Matthew W. Liberatore

Colorado School of Mines, Golden, CO, United States

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Publications (27)48.12 Total impact

  • Journal of Polymer Science B Polymer Physics. 12/2013; 51(24):1751-1760.
  • Journal of Polymer Science B Polymer Physics. 12/2013; 51(24):1761-1769.
  • Journal of Polymer Science B Polymer Physics. 12/2013; 51(24):1743-1750.
  • [show abstract] [hide abstract]
    ABSTRACT: Chemical mechanical polishing (CMP) is an essential technology used in the semiconductor industry to polish and planarize a variety of materials for the fabrication of microelectronic devices (e.g., computer chips). During the high shear (∼1,000,000 s-1) CMP process, it is hypothesized that individual slurry particles are driven together to form large agglomerates (≥0.5 μm), triggering a shear thickening effect. These shear-induced agglomerates are believed to cause defects during polishing. In this study, we examined the shear thickening of a 25 wt% fumed silica slurry with 0.17 M added KCl using in situ small-angle light scattering during rheological characterization (rheo-SALS). The salt-adjusted slurry displays ∼3-fold increase in viscosity at a critical shear rate of 20,000 s-1 during a stepped shear rate ramp from 100 to 25,000 s-1. As the shear rate is reduced back to 100 s-1, the slurry thickens irreversibly displaying a final viscosity that is 100-times greater than the initial viscosity. Corresponding rheo-SALS images indicate the formation of micrometer scale structures (2-3 μm) that directly correlate with the discontinuous and irreversible shear thickening behavior of the fumed silica slurry; these micron scale structures are 10-times the nominal particle diameter (∼0.2 μm). The scattering patterns from the 25 wt% slurry were corroborated through rheo-SALS examination of 27 and 29 wt% slurries (CKCl=0.1 M). All slurries, regardless of ionic strength and solids loading, display scattering patterns that are directly associated with the observed thickening behavior. Scattering was only observable during and after thickening (i.e., no scattering was detected in the absence of thickening). This work serves as the first in situ observation of micrometer scale structures within the fumed silica CMP slurry while under shear.
    Langmuir 09/2013; · 4.19 Impact Factor
  • Eric B Webb, Carolyn A Koh, Matthew W Liberatore
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    ABSTRACT: The in situ formation and flow properties of methane hydrates formed from water-in-oil microemulsions composed of water, dodecane, and aerosol OT surfactant (AOT) were studied using a unique high pressure rheometer. AOT microemulsions have high stability (order of months), well characterized composition, and yield reproducible results compared to hydrate studies in water-in-crude oil emulsions. Viscosity increases on the order of minutes upon hydrate formation, and then decreases on the order of hours. If significant unconverted water remained after the initial formation event, then viscosity increases for a time as methane slowly dissolves and converts additional water to hydrate. In addition to transient formation measurements, yield stresses and flow curves are measured for a set of experimental conditions. Hydrate slurry viscosity and yield stress increase with increasing water volume fraction, increasing initial pressure, decreasing temperature, and decreasing formation shear rate. Hydrate slurry viscosity and yield stress are most sensitive to temperature, followed by water volume fraction, initial pressure, and formation shear rate.
    Langmuir 08/2013; · 4.19 Impact Factor
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    ABSTRACT: Suspensions of corn starch and water are the most common example of a shear thickening system. Investigations into the non-Newtonian flow behavior of corn starch slurries have ranged from simplistic elementary school demonstrations to in-depth rheological examinations that use corn starch to further elucidate the mechanisms that drive shear thickening. Here, we determine how much corn starch is required for the average person to "walk on water" (or in this case, run across a pool filled with corn starch and water). Steady shear rate rheological measurements were employed to monitor the thickening of corn starch slurries at concentrations ranging from 0 to 55wt.% (0-44vol.%). The steady state shear rate ramp experiments revealed a transition from continuous to discontinuous thickening behavior that exists at 52.5wt.%. The rheological data was then compared to macro-scopic (∼5gallon) pool experiments, in which thickening behavior was tested by dropping a 2.1kg rock onto the suspension surface. Impact-induced thickening in the "rock drop" study was not observed until the corn starch concentration reached at least 50wt.%. At 52.5wt.%, the corn starch slurry displayed true solid-like behavior and the falling rock "bounced" as it impacted the surface. The corn starch pool studies were fortified by steady state stress ramps which were extrapolated out to a critical stress value of 67,000Pa (i.e., the force generated by an 80kg adult while running). Only the suspensions containing at least 52.5wt.% (42vol.%) thickened to high enough viscosities (50-250Pas) that could reasonably be believed to support the impact of a man's foot while running. Therefore, we conclude that at least 52.5wt.% corn starch is required to induce strong enough thickening behavior to safely allow the average person to "walk on water".
