Baofu Qiao | Northwestern University (original) (raw)
Papers by Baofu Qiao
We study the static and dynamic properties of water near a poly(styrene sulfonate)/ poly(diallyld... more We study the static and dynamic properties of water near a poly(styrene sulfonate)/ poly(diallyldimethylammonium) (PSS/PDADMA) bilayer adsorbed onto a substrate by atomistic molecular dynamics simulations. Qualitative changes in the dynamics of water in the proximity of the adsorbed bilayer are observed -such as in the lateral diffusion, residence time and hydrogenbonding lifetime -as compared with water in the presence of the bare substrate. Static properties of water are similarly influenced, and a high polarization of water molecules is found to be present surprisingly far from the adsorbed bilayer.
In this work, we present the first molecular dynamics simulation on the formation of a polyelectr... more In this work, we present the first molecular dynamics simulation on the formation of a polyelectrolyte bilayer resolved in atomistic detail, extending a previous study of the adsorption of poly(styrene sulfonate) [B. Qiao, J. J. Cerda`and C. Holm, Macromolecules, 2011, 44, 1707-1718 to the formation of a poly(styrene sulfonate)/poly(diallyldimethylammonium) bilayer. Extensive molecular dynamics simulations of the adsorption process on different substrates (hydrophilic/ hydrophobic, charged/neutral) were performed. Our results seem to indicate that a high enough surface charge density (0.164 C m À2 here) may be required to achieve a multilayer linear growth in the framework of the electrostatic driven mechanism for PEM growth. We furthermore demonstrate that the use of stiff hydroxyl groups for creating a hydrophilic surface from a hydrophilic one can lead to severe simulation artifacts, and we discuss a simple remedy for this problem.
The Journal of …, Jan 1, 2008
Three different ionic liquids are investigated via atomistic molecular dynamics simulations using... more Three different ionic liquids are investigated via atomistic molecular dynamics simulations using the force field of Lopes and Pádua (J. Phys. Chem. B 2006, 110, 19586). In particular, the 1-ethyl-3-methylimidazolium cation EMIM + is studied in the presence of three different anions, namely, chloride Cl -, tetrafluoroborate B F 4 -, and bis((trifluoromethyl)sulfonyly)imide TF 2 N -. In the focus of the present study are the static distributions of anions and cations around a cation as a function of anion size. It is found that the preferred positions of the anions change from being close to the imidazolium hydrogens to being above and below the imidazolium rings. Lifetimes of hydrogen bonds are calculated and found to be of the same order of magnitude as those of pure liquid water and of some small primary alcohols. Three kinds of short-range cation-cation orderings are studied, among which the offset stacking dominates in all of the investigated ionic liquids. The offset stacking becomes weaker from [EMIM][Cl] to [EMIM][BF 4 ] to [EMIM][TF 2 N]. Further investigation of the dynamical behavior reveals that cations in [EMIM][TF 2 N] have a slower tumbling motion compared with those in [EMIM][Cl] and [EMIM] [BF 4 ] and that pure diffusive behavior can be observed after 1.5 ns for all three systems at temperatures 90 K above the corresponding melting temperatures.
