Coil size oscillatory packing in polymer solutions near a surface

Abstract

The theory developed by Scheutjens and Fleer to describe polymer adsorption and depletion is used to calculate the density profile of nonadsorbing polymers near a surface. The theory predicts damped oscillations in the segment density profile with a wavelength of about the coil size. As a consequence, the interaction energy between two surfaces immersed in a solution of nonadsorbing polymers is an oscillatory function of the separation distance, too. The decay length of the oscillations is proportional to the coil size and independent of the polymer concentration. The oscillations are associated with a liquid-like layering of polymer coils near the surface. An increase in concentration or chain length causes a decrease in the amplitude of the oscillations, because the stronger interpenetration of the coils suppresses inhomogeneities. In dilute solutions no oscillations are observed, because the decay length of the oscillations is smaller than the depletion correlation length, in analogy with the Fisher-Widom criterion in simple fluids. For polymer solutions it is found that the Fisher-Widom condition coincides with the overlap concentration. Our results show that the blob size is not the only relevant length scale above the overlap concentration. The size of the individual coils plays a role, too.

Molecular modeling of intermolecular and intramolecular excluded volume interactions for polymers at interfaces

“…Even though the overshoot is small it is well above the statistical noise. In principle these oscillatory features have been reported before and also exist to a lesser extend in the classical SCF results, 20 that is, in calculations that go beyond the GSA. These nonmonotonic profiles were also reported by Bolhuis et al 17 Oscillatory density profile are perhaps best known for densely packed hard spheres near a flat interface.…”

Polymer induced depletion potentials in polymer-colloid mixtures

“…Also, the errors are likely too large to decide whether or not there is a repulsive bump in the potential. If it does exist, it is probably very small 47 . This is in contrast to hard-core systems, where such bumps can be pronounced 20,48,49 .…”

Excluded-volume polymer-induced depletion interaction between parallel flat plates

“…This profile also describes self-consistent mean-field lattice calculations very well [23]. In order to introduce the correct scaling of the correlation length with polymer concentration, we use results from the RG theory [29].…”

“…For a suspension of colloidal spheres between the plates, repulsion due to accumulation is a significant effect which is shown using analytical theory to third order in colloid concentration [19], by computer simulation [20] and recently by density functional theory [21,22]. Oscillations in the polymer concentration profile around the bulk polymer concentration (that lead to a repulsion) for a polymer solution near a wall have been found by using self-consistent mean-field calculations [23] and by SAW simulations [17,18]. However, these oscillations have amplitudes less than a factor of 0.01 of the bulk polymer concentration and the resulting repulsion is therefore extremely weak.…”