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Pablo C Schulz - One of the best experts on this subject based on the ideXlab platform.

  • Aqueous sodium dehydrocholate–sodium deoxycholate mixtures at low concentration
    Journal of colloid and interface science, 2007
    Co-Authors: Marcos D. Fernández-leyes, Paula V Messina, Pablo C Schulz
    Abstract:

    The behavior of the sodium dehydrocholate (NaDHC)-sodium deoxycholate (NaDC) mixed system was studied by a battery of methods that examine effects caused by the different components of the system: monomers, micelles, and both components. The behavior of the mixed micellar system was studied by the application of Rubingh's model. The obtained results show that micellar interaction was repulsive when the aggregates were rich in NaDHC. The gradual inclusion of NaDC in micelles led to a structural transformation in the aggregates and the interaction became attractive. The bile salts' behavior in mixed monolayers at the air-solution interface was also investigated. Mixed monolayers are monotonically rich in NaDC, giving a stable and compact adsorbed layer. Results have shown that the interaction in both micelles and monolayer is not ideal and such behavior is assumed to be due to a structural factor in their Hydrocarbon Backbone.

  • Aqueous sodium oleate–sodium dehydrocholate mixtures at low concentration
    Colloid and Polymer Science, 2003
    Co-Authors: Paula Messina, Marcela A Morini, Pablo C Schulz
    Abstract:

    The aqueous mixed system sodium dehydrocholate (NaDHC)–sodium oleate (NaOL) was studied by several methods to determine the influence of the hydrophobic structure of both surfactants in the mixed micellization and the formation of the mixed monolayer adsorbed at the air–water interface. The molecular area at the critical micelle concentration in pure surfactant solutions suggests that the adsorbed oleate chain was folded to allow the double bond in the middle of the molecule to remain in contact with water, and that the NaDHC molecule was situated with its plane laying parallel to the water surface, allowing the three carbonyl groups in the Hydrocarbon Backbone to form hydrogen bonds with water. The interaction was repulsive at the surface, and in the mixed monolayer some molecules must move away the less hydrophilic groups from water (double bond of NaOL, carbonyl groups of NaDHC). The interaction in mixed micelles was strongly attractive, showing a preferential composition roughly equimolar. The hydrolysis in mixed micelles was augmented in comparison with pure surfactants systems, which could be explained by assuming the existence of a more hydrophobic mixed micelle core. The mixed micelle degree of ionization was below that of the pure micelles, thus indicating a high surface charge density.

  • aqueous sodium oleate sodium dehydrocholate mixtures at low concentration
    Colloid and Polymer Science, 2003
    Co-Authors: Paula V Messina, Marcela A Morini, Pablo C Schulz
    Abstract:

    The aqueous mixed system sodium dehydrocholate (NaDHC)–sodium oleate (NaOL) was studied by several methods to determine the influence of the hydrophobic structure of both surfactants in the mixed micellization and the formation of the mixed monolayer adsorbed at the air–water interface. The molecular area at the critical micelle concentration in pure surfactant solutions suggests that the adsorbed oleate chain was folded to allow the double bond in the middle of the molecule to remain in contact with water, and that the NaDHC molecule was situated with its plane laying parallel to the water surface, allowing the three carbonyl groups in the Hydrocarbon Backbone to form hydrogen bonds with water. The interaction was repulsive at the surface, and in the mixed monolayer some molecules must move away the less hydrophilic groups from water (double bond of NaOL, carbonyl groups of NaDHC). The interaction in mixed micelles was strongly attractive, showing a preferential composition roughly equimolar. The hydrolysis in mixed micelles was augmented in comparison with pure surfactants systems, which could be explained by assuming the existence of a more hydrophobic mixed micelle core. The mixed micelle degree of ionization was below that of the pure micelles, thus indicating a high surface charge density.

