Mériguet Guillaume, Cousin Fabrice, Dubois Emmanuelle, Boué François, Cebers Andrejs, Farago Bela, Perzynski Régine
Laboratoire Liquides Ioniques et Interfaces Chargées, UPMC, UMR CNRS-UPMC-ESPCI 7612, case 51, 4 place Jussieu, 75252 Paris Cedex 05, France.
J Phys Chem B. 2006 Mar 9;110(9):4378-86. doi: 10.1021/jp0558573.
In the present study, the structure of monophasic ionic magnetic fluids under a static magnetic field is explored. In these aqueous electrostatically stabilized ferrofluids, we vary both the isotropic interparticle interactions and the anisotropic dipolar magnetic interaction by tuning the ionic strength and the size of the nanoparticles. Small angle neutron scattering measurements carried out on nanoparticles dispersed in light water exhibit miscellaneous 2D nuclear patterns under a magnetic field with various q-dependent anisotropies. In this nondeuterated solvent where the magnetic scattering is negligible, this anisotropy originates from an anisotropy of the structure of the dispersions. Both the low q region and the peak of the structure factor can be anisotropic. On the scale of the interparticle distance, the structure is better defined in the direction perpendicular to the field. In the thermodynamic limit (q-->0), the model previously described in ref 10 matches the data without any fitting parameters: the interparticle interaction is more repulsive in the direction parallel to the magnetic field. At low q, the amplitude of the anisotropy of the pattern is governed by the ratio of two interaction parameters: the reduced parameter of the anisotropic magnetic dipolar interaction, gamma/Phi, over the isotropic interaction parameter, , in zero field, which is proportional to the second virial coefficient.
在本研究中，探讨了静态磁场下单相离子磁流体的结构。在这些水性静电稳定铁磁流体中，我们通过调节离子强度和纳米颗粒的尺寸来改变各向同性的颗粒间相互作用和各向异性的偶极磁相互作用。对分散在轻水中的纳米颗粒进行的小角中子散射测量表明，在具有各种q依赖性各向异性的磁场下，会出现各种二维核图案。在这种磁散射可忽略不计的非重水溶剂中，这种各向异性源于分散体结构的各向异性。结构因子的低q区域和峰值都可能是各向异性的。在颗粒间距离的尺度上，结构在垂直于磁场的方向上定义得更好。在热力学极限（q→0）下，参考文献10中先前描述的模型无需任何拟合参数就能与数据匹配：颗粒间相互作用在平行于磁场的方向上更具排斥性。在低q时，图案各向异性的幅度由两个相互作用参数的比值决定：各向异性磁偶极相互作用的约化参数γ/Φ与零场下各向同性相互作用参数（与第二维里系数成正比）的比值。
