Regime Diagram for diluted dipolar colloids

V.I. MARCONI; T.S. GRIGERA; D.A. MARTIN

San Luis

Congreso; XVII TREFEMAC; 2019

We present recent results on numerical simulations of Diluted Dipolar Spheres (DDS) in the NVTensemble [Martin, D. A. et al, ?Speeding up the study of diluted dipolar systems? Phys. Rev. E Vol. 99,022604, 2019]. We performed a Monte Carlo speed-up algorithm, "Cluster Move Monte Carlo"(CMMC). Our system of strongly interacting dipolar particles tend to self-organize into intrincatedstructures. We found and characterized several regimes.CMMC combines typical single particle rotation and translation with movements of particle groups, insuch a way that detailed balance is preserved. The algorithm is easy to implement and it speeds-upsimulations by a factor 10 to 100 (compared to traditional Monte Carlo), depending on density andtemperature. It is also faster than other speed-up algorithms. It is efficient for truncated potentials butalso when Ewald sums are used. It may be useful for other, related, on-lattice and off-lattice systems.With the aid of CMMC, we study a set of positional, orientational, and thermodynamical observables, asa function of temperature and density. We draw a regime diagram including simple-fluid, chain-fluid,ring-fluid, gel, and antiparallel columnar regimes.The study of DDS is relevant from the theoretical point of view, but can also be related to systems oftechnological interest, such as magnetic dipolar nanoparticles, for which, several applications havebeen proposed [W. Zhang, ?Nanoscale iron particles for environmental remediation: An overview?, J.Nanopart. Res. Vol. 5, 323, 2003]. Nowadays, nanoparticles with large dipolar moments, comparablewith the ones studied here, can be synthesized [Q. Li et. al., ?Correlation between particle size/domainstructure and magnetic properties of highly crystalline Fe_3O_4 nanoparticles?, Sci. Rep. Vol. 7, 9894,2017]. We mention briefly how our results can be related to reliable applications.