Matthew W. Liberatore

Colorado School of Mines, گلدن، کلرادو, Colorado, United States

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Publications (76)178.2 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: Anion exchange membranes (AEM) are promising solid polymer electrolytes utilized in alkali fuel cells and electrochemical energy conversion devices. AEMs must efficiently conduct ions while maintaining chemical and mechanical stability under a range of operating conditions. The ionic nature of AEMs leads to stiff and brittle membranes under dry conditions while at higher hydrations, water sorption causes significant softening and weakening of the membrane. In this work, a new polyethylene-b-poly(vinylbenzyl trimethylammonium) polymer (70kg/mol) was cast into large (300cm2), thin (12±3μm) membranes. These membranes exhibited improved elasticity over previously tested AEMs, minimal dimensional swelling, and moderate ionic conductivity (5±2mS/cm at 50°C, 95% RH in the bromide form). Extensional testing indicated a 95% reduction in Young's modulus between dry and hydrated states. Further investigation of the complex modulus as a function of hydration, by dynamic mechanical analysis, revealed a sharp decrease in modulus between dry and hydrated states. Mechanical softening was reversible, but the location of the transition displayed hysteresis between humidification and dehumidification. Conductivity increased after membrane softening; suggesting bulk mechanical properties can identify the hydration level required for improved ion transport. Understanding the relationship between ion conduction and mechanical properties will help guide AEM development and identify operating conditions for sustained performance.
    Journal of Membrane Science 01/2016; 497:67-76. DOI:10.1016/j.memsci.2015.09.034 · 5.06 Impact Factor

  • ECS Transactions 10/2015; 69(17):363-367. DOI:10.1149/06917.0363ecst
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    ABSTRACT: Anion exchange membranes (AEM) are solid polymer electrolytes that facilitate ion transport in fuel cells. In this study, a polystyrene-b-poly(vinylbenzyl trimethylammonium) diblock copolymer was evaluated as potential AEM and compared with the equivalent homopolymer blend. The diblock had a 92% conversion of reactive sites with an IEC of 1.72 ± 0.05 mmol g−1, while the blend had a 43% conversion for an IEC of 0.80 ± 0.03 mmol g−1. At 50°C and 95% relative humidity, the chloride conductivity of the diblock was higher, 24–33 mS cm−1, compared with the blend, 1–6 mS cm−1. The diblock displayed phase separation on the length scale of 100 nm, while the blend displayed microphase separation (∼10 μm). Mechanical characterization of films from 40 to 90 microns thick found that elasticity and elongation decreased with the addition of cations to the films. At humidified conditions, water acted as a plasticizer to increase film elasticity and elongation. While the polystyrene-based diblock displayed sufficient ionic conductivity, the films' mechanical properties require improvement, i.e., greater elasticity and strength, before use in fuel cells. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 41596.
    Journal of Applied Polymer Science 10/2015; 132(10). DOI:10.1002/app.41596 · 1.77 Impact Factor
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    ABSTRACT: Despite the importance of fatty-acid methyl esters (FAMEs) as key components of various green solvents, detergents, plasticizers, and biodiesels, our understanding of these systems at the molecular level is limited. An enhanced molecular-level perspective of FAMEs will enable a detailed analysis of the polymorph and crystallization phenomena that adversely impact flow properties at low temperatures. Presented here, is the parameterization and validation of a charge-modified generalized amber force field (GAFF) for eight common FAMEs and two representative biodiesel mixtures. Our simulations accurately reproduce available experimental data (e.g. densities and self-diffusivity coefficients) and their trends, with respect to temperature and degree of unsaturation. Structural analyses from our simulations provide a more detailed picture of liquid-phase molecular ordering in FAMEs and confirm recent experimental hypotheses. This study provides a firm foundation to initiate further studies into the mechanisms that drive crystallization phenomena at the molecular level. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    ChemPhysChem 08/2015; DOI:10.1002/cphc.201500453 · 3.42 Impact Factor
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    Benjamin R. Caire · Melissa A. Vandiver · Matthew W. Liberatore ·
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    ABSTRACT: A new fixture for the mechanical characterization of thin polymer films under controlled temperature and relative humidity conditions is reported. Novel conducting polymers are often synthesized in small quantities and processed into films on the order of 10–100 microns thick. Standard tensile tests do not allow for adequate testing of these small sample sizes. Hence, a modification of the Sentmanat Extensional Rheometer (SER) to perform tensile testing on thin membranes is presented. Since the standard L-shaped pins do not secure thin polymer films at lower temperatures (i.e., below the melting point), screw down clamps were created to allow for mechanical characterization of solid polymer films. The new testing apparatus allows for mechanical characterization with as little as 2 % of the material needed for testing on a traditional tensile tester. In a parallel effort, a humidity delivery system developed for the TA Instruments ARES-G2 rheometer allows for testing at a range of temperatures (30–100 °C) and relative humidity conditions (0–95 % RH). The novel oven was benchmarked with low density polyethylene and Nafion 115Ⓡ. While the new experiment was built for characterization of ion exchange membranes for fuel cells, the oven is capable of characterizing any environmentally sensitive material using all standard rheometer geometries.
