Assembly and photonic properties of superparamagnetic colloids in complex magnetic fields.
Assembly and photonic properties of superparamagnetic colloids in complex magnetic fields.
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DOI：
10.1021/la2026768
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发表时间：
2011-10
期刊：
影响因子：
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通讯作者：
Le He;Yongxing Hu;Xiaogang Han;Yu Lu;Zhenda Lu;Yadong Yin
中科院分区：
文献类型：
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作者：
Le He;Yongxing Hu;Xiaogang Han;Yu Lu;Zhenda Lu;Yadong Yin
粒子间磁偶极子力可以驱动动态超顺磁性胶体粒子链的形成，从而在可见光和近红外光谱中产生具有快速可逆可调结构颜色的光子纳米结构。虽然大多数关于磁性组装的研究都使用简单的永磁体或电磁铁，但原则上磁场可以更复杂，允许组装的局部调制和随后复杂的上层结构的创建。为了探索磁性可调谐光子系统的潜在应用，我们研究了磁性胶体粒子在非理想线性哈尔巴赫阵列产生的复杂磁场中的组装。我们证明了夹在两个垂直磁场之间的水平磁场可以改变粒子链的方向，从而产生高对比度的彩色图案。发现Fe(3)O(4)@SiO(2)粒子从线性颗粒链到三维晶体的相变是由磁偶极子力和填料力以及强静电力的相互作用决定的。当粒子在垂直场的区域以线性链的形式组装时，可以立即创建具有可调结构和衍射的颜色图案，但水平方向的大场梯度可能会破坏链结构的稳定性，并产生3D晶体图案，以补充初始链组装。我们的研究不仅证明了磁响应光子结构在视觉图形应用（如标牌和安全文件）中的巨大潜力，而且指出了当粒子组合受到通常涉及大场梯度的复杂磁场时，图案稳定性的潜在挑战。
Interparticle magnetic dipole force has been found to drive the formation of dynamic superparamagnetic colloidal particle chains that can lead to the creation of photonic nanostructures with rapidly and reversibly tunable structural colors in the visible and near-infrared spectrum. Although most studies on magnetic assembly utilize simple permanent magnets or electromagnets, magnetic fields, in principle, can be more complex, allowing the localized modulation of assembly and subsequent creation of complex superstructures. To explore the potential applications of a magnetically tunable photonic system, we study the assembly of magnetic colloidal particles in the complex magnetic field produced by a nonideal linear Halbach array. We demonstrate that a horizontal magnetic field sandwiched between two vertical fields would allow one to change the orientation of the particle chains, producing a high contrast in color patterns. A phase transition of Fe(3)O(4)@SiO(2) particles from linear particle chains to three-dimensional crystals is found to be determined by the interplay of the magnetic dipole force and packing force, as well as the strong electrostatic force. While a color pattern with tunable structures and diffractions can be instantly created when the particles are assembled in the form of linear chains in the regions with vertical fields, the large field gradient in the horizontal orientation may destabilize the chain structures and produces a pattern of 3D crystals that compliments that of initial chain assemblies. Our study not only demonstrates the great potential of magnetically responsive photonic structures in the visual graphic applications such as signage and security documents but also points out the potential challenge in pattern stability when the particle assemblies are subjected to complex magnetic fields that often involve large field gradients.