Polymer Adsorption onto Selective Mixed Brushes
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0947-A10-02
Polymer Adsorption onto Selective Mixed Brushes Alexander Chervanyov and Gert Heinrich Leibniz Institute for Polymer Research Dresden, Hohe Strasse 6, Dresden, 01069, Germany ABSTRACT We theoretically studied the reversible adsorption of polymers onto selective mixed brushes. Mixed brushes are recently developed self-adoptive materials that reversibly change their morphology in response to altering external stimuli. The above changes in the morphology result in the reversible formation of different patterns on the outer surface of the brush. It is shown that thus achieved patterning of the adsorbing surface of the mixed brush can dramatically enhance the adsorption of polymers onto this brush, as compared to the adsorption onto the homogeneous brush surface. By making use of the developed self-consistent field theory we calculate the surface excesses of homo- and co-polymers adsorbed on the binary mixed brush for the two different morphologies (`ripple' and random). The interplay between the depletion effect caused by the loss of the polymer entropy in the interior of the brush and binding interactions is shown to lead to a rich adsorption-desorption behavior. The surface excess of the adsorbed polymers is calculated as a function of the relation between the radius of gyration of the adsorbed polymers and characteristic size of the surface pattern. Shorter (relative to the size of the pattern) polymers are shown to better adsorb onto the regular patterned brush surface, as compared to the random brush surface. INTRODUCTION Selective mixed brushes can provide an excellent opportunity to enhance the adsorption of polymers from the semi-dilute solution. Mixed brushes are recently developed self-adoptive materials [1,2 ] that can reversibly change their morphology in response to altering external conditions (e.g. quality of the solvent). Figure 1 shows an example of the two such morphologies (the random and ‘ripple’ morphology) that are formed as a result of exposing mixed brush to the solvents of higher and lower quality, respectively. Changing brush morphology results in that the outer, adsorbing surface of the brush assumes various patterns.
Figure 1. Driving homopolymer adsorption-desorption by changing morphology of the mixed brush (the case of desorption is shown).
The aim of the present work is to show that thus achieved patterning of the adsorbing surface of the mixed brush can significantly affect the adsorption of polymers onto this brush. Specifically, the patterning of the adsorbing surface of the brush is shown to produce an effective attraction potential that enhances the adsorption of polymers onto the brush. If the action of this effective potential overcomes the depletion effect caused by the reduction of the polymer conformational entropy in the interior of the brush, this results in the adsorption of polymer on the brush. In the opposite case the polymers are desorbed from the brush surface. The adsorption-desorption of polymers onto the mixed brush is therefore governed by the delicat
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