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In this work, we report on the thermal response and evaporation rate of nanofluids containing plasma-functionalized multi-walled carbon nanotubes (MWCNTs) subjected to localized optical (laser) heating. It is shown that an optical-to-heat energy conversion efficiency of at least 64% occurs using a 200 mW continuous wave 532 nm laser heating a 15 μL droplet, resulting in a localized heat generation rate of at least 133 W cm −3 . From here evaporation of the droplet is caused by an increase of the overall fluid temperature (and therefore increased vapor pressure) and not non-equilibrium vapor production.

Carbon nanotube dispersions are promising candidates for use as working fluids in high-performance solar collectors. However, one major stumbling block in the way of their widespread application is the difficulty in achieving stable nanofluid suspensions at elevated temperatures. In this study, the stability of plasma- and acid-functionalised multi-walled carbon nanotube dispersions at temperatures up to 150°C was investigated. Therminol 55 and propylene glycol were used as the main solvents, while water was used as a reference solvent. The results of UV-VIS-NIR absorption spectroscopy showed that no agglomeration occurred in the plasma-functionalised multi-walled carbon nanotube nanofluids heated to 150°C. However, minor variations were observed in the absorbance of acid-functionalised multi-walled carbon nanotubes in propylene glycol and therminol 55 base fluids at high temperatures.

A method for the incorporation of immobile oxygen-containing functional groups onto multi-walled carbon nanotubes (MWCNTs) rooted in a metallic substrate for supercapacitor (SC) application is presented. Direct growth on the current collector (a 316 stainless steel (SS) mesh) offers the benefit of minimal MWCNT agglomeration, avoidance of using binder, and maintaining the 3-dimensional nanostructure. MWCNTs are grown by thermal-chemical vapour deposition (t-CVD) using SS as substrate and functionalized using an Ar/C2H6/O2 glow discharge. When used as a binder-free SC electrode, these functionalized MWCNTs (f-MWCNTs) show excellent surface stability and large specific capacitance values. At low charging/discharging current densities (0.2 mA cm−2 or 3 A g−1), a specific capacitance of 288 ± 10 F g−1 is achieved. The material shows good rate capability up to charging/discharging current density of 10 mA cm−2 (37 A g−1) and displays excellent reversibility. Consequently, these new binder-free f-MWCNT SC electrodes are excellent candidates for future investigations of MWCNT-based SC electrodes.

Direct volumetric absorption of solar radiation is possible with fluids which have controlled optical properties. As with conventional surface absorbers, it is possible to make direct absorbing collectors ‘selective’ where short wavelength absorption is maximised, but long wavelength emission is minimised. This work investigates the fundamental limits of this concept as it pertains to nanofluid-based direct absorbing collectors. This is especially important at higher operating temperatures (100–600 °C) where radiative losses increase significantly. A study of optical parameters of collector components is conducted herein to investigate the best theoretically (and practically) achievable ‘selective’ nanofluid-based direct absorbing collectors. When the effect of the short wavelength optical properties was investigated, a short wavelength optical depth of 3 was found to be sufficient for efficient absorption of solar radiation while scattering is minimised. It is also advantageous to use a base fluid which shows weak absorption at long wavelengths to reduce emission losses. Overall, this study directs future research of direct absorption by underlying theoretical and real-world limitations of a selective direct absorbing collector – an emerging receiver technology that can be used for efficient solar thermal harvesting.

Colloidal suspensions of functionalized carbon nanotubes (CNT nanofluids) have the potential to be used in a variety of applications, many of which require operation at elevated temperatures. In this study, we examine what effect exposure to an argon/oxygen/ethane RF glow discharge plasma has on the surface chemistry and structure of CNTs and what happens to the plasma-generated functionalities at high temperatures. An analysis performed using X-ray photoelectron spectroscopy and Raman spectroscopy indicates that longer and higher power plasma treatments decrease the sp2 graphitic nature of the CNTs without increasing the degree of oxygen functional groups. Heating of the functionalized-CNTs up to 350 °C in air and 600 °C in argon, both lead to a substantial decrease in the surface oxygen concentration, which can be attributed to the decomposition of carboxylic functionalities at low temperatures (< 350 °C).

Today’s nanofabrication methods have enabled nanoparticles to be synthesized having optical properties which are tailored to a variety of specific applications in the realms of biological and energy systems. These systems are distinctive in that light is absorbed predominantly by the nanoparticles which are distributed throughout the fluid. Here we report the first experimental study which quantitatively compares nanoparticle dispersions [amorphous carbon nanoparticles dispersed in ethylene glycol and multi-walled carbon nanotubes (MWCNTs) dispersed in distilled water] to conventional commercial materials (TiNOX® coated copper substrate) for their performance as selective solar absorbers. It has been found that under similar operating conditions, higher average stagnation temperatures are achievable if the electromagnetic radiation is allowed to directly interact with the bulk of the fluid (which is the case in a volumetric system). Moreover, the performance of these volumetric systems is sensitive to the amount (volume fraction) of the nanoparticles dispersed – which, in the limit, approaches surface absorption for high volume fractions. Furthermore, the spatial temperature distribution has been found to be consistent with the underlying theory of volumetric absorption.

This work presents a simple, inexpensive and scalable method to grow multi-walled carbon nanotubes (CNTs), using chemical vapor deposition, directly from stainless steel 316 mesh, without any pretreatment or the use of an external catalyst. A growth method is proposed based on the generation of particle-like growth sites, which are created as a result of chromium migration to the surface during heating. Acetylene concentrations were modeled within the reactor at various flow conditions and compared to experimental results to show that carbon input can be used as a way of controlling the diameter of the CNTs. All CNTs produced were strongly rooted to the SS substrate, however the larger diameter CNTs were more difficult to break and remove by means of ultrasonication.