    Journal of Colloid and Interface Science 02/2013; · 3.17 Impact Factor
  • Macromolecules 09/2012; 45(18):7495-7503. · 5.52 Impact Factor
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    ABSTRACT: We present a novel setup for a high pressure rheometer operating with concentric cylinders geometry for in situ studies of hydrate formation and rheological characterization. The apparatus uses an external high pressure mixing cell to saturate water-in-oil emulsions with methane gas. The capability of mixing combined with a true rheometer design make this apparatus unique in terms of setup and sample formation. We have used the apparatus to form gas hydrates in situ from water-in-oil emulsions and characterize suspension rheological properties such as yield stress and shear-thinning behavior.
    The Review of scientific instruments 01/2012; 83(1):015106. · 1.52 Impact Factor
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    ABSTRACT: Chemical mechanical polishing (CMP) is a fundamental technology used in the semiconductor manufacturing industry to polish and planarize electronic materials. During the high shear (≥1,000,000 s − 1) polishing process, it is hypothesized that individual slurry particles begin to interact and collide with one another forming large agglomerates (≥0.5 μm). These agglomerates are suspected of causing defects such as scratches or gouges during polishing, which costs the semiconductor industry billions of dollars annually. We have developed a method for investigating the shear thickening behavior of fumed silica slurries (20–34 wt.%) under high shear using a parallel-plate geometry in a conventional rotating rheometer. The CMP slurries displayed irreversible thickening at shear rates exceeding 10,000 s − 1. Viscous heating and sample evaporation are shown to be inconsequential to the witnessed shear thickening behavior. Also, the observed thickening is not a result of a critical rheometer speed, as the thickening was independent of the experimental gap height. In agreement with previous work, the slurries thickened at lower shear rates as silica concentration was increased. The shear thickening of the fumed silica slurries is truly shear-induced, and therefore, the thickening of CMP slurries can be examined using a rotational rheometer at small gap heights (≤100 μm).
    Rheologica Acta 01/2012; 51(7):637. · 1.63 Impact Factor
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    ABSTRACT: Gadolinium metal-organic framework (Gd MOF) nanoparticles are an interesting and novel class of nanomaterials that are being studied as a potential replacement for small molecule positive contrast agents in magnetic resonance imaging (MRI). Despite the tremendous interest in these nanoscale imaging constructs, there are limitations, particularly with respect to controlling the particle size, which need to be overcome before these nanoparticles can be integrated into in vivo applications. In an effort to control the size, shape, and size distribution of Gd MOF nanoparticles, hydrotropes were incorporated into the reverse microemulsion synthesis used to produce these nanoparticles. A study of how hydrotropes influenced the mechanism of formation of reverse micelles offered a great deal of information with respect to the physical properties of the Gd MOF nanoparticles formed. Specifically, this study incorporated the hydrotropes, sodium salicylate (NaSal), 5-methyl salicylic acid, and salicylic acid into the reverse microemulsion. Results demonstrated that addition of each of the hydrotropes into the synthesis of Gd MOFs provided a simple route to control the nanoparticle size as a function of hydrotrope concentration. Specifically, Gd MOF nanoparticles synthesized with NaSal showed the best reduction in size distributions in both length and width with percent relative standard deviations being nearly 50% less than nanoparticles produced via the standard route from the literature. Finally, the effect of the size of the Gd MOF nanoparticles with respect to their MRI relaxation properties was evaluated. Initial results indicated a positive correlation between the surface areas of the Gd MOF nanoparticles with the longitudinal relaxivity in MRI. In particular, Gd MOF nanoparticles with an average size of 82 nm with the addition of NaSal, yielded a longitudinal relaxivity value of 83.9 mM⁻¹ [Gd³⁺] sec⁻¹, one of the highest reported values compared to other Gd-based nanoparticles in the literature to date.
