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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 55 wt.% (0-44 vol.%). The steady state shear rate ramp experiments revealed a transition from continuous to discontinuous thickening behavior that exists at 52.5 wt.%. The rheological data was then compared to macro-scopic (~5 gallon) pool experiments, in which thickening behavior was tested by dropping a 2.1 kg rock onto the suspension surface. Impact-induced thickening in the ‘‘rock drop’’ study was not observed until the corn starch concentration reached at least 50 wt.%. At 52.5 wt.%, 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 67,000 Pa (i.e., the force generated by an 80 kg adult while running). Only the suspensions containing at least 52.5 wt.% (42 vol.%) thickened to high enough viscosities (50-250 Pa s) that could reasonably be believed to support the impact of a man’s foot while running. Therefore, we conclude that at least 52.5 wt.% corn starch is required to induce strong enough thickening behavior to safely allow the average person to ‘‘walk on water’’.

Xanthan gum, a naturally‐occurring, high‐molecular‐weight, anionic polyelectrolyte, exhibits significant drag‐reducing properties at low concentrations in water, suggesting promising applications in geothermal networks. The flow behavior of xanthan solutions are explored, specifically at concentrations in the semi‐dilute (1000 ppm by mass) and entangled (4000 ppm) regimes as well as in both water and various salt solutions across a temperature range of 5–85°C. The viscosity and viscoelastic properties of xanthan solutions examine relationships between polyelectrolyte concentration, temperature, and salt concentration. Viscosity decreases by two orders of magnitude in 4000 ppm xanthan solutions in deionized water and with 50 mM NaCl (in the high salt limit) as the temperature increases from 5 to 85°C. Next, the addition of salts affects viscosity differently in the two concentration regimes. Specifically, at 25°C, the zero‐shear rate viscosity upon salt addition decreases by 63% for 1000 ppm solutions (from 0.54 to 0.2 Pa s) but increases by 280% for 4000 ppm solutions (from 28 to 107 Pa s). At 1000 ppm, salt ions cause chain collapse, reducing viscosity; At 4000 ppm, entanglements led to structural changes, resulting in higher viscosity. Furthermore, three salts commonly found in geothermal waters, namely NaCl, Na2CO3, and NaHCO3, exhibited similar changes in viscosity and shear thinning behavior in the entangled regime across temperatures from 5 to 85°C. [ABSTRACT FROM AUTHOR]

Identifying the different concentration regimes in polyelectrolytes is helpful for tuning the viscosity in personal care products, as well as in creating other polymer materials, including anion exchange membranes. Viscosity scaling distinguishes various concentration regimes in polyelectrolyte solutions, which change in the presence of salt. Here, the first objective was to measure the viscosity scaling for two cationic polyelectrolytes in water, acid (0.1 M HCl), and salt (0.1 M NaCl) solutions. Two polymers containing the same cationic group were compared, namely, a copolymer poly(acrylamide-co-diallyldimethylammonium chloride) (PAAcDMAC) and a homopolymer poly(diallyldimethylammonium chloride) (PDADMAC). Polyelectrolyte concentrations from 0.25 to 18 wt% spanned from dilute to entangled concentration regimes depending on the polyelectrolyte. Acid and salt had comparable effects on the polyelectrolytes' viscosity. Specifically, the viscosity of the PAAcDMAC in 0.1 M NaCl in the dilute region decreased by 57% compared to DI water. Since salt ions screen the electrostatic interactions, polymer chains assume a more compact conformation. Little difference in zero-shear viscosity existed in the semi-dilute regimes for DI water and 0.1 M NaCl solution of PAAcDMAC. However, zero-shear rate viscosity increased by up to 18% with salt addition in the entangled regime. Since the rheology of entangled polyelectrolytes has not been extensively studied, small and large amplitude oscillatory experiments were completed to elucidate differences in viscoelasticity upon the addition of salt. Subtle differences in viscoelastic properties of 18 wt% PAAcDMAC solution were found upon salt addition in entangled regime. For example, large amplitude oscillatory experiments measured changes in maximum and minimum storage moduli upon NaCl addition. Thus, a disproportional change to the elastic behavior was captured upon salt addition. [ABSTRACT FROM AUTHOR]

ABSTRACT Polymer blending allows for new materials to be designed with unique properties. Here, blends of linear low density polyethylene (PE) and oxidized polyethylene (OPE) have been prepared. PE/OPE blends are characterized for their molten state properties by thermal analysis and rheology; the solid state properties are studied by scattering, diffraction, and tensile testing. Melt miscibility was confirmed by a negative Flory-Huggins interaction parameter (χ ∼ −2.3) from Hoffman-Weeks plots. Additionally, a continuous decrease in melting temperature (from 123 to 119 °C) and thermal stability of blends (25% weight loss from 454 to 416 °C) was observed with increasing OPE loading from 0 to 50 wt %. Time-temperature master curves revealed the shifting of the glassy region to higher frequencies and formation of relaxed polymer chains in the glassy region. A plasticization effect was observed with zero shear viscosity of the blends decreasing with increasing OPE loading. Finally, a decrease in lamellar thickness of PE (from 180 to 140 Å) with increasing OPE resulted in increasing the blends' brittleness. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43521. [ABSTRACT FROM AUTHOR]

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 m M 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. [ABSTRACT FROM AUTHOR]

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 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 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. [Copyright &y& Elsevier]

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. [Copyright &y& Elsevier]

Abstract: Variations in the viscosity and other physical properties of heavy oils are poorly understood. The viscosities measured for different heavy oils can vary by orders of magnitude even at the same API gravity, which is the standard metric for lighter oils. Heavy oils are viscoelastic materials, and the shear modulus and the viscosity are coupled. Understanding what controls heavy oil viscosity will provide insight into what controls heavy oil shear modulus. Therefore, using rheology, ultrasonic measurements and molecular beam mass spectroscopy (MBMS) the physical and chemical properties of seven heavy oils from around the globe are explored. The viscoelastic nature of the oils is quantified as a function of temperature. Overall, the heavy oil samples show little correlation between the viscosity or shear modulus and the API gravity, separate resin content or separate asphaltene content as measured from SARA analysis. However, the total resin plus asphaltene content collapses the viscosity and modulus values to provide empirical relations between these quantities. Also, a partial least squares regression analysis provides tight correlations for the chemical signatures from the MBMS. The rapid and quantitative nature of the MBMS make it an attractive substitute for the inconsistencies endemic to SARA analysis. [Copyright &y& Elsevier]

Abstract: Physical properties and chemical components of an Alaska heavy oil from the Ugnu formation were studied by viscosity measurements, molecular beam mass spectrometry (MBMS), Fourier transform infrared spectroscopy (FTIR), and nuclear magnetic resonance spectroscopy (NMR). The viscous samples rheology was measured between −10°C and 60°C using small amplitude oscillatory shear tests for viscosity, which generally decreases with increasing temperature. An activation energy of viscosity was measured as between 85 and 92kJ/mol. The screening method by combined use of FTIR, NMR and a time-resolved MBMS identified several component classes: water, cyclo/straight alkanes, alkenes, mono and multi-ring aromatic molecules, as well as small fractions of other organic molecules. Azeotropic behavior was observed between 100 and 250°C. The partial least squares correlation between molecular masses and the viscosity shows that water, alkylbenzene, and molecules with higher masses have positive correlations to the viscosity, but that the aliphatic molecules were anti-correlated. [Copyright &y& Elsevier]