    Rheologica Acta 04/2015; 54(4). DOI:10.1007/s00397-014-0834-7 · 1.87 Impact Factor
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    ABSTRACT: Gilsonite is a natural fossil resource, similar to a petroleum asphalt high in asphaltenes. Asphaltenes are a class of organic compounds operationally defined based on their solubility in organic solvents, and as a result there is wide range of potential compositions and structures that can fit into this class. Specific compounds are challenging to propose due to its complexity. A sample of the asphaltene derived from the Gilsonite deposit was characterized by Fourier transform infrared spectroscopy, Raman spectroscopy, and high-resolution transmission electron microscopy. The high intensity of the 1600 cm−1 infrared peak, which corresponds to a CC stretching vibrational mode of the aromatic carbons also found prevalent in other asphaltenes, is likely a characteristic asphaltene feature. The high intensity can be explained by the stack structure and/or by polycyclic aromatic infrared transitions with a high dipole moment derivative. The nanosize stack structure was validated by the electron microscope and diffraction patterns, giving inter-sheet distances of 2.54 and 3.77 Å, respectively. Complementary calculations using density functional theory suggest a specific island-type polycyclic aromatic molecular model, with the calculated vibrational modes consistent with all of the characteristic peaks in the infrared spectrum. The method combining theoretical and experimental can be extended for more specific asphaltene molecular structure identifications.
    Fuel 04/2015; 157. DOI:10.1016/j.fuel.2015.04.029 · 3.52 Impact Factor
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    ABSTRACT: Anion exchange membranes (AEM) are polymer electrolytes that facilitate ion transport in alkaline fuel cells and electrochemical devices. Fabrication of mechanically durable AEMs with high ionic conductivity is a challenge. Here, a copolymer of isoprene and vinylbenzyl trimethylammonium and a terpolymer of isoprene, vinylbenzyl trimethylammonium and styrene were crosslinked by various methods, and properties, including conductivity and mechanical strength, were investigated at dry and saturated conditions. Polymer chemistry and degree of crosslinking significantly influenced conductivity, swelling, and mechanical properties. The terpolymer had a higher proportion of vinylbenzyl trimethylammonium units increasing the ion exchange capacity (IEC), but membranes could still be rendered insoluble by crosslinking. The higher IECof the terpolymer resulted in higher chloride conductivity, 20.75 mS/cm at 50°C and 95%RH, compared to 4.17 mS/cm for the copolymer at the same conditions. At dry conditions films were stiff, having Young's moduli between 100.740 MPa, but hydration caused severe softening, reducing moduli by 1.2 orders of magnitude. The severe softening effect of hydration was confirmed by dynamic mechanical analysis. The AEMs studied did not have adequate mechanical durability at hydrated conditions, additional work is needed to determine polymer chemistries and crosslinking methods that will produce robust AEMs for long-term use in fuel cells and electrochemical devices.
    Journal of The Electrochemical Society 01/2015; 162(4):H206-H212. DOI:10.1149/2.0471504jes · 3.27 Impact Factor
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    ABSTRACT: Fibrin is a biopolymer that gives thrombi the mechanical strength to withstand the forces imparted on them by blood flow. Importantly, fibrin is highly extensible, but strain hardens at low deformation rates. The density of fibrin in clots, especially arterial clots, is higher than that in gels made at plasma concentrations of fibrinogen (3-10 mg/mL), where most rheology studies have been conducted. Our objective in this study was to measure and characterize the elastic regimes of low (3-10 mg/mL) and high (30-100 mg/mL) density fibrin gels using shear and extensional rheology. Confocal microscopy of the gels shows that fiber density increases with fibrinogen concentration. At low strains, fibrin gels act as thermal networks independent of fibrinogen concentration. Within the low-strain regime, one can predict the mesh size of fibrin gels by the elastic modulus using semiflexible polymer theory. Significantly, this provides a link between gel mechanics and interstitial fluid flow. At moderate strains, we find that low-density fibrin gels act as nonaffine mechanical networks and transition to affine mechanical networks with increasing strains within the moderate regime, whereas high-density fibrin gels only act as affine mechanical networks. At high strains, the backbone of individual fibrin fibers stretches for all fibrin gels. Platelets can retract low-density gels by >80% of their initial volumes, but retraction is attenuated in high-density fibrin gels and with decreasing platelet density. Taken together, these results show that the nature of fibrin deformation is a strong function of fibrin fiber density, which has ramifications for the growth, embolization, and lysis of thrombi. Copyright © 2015 Biophysical Society. Published by Elsevier Inc. All rights reserved.
