We perform extensive molecular dynamics simulations to study the mass size distribution of a two-... more We perform extensive molecular dynamics simulations to study the mass size distribution of a two-dimensional fragmentation process. Our model consists of a large number of particles interacting through the Lennard–Jones potential. The fragmentation is induced by suddenly imposing a radial component on the particles' velocities, in order to mimic an explosion phenomenon. We then investigate the effect of the input energy on the resulting mass distribution of fragments.
We perform extensive molecular dynamics simulations to study the mass size distribution of a two-... more We perform extensive molecular dynamics simulations to study the mass size distribution of a two-dimensional fragmentation process. Our model consists of a large number of particles interacting through the Lennard–Jones potential. The fragmentation is induced by suddenly imposing a radial component on the particles' velocities, in order to mimic an explosion phenomenon. We then investigate the effect of the input energy on the resulting mass distribution of fragments.
Availability of highly reactive halogen ions at the surface of aerosols has tremendous implicatio... more Availability of highly reactive halogen ions at the surface of aerosols has tremendous implications for the atmospheric chemistry. Yet neither simulations, experiments, nor existing theories are able to provide a fully consistent description of the electrolyte-air interface. In this paper a new theory is proposed which allows us to explicitly calculate the ionic density profiles, the surface tension, and the electrostatic potential difference across the solution-air interface. Predictions of the theory are compared to experiments and are found to be in excellent agreement. The theory also sheds new light on one of the oldest puzzles of physical chemistry -- the Hofmeister effect.
To explore charge regulation (CR) in physicochemical and biophysical systems, we present a model ... more To explore charge regulation (CR) in physicochemical and biophysical systems, we present a model of colloidal particles with sticky adsorption sites which account for the formation of covalent bonds between the hydronium ions and the surface functional groups. Using this model and Monte Carlo simulations, we find that the standard Ninham and Parsegian (NP) theory of CR leads to results which deviate significantly from computer simulations. The problem of NP approach is traced back to the use of bulk equilibrium constant to account for surface chemical reactions. To resolve this difficulty we present a new theory of CR. The fundamental ingredient of the new approach is the sticky length, which is non-trivially related with the bulk equilibrium constant. The theory is found to be in excellent agreement with computer simulations, without any adjustable parameters. As an application of the theory we calculate the effective charge of colloidal particles containing carboxyl groups, as a function of pH and salt concentration. Electrostatic interactions play a fundamental role in physics, chemistry, and biology. The long-range nature of the Coulomb force, however, makes it very difficult to study theoretically 1. In aqueous systems ions are usually hydrated by water molecules. On the other hand, acids lose proton, which associates with the water molecule forming a hydronium ion 2. There are many reactions that are controlled by pH, and the acid-base equilibrium directly influences the functionality of biomolecules. Although pH can be easily tuned in experiments, it is much more difficult to account for the chemical equilibrium in theoretical and simulation studies 3. Colloidal particles often have organic functional groups on their surfaces. In aqueous systems these groups dissociate, loosing a proton, resulting in a colloidal surface charge 4-7. The amount of surface charge strongly depends on the pH of the environment 8,9 and is controlled by the chemical equilibrium between hydronium ions and the functional groups. This process is known as charge regulation (CR) 10-16. The concept of charge regulation was first described by Linderstrøm-Lang 17-19 and studied theoretically by Ninham and Parsegian. 20. CR is of fundamental importance in colloidal science 10,21-32 and biophysics 33-39. It has been applied to explore the stability of electrical double layers 9,40-45 and is of great technological importance in fields as diverse as mineral preparation, agriculture, ceramics, and surface coating 46. Consider a weak acid HA in equilibrium with bulk water, HA+H 2 O ⇄ H 3 O + +A-. For dilute solutions the concentration of all species is controlled by the law of mass a) Electronic mail:
We investigate the adsorption of neutral polyampholytes on charged nanopatterned surfaces. The su... more We investigate the adsorption of neutral polyampholytes on charged nanopatterned surfaces. The surfaces have charged domains but are overall neutral. To perform efficient simulations, we use an approach which combines the explicit form of the interaction potential between the polyampholyte monomers and the surface with a 3d Ewald summation method. We observe that the amount of adsorption and the structure of the adsorbed polyampholytes depend strongly on the surface pattern, the relative size of the surface domains, and the charge distribution along the polyampholyte backbone.
