Extensional Rheological Properties Research Articles

The effects of poly(ethylene glycol) grafting density on the extensional solution flows of high molecular weight polyacrylamide

AbstractControlling the extensional rheological properties of solutions is of great interest for a number of applications, such as printing and coatings, as polymeric additives can modify a fluid's droplet size, formation, and breakup. We have measured the extensional flows of polyacrylamide graft poly(ethylene glycol) amine (PAM‐g‐PEGa) solutions as a function of grafting density. PAM‐g‐PEGa is synthesized with grafting densities of 2.5%, 5.5%, 8%, and 30% and extensional flow was analyzed with drop‐on‐substrate rheology. Flow time scales and profiles are then compared to understand the effects of backbone extension from the addition of side chains. At low grafting densities, the viscous friction from the added side chains is comparable to, and in some cases, counteracts the losses in extensibility to the graft polymer's backbone, leading to increases in the relaxation time of the polymer. At higher grafting densities, the extension of the backbone reduces the relaxation time. By characterizing the effects of the graft density architecture on extensional flows, we are able to fine‐tune and control the breakup dynamics of elastic solutions.

Effects of barium sulfate on rheological properties and IDDSI flow consistency of liquid stimuli prepared using commercial thickening powders.

During videofluoroscopic swallowing study (VFSS), barium sulfate (BaSO4 ) is commonly added into food samples as a radiopaque contrast media for bolus visualization and examination. Accordingly, the consistency and flow behavior of barium stimuli can differ significantly from their non-barium counterparts. Such differences may have a subsequent impact on the validity of VFSS. Therefore, in this study, effects of barium sulfate on the shear and extensional rheological properties and IDDSI (International Dysphagia Diet Standardization Initiative) flow consistency of liquids prepared using various commercial thickening powders were investigated. Results showed that all barium stimuli exhibited shear thinning behavior but with significantly higher shear viscosity compared to the non-barium counterparts. A shift factor of viscosity at shear rate 50 s-1 with values in range of 1.21-1.73 could be used to describe the increase in the viscosity for samples thickened with gum-based thickeners. However, the change in the viscosity was not invariant for the stimuli prepared starch-based thickener. The addition of BaSO4 had a negative impact on extensional properties of samples by demonstrating a faster filament rupture. The extent of impact on the decrease in filament breakup time was more pronounced in xanthan > guar gum ≈ tara gum-based thickeners. Based on the IDDSI flow test, no significant effect of BaSO4 was found on the gum-based thickeners, whereas there was a marked effect in the starch-based sample. These results can be used beneficially to assist clinicians in the dysphagia diagnosis for matching rheological properties of the barium stimuli to enhance effectiveness dysphagia interventions.

Structural and shear and extensional rheological properties of hairy basil seed mucilage for potential application as oropharyngeal dysphagia diets

In this study, mucilage was extracted from the swollen hairy basil (Ocimum × africanum Lour.) seeds using ultrasonic-assisted extraction. Clear mucilage (BSM) was subsequently obtained by centrifugation for studies on its structural and shear and extensional rheological properties. The results revealed that the extracted BSM was rich in galactose and xylose, but low in mannose and galacturonic acid contents which indicated the presence of arabinogalactan and xylan. Small amounts of proteins (∼5%) were also detected. The average molecular weight of BSM was estimated as ∼480 kDa. Shear rheology results showed that aqueous dispersions of BSM at 1.0–2.5%w/v exhibited solid-like viscoelastic behavior with small frequency dependency, resembling a cross-linked gel. All BSM samples also exhibited shear thinning behavior that could be described by the power law model. However, the Cox-Merz rule was not obeyed for all studied BSM gels. The gel's elasticity was enhanced with increasing BSM concentration. For extensional rheology, the apparent extensional viscosity showed an extensional strain-softening behavior and demonstrated higher filament breakup time and extensional viscosity with increasing BSM concentration. A comparison between BSM and commercial thickening agents widely used in dysphagia management showed comparable rheological characteristics, thus suggesting the promising potential of BSM as a thickening agent for this application.

