Small Amplitude Oscillatory Shear Rheometry Research Articles

Secondary structure and stability of a gel-forming tardigrade desiccation-tolerance protein.

Protein-based pharmaceuticals are increasingly important, but their inherent instability necessitates a "cold chain" requiring costly refrigeration during production, shipment, and storage. Drying can overcome this problem, but most proteins need the addition of stabilizers, and some cannot be successfully formulated. Thus, there is a need for new, more effective protective molecules. Cytosolically, abundant heat-soluble proteins from tardigrades are both fundamentally interesting and a promising source of inspiration; these disordered, monodisperse polymers form hydrogels whose structure may protect client proteins during drying. We used attenuated total reflectance Fourier transform infrared spectroscopy, differential scanning calorimetry, and small-amplitude oscillatory shear rheometry to characterize gelation. A 5% (wt/vol) gel has a strength comparable with human skin, and melts cooperatively and reversibly near body temperature with an enthalpy comparable with globular proteins. We suggest that the dilute protein forms α-helical coiled coils and increasing their concentration drives gelation via intermolecular β-sheet formation.

Enzyme cross-linked pectin microgel particles for use in foods

We report on a new enzyme-based method for producing permanently cross-linked pectin microgels. We investigate the shape, size and rheological properties of these microgel particles making comparisons with the more traditional design of calcium cross-linked pectin microgels. Both sets of microgel particles were prepared via the ‘top-down’ mechanical disruption of parent pectin hydrogels. The first hydrogel was prepared from low methoxyl pectin (LMP) (2 wt% pectin) cross-linked using Ca2+ (8.3 mM CaCl2). The LMP microgels show particle sizes ca. 1–100 μm, but are stable only in [Ca2+] = 8.3 mM or above, swelling and/or dissolving rapidly in pure water. The second type of microgel was prepared from sugar beet pectin (SBP) hydrogels covalently cross-linked via laccase. Gelation kinetics were investigated by small amplitude oscillatory shear rheometry. The SBP microgels resisted dissolution in water for several months. Light scattering measurements suggested that the SBP microgel particle sizes were related to the mechanical properties of the parent hydrogels. Various imaging techniques all suggested that SBP microgels have highly irregular shapes, perhaps due to the top-down technique used for their manufacture and their inherent mechanical properties. Concentrating the SBP microgels (to 35–50 wt% microgel, or 0.6–0.8 wt% overall pectin concentration) resulted in suspensions with rheological properties typical of yield stress fluids. When compared at similar overall SBP concentrations, the SBP microgel suspensions offer distinct advantages as bulk rheology modifiers compared to SBP solutions.

Temperature fractionation, physicochemical and rheological analysis of psyllium seed husk heteroxylan

Psyllium husk is a source of natural dietary fibre with marked water absorbability and gelling properties, which makes it an attractive functional ingredient for applications in the food industry, such as gluten free bread and breakfast cereals. The main functional component of psyllium husk is a complex branched heteroxylan. In this study, a straightforward sequential fractionation of hydrated psyllium seed husk powder based on temperature-dependent behaviours was applied. The F20 (20 °C fraction) showed the highest yield followed by F60 while 13.5% of the husk is unextractable (residue).The obtained fractions showed unique rheological properties as analysed using small amplitude oscillatory shear rheometry and the time-temperature superposition (TTS) technique. The results indicate that: 1) only F20 was influenced by heat treatment, 2) high temperature fractions showed stronger gel properties, 3) a three-step softening/melting was observed, 4) F60 has longest relaxation time as shown in TTS master curves. The four fractions were also characterised using the monosaccharide analysis, FTIR and 13C NMR. The arabinose/xylose ratio was found to increase with the increase in fractionation temperature. FTIR and 13C NMR spectra supported that low temperature fraction is less branched.Two hypotheses were therefore proposed: The first one based on models by Haque, Richardson, Morris, and Dea (1993) and Yu et al. (2019) focusing on chemical and structural properties of the molecules. The second hypothesis highlights differences in hierarchical molecular conformations of polysaccharides which is proposed by Diener et al. (2019). Sidechain substitution and composition and length of sidechains are critical and significantly influence the properties of each fraction.

