Showing papers in "Korea-australia Rheology Journal in 2021"
TL;DR: In this paper, a comprehensive review of bypass MR dampers is presented, which includes principles of operation, design structures, analytical models, experimental analysis, and applications of MR damping.
Abstract: Magneto-rheological (MR) dampers using MR fluids with controllable rheological properties are mainly utilized in automobiles, structures, electrical transmission lines, medical applications, agricultural engineering, and military equipment. This paper presents a comprehensive review of bypass MR dampers. The principles of operation, design structures, analytical models, experimental analysis, and applications of MR dampers are classified and reviewed. The bypass MR dampers have better MR fluid stability and sedimentation control compared to MR dampers. This is important for maintaining homogeneous magnetic flux distribution throughout the fluid area. The advantageous features of external bypass MR dampers over internal bypass dampers are the higher shear stress, the damping force controllability, and the higher damping force they can generate.
10 citations
TL;DR: In this article, the authors describe the longitudinal dispersion of passive tracer molecules injected in a steady, fully developed, viscous, incompressible, laminar flow through an annular pipe with a first order heterogeneous boundary absorption at the outer wall, numerically using layer-adapted meshes.
Abstract: This paper describes the longitudinal dispersion of passive tracer molecules injected in a steady, fully developed, viscous, incompressible, laminar flow through an annular pipe with a first order heterogeneous boundary absorption at the outer wall, numerically using layer-adapted meshes. The model is based on steady advection-diffusion equation with Dirichlet and Robin boundary conditions. The solutions are discussed in the form of iso-concentration contours of the tracer molecules in the vertical plane. An artanh transformation is used to convert the infinite domain into a finite one. A combination of central finite difference and 2-point upwind scheme is adopted to solve the governing advection-diffusion equation. It is shown that how the mixing of tracers is affected by the shear flow, aspect ratio and the first-order boundary absorption. When the flow becomes convection dominated, the monotone finite difference on a uniform mesh does not work properly, so a layer-adapted mesh, namely a “Shishkin” mesh, is used to capture the layer phenomena at the different downstream stations. The present results are compared with existing experimental and numerical data and we have earned an excellent agreement with them. It is observed that, due to the use of layer adapted mesh, we have achieved a better agreement with the experimental data than some other previous results available in the literature, especially in the closest downstream location. The results of this study are likely to be of interest to understand the basic mechanism of dispersion process of solute in blood through a catheterized artery with an absorptive arterial wall.
9 citations
TL;DR: In this article, the authors investigate non-Newtonian Casson fluid flow with pulsation in a channel having symmetrical constriction bumps on the upper and lower walls, where the medium is assumed to be porous, following Darcy's law.
Abstract: In this paper, we investigate non-Newtonian Casson fluid flow with pulsation in a channel having symmetrical constriction bumps on the upper and lower walls. The medium is assumed to be porous, following Darcy’s law. The fluid is modeled as electrically low conducting, and the pulsatile flow is subjected to a transverse magnetic field of uniform strength to study the impact of the resulting Lorentz force. We transform the mathematical model using the vorticity-stream function form for obtaining the solution. We analyze influence of the Hartman, Strouhal, Casson fluid, and porosity parameters on various flow profiles. It is revealed that the region of flow separation in the wake of a constriction bump tends to vanish with increasing the magnetic field parameter as well as Casson fluid parameter. The wall shear stress has higher values at the first constriction bump than that at the second constriction bump on a wall. It is also noticed that wall shear stress decreases with increasing the value of the porosity parameter during the pulsation cycle.
8 citations
TL;DR: An overview of the effects of CNCs on the processing, physical properties, and rheology of various types of polymer nanocomposites can be found in this paper.
Abstract: The use of nanocomposites is regarded as a promising strategy to significantly improve the overall performance of polymeric materials using a minimal amount of additives. Recently, environmental pollution issues caused by discarded plastic waste have encouraged manufacturers and researchers to replace petroleum-based non-degradable plastics with biomass-derived degradable plastics. Recent research interest in polymeric nanocomposites has resulted in the development of biodegradable nanocomposites using bio-derived nanofillers. Cellulose nanocrystals (CNCs) are one of the most fascinating and widely investigated reinforcing fillers derived from biomass sources such as plants. Compared with conventional inorganic fillers, including carbon nanotubes and metal nanoparticles, CNCs are the most abundant renewable materials on Earth. They do not result in biodegradability deterioration when incorporated into biodegradable polymers. In addition, CNCs exhibit superior dispersibility and chemical affinity to polymeric matrices, resulting in better reinforcing efficiency. Accordingly, considerable effort has been devoted to achieve the desired processability, rheological behavior, and final performances of CNC-loaded nanocomposites. This review aims to provide an overview of the effects of CNCs on the processing, physical properties, and rheology of various types of polymer nanocomposites.
