Formation and Properties of Anchored Polymers with a Gradual Variation of Grafting Densities on Flat Substrates

Abstract

We show that assemblies comprising anchored polymers with a gradual variation of grafting densities on solid substrates can be generated by first covering the substrate with a molecular gradient of the polymerization initiator, followed by polymerization from the substrate-bound initiator centers (“grafting from”). We apply this technique to prepare grafting density gradients of poly(acrylamide) (PAAm) on flat silica substrates. We demonstrate that using the grafting density gradient geometry, the mushroom-to-brush transition can be accessed on a single sample. This transition is detected by monitoring the dependence of the thickness of the grafted PAAm in a good solvent using variable angle spectroscopic ellipsometry. Wettability experiments performed on the gradient PAAm substrate provide complementary information about the nature of the mushroom-to-brush transition.

Hierarchically Ordered Montmorillonite Block Copolymer Brushes

“…75 Genzer et al studied graft-density effects using a gradient approach in poly(acrylamide) (PAA), and found that in the brush regime the thickness scaled as ρ 1 / 3 g , suggesting all chains along the gradient were the same size. 77 Fukuda et al, however, reported that the brush height in a PMMA system from silica wafers at moderate graft density obeyed the ρ 1 / 3 g law, but at high graft density (ρ g > 0.7 chains nm 2 ) approached ρ 1 / 2 g ; again direct molecular weight measurements of the brush layer were not conducted and so here the possibility of a R p dependence on ρ g cannot be discounted. 85 In this publication we report a strong dependence of R p on ρ g in SI-ATRP of polystyrene (PS) from MMT.…”

“…69,70 In more recent years researchers have realized the potential for utilizing ATRP to modify the surface chemistry of many materials. Colloidal silica, 71 montmorillonite clay (MMT), 72 gold films, [73][74][75] [76][77][78] have been the most frequently studied substrates for surface initiated (SI)-ATRP, where the first is a spherical particle and the last three are high aspect ratio materials.…”

“…These confinement effects can have a marked influence on R p ; to date, studies relating the kinetics of SI-ATRP to those in bulk media have thus far yielded conflicting and sometimes orthogonal conclusions. 71,74,75,77,85 Substrate geometry and graft density should play key roles in the reaction kinetics of SI-ATRP. Densely grafted spherical particles, for instance, initially feature an average chain-end-to-chain-end distance drastically smaller than in an "analogous" bulk system containing the same number of chain ends per volume.…”

Conformational Transitions of Spherical Polymer Brushes: Synthesis, Characterization, and Theory

“…Consequently, the measured brush height in this regime is h ≈ 2R g . 4 Only when these "mushrooms" begin to overlap do the chains begin to behave as brushes.…”

Influence of Graft Density on Kinetics of Surface-Initiated ATRP of Polystyrene from Montmorillonite

“…2,3 In more recent years, researchers have realized the potential for utilizing ATRP to modify the surface chemistry of many materials. Colloidal silica, 4 montmorillonite clay (MMT), 5 gold films, [6][7][8] and silicon wafers [9][10][11] have been the most frequently studied substrates for surface-initiated (SI)-ATRP, where the first is a spherical particle and the last three are high-aspect-ratio materials.…”