Influence of PMMA brushes grafted from GO on rheological properties of PMMA/SAN immiscible blend in shear and elongation flow

In real technological processes, both shear and elongational flow is present. The material properties may differ significantly under both types of flow. Hence, they both define the final morphology and thus properties of the materials. In this work, the morphology of immiscible blends containing polymer hybrid particles was related to extensional rheological properties for the first time. The effect of various lengths of polymer brushes grafted from graphene oxide particles (GO) surface was investigated. As a polymer matrix the immiscible blend of poly(methyl methacrylate)/styrene-co-acrylonitrile (PMMA/SAN) was used. Thus the poly(methyl methacrylate) (PMMA) brushes grafted from GO (GO-g-PMMA) with various number average molar masses (Mn) of PMMA brushes with respect to chain entanglement limit of freely dispersed PMMA were prepared. The extensional rheological properties were affected by Mn of PMMA brushes, while the rheological properties in shear were unchanged. Transmission electron microscopy revealed the compatibilization effect for short densely grafted brushes with Mn of 10,300 g/mol, as smaller domains were observed. On the contrary, the higher Mn PMMA brushes facilitated coalescence. With increasing length of brushes, the elongational viscosity at low elongation rates (∼< 0.1 s−1) decreased, which facilitated the coalescence. The increase of viscosity at higher elongation rates (∼> 0.1 s−1) was not sufficient enough to cause fiber breakup and thus elongated domains were formed.

Effect of isopropanol cosolvent on the rheology and spinnability of aqueous polyacrylic acid solutions

AbstractWe investigate the effect of alcohol fraction (isopropanol, IPA) in a binary water‐alcohol solvent mixture on the shear and extensional rheological properties, as well as the role of viscoelasticity on fiber formation of poly(acrylic acid) (PAA) in electrospinning. Comparison of the scaling of both specific viscosities ηsp and extensional relaxation times λE of PAA in water–IPA mixtures, showed stronger scaling compared to salt‐free aqueous polyelectrolyte solutions, except for the ηsp in the unentangled regime displaying a polyelectrolyte‐like scaling ηsp ~ c0.5 for all IPA%. Such deviation suggested IPA induces association/aggregation of PAA. However, the trends between ηsp and λE magnitudes as a function of IPA% differ for concentrations compared in the entangled regime. The ηsp as well as their elastic moduli exhibit a maximum, whereas λE increases monotonically with IPA%, suggesting a complex interplay of various interactions are dictating their structure in water‐IPA mixtures, affecting their shear and extensional response differently. Electrospinning experiments showed increasing IPA% reduces the onset of both beaded and uniform fibers. Analysis using dimensionless numbers indicated the enhancement of their elasticity by IPA, and the consequent stabilizing effect on their jets/filaments against break‐up during electrospinning, plays a role in the improvement of their fiber formation.

Shear and extensional rheological properties of whole grain rye and oat aqueous suspensions

Whole grain flours contain polysaccharides with techno-functional and nutritional properties which make them good candidates as natural texturisers in foods and beverages, thus reducing the use of highly refined ingredients. However, the use of plant components to develop complex fluids and soft materials, requires an enhanced understanding of the relationship between their physicochemical and rheological properties. Here, we systematically investigated the shear and extensional rheological properties of aqueous suspensions of whole grain rye and oat flours. Our results indicated that both types of suspensions (3.5 wt %) showed similar shear thinning behaviour (n = 0.4) however, oat suspensions presented higher viscosity and gel-like behaviour (G'>G'') compared to rye. Additionally, the oat suspensions exhibited an apparent extensional viscosity, which was not present in rye suspensions. The rheological properties of the continuous and disperse phases, separated by centrifugation, were investigated before and after starch hydrolysis and protein removal. Our results indicate that the distinct behaviour of oat suspensions is mainly due to the molecular structure of starch in the liquid phase of i.e oat starch had a higher amylose/amylopectin ratio than rye. Whilst the presence of protein and cell wall polysaccharides in the solid phase contribute to the overall rheology of the suspensions. Furthermore, our results show that the systems do not follow the Cox-Merz rule, indicating that they behaved as suspensions of soft particles rather than macromolecules in solution. Aqueous suspensions of whole grain rye and oat flours showed rheological properties that could be of interest to design low-medium viscosity food and beverage products.

