Tailoring spontaneous pillar structure using phase-separating organosiloxane sol-gel systems in micro-fabricated grooves

A sharp transition to pillar structure has been observed in simple sol-gel systems accompanying phase separation inside rectangular-sectioned open grooves which were fabricated on a silica glass chip. The structural variation was investigated using two contrastive systems; one with a rapid sol-gel reaction and the other with a sluggish reaction. In the slower system, transition from web-like bicontinuous structure to pillar structure, we call it as "web-to-pillar transition", occurred when the bulk characteristic length Λ _m exceeded the width of the groove D. On the other hand, the transition did not occur in the same condition in the faster system; it occurred when Λ _m became much longer than D. A consistent formation mechanism model was also proposed using a relation between interfacial curvatures and pressure.