  • Aqueous sodium oleate-sodium dehydrocho- late mixtures at low concentration
    2003
    Co-Authors: Paula V Messina, Marcela A Morini, Pablo C Schulz
    Abstract:

    The aqueous mixed system sodium dehydrocholate (NaDHC)- sodium oleate (NaOL) was studied by several methods to determine the influence of the hydrophobic struc- ture of both surfactants in the mixed micellization and the forma- tion of the mixed monolayer ad- sorbed at the air-water interface. The molecular area at the critical micelle concentration in pure sur- factant solutions suggests that the adsorbed oleate chain was folded to allow the double bond in the middle of the molecule to remain in contact with water, and that the NaDHC molecule was situated with its plane laying parallel to the water surface, allowing the three carbonyl groups in the Hydrocarbon Backbone to form hydrogen bonds with water. The interaction was repulsive at the surface, and in the mixed mono- layer some molecules must move away the less hydrophilic groups from water (double bond of NaOL, carbonyl groups of NaDHC). The interaction in mixed micelles was strongly attractive, showing a pref- erential composition roughly equi- molar. The hydrolysis in mixed micelles was augmented in compar- ison with pure surfactants systems, which could be explained by assuming the existence of a more hydrophobic mixed micelle core. The mixed micelle degree of ioni- zation was below that of the pure micelles, thus indicating a high surface charge density.

Johannes H. Knoetze - One of the best experts on this subject based on the ideXlab platform.

  • Phase equilibria of methyl esters in supercritical propane
    The Journal of Supercritical Fluids, 2015
    Co-Authors: Cara E. Schwarz, Q.h. Paulse, Johannes H. Knoetze
    Abstract:

    Abstract High pressure phase equilibria measurements using a static synthetic view cell for methyl decanoate, methyl dodecanoate, methyl hexadecanoate, methyl octadecaonate and methyl docosanoate in supercritical propane were conducted between 376.6 and 412.4 K at methyl ester mass fractions between 0.0178 and 0.660. The data show a linear increase in phase transition pressure with an increase in temperature at constant composition and, within the experimental range, total solubility was achieved below 8.1 MPa for all systems. Comparing the various data sets, an increase in phase transition pressure with increasing Hydrocarbon Backbone is noted, indicating that propane is able to fractionate a mixture of methyl esters.

  • High pressure phase equilibria of ethyl esters in supercritical ethane and propane
    The Journal of Supercritical Fluids, 2013
    Co-Authors: Cara E. Schwarz, C. Schlechter, Johannes H. Knoetze
    Abstract:

    Abstract The high pressure phase equilibria of ethyl esters (ethyl decanoate/caprate, ethyl dodecanoate/laurate, ethyl tetradecanoate/myristate and ethyl hexadecanoate/palmitate) in supercritical ethane and propane have been measured in the temperature ranges 311–358 K (TR = 1.02–1.17) and 376–409 K (TR = 1.02–1.11), respectively. The measurements were conducted in a high pressure view cell for ethyl ester mass fractions between 0.015 and 0.65. The results show a generally linear relationship between the phase transition temperature and pressure. No temperature inversions or three phase regions were observed. An increase in Hydrocarbon Backbone length leads to an increase in phase transition pressure. For ethane as supercritical solvent, this increase is linear. For propane as supercritical solvent, the nature of the increase was not quantified as the magnitude of the increase would be significantly influenced by the experimental measurement error as the observed increase is not very large. Comparison of the phase behaviour of ethyl esters with methyl esters shows very little difference, yet the phase transition pressure of ethyl esters in supercritical ethane and propane is significantly lower than those of the corresponding acids. The phase transition pressure of ethyl esters in ethane and propane is also lower than those in carbon dioxide.

  • Phase equilibrium measurements of long chain acids in supercritical carbon dioxide
    The Journal of Supercritical Fluids, 2012
    Co-Authors: Cara E. Schwarz, Johannes H. Knoetze
    Abstract:

    Abstract Data on the phase behaviour of long chain fatty acids (octanoic, decanoic, undecanoic, dodecanoic, tetradecanoic, hexadecanoic and octadecanoic) in supercritical carbon dioxide is presented at temperatures between 308 and 358 K and pressures up to 27 MPa. No three-phase regions were observed and at constant composition, an increase in temperature leads to an increase in phase transition pressure. An increase in Hydrocarbon Backbone length also leads to an increase in phase transition pressure. Comparison of the measured data with literature data of n-alkanes, 1-alcohols, methyl esters and ethyl esters of the same Hydrocarbon Backbone length shows that carbon dioxide is able to easily distinguish between acids and n-alkanes, methyl esters or ethyl ester and, with selection of the correct conditions, carbon dioxide is also able to distinguish between acids and 1-alcohols. However, unlike for propane, the phase behaviour of an acid in carbon dioxide does not mimic that of an alkane with double the number of carbon atoms, most probably due to the effect of the quadrupole moment of carbon dioxide.

