The results of a study that helps understand the mechanisms of adsorption of polyelectrolytes on
... more The results of a study that helps understand the mechanisms of adsorption of polyelectrolytes on particles, using numerical simulation methods, specifically the one known as dissipative particle dynamics are reported here. The adsorption of cationic polyelectrolytes of two different polymerisation degrees interacting with two types of surfaces, one made of gold and the other of silica, is predicted and compared. We find that a more negatively charged wall does not necessarily adsorb more cationic polyelectrolytes because the electrostatic repulsion between thewall and the polyelectrolytes is stronger. Additionally, intra-chain repulsion plays an important role, because the largest polyelectrolyte chains have larger excluded volume than the shorter ones. In regard to the adsorption dependence on the polyelectrolyte polymerisation degree, we find that the excluded volume drives the adsorption throughout the intra-chain electrostatic repulsion, because the SiO2 surface is strongly negative. These results are expected to be useful for several nanotechnological applications of current interest, such as in gene therapy and in the improvement of drug delivering mechanisms.
The results of a study that helps understand the mechanisms of adsorption of polyelectrolytes on ... more The results of a study that helps understand the mechanisms of adsorption of polyelectrolytes on particles, using numerical simulation methods, specifically the one known as dissipative particle dynamics are reported here. The adsorption of cationic polyelectrolytes of two different polymerization degrees interacting with two types of surfaces, one made of gold and the other of silica is predicted and compared. We find that a more negatively charged wall does not necessarily adsorb more cationic polyelectrolytes because the electrostatic repulsion between the wall and the polyelectrolytes is stronger. Additionally, intra chain repulsion plays an important role, because the largest polyelectrolyte chains have larger excluded volume than the shorter ones. In regard to the adsorption dependence on the polyelectrolyte polymerization degree we find that the excluded volume drives the adsorption throughout the intra–chain electrostatic repulsion, because the SiO2 surface is strongly negative. These results are expected to be useful for several nanotechnological applications of current interest, such as in gene therapy and in the improvement of drug delivering mechanisms.
There is ample evidence that polymer brushes reduce friction between surfaces. Several industrial... more There is ample evidence that polymer brushes reduce friction between surfaces. Several industrial applications take advantage of this fact, such as those in plastic bag production, where the brushes act as slip agents; however, the complex mechanisms that give rise to such reduction of friction are not yet fully understood. In this work we report coarse grained, dissipative particle dynamics simulations carried out for surfaces functionalized with erukamide brushes, a polymer commonly used in the plastics industry as a slip agent between surfaces. We calculate their rheological properties, such as the coefficient of friction (COF) and the viscosity, η, as functions of the number of chains grafted on the surfaces under the influence of stationary, Couette flow. Moreover, we consider also the case when a fraction of the erukamide chains is not adsorbed and moves freely between the surfaces. We show that the COF reaches an equilibrium value of about 0.29 in these two cases, in agreement with experimental results. On other hand, the viscosity grows monotonically, as a result of the increasing collisions when the erukamide content is increased. The force between brushes is found to be in agreement with predictions from scaling theories. We find that the addition to free chains helps stabilize the film formed by the brushes and the solvent, as others have found experimentally. The mechanisms that give rise to these phenomena are studied in detail.
This is a presentation make by Aislinn Dewey, to promote the use of economic readers for student... more This is a presentation make by Aislinn Dewey, to promote the use of economic readers for students in poor places.
We review briefly the concept of colloidal dispersions, their general properties, and some of the... more We review briefly the concept of colloidal dispersions, their general properties, and some of their most important applications,
as well as the basic molecular interactions that give rise to their properties in equilibrium. Similarly, we revisit Brownian motion
and hydrodynamic interactions associated with the concept of viscosity of colloidal dispersion. It is argued that the use of modern
research tools, such as computer simulations, allows one to predict accurately some macroscopically measurable properties by
solving relatively simple models of molecular interactions for a large number of particles. Lastly, as a case study, we report the
prediction of rheological properties of polymer brushes using state-of-the-art, coarse-grained computer simulations, which are in
excellent agreement with experiments.
