la7b03571_si_001.pdf (3.23 MB)
Layer-By-Layer Self-Assembly of Polyelectrolytic Block Copolymer Worms on a Planar Substrate
journal contribution
posted on 2017-11-17, 00:00 authored by Nicholas J. W. Penfold, Andrew J. Parnell, Marta Molina, Pierre Verstraete, Johan Smets, Steven P. ArmesCationic and anionic
block copolymer worms are prepared by polymerization-induced
self-assembly via reversible addition–fragmentation chain transfer
(RAFT) aqueous dispersion copolymerization of 2-hydroxypropyl methacrylate
and glycidyl methacrylate (GlyMA), using a binary mixture of a nonionic
poly(ethylene oxide) macromolecular RAFT agent and either a cationic
poly([2-(methacryloyloxy)ethyl]trimethylammonium chloride) or an anionic
poly(potassium 3-sulfopropyl methacrylate) macromolecular RAFT agent.
In each case, covalent stabilization of the worm cores was achieved
via reaction of the epoxide groups on the GlyMA repeat units with
3-mercaptopropyltriethoxysilane. Aqueous electrophoresis studies indicated
a pH-independent mean zeta potential of +40 mV and −39 mV for
the cationic and anionic copolymer worms, respectively. These worms
are expected to mimic the rigid rod behavior of water-soluble polyelectrolyte
chains in the absence of added salt. The kinetics of adsorption of
the cationic worms onto a planar anionic silicon wafer was examined
at pH 5 and was found to be extremely fast at 1.0 w/w % copolymer
concentration in the absence of added salt. Scanning electron microscopy
(SEM) analysis indicated that a relatively constant worm surface coverage
of 16% was achieved at 20 °C for adsorption times ranging from
just 2 s up to 2 min. Furthermore, the successive layer-by-layer deposition
of cationic and anionic copolymer worms onto planar surfaces was investigated
using SEM, ellipsometry, and surface zeta potential measurements.
These techniques confirmed that the deposition of oppositely charged
worms resulted in a monotonic increase in the mean layer thickness,
with a concomitant surface charge reversal occurring on addition of
each new worm layer. Unexpectedly, two distinct linear regimes were
observed when plotting the mean layer thickness against the total
number of adsorbed worm layers, with a steeper gradient (corresponding
to thicker layers) being observed after the deposition of six worm
layers.
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