Depletion interaction between spheres immersed in a solution of ideal polymer chains

Abstract

The depletion interaction between two spheres due to nonadsorbing ideal polymers is calculated from the polymer concentration profile using the excess ͑negative͒ adsorption. Computer simulations show that the polymer concentration profiles around two spheres are well described by the product function of the concentration profile around a single sphere. From the interaction potential between two spheres the second osmotic virial coefficient, B 2 , is calculated for various polymer-colloid size ratios. We find that when the polymers become smaller than the spheres, B 2 remains positive in the dilute regime. This shows that the depletion interaction is ineffective for relatively small spheres.

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

“…The full curves refer to equation (7) using the result for the correlation length of equation (6) from the RG theory, and they match reasonably well with the simulation results. The differences between the simulation results and the product function that occurs for small h/R g are comparable to those found for ideal polymer chains [3]. For depletion type of interactions the deviation due to the product function approximation at small h/R g will not have a large effect on the results for the interaction potential since the product function only has a significant relative deviation when the polymer concentration between the plates approaches zero.…”

“…assuming that the superposition approximation gives a good description of the concentration profiles between two particles, as was demonstrated for ideal polymer chains [3,28].…”

“…With respect to depletion type of interactions, calculations of the attraction between colloids as induced by non-adsorbing hard rods using the adsorption method has proven to be successful in previous work [26,27]. Recently, the adsorption method was used to calculate the interaction between parallel flat plates, between two spheres [3], and between a sphere and a plate [28] for ideal polymer chains. The fact that this approach can be extended to excluded-volume polymers (or real polymers) is due to the developments that have been made in the renormalization group (RG) theory of polymers.…”

“…The PHS concept was initiated by Vrij [2], who showed that it gives a rather accurate description of the depletion interaction due to ideal polymer chains. In fact, the minimum of the interaction potential of ideal polymers corresponds to that of PHSs if one takes 4R g / √ π as the effective PHS diameter [3], where R g is the polymer's radius of gyration. The strength of the PHS simplification is that it allows a quantitative prediction of the consequences for the colloidal stability and the phase behaviour of colloidal dispersions as induced by non-adsorbing polymers.…”

On the Long-Range Attraction between Proteins Due to Nonadsorbing Polysaccharide

“…6 Thus, the polymer density profiles around the two spheres, obtained from the single sphere density profiles, allow a calculation of the interaction potential. 6 In Figure 1, the structure factor S(Q) is plotted as a function of Qσ (where σ ) 2R) for three colloid-polymer size ratios, R/R g ) 0.1, 0.3, and 0.5, for a volume fraction of the colloids of 0.035 (which is the lysozyme volume fraction in this study) as dashed curves for c/c* ) 0.3, where c is the polymer concentration and c* is the overlap concentration. The full curve is the hard sphere result.…”