![Research paper thumbnail of A comparative study of two classical force fields on statics and dynamics of [EMIM][BF] investigated via molecular dynamics simulations](https://attachments.academia-assets.com/4588622/thumbnails/1.jpg)
](The Journal of chemical …, Jan 1, 2008
The influences of two different commonly employed force fields on statical and dynamical properti... more The influences of two different commonly employed force fields on statical and dynamical properties of ionic liquids are investigated for ͓EMIM͔͓BF 4 ͔. The force fields compared in this work are the one of Canongia Lopes and Padua ͓J. Phys. Chem. B 110, 19586 ͑2006͔͒ and that of Liu et al. ͓J. Phys. Chem. B 108, 12978 ͑2004͔͒. Differences in the strengths of hydrogen bonds are found, which are also reflected in the static ion distributions around the cation. Moreover, due to the stronger hydrogen bonding in the force field of Liu et al., the diffusive motions of cations and anions and the rotational behavior of the cations are slower compared with those obtained with the force field of Canongia Lopes and Padua. Both force fields underestimate the zero-field electrical conductivity, while the experimental dielectric constant can be reproduced within the expected statistical error boundaries. J 2 ͘, we follow the method described in Ref. 63. ͗M ជ D 2 ͘ is computed by direct averaging over the MD, while ͗M ជ J 2 ͘ is obtained with the Einstein-Helfand method, which allows to determine the conductivity and ͗M ជ J 2 ͘ from the MSD of M ជ J , ͓͗M ជ J ͑t͒ − M ជ J ͑0͔͒ 2 ͘ = 6Vk B Tt + 2͗M ជ J 2 ͘. ͑19͒
The Journal of chemical …, Jan 1, 2008
The 1,3-dimethyl imidazolium chloride ͓MMIM͔Cl is an example of ionic liquid and frequently studi... more The 1,3-dimethyl imidazolium chloride ͓MMIM͔Cl is an example of ionic liquid and frequently studied in literature. In this article ͓MMIM͔Cl is studied using an ab initio method ͓second order Møller-Plesset perturbation theory ͑MP2͒, density functional theory ͑DFT͔͒ and classical force field approach with the aim of looking at some properties on different scales. Selected properties are studied with the different methods and compared to each other. The comparison between the results obtained with MP2 and the DFT approach allows us to comment on the validity of this latter and thus on its employment in larger systems. On the other hand, the comparison between the DFT results and those of the classical approach allows us to test the reproducibility of electrostatic properties by this latter approach. As the results show the used DFT setup is rather satisfactory, while the classical force fields are describing the electrostatic properties in an insufficient way. A revision ͑improvement͒ of the classical force fields is at this stage necessary in order to capture the electrostatic properties in a proper way.
The Journal of chemical physics, Jan 1, 2004
The concept of the volume fraction at chain end is proposed, which is the conditional probability... more The concept of the volume fraction at chain end is proposed, which is the conditional probability for a site having been occupied, knowing that an adjacent site is occupied by polymer end. The overall entropy of polymer/solvent system is separated into two fundamentally different parts, i.e., the translational entropy and the conformational entropy. Based on these a theory of polymer solutions is established. When a mean-field approximation is introduced, Flory-Huggins ͑FH͒ theory is recovered. The FH interaction parameters and spinodal curves of the polystyrene/cyclohexane system are calculated and compared with the experimental data. The good prediction of them two is achieved.
The European Physical Journal-Special …, Jan 1, 2009
The present article will give a short overview about the sparse attempts to model films made up b... more The present article will give a short overview about the sparse attempts to model films made up by alternating layers of polyanions and polycations, called polyelectrolyte multilayers. First, we will review the current theoretical understanding of the field, followed by the description of the current modeling strategies,with a stress on pointing out their shortcomings. We then report some results of our our recent attempts to model the structure and dynamics of polyelectrolyte multilayers. We present two approaches: one deals with coarse-grained bead-spring models within a dielectric continuum solvent, and in the other attempt we try to infer the important microscopic interactions via a fully atomistic treatment of small oligomeric polyelectrolytes. We finally give an outlook and discuss possible extensions towards a more realistic modeling of polyelectrolyte multilayers.
Acta Polymerica Sinica, Jan 1, 2004
It is proposed that the overall free energy of a polymer solution has three fundamentally differe... more It is proposed that the overall free energy of a polymer solution has three fundamentally different types of contributions, ie the translational, the configurational and the thermal correction parts. The second and the third parts have the additive properties for segments ...
Macromolecules, Jan 1, 2010
Explicit solvent all-atom molecular dynamics simulations of mixtures of poly(styrenesulfonate)-(P... more Explicit solvent all-atom molecular dynamics simulations of mixtures of poly(styrenesulfonate)-(PSS) and poly(diallyldimethylammonium) (PDADMA) polyelectrolytes at various salt (NaCl) concentrations are performed. We characterize the formed polyelectrolyte complexes (PECs) and relate the observed physical properties of PSS-PDADMA PECs to the properties found in polyelectrolyte multilayers (PEMs) made of the same compositions. Our results reveal a change in the way charges are compensated upon the addition of salt, namely from an intrinsic mechanism (polyanions pair with polycations) toward an extrinsic one (polyions pair with salt ions). The probability of the intrinsic compensating mechanism decreases from about 90% to about 60% when the salt concentration increases from 0.168 to 1 mol/L. The interaction energies of the ion-pairing follow the order of Na-Cl>PSS-Na>PDADMA-Cl=PSS-PDADMA. Furthermore, we investigate thoroughly the water distribution and study the hydration mechanisms in our system. Water is found to be homogeneously distributed inside our investigated systems, while we find a negligible difference between the hydration ability of (PDADMA þ Cl -) and (PSS þ Na þ ). This lack of asymmetric behavior demonstrates that the observed swelling-shrinking switch during the buildup of PEMs cannot be related to the hydration behavior, and we suggest that the presence of a substrate has to play a critical role. A further analysis of the water structure shows that the dielectric constant inside such mixtures is roughly 1 order of magnitude lower than in bulk water, and our determined values compare favorably with experimental measurements. Finally the diffusion of water molecules inside the PE mixtures is found to be 2 orders of magnitude slower than that in pure water.
