Sterically stabilized lock and key colloids: a self-consistent field theory study

Assembling oppositely charged lock and key responsive colloids: A mesoscale analog of adaptive chemistry

We have seen a considerable effort in colloid sciences to copy Nature's successful strategies to fabricate complex functional structures through self-assembly. This includes attempts to design colloidal building blocks and their intermolecular interactions, such as creating the colloidal analogs of directional molecular interactions, molecular recognition, host-guest systems, and specific binding. We show that we can use oppositely charged thermoresponsive particles with complementary shapes, such as spherical and bowl-shaped particles, to implement an externally controllable lock-and-key self-assembly mechanism. The use of tunable electrostatic interactions combined with the temperature-dependent size and shape and van der Waals interactions of these building blocks provides an exquisite control over the selectivity and specificity of the interactions and self-assembly process. The dynamic nature of the mechanism allows for reversibly cycling through various structures that range from weakly structured dense liquids to well-defined molecule-shaped clusters with different configurations through variations in temperature and ionic strength. We link this complex and dynamic self-assembly behavior to the relevant molecular interactions, such as screened Coulomb and van der Waals forces and the geometrical complementarity of the two building blocks, and discuss our findings in the context of the concepts of adaptive chemistry recently introduced to molecular systems.

Quantification of nanoparticle interactions in pure solvents and a concentrated PDMS solution as a function of solvent quality

Using turbidity measurements, we quantified the interactions between PDMS-grafted silica nanoparticles (PDMS-g-silica) in pure solvents and a concentrated polymer solution with a focus on detecting the impact of solvent quality on graft layer stretching. This work is an extension of our previous work where we showed that interfacial wetting of the grafted polymer leads to depletion restabilization in semidilute and concentrated polymer solutions in good solvents (Dutta, N.; Green, D. Langmuir 2008, 24, 5260-5269). Subsequently, we showed that the criterion for depletion restabilization holds for both good and marginally poor solvents (Dutta, N.; Green, D. Langmuir 2010, 26, 16737-16744). In this work, we quantified nanoparticle interactions in terms of the second virial coefficient (B2), which captures the stretching of the brush in a good solvent in comparison to compression in a poor solvent. The transition from stretching to compression of the graft layer as a function of solvent quality was also supported by self-consistent mean-field (SCF) calculations. The PDMS-g-silica nanoparticles in a concentrated polymer solution in a good solvent within the complete wetting region behaved as though they were in a good solvent rather than in a polymer melt where on the basis of the SCF calculations the graft layers were expected to behave ideally. Overall, our results indicate that turbidity measurements can be used to determine the second virial coefficients for polymer-grafted nanoparticles in solvents and concentrated polymer solutions, and the relative values of the coefficients correspond well to those from theoretical calculations.