Structure and dynamic behaviour of anisotropic magnetic particles in complex matrices

复杂基体中各向异性磁性颗粒的结构和动态行为

• 批准号: 238054058
• 负责人: Professor Dr. Joachim Wagner
• 金额: --
• 依托单位: Abteilung Physikalische Chemie
• 依托单位国家: 德国
• 项目类别: Priority Programmes
• 财政年份: 2013
• 资助国家: 德国
• 起止时间: 2012-12-31 至 2022-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/238054058?language=en
• 关键词: Structure; dynamic; behaviour; anisotropic; magnetic

Aim of the project is the investigation of mesoscale structure and dynamics in composites consisting of anisotropic, magnetic nanoparticles and thermosensitive polyelectrolyte-hydrogels. These matrices are prepared by co-polymerization of NIPAM and ionic or ionogenic co-monomers. Their viscoelastic properties are influenced by the polymer volume fraction, the cross-linking density and the charge density which can be varied by the molar fraction of co-monomers. In the case of ionogenic co-monomers, the charge density additionally depends on the pH dependent protolysis of acidic or basic groups of the co-monomers. In addition, repulsive interactions between equal charges in the polymer network can be influenced by the Debye-length depending on the ionic strength. Spindle-shaped hematite particles with widely tunable aspect ratio can be prepared with considerably small polydispersity. These in aqueous suspension by negative surface charges stabilized particles align in presence of moderate external magnetic fields in first approximation perpendicular to the field direction. Therewith, in external fields the rotational mobility of these particles is confined and their translational mobility, caused by anisotropic friction coefficients, is direction-dependent. Field-induced changes of their rotational and translational mobility lead due to particle-matrix interactions to an influence on viscoelastic properties of particle-hydrogel composites. Due to attractive, electrostatic interactions between negatively charged hematite particles and positively charged polyelectrolyte gels, the exceptionally strong particle-matrix coupling in these systems causes significant field-induced changes of their viscoelastic properties. In the project's focus are correlations between field-induced changes of mesoscale structure and dynamics of such composites and related changes of their macroscopic, viscoelastic properties. Due to the significantly larger electron density of hematite particles compared to the polymer matrix, by means of static and quasielastic X-ray scattering experiments (SAXS, XPCS) selectively the structure and dynamics of embedded hematite particles can be addressed. The rotational motion of anisotropic hematite particles under shear can be investigated by means of time-resolved, coupled rheological and X-ray scattering experiments (RheoSAXS). The structure and dynamics of the hydrogel matrix is probed by means of light scattering experiments or neutrons. Macroscopic viscoelastic properties of gels and composites are investigated by means of oscillatory shear experiments in presence of external magnetic fields. Herewith, complex shear moduli are determined in dependence on the frequency and deformation. These quantities characterize the nonlinear viscoelastic properties of both, gels and composites.

该项目的目的是研究由各向异性磁性纳米颗粒和热敏聚电解质水凝胶组成的复合材料的介观结构和动力学。 这些基质通过NIPAM和离子或离子源共聚单体的共聚制备。它们的粘弹性能受聚合物体积分数、交联密度和电荷密度的影响，而电荷密度可以通过共聚单体的摩尔分数而变化。在离子源共聚单体的情况下，电荷密度另外取决于共聚单体的酸性或碱性基团的pH依赖性质子水解。此外，聚合物网络中的相等电荷之间的排斥相互作用可以受到Debye长度的影响，这取决于离子强度。具有宽高比可调的纺锤形赤铁矿颗粒可以以相当小的多分散性制备。这些在水悬浮液中由负表面电荷稳定的颗粒在中等外部磁场的存在下在垂直于场方向的第一近似下排列。因此，在外场中，这些粒子的旋转移动性受到限制，而由各向异性摩擦系数引起的平移移动性是方向相关的。场诱导的旋转和平移迁移率的变化导致由于颗粒-基质相互作用的影响，对颗粒-水凝胶复合材料的粘弹性能。 由于带负电荷的赤铁矿颗粒和带正电荷的凝胶之间的吸引力，静电相互作用，在这些系统中的异常强的颗粒-基质耦合导致显着的场诱导的粘弹性的变化。在该项目的重点是场诱导的介观结构和动态变化的复合材料和相关的宏观，粘弹性性能的变化之间的相关性。由于显着更大的电子密度的赤铁矿颗粒相比，聚合物基体，通过静态和准弹性X射线散射实验（SAXS，XPCS）选择性的嵌入式赤铁矿颗粒的结构和动力学可以解决。剪切作用下各向异性赤铁矿颗粒的旋转运动可以通过时间分辨的流变学和X射线散射耦合实验（RheoSAXS）来研究。通过光散射实验或中子探测水凝胶基质的结构和动力学。通过外加磁场下的振荡剪切实验研究了凝胶和复合材料的宏观粘弹性能。由此，根据频率和变形确定复剪切模量。这些量表征了凝胶和复合材料的非线性粘弹性。