Glass,
Gel, and Liquid Crystals: Arrested States of
Graphene Oxide Aqueous Dispersions
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Abstract
Colloidal systems with competing
interactions are known to exhibit
a range of dynamically arrested states because of the systems’
inability to reach its underlying equilibrium state due to intrinsic
frustration. Graphene oxide (GO) aqueous dispersions constitute a
class of 2D-anisotropic colloids with competing interactionslong-range
electrostatic repulsion, originating from ionized groups located on
the rim of the sheets, and weak dispersive attractive interactions
originating from the unoxidized graphitic domains. We show here that
aqueous dispersions of GO exhibit a range of arrested states, encompassing
fluid, glass, and gels that coexist with liquid-crystalline order
with increasing volume fraction. These states can be accessed by varying
the relative magnitudes of the repulsive and attractive forces. This
can be realized by changing the ionic strength of the medium. We observe
at low salt concentrations, where long-range electrostatic repulsion
dominates, the formation of a repulsive Wigner glass, while at high
salt concentrations, when attractive forces dominate, the formation
of gels exhibits a nematic to columnar liquid-crystalline transition.
The present work highlights how the chemical structure of GOhydrophilic
ionizable groups and hydrophobic graphitic domains coexisting on a
single sheetgives rise to a rich and complex array of arrested
states