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.

No abstract

We have investigated the adsorption of poly(ethylene oxide) (PEO) of molecular weights 56 000, 205 000, 685 000 onto glass surfaces using a development of the atomic force microscope technique. In this method a glass particle is glued to a silicon cantilever to give a particle probe surface forces apparatus. Data are presented for the polymers adsorbed onto one and two surfaces at low and high coverage of adsorbed polymer. In the case of polymers adsorbed onto one surface a strong adhesion is noted on separation of the surfaces. This is due to PEO being pulled o † the glass surface on separation. Similar e †ects are also observed when the polymer is adsorbed onto both surfaces at low surface coverage of polymer. However, rarely is any attraction noted as the surfaces are brought together. This is a consequence of the rapid rate of approach in this method not allowing sufficient time for polymer rearrangement and adsorption to occur. At high coverage of polymer on both surfaces repulsive steric interactions were observed. The range of these interactions increased with the molecular weight of the adsorbed polymer, such that the adsorbed layer thickness d scales roughly with the molecular weight M through a power law with exponent 0.4.

No abstract

Background-Ischemic mitral regurgitation (MR) relates to displacement of the papillary muscles from ischemic ventricular distortion. We tested the hypothesis that repositioning of the papillary muscles can be achieved by injection of polyvinyl-alcohol (PVA) polymer, a biologically inert biomaterial that has been specially formulated to produce an encapsulated, stable, resilient gel once injected into the myocardium. The purpose is to materially support the infarcted myocardium while at the same time repositioning the papillary muscles that become apically tethered in MR. Methods and Results-Nine sheep underwent ligation of circumflex branches to produce acute ischemic MR. PVA polymer was then injected by echo guidance into the myocardium underlying the infarcted papillary muscle.