Rainbow refractrometry: On the validity domain of Airy’s and Nussenzveig’s theories

To measure the temperature of individual droplets or the average temperature in a section of a spray, the analysis of the light scattered around the rainbow angle provides an attractive approach. Up to now, the analysis of recorded rainbow signals has been carried out in the framework of the full Lorenz-Mie theory or of the Airy theory. In this paper, we consider four approaches (Lorenz-Mie, Debye, Airy and Nussenzveig approaches) to compute the light scattered around the rainbow angle, and we compare them in terms of accuracy and time-consumption. It is shown that the Complex Angular Momentum (CAM) theory proposed by Nussenzveig, modified by using empirical coefficients, allows one to accurately compute the light scattered around the rainbow angle in a large angular domain for particles with diameters as small as 10 μm.     

Rainbow refractrometry on particles with radial refractive index gradients

The rainbow refractrometry, under its different configurations (classical and global), is an attractive technique to extract information from droplets in evaporation such as diameter and temperature. Recently a new processing strategy has been developed which increases dramatically the size and refractive index measurements accuracy for homogeneous droplets. Nevertheless, for mono component as well as for multicomponent droplets, the presence of temperature and/or of concentration gradients induce the presence of a gradient of refractive index which affects the interpretation of the recorded signals. In this publication, the effect of radial gradient on rainbow measurements with a high accuracy never reached previously is quantified.     

Sequential deposition of polydisperse particles with double layer interactions: An integral-equation theory

Adsorption of charged colloidal particles to oppositely charged surfaces is usually an irreversible process. The interaction between a pair of particles can be modeled with an exponentially decaying potential originating from double layer interactions. This work explored the effect of the Debye length on monolayer structures using the integral-equation theory which was successfully developed based on a binary-mixture approximation to include the effect of particle size polydispersity. The theoretical results from the integral equations with a Percus-Yevick closure showed that upon increasing the Debye length, the radial distribution functions, g(r), as well as the structure factor, S(k), decreased, in good agreement with simulation results. When the effect of size distributions was investigated, the prominent peak of the radial distribution function increased non-linearly with the product κσ_av, which followed the same trend as was reported for the case of the jamming coverage of the monolayer film.     

Generation and size classification of single-walled carbon nanotube aerosol using atmospheric pressure pulsed laser ablation (AP-PLA)

Gas suspended single-walled carbon nanotubes (SWCNTs) with single tube diameter smaller than 2 nm and length of longer than 500 nm were generated by simple and continuous system using laser ablation technique under atmospheric conditions. Graphite target containing 0.5 wt%-nickel and 0.5 wt%-cobalt was ablated by Nd:YAG laser in an electrical furnace under atmospheric pressure of nitrogen flow that allowed one step and continuous synthesis of the SWCNTs. Size distribution of the gas suspended SWCNTs aerosol was measured using size-classification by a differential mobility analyzer (DMA) coupled with a condensation particle counter (CPC) used as a detector. Characteristics of SWCNT aerosol generated under the different temperature were also investigated using scanning and transmission electron microscopes and Raman scattering. Mono-mobility SWCNT aerosol with mobility diameter of 100 and 200 nm was successfully prepared after the size separation using a DMA.     

Porous characteristics of carbon-coated silica gel beads prepared by liquid phase deposition of organic colloidal nanoparticles

Carbon-coated silica gel beads could be prepared by immersing porous silica gel beads in a resorcinol–formaldehyde (RF) aqueous solution and then following by drying and pyrolysis in nitrogen atmosphere. With the proposed method, deposition of colloidal nanoparticles formed during the sol–gel polycondensation of the RF solution was successfully prepared on the mesopores of the silica gel beads. Both size and concentration of the colloidal particles could be controlled by the gelation time and the mixing ratio (V_EtOH/V_RF) of the RF solution to ethanol. The porous characteristics of the prepared carbon-coated silica gel beads and the amounts of deposited carbon could be controlled by changing V_EtOH/V_RF. Without any significant decrease in mesoporosity, the maximal carbon contents of carbon-coated silica gel beads could be increased up to 18 wt% in the inner part and 53 wt% on the outer surface, respectively.     

On‐Line Polyketide Cyclization into Diverse Medium‐Sized Lactones by a Specialized Ketosynthase Domain

Ketosynthase (KS) domains of modular type I polyketide synthases (PKSs) typically catalyze the Claisen condensation of acyl and malonyl units to form linear chains. In stark contrast, the KS of the rhizoxin PKS branching module mediates a Michael addition, which sets the basis for a pharmacophoric δ‐lactone moiety. The precise role of the KS was evaluated by site‐directed mutagenesis, chemical probes, and biotransformations. Biochemical and kinetic analyses helped to dissect branching and lactonization reactions and unequivocally assign the entire sequence to the KS. Probing the range of accepted substrates with diverse synthetic surrogates in vitro, we found that the KS tolerates defined acyl chain lengths to produce five‐ to seven‐membered lactones. These results show that the KS is multifunctional, as it catalyzes β‐branching and lactonization. Information on the increased product portfolio of the unusual, TE‐independent on‐line cyclization is relevant for synthetic biology approaches.     

