rheology

摘要： Evidences show that the storage period greatly affects the quality of yogurt.In this study,three types of yogurt:control yogurt(CY),non-hydrolyzed potato powder yogurt(PPY)and enzymatically hydrolyzed potato powder yogurt(EHPPY)were prepared at 42°C for 5 h and stored for 28 days at 4°C.The yogurts were evaluated for quality characteristics at different storage periods.Negligible differences in pH values,titratable acidities and viable counts were detected in all three types of yogurt during storage.However,compared to other yogurts,EHPPY exhibited desirable water holding capacity,throughout the storage period.Apart from this,sensory properties and antioxidant activities(2-diphenyl-1-picryl-hydrazyl(DPPH)free radical scavenging activity and ferric reducing antioxidant power(FRAP))of EHPPY were also significantly improved during the storage period.Furthermore,the storage(G’)and loss(G”)modulus of PPY,EHPPY were lower than CY at 4°C while a hysteresis loop was shown by all yogurts at the temperature range of 4-50°C indicating higher G’(elasticity)than G”(viscosity).Based on our findings,EHPP could be an important functional ingredient in improving the quality and storage stability of yogurt for its production at an industrial level.

摘要： In this research, an attempt was made to improve compatibility in a polymer blend composed of incompatible constituents, namely, recycled polystyrene (rPS) and polystyrene-co-acrylonitrile (SAN), through the addition of a compatibilizer. The compatibilizing agent, styrene-ethylenebutadiene-styrene block copolymer (SEBS), was added to the polymer blend in ratios of 5 and 10 wt%. For this purpose, blends of rPS and SAN at different ratios, without and with varying concentrations of compatibilizer, were prepared by melt blending using a co-rotating twin-screwextruder. Mechanical properties including tensile and impact strength, rheological properties (RPA), thermal behaviour (DSC) and morphological characteristics (SEM) were evaluated. According to the results obtained by complex viscosity, the blends behave as a pseudoplastic fluid. The results showed that the addition of SEBS increased the Izod impact strength and the elongation at break and decreased the tensile strength and tensile modulus. rPS/SAN blend modified with SEBS had better mechanical properties than the rPS/SAN alloy. SEM photographs revealed that the SEBS was not only distributed in the SAN phase but also distributed in rPS phase in rPS/SAN/SEBS blend. Furthermore, DSC analysis for blends of rPS/SAN gave a good indication of the improvement on miscibility for most compositions. SEM micrographs of tensile fracture surfaces indicated that the formation of the co-continuous phase and the improvement of interface adhesion are the most important reasons for the excellent tensile properties of the rPS/SAN/SEBS blends. Within the range of analysed compositions, the morphologies investigated by SEM are typical of immiscible blends.

摘要： The existence of an evolving microstructure in a 2.9 vol% fumed silica in paraffin oil and polyisobutylene is demonstrated experimentally and via rheological modeling during steady state and large amplitude oscillatory shear flow. The continuously evolving, rebuilding, and breaking down of the microstructure is shown, and correlated through the rheology experiments, thixo-elastovisco-plastic modeling, and small angle light scattering (SALS). All elements are then connected via a global, stochastic optimization algorithm that will provide parameter estimation with a “best-fit” of the steady state and transient data using the well-known Modified Delaware Thixotropic Model, allowing for the comparison of SALS results with experimental values.

摘要： This paper demonstrates the existence, propagation, transmission, reflection, and interaction of deviatoric stress waves in polymeric fluids for which the mathematical models are derived using conservation and balance laws (CBL) of Classical Continuum Mechanics (CCM) and the constitutive theories are based on the entropy inequality and representation theorem. The physical mechanisms of deformation in polymeric liquids that enable the stress wave physics are identified and are demonstrated to be valid using Maxwell, Oldroyd-B, and Giesekus polymeric fluids, and are illustrated using model problem studies. We assume polymeric fluids to be isotropic and homogeneous at the macro scale so that the CBL of the CCM can be used to derive their mathematical models. For simplicity, we assume the polymeric fluids to be incompressible in the present work.

