PDMS-modified polyurethane films with low water contact angle hysteresis

Polyurethane (PU) films with low water contact angle hysteresis (CAH) were prepared by employing less than 0.2 wt.-% of mono- or bihydroxyl-functionalized polydimethylsiloxane (PDMS) of 60-70 DMS repeat units. A Si content of as low as 0.03 wt.-% was sufficient to lead to a CAH of 20°. The curing temperature demonstrated strong effects on the wetting behavior of the PDMS-modified PU films: a relatively low curing temperature (40°C) resulted in stronger surface segregation of PDMS than higher curing temperatures, giving rise to high water receding CAs and thus low CAH. It was found from angle-resolved X-ray photoelectron spectroscopy analysis that the surface silicon content was greater when cured at a lower temperature. The surface of PDMS-modified PU films was very smooth from AFM observations, but the Si content had strong effects on the surface phase contrast. The chain length of 60-70 DMS repeating units for both mono- and bifunctional PDMS appeared to be long enough to prevent the surface reorganization during the CA measurements.