Viscoelasticity of colloidal polycrystals doped with impurities

Abstract

We investigate how the microstructure of a colloidal polycrystal influences its linear viscoelasticity. We use thermosensitive copolymer micelles that arrange in water in a cubic crystalline lattice, yielding a colloidal polycrystal. The polycrystal is doped with a small amount of nanoparticles, of size comparable to that of the micelles, which behave as impurities and thus partially segregate in the grain boundaries. We show that the shear elastic modulus only depends on the packing of the micelles and does not vary neither with the presence of nanoparticles nor with the crystal microstructure. By contrast, we find that the loss modulus is strongly affected by the presence of nanoparticles. A comparison between rheology data and small-angle neutron scattering data suggests that the loss modulus is dictated by the total amount of nanoparticles in the grain boundaries, which in turn depends on the sample microstructure.

Irreversibility transition of colloidal polycrystals under cyclic deformation

“…The critical strain amplitude for irreversibility should correspond to the depinning stress for grain boundary growth20. Our results should be directly testable in colloidal particle experiments15161718.…”

“…Depending on the experimental conditions colloidal particles can be assembled into desired states, from perfectly ordered crystals13 to disordered amorphous glasses14. In between these two extremes lie colloidal polycrystals, where ordered crystalline regions are separated by extended grain boundaries formed by dislocation arrays15161718. The application of a cyclic shear to colloidal polycrystals allows to follow at the same time the dynamics of individual particles (“atoms”) and the large-scale response of the polycrystalline texture15161718.…”

Transport of nanoparticulate material in self-assembled block copolymer micelle solutions and crystals

“…This also suggests that nanoparticles are not sequestered at the grain boundaries of the polycrystalline material as has been seen in other studies. 20…”

“…[7][8][9][10][11][12][13][14] There has been recent interest in generating hydrophilic nanocomposites based on interspersing nanoparticulate material in these nanostructured block copolymer micelles. [15][16][17][18][19][20] Sequestering hydrophilic nanoparticulate material into the continuous phase of these packed block copolymer systems has the potential to control the spatial arrangement of the nanoparticulate material using the selfassembled structure of the block copolymer micellar solution. This technique has been demonstrated in several different architectures of Pluronic®; F127 (PEO 106 -PPO 70 -PEO 106 ), F87 (PEO 75 -PPO 46 -PEO 75 ) and P123 (PEO 20 -PPO 70 -PEO 20 ) for a variety of nanoparticulate materials with hydrodynamic diameters ranging from 4-7 nm, including silica, lysozyme, and bovine serum albumin (BSA).…”