A Surface Force, Light Scattering, and Osmotic Pressure Study of Semidilute Aqueous Solutions of Ethyl(hydroxyethyl)celluloseLong-Range Attractive Force between Two Polymer-Coated Surfaces

Abstract

Semidilute (above the overlap concentration, c*) aqueous solutions of ethyl(hydroxyethyl)cellulose (EHEC) as a function of concentration were investigated with the surface force apparatus (SFA), and by static light scattering (SLS) and osmotic pressure measurements. The anomalous excess in scattering intensity observed in SLS experiments at small angles indicates concentration inhomogeneities in the samples, probably as a result of association of the EHEC chains. The light scattering and osmotic pressure results show that EHEC in aqueous soluttion does not behave as expected for a polymer in a good solvent. The results from the SFA experiments show that EHEC adsorbs strongly on mica. These adsorbed layers give rise to a short-range steric repulsion when the two EHEC-coated mica surfaces are brought into close contact. The most remarkable result, however, is the very long-range attractive force observed at larger surface separations. This attractive force features oscillations with a periodicity that decreases when the polymer concentration increases. The periodicity corresponded to the mesh network size determined by SLS. To our knowledge, this type of long-range attraction has not previously been reported. The origin of the force could not be explained in terms of bridging or classical depletion effects. Rather, this long-range attraction might be induced by segregation of different polymer fractions, with different surface activities, present in the EHEC solutions.

The relevance of structural features of cellulose and its interactions to dissolution, regeneration, gelation and plasticization phenomena

“…116 The presence of long-lived aggregates was confirmed in investigations using surface force apparatus, static light scattering and flow field fractionation chromatography. 117,118 In conclusion this work points to a hydrophobic association mechanism distinct from the short-lived and weak one of hydrophobically modified water-soluble polymers. Rather association was found to be related to unsubstituted parts of the cellulose derivatives forming microscopic pseudo-crystalline regions.…”

Direct measurements of particle–surface interactions in aqueous solutions with total internal reflection microscopy

“…This so-called depletion interaction was first described by Asakura and Oosawa (AO) and was studied extensively in complex fluid mixtures as well as being speculated to be widely popular in biological interactions. 7,8 Experimental measurements of the depletion force have been reported in the past decades by employing, for instance, atomic force microscopy (AFM), 9 optical tweezers, 10 surface force apparatus (SFA), 11,12 and total internal reflection microscopy (TIRM). [13][14][15][16] Among them, TIRM seems to be the best technique for measuring such kT-scale depletion potentials due to its passive nature and high sensitivity.…”

“…Experimental measurements of depletion force has been reported in the past decades by employing, for instance, atomic force microscopy (AFM) 9 , optical tweezers 10 , surface force apparatus (SFA) 11,12 , and total internal reflection microscopy (TIRM) [13][14][15][16] . Among them, TIRM seems to be the most proper technique for measuring such kT-scale depletion potentials due to its passive nature and high sensitivity.…”

Direct Measurement of Depletion and Structural Forces in Polydisperse, Charged Systems

“…Dinsmore et al used a line optical tweezers technique to determine the depletion energy between two colloidal particles in a solution of smaller nanoparticles (61). The surface forces apparatus (SFA) was employed to directly measure forces between surfactant bilayers adsorbed onto mica or polymer-coated mica sheets in solutions of micelles and polymers (62)(63)(64)(65). Finally, atomic force microscopy (AFM) has been used to probe the nature of depletion forces between a colloidal probe and a plate (or between an AFM tip and a plate) in various aqueous and nonaqueous polymer suspensions (52,56,(66)(67)(68).…”