44 research outputs found
Topological Phase Transition in a Quasi Two Dimensional Coulomb Gas
A system with equal number of positive and negative charges confined in a box
with a small but finite thickness is modeled as a function of temperature using
mesoscale numerical simulations, for various values of the charges. The Coulomb
interaction is used in its three-dimensional form, U(r) ~ 1/r. A topological
phase transition is found in this quasi 2d system. The translational order
parameter, spatial correlation function, specific heat, and electric current
show qualitatively different trends below and above a critical temperature. We
find that a 2d logarithmic Coulomb interaction is not essential for the
appearance of this transition. This work suggests new experimental tests of our
predictions, as well as novel theoretical approaches to probe quasi 2d
topological phase transitions.Comment: 17 pages; 5 figure
Adsorption desorption processes on mesoscopic pores conected to microscopic pores of complex geometry using the Ising model
In this work we report studies of nitrogen adsorption and desorption onto
solid surfaces using computer simulations of the three dimensional Ising model,
for systems with complex porous structures at the mesoscopic and microscopic
levels. A hysteresis cycle between the adsorption and desorption processes
appears and we find that its characteristics are dependent on the geometry of
the pore and on the strength of the surface fluid interaction. We obtained also
an average adsorption isotherm, which represents a combination of differently
shaped pores, and shows robust jumps at certain values of the chemical
potential as a consequence of the structures of the pores. Lastly, we compare
our results with experimental data and also report the filling process of
microscopic pores connected with mesopores. It is argued that these predictions
are useful for researchers working on the enhanced recovery of oil and for the
design of new nanomaterials, among others
Desorption of hydrocarbon chains by association with ionic and nonionic surfactants under flow as a mechanism for enhanced oil recovery
The need to extract oil from wells where it is embedded on the surfaces of
rocks has led to the development of new and improved enhanced oil recovery
techniques. One of those is the injection of surfactants with water vapor,
which promotes desorption of oil that can then be extracted using pumps, as the
surfactants encapsulate the oil in foams. However, the mechanisms that lead to
the optimal desorption of oil and the best type of surfactants to carry out
desorption are not well known yet, which warrants the need to carry out basic
research on this topic. In this work, we report non equilibrium dissipative
particle dynamics simulations of model surfactants and oil molecules adsorbed
on surfaces, with the purpose of studying the efficiency of the surfactants to
desorb hydrocarbon chains, that are found adsorbed over flat surfaces. The
model surfactants studied correspond to nonionic and cationic surfactants, and
the hydrocarbon desorption is studied as a function of surfactant concentration
under increasing Poiseuille flow. We obtain various hydrocarbon desorption
isotherms for every model of surfactant proposed, under flow. Nonionic
surfactants are found to be the most effective to desorb oil and the mechanisms
that lead to this phenomenon are presented and discussed.Comment: 10 figures; to appear in Scientific Report