Wood Dean S, Camp Philip J
School of Chemistry, The University of Edinburgh, Edinburgh, United Kingdom.
Phys Rev E Stat Nonlin Soft Matter Phys. 2011 Jan;83(1 Pt 1):011402. doi: 10.1103/PhysRevE.83.011402. Epub 2011 Jan 7.
The properties of ferrogels in homogeneous magnetic fields are studied using a simple microscopic model and Monte Carlo simulations. The main phenomena of interest concern the anisotropy and enhancement of the elastic moduli that result from applying uniform magnetic fields before and after the magnetic grains are locked in to the polymer-gel matrix by cross-linking reactions. The positional organization of the magnetic grains is influenced by the application of a magnetic field during gel formation, leading to a pronounced anisotropy in the mechanical response of the ferrogel to an applied magnetic field. In particular, the elastic moduli can be enhanced to different degrees depending on the mutual orientation of the fields during and after ferrogel formation. The model represents ferrogels by ensembles of dipolar spheres dispersed in elastic matrices. Experimental trends are shown to be reflected accurately in the simulations of the microscopic model. In addition, the simulations yield microscopic insights on the organization of the magnetic grains. Finally, simple relationships between the elastic moduli and the magnetization are proposed. If supplemented by the magnetization curve, these relationships yield the dependencies of the elastic moduli on the applied magnetic field, which are often measured directly in experiments.
利用一个简单的微观模型和蒙特卡罗模拟研究了铁磁凝胶在均匀磁场中的性质。主要关注的现象涉及弹性模量的各向异性和增强，这是由在磁性颗粒通过交联反应锁定到聚合物凝胶基质之前和之后施加均匀磁场所导致的。磁性颗粒的位置组织受到凝胶形成过程中磁场施加的影响，导致铁磁凝胶对外加磁场的机械响应出现明显的各向异性。特别是，根据铁磁凝胶形成期间和之后磁场的相互取向，弹性模量可以不同程度地增强。该模型用分散在弹性基质中的偶极球体集合来表示铁磁凝胶。实验趋势在微观模型的模拟中得到了准确反映。此外，模拟还对磁性颗粒的组织提供了微观见解。最后，提出了弹性模量与磁化强度之间的简单关系。如果辅以磁化曲线，这些关系就能得出弹性模量对外加磁场的依赖性，而这在实验中通常是直接测量的。
