Speaker
Description
Poly(N-isopropylacrylamide) based microgels are interesting colloidal systems to probe cooperative phenomena such as structural ordering, crystal nucleation, glass formation, etc. They can be packed to effective volume fractions(eff) beyond the hard-sphere close-packing (cp) and their average interparticle distance, as can be smaller than the particle diameter, d[1]. Here, we report the electric field-induced assembly of highly crosslinked poly(N-isopropylacrylamide-co-Acrylic acid) (PNIPAM-co-AAc) microgels studied using confocal laser scanning microscope (CLSM) and small-angle neutron scattering (SANS). At low eff =0.04,0.17, in the presence of an electric field, the microgels form strings, tubes and islands of body-centered cubic (bct) structures. Though ellipsoidal particles under the influence of an electric field formed tubes [2], no analogous tubular assembly has been reported thus far for hard or soft isotropic particles. Beyond the maximum close packing (eff =0.79,1.07 > cp), solid-solid (s-s) phase transition from a hexagonal lattice to a square lattice is observed, suggesting a diffusive nucleation and growth process. We discuss the experimental phase diagram and compare our observations to the theoretical phase diagram for soft dipolar spheres [3].
References
1. J. Brijitta, P. Schurtenberger, Curr Opin Colloid Interface Sci, 2019, 40, 87–103.
2. JJ. Crassous, et al., Nat Commun, 2014, 5, 1–7.
3. A.-P. Hynninen, M. Dijkstra, Phys Rev Lett, 2005, 94, 138303.
