Magnetic Characterization Of Thermal Dynamic Behavior In Magnetic Fluid

This thesis aims to deeply investigate the magnetic characterization of thermal dynamicbehavior shown in the inverse susceptibility-temperature curve of magnetic fluid. Astemperature varies, agglomeration of monomers and disruption of clusters, which will causea superlinear behavior in the inverse susceptibility-temperature curve characterizing thermaldynamic behavior, will take place in the suspended units in magnetic fluid. And research onthermal dynamic behavior of magnetic fluid is of great significance in biomedical field suchas MR contrast agents, hyperthermia for cancer therapy and nanoparticle temperatureestimation. The main content of this dissertation is as following.(1) Based on the classical model of Langevin function, in magnetic fluid the behavior ofthermal-assisted cluster disruption was explained and the critical temperature of clusterdisruption is presented employing second-order-like phase transition of Landau theory. Onthe base, the relative content of monomers and clusters in magnetic fluid is characterizing bythe critical temperature, and a modified Langevin function which has a wide applicabilitywas established. Finally, experiments on thermal dynamic behavior of magnetic fluid werecharacterized to verify the theory stated above.(2) Employing the Rosenswing Model, a model which describes the relationshipbetween the critical temperature (T*) of cluster disruption in magnetic fluid and thefrequency of applied AC filed (f) is presented. Then the model stated above is verified by theexperimental curve of AC applied field frequency (f) and the critical temperature (T*). Atlast, thermal dynamic behavior of magnetic fluid dependence of excitation field frequency isdescribed.(3) By measuring the inverse susceptibility-temperature curves of stock magnetic fluidsample and its diluted sample (1:1.25,1:2and1:5), the critical temperature of cluster disruption, the relative content and the ratio of average effective magnetic moment ofmonomers and clusters dependence of the dilution ratio is investigated. Therefore, theinfluence of dilution ratio upon the thermal dynamic behavior of magnetic fluid is explained.