Discrete potentials can describe properly the liquid vapor boundary that is necessary to
model th... more Discrete potentials can describe properly the liquid vapor boundary that is necessary to model the adsorption of gas molecules in mesoporous systems with computer simulations. Although there are some works in this subject, the simulations are still highly time - consuming. Here we show that an efficient alternative is to use the three - dimensional Ising model, which allows one to model large systems, with geometries as complex as required that accurately represent the liquid vapor boundary. In particular, we report molecular simulations of cylindrical pores of two different geometry, using a discrete potential. The effect of the length of the pore in the hysteresis loop for a finite pore and infinite one is studied in detail. Lastly, we compare our predictions with experimental results and find excellent agreement between the area of the hysteresis loop predicted for the finite pore and that found in adsorption/desorption experiments. Read it http://www.tandfonline.com/doi/full/10.1080/00268976.2015.1070927 … 'Importance of pore length and geometry in the adsorption/desorption process' @tandfmaths
he connection between fundamental interactions acting in molecules in a fluid and macroscopically... more he connection between fundamental interactions acting in molecules in a fluid and macroscopically measured properties, such as the viscosity between colloidal particles coated with polymers, is studied here. The role that hydrodynamic and Brownian forces play in colloidal dispersions is also discussed. It is argued that many – body systems in which all these interactions take place can be accurately solved using computational simulation tools. One of those modern tools is the technique known as dissipative particle dynamics, which incorporates Brownian and hydrodynamic forces, as well as basic conservative interactions. A case study is reported, as an example of the applications of this technique, which consists of the prediction of the viscosity and friction between two opposing parallel surfaces covered with polymer chains, under the influence of a steady flow. This work is intended to serve as an introduction to the subject of colloidal dispersions and computer simulations, for last – year undergraduate students and beginning graduate students who are interested in beginning research in soft matter systems. To that end, a computational code is included that students can use right away to study complex fluids in equilibrium.
In this work, nitrogen adsorption and desorption onto solid
surfaces were studied using computer... more In this work, nitrogen adsorption and desorption onto solid
surfaces were studied 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 it was found that its characteristics are dependent on the
geometry of the pore and on the strength of the surface–fluid interaction. We
also obtained 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 shape of the pores. A comparison of
the results of this study with experimental data is also made. In addition, we
report the filling 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.
Este es un panorama general de las aplicaciones que se pueden hacer en un computador usando un pr... more Este es un panorama general de las aplicaciones que se pueden hacer en un computador usando un procesador grafico y Gromacs. Se presentan resultados de interes general de como la APOA se expande y contrae cuando modificamos la concentracion salina.
This work is aimed at the study of liquid-liquid equilibrium of systems of industrial interest, p... more This work is aimed at the study of liquid-liquid equilibrium of systems of industrial interest, particularly the purification of oil and gas in the oil refining industry. We present experimental results on the solubility of aromatics in the liquid-liquid equilibrium obtained by gas -liquid chromatography at different temperatures. We used a mixture of solvents to improve the characteristics of selectivity and aromatics extraction. The solvent is a binary mixture of N-methyl 2-pyrrolidone (NMP) and diethylene glycol (DEG). The results presented are for two mixtures consisting of 90% NMP + 10% DEG, and 70% NMP +30% DEG. Heptane was used as hydrocarbon solvent and toluene as aromatic compound. Furthermore, we applied the equation of state NRTL (Non Random Two Liquids) and UNIQUAC (Universal Quasi Chemical) for coexistence curves and the critical point.
The role of viscous forces coupled with Brownian forces in momentum
conserving computer simulatio... more The role of viscous forces coupled with Brownian forces in momentum conserving computer simulations is studied here in the context of their contribution to the total average pressure of a simple fluid as derived from the virial theorem, in comparison with the contribution of the conservative force to the total pressure. The specific mesoscopic model used is the one known as dissipative particle dynamics, although our conclusions apply to similar models that obey the fluctuation dissipation theorem for short range interactions and have velocity dependent viscous forces. We find that the average contribution of the random and dissipative forces to the pressure is negligible for long simulations, provided these forces are appropriately coupled and when the finite time step used in the integration of the equation of motion is not too small. Finally, we study the properties of the fluid when the random force is made equal to zero and find that the system freezes as a result of the competition of the dissipative and conservative forces.
