Structure and phase behavior of polymer-linked colloidal gels

Abstract

Low-density "equilibrium" gels that consist of a percolated, kinetically arrested network of colloidal particles and are resilient to aging can be fabricated by restricting the number of effective bonds that form between the colloids. Valence-restricted patchy particles have long served as one archetypal example of such materials, but equilibrium gels can also be realized through a synthetically simpler and scalable strategy that introduces a secondary linker, such as a small ditopic molecule, to mediate the bonds between the colloids. Here, we consider the case where the ditopic linker molecules are low-molecular-weight polymers and demonstrate using a model colloid-polymer mixture how macroscopic properties such as the phase behavior as well as the microstructure of the gel can be designed through the polymer molecular weight and concentration. The low-density window for equilibrium gel formation is favorably expanded using longer linkers, while necessarily increasing the spacing between all colloids. However, we show that blends of linkers with different sizes enable wider variation in microstructure for a given target phase behavior. Our computational study suggests a robust and tunable strategy for the experimental realization of equilibrium colloidal gels.

Assembly of Linked Nanocrystal Colloids by Reversible Covalent Bonds

“…This aldehyde can react with a hydrazide group on the linker to form a DCB, specifically a hydrazone. 62 The versatility of this ligand synthesis approach allows substitution of the functional end group with other DCB groups, tuning of the backbone chemistry and length, 33 and modification of the NC binding domain to match different NC compositions. The linker and capping molecule, oxalyldihydrazide (OD) and 1methyl-1-phenylhydrazine (MH), respectively (Figure 1c), are complementary to the functional DCB aldehyde end group in the ligand (Figure 1b) and work as the molecular control for assembly and disassembly.…”

“…Thermodynamic Driving Force for Assembly. To rationalize our experimental observations, we developed a physical (bead-spring) model [86][87][88][89] for the NC-linker mixtures based on our previous theoretical efforts 33,36 and recent studies of gelforming DNA nanostars 90 . We computed theoretical spinodal boundaries (model and theory details in Supporting Information) for the mixture with respect to the NC volume fraction NC and the linker-to-NC ratio Γ (Figure 4a) using first-order thermodynamic perturbation theory (TPT).…”

“…Better control over NC valence can be achieved using a bifunctional linking molecule (linker) that mediates bonding between surface-bound ligands. 19,20,[33][34][35] With a linker, the NC assembly can be manipulated not only microscopically by design of the linker but also macroscopically by adjusting the linker concentration, 36 all without synthetically modifying the NCs themselves. Moreover, dynamically reconfigurable, or even reversible, NC gel assemblies can be made if reversible linking chemistries are used.…”

Assembly of Linked Nanocrystal Colloids by Reversible Covalent Bonds

“…Better control over NC valence can be achieved using a bifunctional linking molecule (linker) that mediates bonding between surface-bound ligands. 19,20,[33][34][35] With a linker, the NC assembly can be manipulated not only microscopically by design of the linker but also macroscopically by adjusting the linker concentration, 36 all without synthetically modifying the NCs themselves. Moreover, dynamically reconfigurable, or even reversible, NC gel assemblies can be made if reversible linking chemistries are used.…”

Using Patchy Particles to Prevent Local Rearrangements in Models of Non-equilibrium Colloidal Gels

“…In this Article, we propose a model of such soft microgel particles based on an overlay between an isotropic repulsion and a directional attraction, so-called "patchy particles", as a tool to hinder lateral particle reorganization after gelation. This class of models has been extensively studied in the context of equilibrium systems such as polymer gels, associating fluids, proteins, and patchy colloids, [28][29][30][31][32][33][34][35][36] in addition to one very recent study of non-equilibrium colloidal gels formed via depletion attraction. 24 We show here that such patchy particle models are capable of capturing the experimentally observed structures in non-equlibrium colloidal gels formed through arrested spinodal decomposition of soft microgel particles interacting via shortrange attractive interactions and soft repulsion.…”