6 citations
TL;DR: In this paper, amine-based blocking agents were prepared by varying the alkyl substituent attached on both sides of the main nitrogen atom (named DEA, DiPA, NtBEA, and NtBiA) to modify deblocking feature in blocked isocyanates (BIs) and curing reaction under thermal curing conditions.
Abstract: Isocyanate crosslinkers with blocking agents based on various amine derivatives were newly synthesized for automotive clearcoat applications. Amine-based blocking agents were prepared by varying the alkyl substituent attached on both sides of the main nitrogen atom (named DEA, DiPA, NtBEA, and NtBiA) to modify their deblocking feature in blocked isocyanates (BIs) and curing reaction under thermal curing conditions. Curing properties of clearcoats containing amine-based BIs were characterized at the normal curing temperature of 150°C and were compared with those by the commercialized BI, Desmodur® PL350. The dissociation ability of the amine-based BIs was interpreted using the density functional theory (DFT) simulation under their optimized geometric configurations. The urethane reaction between isocyanate group in BIs and hydroxyl group in a hydroxyl-functionalized polyol binder within clearcoats was confirmed from the OH stretching absorbance data via Fourier-transform infrared (FT-IR) spectrometer. The real-time cross-linking dynamics of various clearcoats with amine-based BIs were comprehensively investigated using rotational rheometer and rigid-body pendulum tester. The surface mechanical properties of fully-cured clearcoat films were measured by nano-indentation and nano-scratch testers to address the crosslinked network formation caused by amine-based BIs. It is demonstrated that the amine-based BIs could be favorably applied to thermal curing process of clearcoats, based on their reactivity and curing performance.
6 citations
6 citations
TL;DR: In this article, the authors used a viscoelastic model with four hypotheses to characterize the visco-elastic property of a loach skin mucus published recently by using a variational model.
Abstract: The epidermal mucus secreted by fish is a natural barrier between fish and water, which is a slippery and slightly thick fluid with some biological functions. The present work is to characterize the viscoelastic property of a loach skin mucus published recently by using a viscoelastic model with four hypotheses. The experimental steady shear viscosity with the maximum shear rate of 10 s−1 for the mucus was fitted to obtain the parameters in the model. The other four steady shear viscosity curves with the maximum shear rate of 0.004, 0.01, 0.1, and 1.0 s−1, respectively, and the start-up experiment at the shear rate of 0.1 s−1 were predicted. The phenomenon that the viscosity at the low shear rate in the decreasing shear rate regime is higher than that in the increasing shear rate regime can be illuminated by a structural irreversibility hypothesis, which is based on the varying linear viscoelastic property of the mucus induced by shear rate. The theoretical description on the unusual viscosity curves of the loach mucus provides a base for quantitative analysis on the mucus effect on the swimming of fish, and could promote the understanding on the swimming-related function of skin mucus in fish.
4 citations
TL;DR: In this article, the authors proposed a new method to characterize the sedimentation stability of magnetorheological fluid (MRF) based on the change of shear yield stress during sedimentation process of MRF.
Abstract: The sedimentation stability of Magnetorheological fluid (MRF) is one of the research hotspots in the academic field of magnetorheological science. Excellent sedimentation stability is of great significance for the preservation and application of MRF. Given many traditional methods of characterization of sedimentation stability, this paper proposes a new method to characterize the sedimentation stability of MRF based on the change of shear yield stress during the sedimentation process of MRF. Then, the key components of the self-made MRF shear yield stress test device were introduced in detail, and three different surfactants containing dodecyl benzoate, polyethylene glycol and oleic acid were prepared. And then used the device to test their effects on the sedimentation stability of MRF. The results showed that oleic acid has the best effect on improving the sedimentation stability. Finally, the change law of shear yield stress of MRF in the next 90 days was predicted successfully by fitting experimental data based on the least square method. By comparing the test value and fitting value of 60–75 days, the error of the best fitting result were within 3%, this showed the reliability of the predicted results.
4 citations
TL;DR: In this paper, the authors present an inclusive review of energy harvesting MR dampers, operating principles, structural design, mathematical models, fluid models, experimental investigation, and applications are classified and reviewed.
Abstract: Magnetorheological (MR) dampers are becoming popular smart devices with controllable higher damping properties. This paper presents an inclusive review of energy harvesting MR dampers. The classifications of energy harvesting MR dampers, operating principles, structural design, mathematical models, fluid models, experimental investigation, and applications are classified and reviewed. The regenerative MR dampers have self-power capability, and self-sensing capability to control higher performance and it is an important feature of regenerative MR dampers. The review indicates that regenerative MR dampers have enough power generation capacity to power MR dampers and higher damping performances. It has been found that a single-ended monotube regenerative MR (RMR) damper has maximum power generation capabilities than other RMR dampers.
