End-Adsorbing Chains in Polymer Brushes: Pathway to Highly Metastable Switchable Surfaces
M Koch and D Romeis and JU Sommer, MACROMOLECULES, 53, 7356-7368 (2020).
Polymer brushes are widely used to modify the physico-chemical properties of surfaces. By introducing chains with adsorption-active end groups to a brush, the properties of a surface can be altered by external stimuli, enabling the functionalized ends to be switched between the exposed and the adsorbed, hidden state. We have used self- consistent field calculations, analytical theory, and molecular dynamics simulations to study the structure and adsorption behavior of polymer brushes containing end-adsorbing chains under consideration of an extensive range of parameters. First, monodisperse brushes possessing adsorptionactive groups at the end of every chain are investigated. Second, a minority fraction of end-adsorbing chains, variable in length, is admixed to an unmodified majority brush. In a good solvent, these minority chains are hindered from adsorbing at the substrate because of a large free energy barrier imposed by the brush, which builds up already at moderate grafting densities. A collapse of the surrounding brush due to poor solvent conditions or the co-nonsolvency effect lowers the brush barrier significantly and facilitates the adsorption. When returning to good solvent conditions, the functionalized end groups will, depending on the attachment strength, either detach or remain adsorbed, making the adsorption transition reversible or irreversible, respectively.
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