Adaptive Wetting of Polydimethylsiloxane.
2020
To
better understand the wetting of cross-linked polydimethylsiloxane
(PDMS), we measured advancing and receding contact angles of sessile
water drops on cross-linked PDMS as a function of contact line velocity
(up to 100 μm/s). Three types of samples were investigated:
pristine PDMS, PDMS where oligomers were removed by toluene treatment,
and PDMS with an enriched concentration of oligomers. Depending on
the velocity of advancing contact lines and the contact time with
water, different modes of wetting were observed: one with a relatively
low contact angle hysteresis (Δθ ≈ 10°) and
one with a larger hysteresis. We attribute the low hysteresis state,
called the lubricated state, to the enrichment of free oligomers at
the water–PDMS interface. The enrichment of oligomers is induced
by drop contact. The kinetics of the transition to the lubricated
state can be described by adaptation theory. PDMS adapts to the presence
of water by an enrichment of free oligomers at the interface and a
correlated reduction in interfacial tension.
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