    Biophysical Journal 01/2015; 108(1):173-83. DOI:10.1016/j.bpj.2014.11.007 · 3.97 Impact Factor
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    ABSTRACT: We demonstrate that the true hydroxide conductivity in an e-beam grafted poly(ethylene-co-tetrafluoroethylene) [ETFE] anion exchange membrane (AEM) is as high as 132 mS cm-1 at 90 °C and 95%RH, comparable to a proton exchange membrane, but with very much less water present in the film. To understand this behaviour we studied ion transport of hydroxide, carbonate, bicarbonate and chloride, as well as water uptake and distribution. Water uptake of the AEM in water vapor is an order of magnitude lower than when submerged in liquid water. In addition 19F pulse field gradient spin echo NMR indicates that there is little tortuosity in the ionic pathways through the film. A complete analysis of the IR spectrum of the AEM and the analyses of water absorption using FT-IR led to conclusion that the fluorinated backbone chains do not interact with water and that two types of water domains exist within the membrane. The reduction in conductivity was measured during exposure of the OH- form of the AEM to air at 95% RH and was seen to be much slower than the reaction of CO2 with OH- as the amount of water in the film determines it ionic conductivity and at relative wet RHs its re-organization is slow.
    Physical Chemistry Chemical Physics 12/2014; 17(6). DOI:10.1039/C4CP05755D · 4.49 Impact Factor
  • T. P. Pandey · B. D. Peters · M. W. Liberatore ·
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    ABSTRACT: Conductivity of pure (air controlled) and air exposed hydroxide ion in a commercial Fumasep® FAA anion exchange membrane was compared using a unique sample preparation and conductivity measurements at controlled environment. At 95%RH and 80°C, the membrane had conductivity value of 0.075 S/cm at pure hydroxide form but reduced merely to 0.017 S/cm when the membrane was exposed to ambient CO2 for 2 days. A comparative anionic (OH-, CO32-, and HCO3- forms) conductivity study showed reduced ionic conductivity value (1/4 of its pure form) closed to HCO3- forms of the membrane. This indicated the formation of ionic mixture of CO32-, HCO3-, and residual OH- ions in the hydroxide form of the membrane when exposed to air. The hydroxide ions also showed a smaller ionic energy of activation when compared to other anions indicating a smaller ionic transport energy barrier.
    2014 ECS and SMEQ Joint International Meeting; 10/2014
  • Marc W. Donnelly · Mahilet Hailemichael · Matthew W. Liberatore ·
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    ABSTRACT: The concentration dependence of viscosity is examined for four cationically modified cellulose polymers (UCARE™ JR400, UCARE™ JR30M, UCARE™ LR400, and UCARE™ LR30M) in both salt-free and 50 mM NaCl solution. Similarities in the four polymer systems include: Newtonian viscosity in the dilute regime, shear thinning at higher concentrations, four concentration regimes in salt-free solution, and three concentration regimes in salt solution. The zero shear rate viscosity and the degree of shear thinning increase with increasing polymer concentration in both salt and salt-free solutions. While the addition of salt to the lower molecular weight polymers JR400 and LR400 resulted in small changes in viscosity across all concentrations, JR30M and LR30M exhibited significant decreases (up to 81%) and increases (up to 57%) in viscosity upon the addition of salt in the semidilute and entangled regimes, respectively. This viscosity increase in the entangled regime (when comparing salt-free and 50 mM NaCl solutions) is reported for the first time in cationically modified cellulose polymers. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 41616.
