Auto-organização de partículas patchy carregadas

Abstract

The present stage of development of experimental techniques allows the synthesis of complex colloidal particles whose surface can be precisely "decorated"with different physical and / or chemical properties (active sites). Such colloids are usually defined as patchy particles as a result of the modification of parts of the surface of such particles, the interaction between them is generally characterized by an anisotropic potential. Studying andunderstandingtheprocessofself-assemblyofthisparticularsystemisofgreatinterest bothfromascientificandtechnologicalpointofview,duetoitsuseinfunctionalmaterials. In this thesis, the behavior of a two-dimensional system of charged particles is studied, in which the surface is decorated punctually with a charge of sign opposite to that located in the center of the particle. Thus, each patchy particle has a net charge which is the result of the difference between the surface punctures (active sites) and that at the center of the patchy particle. Using the computational simulation technique of Molecular Dynamics, we study the process of self-assembly of patchy particles as a function of density, net charge, number of active sites, beyond the range of the pair interaction. Structures for different numbers of active sites and different net charge values are also presented in order to show the influence of these parameters in the system configuration. Crystalline structures made by monomers and agglomerates of various forms are observed depending on interaction parameters. In general, it is observed that for high values of net charge (positive or negative) and / or number of active sites, the repulsive potential prevails causing the system to stabilize in a crystalline configuration. Interestingly, due to the anisotropic potential, non-triangular crystalline structures are observed, a fact that is not possible in the case of two-dimensional systems with isotropic repulsive potential. On the other hand, in the case of particles with low net charge value and / or number of active sites, the resulting interaction potential is predominantly attractive, inducing structures composed of agglomerates in the form of rings and lines of particles. Structural phase diagrams are presented for different combinations of net charge, range of the interaction of pairs and number of active sites for several values of density of the system. The selfassembly structures in the case where there is confinement of charged patchy particles are presented. In addition, the possibility of asymmetry in the distribution of the active sites on the surface of the colloid (patchy particles) leads to a polarization of the particle creating different forms of bonding, which generate diverse self-assembly structures. The relation of the asymmetry of the particle with the percolation of the system is studied. In all cases studied, linear clusters, massive clusters and monomer crystals are observed for different combinations of system parameters, which can even be modified experimentally.