Colloids and Surfaces A: Physicochemical and Engineering Aspects 175 (2000) 113 – 120 Dynamic characterization of phospholipid/protein competitive adsorption at the aqueous solution/chloroform interface J. Wu a , J.B. Li a,b , J. Zhao a,b , R. Miller b, * a International Joint Laboratory between Institute of Photographic Chemistry and Max Planck Institute of Colloids and Surfaces, Chinese Academy of Science, De Wai, Bei Sha Tan, 100101 Beijing People’s Republic of China b Max -Planck -Institut fu ¨r Kolloid und Grenzfla ¨chenforschung, Am Mu ¨hlenberg 2, D 14476 Golm/Potsdam Germany Abstract In the present paper, we use the drop volume method to study the dynamics of the competitive adsorption of the zwitterionic phospholipids (DPPC, DPPE, DMPC and DMPE) mixed with proteins (-lactoglobulin, -casein, and human serum albumin, respectively) at the chloroform/water interface. In order to investigate the main factors influencing the equilibrium interfacial tension of the mixed system (drops of lipid in chloroform formed in an aqueous protein solution environment), proteins of different conformation and concentration, and phospholipids of different structure have been investigated. It is observed that, with constant external protein concentration, the equilibrium interfacial tension  decreases with the increase of internal lipid concentration. When the phospholipid concentration is close to the CAC, both the conformation and concentration of the protein do not influence the equilibrium interfacial tension of the mixed systems remarkably. With the same internal phase containing phospholipid in oil solvent and different external phases containing the protein in water, the  – C isotherms show similar tendencies. Moreover, the structure of the phospholipid determines the equilibrium interfacial tension, where the lipid head group is much more significant rather than the chain length. The experimental results show that in DMPC-protein systems, the equilibrium interface tension decreases with the phospholipid concentration more rapidly than in DMPE-protein systems. © 2000 Elsevier Science B.V. All rights reserved. Keywords: Adsorption kinetics; Dynamic interfacial tension; Drop volume technique; Phospholipids; Mixed lipid protein systems www.elsevier.nl/locate/colsurfa 1. Introduction Dynamic surface and interfacial tensions are the most frequently measured non-equilibrium properties of adsorption layers at air/liquid and liquid/liquid interfaces [1]. There exist many tech- niques to cover the time interval from millisec- onds to days. Among the numerous methods, the drop volume method has been developed as a standard technique in surface and interfacial stud- ies. Its major advantages over other methods, such as easy handling, simple temperature control * Corresponding author. 0927-7757/00/$ - see front matter © 2000 Elsevier Science B.V. All rights reserved. PII: S 0 9 2 7 - 7 7 5 7 ( 0 0 ) 0 0 5 4 3 - 4