Preparation of two-dimensional layered materials (2DLM) nanosheets is critical for both fundamental studies and applications. Here we present a systematic study to explore the fundamental factors to control the exfoliation of graphite and MoS2 in aqueous N-methylpyrrolidinone (NMP) using water as the cosolvent. Detailed materials characterizations suggested that the cosolvency significantly influences the yield and the stability of exfoliated nanosheets. The dependence of exfoliation on cosolvency was examined by fundamental factors including solid–liquid interfacial parameters, Hansen Solubility Parameter (HSP), and intermolecular-interaction-sensitive physical parameters of the water–NMP mixed solvent system. Fourier transform infrared spectroscopy (FTIR) study revealed that the water–NMP heteroassociated molecular structures, formed with the addition of water to NMP, could play an important role in the liquid exfoliation of layered materials. Our work provides a guide to rational design of a solvent system to improve the yield and stability of the exfoliated materials.

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Interfacial and micellization behavior of cetyltrimethylammonium bromide (CTAB) have been studied in aqueous polyethylene glycol (PEG) mixed solvent systems of varying concentrations and molar mass. Interfacial behavior of CTAB was investigated by the equilibrium surface tension method. Conductance studies of surfactant solutions under different condition helped in determining the critical micelle concentration (CMC) and degree of dissociation of CTAB micelles. In addition, the limiting molar conductivity of surfactant and micellar species were evaluated from the differential plots. The CMC of CTAB was found to increase with increasing PEG concentration as well as its molar mass, although, the process of interfacial adsorption and micellization was found to be spontaneous, as evidenced by negative free energy change. The viscosity of CTAB micelles in aqueous-PEG mixtures was found to increase with the increase in PEG concentration and molar mass. Dynamic light scattering measurements revealed a size enhancement effect contributed by the PEG oligomers. An increase in the CMC of CTAB and the subsequent presence of a higher number of ionic species in their dissociated form was further established by an overall increase in the zeta potential value in the presence of PEG oligomers. It is proposed that the PEG could wrap around the micelles through their conformational changes. Results also suggest that PEG oligomers could give solvophobic effect which enhances the CMC of CTAB compared to that in pure water.

Ultrathin, flexible, conformal, and skin-like electronic transducers are emerging as promising candidates for noninvasive and nonintrusive human health monitoring. In this work, a wearable sensing membrane is developed by patterning a graphene-based solution onto ultrathin medical tape, which can then be attached to the skin for monitoring human physiological parameters and physical activity. Here, the sensor is validated for monitoring finger bending/movements and for recognizing hand motion patterns, thereby demonstrating its future potential for evaluating athletic performance, physical therapy, and designing next-generation human-machine interfaces. Furthermore, this study also quantifies the sensor's ability to monitor eye blinking and radial pulse in real-time, which can find broader applications for the healthcare sector. Overall, the printed graphene-based sensing skin is highly conformable, flexible, lightweight, nonintrusive, mechanically robust, and is characterized by high strain sensitivity.