Tunable Morphologies of Dried Colloidal Deposits in Graphene Oxide-Laden Aqueous Sessile Droplets Mediated by Mesophase Characteristics.

We experimentally report tunability in the colloidal deposit morphologies of Graphene Oxide (GO) from desiccating sessile droplets, governed by characteristic mesophases driven by spontaneous self-assembly in aqueous media. Observations revealed mesophase-directed regimes of GO-deposit patterns ranging from ring-like to uniform deposits; within the uniform-deposit regime, morphologies span from prominent striped to mosaic-like configurations. Experiments revealed that polydisperse GO suspensions of larger average lateral sheet size (∼2.2 μm) but weaker oxidation (C/O = 14.4) form orientationally ordered nematic domains in the aqueous medium; this characteristic self-assembly subsequently leads to radially striped morphologies after droplet desiccation. Alternatively, smaller in average lateral sheet size (∼0.5 μm) but strongly oxidized (C/O = 10.4) polydisperse GO colloids self-assemble in lamellar smectic-like domains as continuous elastic sheets that conform to the linear smectic elastic framework. Subsequently, this results in uniform deposits with mosaic-like fine-structural morphologies. We also investigated concentration-dependent disordered (isotropic) and ordered phase-driven regimes of ring-like and uniform deposit patterns formed by both of the aforementioned GO suspensions. The mesophase characteristics were analyzed by precision experimental tools including Small-Angle X-ray Scattering (SAXS) and rheological tests to respectively elucidate the mesoscale structural correlations and mechanical strength of the aqueous colloidal suspensions. The measurements corroborate theoretical frameworks involving the orientational order parameter and smectic elastic response. This work elucidates the general rules governing modulation in dried colloidal deposit patterns of GO due to structure-mesophase correlation, addressing variability in deposit patterns across GO samples with different structural features and providing useful insights for inkjet-printed electronic device fabrication.