The Journal of Physical …, Jan 1, 2009
Dissipative particle dynamics simulations were utilized to simulate a model surfactant solution-a... more Dissipative particle dynamics simulations were utilized to simulate a model surfactant solution-air system. Amphiphilic surfactant molecules were modeled as dimers composed of a hydrophilic head and a hydrophobic tail. With a simple model, the influence of conservative interaction parameters on the surfactant's properties, including surfactant efficiency and critical micelle concentration (CMC), was investigated in the present research. It is not the surfactant total concentration, but the bulk concentration, that should be employed to achieve the right surfactant properties. It is found that the adjustment of interaction between water and head or air and tail (a WH or a AT ) will result in the obvious change in surfactant efficiency. The parameter that affects CMC the most significantly is the interaction between water and tail (a WT ). On the basis of the findings about the relationship between conservative interaction parameters and surfactant behaviors, we varied the interaction parameters and simulated a real ionic surfactant system with different tail lengths.
The Journal of Physical …, Jan 1, 2010
Density functional theory (DFT) calculations combined with molecular dynamic (MD) simulations hav... more Density functional theory (DFT) calculations combined with molecular dynamic (MD) simulations have been performed to show in detail the structure characteristic of 1-butylpyridinium tetrafluoroborate ([BPy + ][BF 4 -]), a representative of pyridinium-based ionic liquids (ILs). It is found that the relative stability for ion pair configurations is synergically determined by the electrostatic attractions and the H-bond interactions between the ions of opposite charge. [BPy + ][BF 4 -] IL possesses strong long-range ordered structure with cations and anions alternately arranging. The spatial distributions of anions and cations around the given cations are clearly shown, and T-shaped orientation is indicated to play a key role in the interaction between two pyridine rings. DFT calculations and MD simulations uniformly suggest that the H-bonds of the fluorine atoms with the hydrogen atoms on the pyridine rings are stronger than those of the fluorine atoms with the butyl chain hydrogens. The present results can offer useful information for understanding the physicochemical properties of [BPy + ][BF 4 -] IL and further designing new pyridinium-based ILs.
Macromolecules
Extensive all-atom molecular dynamics simulations have been performed to investigate the effect o... more Extensive all-atom molecular dynamics simulations have been performed to investigate the effect of surface features on the adsorption of poly(styrenesulfonate) (PSS) oligomers on top of a modified graphite substrate. In particular, we have investigated hydrophilic and hydrophobic model surfaces, accompanied by a variable surface charge density σ s in the range 0-0.164 C/m 2 . Our results demonstrate that short-range interactions originating from the adsorbing substrate play a significant role in the layer structure of the adsorbed PSS, and they alone are already sufficient to induce a stable PSS adsorption layer. The presence of additional hydrophilic hydroxyl groups and charges on the adsorbing surface can further enhance the adsorption of PSS sulfonate groups at lower σ s , whereas for the case of σ s = 0.164 C/m 2 , the influence of the surface hydroxyl groups becomes negligible compared to that of the surface charges. The adsorbed PSS chains show mostly conformations where the PSS backbones are approximately parallel to the adsorbing surface. In some case, however, also the PSS backbones stand on top of the surface. Both the obtained surface charge overcompensation and the surface coverage are in good agreement with a previous experimental work [Ahrens et al. Macromolecules 2001, 34, 4504-4512]. Between the first PSS adsorption layer and the adsorbing substrate, we always find a water-rich region. The orientation of the water molecules in this region depends crucially on the features of the adsorbing surface. Our simulations suggest that the water-involved hydrogen bondings play a dominant role in determining the orientation of the water molecules. We also observe a decrease of the dielectric constant of water in the region close to the adsorbing surface in all of the investigated systems that is more pronounced for the hydrophilically modified surface and moreover increases with rising surface charge density. We suggest that this effect could lead to an electrostatic stabilization of the monolayer surface.
