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Transport of milled solid biomass can be problematic in biomass conversion processes due to the material’s high cohesiveness, low bulk density, and poor flowability. Here, the goal is to investigate the flow behavior of compressed biomass under conditions similar to compression-screw feeders. To mimic the flow of woody biomass inside a compression-screw feeder, two lignocellulosic biomass feedstocks were fed to a co-rotating twin-screw microcompounder. Force and screw speed from the microcompounder were correlated to viscosity in a traditional rheometer, where low-density polyethylene served as a control. The deformation of compressed biomass in a lab-scale compounder is strongly dependent on screw speed and moisture content. Shear stress in woody biomass decreased with the shear rate, indicating negative plastic viscosity. Moreover, viscosity decreased one order of magnitude as screw speed increased from 10 to 90 rpm. Increasing moisture from 10 to 50% reduced the viscosity of the compressed biomass by 60%.

We studied the diffusion of gold nanoparticles within entangled solutions and gels formed by high molecular weight (Mw= 89000 g/mol) poly(vinyl alcohol) (PVA) in water by using fluctuation correlation spectroscopy (FCS). The nanoparticle size (2R) was varied between 5 and 30 nm, and the PVA volume fraction (ϕ) was chosen to be in the entangled regime. We found that existing hydrodynamic and obstruction models are inadequate to describe the size dependence of the particle diffusion coefficient (D). For size ratios x= 2R/ae≈ 0.5–2.5, where aeis the entanglement tube diameter in the solution, our results suggest a functional form for D∼ exp(−κx), where κ ≈ 1.4. This result qualitatively agrees with the scaling theory prediction of hopping motion for particles within entangled polymer solutions. For larger particles at higher volume fractions, an additional sharp slowing down of the particle motion was observed, which also exhibited an exponential dependence on the size ratio, but with a much higher value of κ ≈ 7.5. Such a rare hopping process can be explained qualitatively by recently developed force-based nonlinear Langevin theory.

Complex problem solving is one of the skills desired in the 21st century workforce. Students can improve their problem-solving skills by working on homework problems, and creating new problems can be a stimulating and inventive exercise for student as well. Our previous studies explored the impacts of a novel homework pedagogy where students reverse-engineered videos to create course-related homework-quality problems. The present study investigated differences in problem difficulty and student problem-solving ability across two cohorts when solving video-inspired student-written (VISW) problems versus Textbook problems. The current study deployed similar mixed methods research on an additional cohort of undergraduate students in an engineering course focused on material and energy balances to verify and reproduce previous results. For each cohort, findings were drawn from ∼2000 task-load surveys and ∼2500 problem solving scores compiled by multiple raters. In general, outcomes for the second cohort replicated previous findings. The student-written problems were perceived equally as difficult as the Textbook problems. PROCESS scores from the Treatment group revealed better problem-solving skills when students solved VISW than Textbook problems. Students in the Treatment group displayed an increase in problem-solving ability across the ∼4-month long course with small to medium effect sizes (Hedges g = 0.6 and 0.1). Additionally, students in the Treatment group exhibited better problem-solving skills on the most difficult VISW problems compared to the most difficult Textbook problems.

Researchers worldwide have developed bulky cations for incorporation into anion exchange membranes (AEMs) used in energy transfer and storage devices. The bulky cations increase chemical stability by attaching electron-donating groups to the central cation. In this work, we compared the performance of the bulky tris(2,4,6-trimethoxy phenyl) phosphonium cation (TPQP) to the much smaller benchmark trimethylammonium cation (TMA) commonly utilized in alkaline fuel cells. The TPQP cation exhibits higher thermal and chemical stability than the TMA cation. Polyphenylene oxide (PPO) membranes functionalized with TPQP cation show comparable anion1ic conductivity values to similar membranes functionalized with TMA cation. Mechanical testing of 15 um membranes of the tris(2,4,6-trimethoxy phenyl) phosph- onium functionlized PPO (PPO-TPQP) indicates that in order to meet the demands of commercial applications, Young's modulus will need to be reduced and membrane elongation need to be increased.