Physica A: Statistical Mechanics and its Applications
A melting transition for a system of hard spheres interacting by a repulsive Yukawa potential of ... more A melting transition for a system of hard spheres interacting by a repulsive Yukawa potential of DLVO form is studied. To find the location of the phase boundary, we propose a simple theory to calculate the free energies for the coexisting liquid and solid. The free energy for the liquid phase is approximated by a virial expansion. The free energy of the crystalline phase is calculated in the spirit of the Lenard-Jonnes and Devonshire (LJD) theory. The phase boundary is found by equating the pressures and chemical potentials of the coexisting phases. When the approximation leading to the equation of state for the liquid breakes down, the first order transition line is also obtained by applying the Lindemann criterion to the solid phase. Our results are then compared with the Monte Carlo simulations.
We present theory and simulations which allow us to quantitatively calculate the amount of surfac... more We present theory and simulations which allow us to quantitatively calculate the amount of surface adsorption excess of charged nanoparticles to a charged surface. The theory is very accurate for weakly charged nanoparticles and can be used at physiological concentrations of salt. We have also developed an efficient simulation algorithm which can be used for dilute suspensions of nanoparticles of any charge, even at very large salt concentrations. With the help of the new simulation method, we are able to efficiently calculate the adsorption isotherms of highly charged nanoparticles in suspensions containing multivalent ions, for which there are no accurate theoretical methods available.
The phase behavior of the lattice restricted primitive model (RPM) for ionic systems with additio... more The phase behavior of the lattice restricted primitive model (RPM) for ionic systems with additional short-range nearest neighbor (nn) repulsive interactions has been studied by grand canonical Monte Carlo simulations. We obtain a rich phase behavior as the nn strength is varied. In particular, the phase diagram is very similar to the continuum RPM model for high nn strength. Specifically, we have found both gas-liquid phase separation, with associated Ising critical point, and first-order liquid-solid transition. We discuss how the line of continuous order-disorder transitions present for the low nn strength changes into the continuum-space behavior as one increases the nn strength and compare our findings with recent theoretical results by Ciach and Stell [Phys. Rev. Lett. {\bf 91}, 060601 (2003)].
Following the suggestion in the Comment on our previous work by Åström, Linna, and Timonen [Phys.... more Following the suggestion in the Comment on our previous work by Åström, Linna, and Timonen [Phys. Rev. E 65, 048101 (2002)], we performed extensive molecular-dynamics simulations to confirm that our numerical results for the mass distribution of fragments after the ``explosion'' of thermalized samples are consistent with the scaling form n(m)~m-(alpha+1)f(m/M0), where f(m/M0) is a cutoff function, M0 is a
We study, using Monte Carlo simulations, the interaction between infinite heterogeneously charged... more We study, using Monte Carlo simulations, the interaction between infinite heterogeneously charged surfaces inside an electrolyte solution. The surfaces are overall neutral with quenched charged domains. An average over the quenched disorder is performed to obtain the net force. We find that the interaction between the surfaces is repulsive at short distances and is attractive for larger separations.
Physical review. E, Statistical, nonlinear, and soft matter physics, 2012
We introduce an implicit solvent Molecular Dynamics approach for calculating ionic fluxes through... more We introduce an implicit solvent Molecular Dynamics approach for calculating ionic fluxes through narrow nanopores and transmembrane channels. The method relies on a dual-control-volume grand-canonical molecular dynamics (DCV-GCMD) simulation and the analytical solution for the electrostatic potential inside a cylindrical nanopore recently obtained by Levin [Europhys. Lett. 76, 163 (2006)]. The theory is used to calculate the ionic fluxes through an artificial transmembrane channel which mimics the antibacterial gramicidin A channel. Both current-voltage and current-concentration relations are calculated under various experimental conditions. We show that our results are comparable to the characteristics associated to the gramicidin A pore, especially the existence of two binding sites inside the pore and the observed saturation in the current-concentration profiles.
Physical review. E, Statistical, nonlinear, and soft matter physics, 2001
A simple model is presented for the appearance of attraction between two like-charged polyions in... more A simple model is presented for the appearance of attraction between two like-charged polyions inside a polyelectrolyte solution. The polyions are modeled as rigid cylinders in a continuum dielectric solvent. The strong electrostatic interaction between the polyions and the counterions results in counterion condensation. If the two polyions are sufficiently close to each other their layers of condensed counterions can become correlated resulting in attraction between the macromolecules. To explore the counterion induced attraction we calculate the correlation functions for the condensed counterions. It is found that the correlations are of very short range. For the parameters specific to the double stranded DNA, the correlations and the attraction appear only when the surface-to-surface separation is less than 7 A.