We study the static and dynamic properties of water near a poly(styrene sulfonate)/ poly(diallyld... more We study the static and dynamic properties of water near a poly(styrene sulfonate)/ poly(diallyldimethylammonium) (PSS/PDADMA) bilayer adsorbed onto a substrate by atomistic molecular dynamics simulations. Qualitative changes in the dynamics of water in the proximity of the adsorbed bilayer are observed -such as in the lateral diffusion, residence time and hydrogenbonding lifetime -as compared with water in the presence of the bare substrate. Static properties of water are similarly influenced, and a high polarization of water molecules is found to be present surprisingly far from the adsorbed bilayer.
In this work, we present the first molecular dynamics simulation on the formation of a polyelectr... more In this work, we present the first molecular dynamics simulation on the formation of a polyelectrolyte bilayer resolved in atomistic detail, extending a previous study of the adsorption of poly(styrene sulfonate) [B. Qiao, J. J. Cerda`and C. Holm, Macromolecules, 2011, 44, 1707-1718 to the formation of a poly(styrene sulfonate)/poly(diallyldimethylammonium) bilayer. Extensive molecular dynamics simulations of the adsorption process on different substrates (hydrophilic/ hydrophobic, charged/neutral) were performed. Our results seem to indicate that a high enough surface charge density (0.164 C m À2 here) may be required to achieve a multilayer linear growth in the framework of the electrostatic driven mechanism for PEM growth. We furthermore demonstrate that the use of stiff hydroxyl groups for creating a hydrophilic surface from a hydrophilic one can lead to severe simulation artifacts, and we discuss a simple remedy for this problem.
The Journal of …, Jan 1, 2008
Three different ionic liquids are investigated via atomistic molecular dynamics simulations using... more Three different ionic liquids are investigated via atomistic molecular dynamics simulations using the force field of Lopes and Pádua (J. Phys. Chem. B 2006, 110, 19586). In particular, the 1-ethyl-3-methylimidazolium cation EMIM + is studied in the presence of three different anions, namely, chloride Cl -, tetrafluoroborate B F 4 -, and bis((trifluoromethyl)sulfonyly)imide TF 2 N -. In the focus of the present study are the static distributions of anions and cations around a cation as a function of anion size. It is found that the preferred positions of the anions change from being close to the imidazolium hydrogens to being above and below the imidazolium rings. Lifetimes of hydrogen bonds are calculated and found to be of the same order of magnitude as those of pure liquid water and of some small primary alcohols. Three kinds of short-range cation-cation orderings are studied, among which the offset stacking dominates in all of the investigated ionic liquids. The offset stacking becomes weaker from [EMIM][Cl] to [EMIM][BF 4 ] to [EMIM][TF 2 N]. Further investigation of the dynamical behavior reveals that cations in [EMIM][TF 2 N] have a slower tumbling motion compared with those in [EMIM][Cl] and [EMIM] [BF 4 ] and that pure diffusive behavior can be observed after 1.5 ns for all three systems at temperatures 90 K above the corresponding melting temperatures.
