscosities for PDMS mixtures than for pure liquids. Surface segregation of shorter PDMS chains or precursor film may be responsible for this shift.status: publishe