Self-Assembly Dynamics of Reconfigurable Colloidal Molecules

Abstract

Colloidal molecules are designed to mimic their molecular analogues through their anisotropic shape and interactions. However, current experimental realizations are missing the structural flexibility present in real molecules thereby restricting their use as model systems. We overcome this limitation by assembling reconfigurable colloidal molecules from silica particles functionalized with mobile DNA linkers in high yields. We achieve this by steering the self-assembly pathway toward the formation of finite-sized clusters by employing high number ratios of particles functionalized with complementary DNA strands. The size ratio of the two species of particles provides control over the overall cluster size, i.e. , the number of bound particles N , as well as the degree of reconfigurability. The bond flexibility provided by the mobile linkers allows the successful assembly of colloidal clusters with the geometrically expected maximum number of bound particles and shape. We quantitatively examine the self-assembly dynamics of these flexible colloidal molecules by a combination of experiments, agent-based simulations, and an analytical model. Our “flexible colloidal molecules” are exciting building blocks for investigating and exploiting the self-assembly of complex hierarchical structures, photonic crystals, and colloidal metamaterials.

Flexible Colloidal Molecules with Directional Bonds and Controlled Flexibility

“…First, it is based on packing considerations, according to which each bounded sphere limits the available space for others to bind depending on its excluded volume. 13 This effect has been extensively explored in terms of yield and cluster size distribution for flexible colloidal molecules made of spheres only, 13 and for electrostatically assembled rigid colloidal molecules made from spheres and cubes. 28 For the latter, colloidal molecules with coordination number 6, AB 6 , were found for sphere-to-cube size ratio α < 2, while AB 4…”

“…So far, only a combination of gravitational confinement and steric hindrance of the bound particles could keep their positional order unchanged, but could not confine their motion. 13 Here, we experimentally realize flexible colloidal molecules with controlled flexibility and directionality by exploiting solid colloidal joints with an anisotropic particle shape. We demonstrate the creation of flexible colloidal molecules with directional bonds and controlled flexibility by mixing colloidal cubes equipped with surface mobile DNA-linkers 12,14,16 with an excess number of spheres functionalized with complementary strands.…”

Self-Assembly of DNA-Grafted Colloids: A Review of Challenges

“…Having mobile strands also helps with any surface heterogeneities and non-uniform distribution of grafts. In this spirit, there have been continuous studies to understand and to enrich the phase diagram of the assembly of the system of particles that are grafted with mobile strands [ 107 , 108 , 109 , 110 ].…”

Exploiting anisotropic particle shape to electrostatically assemble colloidal molecules with high yield and purity

“…This approach is not restricted to colloids interacting through electrostatic interactions, but it has also been shown for spheres modified with complementary DNA strands. [17,29,18] Here, we use cubic particles made from hematite as the core particles of the cluster because they feature two crucial advantages: (1) their non-spherical, cubic shape can be exploited as a mean to control the number of bound satellite particles and thus the shape of the resulting colloidal molecules, and (2) their permanent magnetic dipole moment can be used to separate the colloidal molecules from other particles after assembly.…”

“…In contrast, self-assembly strategies typically provide access to more complex particle shapes and interactions. Assembly can be driven by a manifold of approaches ranging from the hybridization of surface-bound [17] or surface-mobile DNA linkers, [18] hydrophobic [19] and depletion interactions, [20] to the assembly driven by opposite charges. [21,22,23,24] On the other hand, they also require strategies to limit the assembly to finite-sized clusters with a predetermined valence, [25,26,27,28] a mechanism to achieve a uniform arrangement of the constituent particles in the clusters, and separation of the resultant colloidal molecules by their size or type.…”