Abstract
Here, we develop a framework for assembly, understanding, and application of functional emulsions stabilized by few-layer pristine two-dimensional (2D) nanosheets. Liquid-exfoliated graphene and MoS2 are demonstrated to stabilize emulsions at ultralow nanosheet volume fractions, approaching the minimum loading achievable with 2D materials. These nanosheet-stabilized emulsions allow controlled droplet deposition free from the coffee ring effect to facilitate single-droplet devices from minute quantities of material or assembly into large-area films with high network conductivity. To broaden the range of compositions and subsequent applications, an understanding of emulsion stability and orientation in terms of surface energy of the three phases is developed. Importantly, this model facilitates determination of the surface energies of the nanosheets themselves and identifies strategies based on surface tension and pH to allow design of emulsion structures. Finally, this approach is used to prepare conductive silicone emulsion composites with a record-low loading level and excellent electromechanical sensitivity. The versatility of these nanosheet-stabilized emulsions illustrates their potential for low-loading composites, thin-film formation and surface energy determination, and the design of functional structures for a range of segregated network applications.
Highlights
Liquid phase exfoliation of pristine graphene and related two-dimensional (2D) materials has enabled assembly of solution-processed nanosheet networks with a broad range of electronic, electrochemical, thermal and mechanical properties.[1]
While Pickering emulsification has been studied for clays[10,11], graphene oxide (GO)[12], reduced GO[13] and graphitic multilayers[14–16], emulsions stablized by pristine few-layer nanosheets have not yet been realized
Nanosheet-stablized emulsions represent an unexplored approach for assembly of layered materials where the combination of high surface area and functional properties have much promise for applications
Summary
Liquid phase exfoliation of pristine graphene and related two-dimensional (2D) materials has enabled assembly of solution-processed nanosheet networks with a broad range of electronic, electrochemical, thermal and mechanical properties.[1]. While thin film applications such as printed electronics[2] and energy storage materials[3,4] are well-developed, macroscopic structures are typically limited to random networks in polymer matrices.[5] This limits the range of accessible applications and often requires high loadings to achieve the desired properties. For 2D nanosheets, this presents a route towards assembly of structures where the degree of exfoliation is maintained in situ, preserving high number densities of nanosheets, which act as both emulsion stablizer and functional filler Their atomically-thin nature and correspondingly high specific surface area could allow stabilisation of microscale droplets with nanoscale film thickness, potentially enabling macroscopic functionality at low nanosheet loadings. While Pickering emulsification has been studied for clays[10,11], graphene oxide (GO)[12], reduced GO[13] and graphitic multilayers[14–16], emulsions stablized by pristine few-layer nanosheets have not yet been realized This is likely because of the difficulty in exfoliating these materials in appropriate liquids to allow emulsification. We develop a framework for understanding and design of emulsion stablized by pristine few-layer nanosheets to enable their applications including ultra-low loading functional composites and energy storage materials
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