INTERFACIAL FREE-ENERGY CHANGES OCCURRING DURING BSA ADSORPTION IN SOLUTION DROPLETS ON FEP-TEFLON SURFACES AS MEASURED BY ADSA-P

Axisymmetric drop shape analysis by profile (ADSA-P) was employed to determine the interfacial free energy changes occurring during bovine serum albumin (BSA) adsorption from solution droplets on fluoroethylenepropylene-Teflon (FEP-Teflon). 100-mu-l droplets of BSA solutions on FEP-Teflon were followed by ADSA-P as a function of time, for up to 60 min, yielding the contact angle and the surface tension, gamma-lv. By combining these data with Young's equation, while assuming the surface free energy, gamma-sv, of FEP-Teflon to be 20 mJ m-2, the interfacial free energy gamma-sl could be calculated. Both gamma-lv and gamma-sl were found to decrease as a function of time, since after positioning of a droplet, BSA adsorption occurs both at the liquid-vapor as well as the solid-liquid interface. Furthermore, linear relations were obtained when plotting gamma-lv (t).cos-theta(t), vs gamma-lv(t) with BSA concentration dependent slopes. By employing the Lucassen-Reynders equation and radio-activity data obtained for BSA adsorption on FEP-Teflon, it was possible to estimate BSA adsorption at the liquid-vapor interface.