Interactions between Poly(ethylene oxide) Layers Adsorbed to Glass Surfaces Probed by Using a Modified Atomic Force Microscope

Abstract

We have investigated the adsorption of 56 000 molecular weight poly(ethylene oxide) in an aqueous system (good solvent) to glass using a development of the atomic force microscope technique. A glass particle is glued to a silicon cantilever to give a particle probe surface forces apparatus. The design of this custom built machine is discussed with reference to the particular problems inherent to the investigation. The data presented describe the evolution of the adsorbed polymer layer with time and the changes resulting from only allowing one surface to adsorb polymer. We also examine the change of the layer conformation with repeated compressions. Scans are carried out at close to Brownian collision rates and energies. The results are discussed in the light of previous surface force apparatus work. The development of the layer is clearly tracked from an initially thin coverage up to a stable equilibrium layer of some 90 nm. The “equilibrium” thickness is greater than those reported on the surface force apparatus. This is due to the increased resolution of the current apparatus, which enables energies as small as 0.5 μJ m-2 to be measured. At partial coverages of polymer on approach of the surfaces, a weak attraction is occasionally observed due to bridging of the polymer between the two surfaces. On separation a strong adhesion is noted. The lack of consistent strong attractions on approach of the surfaces is due to the relatively rapid rate of approach of the two surfaces, which does not allow sufficient time for the polymer to bridge between the surfaces and bring about an attraction. At full coverages of polymer, repulsive interactions at all surface separations are observed. However following many rapid approaches and separations at such coverages, attractive interactions may be observed, indicating that the structure of the adsorbed layer is changing and being disrupted with time. The results therefore demonstrate physically important interactions that would not be easily observed by any other force sensing technique.

Interaction forces and molecular adhesion between pre-adsorbed poly(ethylene imine) layers

“…Occasionally, events with a single minimum are observed (Fig. 5b, curve I), which strongly remind of single molecule pulling events as observed for linear neutral polymers and polyelectrolytes [23,[42][43][44][45]. It should be pointed out, however, that the present force-extension curves show typically much less curvature than in the case of linear polymers.…”

“…This technique has the advantage of well-defined interaction geometry, as the SFA or the MASIF. Due to the use of an AFM-cantilever with a low spring constant, the colloidal probe technique is also sensitive to the bridging of single polymers during the separation of probe and sample [22][23][24][25]. Thus, this technique is ideally suited to study the long-range interactions as well as the adhesion forces between adsorbed polyelectrolyte layers.…”

Force measurements with the atomic force microscope: Technique, interpretation and applications

“…Due to the high melting point of silica (1723 8C) it is unpractical to sinter them to cantilevers. In this respect glass particles [16,163,164], which are usually made from a borosilicate glass, are easier to sinter since their melting point is below 800 8C. Their surface is as smooth as that of silica particles.…”

“…In some cases the interaction between physisorbed layers can also be described by one of the above equations [188]. In many cases the adsorbed layers are not in thermodynamic equilibrium and the interaction changes the structure of the adsorbed polymer [163,342,846]. In some studies the adsorption per se was studied.…”

Interaction forces between particles stabilized by a hydrophobically modified inulin surfactant

“…No scanning capability was incorporated into the instrument. A full description of the instrument and its operation was given elsewhere [18]. To minimize the drifts and noise from both the environment and the mechanical apparatus itself, the apparatus was set up in a basement laboratory, placed on an antivibration table and covered with a custom-made box to control the local environment.…”