    ACS Applied Materials & Interfaces 04/2011; 3(5):1502-10. · 5.01 Impact Factor
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    ABSTRACT: Pyrolysis oils were produced from hardwood or softwood feedstocks in a vacuum batch reactor and trapped at 0°C. The vacuum process was used to intentionally avoid the presence of entrained char particles. The hardwood feedstock was a pelletized mixture of various Eastern tree species. The softwood samples were de-barked Lodgepole pine (Pinus contorta) and Douglas Fir (Pseudotsuga menziesii) wood cut into the same dimensions as the pellets. The oils’ physical (viscosity) and chemical (speciation) properties were measured as-produced and after aging. The total liquid and char yields ranged from ∼50 to 55% and 25 to 27% respectively. Measured water contents were 30% or more, which are greater typically reported from fast pyrolysis oils produced in fluidized beds. Aging took place in covered glass containers at room temperature over a period of 5 months. Gas chromatography–mass spectrometry (GCMS) was used to characterize the oils’ volatile components. Since bio-oils are mixtures of hundreds of different compounds with wide-ranging molecular weights and polarities, the oils were extracted using benzene followed by methanol. Out of ca. 80 non-polar and 100+ polar compounds GCMS showed a few chemical species present in the freshly produced oils were absent in the aged oils. The oils’ viscosities at shear rates (measured between 1 and 1000s−1) increased by approximately a factor of 2.5 during aging. To determine if this was due to polymerization reactions during aging or simply water and other volatile material losses, freshly made oils were aged at an accelerated rate by using elevated temperatures (65°C and 85°C) in a water-saturated environment between 1 and 7 days. The oils are fairly stable with respect to aging both over long periods of time (months) at room temperature and at elevated temperatures, 65°C and 85°C for shorter time periods (days). It is concluded that high water content and char-free characteristics act to slow polymerization reactions.
    Journal of Analytical and Applied Pyrolysis - J ANAL APPL PYROL. 01/2011; 91(1):190-198.
  • Nicholas B. Wyatt, Casey M. Gunther, Matthew W. Liberatore
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    ABSTRACT: The viscosity of several polyelectrolytes is measured in both salt free solutions and solutions in the high salt limit. At low polymer concentrations, the zero shear rate viscosity decreases as much as 100-fold upon addition of a monovalent salt, namely NaCl. However, as polymer concentration increases, the viscosity difference between polymer in salt free and in monovalent salt solution diminishes. Further, the zero shear rate viscosity becomes independent of added monovalent salt at the critical polyelectrolyte concentration cD. Above cD, the addition of monovalent salt increases the zero shear rate viscosity of the entangled polyelectrolyte solutions. The viscosity increase agrees with viscosity scaling theory for polyelectrolytes in the entangled regime. Polyelectrolytes exhibiting an increase in viscosity above cD in the presence of monovalent salt include three natural anionic polyelectrolytes (xanthan, carrageenan, welan), one synthetic anionic polyelectrolyte (hydrolyzed polyacrylamide), and one natural cationic polyelectrolyte (chitosan). Generally, these polyelectrolytes are relatively high molecular weight (>1 M Dalton), which makes cD experimentally accessible (e.g., cD = 0.2 wt% for xanthan). The magnitude of the viscosity increase is as high as 300% for xanthan and nearly independent of monovalent salt concentration in the high salt limit. The increase in viscosity in monovalent salt solution and magnitude of cD appear to be heavily influenced by the molecular characteristics of the polymers such as monomer weight, molecular structure, and chain conformation.Graphical abstract
    Polymer. 01/2011; 52(11):2437-2444.
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    ABSTRACT: Molecular inclusion compounds called clathrate hydrates are a common concern in oil and gas pipelines, as they cause disruption to production. These crystalline compounds are over 80mol% water and are often only stable at high pressures and low temperatures. As a means to understand the rheology of clathrate hydrates, we investigated ice slurries, in crude oil, as a simple analogy to clathrate hydrates. A series of water-in-oil emulsions were prepared at different volume fractions of water, ranging from 0.10 to 0.70. Water used in the samples was deionized watger or a 3.5 wt% NaCl brine solution. The emulsions were cooled to -10°C and the viscosity and yield stress were analyzed as a function of time after nucleation.No yield stresses were observed at volume fractions below 0.2 for fresh water and 0.3 for brine solution. In the fresh water system, the yield stress varied with increasing volume fraction. Between volume fractions of 0.25–0.55, yield stresses were on the order of 300Pa, and at larger volumer fractions (0.6–0.7) yield stress quickly increased to an unmeasurable value (greater than 3000Pa, the instrument’s limit). In the brine system, yield stress increased with volume fraction of water. After formation of ice, flow was stopped and the system was “annealed”. During the “annealing” period, the magnitude of complex viscosity of the fresh water system reached a peak value after two hours, decreased for approximately four hours, and then changed little for the next forty hours. The yield stress during “annealing” mimicked the trend of the magnitude of complex viscosity. In the brine system, the magnitude of complex viscosity increased over the first three hours, then changed little. However, the yield stress decreased as the “annealing” time increased. Following the measurements of yield stress, the slurry was conditioned at 500s-1 and the apparent viscosity was analyzed as a function of shear rate. At volume fractions greater than 0.10 the slurry was found to be shear thinning and exhibited a viscosity increase compared to the initial emulsion.