Metodologia A metodologia a ser utilizada envolve a utilização de simulação computacional, atravé... more Metodologia A metodologia a ser utilizada envolve a utilização de simulação computacional, através da utilização do pacote ESPResSo (veja http://www. espresso. mpg. de). O pacote foi desenvolvido para realizar simulação computacional utilizando o ...
The behavior of a neutral polyampholyte (P A) chain with N monomers, in an ionic solution, is ana... more The behavior of a neutral polyampholyte (P A) chain with N monomers, in an ionic solution, is analyzed in the framework of the full Debye-Hückel-Bjerrum-Flory (DHBjF) theory. A P A chain, that in addition to the neutral monomers, also contains an equal number of positively and negatively charged monomers, is dissolved in an ionic solution. For high concentrations of salt and at high temperatures, the P A exists in an extended state. As the temperature is decreased, the electrostatic energy becomes more relevant and at a T = T θ the system collapses into a dilute globular state, or microelectrolyte. This state contains a concentration of salt higher than the surrounding medium. As the temperature is decreased even further, association between the monomers of the polymer and the ions of the salt becomes relevant and there is a crossover from this globular state to a low temperature extended state. For low densities of salt, the system is collapsed for almost all temperatures and exhibits a first-order phase transition to an extended state at an unphysical low temperature.
Sine-Gordon field theory is used to investigate the phase diagram of a neutral Coulomb gas. A var... more Sine-Gordon field theory is used to investigate the phase diagram of a neutral Coulomb gas. A variational mean field free energy is constructed and the corresponding phase diagrams in two (2d) and three dimensions (3d) are obtained. When analyzed in terms of chemical potential, the Sine-Gordon theory predicts the phase diagram topologically identical with the Monte Carlo simulations and a recently developed Debye-Hückel-Bjerrum (DHBj) theory. In 2d we find that the infinite order Kosterlitz-Thouless line terminates in a tricritical point, after which the metal-insulator transition becomes first order. However, when the transformation from chemical potential to the density is made the whole of the insulating phase is mapped onto zero density.
We investigate the explosive fragmentation process in two dimensions using molecular-dynamics sim... more We investigate the explosive fragmentation process in two dimensions using molecular-dynamics simulations. We show that the mass distribution of fragments follows a power law, with a scaling exponent that is strongly dependent on the macroscopic characteristics of the system prior to the explosion process. In particular, for thermalized initial configurations at low temperatures, we observe that the exponent is close to -1. We suggest that this result can be interpreted in terms of a multiplicative fracture process.
We investigate through non-equilibrium molecular dynamic simulations the flow of core-softened fl... more We investigate through non-equilibrium molecular dynamic simulations the flow of core-softened fluids inside nanotubes. Our results reveal a anomalous increase of the overall mass flux for nanotubes with sufficiently smaller radii. This is explained in terms of a transition from a single-file type of flow to the movement of an ordered-like fluid as the nanotube radius increases. The occurrence of a global minimum in the mass flux at this transition reflects the competition between the two characteristics length scales of the core-softened potential. Moreover, by increasing further the radius, another substantial change in the flow behavior, which becomes more evident at low temperatures, leads to a local minimum in the overall mass flux. Microscopically, this second transition results from the formation of a double-layer of flowing particles in the confined nanotube space. These special nano-fluidic features of core-softened particles closely resemble the enhanced flow behavior observed for liquid water inside carbon nanotubes.
We present a theory of dilute aqueous suspensions of microgel particles. It is found that as the ... more We present a theory of dilute aqueous suspensions of microgel particles. It is found that as the number of charged monomers in the polymer network composing mesoscopic gel increases, the particles undergo a swelling transition. Depending on the hydrophobicity of the polymer, this transition can be either continuous or discontinuous. Furthermore, similar to charge stabilized colloidal particles, we find that the electrophoretic mobility of the microgel is controlled by an effective charge. Unlike the colloids, however, for which the effective charge grows asymptotically with the logarithm of the bare charge, the effective charge of an ionic microgel scales as Z eff ϳZ 0.5. The findings are in good agreement with the experimental measurements.
