Relating microstructure and particle-level stress in colloidal crystals under increased confinement

Abstract

The mechanical properties of crystalline materials can be substantially modified under confinement. Such modified macroscopic properties are usually governed by the altered microstructures and internal stress fields. Here, we use a parallel plate geometry to apply a quasi-static squeeze flow crushing a colloidal polycrystal while simultaneously imaging it with confocal microscopy. The confocal images are used to quantify the local structure order and, in conjunction with Stress Assessment from Local Structural Anisotropy (SALSA), determine the stress at the single-particle scale. We find that during compression, the crystalline regions break into small domains with different geometric packing. These domains are characterized by a pressure and deviatoric stress that are highly localized with correlation lengths that are half those found in bulk. Furthermore, the mean deviatoric stress almost doubles, suggesting a higher brittleness in the highly-confined samples.

Particle Size Effects in Flow-Stabilized Solids

“…First, our device geometry, with close to one monolayer of colloidal particles, does not match the common assumption of a porous solid that is semi-infinite. Such effects have been observed in recent work on microstructure and stress [58], colloidal assembly [59], and active particle diffusivity [60]. Note that there is a possible dependence of the permeability on the channel height, as the collapse in Fig.…”

Dynamical modes of sheared confined microscale matter

“…Further, the material response to shear is intimately connected to the nonequilibrium dynamics of the constituent elements, that have been the subject of recent research with non-Brownian particles, 13,14 polymer-, 15 active bacteria-, 16 and colloidal suspensions in amorphous, [17][18][19] fluid-, 20,21 as well as crystalline states. [22][23][24][25] Colloidal suspensions under external fields have proven to be a powerful test bed system, that is used to study the role of channel geometry 9,17,26 hydrodynamic interactions, 24,27 frictional interparticle contact and lubrication, 28,29 as well as plastic events, [30][31][32] to cite a few. Key advantages of using colloidal particles are the possibilities to directly visualize the particle dynamics via video microscopy, and to tune the pair interactions using external fields.…”

Dynamical modes of sheared confined microscale matter

“…Placing such materials inside strong spatial confinement has severe impact on their response to external deformations, which is crucial for a multitude of applications such as thin-film lubrication [4][5][6][7], microfluidic devices [8,9] and colloidal machines at the microscale [10][11][12], to name a few. Further, the material response to shear is intimately connected to the non-equilibrium dynamics of the constituent elements, that have been the subject of recent research with non-Brownian particles [13,14], polymer- [15], active bacteria- [16], and colloidal suspensions in amorphous [17][18][19], fluid- [20,21], as well as crystalline states [22][23][24][25].…”