Nematic Order Drives Macroscopic Patterns of Graphene Oxide in Drying Drops

Abstract

We report on a series of experiments on large-area ordered patterns of graphene oxide on solid substrates deposited from aqueous dispersions by directed drop evaporation. The aqueous dispersion of graphene oxide exhibits phase transitions from isotropic to liquid crystalline nematic phases via a biphasic region with increasing concentration. In the single nematic phase, schlieren textures accompanied by oriented bands are frequent. Drying of drops in each phase results in deposition covering the whole drop base. The dynamic process of drop drying is analyzed based on the weight loss, radius change, and texture change over time. It is found that the radial bands develop in the nematic drops in the vicinity of the receding of the contact line and subsequently transform into birefringent stripes after drying. Study into the structure and morphology of the stripes reveals anisotropic wrinkling of graphene oxide sheets. The nature of stripe orientation is strongly dependent on the local nematic order at the dewetting water front. Various macroscopic patterns with different stripe orientations including radial spokes, spider webs, and parallel stripes have been generated by tuning the nematic order of drops.

Bottom-up and top-down manipulations for multi-order photonic crystallinity in a graphene-oxide colloid

“…3,26,27 In a colloid, the EDL acts as a large shell surrounding the bare particle, thereby resulting in a significant (that is, 450-fold) increase in the effective thickness of the particles. 28 However, most studies have overlooked the EDL in Onsager-type calculations for GO liquid crystals, [29][30][31][32] and Φ T was simply estimated by determining the aspect ratio of the dried GO sheet. By assuming that the effective thickness (T eff ) is m times that of the dried GO (T GO ) and using the approximation Φ T~4 .5 T/D, the actual phase-transition concentration to the nematic phase including EDL (Φ EDL ) is given as:…”

“…32,35 Figure 5a shows the cross-sectional SEM image of a dried GO film with a wrinkle, which was made by drying a 1 wt% GO droplet. The inset image shows closely packed GO sheets.…”

Morphogenesis of polycrystalline dendritic patterns from evaporation of a reactive nanofluid sessile drop

“…A widely studied system for spontaneous pattern formation is evaporative drying of a sessile drop containing non-volatile particles. [1] The most familiar pattern is the "coffee ring", due to an outward capillary flow that shuttles dispersed particles towards the peripheral contact line where they get trapped. [2] Marangoni effects [3] may counteract this capillary flow, [4] and the residual pattern may be further influenced by instabilities triggered by a temperature gradient across the solvent layer that manifest in different convective patterns, e.g.…”

Toward High Performance Nanocarbon Fibers

“…21 According to Onsager's theory, anisometric particles will orient themselves into an anisotropic phase above some critical concentration, driven by the entropy of their excluded free volume, and an increase in packing entropy. 22 The more anisometric the particles are, the lower the critical concentration will be. 23 So, above a critical concentration, anisometric particles will self-assemble, which can be advantageous, because many physical properties like electrical, magnetic, and mechanical properties depend on orientation.…”

“…In previous literature, GO sheets produced using a very similar method had a mean size of only ~5.0 µm. 22 To effectively use this technique to identify singular GO sheets based on contrast measurements from optical reflectance images, a more powerful lens would be necessary. Raman spectroscopy can be especially useful for carbon-based materials because while IR requires bonds with a dipole, Raman simply requires that the bonds be polarizable, so Raman can offer meaningful information about carbon-based materials like graphene and CNTs.…”