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Papers by Isaac Sanchez

The journal of physical chemistry. B, Jan 26, 2009

An analysis of the expected divergences in thermodynamic properties at the close-pack density (et... more An analysis of the expected divergences in thermodynamic properties at the close-pack density (eta(cp) = pi square root(2)/6) along with the known virial coefficients up to 10th order suggests a weak logarithmic singularity in the excess fluid entropy. The corresponding equation of state (EOS) also possesses a singularity at eta(cp). The new EOS accurately describes extant molecular dynamics data up to the fluid-solid transition (eta approximately 0.494) with differences of less than 1 part per thousand. This accuracy is maintained into the metastable fluid regime up to eta approximately 0.52. In terms of accuracy, the new EOS is no better than Pade approximants, but the new EOS, unlike the Pade approximants, diverges at eta(cp). In addition, a new order parameter is defined that enables all system configurations to be classified as either disordered or ordered. Monte Carlo simulations are used to determine this order parameter in the metastable fluid range. Using this new order parameter, evidence is presented to support a thermodynamic glass transition at eta approximately 0.54. With respect to this transition, congruence is found with the traditional ideas espoused by Gibbs and DiMarzio and Adam and Gibbs. It is the rapid disappearance of disordered (random) configurations with increasing density that drives the glass transition and slows the dynamics.

Scientific reports, 2014

Globular proteins contain cavities/voids that play specific roles in controlling protein function... more Globular proteins contain cavities/voids that play specific roles in controlling protein function. Elongated cavities provide migration channels for the transport of ions and small molecules to the active center of a protein or enzyme. Using Monte Carlo and Molecular Dynamics on fully atomistic protein/water models, a new computational methodology is introduced that takes into account the protein's dynamic structure and maps all the cavities in and on the surface. To demonstrate its utility, the methodology is applied to study cavity structure in myoglobin and five of its mutants. Computed cavity and channel size distributions reveal significant differences relative to the wild type myoglobin. Computer visualization of the channels leading to the heme center indicates restricted ligand access for the mutants consistent with the existing interpretations. The new methodology provides a quantitative measure of cavity structure and distributions and can become a valuable tool for the structural characterization of proteins.

The journal of physical chemistry. B, Jan 7, 2014

Equations of state in the van der Waals genre suggest that saturated liquids should adhere to the... more Equations of state in the van der Waals genre suggest that saturated liquids should adhere to the following corresponding states principle (CSP): saturated liquids at the same reduced density (ρR = ρ/ρc) have comparable dimensionless thermodynamic properties. This CSP is shown to be applicable to a variety of thermodynamic properties that include entropy of vaporization, cohesive energy density, thermal expansion coefficient, isothermal compressibility, thermal pressure coefficient, compressibility factor, temperature coefficient of the vapor pressure, heat capacity difference, and surface tension. For two classes of liquids, all properties rendered dimensionless by the proper choice of scaling variables superpose to form "master curves" that illustrate the CSP. Using scaled particle theory, an improved van der Waals model is developed whose results are compared with existing experimental thermodynamic data in dimensionless form. Properly expressing thermodynamic properties in dimensionless form acts to consolidate and harmonize liquid state properties.

The journal of physical chemistry. B, Jan 26, 2014

For 68 fluids that include hydrogen bonding and quantum fluids, the fugacity coefficient that def... more For 68 fluids that include hydrogen bonding and quantum fluids, the fugacity coefficient that defines the residual chemical potential adopts a near universal value of 2/3 at the critical point. More precisely, the reciprocal of the fugacity coefficient equals 1.52 ± 0.02 and includes fluids as diverse as helium (1.50), dodecafluoropentane (1.50), and water (1.53). For 65 classical fluids, a dimensionless thermal pressure coefficient and internal pressure attain critical values of 1.88 ± 0.11 and 1.61 ± 0.11, respectively. From equations of state, values of these new critical constants have been calculated and agree favorably with experimental values. Specifically, for the critical fugacity coefficient, the following results were obtained for its reciprocal: van der Waals (1.44), lattice gas (1.43), scaled particle theory (1.46), and the Redlich-Kwong eq (1.50). The semiempirical Redlich-Kwong equation is also the most accurate for the thermal pressure coefficient (1.86) and internal pressure (1.53). Physical interpretations of these results are discussed as well as their implications for other critical phenomena.

2012 IEEE International Conference on Systems, Man, and Cybernetics (SMC), 2012

Journal of Research of the National Bureau of Standards Section A: Physics and Chemistry, 1973

New Trends in Physics and Physucal Chemistry of Polymers, 1989

Journal of Material Science & Engineering, 2013

2012 IEEE International Conference on Systems, Man, and Cybernetics (SMC), 2012

The Journal of Physical Chemistry, 1989

Page 1. J. Phys. Chem. 1989, 93, 6983-6991 6983 was not very sensitive to any of these model vari... more Page 1. J. Phys. Chem. 1989, 93, 6983-6991 6983 was not very sensitive to any of these model variables. The exponent, a, was fixed at 0.8; the fit for eq 5 was not sensitive to the value of a. The uncertainty in the viscosity was ...