Interactions between polymers and flows in macro and micro length scales.

Polymer solution with large molecular weights show scale dependent nonlinear behavior. The dynamics of such polymer solution in a meter length scale are very different from those in a micrometer length scale. To clarify this scale dependent behavior, we have conducted several experiments that focus on interactions between polymers and flows in multiple length scales [1Hidema R. Suzuki H. Hisamatsu S. Komoda Y. Furukawa H. Effects of the extensional rate on two-dimensional turbulence of semi-dilute polymer solution flows.Rheol. Acta. 2013; 52: 949https://doi.org/10.1007/s00397-013-0733-3Crossref Scopus (13) Google Scholar, 2Hidema R. Suzuki H. Hisamatsu S. Komoda Y. Characteristic scales of two-dimensional turbulence in polymer solutions.AICHE J. 2014; 60: 1854https://doi.org/10.1002/aic.14364Crossref Scopus (15) Google Scholar, 3Hidema R. Murao I. Komoda Y. Suzuki H. Effects of the extensional rheological properties of polymer solutions on vortex shedding and turbulence characteristics in a two-dimensional turbulent flow.J. Non-Newtonian Fluid Mech. 2018; 254: 1https://doi.org/10.1016/j.jnnfm.2018.02.001Crossref Scopus (12) Google Scholar, 4Hidema R. Fukushima K. Yoshida R. Suzuki H. Vortex deformation and turbulent energy of polymer solution in a two-dimensional turbulent flow.J. Non-Newtonian Fluid Mech. 2020; 285104385https://doi.org/10.1016/j.jnnfm.2020.104385Crossref Scopus (3) Google Scholar, 5Fukushima K. Kishi H. Suzuki H. Hidema R. Modification of turbulence caused by cationic surfactant wormlike micellar structures in two-dimensional turbulent flow.J. Fluid Mech. 2022; 933: A9https://doi.org/10.1017/jfm.2021.1058Crossref Scopus (1) Google Scholar, 6Hidema R. Hayashi S. Suzuki Hiroshi Drag force of polyethyleneglycol in flow measured by a scanning probe microscope.Phys. Rev. Fluids. 2019; 4074201https://doi.org/10.1103/PhysRevFluids.4.074201Crossref Scopus (2) Google Scholar, 7Hidema Ruri Fujito Ken-ya Suzuki Hiroshi Drag force of polyethyleneglycol in flows of polymer solutions measured by a scanning probe microscope.Soft Matter. 2022; 18: 455https://doi.org/10.1039/D1SM01305JCrossref PubMed Google Scholar].In the first part of this talk, I will highlight characteristic vortex deformation and energy transfer caused by polymers in a two-dimensional turbulent flow [1Hidema R. Suzuki H. Hisamatsu S. Komoda Y. Furukawa H. Effects of the extensional rate on two-dimensional turbulence of semi-dilute polymer solution flows.Rheol. Acta. 2013; 52: 949https://doi.org/10.1007/s00397-013-0733-3Crossref Scopus (13) Google Scholar, 2Hidema R. Suzuki H. Hisamatsu S. Komoda Y. Characteristic scales of two-dimensional turbulence in polymer solutions.AICHE J. 2014; 60: 1854https://doi.org/10.1002/aic.14364Crossref Scopus (15) Google Scholar, 3Hidema R. Murao I. Komoda Y. Suzuki H. Effects of the extensional rheological properties of polymer solutions on vortex shedding and turbulence characteristics in a two-dimensional turbulent flow.J. Non-Newtonian Fluid Mech. 2018; 254: 1https://doi.org/10.1016/j.jnnfm.2018.02.001Crossref Scopus (12) Google Scholar, 4Hidema R. Fukushima K. Yoshida R. Suzuki H. Vortex deformation and turbulent energy of polymer solution in a two-dimensional turbulent flow.J. Non-Newtonian Fluid Mech. 2020; 285104385https://doi.org/10.1016/j.jnnfm.2020.104385Crossref Scopus (3) Google Scholar, 5Fukushima K. Kishi H. Suzuki H. Hidema R. Modification of turbulence caused by cationic surfactant wormlike micellar structures in two-dimensional turbulent flow.J. Fluid Mech. 2022; 933: A9https://doi.org/10.1017/jfm.2021.1058Crossref Scopus (1) Google Scholar]. The effects of the extensional rheological properties of polyethylene oxide solutions were focused to understand the vortex deformation in turbulent flow and turbulent statistics of the polymer solution. In the polymer solution, although the turbulent energy production was virtually zero, a characteristic peak appeared in turbulent energy. The results imply the extension and relaxation of polymers affect the energy transfer.In the second part, I will introduce a method to measure the drag force due to synthetic polymers in flowing fluids by using a scanning probe microscope [[6]Hidema R. Hayashi S. Suzuki Hiroshi Drag force of polyethyleneglycol in flow measured by a scanning probe microscope.Phys. Rev. Fluids. 2019; 4074201https://doi.org/10.1103/PhysRevFluids.4.074201Crossref Scopus (2) Google Scholar,[7]Hidema Ruri Fujito Ken-ya Suzuki Hiroshi Drag force of polyethyleneglycol in flows of polymer solutions measured by a scanning probe microscope.Soft Matter. 2022; 18: 455https://doi.org/10.1039/D1SM01305JCrossref PubMed Google Scholar]. The conformation of polymers attached to the cantilever probe was predicted, and the drag force due to the deformed polymers in a flow was calculated. The drag forces obtained by model calculations were compared to the force detected by experiments, and found to be reasonably close.