摘要： Sourdough starters for making traditional steamed bread are rich in microbes.Studies have shown that,in addition to yeast and lactic acid bacteria(LAB),acetic acid bacteria(AAB)are other functional species in sourdough,but the influences of AAB on the properties of sourdough and steamed bread were rarely reported.This study aimed to assess the effects of a selected strain of acetic acid bacterium on the properties of sourdough and steamed bread.Sourdoughs and steamed breads were prepared from five different starter cultures,marked as CK(control check,with no starters),Y(only yeast),YL(yeast+LAB),YA(yeast+AAB)and YLA(yeast+LAB+AAB),and their properties were determined.The results of sour dough properties showed that the YLA sourdough had the highest total titratable acid of 14.6 mL and the lowest pH of 3.87 compared with the other groups after fermentation to 8 h;and the YLA sourdough had the greatest elasticity and viscosity.The results of quality properties of steamed bread revealed that the L*value(88.40±0.09)of the YA steamed bread was significantly higher than those of the YLA and YL steamed breads;the YLA steamed bread had the highest specific volume and the highest sensory score of 89.6±3.31 in comparison to those of the other groups;the hardness and chewiness of YLA and YA steamed breads were significantly lower than those of the other groups.Volatile compounds in the steamed breads were also determined by SPME-GC-MS.A total of 42 flavor substances were detected,including 3 kinds of alcohols,8 kinds of aldehydes,7 kinds of ketones,2 kinds of acids,15 kinds of esters,1 furan,and 6 kinds of other types of compounds,mainly alkanes and esters,followed by alcohols and aldehydes.The YLA steamed bread was richer in esters,aldehydes,and acids than those from the other treatment groups.By contrast,alkanes and aldehydes were dominant in the Y and YL steamed breads.Therefore,the flavor and quality of the steamed bread made from the YLA sourdough could be improved obviously.These results could provide references for the application of AAB in dough fermentation and the improvement of new kinds of starters.

摘要： Coronavirus disease 2019(COVID-19)caused by acute respiratory syndrome coronavirus 2(SARS-Cov-2)is still threatening the human life and society throughout the world.For those critically ill patients,mechanical ventilation(MV)is essential to provide life support during treatment.However,both the virus infection and MV disrupt the balance between secretion and elimination of airway mucus and lead to mucus accumulation in the lung.Postmortem examination verified that the lungs in patients died of COVID-19 are indeed filled with sticky mucus,suggesting a great need to improve airway mucus clearance in critically ill COVID-19 patients.Therefore,it may be helpful to comprehensively review the current understanding regarding the changes of biochemical and rheological features of airway mucus associated with the disease,as well as the physiological principles and algorithm to decide airway clearance techniques suitable for the critically ill COVID-19 patients.Based on these considerations,optimized strategies may be developed to eliminate the airway mucus accumulated in the airways of critically ill COVID-19 patients.

摘要： Cancer metastasis is still a major social issue with limited knowledge of the formation of tumors and their growth.In addition the formation of metastases is very difficult to understand,since it involves very complex physical mechanisms such as cellular interactions and cell rheology,which are flow-dependent.Previous studies investigated transendothelial migration using sophisticated techniques such as microfluidics,traction force microscopy(TFM)or Atomic Force Microscopy(AFM),combined with physical modeling.Here we summarize recent results and suggest new ways to investigate the precise mechanisms used by cancer cells to undergo transendothelial migration.

