(374d) Polymer-Grafted Nanoparticles As Patchy Colloids

Polymer-Grafted Nanoparticles as Patchy Colloids
Nathan A. Mahynski, and Athanassios Z. Panagiotopoulos
Department of Chemical and Biological Engineering, Princeton University, Princeton, NJ 08544, USA
Spherical nanoparticles uniformly grafted with linear polymer chains behave as â??nanoparticle amphiphilesâ? when the nanoparticle cores thermally interact differently with one another than with their polymer coronas [1]. In the sparse grafting limit, the corona cannot shield its core isotropically, suggesting an interesting analogy to patchy colloids [2]. The fluid phase behavior of patchy colloids, such as laponite clay [3], is known to exhibit a unique feature whereby the density difference between the high and low density phases collapses as the patchiness becomes more anisotropic, producing so-called â??empty liquidsâ? with arbitrarily low densities. We explore this analogy using grand canonical Monte Carlo simulations on a high- coordination number lattice, to reveal how the phase behavior of sparsely grafted, high-curvature particles can, in fact, be alternated between traditional and patchy behavior purely by tuning the coronaâ??s anisotropy. We observe self assembly in the high-density phase of the patchy systems into ordered structures reminiscent of the assembly observed with grafted nanoparticles in polymer matrices [1], while for all other cases, the high-density phase was disordered. In such cases, the fluid-phase behavior was found to behave in a qualitatively different fashion as the corona transitioned between the â??mushroomâ? and the semi-dilute polymer brush regimes, consistent with a recent experimental study [4]. We found that simple scaling laws were sufficient to describe this behavior and clearly indicate the coincidence of a change in thermodynamic behavior and corona structure.
[1] P. Akcora, et al., Nature Materials, 8, 354â??359 (2009).
[2] E. Bianchi, et al., Physical Review Letters, 97, 168301 (2006). [3] B. Ruzicka, et al., Nature Materials, 10, 56â??60 (2011).
[4] H. Koerner, et al., Macro Letters, 2, 607â??676 (2013).