Ural Federal University, Yekaterinburg, Russian Federation.
Soft Matter. 2017 May 14;13(18):3359-3372. doi: 10.1039/c7sm00534b. Epub 2017 Apr 20.
A new kind of ferrogel with entrapped metallic iron nanoparticles causing unusual magnetodeformation is presented. Crosslinked polyacrylamide (PAAm) based ferrogels embedded with iron nanoparticles (MNPs) were synthesized by free radical polymerization in aqueous medium. Spherical iron MNPs with average diameter 66 nm were synthesized by the electrical explosion of wire and modified by interfacial adsorption of linear polyacrylamide (LPAAm). Extended Derjaguin-Landau-Verwey-Overbeek (xDLVO) calculations based on the superposing of van der Waals, electrostatic, steric, and magnetic contributions showed that polymeric encapsulation of nanoparticles by LPAAm is one of the most suitable pathways for preparing stable aqueous dispersions of iron nanoparticles. Microcalorimetry confirmed the presence of strong interfacial adhesion forces between LPAAm chains and the surface of iron nanoparticles. By keeping the same crosslinking density of a polymer network (i.e. 100 : 1, monomer to crosslinker ratio) and varying the initial monomer concentration, an influence of the extent of polymer network reticulation on the mechanical properties and subsequently, magneto-elastic properties was demonstrated. It was found that the upper limit of the shear modulus for the synthesis of a new kind of polyacrylamide based ferrogel to exhibit any usable magnetodeformation under the application of a uniform external magnetic field of 420 mT is ca. 1 kPa. Magnetodeformation of cylindrical ferrogel samples was observed in the form of an overall volume contraction accompanied by a homogeneous decrease in all dimensions. The deformation was found to be maximum (around 10%) for the aspect ratio of 1/1 and it was lower and similar for the samples with 1/2 and 2/1 aspect ratios. Such a type of magnetic response is significantly different from the behavior observed in the existing reports on ferroelastomers.
一种新型的铁凝胶，其中嵌入了导致异常磁变形的金属铁纳米粒子。通过在水介质中自由基聚合合成了交联的聚丙烯酰胺（PAAm）基铁凝胶，其中嵌入了铁纳米粒子（MNPs）。通过电线的电爆炸合成了平均直径为 66nm 的球形铁 MNPs，并通过线性聚丙烯酰胺（LPAAm）的界面吸附进行了修饰。基于范德华力、静电、位阻和磁贡献的扩展 Derjaguin-Landau-Verwey-Overbeek（xDLVO）计算表明，通过 LPAAm 对纳米粒子进行聚合物封装是制备铁纳米粒子稳定水性分散体的最适宜途径之一。微量热法证实了 LPAAm 链与铁纳米粒子表面之间存在强界面粘附力。通过保持聚合物网络的相同交联密度（即 100:1，单体与交联剂的比例）并改变初始单体浓度，证明了聚合物网络交联程度对机械性能以及随后的磁弹性性能的影响。发现了一种新型的基于聚丙烯酰胺的铁凝胶的合成，在 420mT 的均匀外磁场下，要表现出任何可用的磁变形，其剪切模量上限约为 1kPa。观察到圆柱形铁凝胶样品的磁变形形式为整体体积收缩，同时所有尺寸均匀减小。对于纵横比为 1/1 的样品，变形最大（约 10%），而纵横比为 1/2 和 2/1 的样品的变形较小且相似。这种类型的磁响应与现有铁弹性体报告中观察到的行为明显不同。