Viscoelastic properties of PS–POSS hybrid materials prepared by reactive processing

The viscoelastic properties of hybrid nanocomposites of polystyrene and polyhedral oligomeric silsesquioxane (PS–POSS) are determined in the molten state by small-amplitude oscillatory shear rheometry (SAOS) and in the solid state by dynamical-mechanical thermal analysis (DMA). PS–POSS samples synthesized to form various molecular structures and phase morphologies are investigated. Overall, both viscoelastic data sets correlate well with the POSS dispersion level and with the degree of grafting of the PS–POSS samples. From the SAOS data, enhanced POSS dispersion and degrees of grafting are characterized by deviations of the zero-frequency viscosity ratios of the Einstein and Einstein–Batchelor models and by linearity in the Han plots. PS–POSS samples with enhanced POSS dispersion and degrees of grafting are characterized as those with higher free-volume fractions and lower flow activation energies, as determined by storage modulus master curves that stem from applying the time-temperature superposition (TTS) principle to the DMA data.

Non-isothermal curing kinetics, chemorheological behaviour, and IR spectral study of two trifunctional phenylethynyl-terminated imide oligomers compared with the corresponding bifunctional structure

Two trifunctional phenylethynyl-terminated imide oligomers, m-TPEPA and p-TPEPA, were systematically compared with the corresponding bifunctional phenylethynyl-terminated imide oligomer, BPEPA. The non-isothermal curing kinetics, Master Plots method, and rheological behaviour of the three high performance oligomers were systematically studied by dynamic DSC, small amplitude oscillatory shear rheometry, and infrared spectroscopy. The results show that the activation energy ( Ea) depended on the extent of conversion evaluated with three different methods, and the lower Ea values of the trifunctional oligomers, which may lead to different curing reactions, compared with the sustained growth of Ea values of BPEPA. The chemorheological properties of the oligomers were measured and fit numerically with the dual Arrhenius model and gel model. Moreover, the degree of cure (agel ) at the gel time (tgel ) was calculated by the value of glass transform temperature at different curing temperature combined with rheological and isothermal DSC results. According to structural changes during the curing reaction characterised using FTIR spectra, it was inferred that the structures of the cured trifunctional imide resins have cis-configurations, which may change the part of the configuration from cis to trimerisation with the lower activation energies found in the later part of the conversion, while the difunctional imide structure is trans.

Investigation of the Fluid Behavior of Asphaltenes and Toluene Insolubles by High-Temperature Proton Nuclear Magnetic Resonance and Rheometry and Their Application to Visbreaking

The fluid behavior of asphaltenes at elevated temperatures impacts coke formation in a number of hydrocarbon conversion processes, including visbreaking and delayed coking. In this study, the asphaltenes from a number of sources, namely, a vacuum residue, a petroleum source rock (Kimmeridge clay) bitumen obtained by hydrous pyrolysis, and bitumen products from a sub-bituminous coal and pine wood obtained by thermolytic solvent extraction using tetralin, have been characterized using high-temperature proton nuclear magnetic resonance (1H NMR), and the results correlated with those from small-amplitude oscillatory shear rheometry. Further for comparison, the coke (toluene insolubles) obtained from visbreaking the vacuum residue was also characterized. All of the asphaltenes became completely fluid by 300 °C, with hydrogen being completely mobile with coke formation, identified as a solid phase, not occurring to a significant extent until 450 °C. Extremely good agreement was obtained between high-temperature 1H NMR and rheometry results, which confirmed that the asphaltenes were highly fluid from 300 °C, with initial signs of resolidification being observed at temperatures of around 450 °C. During softening, extremely good correlations between fluid hydrogen and phase angle were obtained as the asphaltenes softened. The toluene insolubles however did contain some fluid material; thus, it cannot be regarded as strictly solid coke, but clearly, with increasing temperature, the fluid material did convert to coke. Under actual process conditions, this fluid material could be responsible for coke adhering to reactor surfaces.

폴리염화비닐의 친환경 가소제로서 Poly(1,2-propylene glycol adipate)

Poly(1,2-propylene glycol adipate) (PPA) was used as an environmentally friendly plasticizer in flexible poly(vinyl chloride) (PVC). Thermal, mechanical, and rheological properties of the PVC/PPA blends were characterized by differential scanning calorimetry, dynamic mechanical analysis, tensile test, scanning electron microscopy and small amplitude oscillatory shear rheometry. The results showed that PPA lowered the glass transition temperature of PVC. The introduction of PPA could decrease tensile strength and Young's modulus of the PVC/PPA blends; however, elongation-at-break was dramatically increased due to the plastic deformation. The plasticization effect of PPA was also manifested by the decrease of dynamic storage modulus and viscosity in the melt state of the blends. The results indicated that PPA had a good plasticizing effect on PVC.