The folding of the cholesterol trapping apolipoprotein A1 in aqueous solution at increasing ionic... more The folding of the cholesterol trapping apolipoprotein A1 in aqueous solution at increasing ionic strength is studied using atomically detailed molecular dynamics simulations.
The solvation pressures arising from the confinement of a fluid by surfaces are calculated under ... more The solvation pressures arising from the confinement of a fluid by surfaces are calculated under two different thermodynamic conditions, namely at constant density and at constant chemical potential, through mesoscopic scale simulations. We consider two types of fluids, a model monomeric solvent on the one hand, and a fluid composed of linear polymers dissolved in a monomeric solvent, on the other. For these systems our simulations show that the prediction of the solvation (or disjoining) pressure when the chemical potential is kept fixed is different from that obtained when the total density is fixed. We find however, that the same trend between both types of simulations can be obtained when the value of the fixed density is chosen as the average value of the density obtained at constant chemical potential.
The solvation pressures arising from the confinement of a fluid by surfaces are calculated under ... more The solvation pressures arising from the confinement of a fluid by surfaces are calculated under two different thermodynamic conditions, namely at constant density and at constant chemical potential, through mesoscopic scale simulations. We consider two types of fluids, a model monomeric solvent on the one hand, and a fluid composed of linear polymers dissolved in a monomeric solvent, on the other. For these systems our simulations show that the prediction of the solvation (or disjoining) pressure when the chemical potential is kept fixed is different from that obtained when the total density is fixed. We find however, that the same trend between both types of simulations can be obtained when the value of the fixed density is chosen as the average value of the density obtained at constant chemical potential.
Dimorphic pore substrates (i.e. mesoporous solids made of separated grains of cylindrical and sp... more Dimorphic pore substrates (i.e. mesoporous solids made of separated grains of cylindrical and spherical void entities) have been recently synthesized. This type of adsorbent possesses special properties highly appreciated in separation processes due to their bimodal pore size distribution. The simulation of these intricate structures sets a difficult problem with current Molecular methods such as Monte Carlo and Molecular Dynamics. Besides the computational effort it is difficult to formulate a general framework predicting the experimental conditions and the chemical variables conducting to different types of structures. In this work we present simulated results based on the use of a lattice model known as the Dual Site-Bond Model. We sacrifice microscopic structure details in order to build a basic conceptual support to characterize and describe the different kinds of possible textures of these complex pore solids. Our aims is to express in a clear way how different spatial arrangements of connected cavities and necks can describe the basic textural aspects that lead to interesting sorption properties of these complex solid substrata.
The results of a study that helps understand the mechanisms of adsorption of polyelectrolytes on
... more The results of a study that helps understand the mechanisms of adsorption of polyelectrolytes on particles, using numerical simulation methods, specifically the one known as dissipative particle dynamics are reported here. The adsorption of cationic polyelectrolytes of two different polymerisation degrees interacting with two types of surfaces, one made of gold and the other of silica, is predicted and compared. We find that a more negatively charged wall does not necessarily adsorb more cationic polyelectrolytes because the electrostatic repulsion between thewall and the polyelectrolytes is stronger. Additionally, intra-chain repulsion plays an important role, because the largest polyelectrolyte chains have larger excluded volume than the shorter ones. In regard to the adsorption dependence on the polyelectrolyte polymerisation degree, we find that the excluded volume drives the adsorption throughout the intra-chain electrostatic repulsion, because the SiO2 surface is strongly negative. These results are expected to be useful for several nanotechnological applications of current interest, such as in gene therapy and in the improvement of drug delivering mechanisms.
The results of a study that helps understand the mechanisms of adsorption of polyelectrolytes on ... more The results of a study that helps understand the mechanisms of adsorption of polyelectrolytes on particles, using numerical simulation methods, specifically the one known as dissipative particle dynamics are reported here. The adsorption of cationic polyelectrolytes of two different polymerization degrees interacting with two types of surfaces, one made of gold and the other of silica is predicted and compared. We find that a more negatively charged wall does not necessarily adsorb more cationic polyelectrolytes because the electrostatic repulsion between the wall and the polyelectrolytes is stronger. Additionally, intra chain repulsion plays an important role, because the largest polyelectrolyte chains have larger excluded volume than the shorter ones. In regard to the adsorption dependence on the polyelectrolyte polymerization degree we find that the excluded volume drives the adsorption throughout the intra–chain electrostatic repulsion, because the SiO2 surface is strongly negative. These results are expected to be useful for several nanotechnological applications of current interest, such as in gene therapy and in the improvement of drug delivering mechanisms.
