Chuanxiang Xu

The Mechanism Analysis of NaCl Solution Ice Formation Suppressed by Electric Field

The cells and tissues usually may be subjected to cryo-injure, but caused to die during freezing process for cryo-preservation. Among them, the most direct reason is extra-cellular and intra-cellular ice formation. How to control, reduce, or eliminate the ice formation has been an important research topic in fundamental cryobiology. The objective of this study was to test a hypothesis that the alternated electric field could significantly influence the solution of 0.9% NaCl freezing property at a relative slow cooling rate. The test sample consisted of 0.9% NaCl solution and it was frozen in 0.26 K/min cooling rate, simultaneously was exposed to alternating electric fields ranging from 50 Hz to 5M Hz. A system was built and utilized to measure the temperature of the test sample continually. It was founded that alternated electric fields strongly influenced the freezing property of the solution, included the undercooling point temperature of the solution and the latent heat produced by phrase transition during freezing process. The results were analyzed by using dielectric theory and ions moving phenomena, it indicated that the icons moving under alternated electric field is main factor influencing the property of 0.9% NaCl solution during freezing process

A fast way to fabricate polymethyl methacrylate for graded-index polymer optical fibers

ABSTRACT The coextrusion process was considered to be a main approach to prepare graded-index polymer optical fibers (GI-POFs) and the primary polymer to fabricate that is poly-methyl methacrylate (PMMA). The current process to polymerize methyl methacrylate (MMA) requires long hours. In this article, the heat transfer in the bulk polymerization was analyzed and calculated, according to which polymerization speed could enhance by removing the polymerization heat timely via the decompression of the reactant. It was validated by the experiments, and the optimum parameters of the reaction were obtained; thus, the polymerization of the MMA could be completed within hours. Analyses of the polymer showed that it was of a narrow polydispersity and a higher glass transition temperature. By means of decompression of the reactant, not only could MMA polymerize quickly but also its product properties were improved.

Effect of Alternated Electric Field on the Ice Formation During Freezing Process of 0.9%K2MnO4 Water

The effect of alternated electric field on the ice formation of 0.9%K2MnO4 water during freezing process is investigated. The pattern of ice crystal and frozen time are observed by a simple microscope system. The relationship between the ice formation and the frequency of applied electric field in the range from 1 kHz to 200 kHz is investigated. It is found that the influence of electric field is strongly dependent on the frequency of eclectic field. With the increase of the frequency, domain size of ice crystal and the frozen time decrease and reach the minimum at the frequency of 50 kHz. A candidate mechanism concerned with dielectric polarization and relaxation loss properties during the freezing process is assumed

Effect of applied electric field on the formation and structure of ice in biomaterials during freezing

The extra or intracellular ice crystal during the freezing of biomaterials is lethal to cells. It is an important topic in cryobiology how to control, reduce, or even eliminate the ice formation. The purpose of this study is to testify an assumption that electric field could significantly influence ice formation and induce the structure of microcrystal or glassy ice in some samples at a relative slow cooling rate. Physiological saline (0.9wt. %) as the sample, was applied a uniform electric field with the strength of 0~103V/m. The formation and structure of ice were analyzed by thermodynamic course and dielectric spectroscopy, which indicated that under electric field saltine ice increased and pure ice decreased significantly. When E=1×103 V/m, supercooling and relative dielectric constant increased conspicuously. Furthermore, the related theories of crystallography and dielectric physics were used to explain the experimental results. This preliminary results show that a certain electric field might be such a promising approach to control the formation and structure of ice during the slow cooling process of biomaterials.

