Combinatorial Study of the Mushroom-to-Brush Crossover in Surface Anchored Polyacrylamide

Abstract

We present a method for fabricating anchored polymers with a gradual variation of grafting densities on solid substrates. The technique for generating such structures comprises (i) formation of a molecular gradient of polymerization initiator on the solid substrate and (ii) polymerization from the substrate-bound initiator centers ("grafting from"). We measure the mushroom-to-brush transition in grafted polyacrylamides and show that the mushroom and brush behavior can be described using existing scaling theories.

From Self-Assembled Monolayers to Coatings: Advances in the Synthesis and Nanobio Applications of Polymer Brushes

“…Theoretical and experimental studies have shown that the exponent ν varies with the grafting density and the solvent quality [123,124]. Figure 8 shows the general scaling behavior of polymer brushes and identifies three regimes: mushroom, moderate-density brush, and high-density brush.…”

“…Figure 8 shows the general scaling behavior of polymer brushes and identifies three regimes: mushroom, moderate-density brush, and high-density brush. In the mushroom regime, the average distance (D) between chains is larger than 2Rg, resulting in ν-0 [124]. However, when D is smaller than 2Rg, the system moves into the brush regime, leading to higher ν and hence a moderate-density or high-density brush regime.…”

“…For example, initiators bound to the surface through silane chemistry (Siinitiator-O-Sisubstrate bond) or thiol-Au bonds can be cleaved using suitable reagents. Hydrofluoric acid has been one of the common reagents used for this strategy [124,135,136]. Recently, it was reported that a much milder reagent, tetrabutylammonium fluoride (TBAF), is also effective for degrafting from silicon dioxide [126,132].…”

Poly(l-lysine)-grafted-poly(ethylene glycol)-based surface-chemical gradients. Preparation, characterization, and first applications

“…these mechanisms. 43 A variety of techniques to generate grafted polymer gradients is available, including the preparation of initiator gradients by corona discharge, 44,45 by vapor diffusion, 46,47 by controlling adsorption kinetics 48 or temperature, 49 the control of the polymerization conditions, e.g., time 50,51 or temperature, 52 and diffusion methods. 53,54 Some of these surfaces have been used to study cell growth.…”

Construction and Reactivity Screening of a Surface Composition Gradient for Combinatorial Discovery of Electro‐Oxidation Catalysts.

“…18,19 Gradients have been used for numerous applications, including the study of protein interactions with surfaces, 12 induced motion of liquid drops, 11 demixing in lipid bilayer membranes, 19 substrate-induced liquid crystal orientation, 15 imaging the spatially controlled oxidation of hydrogen peroxide, 16 and studies on spatially localized metal deposition. 16,17 Recently, combinatorial studies have demonstrated the use of gradient libraries to examine temperature-and thicknessdependent polymer thin-film dewetting, 20 construct phase diagrams, 21 study mushroom-to-brush crossover in surface anchored polyacrylamide films, 22 and perform coveragedependent reactivity mapping of heterogeneous catalysts. 17 In the fabrication method described here, a surface gradient is created by controlled diffusion of precursor materials into a swollen polymer gel.…”