A chemically stable copolymer [poly(2,6 dimethyl 1,4 phenylene oxide)-b-poly(vinyl benzyl trimethyl ammonium)] with two ion exchange capacities, 3.2 and 2.9 meq g[?]1, was prepared as anion exchange membranes (AEM-3.2 and AEM-2.9). These materials showed high OH[?] conductivities of 138 mS.cm[?]1 and 106 mS.cm[?]1, for AEM-3.2 and AEM-2.9 respectively, at 60degC, and 95% RH. The OH[?] conductivity = 45 mS.cm[?]1 for AEM-3.2 at 60% RH and 60degC in the absence of CO2. Amongst the ions studied, only OH[?] is fully dissociated at high RH. The lower Ea = 10-13 kJ.mol[?]1 for OH[?] compared to F[?] [?] 20 kJ.mol[?]1 in conductivity measurements, and of H2O from self-diffusion coefficients suggests the presence of a Grotthuss hopping transport mechanism in OH[?] transport. PGSE-NMR of H2O and F[?] show that the membranes have low tortuosity, 1.8 and 1.2, and high water self-diffusion coefficients, 0.66 and 0.26 x 10[?]5 cm2.s[?]1, for AEM-3.2 and AEM-2.9 respectively. SAXS and TEM show that the membrane has several different sized water environments, ca. 62 nm, 20 nm, and 3.5 nm. The low water uptake, l = 9-12, reduced swelling, and high OH[?] conductivity, with no chemical degradation over two weeks, suggests that the membrane is a strong candidate for electrochemical applications.

Ion exchange membranes are a promising class of materials for use in fuel cells, barrier layers, and water splitting devices. While the majority of research related to anion exchange membranes is on improving the chemical stability and increasing ionic conductivity, the mechanical performance under relevant operating conditions is vital to device lifetime. Using tensile testing and humidity cycling, we report the mechanical performance of Nafion 115, polyethylene-b-polyvinyl benzyl trimethylammonium diblock copolymer (PE-b-PVBTMA), poly[t-butyl styrene-b-hydrogenated isoprene-b-vinyl benzyl trimethylammonium-b-hydrogenated isoprene-b-t-butyl styrene] (QP43), and aminated tetramethyl polyphenylene (ATMPP). Nafion 115 serves as a well-studied material to compare with the developmental anion exchange membranes. A home-built environmental chamber attached to a rheometer was utilized to perform all measurements under elevated temperature and relative humidity conditions. Standard mechanical properties are important to understanding membrane performance, but a simple metric comparing the mechanical elongation in a dry condition with the in-plane swelling percentage in liquid water can be used to predict how membranes will perform under hygral cycling.

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.

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 IEC of the terpolymer resulted in higher chloride conductivity, 20-75 mS/cm at 50degC 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.

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.

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 60degC 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 30degC. 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 30degC. 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.

There is increasing interest in the alkaline exchange membrane (AEM) fuel cells as this device, if realized, could allow the use of inexpensive metal catalysts and the oxidation of a variety of convenient liquid fuels. While there have been some dramatic early achievements, there is still a need for a fundamental study of anion transport, cation stability and the formation of robust thin films in this area. We have undertaken a comprehensive study of AEMs where theory is linked to well-defined model systems, both in solution and in the solid state, which are characterized using very careful environmental control such that the models can be validated and used predictively. We are also fabricating a number of random copolymer AEMs that can be produced readily in large quantities, allowing us to understand film formation coupled with transport and stability. Those based on perfluorinated backbones invite interesting comparisons with the analogous proton exchange membranes.

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 vivoapplications. 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.

Researchers worldwide have developed bulky cations for incorporation into anion exchange membranes (AEMs) used in energy transfer and storage devices. The bulky cations increase chemical stability by attaching electron-donating groups to the central cation. In this work, we compared the performance of the bulky tris(2,4,6-trimethoxy phenyl) phosphonium cation (TPQP) to the much smaller benchmark trimethylammonium cation (TMA) commonly utilized in alkaline fuel cells. The TPQP cation exhibits higher thermal and chemical stability than the TMA cation. Polyphenylene oxide (PPO) membranes functionalized with TPQP cation show comparable anion1ic conductivity values to similar membranes functionalized with TMA cation. Mechanical testing of 15 μm membranes of the tris(2,4,6-trimethoxy phenyl) phosph- onium functionlized PPO (PPO-TPQP) indicates that in order to meet the demands of commercial applications, Young’s modulus will need to be reduced and membrane elongation need to be increased.

A chemically stable copolymer [poly(2,6 dimethyl 1,4 phenylene oxide)-b-poly(vinyl benzyl trimethyl ammonium)] with two ion exchange capacities, 3.2 and 2.9 meq g−1, was prepared as anion exchange membranes (AEM-3.2 and AEM-2.9). These materials showed high OH−conductivities of 138 mS.cm−1and 106 mS.cm−1, for AEM-3.2 and AEM-2.9 respectively, at 60°C, and 95% RH. The OH−conductivity = 45 mS.cm−1for AEM-3.2 at 60% RH and 60°C in the absence of CO2. Amongst the ions studied, only OH−is fully dissociated at high RH. The lower Ea= 10–13 kJ.mol−1for OH−compared to F−∼ 20 kJ.mol−1in conductivity measurements, and of H2O from self-diffusion coefficients suggests the presence of a Grotthuss hopping transport mechanism in OH−transport. PGSE-NMR of H2O and F−show that the membranes have low tortuosity, 1.8 and 1.2, and high water self-diffusion coefficients, 0.66 and 0.26 × 10−5cm2.s−1, for AEM-3.2 and AEM-2.9 respectively. SAXS and TEM show that the membrane has several different sized water environments, ca. 62 nm, 20 nm, and 3.5 nm. The low water uptake, λ = 9–12, reduced swelling, and high OH−conductivity, with no chemical degradation over two weeks, suggests that the membrane is a strong candidate for electrochemical applications.

