Controllable Synthesis Of Superparamagnetic Fe₃O₄ Clusters And Their Application Of Magnetothermal Properties

Superparamagnetic Fe3O4 clusters without coercivity and remanence have exhibited obvious advantages in the field of magnetically responsive photonic crystals and magnetic hyperthermia.However,there are some problems in the controllable synthesis of superparamagnetic Fe3O4 clusters and the above applications:the method of particle size control is limited;the magnetic field responsive chromic capability will disappear after the diffraction color is stabilized by a hydrogel matrix;the possible instantaneous high temperature will occur when the temperature control system of magnetic hyperthermia fails.In this thesis,aimed to solve above issues,a mixed-solvent solvothermal method using small molecule compounds as the functional ligands is used for controlled synthesis of water-dispersible superparamagnetic Fe3O4 clusters.The magnetochromic color display of magnetic photonic hydrogel is realized under an alternating magnetic field by using magnetothermal effect of the Fe3O4 clusters.Moreover,combined with the magnetothermal effect of the Fe3O4 clusters and temperature control characteristic by a phase transition of phase change material,the effectively temperature control in magnetic hyperthermia is achieved.According to the differences in reducibility,coordination ability with Fe3+,and viscosity of ethylene glycol and diethylene glycol,the growth of nanocrystals and the formation of clusters can be controlled effectively by varying the volume ration of ethylene glycol/diethylene glycol in a mixed-solvent solvothermal process.Thus,the size of nanocrystals and clusters can be controlled.The superparamagnetic Fe3O4 clusters are synthesized using solvothermal route with the mixed-solvent system of ethylene glycol/diethylene glycol.The particle size can be tuned in the range of 186 nm-403 nm and 104 nm-230 nm for using 5-sulfosalicylic acid and sodium citrate as the functional ligands,respectively.The obtained clusters are hydrophilic,highly saturated magnetization and superparamagnetic.Particularly,the Fe3O4 clusters prepared with sodium citrate as the ligand demonstrated excellent water dispersibility and dispersing stability owing to the presence of many citrate groups attached on the surface.The Fe3O4 clusters(168 nm)can readily self-assemble in deionized water(10.0 mg/mL)into photonic crystals upon application of a static magnetic field,resulting brilliant structure color.Moreover,the clusters exerts an excellent magnetothermal property in an altern ating magnetic field.Temperature-sensitive magnetic photonic crystal structure color hydrogels are fabricated through the magnetically induced self-assembly of highly concentrated Fe3O4@SiO2 colloids(15.6 mg/mL)and an instant UV curing process.The photonic structures is fixed inside a PNIPAM hydrogel.The volume of the hydrogel matrix can vary due to the hydrophilic-hydrophobic transition caused by the magnetothermal effect.Consequently,the interparticle distance(d)of the one-dimensional photonic structures fixed in the matrix changes,thereby shifting the diffraction wavelength and creating a color change according to Bragg's diffraction law ?=2ndsin?.With magnetic heating(6 min)under an alternating magnetic field,the temperature of the hydrogel gradually increases from 11.6 ?(initial temperature)to 33.6 ?.The diffraction color changes gradually with time from yellow to blue.The diffraction peak blueshifts from an initial wavelength of 583 nm to 457 nm,correspondingly.This study realized the controllable magnetochromic display with a solid magnetic photonic hydrogel.Taking advantage of the magnetothermal effect of the magnetic particles and temperature control characteristic by a phase transition of phase change materials,the magnetic shape-stabilized phase change materials able to control the temperature in magnetic hyperthermia are obtained by introducing Fe3O4@SiO2 colloids into phase change heat storage materials(TTIPU/paraffin).On the one hand,Fe3O4@SiO2 colloids act as the function materials for magnetothermal conversion,which are used to provide thermal energy by their excellent magnetothermal properties in an alternating magnetic field.On the other hand,the magnetic phase change materials have high fusion enthalpies(>113 J/g)within a temperature range of 41-47 ?.The heat energy caused by the magnetothermal effect can be gradually stored in the phase change materials as latent heat.Thus,the required temperature in the magnetic hyperthermia will be maintained for a long time and achieved the effective control of temperature for magnetic hyperthermia.