Biopolymer-Based Structuring of Liquid Oil into Soft Solids and Oleogels Using Water-Continuous Emulsions as Templates

Physical trapping of a hydrophobic liquid oil in a matrix of water-soluble biopolymers was achieved using a facile two-step process by first formulating a surfactant-free oil-in-water emulsion stabilized by biopolymers (a protein and a polysaccharide) followed by complete removal of the water phase (by either high- or low-temperature drying of the emulsion) resulting in structured solid systems containing a high concentration of liquid oil (above 97 wt %). The microstructure of these systems was revealed by confocal and cryo-scanning electron microscopy, and the effect of biopolymer concentrations on the consistency of emulsions as well as the dried product was evaluated using a combination of small-amplitude oscillatory shear rheometry and large deformation fracture studies. The oleogel prepared by shearing the dried product showed a high gel strength as well as a certain degree of thixotropic recovery even at high temperatures. Moreover, the reversibility of the process was demonstrated by shearing the dried product in the presence of water to obtain reconstituted emulsions with rheological properties comparable to those of the fresh emulsion.

Thermal, mechanical, and rheological properties of polylactide/poly(1,2‐propylene glycol adipate)

AbstractPolylactide (PLA) was melt blended with poly(1,2‐propylene glycol adipate) (PPA) in a Thermo‐Haake mixer. Thermal, mechanical, and rheological properties of the blends were investigated by means of differential scanning calorimetry, dynamic mechanical analysis, tensile test, and small amplitude oscillatory shear rheometry. PPA lowered the glass transition temperature and increased the ability of PLA to cold crystallization. With the increase in PPA content (5–25 wt%), the blends showed decreased tensile strength and Young's modulus; however, impact strength and elongation‐at‐break along were dramatically increased due to the plastic deformation. Morphological results of PLA/PPA blends showed that PPA was good compatible with PLA. The plasticization effect of PPA was also manifested by the lowering of dynamic storage modulus and viscosity in the melt state of the blends compared with neat PLA. POLYM. ENG. SCI., 2013. © 2012 Society of Plastics Engineers

Thermorheological analysis of blend of high- and low-density polyethylenes

The effect of temperature on dynamic viscoelastic properties of high density polyethylene and low density polyethylene blends with different weight fractions was investigated in the molten state by means of small amplitude oscillatory shear rheometry. It was found that the blends at various compositions do follow well the time-temperature superposition principle and show thermorheologically simple behavior. This behavior is attributed to both similarity in glass-transition temperature of the constituents and phase stability in the blends at various temperatures. The latter was suggested via coincidence of G′-G′′ plots and δ-G* plots at different temperatures. That was furthur supported using G′ vs. temperature curves which showed no breakdown in the linear relation. Horizontal shift factors, which reflect temperature dependence of relaxation times, obtained to draw G′ and G′′ master curves, followed an Arrhenius equation with temperature. Analysis of terminal relaxation times of components revealed that terminal dynamics of components is similar at limited particular temperatures but different at others. Moreover, depending to test temperature, dynamics of a given component in the blend may be faster or slower than in the pure state.

Gelation and microstructure of dilute gellan solutions with calcium ions

The viscoelasticity at 25 °C and microstructure of 0.02–0.07 wt% of low acyl gellan aqueous media were investigated for ratios of Ca2+ to gellan in the range of 0–38.8, using small amplitude oscillatory shear rheometry and confocal laser scanning microscopy (CLSM), respectively. The total ionic concentration (CT = γ CP + CS, being CP and CS the gellan and calcium concentrations, respectively, and γ the mean activity coefficient) of the systems was found to be the triggering and critical factor for the gelation and elasticity of gellan systems. The gel point (Tgel) and storage moduli (G′) increased upon increasing CT. However, G′ showed a maximum for CT = 9.3 ± 1.2 meq/L, followed by a progressive reduction as CT increased; this was primarily due to further addition of calcium, as CP had a low contribution to CT of the systems. CLSM demonstrated that the level of counter-ions was enough to induce the formation of a network, whose connection depended on CP and whose reinforcement was ion dependent. Therefore, even at very low levels of gellan, it is possible to create a wide spectrum of viscoelastic behaviors going from structured liquids to strong gels through the specific combinations of gellan and cation concentrations.

