Due to the PDMS-to-PDMS adhesion problem, anti-adhesion
treatment is needed before the PDMS layer with negative structures
can be used as the mold for second PDMS molding. As shown
in Fig. 1, the PDMS negative mold was first activated with corona
discharge plasma for 2 min to generate silanol groups at the PDMS
surface. The surface activated PDMS was then placed in a PFDTS
vapor coating system for 40 min. After that, the PDMS negative
mold was kept in a 60 ◦C oven for 3 h.