Synthesis of
Raspberry-like Nanoparticles via Surface
Grafting of Positively Charged Polyelectrolyte Brushes: Colloidal
Stability and Surface Properties
posted on 2024-03-08, 20:33authored byBashayer
Saad Aldakkan, Nikolaos Chalmpes, Genggeng Qi, Mohamed Amen Hammami, Mazen Yousef Kanj, Emmanuel P. Giannelis
A method to synthesize stable, raspberry-like nanoparticles
(NPs),
using surface grafting of poly(glycidyl methacrylate) (PGMA) brushes
on a polystyrene (PS) core with varying grafting densities, is reported.
A two-step functionalization reaction of PGMA epoxide groups comprising
an amination step first using ethylene diamine and then followed by
a quaternization using glycidyltrimethylammonium chloride generates
permanently and positively charged polyelectrolyte brushes, which
result in both steric and electrostatic stabilization. The dispersion
stability of the brush-bearing NPs is dramatically improved compared
to that of the pristine PS core in salt solutions at ambient (25 °C)
and elevated temperatures (60 °C). Additionally, the grafted
polyelectrolyte chains undergo a reversible swelling in the presence
of different ionic strength (IS) salts, which modulate the surface
properties, including roughness, stiffness, and adhesion. An atomic
force microscope under both dry and wet conditions was used to image
conformational changes of the polyelectrolyte chains during the swelling
and deswelling transitions as well as to probe the nanomechanical
properties by analyzing the corresponding force–sample separation
curves. The quaternized polyelectrolyte brushes undergo a conformational
transition from a collapsed state to a swelled state in the osmotic
brush (OB) regime triggered by the osmotic gradient of mobile ions
to the interior of the polymer chain. At IS ∼ 1 M, the brushes
contract and the globules reform (salted brush state) as evidenced
by an increase in the surface roughness and a reduction in the adhesion
of the brushes. Beyond IS ∼ 1 M, quartz crystal microbalance
with dissipation monitoring measurements show that salt uptake continues
to take place predominantly on the exterior surface of the brush since
salt adsorption is not accompanied by a size increase as measured
by dynamic light scattering. The study adds new insights into our
understanding of the behavior of NPs bearing salt-responsive polyelectrolyte
brushes with adaptive swelling thresholds that can ultimately modulate
surface properties.