The Journal of chemical …, Jan 1, 2008
The influences of two different commonly employed force fields on statical and dynamical properti... more The influences of two different commonly employed force fields on statical and dynamical properties of ionic liquids are investigated for ͓EMIM͔͓BF 4 ͔. The force fields compared in this work are the one of Canongia Lopes and Padua ͓J. Phys. Chem. B 110, 19586 ͑2006͔͒ and that of Liu et al. ͓J. Phys. Chem. B 108, 12978 ͑2004͔͒. Differences in the strengths of hydrogen bonds are found, which are also reflected in the static ion distributions around the cation. Moreover, due to the stronger hydrogen bonding in the force field of Liu et al., the diffusive motions of cations and anions and the rotational behavior of the cations are slower compared with those obtained with the force field of Canongia Lopes and Padua. Both force fields underestimate the zero-field electrical conductivity, while the experimental dielectric constant can be reproduced within the expected statistical error boundaries. J 2 ͘, we follow the method described in Ref. 63. ͗M ជ D 2 ͘ is computed by direct averaging over the MD, while ͗M ជ J 2 ͘ is obtained with the Einstein-Helfand method, which allows to determine the conductivity and ͗M ជ J 2 ͘ from the MSD of M ជ J , ͓͗M ជ J ͑t͒ − M ជ J ͑0͔͒ 2 ͘ = 6Vk B Tt + 2͗M ជ J 2 ͘. ͑19͒
The Journal of chemical …, Jan 1, 2008
The 1,3-dimethyl imidazolium chloride ͓MMIM͔Cl is an example of ionic liquid and frequently studi... more The 1,3-dimethyl imidazolium chloride ͓MMIM͔Cl is an example of ionic liquid and frequently studied in literature. In this article ͓MMIM͔Cl is studied using an ab initio method ͓second order Møller-Plesset perturbation theory ͑MP2͒, density functional theory ͑DFT͔͒ and classical force field approach with the aim of looking at some properties on different scales. Selected properties are studied with the different methods and compared to each other. The comparison between the results obtained with MP2 and the DFT approach allows us to comment on the validity of this latter and thus on its employment in larger systems. On the other hand, the comparison between the DFT results and those of the classical approach allows us to test the reproducibility of electrostatic properties by this latter approach. As the results show the used DFT setup is rather satisfactory, while the classical force fields are describing the electrostatic properties in an insufficient way. A revision ͑improvement͒ of the classical force fields is at this stage necessary in order to capture the electrostatic properties in a proper way.
The Journal of chemical physics, Jan 1, 2004
The concept of the volume fraction at chain end is proposed, which is the conditional probability... more The concept of the volume fraction at chain end is proposed, which is the conditional probability for a site having been occupied, knowing that an adjacent site is occupied by polymer end. The overall entropy of polymer/solvent system is separated into two fundamentally different parts, i.e., the translational entropy and the conformational entropy. Based on these a theory of polymer solutions is established. When a mean-field approximation is introduced, Flory-Huggins ͑FH͒ theory is recovered. The FH interaction parameters and spinodal curves of the polystyrene/cyclohexane system are calculated and compared with the experimental data. The good prediction of them two is achieved.
The European Physical Journal-Special …, Jan 1, 2009
The present article will give a short overview about the sparse attempts to model films made up b... more The present article will give a short overview about the sparse attempts to model films made up by alternating layers of polyanions and polycations, called polyelectrolyte multilayers. First, we will review the current theoretical understanding of the field, followed by the description of the current modeling strategies,with a stress on pointing out their shortcomings. We then report some results of our our recent attempts to model the structure and dynamics of polyelectrolyte multilayers. We present two approaches: one deals with coarse-grained bead-spring models within a dielectric continuum solvent, and in the other attempt we try to infer the important microscopic interactions via a fully atomistic treatment of small oligomeric polyelectrolytes. We finally give an outlook and discuss possible extensions towards a more realistic modeling of polyelectrolyte multilayers.
Acta Polymerica Sinica, Jan 1, 2004
It is proposed that the overall free energy of a polymer solution has three fundamentally differe... more It is proposed that the overall free energy of a polymer solution has three fundamentally different types of contributions, ie the translational, the configurational and the thermal correction parts. The second and the third parts have the additive properties for segments ...
Macromolecules, Jan 1, 2010
Explicit solvent all-atom molecular dynamics simulations of mixtures of poly(styrenesulfonate)-(P... more Explicit solvent all-atom molecular dynamics simulations of mixtures of poly(styrenesulfonate)-(PSS) and poly(diallyldimethylammonium) (PDADMA) polyelectrolytes at various salt (NaCl) concentrations are performed. We characterize the formed polyelectrolyte complexes (PECs) and relate the observed physical properties of PSS-PDADMA PECs to the properties found in polyelectrolyte multilayers (PEMs) made of the same compositions. Our results reveal a change in the way charges are compensated upon the addition of salt, namely from an intrinsic mechanism (polyanions pair with polycations) toward an extrinsic one (polyions pair with salt ions). The probability of the intrinsic compensating mechanism decreases from about 90% to about 60% when the salt concentration increases from 0.168 to 1 mol/L. The interaction energies of the ion-pairing follow the order of Na-Cl>PSS-Na>PDADMA-Cl=PSS-PDADMA. Furthermore, we investigate thoroughly the water distribution and study the hydration mechanisms in our system. Water is found to be homogeneously distributed inside our investigated systems, while we find a negligible difference between the hydration ability of (PDADMA þ Cl -) and (PSS þ Na þ ). This lack of asymmetric behavior demonstrates that the observed swelling-shrinking switch during the buildup of PEMs cannot be related to the hydration behavior, and we suggest that the presence of a substrate has to play a critical role. A further analysis of the water structure shows that the dielectric constant inside such mixtures is roughly 1 order of magnitude lower than in bulk water, and our determined values compare favorably with experimental measurements. Finally the diffusion of water molecules inside the PE mixtures is found to be 2 orders of magnitude slower than that in pure water.