We perform extensive molecular dynamics simulations to study the mass size distribution of a two-... more We perform extensive molecular dynamics simulations to study the mass size distribution of a two-dimensional fragmentation process. Our model consists of a large number of particles interacting through the Lennard–Jones potential. The fragmentation is induced by suddenly imposing a radial component on the particles' velocities, in order to mimic an explosion phenomenon. We then investigate the effect of the input energy on the resulting mass distribution of fragments.
We perform extensive molecular dynamics simulations to study the mass size distribution of a two-... more We perform extensive molecular dynamics simulations to study the mass size distribution of a two-dimensional fragmentation process. Our model consists of a large number of particles interacting through the Lennard–Jones potential. The fragmentation is induced by suddenly imposing a radial component on the particles' velocities, in order to mimic an explosion phenomenon. We then investigate the effect of the input energy on the resulting mass distribution of fragments.
Availability of highly reactive halogen ions at the surface of aerosols has tremendous implicatio... more Availability of highly reactive halogen ions at the surface of aerosols has tremendous implications for the atmospheric chemistry. Yet neither simulations, experiments, nor existing theories are able to provide a fully consistent description of the electrolyte-air interface. In this paper a new theory is proposed which allows us to explicitly calculate the ionic density profiles, the surface tension, and the electrostatic potential difference across the solution-air interface. Predictions of the theory are compared to experiments and are found to be in excellent agreement. The theory also sheds new light on one of the oldest puzzles of physical chemistry -- the Hofmeister effect.
To explore charge regulation (CR) in physicochemical and biophysical systems, we present a model ... more To explore charge regulation (CR) in physicochemical and biophysical systems, we present a model of colloidal particles with sticky adsorption sites which account for the formation of covalent bonds between the hydronium ions and the surface functional groups. Using this model and Monte Carlo simulations, we find that the standard Ninham and Parsegian (NP) theory of CR leads to results which deviate significantly from computer simulations. The problem of NP approach is traced back to the use of bulk equilibrium constant to account for surface chemical reactions. To resolve this difficulty we present a new theory of CR. The fundamental ingredient of the new approach is the sticky length, which is non-trivially related with the bulk equilibrium constant. The theory is found to be in excellent agreement with computer simulations, without any adjustable parameters. As an application of the theory we calculate the effective charge of colloidal particles containing carboxyl groups, as a function of pH and salt concentration. Electrostatic interactions play a fundamental role in physics, chemistry, and biology. The long-range nature of the Coulomb force, however, makes it very difficult to study theoretically 1. In aqueous systems ions are usually hydrated by water molecules. On the other hand, acids lose proton, which associates with the water molecule forming a hydronium ion 2. There are many reactions that are controlled by pH, and the acid-base equilibrium directly influences the functionality of biomolecules. Although pH can be easily tuned in experiments, it is much more difficult to account for the chemical equilibrium in theoretical and simulation studies 3. Colloidal particles often have organic functional groups on their surfaces. In aqueous systems these groups dissociate, loosing a proton, resulting in a colloidal surface charge 4-7. The amount of surface charge strongly depends on the pH of the environment 8,9 and is controlled by the chemical equilibrium between hydronium ions and the functional groups. This process is known as charge regulation (CR) 10-16. The concept of charge regulation was first described by Linderstrøm-Lang 17-19 and studied theoretically by Ninham and Parsegian. 20. CR is of fundamental importance in colloidal science 10,21-32 and biophysics 33-39. It has been applied to explore the stability of electrical double layers 9,40-45 and is of great technological importance in fields as diverse as mineral preparation, agriculture, ceramics, and surface coating 46. Consider a weak acid HA in equilibrium with bulk water, HA+H 2 O ⇄ H 3 O + +A-. For dilute solutions the concentration of all species is controlled by the law of mass a) Electronic mail:
We investigate the adsorption of neutral polyampholytes on charged nanopatterned surfaces. The su... more We investigate the adsorption of neutral polyampholytes on charged nanopatterned surfaces. The surfaces have charged domains but are overall neutral. To perform efficient simulations, we use an approach which combines the explicit form of the interaction potential between the polyampholyte monomers and the surface with a 3d Ewald summation method. We observe that the amount of adsorption and the structure of the adsorbed polyampholytes depend strongly on the surface pattern, the relative size of the surface domains, and the charge distribution along the polyampholyte backbone.
