Xianju Wang

Influence of pH on the Stability Characteristics of Nanofluids

In this paper, we investigated the dispersion behavior oftwo particular water-based nanofluids, namely water-Al2O3 and water-Cu mixtures. Under different pH values the absorbencyand zeta potential of the nanofluids were measured. The resultsshowed that the stability of nanofluids was highly dependent on pH values, an optimal pH value can result in the highest stability ofthe nanofluids. The calculated DerjaguinLandau-Verwey-Overbeek (DLVO) inter-particle interaction potentials verified theexperimental results of the pH effect on the stability behavior.

Phase Transitions in Dipalmitoylphosphatidylcholine Monolayers

A self-assembled phospholipid monolayer at an air-water interface is a well-defined model system for studying surface thermodynamics, membrane biophysics, thin-film materials, and colloidal soft matter. Here we report a study of two-dimensional phase transitions in the dipalmitoylphosphatidylcholine (DPPC) monolayer at the air-water interface using a newly developed methodology called constrained drop surfactometry (CDS). CDS is superior to the classical Langmuir balance in its capacity for rigorous temperature control and leak-proof environments, thus making it an ideal alternative to the Langmuir balance for studying lipid polymorphism. In addition, we have developed a novel Langmuir-Blodgett (LB) transfer technique that allows the direct transfer of lipid monolayers from the droplet surface under well-controlled conditions. This LB transfer technique permits the direct visualization of phase coexistence in the DPPC monolayer. With these technological advances, we found that the two-dimensional phase behavior of the DPPC monolayer is analogous to the three-dimensional phase transition of a pure substance. This study has implications in the fundamental understanding of surface thermodynamics as well as applications such as self-assembled monolayers and pulmonary surfactant biophysics.

Experimental Investigation on Viscosity of Nanofluids

The effects due to fluid pH and dispersant concentration on the dynamic viscosity for the Al2O3–water and TiO2–water nanofluids had been experimentally investigated. The viscosity of the two kinds of nanofluids was measured using capillary viscometers. The experimental results showed that there exists an optimized value of pH (pH≈8.0) at which the viscosities of the two nanofluids take their minima values. The experimental results also showed that the influence of dispersant concentration on the viscosity of Al2O3–water suspension was relatively large comparing with that of the TiO2–water nanofluid, and the dispersion of alumina powder is poorer than that of titanium dioxide powder at the same pH value and same mass fraction.

Double Symmetry Breaking of Modes in Dual-Core Rotating System

We study spontaneous symmetry breaking in a dual-core system with a rotating double well potential in self-focusing nonlinearity. By tuning the coupling parameter and total optical power, four types of mode have been found. Double symmetry breaking, which is a combination of the symmetry breaking of the waveform and the optical power distribution, occurs under specific conditions. The numerical simulations show that there are some overlaps among the different stable modes, which have confirmed the coexistence of the modes. It is found that the region where the four stable modes coexist shifts with the variation in the rotating speed, and the corresponding parameters, the coupling parameter and total power, decrease sharply with the increase in the rotating speed.

Study of the Structural and the Spectral Characteristics of [C3N3(NH2)3]n (n = 1–4) Clusters

Previous research has shown that interactions between melamine molecules within a cluster can give rise to the molecular self-assembly and that the spectral characteristic of melamine can be used to inspect melamine in a carrier. Although the structural and spectral characteristics of an isolated single melamine molecule and the molecular arrays on metal or semiconductor surfaces have been studied extensively, little is known about that of isolated multimolecular melamine clusters. In this work, density functional theory (DFT) calculations at the ω-B97XD/6-311++G(d,p) level were performed to study the structural and spectral characteristics of isolated melamine clusters [C3N3(NH2)3]n (n = 1-4) in the ground state. The calculation shows that a ground-state single melamine molecule takes a quasi-planar structure. The C and N atoms of the molecule are in one plane, which we call the molecular plane, while the H atoms deviate slightly from the molecular plane. When melamine molecules gather to form a cluster, the intermolecular hydrogen bonds (IHBs) N-H···N will arise, with the lengths of H···N in the range from 1.960 to 1.970 Å; the length of N-H will be elongated to 1.022 Å from its original of 1.004 Å, the N-H···N bond angles will be about 176°, and the average single-bond binding energy will be approximately -0.285 eV. In a multimolecular cluster, each melamine molecule still takes the quasi-planar structure. Each molecular plane in the cluster retains a planar structure, and some H atoms diverge more from their molecular planes. The molecular planes in a cluster are not coplanar, and the dihedral angle between the molecular planes of two neighboring melamine molecules ranges from 38 to 40°. In addition, the theoretical study of the infrared (IR) spectrum and nuclear magnetic resonance (NMR) spectrum of [C3N3(NH2)3]n (n = 1-4) was conducted. The results confirm the existence of IHBs in a multimolecular melamine cluster and reveal the symmetry of the electron cloud distribution in the melamine clusters. Experimental study of the IR for solid-state melamine and (13)C NMR spectra for both solid- and liquid-state melamine samples were also carried out, in which the corresponding spectral characteristics of [C3N3(NH2)3]n (n = 2-4) clusters deduced from theoretical study were observed. Findings of this study may serve as theoretical references for future identification and utilization of melamine clusters.

