Dilute sodium dodecyl sulfate droplets impact on micropillar-arrayed non-wetting surfaces

Impinging dilute sodium dodecyl sulfate (SDS) droplets on micropillar-arrayed polydimethylsiloxane surfaces were experimentally investigated. It was found that the behaviors of impinging droplets greatly depend on surface roughness and SDS concentration. Similar to pure water droplets, there exists a narrow range of dimensionless Weber number, We, for the complete rebound of impacting SDS droplets. The lower and upper limits of impact velocity were theoretically analyzed and compared with experimental data. The addition of SDS could greatly shorten the contact time of bouncing droplets. Besides, surface roughness has little influence on the maximum spreading factor while SDS concentration has an obvious influence and the maximum spreading factor nearly follows a scaling law of We( 1 / 4).