%0 Journal Article
%A Abbott, Stephen B.
%A M. de Vos, Wiebe
%A L. E. Mears, Laura
%A Skoda, Maximilian
%A Dalgliesh, Robert
%A Edmondson, Steve
%A Richardson, Robert M.
%A Prescott, Stuart W.
%D 2016
%T Switching the Interpenetration of Confined Asymmetric
Polymer Brushes
%U https://acs.figshare.com/articles/journal_contribution/Switching_the_Interpenetration_of_Confined_Asymmetric_Polymer_Brushes/3405850
%R 10.1021/acs.macromol.6b00310.s001
%2 https://acs.figshare.com/ndownloader/files/5319451
%K Confined Asymmetric Polymer Brushes
%K polymer brush pairs
%K PEO
%K brush interpenetration
%K surface force type apparatus
%K compacting polymer brushes
%K PDMAEMA
%K hydrating solution
%K polymer brushes
%X The interpenetration of two polymer
brushes on approaching flat surfaces has been investigated. When compacting
polymer brushes with an asymmetric charge on each surface, one neutral
and the other weakly charged, we find that the brush interpenetration
becomes a parameter that can be controlled by the pH of the hydrating
solution. The switching between high and low degrees of brush interpenetration
was investigated with numerical self-consistent field theory (nSCF)
and experimentally using a sample environment which combines neutron
reflectometry with a surface force type apparatus. Initially, a pair
of uncharged poly(ethylene oxide), PEO, brushes are examined, where
one of the brushes is deuterated to distinguish it from a hydrogenous
counterpart. We find in both nSCF and these experiments that there
is no significant overlap between the brushes as both compact into
polymer blocks with little hydration. However, when a weak polyelectrolyte
poly(2-(dimethylamino)ethyl methacrylate), PDMAEMA, brush is confined
against a deuterated neutral PEO brush and the pH of the hydrating
solution is below the polycation’s pKa of 7.5, then the presence of charged groups
on the PDMAEMA allows significant interpenetration to occur between
the two polymer brushes on contact. This interpenetration remains
once the polymer brushes dehydrate due to the confining pressure that
is applied. Raising the pH to a value above the pKa, removes the charges from the polyelectrolyte
brush resulting in little to no interpenetration between the two brushes.
Therefore, by simply adjusting the pH of the hydrating solution the
interpenetration state between polymer brush pairs can be switched
when one brush is a weak polyelectrolyte. Since polymer brushes are
widely investigated and used to reduce friction between solid surfaces,
this effect may have significant implications in the design and operation
of polymer brushes with controllable friction properties.
%I ACS Publications