Physica A: Statistical Mechanics and its Applications
A melting transition for a system of hard spheres interacting by a repulsive Yukawa potential of ... more A melting transition for a system of hard spheres interacting by a repulsive Yukawa potential of DLVO form is studied. To find the location of the phase boundary, we propose a simple theory to calculate the free energies for the coexisting liquid and solid. The free energy for the liquid phase is approximated by a virial expansion. The free energy of the crystalline phase is calculated in the spirit of the Lenard-Jonnes and Devonshire (LJD) theory. The phase boundary is found by equating the pressures and chemical potentials of the coexisting phases. When the approximation leading to the equation of state for the liquid breakes down, the first order transition line is also obtained by applying the Lindemann criterion to the solid phase. Our results are then compared with the Monte Carlo simulations.
We present theory and simulations which allow us to quantitatively calculate the amount of surfac... more We present theory and simulations which allow us to quantitatively calculate the amount of surface adsorption excess of charged nanoparticles to a charged surface. The theory is very accurate for weakly charged nanoparticles and can be used at physiological concentrations of salt. We have also developed an efficient simulation algorithm which can be used for dilute suspensions of nanoparticles of any charge, even at very large salt concentrations. With the help of the new simulation method, we are able to efficiently calculate the adsorption isotherms of highly charged nanoparticles in suspensions containing multivalent ions, for which there are no accurate theoretical methods available.
The phase behavior of the lattice restricted primitive model (RPM) for ionic systems with additio... more The phase behavior of the lattice restricted primitive model (RPM) for ionic systems with additional short-range nearest neighbor (nn) repulsive interactions has been studied by grand canonical Monte Carlo simulations. We obtain a rich phase behavior as the nn strength is varied. In particular, the phase diagram is very similar to the continuum RPM model for high nn strength. Specifically, we have found both gas-liquid phase separation, with associated Ising critical point, and first-order liquid-solid transition. We discuss how the line of continuous order-disorder transitions present for the low nn strength changes into the continuum-space behavior as one increases the nn strength and compare our findings with recent theoretical results by Ciach and Stell [Phys. Rev. Lett. {\bf 91}, 060601 (2003)].
Following the suggestion in the Comment on our previous work by Åström, Linna, and Timonen [Phys.... more Following the suggestion in the Comment on our previous work by Åström, Linna, and Timonen [Phys. Rev. E 65, 048101 (2002)], we performed extensive molecular-dynamics simulations to confirm that our numerical results for the mass distribution of fragments after the ``explosion'' of thermalized samples are consistent with the scaling form n(m)~m-(alpha+1)f(m/M0), where f(m/M0) is a cutoff function, M0 is a
We study, using Monte Carlo simulations, the interaction between infinite heterogeneously charged... more We study, using Monte Carlo simulations, the interaction between infinite heterogeneously charged surfaces inside an electrolyte solution. The surfaces are overall neutral with quenched charged domains. An average over the quenched disorder is performed to obtain the net force. We find that the interaction between the surfaces is repulsive at short distances and is attractive for larger separations.
Physical review. E, Statistical, nonlinear, and soft matter physics, 2012
We introduce an implicit solvent Molecular Dynamics approach for calculating ionic fluxes through... more We introduce an implicit solvent Molecular Dynamics approach for calculating ionic fluxes through narrow nanopores and transmembrane channels. The method relies on a dual-control-volume grand-canonical molecular dynamics (DCV-GCMD) simulation and the analytical solution for the electrostatic potential inside a cylindrical nanopore recently obtained by Levin [Europhys. Lett. 76, 163 (2006)]. The theory is used to calculate the ionic fluxes through an artificial transmembrane channel which mimics the antibacterial gramicidin A channel. Both current-voltage and current-concentration relations are calculated under various experimental conditions. We show that our results are comparable to the characteristics associated to the gramicidin A pore, especially the existence of two binding sites inside the pore and the observed saturation in the current-concentration profiles.
Physical review. E, Statistical, nonlinear, and soft matter physics, 2001
A simple model is presented for the appearance of attraction between two like-charged polyions in... more A simple model is presented for the appearance of attraction between two like-charged polyions inside a polyelectrolyte solution. The polyions are modeled as rigid cylinders in a continuum dielectric solvent. The strong electrostatic interaction between the polyions and the counterions results in counterion condensation. If the two polyions are sufficiently close to each other their layers of condensed counterions can become correlated resulting in attraction between the macromolecules. To explore the counterion induced attraction we calculate the correlation functions for the condensed counterions. It is found that the correlations are of very short range. For the parameters specific to the double stranded DNA, the correlations and the attraction appear only when the surface-to-surface separation is less than 7 A.