  • solubility measurements of high molecular mass n alkanes n alcohols and alcohol ethoxylates in supercritical propane
    Fluid Phase Equilibria, 2006
    Co-Authors: C E Schwarz, Izak Nieuwoudt, Johannes H. Knoetze
    Abstract:

    Abstract Pseudo binary high-pressure solubility measurements of a commercial mixture of high molecular mass n-alcohols (Mave = 566 g/mol) in propane and a commercial mixture of high molecular mass alcohol ethoxylates (50% ethoxylated, Mave = 1100 g/mol) in propane were conducted at temperatures between 375 and 410 K and pressures up to 275 bar. The propane–n-alcohol solubility curve shows complete solubility at pressures below 150 bar. At these conditions the propane–alcohol ethoxylate solubility curve shows a region of liquid-fluid immiscibility as well as a solubility inversion with temperature. Comparing the solubility of an n-alkane, an n-alcohol and a 50% ethoxylated alcohol ethoxylate, all with the same average Hydrocarbon Backbone length, in propane it is seen that the n-alkane is the most soluble, followed by the n-alcohol and the alcohol ethoxylate is the least soluble.

Cara E. Schwarz - One of the best experts on this subject based on the ideXlab platform.

  • High Pressure Phase Equilibria of the CO2/Saturated Ethyl Esters Homologous Series
    Journal of Chemical & Engineering Data, 2018
    Co-Authors: Cara E. Schwarz
    Abstract:

    A systematic study on the phase behavior of saturated ethyl esters with supercritical CO2 is presented. High pressure phase behavior measurements for the systems CO2/ethyl decanoate, CO2/ethyl dodecanoate, CO2/ethyl tetradecanoate, and CO2/ethyl hexadecanoate were conducted in a static synthetic view cell in the temperature range 308–358 K. Phase transition pressures were measured in the range 5.86–23.01 MPa for ethyl ester mass fractions in the range 0.0174–0.657 and complement existing literature data. Throughout the temperature and compositional range measured, which encompassed the liquid phase, mixture critical region, and vapor phase, an increase in temperature leads to an increase in phase transition pressure with no temperature inversions or three phase regions observed. Additionally, an increase in Hydrocarbon Backbone length leads to an ever-increasing phase-transition pressure, suggesting fractionation of ethyl esters according to molecular mass with supercritical CO2 is possible. Finally, the ...

  • Phase equilibria of methyl esters in supercritical propane
    The Journal of Supercritical Fluids, 2015
    Co-Authors: Cara E. Schwarz, Q.h. Paulse, Johannes H. Knoetze
    Abstract:

    Abstract High pressure phase equilibria measurements using a static synthetic view cell for methyl decanoate, methyl dodecanoate, methyl hexadecanoate, methyl octadecaonate and methyl docosanoate in supercritical propane were conducted between 376.6 and 412.4 K at methyl ester mass fractions between 0.0178 and 0.660. The data show a linear increase in phase transition pressure with an increase in temperature at constant composition and, within the experimental range, total solubility was achieved below 8.1 MPa for all systems. Comparing the various data sets, an increase in phase transition pressure with increasing Hydrocarbon Backbone is noted, indicating that propane is able to fractionate a mixture of methyl esters.

  • High pressure phase equilibria of ethyl esters in supercritical ethane and propane
    The Journal of Supercritical Fluids, 2013
    Co-Authors: Cara E. Schwarz, C. Schlechter, Johannes H. Knoetze
    Abstract:

    Abstract The high pressure phase equilibria of ethyl esters (ethyl decanoate/caprate, ethyl dodecanoate/laurate, ethyl tetradecanoate/myristate and ethyl hexadecanoate/palmitate) in supercritical ethane and propane have been measured in the temperature ranges 311–358 K (TR = 1.02–1.17) and 376–409 K (TR = 1.02–1.11), respectively. The measurements were conducted in a high pressure view cell for ethyl ester mass fractions between 0.015 and 0.65. The results show a generally linear relationship between the phase transition temperature and pressure. No temperature inversions or three phase regions were observed. An increase in Hydrocarbon Backbone length leads to an increase in phase transition pressure. For ethane as supercritical solvent, this increase is linear. For propane as supercritical solvent, the nature of the increase was not quantified as the magnitude of the increase would be significantly influenced by the experimental measurement error as the observed increase is not very large. Comparison of the phase behaviour of ethyl esters with methyl esters shows very little difference, yet the phase transition pressure of ethyl esters in supercritical ethane and propane is significantly lower than those of the corresponding acids. The phase transition pressure of ethyl esters in ethane and propane is also lower than those in carbon dioxide.

