Biswal Sibani Lisa, Gast Alice P
Department of Chemical Engineering, Stanford University, Stanford, California 94305, USA.
Phys Rev E Stat Nonlin Soft Matter Phys. 2003 Aug;68(2 Pt 1):021402. doi: 10.1103/PhysRevE.68.021402. Epub 2003 Aug 7.
Magnetorheological particles, permanently linked into chains, provide a magnetically actuated means to manipulate microscopic fluid flow. Paramagnetic colloidal particles form reversible chains by acquiring dipole moments in the presence of an external magnetic field. By chemically connecting paramagnetic colloidal particles, flexible magnetoresponsive chains can be created. We link the paramagnetic microspheres using streptavidin-biotin binding. Streptavidin coated microspheres are placed in a flow cell and a magnetic field is applied, causing the particles to form chains. Then a solution of polymeric linkers of bis-biotin-poly(ethylene glycol) molecules is added in the presence of the field. These linked chains remain responsive to a magnetic field; however, in the absence of an external magnetic field these chains bend and flex due to thermal motion. The chain flexibility is determined by the length of the spacer molecule between particles and is quantified by the flexural rigidity or bending stiffness. To understand the mechanical properties of the chains, we use a variety of optical trapping experiments to measure the flexural rigidity. Increasing the length of the poly(ethylene glycol) chain in the linker increases the flexibility of the chains.
磁流变颗粒永久连接成链，提供了一种磁驱动手段来操控微观流体流动。顺磁性胶体颗粒在外部磁场存在下通过获得偶极矩形成可逆链。通过化学连接顺磁性胶体颗粒，可以创建柔性磁响应链。我们使用链霉亲和素 - 生物素结合来连接顺磁性微球。将链霉亲和素包被的微球置于流动池中并施加磁场，使颗粒形成链。然后在磁场存在下加入双生物素 - 聚乙二醇分子的聚合物连接体溶液。这些连接的链仍对磁场有响应；然而，在没有外部磁场时，这些链由于热运动而弯曲和挠曲。链的柔韧性由颗粒间间隔分子的长度决定，并通过弯曲刚度或挠曲刚度来量化。为了解链的力学性能，我们使用各种光镊实验来测量弯曲刚度。增加连接体中聚乙二醇链的长度会增加链的柔韧性。