Characterization of industrial low-density polyethylene: a thermal, dynamic mechanical, and rheological investigation

Thestudy of commercial low-density polyethylenes (LDPEs) has always focused on the effects of the molecular architecture of the polymer on its shear and extensional rheological properties due to their direct influence on manufacturability. However, the complex morphology of industrial-grade LDPEs also affects the crystallization kinetics and dynamic mechanical properties of the polymers, which are key to the processibility and applications. Therefore, a comprehensive investigation was conducted into the areas of crystallization kinetics, crystallinity, dynamic mechanical, and linear and non-linear shear rheological properties of two industrial-grade LDPEs to build a cohesive insight into the influence of morphology on these material properties. We further analyzed the steady-state and transient shear viscosity data obtained from the two LDPEs in comparison with constitutive model predictions using the hierarchical multi-mode molecular stress function (HMMSF) and found excellent agreement within experimental accuracy between predictions by the HMMSF model and shear stress as well as normal stress data of the LDPEs investigated.

Nonlinear rheology of entangled wormlike micellar solutions predicted by a micelle-slip-spring model

We examine linear and nonlinear shear and extensional rheological properties using a “micelle-slip-spring model” [T. Sato et al., J. Rheol. 64, 1045–1061 (2020)] that incorporates breakage and rejoining events into the slip-spring model originally developed by Likhtman [Macromolecules 38, 6128–6139 (2005)] for unbreakable polymers. We here employ the Fraenkel potential for main chain springs and slip-springs to address the effect of finite extensibility. Moreover, to improve extensional properties under a strong extensional flow, stress-induced micelle breakage (SIMB) is incorporated into the micelle-slip-spring model. Thus, this model is the first model that includes the entanglement constraint, Rouse modes, finite extensibility, breakage and rejoining events, and stress-induced micelle breakage. Computational expense currently limits the model to micellar solutions with moderate numbers of entanglements (≲7), but for such solutions, nearly quantitative agreement is attained for the start-up of the shearing flow. The model in the extensional flow cannot yet be tested owing to the lack of data for this entanglement level. The transient and steady shear properties predicted by the micelle-slip-spring model for a moderate shear rate region without significant chain stretch are fit well by the Giesekus model but not by the Phan–Thien/Tanner (PTT) model, which is consistent with the ability of the Giesekus model to match experimental shear data. The extensional viscosities obtained by the micelle-slip-spring model with SIMB show thickening followed by thinning, which is in qualitative agreement with experimental trends. Additionally, the extensional rheological properties of the micelle-slip-spring model with or without SIMB are poorly predicted by both the Giesekus and the PTT models using a single nonlinear parameter. Thus, future work should seek a constitutive model able to capture the behavior of the slip-spring model in shear and extensional flows and so provide an accurate, efficient model of micellar solution rheology.