    Fuel and Energy Abstracts 01/2011; 166(14):859-866.
  • Nicholas B. Wyatt, Casey M. Gunther, Matthew W. Liberatore
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    ABSTRACT: AbstractThe ability to reduce the frictional drag in turbulent flow in pipes and channels by addition of a small amount of a high molecular weight polymer has application in myriad industries and processes. Here, the drag reduction properties of the polyelectrolyte xanthan are explored in differing solvent environments (salt free versus salt solution) and delivery configurations (homogeneous versus stock solution dilution). Drag reduction effectiveness increases when an entangled xanthan solution is diluted compared to solutions prepared in the dilute regime. Based on dynamic rheological measurements of the elastic modulus, residual entanglements and network structure are hypothesized to account for the observed change in drag reduction effectiveness. Drag reduction effectiveness is unchanged by the presence of salt when the stock solution concentration is sufficiently above the critical concentration cD. Finally, the drag reduction effectiveness decreases with time when diluted from an entangled stock solution but remains greater than the homogeneous case after more than 24 h.
    Journal of Non-Newtonian Fluid Mechanics. 01/2011;
  • Jeffrey S. Knutsen, Matthew W. Liberatore
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    ABSTRACT: An analysis was completed to assess the economic benefits of rheology modifiers because of reduced viscosity and yield stress of high-solids pretreated corn stover (PCS) suspensions in a biomass-to-ethanol conversion facility. A process design developed by the National Renewable Energy Laboratory was used as a base scenario. Rheological modifiers can result in economic benefits because of (1) decreased utility costs associated with pumping and mixing of slurries, (2) decreased capital costs associated with increased pump and reactor lifetimes, and (3) decreased capital costs associated with smaller reaction vessels. Standard mixing and transport analyses for power-law and Herschel−Bulkley fluids were used to develop correlations for power consumption as a function of process variables, such as pipe diameter, volumetric flow rate, impeller geometry, and mixing speed. A 3-fold reduction in the yield stress can result in 50−60% reductions in the pressure gradient of PCS suspensions flowing through a length of pipe, while a 25% reduction in the viscosity can result in a 25% reduction in the mixing power. Because of enhanced reaction kinetics associated with the modifiers, reactor sizes and capital costs can be reduced by 20%. These combined savings can reduce the minimum ethanol selling price by roughly 0.5% if the price of the rheology modifiers remains low.
    11/2010;
  • Jeffrey S. Knutsen, Matthew W. Liberatore
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    ABSTRACT: Chemical additives that reduce the yield stress and viscosity of pretreated corn stover slurries and also enhance the kinetics and overall conversion of cellulose during enzymatic saccharification were explored. Additives included polymers, proteins, and nonionic, anionic, and cationic surfactants. Rheological measurements assessed changes in the yield stress of the suspensions, and enzymatic saccharification experiments were conducted to assess the effect of the additives on enzyme kinetics. For high-solid slurries with an insoluble solids content of about 20%, a 3- to 4-fold reduction in the yield stress was observed upon addition of 2% (w/w) cetylpyridinium chloride (CPCl), cetyl trimethylammonium bromide (CTAB), sodium dodecylbenzene sulfonate (NaDBS), and sodium dodecyl sulfonate (SDS). However, the presence of bovine serum albumin (BSA) at the same concentration doubled the yield stress. Although NaDBS and SDS were both very effective at reducing the yield stress, their presence was very detrimental to the saccharification kinetics, cutting cellulose conversions from 80% to less than 20% over one week due to chemical inhibition of the enzymes. However, the surfactants CPCl and CTAB synergistically reduced the yield stress and increased the relative extent of cellulose conversion by up to 35% during the first 24 h of saccharification. The presence of BSA slightly reduced the extent of cellulose conversion. It is hypothesized that the increased rate of saccharification observed with the presence of CPCl and CTAB and the decreased rate observed with BSA are associated with the respective increases and decreases in the suspensions’ yield stresses, which in turn may affect the uniformity of mixing within the saccharification reactors. Of the modifiers tested, CPCl and CTAB appear to be the most efficacious, as they both reduce the yield stress at concentrations as low as 0.1% (w/w) and improve the kinetics of enzymatic saccharification. Lastly, the economic implications of rheology modifiers in a hypothetical lignocellulosic biomass-to-ethanol pilot facility are discussed.
    Energy & Fuels - ENERG FUEL. 04/2010; 24(5).
