A SURFACE FORCE, LIGHT-SCATTERING, AND OSMOTIC-PRESSURE STUDY OF SEMIDILUTE AQUEOUS-SOLUTIONS OF ETHYL(HYDROXYETHYL)CELLULOSE-LONG-RANGE ATTRACTIVE FORCE BETWEEN 2 POLYMER-COATED SURFACES

Semidilute (above the overlap concentration, c) aqueous solutions of ethyl(hydroxyethyl)cellulose (EHEC) as a function of concentration wer e investigated with the surface force apparatus (SFA), and by static l ight scattering (SLS) and osmotic pressure measurements. The anomalous excess in scattering intensity observed in SLS experiments at small a ngles indicates concentration inhomogeneities in the samples, probably as a result of association of the EHEC chains. The light scattering a nd osmotic pressure results show that EHEC in aqueous solution does no t behave as expected for a polymer in a good solvent. The results from the SFA experiments show that EHEC adsorbs strongly on mica. These ad sorbed layers give rise to a short-range steric repulsion when the two EHEC-coated mica surfaces are brought into close contact. The most re markable result, however, is the very long-range attractive force obse rved at larger surface separations. This attractive force features osc illations with a periodicity that decreases when the polymer concentra tion increases. The periodicity corresponded to the mesh network size determined by SLS. To our knowledge, this type of long-range attractio n has not previously been reported. The origin of the force could not be explained in terms of bridging or classical depletion effects. Rath er, this long-range attraction might be induced by segregation of diff erent polymer fractions, with different surface activities, present in the EHEC solutions.