Fabrication and Characterization of Non-Brownian Particle-Based Crystals

Abstract

Particle-based crystals have been explored in the literature for applications in molecular electronics, photonics, sensors, and drug delivery. However, much of the research on these crystals has been focused on particles of nano- and submicrometer dimensions (so-called colloidal crystals) with limited attention directed toward building blocks with dimensions ranging from tens to hundreds of micrometers. This can be attributed, in part, to the fact that the underlying thermal effects in these larger systems typically cannot naturally overcome kinetic barriers at the meso- and macroscales so that many of the methods used for nanoscale particle assembly cannot be directly applied to larger components, as they become kinetically arrested in nonequilibrium states. In this work, ultrasonic agitation is being explored as a means of allowing large, non-Brownian microparticles (18-750 μm) to overcome the kinetic barriers to packing in the creation of close-packed, highly ordered, crystalline structures. In addition, we study how the energy input affects bulk particle behavior and describe several new ways to characterize particle-based crystals made from microparticles.

Non‐Brownian Particle‐Based Materials with Microscale and Nanoscale Hierarchy

“…Angewandte microparticle-based structures can be created with new opportunities for varying macroscopic hierarchy,s urface functionalization, and the diffusive properties.E ngineering these aforementioned properties allows the design of novel materials for applications for which nanoscale features are not suitable.H erein we explore an ew method of creating autonomously assembled, microparticle-based crystals from particles with varying dimensions and compositions.S pecifically,w ee mploy sonication as am eans of artificially thermally treating as ystem of large,n on-Brownian microparticles such that we induce organization among particles up to 0.1 mm in size. [11] Furthermore,w eo bserve that it is possible to produce av ariety of predictable stoichiometric patterns (corresponding to N S/L )from particles that are two to three orders of magnitude larger than those previously studied. We have achieved particle organization for mixtures containing particles as small as d S = 0.6 mma nd as large as d S = 21 mmc ombined with d L = 100 mm, where d is particle diameter, and Sa nd Lr epresent the small and large particle populations,respectively.Byfurther increasing the g S/L above 0.21, we have formed crystals among particles where d S = 21 mma nd d L = 75 mm, yielding ar atio of g S/L = 0.28.…”

“…[10] Recently,weshowed that one can bridge this gap in materials fabrication by using ultrasonic agitation to mimic Brownian motion (or granular vibration), and induce spontaneous assembly of microspheres with dimensions ranging from the nano-to the milliscales into hexagonal close-packed (HCP) two-and three-dimensional crystals. [11] Herein, we extend this bottom-up assembly approach to mixed systems of particles that include as pan in length scale that is larger than any explored to date to attain complex hierarchical crystalline formations from binary and multicomponent particle mixtures.B yd oing so,w eh ave created stoichiometric configurations of large,non-Brownian particles that resemble those formed naturally by atoms and molecules and heretofore have been reported only for nanoparticles. [12][13][14] Specifically,w ee xamine ar ange of radii ratios (g S/L )a nd number ratios (N S/L )o fs mall (S) and large (L) microparticles within amixture to explore awide range of resulting microstructures.Additionally,through post-processing of these microstructures,w eh ave demonstrated that it is possible to evolve these ordered arrays into binary,i nverted crystalline structures with customizable hierarchically ordered features and pore configurations that mimic those in naturally occurring porous materials (such as zeolites).…”

“…In the context of particle self-assembly,the understanding of interparticle interactions is crucial to interpreting particle phenomena. [11,15,16] Many parameters,i ncluding the particle material composition/density,s ize,a nd charge,a re key contributors to such behavior, especially in particle mixtures [13] where size mismatch has also been shown to strongly influence the resultant particle structures. [16] In fact, in hard sphere (screen-charged) mixtures of nanoscale particles,ithas been observed that g S/L and N S/L determine whether the system attains as toichiometric or amorphous configuration.…”

“…[23][24][25] Between each vibration, various metastable configurations may exist in the particle bed and these states last until the next vibration occurs. [10,11,25,26] Several factors affect the mixing/segregation behavior of large granular particles,i ncluding the frequency and amplitude of the vibration as well as the mass,d ensity, diameter ratio of binary mixture,a nd the inter-particle and particle-wall coefficients of friction. [26] Less is known about the assembly behavior of large,non-Brownian microparticles than nano-and granular (centi/ milli-) scale particle behavior.…”

Observing magnetic objects in fluids

“…Also on centimetrescales, magnetic forces have been used to form particles rather than structures, such as the spontaneously folding elastomeric sheets with embedded electronics; as demonstrated by Boncheva et al (2005). Lash et al (2015) showed that polystyrene beads self-assemble into HCP packed structures by solvent evaporation. Larger polystyrene particles (>18 µm) required additional disturbing energy (ultrasonic energy) as a disturbing energy source to self-assemble.…”