  • Phase equilibrium measurements of long chain acids in supercritical carbon dioxide
    The Journal of Supercritical Fluids, 2012
    Co-Authors: Cara E. Schwarz, Johannes H. Knoetze
    Abstract:

    Abstract Data on the phase behaviour of long chain fatty acids (octanoic, decanoic, undecanoic, dodecanoic, tetradecanoic, hexadecanoic and octadecanoic) in supercritical carbon dioxide is presented at temperatures between 308 and 358 K and pressures up to 27 MPa. No three-phase regions were observed and at constant composition, an increase in temperature leads to an increase in phase transition pressure. An increase in Hydrocarbon Backbone length also leads to an increase in phase transition pressure. Comparison of the measured data with literature data of n-alkanes, 1-alcohols, methyl esters and ethyl esters of the same Hydrocarbon Backbone length shows that carbon dioxide is able to easily distinguish between acids and n-alkanes, methyl esters or ethyl ester and, with selection of the correct conditions, carbon dioxide is also able to distinguish between acids and 1-alcohols. However, unlike for propane, the phase behaviour of an acid in carbon dioxide does not mimic that of an alkane with double the number of carbon atoms, most probably due to the effect of the quadrupole moment of carbon dioxide.

Paula V Messina - One of the best experts on this subject based on the ideXlab platform.

  • Aqueous sodium dehydrocholate–sodium deoxycholate mixtures at low concentration
    Journal of colloid and interface science, 2007
    Co-Authors: Marcos D. Fernández-leyes, Paula V Messina, Pablo C Schulz
    Abstract:

    The behavior of the sodium dehydrocholate (NaDHC)-sodium deoxycholate (NaDC) mixed system was studied by a battery of methods that examine effects caused by the different components of the system: monomers, micelles, and both components. The behavior of the mixed micellar system was studied by the application of Rubingh's model. The obtained results show that micellar interaction was repulsive when the aggregates were rich in NaDHC. The gradual inclusion of NaDC in micelles led to a structural transformation in the aggregates and the interaction became attractive. The bile salts' behavior in mixed monolayers at the air-solution interface was also investigated. Mixed monolayers are monotonically rich in NaDC, giving a stable and compact adsorbed layer. Results have shown that the interaction in both micelles and monolayer is not ideal and such behavior is assumed to be due to a structural factor in their Hydrocarbon Backbone.

  • aqueous sodium oleate sodium dehydrocholate mixtures at low concentration
    Colloid and Polymer Science, 2003
    Co-Authors: Paula V Messina, Marcela A Morini, Pablo C Schulz
    Abstract:

    The aqueous mixed system sodium dehydrocholate (NaDHC)–sodium oleate (NaOL) was studied by several methods to determine the influence of the hydrophobic structure of both surfactants in the mixed micellization and the formation of the mixed monolayer adsorbed at the air–water interface. The molecular area at the critical micelle concentration in pure surfactant solutions suggests that the adsorbed oleate chain was folded to allow the double bond in the middle of the molecule to remain in contact with water, and that the NaDHC molecule was situated with its plane laying parallel to the water surface, allowing the three carbonyl groups in the Hydrocarbon Backbone to form hydrogen bonds with water. The interaction was repulsive at the surface, and in the mixed monolayer some molecules must move away the less hydrophilic groups from water (double bond of NaOL, carbonyl groups of NaDHC). The interaction in mixed micelles was strongly attractive, showing a preferential composition roughly equimolar. The hydrolysis in mixed micelles was augmented in comparison with pure surfactants systems, which could be explained by assuming the existence of a more hydrophobic mixed micelle core. The mixed micelle degree of ionization was below that of the pure micelles, thus indicating a high surface charge density.