There is ample evidence that polymer brushes reduce friction between surfaces. Several industrial... more There is ample evidence that polymer brushes reduce friction between surfaces. Several industrial applications take advantage of this fact, such as those in plastic bag production, where the brushes act as slip agents; however, the complex mechanisms that give rise to such reduction of friction are not yet fully understood. In this work we report coarse grained, dissipative particle dynamics simulations carried out for surfaces functionalized with erukamide brushes, a polymer commonly used in the plastics industry as a slip agent between surfaces. We calculate their rheological properties, such as the coefficient of friction (COF) and the viscosity, η, as functions of the number of chains grafted on the surfaces under the influence of stationary, Couette flow. Moreover, we consider also the case when a fraction of the erukamide chains is not adsorbed and moves freely between the surfaces. We show that the COF reaches an equilibrium value of about 0.29 in these two cases, in agreement with experimental results. On other hand, the viscosity grows monotonically, as a result of the increasing collisions when the erukamide content is increased. The force between brushes is found to be in agreement with predictions from scaling theories. We find that the addition to free chains helps stabilize the film formed by the brushes and the solvent, as others have found experimentally. The mechanisms that give rise to these phenomena are studied in detail.
This is a presentation make by Aislinn Dewey, to promote the use of economic readers for student... more This is a presentation make by Aislinn Dewey, to promote the use of economic readers for students in poor places.
We review briefly the concept of colloidal dispersions, their general properties, and some of the... more We review briefly the concept of colloidal dispersions, their general properties, and some of their most important applications,
as well as the basic molecular interactions that give rise to their properties in equilibrium. Similarly, we revisit Brownian motion
and hydrodynamic interactions associated with the concept of viscosity of colloidal dispersion. It is argued that the use of modern
research tools, such as computer simulations, allows one to predict accurately some macroscopically measurable properties by
solving relatively simple models of molecular interactions for a large number of particles. Lastly, as a case study, we report the
prediction of rheological properties of polymer brushes using state-of-the-art, coarse-grained computer simulations, which are in
excellent agreement with experiments.
Discrete potentials can describe properly the liquid vapor boundary that is necessary to
model th... more Discrete potentials can describe properly the liquid vapor boundary that is necessary to model the adsorption of gas molecules in mesoporous systems with computer simulations. Although there are some works in this subject, the simulations are still highly time - consuming. Here we show that an efficient alternative is to use the three - dimensional Ising model, which allows one to model large systems, with geometries as complex as required that accurately represent the liquid vapor boundary. In particular, we report molecular simulations of cylindrical pores of two different geometry, using a discrete potential. The effect of the length of the pore in the hysteresis loop for a finite pore and infinite one is studied in detail. Lastly, we compare our predictions with experimental results and find excellent agreement between the area of the hysteresis loop predicted for the finite pore and that found in adsorption/desorption experiments. Read it http://www.tandfonline.com/doi/full/10.1080/00268976.2015.1070927 … 'Importance of pore length and geometry in the adsorption/desorption process' @tandfmaths
he connection between fundamental interactions acting in molecules in a fluid and macroscopically... more he connection between fundamental interactions acting in molecules in a fluid and macroscopically measured properties, such as the viscosity between colloidal particles coated with polymers, is studied here. The role that hydrodynamic and Brownian forces play in colloidal dispersions is also discussed. It is argued that many – body systems in which all these interactions take place can be accurately solved using computational simulation tools. One of those modern tools is the technique known as dissipative particle dynamics, which incorporates Brownian and hydrodynamic forces, as well as basic conservative interactions. A case study is reported, as an example of the applications of this technique, which consists of the prediction of the viscosity and friction between two opposing parallel surfaces covered with polymer chains, under the influence of a steady flow. This work is intended to serve as an introduction to the subject of colloidal dispersions and computer simulations, for last – year undergraduate students and beginning graduate students who are interested in beginning research in soft matter systems. To that end, a computational code is included that students can use right away to study complex fluids in equilibrium.
