Complex patchy colloids shaped from deformable seed particles through capillary interactions.

V Meester,D J Kraft

doi:10.1039/c7sm02020a

Abstract

We investigate the mechanisms underlying the reconfiguration of random aggregates of spheres through capillary interactions, the so-called "colloidal recycling" method, to fabricate a wide variety of patchy particles. We explore the influence of capillary forces on clusters of deformable seed particles by systematically varying the crosslink density of the spherical seeds. Spheres with a poorly crosslinked polymer network strongly deform due to capillary forces and merge into large spheres. With increasing crosslink density and therefore rigidity, the shape of the spheres is increasingly preserved during reconfiguration, yielding patchy particles of well-defined shape for up to five spheres. In particular, we find that the aspect ratio between the length and width of dumbbells, L/W, increases with the crosslink density (cd) as L/W = B - A·exp(-cd/C). For clusters consisting of more than five spheres, the particle deformability furthermore determines the patch arrangement of the resulting particles. The reconfiguration pathway of clusters of six densely or poorly crosslinked seeds leads to octahedral and polytetrahedral shaped patchy particles, respectively. For seven particles several geometries were obtained with a preference for pentagonal dipyramids by the rigid spheres, while the soft spheres do rarely arrive in these structures. Even larger clusters of over 15 particles form non-uniform often aspherical shapes. We discuss that the reconfiguration pathway is largely influenced by confinement and geometric constraints. The key factor which dominates during reconfiguration depends on the deformability of the spherical seed particles.

Highlights

We explore the influence of capillary forces on clusters of deformable seed particles by systematically varying the crosslink density of the spherical seeds
We studied the shape and assembly pathway of patchy particles constructed from spheres of varying rigidity
To investigate how spheres of varying rigidity are influenced by capillary forces we studied particles made from spherical seed particles with a crosslink density of 0.2, 0.5, 0.7, 1.4, 2.1, 3.0, 4.3 or 8.3% v/v and a diameter of approximately 1.5 mm, see Table 1 and Fig. S1 (ESI†) for details and methods

Summary

Introduction

Patchy colloids are excellent building blocks for self-assembly, since their anisotropy in surface chemistry allows them to form complex structures.[1,2,3] While spheres with isotropic interactions only crystallize in a randomly stacked hexagonal closed packed structure, particles with a single patch already assemble into micelles[4] and tubules.[5,6] Particles with multiple patches have been predicted to exhibit an even richer phase behavior,[7,8] such as crystallization into dense diamond,[9] body-centered-cubic and facecentered-cubic[10] lattices as well as open networks.[11]. The reconfiguration pathway of clusters of six densely or poorly crosslinked seeds leads to octahedral and polytetrahedral shaped patchy particles, respectively.

Results

Conclusion