Surface free energy of polypropylene and polycarbonate solidifying at different solid surfaces

Advancing and receding contact angles of water, formamide, glycerol and diiodomethane were measured on polypropylene (PP) and polycarbonate (PC) sample surfaces which solidified at Teflon, glass or stainless steel as matrix surfaces. Then from the contact angle hystereses (CAH) the apparent free energies γstot of the surfaces were evaluated. The original PP surface is practically nonpolar, possessing small electron donor interaction (γs-=1.91mJ/m2), as determined from the advancing contact angles of these liquids. It may result from impurities of the polymerization process. However, it increases up to 8-10 mJ/m2 for PP surfaces contacted with the solids. The PC surfaces both original and modified show practically the same γs-=6.56.7mJ/m2. No electron acceptor interaction is found on the surfaces. The γstot of modified PP and PC surfaces depend on the kind of probe liquid and contacted solid surface. The modified PP γstot values determined from CAH of polar liquids are greater than that of original surface and they increase in the sequence: Teflon, glass, stainless steel surface, at which they solidified. No clear dependence is observed between γstot and dielectric constant or dipole moment of the polar probe liquids. The changes in γstot of the polymer surfaces are due to the polymer nature and changes in its surface structure caused by the structure and force field of the contacting solid. It has been confirmed by AFM images.