Electrophoretic microrheology of a dilute lamellar phase: relaxation mechanisms in frequency-dependent mobility of nanometer-sized particles between soft membranes.
Electrophoretic microrheology of a dilute lamellar phase: relaxation mechanisms in frequency-dependent mobility of nanometer-sized particles between soft membranes.
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DOI：
10.1103/physreve.70.011509
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发表时间：
2004
期刊：
影响因子：
--
通讯作者：
D. Mizuno;Y. Kimura;R. Hayakawa
中科院分区：
文献类型：
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作者：
D. Mizuno;Y. Kimura;R. Hayakawa
在微观尺度上，复杂流体的粘弹性特性可以通过测量嵌入的小探针颗粒的输运特性来研究。我们测量了分散在溶致层状相中的纳米颗粒的复杂电泳迁移率微*(omega)，该层状相显示出大约1 kHz（高频弛豫，HF）和1 Hz（低频弛豫，LF）的两个弛豫过程。定量地表明，这些过程是由层状相中两个具有特征尺寸的局部结构（层间距离和持续长度）中的粒子捕获引起的。本研究通过另外两种互补方法——介电光谱和在光学显微镜下直接观察荧光标记探针粒子——获得的数据，进一步研究和增强了所观察到的弛豫的起源。结果表明，层状相的局部畸变场是由胶粒与膜的碰撞引起的额外空间相互作用引起的。由此产生的扭曲场阻碍了与膜平行（而不是垂直）的胶体粒子的布朗运动，并导致观察到的HF弛豫。另一方面，LF弛豫的起源可能是由于层状结构中的缺陷。由于本研究结果表明，输运性质受到微观环境的强烈影响，因此这种方法被称为电泳微流变学。
Viscoelastic properties of complex fluids in the microscopic scale can be studied by measuring the transport properties of small, embedded probe particles. We have measured the complex electrophoretic mobility micro*(omega) of nanometer-sized particles dispersed in a lyotropic lamellar phase, which shows two relaxation processes at approximately 1 kHz (high frequency relaxation, HF) and 1 Hz (low frequency relaxation, LF). It is shown quantitatively that these processes are caused by the trapping of particles within two local structures of characteristic size in the lamellar phase: the interbilayer distance and the persistence length. The origin of observed relaxations is further investigated and augmented in this study with data obtained by two other complementary methods, dielectric spectroscopy and the direct observation of fluorescently labelled probe particles under an optical microscope. It is shown that the local distortion field of the lamellar phase is induced by the extra steric interaction involving the collision of a colloidal particle with the membrane. The resulting distortion field hinders the Brownian motion of colloidal particles parallel to the membranes (not vertical), and causes the observed HF relaxation. On the other hand, the origin of LF relaxation is presumably a result of the defects in the lamellar structure. Since the results of this study show that the transport property is strongly influenced by microscopic environments, this method is referred to as electrophoretic microrheology.