Journal of Polymer Science: Polymer Symposia, 1977

... ISAAC C. SANCHEZ* Materials Research Laboratory. ... be developed for a spherical crystal, or... more ... ISAAC C. SANCHEZ* Materials Research Laboratory. ... be developed for a spherical crystal, or any crystal for which the dimensions of the crystal surface increase as r?. In this case the number of nucleation sites is approxi-mately ( S ~ ) ~ / U ~ and the Binsbergen cube root law ...

Physics of Polymer Surfaces and Interfaces, 1992

Journal of Modern Physics, 2011

Physics of Polymer Surfaces and Interfaces, 1992

The Journal of Physical Chemistry, 1976

... LL phase diagram can be ascertained by characterizing the temperature dependence of these ...... more ... LL phase diagram can be ascertained by characterizing the temperature dependence of these ... in I1 and IV require an almost fortuitous combination of the pure component parameters and x ...behavior is characteristic of polymer solutions1' but not of low molecular weight solutions. ...

Colloids and surfaces. B, Biointerfaces, 2013

The relationship between electrical conductivity, structure and antibacterial properties of chito... more The relationship between electrical conductivity, structure and antibacterial properties of chitosan-silver nanoparticles (CS/AgnP) biocomposites has been analyzed. To test the film's antimicrobial activity, Gram-positive and Gram-negative bacteria were studied. The interactions between silver nanoparticles with chitosan suggest the formation of silver ions which plays a major role in nanocomposite's bactericidal potency. In CS/AgnP biocomposites, the bactericide effectiveness increases by increasing AgnP concentrations up to 3 wt%, which is close to the electrical percolation threshold of ca. 3 wt%. As the AgnP concentration increases above this threshold, the bactericidal potency is greatly diminished. The elucidated correlation between electrical conductivity and antibacterial activity could be useful in the design of other nanocomposites that involve polymeric-based matrices.

Polymer, 1995

Recently it has been shown that the compression response of polymer liquids, glasses and solution... more Recently it has been shown that the compression response of polymer liquids, glasses and solutions satisfies a strong temperature—pressure superposition principle. Using a phenomenological argument, a new isothermal equation of state was developed to describe this new principle quantitatively. In this paper we extend the range of applicability of this new equation of sate, enabling it to describe quantitatively polymer

The Wiley Database of Polymer Properties, 2003

The journal of physical chemistry. B, Jan 26, 2009

An analysis of the expected divergences in thermodynamic properties at the close-pack density (et... more An analysis of the expected divergences in thermodynamic properties at the close-pack density (eta(cp) = pi square root(2)/6) along with the known virial coefficients up to 10th order suggests a weak logarithmic singularity in the excess fluid entropy. The corresponding equation of state (EOS) also possesses a singularity at eta(cp). The new EOS accurately describes extant molecular dynamics data up to the fluid-solid transition (eta approximately 0.494) with differences of less than 1 part per thousand. This accuracy is maintained into the metastable fluid regime up to eta approximately 0.52. In terms of accuracy, the new EOS is no better than Pade approximants, but the new EOS, unlike the Pade approximants, diverges at eta(cp). In addition, a new order parameter is defined that enables all system configurations to be classified as either disordered or ordered. Monte Carlo simulations are used to determine this order parameter in the metastable fluid range. Using this new order parameter, evidence is presented to support a thermodynamic glass transition at eta approximately 0.54. With respect to this transition, congruence is found with the traditional ideas espoused by Gibbs and DiMarzio and Adam and Gibbs. It is the rapid disappearance of disordered (random) configurations with increasing density that drives the glass transition and slows the dynamics.

Scientific reports, 2014

Globular proteins contain cavities/voids that play specific roles in controlling protein function... more Globular proteins contain cavities/voids that play specific roles in controlling protein function. Elongated cavities provide migration channels for the transport of ions and small molecules to the active center of a protein or enzyme. Using Monte Carlo and Molecular Dynamics on fully atomistic protein/water models, a new computational methodology is introduced that takes into account the protein's dynamic structure and maps all the cavities in and on the surface. To demonstrate its utility, the methodology is applied to study cavity structure in myoglobin and five of its mutants. Computed cavity and channel size distributions reveal significant differences relative to the wild type myoglobin. Computer visualization of the channels leading to the heme center indicates restricted ligand access for the mutants consistent with the existing interpretations. The new methodology provides a quantitative measure of cavity structure and distributions and can become a valuable tool for the structural characterization of proteins.