  • Nicholas B. Wyatt, Matthew W. Liberatore
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    ABSTRACT: Entangled polymer solutions play an important role in many industries and applications, however the dynamics of these solutions are poorly understood. Here, the addition of salt to entangled polylectrolyte solutions (above cD) results in an increase in viscosity. The rheological properties of entangled xanthan solutions above the critical concentration cD are examined in a number of inorganic salt solutions. The effect of salt counterion size and valency on the magnitude of the viscosity increase is elucidated. A hypothesis that larger salt counterions produce higher viscosities is confirmed for both monovalent and divalent salts. Further, divalent salts are observed to produce higher viscosities than monovalent salts of similar ionic radius. Lastly, an alternative hypothesis incorporating ion bridging between polymer chains is proposed to explain the effect of counterion valency in the observed viscosity differences.
    Soft Matter 01/2010; 6(14). · 3.91 Impact Factor
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    ABSTRACT: A quantitative study of the shear-induced phase separation of a polycation/anionic-nonionic micelle coacervate is presented. Simultaneous rheology and small-angle light scattering (SALS) measurements allow the elucidation of micrometer-scale phase separation under flow in three coacervate solutions. Below 18 degrees C, all three of the coacervate solutions are optically clear Newtonian fluids across the entire shear rate range investigated. Once a critical temperature range and/or shear rate is achieved, phase separation is observed in the small-angle light scattering images and the fluid exhibits shear thinning. Two definitive SALS patterns demonstrate the appearance of circular droplets at low shear rates near the critical temperature and ellipsoidal droplets at higher temperatures and shear rates. The shear-induced droplets range in size from approximately 1 to 4 mum. The ellipsoidal droplets have aspect ratios as high as 4. A conceptual picture in which shear flow extends the polyelectrolyte chains of the clear coacervate liquid phase is proposed. The extended chains create interpolyelectrolyte-micelle interactions and promote expulsion of small ions from the complex, resulting in the formation of micrometer-scale phase-separated droplets.
    Langmuir 10/2009; 25(23):13376-83. · 4.19 Impact Factor
  • Nicholas B. Wyatt, Matthew W. Liberatore
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    ABSTRACT: The viscosity as a function of concentration for xanthan gum in both salt-free solution and in 50 mM NaCl is measured and compared with a scaling theory for polyelectrolytes. In general, the zero shear rate viscosity and the degree of shear thinning increase with polymer concentration. In addition, shear thinning was observed in the dilute regime in both solvents. In salt-free solution, four concentration regimes of viscosity scaling and three associated critical concentrations were observed (c* ≈ 70 ppm, ce ≈ 400 ppm, and cD ≈ 2000 ppm). In salt solution, only three concentration regimes and two critical concentrations were observed (c* ≈ 200 ppm and ce ≈ 800 ppm). In the presence of salt, the polymer chain structure collapses and occupies much less space resulting in higher values of the critical concentrations. The observed viscosity-concentration scaling is in very good agreement with theory in the semidilute unentangled and semidilute entangled regimes in both salt-free and 50 mM NaCl solution. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009
    Journal of Applied Polymer Science 08/2009; 114(6):4076 - 4084. · 1.40 Impact Factor
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    ABSTRACT: Effective and efficient breakdown of lignocellulosic biomass remains a primary barrier for its use as a feedstock for renewable transportation fuels. A more detailed understanding of the material properties of biomass slurries during conversion is needed to design cost-effective conversion processes. A series of enzymatic saccharification experiments were performed with dilute acid pretreated corn stover at initial insoluble solids loadings of 20% by mass, during which the concentration of particulate solids and the rheological property yield stress (tau(y)) of the slurries were measured. The saccharified stover liquefies to the point of being pourable (tau(y) <or= 10 Pa) at a total biomass conversion of about 40%, after roughly 2 days of saccharification for a moderate loading of enzyme. Mass balance and semi-empirical relationships are developed to connect the progress of enzymatic hydrolysis with particle concentration and yield stress. The experimental data show good agreement with the proposed relationships. The predictive models developed here are based on established physical principles and should be applicable to the saccharification of other biomass systems. The concepts presented, especially the ability to predict yield stress from extent of conversion, will be helpful in the design and optimization of enzymatic hydrolysis processes that operate at high-solids loadings.
    Biotechnology and Bioengineering 05/2009; 104(2):290-300. · 3.65 Impact Factor

Publication Stats

88 Citations
4 Downloads
1k Views
48.12 Total Impact Points

Institutions

  • 2008–2013
    • Colorado School of Mines
      • Department of Chemical and Biological Engineering
      Golden, CO, United States
  • 2009
    • National Renewable Energy Laboratory
      Golden, Colorado, United States