Experimental Study Of Magnetic Field Effect On Freezing Process Of Deionized Water And Solution

The rate of organism metabolism drops with temperature. In order to sustain the activity of biological samples, people have used this feature long before. Although biological tissues can be saved effectively at low temperature, they could be damaged by ice crystals of solution on freezing and thawing process easily, which seriously affects the integrity and effectiveness of the biological tissues that are preserved. Some researchers have studied the freezing process of solution under physical fields such as ultrasonic wave, microwave, and electric field. Their impact on supercooling degree, supercooling time, and ice crystal morphology of solution is not significant and couldn’t control the freezing process effectively. This paper focuses on mechanism of freezing process of solution under magnetic field.In order to find out how the freezing process of solution changes under different magnetic field intensity, supercooling process and ice crystal morphology of deionized water, sucrose solution and sodium chloride solution under a weak direct current magnetic field were investigated. The sucrose solution and the sodium chloride solution were chosen with four different concentrations (ω1= 2%,ω2= 5%, ω3= 8%,ω4= 10%). The magnetic field was generated by a pair of Helmholtz coils and evenly distributed. Data and photos were collected during the freezing process.The supercooling processes of deionized water, sucrose solution, and sodium chloride solution under a weak direct current magnetic field were investigated experimentally. The experiment involved ten magnetic field strength: 0,3,6,9,12,15,20,25,30and35G respectively. Results show that:both supercooling degree and supercooling time of deionized water increase under magnetic field. They reach maximum values at 15G magnetic intensity, an increase of 2.55 ℃,46% of supercooling degree, and an increase of 186% of supercooling time, compared to that without magnetic field. The effect of magnetic field on sucrose solution and sodium chloride solution is different under different experimental conditions, and the influence on the supercooling process of sucrose solution with different concentration presents a multi-extreme phenomenon.The influence of magnetic field on ice crystal morphology of deionized water, sucrose solution and sodium chloride solution were investigated during their freezing process. The ice crystal morphology of freezing process was observed by stereomicroscope, and filmed by a CCD digital camera.The conclusion was drawn by comparing ice crystal morphology of water, sucrose solution and sodium chloride solution with different magnetic fields during freezing process. It showed that weak direct current magnetic field affected ice crystal growth in deionized water, sucrose solution and sodium chloride solution to a certain degree. The crystal morphology is also changed from barrel-like shape into more round shape. The size of ice crystals becomes bigger or smaller according to different strength of magnetic fields.Explanations were made on the mechanism that magnetic field influences the freezing process in microscopic view. Hydrated ions of deionized water produce Lorentz force under the magnetic field and hydrogen bonds between hydrated ion ruptures and fractures. Therefore the physical properties of deionized water is influenced. Magnetic field influences the movement of water molecules and affects molecule internal energy, radial distribution function and hydrogen bonds of solution. Hence the molecule nucleation energy and the freezing process of solution is affected.In conclusion, some general rules of the magnetic field affecting the freezing process were summarized through analysis of a large amount of data, which could provide an effective guidance for cryopreservation of organisms by applying magnetic field.