Dynamic Oscillatory Data Research Articles

Rheology of automotive adhesives during dispensing: A direct comparison of epoxy and rubber based systems via drag and pressure driven flows

Construction of vehicles requires adhesive dispensing for body-in-white assembly, hemming of closure panels, decking of windshields and the manufacture of battery packs. Knowledge of the rheological properties of adhesives applied using common dispensing systems is important for optimization of dispensing and application conditions. However, flow behavior of adhesives at shear rates used in dispensing is not well understood. Therefore, this study combines parallel plate and capillary rheology techniques to directly compare the rheological properties of an epoxy structural adhesive used in hemming applications and a rubber ‘topical sealer’ used to seal water leak paths across the range of shear rates observed in dispensing. Shear viscosity (η) and complex viscosity (η*) master curves were created from time-temperature-superposition (TTS) of steady shear and dynamic oscillatory data. Both adhesives did not follow the Cox-Merz rule. It was found that the Carreau-Yasuda model fit the steady shear viscosity master curve of the epoxy structural adhesive, while a simpler power law model fit the steady shear viscosity master curve of the rubber topical sealer. An inexpensive capillary rheometer was developed to simulate the adhesive dispensing process. Viscosity data was corrected for entrance pressure losses and a non-Newtonian flow front using Bagley and Weissenberg-Rabinowitsch corrections, respectively. It was observed that complex viscosity master curves better predicted viscosity during dispensing, as compared to steady shear viscosity master curves. Linear stress ramp measurements showed that the adhesives have widely different yield stresses, while the capillary rheometry measurements showed they have similar viscosities during dispensing. Furthermore, the capillary rheometer ‘shot meter’ pressures were related to the apparent and doubly corrected viscosity values through power law functions. A new quality control method based on the capillary rheology data is proposed.

A Hybrid Supramolecular Polymeric Hydrogel with Rapid Self-Healing Property.

A hybrid supramolecular polymeric hydrogel is conveniently constructed via host-guest interaction of a host cyclodextrin polymer (poly-CD) with a guest α-bromonaphthalene polymer (poly-BrNp) and mixing with 6-thio-β-cyclodextrin (β-SH-CD) modified gold nanoparticles (GPCDs) in aqueous solution. According to the dynamic oscillatory data, the hydrogel exhibits markedly enhanced stiffness compared with the GPCD-free one (both G' and G" values are almost twice as high as those of the original GPCD-free hydrogel) due to the introduction of the inorganic gold nanoparticles. This hybrid supramolecular polymeric hydrogel has a rapid and excellent self-healing property (only about 1 min, and the G' and G" of the self-healed hydrogel almost turned back to their original levels after 1 hour) in air (without adding any solvent or additive).

Optimization of rheological properties of gluten-free pasta dough using mixture design

The rising demand of gluten-free products for celiac people has led to important technological research on the replacement of the gluten matrix in the production of high quality gluten-free foods. The objective of this work was to evaluate the effect of composition (hydrocolloids, water, and proteins) on the rheological and textural properties of gluten-free dough used for producing pasta based on corn-starch and corn flour. Extensibility and rheological properties of gluten-free pasta dough were studied. Rising protein or gum contents produced a marked increase of deformation at break. However protein content was negatively correlated with breaking force. The increase in gums content produced an increase in storage and loss moduli (G′, G″). G′ was always larger than G″ with a small increase of both moduli with frequency. The mechanical relaxation spectrum was predicted from dynamic oscillatory data using the broadened Baumgaertel–Schausberger–Winter model. Application of a mixture design allowed finding the optimal composition to achieve the desirable textural properties using response surface methodology. A formulation containing 35.5% water, 2.5% gums, 4.7% proteins, 42.8% corn-starch, 10.7% corn flour, 1% NaCl, and 2.8% sunflower oil led to the highest values of G′, breaking force, and extensibility according to the optimization analysis performed.

Cold, gel-like soy protein emulsions by microfluidization: Emulsion characteristics, rheological and microstructural properties, and gelling mechanism

In this paper we reported the rheological and microstructural properties of a kind of novel cold, gel-like soy protein isolate (SPI) emulsions obtained by means of microfluidization. These gel-like emulsions were formed from untreated and preheated (95 °C, 15 min) SPI at a protein concentration of 6% (w/v), and various oil volume fractions (Φ; 0.2–0.6) and NaCl concentrations (0–500 mM). The rheological properties and microstructure were characterized using steady viscosity and dynamic oscillatory measurements, as well as confocal laser scanning microscopy (CLSM). The characteristics (e.g. droplet size distribution and creaming stability) of the emulsions, formed at lower protein concentrations (e.g. 0.5–4.0%), were also characterized, aiming to reveal the mechanism of the gel-like network formation. The dynamic oscillatory data indicated that both untreated and preheated SPI emulsions exhibited gel-like rheological properties, but the specific apparent viscosity (η) and storage modulus (G′) of the latter ones were much higher at a comparable Φ. Both η and G′ progressively increased upon Φ increasing, indicating enhanced inter-droplet interactions. At a given Φ value (0.3), increasing NaCl concentration progressively increased η and G′ of the preheated SPI emulsions, indicating the importance of electrostatic screening for the gel-like network formation. The CLSM analyses confirmed formation of the gel-like network, mainly composed of aggregated oil droplets, which was closely dependent on the Φ and NaCl concentration. The gel-like network was formed by bridging flocculation of oil droplets, mainly through inter-droplet hydrophobic interactions between the proteins adsorbed at the interface. These results suggested that soy proteins exhibit excellent potential to produce cold, gel-like emulsions, especially through a heat pretreatment followed by microfluidization, which might be of vital importance for the development of soy protein-based formulations, especially as carriers for heat-labile ingredients with health effects.