In this work, nitrogen adsorption and desorption onto solid
surfaces were studied using computer... more In this work, nitrogen adsorption and desorption onto solid
surfaces were studied 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 it was found that its characteristics are dependent on the
geometry of the pore and on the strength of the surface–fluid interaction. We
also obtained 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 shape of the pores. A comparison of
the results of this study with experimental data is also made. In addition, we
report the filling 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.
Este es un panorama general de las aplicaciones que se pueden hacer en un computador usando un pr... more Este es un panorama general de las aplicaciones que se pueden hacer en un computador usando un procesador grafico y Gromacs. Se presentan resultados de interes general de como la APOA se expande y contrae cuando modificamos la concentracion salina.
This work is aimed at the study of liquid-liquid equilibrium of systems of industrial interest, p... more This work is aimed at the study of liquid-liquid equilibrium of systems of industrial interest, particularly the purification of oil and gas in the oil refining industry. We present experimental results on the solubility of aromatics in the liquid-liquid equilibrium obtained by gas -liquid chromatography at different temperatures. We used a mixture of solvents to improve the characteristics of selectivity and aromatics extraction. The solvent is a binary mixture of N-methyl 2-pyrrolidone (NMP) and diethylene glycol (DEG). The results presented are for two mixtures consisting of 90% NMP + 10% DEG, and 70% NMP +30% DEG. Heptane was used as hydrocarbon solvent and toluene as aromatic compound. Furthermore, we applied the equation of state NRTL (Non Random Two Liquids) and UNIQUAC (Universal Quasi Chemical) for coexistence curves and the critical point.
The role of viscous forces coupled with Brownian forces in momentum
conserving computer simulatio... more The role of viscous forces coupled with Brownian forces in momentum conserving computer simulations is studied here in the context of their contribution to the total average pressure of a simple fluid as derived from the virial theorem, in comparison with the contribution of the conservative force to the total pressure. The specific mesoscopic model used is the one known as dissipative particle dynamics, although our conclusions apply to similar models that obey the fluctuation dissipation theorem for short range interactions and have velocity dependent viscous forces. We find that the average contribution of the random and dissipative forces to the pressure is negligible for long simulations, provided these forces are appropriately coupled and when the finite time step used in the integration of the equation of motion is not too small. Finally, we study the properties of the fluid when the random force is made equal to zero and find that the system freezes as a result of the competition of the dissipative and conservative forces.
The folding of the cholesterol trapping apolipoprotein A1 in aqueous solution at increasing ionic... more The folding of the cholesterol trapping apolipoprotein A1 in aqueous solution at increasing ionic strength is studied using atomically detailed molecular dynamics simulations.
The solvation pressures arising from the confinement of a fluid by surfaces are calculated under ... more The solvation pressures arising from the confinement of a fluid by surfaces are calculated under two different thermodynamic conditions, namely at constant density and at constant chemical potential, through mesoscopic scale simulations. We consider two types of fluids, a model monomeric solvent on the one hand, and a fluid composed of linear polymers dissolved in a monomeric solvent, on the other. For these systems our simulations show that the prediction of the solvation (or disjoining) pressure when the chemical potential is kept fixed is different from that obtained when the total density is fixed. We find however, that the same trend between both types of simulations can be obtained when the value of the fixed density is chosen as the average value of the density obtained at constant chemical potential.
The solvation pressures arising from the confinement of a fluid by surfaces are calculated under ... more The solvation pressures arising from the confinement of a fluid by surfaces are calculated under two different thermodynamic conditions, namely at constant density and at constant chemical potential, through mesoscopic scale simulations. We consider two types of fluids, a model monomeric solvent on the one hand, and a fluid composed of linear polymers dissolved in a monomeric solvent, on the other. For these systems our simulations show that the prediction of the solvation (or disjoining) pressure when the chemical potential is kept fixed is different from that obtained when the total density is fixed. We find however, that the same trend between both types of simulations can be obtained when the value of the fixed density is chosen as the average value of the density obtained at constant chemical potential.
