Kim Junhyung, Guelcher Scott A, Garoff Stephen, Anderson John L
Center for Complex Fluids Engineering, Department of Chemical Engineering, Carnegie Mellon University, Pittsburgh, PA 15213, USA.
Adv Colloid Interface Sci. 2002 Feb 25;96(1-3):131-42. doi: 10.1016/s0001-8686(01)00078-1.
The relative motion between pairs of negatively charged latex particles 9.7 microm in diameter and deposited on an electrode was measured by optical microscopy and image analysis. At an rms field of approximately 30 V cm(-1), the two particles moved toward each other at frequencies below 500 Hz, but they separated at 1000 Hz. In the cases of aggregation, there are several interesting characteristics. First, when the center-to-center separation of a pair was initially 6 particle radii or more apart, a transient 'incubation' period of tens of seconds was observed before the particles began to move toward each other. Second, the two particles never came into contact, rather at long times the pair maintained a stationary gap between them equal to approximately one-half the particle radius. This stationary gap between particles was also observed for the aggregation of clusters of three or more particles. Finally, the rate of approach for a pair of particles decreased as the frequency increased. Larger fields are required to move particles together in ac compared to dc fields; at 30 Hz the ac field must be 130 times greater than the dc field to achieve the same rate of approach. Taking advantage of the qualitative and quantitative differences of the cooperative motion of particles in dc vs. ac fields, one should be able to re-position particles by alternating between these two modes. We demonstrated that the same pair of particles can be brought together at low frequency (100 or 200 Hz) and then separated at high frequency (1000 Hz).
通过光学显微镜和图像分析测量了直径为9.7微米、沉积在电极上的成对带负电乳胶颗粒之间的相对运动。在均方根场约为30 V cm⁻¹时，两个颗粒在低于500 Hz的频率下相互靠近，但在1000 Hz时分开。在聚集的情况下，有几个有趣的特征。首先，当一对颗粒的中心距最初相隔6个颗粒半径或更远时，在颗粒开始相互靠近之前会观察到数十秒的短暂“潜伏期”。其次，两个颗粒从未接触，相反，长时间来看，这一对颗粒之间保持着一个固定的间隙，大约等于颗粒半径的一半。在三个或更多颗粒的团簇聚集中也观察到了颗粒之间的这种固定间隙。最后，一对颗粒的靠近速率随着频率的增加而降低。与直流场相比，在交流场中需要更大的场才能使颗粒聚集在一起；在30 Hz时，交流场必须比直流场大130倍才能达到相同的靠近速率。利用直流场和交流场中颗粒协同运动的定性和定量差异，应该能够通过在这两种模式之间交替来重新定位颗粒。我们证明了同一对颗粒可以在低频（100或200 Hz）下聚集在一起，然后在高频（1000 Hz）下分开。
