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

Figure – 4.14: Atomic Force Microscopy images of PMMA-b-PODMA coating over PMMA substrate; a) The blue lineindicates the direction of change in the surface modification, b) Variation of height along the blue line from right toleft in first image, c) Higher resolution image of the copolymer micelles’ assemblyThe contact angle measurements gave a value of 75±2° for the virgin PMMA film however afterfunctionalization with a micelle monolayer, the contact angle increased to a value of 88±2° which is inagreement with the change in the surface properties marked by higher hydrophobicity. Based on theseresults it can be suggested that when dipped in the micellar solution, the PMMA substrate offers aninterface which will be covered by block copolymer unimers. The THF present in the solvent mixture isinduces a superficial swelling of the PMMA film coated onto the silicon wafer. Consequently, the PMMAblock from the copolymer penetrate the film surface and thus acting as anchor for the block copolymerchain once the interface has dried. This leaves only the PODMA block emanating from the surface whichis responsible for higher hydrophobicity of the surface (Figure – 4.15). The newly formed blockcopolymer interface is now available to welcome the micelles through a zipper-assembly with n-octadecyl chains from the micelles and the surface interweaving themselves.113