We use ionic poly(N-isopropylacrylamide) (PNIPAM) microgels as a model system to study interactions in soft colloidal systems. Due to the intrinsic and tuneable softness of the particles they are ideally suited to study the complex phase behavior found for soft particles [1]. Subjecting the particles to an alternating electric field results in an additional dipolar contribution to the interaction potential, which strongly depends on the strength and frequency of the field. Here we describe the new phases that emerge with increasing dipolar interactions (Fig. 1) [2].
Figure 1. Field induced structures monitored in CLSM.
We use a combination of complementary techniques such as confocal laser scanning microscopy (CLSM) and light, neutron and x-ray scattering to monitor and understand the various equilibrium and non-equilibrium transitions. We show in particular that the combination of SANS using the so-called zero average contrast method, SAXS and CLSM allows us for the first time to disentangle interparticle correlation effects due to superlattice formation and changes of the particle size and shape as a function of an increasing dipolar attraction.
[1] P. S. Mohanty, D. Paloli, J. Crassous and P. Schurtenberger, in “Hydrogel and Micro-Nanoparticles”, L. A. Lyon and M. J. Serpe, Eds. Wiley VCH (2012)
[2] S. Nöjd, P. S. Mohanty, P. Bagheri, A. Yethiraj and P. Schurtenberger, Soft Matter, 9 (2013) 9199
sofi.nojd@fkem1.lu.se