摘要： Polylactide(PLA)/poly(butylene adipate-co-terephthalate)(PBAT)blend nanocomposites including 3 wt%of cel-lulose nanocrystals(CNCs)were prepared by melt compounding method in a twin-screw extruder and an inter-nal mixer.Blend nanocomposites were formulated by diluting three different masterbatches prepared by solution casting method that contained 7 wt%of CNC.These masterbatches were:(m1)PLA/PBAT/CNC masterbatch;(m2)PLA/CNC masterbatch;and(m3)PBAT/CNC masterbatch.These were to explore how different prepara-tion methods affect the dispersion and localization of CNC and hence the properties of PLA/PBAT/CNC blend nanocomposites.Scanning electron microscopy(SEM)was used to study the structural changes of the blends.Rheological properties of PLA/PBAT blends and PLA/PBAT/CNC blend nanocomposites were also investigated.In the samples prepared by internal mixer,the rheological behavior of blend nanocomposite prepared through premixing of CNC particles with PLA showed a transition from liquid-like to a gel-like behavior.According to the rheological results and differential scanning calorimetry(DSC)analysis,it was found that the CNC overall enhanced the viscoelastic properties of blends and improved the PLA crystallization,respectively.Dynamic mechanical analysis(DMA)illustrated that the incorporation of CNC also enhanced the elastic modulus of PLA/PBAT blends specifically above the glass transition temperature of PLA.The expected improvements in mechanical properties did not occur due to the possible existence of residual solvent in the blends.

摘要： The rheological characteristics of a physical gelation system,in which cellulose nanocrystals(CNC_(s))induced the entanglement of poly(acrylic acid)(PAA)chains and partial hydrophobic association of octylphenol polyoxyethylene acrylate(OP-10-AC)branches in a micellar solution of sodium dodecyl sulfate(SDS),were investigated.The gelation time of the physical gels decreased as the CNC content and number of hydrophobic branch units increased.At the gel point,the storage modulus(G')and loss modulus(G")followed the same frequency dependence(G'≈G"≈ωn),where the hydrophobic moieties attached to the side chains had a significant impact on the values of viscoelastic exponent(n).Beyond the gel point,the initial polymer solution was transformed to a solid-like gel,and the strength of the gel network was governed by associations between both the CNCs and hydrophobic groups.The evolution of the viscoelasticity during the gel-sol transition was monitored,demonstrating that due to a reversible arrangement of the hydrophobic units,a large proportion of physical cross-links dissociated under a thermal trigger and were reversibly reformed when the solution was cooled,while no such partial recovery was observed in the case of the single CNC-induced network systems(with no hydrophobic branches).

摘要： Yielding behaviors of waxy crude oil is one of the key issues of flow assurance challenges. The yielding of waxy crude under constant stress is actually a creep process of strain accumulation to structural failure,to describe the process completely and accurately is the basis of numerical simulation of restart process of the pipeline. The creep and yield behaviors of two gelled waxy crudes were investigated experimentally under different constant applied stresses. The results clearly show that the creep process of waxy crude is related to the applied stress and time. The greater the applied stress, and the longer the loaded time, the more obvious the nonlinear features. Based on the fractional calculus theory, a fractional viscous element was developed to describe the decelerated and steady creep process of gelled waxy crude. On the basis of the damage theory, an elastic damage element was proposed to describe the accelerated creep after the yielding. According to the idea of mechanical analogy, a nonlinear creep model was established by a fractional viscous element, an elastic damaged element, and an elastic element in series, which can accurately describe the whole creep and yielding process of gelled waxy crude.

摘要： The rheologycal behavior of polyacrylonitrile/1-Butyl-3-methylimidazolium chloride (PAN/[BMIM]CI)solutions was investigated. The traditional shear-thinning phenomena were observed in the steady-state rheology experiments.However，both the zero-viscosity and flow activity energy are higher than that of PAN in the conventional solvent. From the dynamic rheology，there is no gel point was observed in the experimental range，which indicates that PAN/[BMIM]CI solutions is stable. The dominance of viscons behavior and elastic behavior，is affected by PAN concentration and molecular weight. At lower concentrations and molecular weight，solutions show viscous，inelastic behavior at the same deformation rate. Solutions with higher concentration and molecular weight are more elastic behavior. At low angular frequencies，the PAN solution behaves as a viscous liquid，the elastic component in viscoelastic behavior decreasing as the temperature of the solution is increased. Temperature and deformation rates can be used as parameters to control the rheological behavior of PAN solutions。