Ion exchange membranes are a promising class of materials for use in fuel cells, barrier layers, and water splitting devices. While the majority of research related to anion exchange membranes is on improving the chemical stability and increasing ionic conductivity, the mechanical performance under relevant operating conditions is vital to device lifetime. Using tensile testing and humidity cycling, we report the mechanical performance of Nafion 115, polyethylene-b-polyvinyl benzyl trimethylammonium diblock copolymer (PE-b-PVBTMA), poly[t-butyl styrene-b-hydrogenated isoprene-b-vinyl benzyl trimethylammonium-b-hydrogenated isoprene-b-t-butyl styrene] (QP43), and aminated tetramethyl polyphenylene (ATMPP). Nafion 115 serves as a well-studied material to compare with the developmental anion exchange membranes. A home-built environmental chamber attached to a rheometer was utilized to perform all measurements under elevated temperature and relative humidity conditions. Standard mechanical properties are important to understanding membrane performance, but a simple metric comparing the mechanical elongation in a dry condition with the in-plane swelling percentage in liquid water can be used to predict how membranes will perform under hygral cycling.

Anion Exchange membranes (AEMs) are being developed for a variety of applications. Among these are fuel cells and electrolyzers that require the AEM to conduct hydroxide anions. Measurement of the ionic conductivity of hydroxide is challenging because the hydroxide is a strong nucleophile and attacks polar groups in the AEM and also rapidly reacts with atmospheric CO2to form the less conductive carbonate and bicarbonate counter anions. We have developed a rigorous method to fully exchange AEMs into the hydroxide form while excluding CO2and remove all residual inorganic salt from the film prior to measurement. These measurements of the hydroxide ion conductivity coupled with self diffusion measurements of water and the similarly sized fluoride anion in these films are beginning to shed insight into how hydroxide anion transport can be maximized in state of the art AEMs.

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 IEC of 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.

Conductivity of pure (air controlled) and air exposed hydroxide ion was compared using a unique sample preparation and conductivity measurements at controlled environment for a commercial FumasepÒ FAA anion exchange membrane. At 95%RH and 80°C, the membrane had conductivity value of 0.075 S/cm at the pure hydroxide form but reduced merely to 0.017 S/cm when the membrane was exposed to ambient CO2for 2 days. A comparative anionic (OH-, CO32-, and HCO3- forms) conductivity study showed the reduced ionic conductivity value by ¼ 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.

Extensive transport and modeling studies have been performed on a series of polymers based on the benzyltrimethylamonium cations. We have created a realistic reactive model of solvated hydroxide that has interesting properties in the polymer matrix. In ordered di-block polymers we have strong theoretical evidence for a heterogeneous distribution of water across the channel. Fluoride is used as a non-reactive surrogate for hydroxide to increase the computational efficiency of transport calculations that can be performed. In addition to these studies we are discovering new base stable processable robust polymer backbones and cations. These bulky cations seem to dramatically affect the transport properties of the anions showing a VTF rather than an Arrhenius behavior with temperature.

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°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°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°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.

Infrared study of water in a poly(ethylene-co-tetrafuloroethylene) anion exchange membrane at different level of hydration (%RH 0, 25, 50, 75 and 100) was performed using a Fourier transform infrared (FTIR) microscope. FTIR spectra showed at least two different states of water present in the membrane. The presence of both the non-hydrogen bonded water molecules at the lower hydration level and the hydrogen bonded water molecules at the higher hydration level, unambiguously, are altered with changing humidity.

Alkali anion exchange membrane (AEM) fuel cells have the potential for electrochemical energy conversion using inexpensive catalyst and a variety of fuel types. Stability and transport must be improved in AEMs before these devices can be fully realized. Mechanical failure of the membrane can contribute to failure of the fuel cell, thus membrane durability is critical to overall system design. Compared to well researched proton exchange membranes, there is no standard baseline AEM to compare mechanical properties. This work attempts a fundamental study of the mechanical properties of three well-established AEMs using a modified extensional rheometer platform that simulates tensile testing using small membrane samples. The limitations of using this instrument for tensile tests with brittle polymers are also discussed.