  • Aqueous sodium oleate-sodium dehydrocho- late mixtures at low concentration
    2003
    Co-Authors: Paula V Messina, Marcela A Morini, Pablo C Schulz
    Abstract:

    The aqueous mixed system sodium dehydrocholate (NaDHC)- sodium oleate (NaOL) was studied by several methods to determine the influence of the hydrophobic struc- ture of both surfactants in the mixed micellization and the forma- tion of the mixed monolayer ad- sorbed at the air-water interface. The molecular area at the critical micelle concentration in pure sur- factant solutions suggests that the adsorbed oleate chain was folded to allow the double bond in the middle of the molecule to remain in contact with water, and that the NaDHC molecule was situated with its plane laying parallel to the water surface, allowing the three carbonyl groups in the Hydrocarbon Backbone to form hydrogen bonds with water. The interaction was repulsive at the surface, and in the mixed mono- layer some molecules must move away the less hydrophilic groups from water (double bond of NaOL, carbonyl groups of NaDHC). The interaction in mixed micelles was strongly attractive, showing a pref- erential composition roughly equi- molar. The hydrolysis in mixed micelles was augmented in compar- ison with pure surfactants systems, which could be explained by assuming the existence of a more hydrophobic mixed micelle core. The mixed micelle degree of ioni- zation was below that of the pure micelles, thus indicating a high surface charge density.

Paul A. Kohl - One of the best experts on this subject based on the ideXlab platform.

  • High Conductivity, Lithium Ion Conducting Polymer Electrolyte Based on Hydrocarbon Backbone with Pendent Carbonate
    Journal of The Electrochemical Society, 2020
    Co-Authors: Nian Liu, Paul A. Kohl
    Abstract:

    Solid polymer electrolytes (sPE) offer a pathway for safer, less flammable lithium batteries. However, developing a polymer that provides high Li+ mobility as well electrochemical stability remains a challenge, because ion conductive functional units in the polymer main-chain (e.g., polycarbonate and polyether) usually suffer from poor electrochemical stability at high and low potentials. Herein, an sPE with pendent carbonate on a Hydrocarbon Backbone has been designed and synthesized to overcome conductivity and electrochemical stability problems. This pendant polycarbonate is different from conventional polycarbonate electrolytes because the carbonate moiety is in the sidechain, which mitigates polycarbonate Backbone stability problems while still providing high ionic conductivity when used with a plasticizer Conductivity as high as 1.1 mS/cm at 22oC was obtained. Stable lithium metal plating using and stripping using the sPE was observed for 1,200 hours and electrochemical stability up to 4.6 V vs Li+/Li has been demonstrated. The low interfacial resistance (

  • high conductivity lithium ion conducting polymer electrolyte based on Hydrocarbon Backbone with pendent carbonate
    Journal of The Electrochemical Society, 2020
    Co-Authors: Nian Liu, Paul A. Kohl
    Abstract:

    Solid polymer electrolytes (sPE) offer a pathway for safer, less flammable lithium batteries. However, developing a polymer that provides high Li+ mobility as well electrochemical stability remains a challenge, because ion conductive functional units in the polymer main-chain (e.g., polycarbonate and polyether) usually suffer from poor electrochemical stability at high and low potentials. Herein, an sPE with pendent carbonate on a Hydrocarbon Backbone has been designed and synthesized to overcome conductivity and electrochemical stability problems. This pendant polycarbonate is different from conventional polycarbonate electrolytes because the carbonate moiety is in the sidechain, which mitigates polycarbonate Backbone stability problems while still providing high ionic conductivity when used with a plasticizer Conductivity as high as 1.1 mS/cm at 22oC was obtained. Stable lithium metal plating using and stripping using the sPE was observed for 1,200 hours and electrochemical stability up to 4.6 V vs Li+/Li has been demonstrated. The low interfacial resistance (<160 ohmcm2 at 22oC) and reasonable ionic conductivity have enabled acceptable cycling performance in a Li-LiFePO4 battery at 0.98 mA/cm2 for 2,300 cycles.