Dimorphic pore substrates (i.e. mesoporous solids made of separated grains of cylindrical and sp... more Dimorphic pore substrates (i.e. mesoporous solids made of separated grains of cylindrical and spherical void entities) have been recently synthesized. This type of adsorbent possesses special properties highly appreciated in separation processes due to their bimodal pore size distribution. The simulation of these intricate structures sets a difficult problem with current Molecular methods such as Monte Carlo and Molecular Dynamics. Besides the computational effort it is difficult to formulate a general framework predicting the experimental conditions and the chemical variables conducting to different types of structures. In this work we present simulated results based on the use of a lattice model known as the Dual Site-Bond Model. We sacrifice microscopic structure details in order to build a basic conceptual support to characterize and describe the different kinds of possible textures of these complex pore solids. Our aims is to express in a clear way how different spatial arrangements of connected cavities and necks can describe the basic textural aspects that lead to interesting sorption properties of these complex solid substrata.
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particles, using numerical simulation methods, specifically the one known as dissipative particle
dynamics are reported here. The adsorption of cationic polyelectrolytes of two different polymerisation
degrees interacting with two types of surfaces, one made of gold and the other of silica, is
predicted and compared. We find that a more negatively charged wall does not necessarily adsorb
more cationic polyelectrolytes because the electrostatic repulsion between thewall and the polyelectrolytes
is stronger. Additionally, intra-chain repulsion plays an important role, because the largest
polyelectrolyte chains have larger excluded volume than the shorter ones. In regard to the adsorption
dependence on the polyelectrolyte polymerisation degree, we find that the excluded volume
drives the adsorption throughout the intra-chain electrostatic repulsion, because the SiO2 surface is
strongly negative. These results are expected to be useful for several nanotechnological applications
of current interest, such as in gene therapy and in the improvement of drug delivering mechanisms.
as well as the basic molecular interactions that give rise to their properties in equilibrium. Similarly, we revisit Brownian motion
and hydrodynamic interactions associated with the concept of viscosity of colloidal dispersion. It is argued that the use of modern
research tools, such as computer simulations, allows one to predict accurately some macroscopically measurable properties by
solving relatively simple models of molecular interactions for a large number of particles. Lastly, as a case study, we report the
prediction of rheological properties of polymer brushes using state-of-the-art, coarse-grained computer simulations, which are in
excellent agreement with experiments.
model the adsorption of gas molecules in mesoporous systems with computer simulations.
Although there are some works in this subject, the simulations are still highly time -
consuming. Here we show that an efficient alternative is to use the three - dimensional Ising
model, which allows one to model large systems, with geometries as complex as required
that accurately represent the liquid vapor boundary. In particular, we report molecular
simulations of cylindrical pores of two different geometry, using a discrete potential. The
effect of the length of the pore in the hysteresis loop for a finite pore and infinite one is
studied in detail. Lastly, we compare our predictions with experimental results and find
excellent agreement between the area of the hysteresis loop predicted for the finite pore and
that found in adsorption/desorption experiments.
Read it http://www.tandfonline.com/doi/full/10.1080/00268976.2015.1070927 … 'Importance of pore length and geometry in the adsorption/desorption process' @tandfmaths
ON THE COMPUTATIONAL MODELING OF THE VISCOSITY OF COLLOIDAL DISPERSIONS AND ITS RELATION WITH BASIC MOLECULAR INTERACTIONS. Available from: https://www.researchgate.net/publication/278668932_ON_THE_COMPUTATIONAL_MODELING_OF_THE_VISCOSITY_OF_COLLOIDAL_DISPERSIONS_AND_ITS_RELATION_WITH_BASIC_MOLECULAR_INTERACTIONS [accessed Jun 18, 2015].
surfaces were studied 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 it was found that its characteristics are dependent on the
geometry of the pore and on the strength of the surface–fluid interaction. We
also obtained 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 shape of the pores. A comparison of
the results of this study with experimental data is also made. In addition, we
report the filling 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.
