Shear-induced assembly of graphene oxide particles into stripes near surface

ABSTRACT

We report the shear-induced assembly of graphene oxide (GO) particles into periodic stripe-like patterns near the surface. These stripe-like patterns, which have an average periodic length of 100–250 μm, are aligned in a wavy manner along the normal to the flow direction. The self-assembled GO structures are investigated at different depths using three different analysis methods, namely, reflective microscopy observations of the photonic-crystalline GO dispersion, polarized optical microscopy, and fluorescence confocal laser scanning microscopy. The surface microstructures observed in reflection mode are different from the shear-induced band structures formed in bulk thermotropic liquid crystals and liquid crystal polymers, in terms of the shape and scale of the stripes. Further, there is also a difference in terms of the dependence of the stripe width on the shear rate. The observations suggest that the stripes are formed because of a competition between the stable surface-field-induced planar alignment of the GO particles near the surface and their relatively unstable shear-induced vertical alignment in the bulk. The findings of this study should advance our understanding of GO assembly under shear stress. Further, the proposed method is a novel one for inducing the assembly of GO particles into microstructures shaped as thread-like stripes.

Graphical Abstract

KEYWORDS:

• Graphene oxide
• colour reflectance
• liquid crystals
• shear-induced alignment

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was supported by the Korea Research Fellowship Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Science and ICT [Grant Number NRF-2016H1D3A1938043].