Nonlinear Extensional Rheology of Poly(n-alkyl methacrylate) Melts with a Fixed Number of Kuhn Segments and Entanglements per Chain

Molecular theories for dynamics of entangled polymers are based on both the number of Kuhn segments per entanglement Ne and the number of entanglements per chain N/Ne. Extensive studies have shown that, for polymer chains in the solutions or melts, linear viscoelasticity can be properly normalized, whereas the nonlinear extensional rheological properties cannot be normalized when N/Ne is kept the same. The failure of the latter normalization has been attributed to a difference in Ne. Nevertheless, nonlinear rheological studies are lacking for a suitable model system with fixed Ne and N/Ne. In this study, we identify poly(n-alkyl methacrylate)s with the number of carbons per alkyl group below seven as a model system. We find that the degree of the transient strain hardening during extensional flow strengthens with increasing the size of the alkyl group even when Ne and N/Ne are kept the same, which is attributable to the weaker friction reduction when the main backbones are more separated.

Effects of flow history on extensional rheological properties of wormlike micelle solution.

A wormlike micelle (WLM) solution is a complex fluid that forms when the surfactant concentration is high. It has rheological properties similar to those of polymer solutions. However, unlike polymer molecules, WLM chains possess the dynamic microstructure that can be reversibly broken and reassembled in flows. Therefore, the rheological properties and flow behavior of WLM solutions have attracted much attention owing to their unique dynamic microstructures. However, the effects of the flow history on the extensional rheological properties of WLM solutions remain unclear. In this study, the change in the extensional rheological properties of WLM solutions depending upon on their shear flow histories was investigated by combining the dripping-onto-substrate/capillary break-up extensional rheometry technique with a compressed gas flow (stop-flow) control method. This approach precisely controls the shear flow histories of the WLM solutions. The results revealed that the shear flow history has a substantial impact on elongational rheological properties such as relaxation time. They also showed that the effects of the characteristic shear rate are highly dependent on the surfactant concentration. We expect that the current findings can be applied to understand the extensional rheological properties of complex fluids in industrially relevant processes such as coating and printing.

Solvent Effects on the Elasticity of Electrospinnable Polymer Solutions.

Ultrafine fibers manufactured through electrospinning are a frontrunner for advanced fiber applications, but transitioning from potential to commercial applications for ultrafine fibers requires a better understanding of the behavior of polymer solutions in electrospinning to enable the design of more complex spinning dopes. In complex fluids, there are viscoelastic stresses and microstructural transitions that alter free surface flows. These may not be seen in shear rheology; therefore, an in-depth analysis of the extensional rheological behavior must be performed. In this work, we use dripping-onto-substrate rheometry to characterize the extensional viscosities of electrospinning dopes from four polymer solutions commonly used in electrospinning (low- and high-molecular-weight polyvinylpyrrolidone in methanol and water as well as poly(ethylene oxide) and poly(vinyl alcohol) in water). We link the electrospinnability, characterized through fiber morphology, to the extensional rheological properties for semidilute and entangled polymer solutions and show that high-surface-tension solvents require higher extensional viscosities and relaxation times to form smooth fibers and that the Deborah and Ohnesorge numbers are a promising method of determining electrospinnability. Through this tie between solvent characteristics, viscoelasticity, and electrospinnability, we will enable the design of more complex spinning dopes amenable to applications in wearable electronics, pharmaceuticals, and more.