Simulation study of second-harmonic microscopic imaging signals through tissue-like turbid media.

We establish, for the first time, a simulation model for dealing with the second-harmonic signals under a microscope through a tissue-like turbid medium, based on the Monte Carlo method. With this model, the angle-resolved distribution and the signal level eta of second-harmonic light through a slab of the turbid medium are demonstrated and the effects of the thickness (d) of the turbid medium, the numerical aperture (NA) of the objective as well as the size (rho) of the scatterers forming the turbid medium are explored. Simulation results reveal that the use of a small objective NA results in a narrow angle distribution but strong second-harmonic signals. A turbid medium consisting of large scattering particles has a strong influence on the angle distribution and the signal level eta, which results in a low penetration limit for second-harmonic signals made up of ballistic photons. It is approximately 30 microm in our situation.

Influence of SDBS on Stability of Copper Nano-Suspensions

Dispersion and stability of Cu nano-suspensions with dispersant is the important base for the study of rheology and heat transfer enhancement of the suspensions. This paper presented a procedure for preparing a nanofluid which was a suspension consisting of nanophase powders and a base liquids. By means of the procedure, Cu-H2 O nanofluids with and without dispersant were prepared, whose sedimentation photographs were given to illustrate the stability and evenness of suspension with dispersant. Dispersion and stability of Cu nanoparticles in water were studied under different pH values and the concentration of sodium dodecylbenzenesulfonate (SDBS) dispersant by the method of zeta potential, absorbency and sedimentation photographs. The results show that zeta potential has very corresponding relation with absorbency, and the higher absolute value of zeta potential and absorbency are, the better dispersion and stability in system is. The absolute value of zeta potential and absorbency are higher at pH 9.5. SDBS can significantly increase the absolute value of the zeta potential of the particle surfaces by electrostatic repulsions, which leads to the enhancement of the stability of the Cu suspensions. The optimizing concentration for SDBS in the 0.1% copper nano-suspensions is 0.07%, which has the best disperse results.Copyright

Grashof Number Effects on Nanofluids in Natural Convection Heat Transfer

The natural convection of nanofluids in a two-dimensional enclosure is numerically simulated. The effects of nanoparticle concentration and Grashof number (Gr) on heat transfer properties are investigated. The results indicate that for a given initial Gr value, the heat transfer rate of the nanofluid increases remarkably with the increase of nanoparticles mass fraction, and that for low Gr value the heat transfer process is dominant with the heat exchange, while for high Gr value it is dominant with the natural convection. In addition, the intensity of the streamline is increased with the increases of the Gr values.

Influence of CATB on Stability of Copper Nano-Suspensions

Dispersion and stability of Cu nano-suspensions with dispersant is the important base for the study of rheology and heat transfer enhancement of the suspensions. This paper presented a procedure for preparing a nanofluid which was a suspension consisting of nanophase powders and a base liquids. By means of the procedure, Cu-H2O nanofluids with and without dispersant were prepared, whose sedimentation photographs were given to illustrate the stability and evenness of suspension with dispersant. Dispersion and stability of Cu nanoparticles in water were studied under different pH values and the concentration of hexadecyl trimethyl ammonium bromide (CATB) dispersant by the method of zeta potential and absorbency. The results show that zeta potential has very corresponding relation with absorbency, and the higher absolute value of zeta potential and absorbency are, the better dispersion and stability in system is. The absolute value of zeta potential is higher at pH 9.5. CATB can significantly increase the absolute value of the zeta potential of the particle surfaces by electrostatic repulsions, which leads to the enhancement of the stability of the Cu suspensions. The optimizing concentration for CATB in the 0.1% copper nano-suspensions is 0.05%, which has the best disperse results.

Evaluation of low-intensity laser external radiotherapy through thermal texture mapping (TTM) technology

This paper aims to evaluate the curative effects of low-intensity laser external radiotherapy through thermal texture mapping (TTM) technology. The influences of 30 min nasal cavity irradiation of semiconductor laser (650 nm, 5 mW, continuous wave) on microcirculation were investigated through TTM. At the same time, with the aid of TTM, the influences of the irradiation on the whole body thermal balances and the functions of the liver and kidney were also studied. Altogether, 32 cases of microcirculation depression were investigated. After the 30 min nasal cavity irradiation, the total efficiency of microcirculation reached 100%. The effective ratio kept 96.9% 30 minutes later but the effect almost disappeared completely 150 minutes after the irradiation. No ill influence on the whole body thermal balance or metabolic functions of liver and kidney was found. Low-intensity laser external radiotherapy was a promising therapy to improve microcirculation. TTM was the ideal evaluation technology promoting this therapy.