Experimental study on the fluctuations of dipolar chains - art. no. 011506

Dynamic light scattering is used to study experimentally the dynamics of di polar chains consisting of ferrofluid particles subjected to a magnetic fie ld (H-0). The effective diffusion coefficient shows a pronounced dependence on the scattering wave vector q, reflecting two modes of motion: translati onal diffusion of the whole chain, and fluctuations of particles within a c hain. The characteristic probed frequency of particle displacements is inve rsely proportional to H-0. and exhibits a q(3) dependency. Based on the str iking analogy to polymer chain dynamics, we attribute these behaviors to th e contribution of hydrodynamic interactions (HI's) that couples particles m otion within a chain. This work suggests that chain fluctuations cannot be ignored even for the very strong magnetic field applied (coupling constant< 10(6)). HI's can still be important, even at an extremely low particle volu me fraction of 10(-5).