The cluster-cluster aggregation processes of Ising dipolar particles under thermal noise are investigated in the dilute condition. As the temperature increases, changes in the typical structures of clusters are observed from chainlike (D1) to crystalline (D2) through fractal structures (D1.45), where D is the fractal dimension. By calculating the bending energy of the chainlike structure, it is found that the transition temperature is associated with the energy gap between the chainlike and crystalline configurations. The aggregation dynamics changes from being dominated by attraction to diffusion involving changes in the dynamic exponent z=0.2 to 0.5. In the region of temperature where the fractal clusters grow, different growth rates are observed between charged and neutral clusters. Using the Smoluchowski equation with a twofold kernel, this hetero-aggregation process is found to result from two types of dynamics: the diffusive motion of neutral clusters and the weak attractive motion between charged clusters. The fact that changes in structures and dynamics take place at the same time suggests that transitions in the structure of clusters involve marked changes in the dynamics of the aggregation processes. © 2009 The American Physical Society.
Bibliographical noteKAUST Repository Item: Exported on 2020-10-01
Acknowledged KAUST grant number(s): KUK-I1-005-04
Acknowledgements: The authors thank T. Shimada and H. Watanabe for fruitful discussions. The present study was supported by the 21st COE program, "Frontiers of Computational Science," Nagoya University, and by Grants-in-Aid for Scientific Research (Contract No. 19340110) from the Ministry of Education, Culture, Sports, Science and Technology, and by KAUST GRP(KUK-I1-005-04). F. K. was supported by the Hungarian Academy of Sciences.
This publication acknowledges KAUST support, but has no KAUST affiliated authors.