Heat transfer and two-phase flow characteristics of refrigerants flowing under varied heat flux in a double-pipe evaporator

A mathematical model based on the annular flow pattern is developed to simulate the evaporation of refrigerants flowing under varied heat flux in a double tube evaporator. The finite difference form of governing equations of this present model is derived from the conservation of mass, energy and momentum. The experimental set-up is designed and constructed to provide the experimental data for verifying the simulation results. The test section is a 2.5 m long counterflow double tube heat exchanger with a refrigerant flowing in the inner tube and heating water flowing in the annulus. The inner tube is made from smooth horizontal copper tubing of 9.53 mm outer diameter and 7.1 mm inner diameter. The agreement of the model with the experimental data is satisfactory. The present model can be used to investigate the axial distributions of the temperature, heat transfer coefficient and pressure drop of various refrigerants. Moreover, the evaporation rate or the other relevant parameters that is difficult to measure in the experiment are predicted and presented here. The results from the present mathematical model show that the saturation pressure and temperature of refrigerant decrease along the tube due to the tube wall friction and the flow acceleration of refrigerant. The liquid heat transfer coefficient increases with the axial length due to reducing the thickness of the liquid refrigerant film. Due to increase of the liquid heat transfer coefficient, increasing wall heat flux is obtained.Finally, the evaporation rate of refrigerant increases with increasing wall heat flux.     

Characteristics of carbon nanoparticles synthesized by a submerged arc in alcohols, alkanes, and aromatics

Fullerene-related carbon nanostructures can be synthesized by an arc-in-liquid system as a cost-effective technique. In this work, we investigated the effects of additional carbon sources from liquid media that were alcohols (C(m)H(2m+1)OH, m = 1-8), alkanes (C(m)H(2m+2), m = 6-7), and aromatic compounds (C6H6-C(n)H(2n), n = 1-2) on the product structures and the yield of nanocarbon-rich deposits. It was found that carbon nanoparticles (CNPs) that included multi-walled carbon nanotubes (MW-CNTs) and multi-shelled carbon nanoparticles were produced at high concentrations in the hard deposit at the cathode tip formed by the arc in the alcohols and alkanes, similar to that in a water environment. Importantly, not only graphite electrodes but also these organic compounds played a role of a carbon source to produce CNPs that led to an approximately 8-100 times higher yield than the arc-in-water system. There was a tendency that the increase in alcohol concentration and carbon content in the organic molecules positively affected the yield and production rate of the CNPs. However, the selectivity of MW-CNTs was significantly reduced when aromatic compounds were used. Structural analyses by dynamic light scattering and Raman spectroscopy revealed the dependency of the hydrodynamic particle sizes of CNPs and their crystallinity on the liquid components. For a discussion on the reaction mechanism, optical emission spectra of the arc plasma were analyzed to estimate the arc temperature. In addition, liquid byproducts were analyzed by a UV-vis absorbance spectrometer.     

Microwave-induced fabrication of copper nanoparticle/carbon nanotubes hybrid material

Copper nanoparticle/multi-walled carbon nanotube (MWCNT) hybrid material could be fabricated by microwave irradiation to a suspension of MWCNTs dispersed in copper precursor with the presence of ethylene glycol. Microscopic and spectroscopic analyses could confirm the uniform dispersion of copper oxide nanoparticles hybridized on the outer surface of MWCNTs. Reduction of Cu²⁺ ions to Cu₂O and Cu nanoparticles was ascribed to functional groups which were generated after the precursor was irradiated by microwave. Sufficient irradiation time of 5 min or longer played an important role to induce the agglomeration of copper oxide nanoparticles on the MWCNT surface.     

Random sequential adsorption of polydisperse spherical particles: An integral-equation theory

Our previously developed integral-equation theories were applied to incorporate the effect of polydispersity in the study of the random sequential addition of spherical particles. By using the simplest uniform size distribution, we found that results from theories were in consistence with the Monte Carlo simulation results. Some deviations were seen, which resulted from the exclusion effects of polydisperse particles. It was found in the simulations that with increasing densities, small particles adsorbed preferentially and the size distribution skewed towards the smaller particles. Therefore, to accurately predict the correct radial distribution functions, the more appropriate size distributions are needed. For all size ranges, which were 0.40d–1.60d, 0.75d–1.25d, and 0.90d–1.10d, the radial distribution functions from theory at number densities of 0.2, 0.4 and 0.65 were in good agreements with those from the simulations.