Wetting of aqueous sodium dodecyl sulfate droplets on polydimethylsiloxane surfaces during evaporation

Wetting of aqueous sodium dodecyl sulfate (SDS) droplets on polydimethylsiloxane (PDMS) surfaces during evaporation were experimentally studied. After a short-time spontaneous spreading, sessile droplets experienced a period of the constant contact radius (CCR) stage. And it was found that substrate elasticity was found to have an influence on the duration of the CCR stage during the evaporation of aqueous SDS droplets on PDMS surfaces. Moreover, a local contact angle minimum was found during the evaporation of aqueous SDS droplets with an initial SDS concentration below 0.5 CMC. A physical mechanism taking into account the structure of SDS mol-ecules adsorbed at PDMS surfaces was developed for the occurrence of the CCR stage and the local contact angle minimum. Furthermore, two-third power of the instantaneous droplet volume nearly varies linearly with time for all cases.

Automated summary

The wetting behavior of aqueous SDS droplets on PDMS surfaces was studied, and it was found that substrate elasticity and initial SDS concentration have an influence on the wetting behavior. A physical mechanism was proposed to explain the phenomena.