conserving computer simulations is studied here in the context of their
contribution to the total average pressure of a simple fluid as derived from
the virial theorem, in comparison with the contribution of the conservative
force to the total pressure. The specific mesoscopic model used is the one
known as dissipative particle dynamics, although our conclusions apply to
similar models that obey the fluctuation dissipation theorem for short range
interactions and have velocity dependent viscous forces. We find that the
average contribution of the random and dissipative forces to the pressure is
negligible for long simulations, provided these forces are appropriately
coupled and when the finite time step used in the integration of the equation
of motion is not too small. Finally, we study the properties of the fluid when
the random force is made equal to zero and find that the system freezes as a
result of the competition of the dissipative and conservative forces.
particles, using numerical simulation methods, specifically the one known as dissipative particle
dynamics are reported here. The adsorption of cationic polyelectrolytes of two different polymerisation
degrees interacting with two types of surfaces, one made of gold and the other of silica, is
predicted and compared. We find that a more negatively charged wall does not necessarily adsorb
more cationic polyelectrolytes because the electrostatic repulsion between thewall and the polyelectrolytes
is stronger. Additionally, intra-chain repulsion plays an important role, because the largest
polyelectrolyte chains have larger excluded volume than the shorter ones. In regard to the adsorption
dependence on the polyelectrolyte polymerisation degree, we find that the excluded volume
drives the adsorption throughout the intra-chain electrostatic repulsion, because the SiO2 surface is
strongly negative. These results are expected to be useful for several nanotechnological applications
of current interest, such as in gene therapy and in the improvement of drug delivering mechanisms.
as well as the basic molecular interactions that give rise to their properties in equilibrium. Similarly, we revisit Brownian motion
and hydrodynamic interactions associated with the concept of viscosity of colloidal dispersion. It is argued that the use of modern
research tools, such as computer simulations, allows one to predict accurately some macroscopically measurable properties by
solving relatively simple models of molecular interactions for a large number of particles. Lastly, as a case study, we report the
prediction of rheological properties of polymer brushes using state-of-the-art, coarse-grained computer simulations, which are in
excellent agreement with experiments.
model the adsorption of gas molecules in mesoporous systems with computer simulations.
Although there are some works in this subject, the simulations are still highly time -
consuming. Here we show that an efficient alternative is to use the three - dimensional Ising
model, which allows one to model large systems, with geometries as complex as required
that accurately represent the liquid vapor boundary. In particular, we report molecular
simulations of cylindrical pores of two different geometry, using a discrete potential. The
effect of the length of the pore in the hysteresis loop for a finite pore and infinite one is
studied in detail. Lastly, we compare our predictions with experimental results and find
excellent agreement between the area of the hysteresis loop predicted for the finite pore and
that found in adsorption/desorption experiments.
Read it http://www.tandfonline.com/doi/full/10.1080/00268976.2015.1070927 … 'Importance of pore length and geometry in the adsorption/desorption process' @tandfmaths
ON THE COMPUTATIONAL MODELING OF THE VISCOSITY OF COLLOIDAL DISPERSIONS AND ITS RELATION WITH BASIC MOLECULAR INTERACTIONS. Available from: https://www.researchgate.net/publication/278668932_ON_THE_COMPUTATIONAL_MODELING_OF_THE_VISCOSITY_OF_COLLOIDAL_DISPERSIONS_AND_ITS_RELATION_WITH_BASIC_MOLECULAR_INTERACTIONS [accessed Jun 18, 2015].
surfaces were studied 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 it was found that its characteristics are dependent on the
geometry of the pore and on the strength of the surface–fluid interaction. We
also obtained 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 shape of the pores. A comparison of
the results of this study with experimental data is also made. In addition, we
report the filling 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.
conserving computer simulations is studied here in the context of their
contribution to the total average pressure of a simple fluid as derived from
the virial theorem, in comparison with the contribution of the conservative
force to the total pressure. The specific mesoscopic model used is the one
known as dissipative particle dynamics, although our conclusions apply to
similar models that obey the fluctuation dissipation theorem for short range
interactions and have velocity dependent viscous forces. We find that the
average contribution of the random and dissipative forces to the pressure is
negligible for long simulations, provided these forces are appropriately
coupled and when the finite time step used in the integration of the equation
of motion is not too small. Finally, we study the properties of the fluid when
the random force is made equal to zero and find that the system freezes as a
result of the competition of the dissipative and conservative forces.