Clathrate hydrates are currently being studied for their applications in many areas such as natural gas storage and transportation, component separation, and carbon dioxide sequestration. The ability to increase hydrate production is integral in the success of these innovative technologies. It has been found that the addition of multi-wall carbon nanotubes (MWNTs) to hydrate systems promotes clathrate formation. In order to better understand how this occurs, an analysis of the heat transfer during the formation of tetrahydrofuran (THF) hydrates was performed. Two concentrations of both conventional (hydrophobic) and plasma-functionalized (hydrophilic) MWNTs were added to a THF–water hydrate-forming solution. With the use of infrared imaging, the velocity and temperature of the thermal front during hydrate formation was measured. It was found that in both cases, the presence of MWNTs elevated the velocity of the front for a given system sub-cooling. Furthermore, as the MWNT concentration increased, so did ...

High solids content poly(butyl acrylate)/poly(methyl methacrylate) core–shell latex particles were produced using miniemulsion polymerisation in a continuous linear tubular reactor. The resulting products were and shown to be comparable to a batch process. Final solids contents of 41 and 48 wt.% were shown to be possible in a simple tubular reactor. Differential scanning calorimeter analysis indicated that core–shell particles were formed under these conditions. © 2011 Canadian Society for Chemical Engineering

Recently, direct solar collection through the use of broadly absorbing nanoparticle suspensions (known as nanofluids) has been shown as a promising method to improve efficiencies in solar thermal devices. By utilizing a volatile base fluid, this concept could also be applied to the development of a direct absorption heat pipe for an evacuated tube solar collector. However, for this to happen or for any other light-induced vapor production applications, the nanofluid must remain stable over extended periods of time at high temperatures and throughout repetitive evaporation/condensation cycles. In this work, we report for the first time a nanofluid consisting of plasma-functionalized multiwalled carbon nanotubes (MWCNTs) suspended in denatured alcohol, which achieves this required stability. In addition, optical characterization of the nanofluid demonstrates that close to 100% of solar irradiation can be absorbed over a relatively small nanofluid thickness.

Much research has gone into the advancement of products containing carbon nanotubes (CNTs). However, very little-to-no CNT-containing devices actually make it to the commercial distribution stage. This is surprising as multi-walled CNTs (MWCNTs) have excellent mechanical and electrical properties and have potential use in a myriad of applications; specifically, electrochemical energy storage devices. It is well known that carbonaceous materials are good electrodes for electrochemical capacitors (supercapacitors (SCs)) owing to their relatively large double-layer potential region (ca. 1 V in aqueous electrolytes), global abundance, possibility of achieving structures of high surface area, and their low cost.1 However, in the case of MWCNTs, specific capacitance (C sp) values are quite low (ca. 30-50 F g-1). Hybrid capacitors, whose capacitance is derived from both electrochemical double-layer and pseudocapacitive properties, are being developed to increase the C sp of various carbons. Hybrid MWCNT SC electrodes have achieved specific capacitances upwards of 130 F g-1.2 However, larger values are still desirable to decrease size/volume, mass, and overall cost of electrodes. In this talk, a presentation of our work on the development of a simple, two-step method to synthesize an improved hybrid SC electrode is given along with the results of preliminary surface and electrochemical analyses and performance data. We show that grafting stably immobilized oxygen-containing functional groups to MWCNTs grown on stainless steel surfaces leads to the largest specific capacitance for any binder-free electrode reported to-date. Thermal-chemical vapour deposition (t-CVD) was used to grow MWCNTs directly onto a 316 stainless steel mesh (400 series) according to the method presented in ref.3 The MWCNTs were then exposed to a low pressure Ar/C2H6/O2glow-discharge to immobilize oxygen-containing functional groups onto their surface, thus forming plasma-functionalized MWCNTs (f-MWCNTs). The f-MWCNTs were characterized by XPS while the f-MWCNT SC electrodes were characterized using galvanostatic charge/discharge (GCD) cycling and electrochemical impedance spectroscopy (EIS) to determine the electrode’s specific capacitance. Fig. 1a displays surface chemistry survey results from XPS showing the presence of oxygen-containing surface groups on the f-MWCNT SC electrodes. Further, the results show that the functional groups are stably bound even after 300 GCD cycles. Figs. 1b and 1c support the survey scan by examining the C1s peak before and after plasma functionalization (b) as well as after 100 and 300 GCD cycles (c). Stability of the f-MWCNT SC electrodes is excellent even after many GCD cycles. Fig. 2 shows typical C sp values with GCD cycle number (a) and the potential curve used to compute these values (b). From GCD, a maximum of ca. 200 F g-1 was recorded at 0.2 mA cm-2 after stabilization of the electrode. Using EIS, a similar C sp value of 251 F g-1was determined. We believe the reason that the C sp of our own f-MWCNT SC electrodes is so large is due to the large number of MWCNT defect sites introduced during t-CVD growth combined with the large surface-to-volume ratio of f-MWCNTs.4 These defect sites act as excellent anchor points to immobilize oxygen-containing functionalities. It is these functionalities that lead to a source of additional charge which increases the total capacitance of the material. References: 1. B. E. Conway, Electrochemical Supercapacitors: Scientific Fundamentals and Technological Applications, p. 734, Springer, (1999). 2. S. K. Park, Q. Mahmood, and H. S. Park, Nanoscale, 5, 12304–12309 (2013). 3. N. Hordy, S. Coulombe, and J.-L. Meunier, Plasma Process. Polym., 10, 110–118 (2013). 4. D.-Q. Yang and E. Sacher, J. Phys. Chem. C, 112, 4075–4082 (2008).