Modification of turbulence caused by cationic surfactant wormlike micellar structures in two-dimensional turbulent flow

An experimental study is performed to investigate the effects of the extensional rheological properties of drag-reducing wormlike micellar solutions on the vortex deformation and turbulence statistics in two-dimensional (2-D) turbulent flow. A self-standing 2-D turbulent flow was used as the experimental set-up, and the flow was observed through interference pattern monitoring and particle image velocimetry. Vortex shedding and turbulence statistics in the flow were affected by the formation of wormlike micelles and were enhanced by increasing the molar ratio of the counter-ion supplier to the surfactant, ξ, or by applying extensional stresses to the solution. In the 2-D turbulent flow, extensional and shear rates were applied to the fluids around a comb of equally spaced cylinders. This induced the formation of a structure made of wormlike micelles just behind the cylinder. The flow-induced structure influenced the velocity fields around the comb and the turbulence statistics. A characteristic increase in turbulent energy was observed, which decreased slowly downstream. The results implied that the characteristic modification of the 2-D turbulent flow of the drag-reducing surfactant solution was affected by the formation and slow relaxation of the flow-induced structure. The relaxation process of the flow-induced structure made of wormlike micelles was very different from that of the polymers.

SEBS as an Effective Nucleating Agent for Polystyrene Foams.

Different percentages of an elastomeric phase of styrene-ethylene-butylene-styrene (SEBS) were added to a polystyrene (PS) matrix to evaluate its nucleating effect in PS foams. It has been demonstrated that a minimum quantity of SEBS produces a high nucleation effect on the cellular materials that are produced. In particular, the results show that by adding 2% of SEBS, it is possible to reduce the cell size by 10 times while maintaining the density and open cell content of the foamed materials. The influence of this polymeric phase on the glass transition temperature (Tg) and the shear and extensional rheological properties has been studied to understand the foaming behavior. The results indicate a slight increase in the Tg and a decrease of the shear viscosity, extensional viscosity, and strain hardening coefficient as the percentage of SEBS increases. Consequently, an increase in the density and a deterioration of the cellular structure is detected for SEBS amounts higher than 3%.

Extensional gravity-rheometry (EGR) for yield stress fluids

In order to measure the extensional rheological properties of yield stress fluids, we developed a rheometrical approach based on the analysis of the deformations of a fluid extrudate flowing downward and breaking in successive elongated drops due to gravity. Assuming the gradients of longitudinal velocity in radial planes are negligible, the local instantaneous strain rate is deduced from the variations of the filament diameter in each cross section, while the normal stress is computed from the acceleration and weight of the material below this point. The observation of the filament profile in time allows us to identify a solid region, in which the deformations tend to saturate, and a liquid region, in which the deformations continuously increase. A further analysis allows us to distinguish the data for which pure elongational stress and strain rate components are effectively dominant so that the elongational flow curve of the material over several decades of the strain rate can be deduced. For two typical yield stress fluids (emulsion and clay suspension) with different internal structures, all the normal stress vs extensional rate data obtained under these different flow conditions fall along a single master curve for each material. This flow curve in elongation appears to be well represented by the standard 3D Herschel–Bulkley model under the condition that a slightly different power of the strain rate than in simple shear is used. For both material types, the elongational yield stress value found in this way is very close to the simple shear yield stress times the square root of 3.

Vortex deformation and turbulent energy of polymer solution in a two-dimensional turbulent flow

An experimental study was performed to investigate the effects of the extensional rheological properties of polymer solutions on vortex deformation in turbulent flow and turbulent statistics. To focus on the extensional properties, a self-standing two-dimensional (2D) turbulent flow was used as an experimental setup, and the flow was observed through interference patterns and particle image velocimetry (PIV). Vortex shedding and the resulting deformation in the 2D flow were categorized into three types. The vortex flow regime was defined by the shedding frequency and relaxation time of the polymer solution. Turbulent energy was suppressed by polymer additives; however, a characteristic peak reappeared with increasing concentration. The results imply that the characteristic turbulent energy peak is influenced by the relaxation process of the extended polymers in the flow.

Sensory perception of guar gum-induced thickening: Correlations with rheological analysis

This work studies the connection between the orally-perceived thickness and easiness to swallow of guar gum dispersions with their shear and extensional rheological properties. The concentration dependence of the orally-perceived thickness scales with the decimal logarithm of the extensional viscosity. The easiness in swallowing, as perceived by sensory testers, is linked to the Trouton's ratio and scales with the logarithm of the extensional viscosity. The transition of the polymers to the semi-dilute regime leads to a marked change to the Trouton's ratio and, above 0.75 g dL−1, its value closes to 5. This study concludes that extensional, rather more than shear viscosity, is responsible for the perception of thickness and easiness in swallowing; however, at higher concentrations, both viscosities become of importance in the regulation of oral polysaccharide flow.

