Particle adsorption at polydimethylsiloxane (PDMS)/water interfaces in the presence of a cross-linking reaction.

The adsorption of polymeric particles at the interface of spherical drops of polydimethylsiloxane (PDMS) with water is studied in presence of a cross-linking reaction. Hydrophobic colloidal particles are first uniformly dispersed in water with the help of a nonionic surfactant. The PDMS droplets are then introduced to this dispersion. The particles adsorb to the PDMS-water interface, as the dispersion is being stirred, while the PDMS undergoes a cross-linking reaction at an elevated temperature. The effect of parameters such as particle mass fraction in the dispersion, PDMS cross-linker concentration, and curing temperature on the adsorption behavior and surface coverage of the resulting beads are examined. The surface coverage increases with increasing particle mass fraction, but decreases as the curing temperature or cross-linker concentration is increased. Using an Arrhenius equation, we correlate the adsorption efficiency to the reaction rate and show that the surface coverage of the beads increases logarithmically with the reaction time.