    Journal of Applied Polymer Science 10/2014; 132(11). DOI:10.1002/app.41616 · 1.77 Impact Factor
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    ABSTRACT: The morphology and anion transport of an α-C modified imidazolium functionalized anion exchange membrane, 1,4,5-trimethyl-2-(2,4,6-trimethoxyphenyl)imidazolium functionalized polyphenylene oxide (with ion exchange capacity {IEC} = 1.53 or 1.82 mequiv/g), were studied in detail. The novel cation is less susceptible to OH- attack (0% degradation) compared to unsubstituted imidazolium functionalized polyphenylene oxide (25% degradation) after 24 h at 80 °C in 1 M KOH. The two different IEC materials (with the same protected cation) show interesting differences in membrane performance. From AFM and SAXS under humid conditions, the domain sizes of the membrane change, which impact the transport properties. The lower IEC sample showed a smaller tortuosity and, thus, needs a longer diffusion time for the water molecules to be fully hindered inside the hydrophobic clusters, which is confirmed by water self-diffusion measurements from pulsed field gradient NMR. From conductivity and diffusion measurements, the higher IEC sample exhibited Vogel-Tammann-Fulcher behavior, thus indicating that the polymer chain’s movement dominates the transport. However, the lower IEC sample exhibited the linear Arrhenius behavior signifying water-mediated transport. The maximum Cl- conductivity observed was 23 mS/cm at 95% RH and 90 °C.
    The Journal of Physical Chemistry C 07/2014; 118(28):15136-15145. DOI:10.1021/jp5027674 · 4.77 Impact Factor
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    ABSTRACT: Alkali anion exchange membrane (AEM) based devices have the potential for electrochemical energy conversion using inexpensive catalysts and a variety of fuel types. Membrane stability and anion transport must be improved in AEMs before these devices can be fully realized. Mechanical failure of the membrane can contribute to failure of the device, thus membrane durability is critical to overall system design. Here, a study of the Mechanical properties of three well-established AEMs uses a modified extensional rheometer platform to simulate tensile testing using small membrane samples. Mechanical properties were tested at 30 and 60 degrees C under dry or water saturated gas conditions. Water in the membrane has a plasticizing effect, softening the membrane and reducing strength. PEEK membrane reinforcement limits swelling producing negligible softening and only a 9% decrease in strength from dry to hydrated conditions at 30 degrees C. Higher cation concentration increases water uptake resulting in significant softening, a 57% reduction in Young's modulus, and a 67% reduction in strength when hydrated at 30 degrees C. In a working electrochemical device, AEMs must maintain integrity over a range of temperatures and hydrations, making it critical to considering mechanical properties when designing new membranes.
    Journal of The Electrochemical Society 06/2014; 161(10):H677-H683. DOI:10.1149/2.0971410jes · 3.27 Impact Factor
  • Eric B. Webb · Carolyn A. Koh · Matthew W. Liberatore ·
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    ABSTRACT: Structure I methane hydrates are formed in situ from water-in-mineral oil emulsions in a high pressure rheometer cell. Viscosity is measured as hydrates form, grow, change under flow, and dissociate. Experiments are performed at varying water volume fraction in the original emulsion (0–0.40), temperature (0–6 °C), and initial pressure of methane (750–1500 psig). Hydrate slurries exhibit a sharp increase in viscosity upon hydrate formation, followed by complex behavior dictated by factors including continued hydrate formation, shear alignment, methane depletion/dissolution, aggregate formation, and capillary bridging. Hydrate slurries possess a yield stress and are shear-thinning fluids, which are described by the Cross model. Hydrate slurry viscosity and yield stress increased with increasing water volume fraction. As driving force for hydrate formation decreases (increasing temperature, decreasing pressure), hydrate slurry viscosity increases, suggesting that slower hydrate formation leads to larger and more porous aggregates. In total, addition of water to a methane saturated oil can cause more than a fifty-fold increase in viscosity if hydrates form.