Dynamic Vulcanization of HDPE/EVA Blend Using Silane

Dynamic vulcanization of high-density polyethylene and ethylene vinyl acetate (HDPE/EVA) blends (50/50 wt%) in the mixing chamber of a torque rheometer was investigated. EVA was selectively cross-linked within the HDPE phase by transesterification reaction between ester groups of the EVA and alkoxysilane groups of tetrapropoxysilane, catalyzed by dibutyl tin oxide. Torque level and temperature in the torque rheometer chamber were monitored to follow the evolution of the EVA cross-linking during dynamic vulcanization. The degree of cross-linking of EVA in the HDPE/EVA materials was estimated by the gel content (insoluble EVA fraction). The changes in the HDPE/EVA phase morphology caused by different degrees of EVA cross-linking were investigated by scanning electron microscopy. Melt-state linear viscoelastic properties of the materials were investigated by small amplitude oscillatory shear rheometry. For the composition and processing conditions adopted in this study, the HDPE/EVA showed a coarse co-continuous phase morphology, with large EVA domains interconnected with HDPE domains. Following the dynamic vulcanization, this changed to a more refined co-continuous morphology. The linear viscoelastic relaxation behavior of dynamically vulcanized HDPE/EVA materials suggests the existence of a percolated network structure of high viscous and elastic EVA domains interconnected with thermoplastic HDPE domains.

Use of small-amplitude oscillatory shear rheometry to study the flow properties of pure and potassium-doped Li 2ZrO 3 sorbents during the sorption of CO 2 at high temperatures

It has been previously recognized that the addition of lithium/potassium carbonates salts to pure Li 2ZrO 3 improves significantly the diffusion of CO 2 uptake and, consequently, the CO 2 sorption capacity. This effect has been associated with the formation of a eutectic molten carbonate layer on the outer surface of the reactant Li 2ZrO 3 particles. The present work proposes for the first time the use of small-amplitude oscillatory shear (SAOS) rheometry to determine the rheological properties of pure Li 2ZrO 3 and K-doped Li 2ZrO 3 under CO 2 atmosphere and understand the interplay between these properties and the CO 2 absorbed. The results have shown that the rheological parameters (storage modulus, G′; loss modulus, G″; and phase angle, δ) of the samples depend on the type of carbonate mixture and the extent of diffusion and sorption of CO 2.

Thermal, mechanical and rheological properties of poly (lactic acid)/epoxidized soybean oil blends

Poly(lactic acid) (PLA) was melt blended with epoxidized soybean oil (ESO) in an internal mixer and thermal, mechanical and rheological properties of the blends were investigated by means of differential scanning calorimetry, dynamic mechanical analysis, tensile test and small amplitude oscillatory shear rheometry. ESO lowered glass transition temperature and increased the ability of PLA to cold crystallization. The blend exhibited improved elongation-at-break along with a plastic deformation. The plasticization effect by ESO was also manifested by the lowering of dynamic storage modulus and viscosity in the melt state of the blends compared with neat PLA.

Gelation on the microscopic scale

Particle-tracking methods are used to study gelation in a colloidal suspension of Laponite clay particles. We track the motion of small fluorescent polystyrene spheres added to the suspension, and obtain the micron-scale viscous and elastic moduli of the material from their mean-squared displacement. The fluorescent spheres move subdiffusively due to the microstructure of the suspension, with the diffusive exponent decreasing from close to one at early times to near zero as the material gels. The particle-tracking data show that the system becomes more heterogeneous on the microscopic scale as gelation proceeds. We also determine the bulk-scale moduli using small-amplitude oscillatory shear rheometry. Both the macroscopic and microscopic moduli increase with time, and on both scales we observe a transition from a primarily viscous fluid to an elastic gel. We find that the gel point, determined as the time at which the viscous and elastic moduli are equal, is length-scale dependent--gelation occurs earlier on the bulk scale than on the microscopic scale.

Curing kinetics and chemorheological analysis of polyurethane formation

AbstractThe cross‐linking kinetics and the rheological behavior of a polyurethane system during curing are investigated by DSC and small amplitude oscillatory shear rheometry. In this study, isoconversional methods are applied to understand the reaction complexity. The activation energy depends on the extent of conversion. It can be shown that three parallel reactions occur during the evolution of the global reaction in non‐isothermal conditions. An original multi‐step model can involve these three parallel independent reactions. Dynamic viscosity is measured as a function of time and is found independent of shear rate. Isothermal viscosity rise is related to reaction extent by a phenomenological model. The gelation time is determined by the tanδ crossover at different frequencies. Polym. Eng. Sci. 44:518–527, 2004. © 2004 Society of Plastics Engineers.

Relaxation Dynamics of Entangled and Unentangled Multiarm Polymer Solutions: Experiment

Relaxation dynamics of several model A3−A−A3 multiarm 1,4-polybutadiene melts and solutions are investigated experimentally using small amplitude oscillatory shear rheometry over a broad temperatur...