Anomalous high permittivity in salty ice-a new dielectric phenomenon

The dielectric properties of salty ice including some one-valence alkali halides have been studied in the temperature range from -5 degrees C to -60 degrees C. It has been discovered that the salty ice has a very high permittivity, which can be over ten times higher than that for ordinary ice at the same conditions. The permittivity can be over 1000 and depends on the saline ionic concentration and radius of ion in salty ice. The authors conclude that the anomalous high-permittivity phenomenon is produced by the additional polarization effect in salty ice. The mechanism is due to thermionic polarization by the action of a high effective electric field.<<ETX>>

Dielectric properties of red blood cell suspensions based on broadband dielectric spectrum

The dielectric properties of red blood cell suspension (RBCs) samples with different packed cell volume (PCV) values were measured by using Novocontrols Concept 80 Broadband Dielectric Spectrometer of 1 Hz to 1 GHz at temperature ranging from 0°C to 42 °C. There are two relaxation processes on the dielectric spectrum of RBCs samples; one is related to the ions accumulated on double layer boundary of cells and the other to Maxwell-Wagner interface polarization. It was observed that along with the rise of temperature, the peak of dielectric loss moved to high-frequency area and the RBCs sample with higher PCV value got a lower peak. With characteristic relaxation time at various temperatures, RBCs relaxation activation energy and the relative permittivity of cellular membrane were calculated as being close to the known value of phospholipids.1

The Dielectric Behaviors of Cells under Nonuniform AC Fields

Study on the dielectric phenomena of cells is an important part of the bio-effects of electromagnetic fields. Using one kind of mushroom spore to be sample, the movement of spores under non-uniform ac fields was investigated by means of a micro-electrode system. It was found that there was an optimized frequency in the range of 10 kHz to 10MHz. At the optimized frequency point, it would take the shortest time for spores to turn round, move toward the direction of applied field and at last form clusters, which shows that the electric force on spores is the maximum. Meanwhile, this optimized frequency point depends on the applied voltage wave. The square-wave has better effect on forming clusters than sine-wave. Those could be explained by the spores polarization basis of a dielectric model in electric fields

Study on Dielectric Monitoring on Polymerization Process of MMA

Polymethyl methacrylate (PMMA) is widely used in the fabrication of polymer optical fiber and devices. It is necessary to obtain lower loss PMMA by monitoring and controlling the polymerization process of methyl methacrylate (MMA). In this paper, a polymerization process monitoring system with two-electrodes is designed to investigate changes of dielectric properties of samples with reactive time during polymerization process of pure MMA. The relation of dielectric properties of samples and the conversion rate of MMA is obtained based on a two-phase model of composite. Simultaneously, the influence of reactive temperature, reactive time, conversion rate of prepolymerization and oxygen on polymerization process is discussed. It is shown that the gel effect will be observed in 2h after beginning of reaction at 50°C, when conversion rate of prepolymer is 24% without oxygen. This new method showed high efficiency compared with the refractive index measurement for the monitoring of polymerization process.

A New Method to Fabricate GI-POF Rod and its RID Adjustment

Graded index polymer optical fiber (GI-POF) has been an important research topic in the world for its special advantages such as a large bandwidth. The existing methods to fabricate GI-POF have only limited abilities to regulate the refractive index distribution (RID), which has a strong effect to the bandwidth in the fibers and those need improvement. In this paper a new method to fabricate GI-POF preform called multi-layer polymerization in a centrifugal field was given and this method could control the RID freely. The regulating methods were explained by theory simulation and calculation, and the effects of reaction temperature were also discussed. The results indicated that the RID of GI-POF preform would approach the optimal distribution gradually with the layers of polymer increased, and the reaction temperature has little effect to the RID

Study on Dielectric Behaviors of PMMA during Thermal Aging

During the accelerated thermal aging at various temperature of pure polymethyl methacrylate (PMMA) which was applied as the core material of polymer optical fiber (POP), it was found that the relative permittivity decreased at first and then increased with the aging time increasing. For explaining it, a hypothesis of unification of dipole depolarization and dipole repolarization was proposed. On the basis of relative experimental analysis of infrared spectrogram (IR), refractive index and weight loss rate, both degree of depolarization and degree of repolarization were defined to describe the novel dielectric phenomena quantificationally