Unveiling the Effects of In Situ Layer–Layer Interfacial Reaction in Multilayer Polymer Films via Multilayered Assembly: From Microlayers to Nanolayers

AbstractMultilayered polymer films are increasingly used in the daily life, but their macroscopic properties are always limited by the layer–layer interfacial compatibility. In this work, the influence of interface modification through in situ layer–layer interfacial reaction during a multilayered assembly is revealed from micro‐ to nanolayer films, based on maleated poly(vinylidene fluoride) and polyamide‐6. In the presence of interfacial reaction and confinement, layer architecture and microstructure are highly dependent on the number of layers. Specifically, for nanolayer films having smaller layer thicknesses and higher reaction extent, layer integrity is reduced with the occurrence of interfacial instabilities. Depending on the microstructural evolution from multilayer assembly, those films exhibit quantitatively different extensional rheological and dielectric properties from micro‐ to nanolayers. More importantly, dielectric spectroscopy reveals the contribution of copolymer‐rich interphases to the dielectric performance of micro/nanolayered films. Additionally, charge transport dynamics in nanolayered films also differ significantly from their microlayered counterparts. They are attributed to the strong dependence of interfacial reaction extent and resulting microstructure on the number of layers and layer thicknesses. This work clearly illustrates how the control of layer–layer interfacial reaction in micro/nanolayer assembly can tune the interfacial, microstructure, and macroscopic properties of multilayered products.

Extensional rheological properties in mixed and fermented/rested dough and relationships with steamed bread quality

In this study, sixteen wheat varieties for cultivation in China were examined for the flour characteristics using the farinograph, extensograph and rheofermentometer, uniaxial extensional rheology employing the extensograph and the Kieffer extensibility rig and biaxial extension by uniaxial compression of mixed dough with and without yeast, rested and fermented dough, and steamed bread quality including specific volume and texture properties. Three statistical analysis methods including Pearson correlation, principle component and stepwise multiple regression analysis were carried out to correlate dough properties with steamed bread quality. Biaxial extension viscosity was positively correlated with texture properties (hardness and chewiness) of steamed bread (r = 0.521–0.685, p < 0.05). Based on the correlation coefficients and the model (r2 = 0.852, p = 0.003) obtained using stepwise multiple regression analysis, the best predictors for specific volume of steamed bread were the maximum resistance to extension of rested dough (r = 0.664, p < 0.01) and total work for breakage of fermented dough (r = 0.662, p < 0.01). Principal component analysis of rheological properties of fermented dough and flour characteristics provided more useful information for discriminating wheat flour quality and help breeders to select most convenient wheat flour for the steamed bread making.

Comparison of uniaxial/biaxial extensional rheological properties of mixed dough with traditional rheological test results: relationship with the quality of steamed bread

SummaryThe formula and preparation of steamed bread are different from those of western bread. The extensional rheological behaviour plays a key role in the development of steamed bread dough. However, there are inadequate studies on the rheological properties of mixed dough with yeast. In this study, the relationship between properties of dough in the presence or absence of yeast was elucidated. Besides, the flour characteristics and quality of steamed bread prepared from different wheat varieties were evaluated. The uniaxial/biaxial extensional rheological properties of wheat dough were compared with traditional rheological test results. Large deformations in the extensional properties were measured by Extensograph and the Kieffer extensibility rig, while the biaxial extension was quantified using uniaxial compression. These characteristics of dough and flour correlated with each other in different ways. Correlation analysis illustrated that the uniaxial extensional rheological properties of dough with yeast better indicated the quality of the steamed bread. Moreover, the total work for breakage of the dough with yeast was the best predictor for specific volume of steamed bread. The texture‐based properties of steamed bread showed correlation with biaxial extension viscosity. The rheological tests provide useful information for evaluating wheat flour and steamed bread quality.