la9b02610_si_001.pdf (2.88 MB)
Mechanochemical Degrafting of a Surface-Tethered Poly(acrylic acid) Brush Promoted Etching of Its Underlying Silicon Substrate
journal contribution
posted on 2019-10-10, 21:43 authored by Yuanchao Li, Yiliang Lin, Yunkai Dai, Yeongun Ko, Jan GenzerThe stability of
surface-tethered polyelectrolyte brushes has been
investigated during the past few years. We have previously reported
on the degrafting of poly(acrylic acid) (PAA) polymer brushes from
flat silicon substrates. Here, we present a detailed study on the
effects of NaCl concentration and the grafting density and molecular
weight on the stability of PAA brushes during incubation in 0.1 M
ethanolamine buffer (pH 9.0) solutions. Without NaCl in the buffer
solution, the PAA brushes remain intact. Adding NaCl facilitates etching
of the substrate due to accelerating dissolution of the top silica
layer and promoting degrafting of the PAA chains. The PAA grafting
density and molecular weight play an important role in the substrate
etching by affecting the penetration barrier and local concentration
of the etchants. We also tested the stability of self-assembled monolayers
(SAMs) made of hydrophobic alkyltrichlorosilanes anchored on silicon
substrates. The results demonstrated that the SAMs were too thin to
protect the substrates from etching, in contrast to thick poly(methyl
methacrylate) brushes. Our findings suggest that both polymer brushes
(especially polyelectrolyte brushes) and SAMs anchored to silicon
substrates may undergo erosion/etching on the substrates in basic
environments, which compromises their stability and therefore jeopardizes
their applications in coating, biosensing, and so forth.