title: Strong Selective Adsorption of Polymers.
abstract: A scaling theory is developed for selective adsorption of polymers induced by the strong binding between specific monomers and complementary surface adsorption sites. By "selective" we mean specific attraction between a subset of all monomers, called "sticky", and a subset of surface sites, called "adsorption sites". We demonstrate that, in addition to the expected dependence on the polymer volume fractionϕbulkin the bulk solution, selective adsorption strongly depends on the ratio between two characteristic length scales, the root-mean-square distancelbetween neighboring sticky monomers along the polymer, and the average distancedbetween neighboring surface adsorption sites. The role of the ratiol/darises from the fact that a polymer needs to deform to enable the spatial commensurability between its sticky monomers and the surface adsorption sites for selective adsorption. We study strong selective adsorption of both telechelic polymers with two end monomers being sticky and multisticker polymers with many sticky monomers between sticky ends. For telechelic polymers, we identify four adsorption regimes atl/d< 1 that are characterized by the fraction of occupied adsorption sites and whether the dominant conformation of adsorbed chains is a single-end-adsorbed "mushroom" or double-end-adsorbed loop. Forl/d> 1, we expect that the adsorption layer at exponentially lowϕbulkconsists of separated unstretched loops, while asϕbulkincreases the layer crosses over to a brush of extended loops with a second layer of weakly overlapping tails. For multisticker chains, in the limit of exponentially lowϕbulk, adsorbed polymers are well separated from each other. Asl/dincreases, the conformation of an individual polymer changes from a single-end-adsorbed "mushroom" to a random walk of loops. For highϕbulk, adsorbed polymers at smalll/dare mushrooms that cover all the adsorption sites. At sufficiently largel/d, adsorbed multisticker polymers strongly overlap. We anticipate the formation of a self-similar carpet and with increasingl/da two-layer structure with a brush of loops covered by a self-similar carpet. Asl/dexceeds the threshold determined by the adsorption energy, the brush of loops under the carpet reaches a saturated state, resulting in al/d-independent brush-under-carpet structure, which can also be applied to describe adsorbed multisticker polymers in nonselective adsorption where a sticker can strongly bind to any place on the adsorption surface. We examine the adsorbed amount Γ of multisticker polymers in different regimes for selective adsorption. If the adsorbed multisticker polymers are nonoverlapping mushrooms, the adsorbed amount Γ increases linearly with the surface density of adsorption sites Σ ≈ 1/d2. In the self-similar carpet regime, Γ increases sublinearly as Σ0.15in a good solvent, while only logarithmically in a theta solvent. Formation of a brush layer under the carpet contributes an additional adsorbed amount. This additional amount increases linearly with Σ and eventually dominates the overall adsorbed amount Γ before saturating at a plateau value controlled by the adsorption energy.
authors.affiliation: Department of Chemistry, University of North Carolina, Chapel Hill, North Carolina 27599-3290, United States.
authors.forename: Ting
authors.initials: T
authors.lastname: Ge
authors.affiliation: Department of Chemistry, University of North Carolina, Chapel Hill, North Carolina 27599-3290, United States.
authors.forename: Michael
authors.initials: M
authors.lastname: Rubinstein