(673i) Designing Shape-Changing Nanoscale Building Blocks for Self-Assembly Via Surface-Charge-Patterning of Deformable Nanoparticles

Many experimental and computational investigations have probed the use of rigid nanoscale building blocks of different shapes (e.g., spheres, rods, cubes) to design new materials via self-assembly for applications in catalysis, photonics, and nanomedicine. Often, the self-assembly process is electrostatically-driven. Deformable charge-patterned nanoparticles offer the capacity to combine electrostatics-driven deformation of building blocks with the electrostatics-driven assembly of building blocks, giving access to unique assembly pathways inaccessible to rigid (static) building blocks. However, in order to fully utilize these capabilities, a fundamental understanding of the nature of deformations tailorable in flexible nanoparticles and a comprehensive elucidation of the links between surface charge patterns and energetically-favored shapes of deformable nanoparticles is required. In this paper, using molecular dynamics based simulated annealing methods, we demonstrate the capabilities of the electrostatic control of the shape of flexible nanoparticles via the synthesis of nanoparticles with specific surface-charge patterns.
We show that hollow nanoparticles or nanocontainers, 40 nanometers in diameter, with surface charge patterns such as Janus patches, stripes, and polyhedrally-distributed patches adapt their shape in response to changes in pattern attributes, transforming into variably dimpled hemispheres, spinning-tops, bowls, discs, and polyhedral protrusions.
The pattern designs and solution conditions used in our simulations are informed by experiments on inverse patchy colloids, coacervated micelles and polymeric nanoparticles.
We show how shape modulation can be further tuned by changing salt concentration, a parameter known to modulate self-assembly, and material elasticity. Shape maps linking surface charge patterns with the corresponding energetically-stable shapes for a wide range of salt concentration (0.2 - 20 mM) and elastic properties are shown.
Scenarios in which surface charge asymmetry is the primary driver of shape transitions in deformable nanocontainers are isolated and the links between surface charge anisotropy and the anisotropic local elastic energy distributions on the nanoparticle surface are highlighted. Elucidation of these mechanisms help toward formulating the design strategies to control the assembly of shape-changing, dynamic building blocks in order to fabricate responsive or reconfigurable materials.