Time-dependent scattering of incident light of various wavelengths in ferrofluids under external magnetic field
Time-dependent scattering of incident light of various wavelengths in ferrofluids under external magnetic field
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DOI：
10.1016/j.jmmm.2017.09.066
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发表时间：
2018-02-01
影响因子：
2.7
通讯作者：
Jing, Dengwei
中科院分区：
文献类型：
--
作者：
Jin, Jingyu;Song, Dongxing;Jing, Dengwei
铁磁流体在磁场作用下表现出各向异性的热力学性质。磁流体在磁场作用下的动态光学特性由于其作为各种光学器件的潜在应用而引起了人们的特别关注。虽然铁磁流体的随时间光散射已经得到了广泛的研究，但入射光波长的影响却很少被考虑。本文首次研究了含Fe3O4纳米颗粒的水基铁磁流体在外加磁场作用下随时间和波长变化的光散射。首先通过热导率测量和数值模拟确定并验证了制备的铁磁流体样品的场致响应行为。采用双光束紫外可见分光光度计记录了不同波长入射光穿过铁磁流体样品并平行于应用场传播的透射强度随时间的变化。正如预期的那样，由于热波动引起的柔性粒子链内部的无序，光强在场打开后立即下降到一定值。然后，光强度随着时间的推移进一步降低，直到在时间tau(0)出现最小值，然后反向增加，最后在特定时间达到平衡。更重要的是，发现特征反演时间tau(0)随入射光波长呈幂律增加(tau（0)与lambda（alpha）相似，其中alpha = 2.07）。基于时域有限差分（FDTD）方法，对特征时间的波长依赖性进行了定量解释。模拟结果与实验结果吻合较好。考虑到粒子链的粗化过程和磁散射体内部共振的发生，对不同入射波长下铁磁流体中随时间变化的光散射进行了合理化。我们的发现对各种光可调谐光学器件的开发具有一定的价值。(c) 2017 Elsevier B.V.版权所有
Ferrofluids can exhibit the anisotropic thermodynamic properties under magnetic fields. The dynamic optical properties of ferrofluids in the presence of magnetic fields are of particular interest due to their potential application as various optical devices. Although time-dependent light scattering by ferrofluids have been extensively studied, the effect of wavelength of incident light have been rarely considered. Here, for the first time, we investigated both the time-and wavelength-dependent light scattering in water based ferrofluids containing Fe3O4 nanoparticles under an external magnetic field. The field-induced response behavior of the prepared ferrofluid samples was determined and verified first by thermal conductivity measurement and numerical simulation. Double-beam UV-Vis spectrophotometer was employed to record the temporal evolution of transmitted intensity of incident light of various wavelengths passing through the ferrofluid sample and propagating parallel to the applied field. As expected, the light intensity decreases to a certain value right after the field is turned on due to the thermal fluctuation induced disorder inside the flexible particle chains. Then the light intensity further decreases with time until the appearance of a minimum at time tau(0) followed by an inversed increase before finally reaches equilibrium at a particular time. More importantly, the characteristic inversion time tau(0) was found to follow a power law increase with the wavelength of incident light (tau(0) similar to lambda(alpha), where alpha = 2.07). A quantitative explanation for the wavelength dependence of characteristic time was proposed based on the finite-difference time-domain (FDTD) method. The simulation results are in good agreement with our experimental observations. The time-dependent light scattering in ferrofluids under different incident wavelengths was rationalized by considering both the coarsening process of the particle chains and the occurrence of resonance within the magnetic scatterers. Our finding should be of value for the development of various light-tunable optical devices. (c) 2017 Elsevier B.V. All rights reserved.