Effect of molecular weight on the interactions between poly(ethylene oxide) layers adsorbed to glass surfaces

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.

Interaction forces between particles stabilized by a hydrophobically modified inulin surfactant

“…4b indicate that the repulsion initiates at a separation distance of 8 nm. The use of AFM techniques to determine the layer thickness suffers from having an ambiguous point of zero distance separation [31], but it could be assumed that the layer thickness is half the separation where the repulsion between the two surfaces begins to occur. However, since in this case the repulsion disappears on withdrawal, one cannot use this value as a real thickness.…”

Study of a Solvated Adsorbed Gelatin Layer Using a Modified Force Microscope

“…As a comparison, the gelatin sample of Pezron et al (7) had M w ϭ 19,000 with a polydispersity of 2.3, Kamiyama and Israelachvili (5) had M w ϭ 100,000, and Kawanishi et al (4) had M w ϭ 300,000 (the last two sets of authors did not explicitly quote the polydispersity, but from the spread of weight fractions it was clearly high). The gelatin sample used here has a higher polydispersity than PEO described in previous work (3,22), which creates difficulties in interpretation of the information. The IEP for this gelatin occurs at a pH of 4.9 and according to Kamiyama and Israelachvili (5), gelatin of molecular weight 100,000 has an expected radius of gyration of 23 nm in dilute solutions at the IEP, where it should behave most like an ideal polymer in a theta solvent.…”

“…For this reason the AFM (20) has recently become a popular alternative for force-sensing work. Many authors have now used AFM or derivatives to sense forces against substrates (3,11,12,(21)(22)(23)) with a variety of polymer systems. In this work we extend the use of our custom built AFM (3,22) from uncharged homopolymer systems such as PEO toward the more complex biopolymer and polyampholyte gelatin.…”

“…Gelatin has some particular features that make its study harder than that of the rather simple "ideal" homopolymers of our previous work (3). It is obtained from the hydrolysis of collagen (obtained from animal skin, bones, tendons, etc.…”

Ultrafine cohesive powders: From interparticle contacts to continuum behaviour

“…Some groups have chosen to build custom made devices optimised for this technique (Butt 1994;Pierce 1994;Craig 1996;Braithwaite 1997;Toikka 2001), because standard AFMs have some technical limitations that make them inadequate for colloidal probe experiments. The tip apex of an AFM tip typically has a radius of 5 -50 nm, whereas the radii of colloidal probes are in the range of 1 -50 µm, resulting in much higher adhesion forces.…”