The Journal of Physical …, Jan 1, 2009
Dissipative particle dynamics simulations were utilized to simulate a model surfactant solution-a... more Dissipative particle dynamics simulations were utilized to simulate a model surfactant solution-air system. Amphiphilic surfactant molecules were modeled as dimers composed of a hydrophilic head and a hydrophobic tail. With a simple model, the influence of conservative interaction parameters on the surfactant's properties, including surfactant efficiency and critical micelle concentration (CMC), was investigated in the present research. It is not the surfactant total concentration, but the bulk concentration, that should be employed to achieve the right surfactant properties. It is found that the adjustment of interaction between water and head or air and tail (a WH or a AT ) will result in the obvious change in surfactant efficiency. The parameter that affects CMC the most significantly is the interaction between water and tail (a WT ). On the basis of the findings about the relationship between conservative interaction parameters and surfactant behaviors, we varied the interaction parameters and simulated a real ionic surfactant system with different tail lengths.
The Journal of Physical …, Jan 1, 2010
Density functional theory (DFT) calculations combined with molecular dynamic (MD) simulations hav... more Density functional theory (DFT) calculations combined with molecular dynamic (MD) simulations have been performed to show in detail the structure characteristic of 1-butylpyridinium tetrafluoroborate ([BPy + ][BF 4 -]), a representative of pyridinium-based ionic liquids (ILs). It is found that the relative stability for ion pair configurations is synergically determined by the electrostatic attractions and the H-bond interactions between the ions of opposite charge. [BPy + ][BF 4 -] IL possesses strong long-range ordered structure with cations and anions alternately arranging. The spatial distributions of anions and cations around the given cations are clearly shown, and T-shaped orientation is indicated to play a key role in the interaction between two pyridine rings. DFT calculations and MD simulations uniformly suggest that the H-bonds of the fluorine atoms with the hydrogen atoms on the pyridine rings are stronger than those of the fluorine atoms with the butyl chain hydrogens. The present results can offer useful information for understanding the physicochemical properties of [BPy + ][BF 4 -] IL and further designing new pyridinium-based ILs.
Macromolecules
Extensive all-atom molecular dynamics simulations have been performed to investigate the effect o... more Extensive all-atom molecular dynamics simulations have been performed to investigate the effect of surface features on the adsorption of poly(styrenesulfonate) (PSS) oligomers on top of a modified graphite substrate. In particular, we have investigated hydrophilic and hydrophobic model surfaces, accompanied by a variable surface charge density σ s in the range 0-0.164 C/m 2 . Our results demonstrate that short-range interactions originating from the adsorbing substrate play a significant role in the layer structure of the adsorbed PSS, and they alone are already sufficient to induce a stable PSS adsorption layer. The presence of additional hydrophilic hydroxyl groups and charges on the adsorbing surface can further enhance the adsorption of PSS sulfonate groups at lower σ s , whereas for the case of σ s = 0.164 C/m 2 , the influence of the surface hydroxyl groups becomes negligible compared to that of the surface charges. The adsorbed PSS chains show mostly conformations where the PSS backbones are approximately parallel to the adsorbing surface. In some case, however, also the PSS backbones stand on top of the surface. Both the obtained surface charge overcompensation and the surface coverage are in good agreement with a previous experimental work [Ahrens et al. Macromolecules 2001, 34, 4504-4512]. Between the first PSS adsorption layer and the adsorbing substrate, we always find a water-rich region. The orientation of the water molecules in this region depends crucially on the features of the adsorbing surface. Our simulations suggest that the water-involved hydrogen bondings play a dominant role in determining the orientation of the water molecules. We also observe a decrease of the dielectric constant of water in the region close to the adsorbing surface in all of the investigated systems that is more pronounced for the hydrophilically modified surface and moreover increases with rising surface charge density. We suggest that this effect could lead to an electrostatic stabilization of the monolayer surface.