Metodologia A metodologia a ser utilizada envolve a utilização de simulação computacional, atravé... more Metodologia A metodologia a ser utilizada envolve a utilização de simulação computacional, através da utilização do pacote ESPResSo (veja http://www. espresso. mpg. de). O pacote foi desenvolvido para realizar simulação computacional utilizando o ...
The behavior of a neutral polyampholyte (P A) chain with N monomers, in an ionic solution, is ana... more The behavior of a neutral polyampholyte (P A) chain with N monomers, in an ionic solution, is analyzed in the framework of the full Debye-Hückel-Bjerrum-Flory (DHBjF) theory. A P A chain, that in addition to the neutral monomers, also contains an equal number of positively and negatively charged monomers, is dissolved in an ionic solution. For high concentrations of salt and at high temperatures, the P A exists in an extended state. As the temperature is decreased, the electrostatic energy becomes more relevant and at a T = T θ the system collapses into a dilute globular state, or microelectrolyte. This state contains a concentration of salt higher than the surrounding medium. As the temperature is decreased even further, association between the monomers of the polymer and the ions of the salt becomes relevant and there is a crossover from this globular state to a low temperature extended state. For low densities of salt, the system is collapsed for almost all temperatures and exhibits a first-order phase transition to an extended state at an unphysical low temperature.
Sine-Gordon field theory is used to investigate the phase diagram of a neutral Coulomb gas. A var... more Sine-Gordon field theory is used to investigate the phase diagram of a neutral Coulomb gas. A variational mean field free energy is constructed and the corresponding phase diagrams in two (2d) and three dimensions (3d) are obtained. When analyzed in terms of chemical potential, the Sine-Gordon theory predicts the phase diagram topologically identical with the Monte Carlo simulations and a recently developed Debye-Hückel-Bjerrum (DHBj) theory. In 2d we find that the infinite order Kosterlitz-Thouless line terminates in a tricritical point, after which the metal-insulator transition becomes first order. However, when the transformation from chemical potential to the density is made the whole of the insulating phase is mapped onto zero density.
We investigate the explosive fragmentation process in two dimensions using molecular-dynamics sim... more We investigate the explosive fragmentation process in two dimensions using molecular-dynamics simulations. We show that the mass distribution of fragments follows a power law, with a scaling exponent that is strongly dependent on the macroscopic characteristics of the system prior to the explosion process. In particular, for thermalized initial configurations at low temperatures, we observe that the exponent is close to -1. We suggest that this result can be interpreted in terms of a multiplicative fracture process.
We investigate through non-equilibrium molecular dynamic simulations the flow of core-softened fl... more We investigate through non-equilibrium molecular dynamic simulations the flow of core-softened fluids inside nanotubes. Our results reveal a anomalous increase of the overall mass flux for nanotubes with sufficiently smaller radii. This is explained in terms of a transition from a single-file type of flow to the movement of an ordered-like fluid as the nanotube radius increases. The occurrence of a global minimum in the mass flux at this transition reflects the competition between the two characteristics length scales of the core-softened potential. Moreover, by increasing further the radius, another substantial change in the flow behavior, which becomes more evident at low temperatures, leads to a local minimum in the overall mass flux. Microscopically, this second transition results from the formation of a double-layer of flowing particles in the confined nanotube space. These special nano-fluidic features of core-softened particles closely resemble the enhanced flow behavior observed for liquid water inside carbon nanotubes.
We present a theory of dilute aqueous suspensions of microgel particles. It is found that as the ... more We present a theory of dilute aqueous suspensions of microgel particles. It is found that as the number of charged monomers in the polymer network composing mesoscopic gel increases, the particles undergo a swelling transition. Depending on the hydrophobicity of the polymer, this transition can be either continuous or discontinuous. Furthermore, similar to charge stabilized colloidal particles, we find that the electrophoretic mobility of the microgel is controlled by an effective charge. Unlike the colloids, however, for which the effective charge grows asymptotically with the logarithm of the bare charge, the effective charge of an ionic microgel scales as Z eff ϳZ 0.5. The findings are in good agreement with the experimental measurements.
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Papers by Alexandre Diehl