Enhanced Thermal Conductivity of High Internal Phase Emulsions with Ultra-Low Volume Fraction of Graphene Oxide.

Thermal conductivity enhancement in a multiphase fluid such as water-in-oil emulsion can substantially improve efficacies in a broad range of applications. However, nanoparticle additives that are often used to do so can catastrophically destabilize a delicate emulsion system, in our case, a high internal phase emulsion (HIPE), whereas large concentration of additives can adversely impact practical processing aspects. Therefore, means to enhance the thermal conductivity of emulsions with a minute concentration of additives (<1 wt %) is a major scientific challenge. We report the enhancement in thermal conductivity of HIPE, by consigning either lipophilic GO (fGO) in the oil phase or hydrophilic GO in the water phase in combination with a well-known emulsifier. The rheological properties of fGO-HIPE showed non-Newtonian viscoelastic behavior similar to that of the original emulsion but with lower elastic modulus and viscosity, indicating that GO incorporation has enhanced processability. The thermal conductivity enhancements can be predicted by thermal circuit models, and the HIPEs with fGO and GO demonstrated 21 and 13% enhancements over the parent emulsion with a minor 0.1 w/w addition, respectively. A possible role of ordered colloidal structures of GO and fGO underlining this prepercolation behavior is inferred from comprehensive imaging and thermal studies.

Synthesis and Stability of Water-in-Oil Emulsion Using Partially Reduced Graphene Oxide as a Tailored Surfactant.

Graphene oxide (GO) is widely known as an amphiphile having hydrophilic oxygen functionality and unoxidized graphitic patches as the hydrophobic domains. Exploiting this amphiphilicity, GO serves as a surfactant to stabilize oil-water interfaces. While there are numerous reports on GO as a surfactant, most of these reports concern oil-in-water (O/W) emulsions, and there are very few on the formation of water-in-oil (W/O) emulsions. We prepared W/O emulsions using partially reduced graphene oxide (prGO) as a surfactant. The partial reduction introduces a subtle hydrophilic-lipophilic balance (HLB), which favors the formation of the W/O emulsion. The morphological features and rheological characteristics of the W/O emulsion with 75:25 water-to-oil ratio were investigated and analyzed in detail. The W/O emulsion was found to have polydispersity with wide range of droplet sizes varying between 2 to 500 µm. Using confocal microscopy, the role of parameters such as extent of reduction, continuous phase volume fraction and the concentration of GO on the stability, microstructure and variation of droplet size distribution of the W/O emulsion were carefully monitored. With prGO concentration as large as 0.05% (w/w), highly concentrated emulsion will form, and are stable up to 20 days from formation; destabilization occurred from sedimentation and subsequent coalescence as the partially reduced GO was limited by its dispersion ability in the oil-phase studied here. Understanding the mechanisms behind the transient stability will enable the development of novel emulsion compositions containing GO as a multifunctional additive.

Tattoolike Polyaniline Microparticle-Doped Gold Nanowire Patches as Highly Durable Wearable Sensors.

Wearable and highly sensitive strain sensors are essential components of electronic skin for future biomonitoring and human machine interfaces. Here we report a low-cost yet efficient strategy to dope polyaniline microparticles into gold nanowire (AuNW) films, leading to 10 times enhancement in conductivity and ∼8 times improvement in sensitivity. Simultaneously, tattoolike wearable sensors could be fabricated simply by a direct "draw-on" strategy with a Chinese penbrush. The stretchability of the sensors could be enhanced from 99.7% to 149.6% by designing curved tattoo with different radius of curvatures. We also demonstrated roller coating method to encapusulate AuNWs sensors, exhibiting excellent water resistibility and durability. Because of improved conductivity of our sensors, they can directly interface with existing wireless circuitry, allowing for fabrication of wireless flexion sensors for a human finger-controlled robotic arm system.

Synthesis of silicalite-poly(furfuryl alcohol) composite membranes for oxygen enrichment from air.

Silicalite-poly(furfuryl alcohol) [PFA] composite membranes were prepared by solution casting of silicalite-furfuryl alcohol [FA] suspension on a porous polysulfone substrate and subsequent in situ polymerization of FA. X-ray diffraction, nitrogen sorption, thermogravimetric analysis, scanning electron microscopy, and energy-dispersive X-ray spectroscopy were used to characterize silicalite nanocrystals and silicalite-PFA composite membranes. The silicalite-PFA composite membrane with 20 wt.% silicalite loading exhibits good oxygen/nitrogen selectivity (4.15) and high oxygen permeability (1,132.6 Barrers) at 50°C. Silicalite-PFA composite membranes are promising for the production of oxygen-enriched air for various applications.