The journal of physical chemistry. B, Jan 7, 2014

Equations of state in the van der Waals genre suggest that saturated liquids should adhere to the... more Equations of state in the van der Waals genre suggest that saturated liquids should adhere to the following corresponding states principle (CSP): saturated liquids at the same reduced density (ρR = ρ/ρc) have comparable dimensionless thermodynamic properties. This CSP is shown to be applicable to a variety of thermodynamic properties that include entropy of vaporization, cohesive energy density, thermal expansion coefficient, isothermal compressibility, thermal pressure coefficient, compressibility factor, temperature coefficient of the vapor pressure, heat capacity difference, and surface tension. For two classes of liquids, all properties rendered dimensionless by the proper choice of scaling variables superpose to form "master curves" that illustrate the CSP. Using scaled particle theory, an improved van der Waals model is developed whose results are compared with existing experimental thermodynamic data in dimensionless form. Properly expressing thermodynamic properties in dimensionless form acts to consolidate and harmonize liquid state properties.

The journal of physical chemistry. B, Jan 26, 2014

For 68 fluids that include hydrogen bonding and quantum fluids, the fugacity coefficient that def... more For 68 fluids that include hydrogen bonding and quantum fluids, the fugacity coefficient that defines the residual chemical potential adopts a near universal value of 2/3 at the critical point. More precisely, the reciprocal of the fugacity coefficient equals 1.52 ± 0.02 and includes fluids as diverse as helium (1.50), dodecafluoropentane (1.50), and water (1.53). For 65 classical fluids, a dimensionless thermal pressure coefficient and internal pressure attain critical values of 1.88 ± 0.11 and 1.61 ± 0.11, respectively. From equations of state, values of these new critical constants have been calculated and agree favorably with experimental values. Specifically, for the critical fugacity coefficient, the following results were obtained for its reciprocal: van der Waals (1.44), lattice gas (1.43), scaled particle theory (1.46), and the Redlich-Kwong eq (1.50). The semiempirical Redlich-Kwong equation is also the most accurate for the thermal pressure coefficient (1.86) and internal pressure (1.53). Physical interpretations of these results are discussed as well as their implications for other critical phenomena.

2012 IEEE International Conference on Systems, Man, and Cybernetics (SMC), 2012

Journal of Research of the National Bureau of Standards Section A: Physics and Chemistry, 1973

New Trends in Physics and Physucal Chemistry of Polymers, 1989

Journal of Material Science & Engineering, 2013

2012 IEEE International Conference on Systems, Man, and Cybernetics (SMC), 2012

The Journal of Physical Chemistry, 1989

Page 1. J. Phys. Chem. 1989, 93, 6983-6991 6983 was not very sensitive to any of these model vari... more Page 1. J. Phys. Chem. 1989, 93, 6983-6991 6983 was not very sensitive to any of these model variables. The exponent, a, was fixed at 0.8; the fit for eq 5 was not sensitive to the value of a. The uncertainty in the viscosity was ...

Journal of Polymer Science: Polymer Symposia, 1977

... ISAAC C. SANCHEZ* Materials Research Laboratory. ... be developed for a spherical crystal, or... more ... ISAAC C. SANCHEZ* Materials Research Laboratory. ... be developed for a spherical crystal, or any crystal for which the dimensions of the crystal surface increase as r?. In this case the number of nucleation sites is approxi-mately ( S ~ ) ~ / U ~ and the Binsbergen cube root law ...

Physics of Polymer Surfaces and Interfaces, 1992

Journal of Modern Physics, 2011

Physics of Polymer Surfaces and Interfaces, 1992

The Journal of Physical Chemistry, 1976

... LL phase diagram can be ascertained by characterizing the temperature dependence of these ...... more ... LL phase diagram can be ascertained by characterizing the temperature dependence of these ... in I1 and IV require an almost fortuitous combination of the pure component parameters and x ...behavior is characteristic of polymer solutions1' but not of low molecular weight solutions. ...

Colloids and surfaces. B, Biointerfaces, 2013

The relationship between electrical conductivity, structure and antibacterial properties of chito... more The relationship between electrical conductivity, structure and antibacterial properties of chitosan-silver nanoparticles (CS/AgnP) biocomposites has been analyzed. To test the film's antimicrobial activity, Gram-positive and Gram-negative bacteria were studied. The interactions between silver nanoparticles with chitosan suggest the formation of silver ions which plays a major role in nanocomposite's bactericidal potency. In CS/AgnP biocomposites, the bactericide effectiveness increases by increasing AgnP concentrations up to 3 wt%, which is close to the electrical percolation threshold of ca. 3 wt%. As the AgnP concentration increases above this threshold, the bactericidal potency is greatly diminished. The elucidated correlation between electrical conductivity and antibacterial activity could be useful in the design of other nanocomposites that involve polymeric-based matrices.

Polymer, 1995

Recently it has been shown that the compression response of polymer liquids, glasses and solution... more Recently it has been shown that the compression response of polymer liquids, glasses and solutions satisfies a strong temperature—pressure superposition principle. Using a phenomenological argument, a new isothermal equation of state was developed to describe this new principle quantitatively. In this paper we extend the range of applicability of this new equation of sate, enabling it to describe quantitatively polymer

The Wiley Database of Polymer Properties, 2003