Step-growth dispersion
polymerization is a powerful method to produce
uniform and monodisperse particles of π-conjugated polymers
with tunable sizes. While the growth period in such step-growth dispersion
polymerizations is well understood, it remains unknown whether or
not the nucleation process comprises an aggregation or coalescence
step. Only a complete understanding of the entire mechanism of particle
formation during step-growth dispersion polymerization will provide
information about the morphology inside of the polymer particles and
enable design of synthesis strategies to give access to more sophisticated
particle architectures, such as core–shell or patchy particles.
We employ spectroscopic and light scattering analysis to shed light
on the nucleation event in a Heck-type C–C cross-coupling dispersion
polymerization. In contrast to the typical mechanism, our dispersion
polymerization of conjugated polymer particles does not feature the
aggregation step.
Although template-assisted self-assembly
methods are very popular
in materials and biological systems, they have certain limitations
such as lack of tunability and switchable functionality because of
the irreversible association of cells and their matrix components.
With an aim to achieve more tunability, we have made an attempt to
investigate the self-assembly behavior of rod-shaped living bacteria
subjected to an external alternating electric field using confocal
microscopy. We demonstrate that rod-shaped living bacteria dispersed
in a low salinity aqueous medium form different types of reversible
freely suspended structures when subjected to an external alternating
electric field. At low field strength, an oriented phase is observed
where individual bacterium orients with its major axis aligned along
the field direction. At intermediate field strength, bacteria align
in the form of one-dimensional (1D) chains that lie along the field
direction. Further, at high field strength, more bacteria associate
with these 1D chains laterally to form a two-dimensional (2D) array.
At higher bacterial concentration, these field-induced 2D arrays extend
to form three-dimensional columnar structures. These results are discussed
in the context of previously reported studies on bacterial self-assembly.
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