E nhanced water flow through atomic smooth and hydrophobic carbon nanotubes (CNTs) have been demonstrated by both theoretical calculations and experiments. 1À5 There is, however, a great controversy between theory and experiments and even between experiments. The very limited experiments using CNTs membrane demonstrated enormous water flow velocity up to 5 orders of magnitude faster than predicted from conventional fluid-flow theory with three orders of deviation from different sources.1,2 In contrast, molecular dynamics (MD) calculation only gives a rate enhancement of 47À6500 for CNTs with diameters of 4.99À0.81 nm.3,5 One more general debate is whether there exists a clear transition from continuum to subcontinuum transport as the tube diameter shrinks to subnanometer regime. 5 The bottleneck for experimental attempts arises from fabrication of CNTs membrane with well-defined structures and the rational estimation of the available flow area.1 Here we show a single-tube level approach for elucidating such fundamental nanofluidic issues. The unique field effect transistors (FETs) array-based experimental design enables a direct measurement of water flow velocity inside individual CNTs. Our work demonstrates a rate enhancement of 51 to 882 for CNTs with diameters of 1.59 to 0.81 nm, which supports the MD calculation.3,5 Additionally, we achieved the first experimental evidence for the transition from continuum to subcontinuum flow by varying the diameters of CNTs.The key of our approach is to trace the water flow "front" inside an individual millimeter long CNT electrically with a configuration of three FETs in series (Figure 1a,b). The FET1 is used to "in-situ" open the tube end under water droplet by electrical breakdown, 6,7 and the synchronous FET2 and FET3 to detect the water front flowing in based on its influence on the current flow (Figure 2). 8,9 It should be emphasized that opening the tube end under water is a determinant factor for the success of this experimental design. A bias voltage of 0.01 V was applied on FET2 and FET3 (no gate voltage) all the time to detect current change. Simply by measuring the time delay of current signal jumps between FET2 and FET3 with a given interspacing, we can then estimate the average water flow velocity inside the nanotube. The CNT-FETs structure was constructed through directly growing ultralong CNT on SiO 2 /Si substrate with predesigned Pt-pattern (Figure 1b,c). Carbon nanotubes were synthesized by gas flow-directed chemical vapor deposition (CVD) method. 10À12 The catalysts pattern was made on growth substrate using PDMS stamp from the ethanol solution of 0.01 mol/L FeCl 3 . The typical growth conditions are 930À950°C, 3 sccm CH 4 and 5 sccm H 2 . Pt was sputtered and patterned as electrodes on SiO 2 /Si substrate by standard technique of photolithography and magnetron sputtering. The as-grown CNTs were characterized by scanning electron microscopy (SEM) followed by gold-wire wedge bonding, water filling and velocity measurement. A drop of pure water (18.2MΩ ...

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Seeking highly-efficient, rapid, universal and low-cost demulsification materials to break up the crude/heavy oil-in-water emulsion and emulsified oily wastewater at ambient condition has been the goal of petroleum industry. In this work, an amphiphilic material, graphene oxide nanosheets (GO), was introduced as a versatile demulsifier to break up the oil-in-water emulsion at room temperature. It was encouraging to find that the small oil droplets in the emulsion quickly coalesced to form the oil phase and separated with the water within a few minutes. The demulsification tests indicated that the residual oil in separated water samples were as low as ∼30 mg/L corresponding to a demulsification efficiency over 99.9% at an optimum GO dosage. More importantly, GO is not only useful for ordinary crude oil emulsion, but also can be used to break up the extra heavy oil emulsion. Effect of the 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 2 emulsion pH on the demulsification was also investigated. It was interesting to find that the distribution of GO either in oil or in water phase after demulsification was dependent on the pH value of the solution, which was attributed to the pH-dependent amphiphilicity of GO. The prominent demulsification ability of GO was attributed to the strong adsorption between the GO nanosheets and molecules of asphaltenes/resins driven by π-π interaction and/or n-π interaction. The findings in this work indicate that the GO nanosheets is a simple, high-efficient and universal demulsifier to separate the oil from the crude/heavy oil-in-water emulsions at ambient condition, which shows a good application prospect in oil industry.