Building on the WLF/Free Volume Framework: Utilization of the Coupling Model in the Relaxation Dynamics of the Gelatin/Cosolute System

The onset of softening in the glass transition dispersion of the gelatin/cosolute system at 78% solids was examined using the stress relaxation modulus and dynamic oscillatory data on shear. Measurements were made between 5 and -70 degrees C, and isothermal runs were reduced to a master curve covering 21 orders of magnitude in the time domain. The sharpness with which the mechanical properties of our system changed with temperature was reflected in the shift factor a(T) used to pinpoint the glass transition temperature (T(g)). The prevalent analytical framework traditionally employed to follow the transition from the rubbery to glasslike consistency in biomaterials is that of the free volume theory in conjunction with the WLF equation. Increasingly, the combined WLF/free volume approach is challenged by the coupling model, which is able to provide additional insights into the physics of intermolecular interactions in synthetic materials at the vicinity of T(g). The model in the form of the Kohlrausch-Williams-Watts function described well the spectral shape of the local segmental motions of gelatin/cosolute at T(g). The analysis provided the intermolecular interaction constant and apparent relaxation time, parameters which depend on chemical structure. Results appear to be encouraging for further explorations of the dynamics of densely packed biomaterials at the glass transition region.

A Reptation-Based Lattice Model with Tube-Chain Coupling for the Linear Dynamics of Bidisperse Entangled Linear Polymer

A reptation-based lattice model for simulating the linear dynamics of entangled linear polymers that accounts for an essential coupling in tube-chain motions during constraint release is proposed. The predictions are tested against a representative set of dynamic oscillatory data on bidisperse polybudadiene (PBd) melts. The special feature of the current model lies in that the motion of the primitive chain coincides exactly with that of the ‘tube,’ so that it is possible to mimic the longitudinal relaxation that is cooperative with the lateral one (i.e., double reptation) during constraint release. The simulation is shown to capture the central feature of constraint release for the investigated system without demanding factorizability for the stress relaxation function, as usually enforced in existing tube theories. Furthermore, the simulation suggests that the longitudinal chain relaxation currently incorporated might account for an important partition of stress relaxation that had customarily been attributed to the effect of double reptation or similar tube motions alone.

An experimental appraisal of the Cox–Merz rule and Laun's rule based on bidisperse entangled polystyrene solutions

The empirical relationship provided by the Cox–Merz rule or Laun's rule has frequently been employed for linking rheological data collected in steady-state shear experiment to those in dynamic oscillatory experiment for entangled polymer liquids. Good applicability of these empirical rules has generally been found, especially for nearly monodipserse systems; for polydisperse systems, however, discrepancies have occasionally been reported without explanations. To throw some light on the impact of blending on the applicability of these empirical rules for entangled polymer liquids, we scrutinize simultaneously the steady state and dynamic oscillatory data on a series of bidisperse entangled polystyrene solutions. The primary finding is that deviations from the predictions of these empirical rules are generally observable as the long chain becomes markedly dilute, especially for the case of Laun's rule. The phenomenological effects of blending are tentatively interpreted in view of the contribution of chain stretching.

The glass transition zone in high solids pectin and gellan preparations

Dynamic oscillatory data on deacylated gellan and high methoxy pectin, in the presence of sucrose and glucose syrup, and presented over a wide temperature range. High levels of the co-solute induce a transition from rubberlike to glasslike consistency in the two biopolymers. The time-temperature superposition method is employed to construct composite curves, around the glass transition region, covering a nine-decade frequency range. The shift factors thus derived are fitted against the experimental temperatures using the Williams, Landel and Ferry equation. These observations are interpreted on the basis of the free volume theory which allows calculation of thermal expansion coefficient and fractional free volume parameters, at the glass transition temperatures of the high solids gellan and pectin systems. Values are in excellent agreement with those for synthetic polymers, a result which emphasizes the universal utility of the above approach (experiment and theory) in studying glasses of synthetic or biological origin.

Determination of a discrete relaxation spectrum from dynamic experimental data using the Padé-Laplace method

The Padé-Laplace method using the Laplace transform and the Pade approximants has been used to recover a discrete relaxation spectrum from dynamic oscillatory data in the molten state for polymers. The method detects by its own stability the number of modes of the spectrum and has been shown to be able to provide spectra with a low number of modes. These spectra are found to be sufficient to obtain an accurate description of the linear viscoelastic behavior in a large frequency range from the terminal zone to the plateau zone. Some intrinsic parameters of the numerical technique have been extensively studied in order to refine it. Its applicability is shown in the case of polystyrene having monomolecular, bimodal or broad molecular weight distributions. It can easily be implemented on a personal computer and the computing time is of the order of a few seconds.

Melt elasticity of incompatible blends of poly(butylene terephthalate)(PBT) and polyamide 6 (PA6)

AbstractThe extrudate swell and the dynamic rheological properties of poly(butylene terephthalate) (PBT) and polyamide 6 (PA6) binary blends were investigated at 240°C. The extrudate swell of the blend varies with the viscosity ratio and composition of constituents, and it is several times larger than that of homopolymers when the viscosity ratio of constituents is around unity. The dynamic oscillatory data could be interpreted by Oldroyd's emulsion model proposed by Graebling, et al. These results suggest that the extrudate swell is caused by the shape recovery of the dispersed particles. A semi‐empirical method to estimate the terminal relaxation time with experimental data was introduced, and a clear correlation between the extrudate swell and the terminal relaxation time was obtained.