Assembly and Dynamic Analysis of Square Colloidal Crystals via Templated Capillary Assembly

Abstract

Capillary assembly has the ability to engineer centimeter-sized regions of discrete colloidal superstructures and microarrays. However, its use as a tool for directing crystallization of colloids into surface-bound nonclose-packed arrays is limited. Furthermore, the use of quantitative particle tracking tools to investigate evaporative assembly dynamics is rarely employed. In this contribution, we use templated capillary assembly to fabricate square-packed lattices of spherical, organosilica colloids using designed patterned boundaries. Particle tracking algorithms reveal that the assembly of square-packed regions is controlled by the interplay between confinement-driven nuclei formation and osmotic pressure-driven restructuring. We find that the incorporation of a square template increases the yield of particles bearing four nearest neighbors (Z n = 4) from 4 to 39%, obtained using a heavier and more viscous solvent. Maximal square-packed domains occur at specific initial particle concentrations (1.75–2.25 wt % or φ = 0.013–0.017), indicating that rearrangements are a function of osmotic force. We use particle tracking methods to dynamically monitor conversions between square and hexagonal packing, revealing a cyclical transition between 4 and 6 coordinated particles throughout meniscus recession. Our method is highly scalable and inexpensive and can be adapted for use with different particle sizes and compositions, as well as for targeted open-packed geometries. Our findings will inform the large area, defect-free assembly of nonclose-packed lattices of unexplored varieties that are necessary for the continued expansion of colloid-based materials with vast applications in optical electronics.

Capillary Assembly of Liquid Particles

“…In addition to the capillary force F c that anchors particles within the template, immersion capillary forces act on particles when residual solvent bridges remain after meniscus unpinning. [ 54,55 ] This immersion capillary force separates particles toward the edges of the cavities due to lateral forces driven by solvent pinning to the edges of the traps (Figure S6B, Supporting Information). [ 3 ] In our experiments, this phenomenon results in more TPM, and by extension brighter regions, along the edges of a square cavity with darker regions and less TPM in the center, akin to separated particles seen in solid particle capillary assembly experiments.…”

Top-Down Heterogeneous Colloidal Engineering Using Capillary Assembly of Liquid Particles

“…In previous reports, we discussed the dependency of particle deposition geometry on input particle concentration. 61,64 In congruity with these previous studies, it is apparent that the concentration of colloids employed in CALP directly dictates the osmotic pressure in the accumulation zone (i.e., the densely packed meniscus). By extension, the heightened pressure deforms the PDMS and compresses more colloids into the traps.…”

“…At 3% w/v, pentamer patchy particles were formed in which a fifth colloid squeezed into the center of the 4-fold particles and was vertically offset, resulting in square pyramidal particles (Figure D). In previous reports, we discussed the dependency of particle deposition geometry on input particle concentration. , In congruity with these previous studies, it is apparent that the concentration of colloids employed in CALP directly dictates the osmotic pressure in the accumulation zone (i.e., the densely packed meniscus). By extension, the heightened pressure deforms the PDMS and compresses more colloids into the traps.…”

“…Dyed LPs were injected into one end of the channel, and the solvent was evaporated under ambient conditions. Particles densely pack at the meniscus owing to a viscous drag force, generating a high osmotic pressure at the evaporation front that pushes LPs into the traps. ,, Negative charges on the LP surface preclude particle coalescence in aqueous suspension. Once the solvent evaporates from the surface of LPs within the traps, the force of solvent unpinning anchors the LPs within the traps and withdraws electrostatic stabilization.…”

Controlling disorder in self-assembled colloidal monolayers via evaporative processes

“…Shillingford et al were able to create hexagonally close-packed, square, and disordered packings within arrays of square traps by changing particle volume fraction, and tuning the depth and resolution of the traps. 222 Disordered packings were observed at low volume fractions, with square and hexagonally close-packed organization at higher fractions. Amorphous monolayers could be obtained using poorly resolved traps featuring kinks and breaks which disrupted lattice order.…”