Colloids and Surfaces A: Phvsicochemical and Engineering Aspects, 17 (1993) 91-100 Elsevier Science-Publishers B.V., Amsterdam Effects of solvency on the interfacial aqueous non-ionic polymer systems 91 behaviour in Martin MalmstenaT*, Fredrik Tibergb, Bjijrn Lindmanb and Krister Holmberg” aAstra Arcus AB, S-151 85 Sdderttilje, Sweden bPhysical Chemistry I, Chemical Center, P.O. Box 124, S-221 00 Lund, Sweden ‘Institute for Surface Chemistry, P.O. Box 5607, S-114 86 Stockholm, Sweden (Received 2 October 1992; accepted 18 November 1992) Abstract The effects of solvency on the interfacial behaviour of non-ionic ethylene oxide-containing polymers have been investigated. In particular, ethyl(hydroxyethyl)cellulose (EHEC) and poly(ethylene oxide)-poly(propylene oxide) (PEO-PPO) copolymers were considered. Both these types of polymers adsorb at a variety of interfaces. On worsening the solvency, e.g. by increasing the temperature or adding cosolutes which lower the cloud point of the polymer solution, there is a concomitant tendency to increase the adsorbed amount and decrease the adsorbed layer thickness. The outcome of the competition, however, depends on for example, the relative increase in the adsorbed amount. Thus, if the adsorbed amount increases strongly on worsening the solvency, the contraction of the adsorbed layer may be masked, and the adsorbed layer thickness may increase with increasing temperature. If the adsorbed amount is kept constant, however, the only effect of worsening the solvency is a contraction of the adsorbed layer. The forces between polymer-coated surfaces also display a strong solvency dependence. Thus, under good solvency conditions, the interaction force is monotonically repulsive, whereas in poor solvents, an attractive region appears in the force-distance curve. Finally, the solvency-dependent adsorption and interaction properties of these polymers strongly affect their performance, for example, as steric stabilizers or surface modifiers. Keywords: Adsorption; copolymers; ethyl(hydroxyethyl)cellulose; Pluronics; solvency; steric stabilization; surface forces; surface modification. Introduction Modification of the surface properties of materi- als is a field of growing importance for biomedical applications [ 11. Hence, surface hydrophilization has proven useful for avoiding immunoreactions, for example, in connection with transplants and for the conditioning of contact lenses. The basic idea behind surface hydrophilization is to reduce the adsorption of proteins and other biomolecules. In order to succeed in this, several requirements must be met. Firstly, it is essential that the polymer *Corresponding author. Present address: Institute for Surface Chemistry, P.O. Box 5607, S-l 1486 Stockholm, Sweden. binds strongly, in order to avoid protein-induced polymer desorption. Secondly, the protein should not be able to adsorb on top of the polymer layer, which requires elimination of significant van der Waals, electrostatic and hydrophobic attractive interactions between the protein molecules and the polymer layer. Thirdly, the adsorbed polymer layer should be sufficiently thick to eliminate significant interactions between the protein and the under- lying surface. Considering the two latter require- ments, non-ionic hydrophilic polymers (e.g. poly(ethylene oxide) (PEO)) are ideal, and accord- ingly, these polymers are used extensively for hydrophilization purposes [ 11. These polymers, however, do not adsorb very 0927-7757/93/$06.00 0 1993 ~ Elsevier Science Publishers B.V. All rights reserved.