4(%3)3 - Ecole nationale supérieure de chimie de Montpellier

micelles’ assembly was totally removed from the surface leaving behind a relatively flat surface devoid ofany structural entity.The contact angle measurements of the washed substrate further pointed towards substantialremoval of the micelles’ assembly as clearly a decrease in contact angle to a value of 80±2° from PODMAsurface (88-89 o ) was observed (Figure – 4.21a,b inset). However this value is higher than that for virginPMMA (75°) surface, which indicates that presence of some remaining scattered block copolymer chainsstill entrapped over the PMMA film. To further substantiate the reversibility of the assembly, 3 cycles ofzipping and unzipping of micelles were performed over a PMMA coated silicon surface and therespective contact angle values were obtained. While the coating was performed by drop casting threetimes over a swelled PMMA film, followed by rinsing with cold cyclohexane; the unzipping process wascarried out by leaving the PMMA coated wafer (having zipper assembly) into a bath of cyclohexaneheated at 60 o C for 30 minutes followed by rinsing with cold cyclohexane. As expected, the values ofcontact angle showed a zig-zag pattern (Figure – 4.22) which is consistent with the argument that theoverall mechanism of the assembly is likely to be a combination of an efficient inter-micelle zipping and asurface anchorage through randomly distributed anchoring points.Contact Angle1009896949290888684828078767472701 st ZipperAssemblyVirgin PMMA Film1 st Disassembly2 nd ZipperAssembly3 rd ZipperAssembly2 nd Disassembly 3 rd Disassembly0 1 2 3 4 5 6 7 8Figure – 4.22: Contact Angle measurements of a PMMA coated silicon wafer after 3 cycles of zipper assembly bydrop casting and subsequent disassembly by washing in cyclohexane at 60 o C.4.4 CALORIMETRIC STUDY OF ZIPPED ASSEMBLY119