    Industrial & Engineering Chemistry Research 04/2014; 53(17):6998–7007. DOI:10.1021/ie5008954 · 2.59 Impact Factor
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    ABSTRACT: Block copolymers of polystyrene-b-poly(vinyl benzyl trimethylammonium tetrafluoroborate) (PS-b-[PVBTMA][BF4]) were synthesized by sequential monomer addition using atom transfer radical polymerization. Membranes of the block copolymers were prepared by drop casting from dimethylformamide. Initial evaluation of the microphase separation in these PS-b-[PVBTMA][BF4] materials via SAXS revealed the formation of spherical, cylindrical, and lamellar morphologies. Block copolymers of polystyrene-b-poly(vinyl benzyl trimethylammonium hydroxide) (PS-b-[PVBTMA][OH]) were prepared as polymeric alkaline anion exchange membranes materials by ion exchange from PS-b-[PVBTMA][BF4] with hydroxide in order to investigate the relationship between morphology and ionic conductivity. Studies of humidity [relative humidity (RH)]-dependent conductivity at 80 °C showed that the conductivity increases with increasing humidity. Moreover, the investigation of the temperature-dependent conductivity at RH = 50, 70, and 90% showed a significant effect of grain boundaries in the membranes against the formation of continuous conductive channels, which is an important requirement for achieving high ion conductivity. © 2012 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2013, 51, 1751–1760, 2013
    Journal of Polymer Science Part B Polymer Physics 12/2013; 51(24):1751-1760. DOI:10.1002/polb.23170 · 3.83 Impact Factor
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    ABSTRACT: In this study, new alkaline exchange membranes were prepared from the perfluorinated 3M ionomer with various quaternary ammonium cations attached with sulfonamide linkage. The degree of functionalization varied depending on the cation species, resulting in different ion exchange capacities (IECs), 0.33–0.72 meq g−1. There was evidence of polymer degradation when the films were exposed to hydroxide, and hence all membrane characterization was performed in the chloride form. Conductivity was dependent on cation species and IEC, Ea = 36–59 kJ mol−1. Diffusion of water through the membrane was relatively high 1.6 × 10−5 cm2 s−1 and indicated restriction over a range of diffusion times, 6–700 ms. Water uptake (WU) in the membranes was generally low and the hydration level varied based on cation species, λ = 6–11. Small-angle scattering experiments suggested ionic aggregation, 37–42 Å, independent of cation species but slight differences in long-range order with cation species. © 2012 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2013, 51, 1761–1769, 2013
    Journal of Polymer Science Part B Polymer Physics 12/2013; 51(24):1761-1769. DOI:10.1002/polb.23171 · 3.83 Impact Factor
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    ABSTRACT: An alkaline exchange membrane (AEM) based on an aminated trimethyl poly(phenylene) is studied in detail. This article reports hydroxide ion conductivity through an in situ method that allows for a more accurate measurement. The ionic conductivities of the membrane in bromide and carbonate forms at 90 °C and 95% RH are found to be 13 and 17 mS cm−1 respectively. When exchanged with hydroxide, conductivity improved to 86 mS cm−1 under the same experimental conditions. The effect of relative humidity on water uptake and the SAXS patterns of the AEM membranes were investigated. SAXS analysis revealed a rigid aromatic structure of the AEM membrane with no microphase separation. The synthesized AEM is shown to be mechanically stable as seen from the water uptake and SAXS studies. Diffusion NMR studies demonstrated a steady state long-range diffusion constant, D∞ of 9.8 × 10−6 cm2 s−1 after 50–100 ms. © 2012 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2013, 51, 1743–1750, 2013
    Journal of Polymer Science Part B Polymer Physics 12/2013; 51(24):1743-1750. DOI:10.1002/polb.23164 · 3.83 Impact Factor
  • Nathan C. Crawford · S. Kim R. Williams · David Boldridge · Matthew W. Liberatore ·
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    ABSTRACT: During the chemical mechanical polishing (CMP) process, it is believed that shear thickening of the slurry, caused by particle agglomeration, has the potential to result in a significant increase in particle-induced surface defects (i.e, scratches, gouges, pits, etc.). In this study, we have developed a methodology for the synchronized measurement of rheological behavior while polishing a semiconductor wafer, the first of its kind (a technique termed rheo-polishing). We investigate the shear thickening of a 25 wt% fumed silica slurry with 0.15 M added KCl and its impact on polishing performance and subsequent surface damage. The thickened slurry displays a ∼5-fold increase in viscosity with increasing shear rate. As the shear rate is reduced back to zero, the slurry continues to thicken showing a final viscosity that is ∼100x greater than the initial viscosity. Optical microscopy and non-contact profilometry were then utilized to directly link slurry thickening behavior to more severe surface scratching of “polished” TEOS wafers. The thickened slurry generated up to 7x more surface scratches than a non-thickened slurry. Both slurry thickening and surface scratching were associated with a dramatic increase in the population of “large” particles (≥300 nm) which were undetectable in the non-thickened slurry. These “large” and potentially scratch-generating particles are believed to instigate measurable surface damage.
    Colloids and Surfaces A Physicochemical and Engineering Aspects 11/2013; 436. DOI:10.1016/j.colsurfa.2013.06.003 · 2.75 Impact Factor

  • Electrochimica Acta 11/2013; 110:260-266. · 4.50 Impact Factor

Publication Stats

832 Citations
178.20 Total Impact Points


  • 2008-2015
    • Colorado School of Mines
      • Department of Chemical and Biological Engineering
      گلدن، کلرادو, Colorado, United States
  • 2003-2005
    • University of Illinois, Urbana-Champaign
      • Department of Chemical and Biomolecular Engineering
      Urbana, IL, United States