  • highly conductive anion exchange membranes based on cross linked poly norbornene vinyl addition polymerization
    ACS Applied Energy Materials, 2019
    Co-Authors: Mrinmay Mandal, Garrett Huang, Paul A. Kohl
    Abstract:

    Cross-linked (XL) anion-exchange membranes (AEMs) synthesized by vinyl addition polymerization of norbornene were prepared for use in anion-exchange membrane electrochemical devices, including fuel cells and electrolyzers. Tetrablock copolymers composed of an all-Hydrocarbon Backbone with a very high ion-exchange capacity (IEC), 3.46 mequiv/g, were synthesized. Light cross-linking was found to be adequate for providing critical control over unwanted water uptake. This enabled use of very high IEC membranes. Without light cross-linking, the unwanted water uptake would cause swelling and softening of the membrane. The best performing membrane had no significant drop in ionic conductivity over 1000 h of aging in 1 M NaOH at 80 °C and a record high ionic conductivity of 198 mS/cm at 80 °C (for a chemically stable AEM). The number of bound and free water molecules per ion pair is described along with ion mobility comparisons to previous materials. The membranes are suitable for electrochemical devices and were...

  • highly conducting anion exchange membranes based on cross linked poly norbornene ring opening metathesis polymerization
    ACS Applied Energy Materials, 2019
    Co-Authors: Mrinmay Mandal, Garrett Huang, Wanting Chen, Xuemei Wu, Gaohong He, Paul A. Kohl
    Abstract:

    A series of cross-linked (XL) anion-exchange membranes (AEMs) were synthesized on the basis of the ring opening metathesis polymerization (ROMP) of norbornene monomers (rPNB). Poly(bromopropyl norbornene)-block-poly(butyl norbornene) diblock copolymers and poly(bromopropyl norbornene) homopolymers have an all-Hydrocarbon Backbone and a high ion-exchange capacity (IEC), up to 4.73 mequiv/g. N,N,N′,N′-Tetramethyl-1,6-hexanediamine (TMHDA) was used as a cross-linking agent to control the water uptake and mechanical instability. The cross-linked (20 mol % concentration) membrane made from high molecular weight poly(bromopropyl norbornene) (XL20-rPNB-LY100) had the highest conductivity of 99 mS/cm at 25 °C and 195 mS/cm at 80 °C. The alkaline stability of the best membrane was excellent with no detectable degradation in conductivity after 792 h in 1 M NaOH at 80 °C. Membranes were successfully tested as the polymer electrolyte in an AEM fuel cell.

  • anionic multiblock copolymer membrane based on vinyl addition polymerization of norbornenes applications in anion exchange membrane fuel cells
    Journal of Membrane Science, 2019
    Co-Authors: Mrinmay Mandal, Garrett Huang, Paul A. Kohl
    Abstract:

    Abstract Stable, non-hydrolysable, hydroxide-conducting polymers are of interest for electrochemical devices such as fuel cells, electrolyzers and flow-batteries. In this study, a series of tetrablock copolymers containing an all-Hydrocarbon Backbone were synthesized. The synthesis is based on vinyl addition polymerization of norbornene using (η3-allyl)Pd(iPr3P)Cl as the catalyst and lithium tetrakis(pentafluorophenyl)-borate·(2.5Et2O) (Li[FABA]) as the activator. The tetrablock polymers were cast into membranes with an ion-exchange capacity (IEC) between 1.55 and 2.60 milliequivalents per gram (meq/g). The number of bound and unbound water molecules per ion pair was measured and correlated with conductivity. The membrane with the highest IEC (2.60 meq/g) had 10.6 unbound (i.e. free) and 17.9 bound water molecules per ion pair within the polymer. The presence of excess unbound water has led to flooding of the ion conductive channels and low hydroxide ion conductivity. The optimal anion conductivity was found with about 6.7 unbound and 11.9 bound water molecules per ion pair. Excellent hydroxide conductivity (>120 mS/cm at 80 °C) was obtained at an ion-exchange capacity of 1.88 meq/g. The results show that hydroxide mobility is aided by phase segregation within the copolymer. The ion conducting polymer was stable in 1 M NaOH solution at 80 °C, showing essentially no loss in ion conductivity in 1200 h. Thermogravimetric analysis showed that the membrane Backbone was stable up to 400 °C, consistent with previous polynorbornene-based materials. The peak power density of a H2/O2, hydroxide conducting fuel cell containing one of these membranes was 542.57 mW/cm2 at 0.43 V and current density of 1.26 A/cm2 at 60 °C.