Microstructures in Strongly Interacting Dipolar Fluids
XU Chen1,2, MA Yu-Qiang1, HUI Pak-Ming3, TONG Fu-Qiang2
1National Laboratory of Solid State Microstructures, Nanjing University, Naning 210093
2Department of Physics, Suzhou University, Suzhou 215006
3Department of Physics, The Chinese University of Hong Kong, Shatin, New Territories, Hong Kong
Microstructures in Strongly Interacting Dipolar Fluids
1National Laboratory of Solid State Microstructures, Nanjing University, Naning 210093
2Department of Physics, Suzhou University, Suzhou 215006
3Department of Physics, The Chinese University of Hong Kong, Shatin, New Territories, Hong Kong
Abstract： The formation of ring- and chain-like microstructures in ferrofluids consisting of interacting magnetic particles coated by a surfactant layer is studied by Monte Carlo simulations. For thin coating layers, it is found that ring- and chain-like structures coexist. The ring-like structures are suppressed by thicker coating layers. These observations are in agreement with recent experiments. Also, the ring-like structures are formed by dynamical aggregation of particles, instead of bending of linear chains. The latter process is forbidden by a substantial energy barrier. More generally, it is found that the ring structures exist when the parameter α=μ2 /[kBT (d+2δ)3] is higher than a critical value αc, where μ is the magnitude of magnetic moment, d is the diameter, and δ is the coating thickness of a particle. We find that when α<αc, the ring structures cannot be formed spontaneously, while the chain-like structures still exist. Furthermore, the critical value αc is almost independent of magnetic particle volume density in the low density range.
2005, Vol. 22 