3 citations
3 citations
TL;DR: In this article, the authors used a thixo-elasto-visco-plastic (TEVP) model to model the rheological behavior of human blood.
Abstract: Recent work modeling the rheological behavior of human blood indicates that it has all the hallmark features of a complex material, including shear-thinning, viscoelastic behavior, a yield stress, and thixotropy. After decades of modeling steady state blood data, and the development of simple steady state models, like the Casson and Herschel-Bulkley the advancement and evolution of blood modeling to incorporate more thixo-elasto-visco-plastic (TEVP) features to accurately capture transient flow has renewed interest. With recently collected steady state and oscillatory shear flow rheological data from a DHR-3 using human blood, we show modeling efforts with a contemporary thixo-elasto-visco-plastic (TEVP) model. Best fit rheological model parameters are used to determine values for normal, healthy blood and corroborate correlations from literature. Series of physical processes (SPP) analysis is incorporated to illustrate how mechanical properties are tied to the transient, evolving microstructure of human blood and physiological parameters. Using LAOS data predictions of the structure parameter, λ is compared, and correlated with the transient elastic modulus, G
t
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TL;DR: In this paper, the authors investigated polyethylene (PE)/silica polymer nanocomposites (PNCs) mainly using rheological measurements and found that LDPE/silica PNCs showed the best filler dispersion in TEM images but were the poorest in terms of Rheological property enhancement.
Abstract: Polyethylene (PE)/silica polymer nanocomposites (PNCs) were investigated mainly using rheological measurements. Various PEs [linear low-density polyethylene (LLDPE), high-density polyethylene (HDPE), and low-density polyethylene (LDPE)] were selected as polymer matrices, and two comparable particulate silicas were utilized as favorable (hydrophobic, R202) or unfavorable (hydrophilic, A90) fillers. Small amplitude oscillatory shear (SAOS), large amplitude oscillatory shear (LAOS), elongational rheometry, tensile tests, and TEM were adopted to characterize PE/silica PNCs. LDPE/silica nanocomposites showed the best filler dispersion in TEM images but were the poorest in terms of rheological property enhancement. Linear viscoelasticity as determined by SAOS testing was discordant with their morphology. However, nonlinear viscoelasticity as determined by FT-rheology in LAOS testing adequately determined dispersion states. Elongational viscosity revealed LDPE/silica PNCs show strain-hardening behavior, which resulted in intense mixing conditions and best compatibilization on LDPE/silica PNCs. To quantify the strain-hardening effect, strain hardening coefficients (SHCs) were calculated for LDPE/silica PNCs and found to decrease with increasing silica concentration. In addition, tensile testing showed mechanical properties deteriorated with silica content.
TL;DR: In this article, the authors performed direct simulations of particle suspensions in a simple shear flow with a viscoplastic model (Bingham fluid) using a finite-element/fictitious-domain method, as a model system for cuttings transport with a drilling mud in the oil and gas exploration.
Abstract: In this study, we performed direct simulations of particle suspensions in a simple shear flow with a viscoplastic model (Bingham fluid) using a finite-element/fictitious-domain method, as a model system for cuttings transport with a drilling mud in the oil and gas exploration. Bulk rheology and particle interaction were investigated via several example problems including single-particle, two-interacting particle, and many-particle problems for various solid fractions in both Bingham and Newtonian fluids. We report that, at low shear rate, huge reductions occur in both the relative bulk viscosity and angular velocity of particle suspension in a Bingham fluid compared to that in a Newtonian fluid. This indicates that, although particle incorporation increases bulk viscosity in a Bingham fluid, the amount of increase appears much smaller than that with the Newtonian medium, and particle motions were restricted to some extend at a low shear rate with a yield stress fluid. Moreover, the suppression in viscosity increase with particles disappears at a high shear rate, just like Newtonian particle suspension. This phenomenon has been interpreted by the suppressed particle angular rotation in a Bingham fluid. In addition, flow fields with low shear regions, where the viscosity of a Bingham fluid is high and the fluid mobility decreased significantly, on the left and right sides of a particle also confirm this interpretation. The two-interacting particle problem reveals delayed particle interaction with increased time period in particle trajectories (drafting, kissing, tumbling and separation) in a Bingham fluid. Similar behaviors with the suppression in viscosity increase can be also observed in the many-particle problem.
TL;DR: In this article, a negative wake is observed on the sides of the tail of a tail and a bump appears at the tip of the tails of a droplet, indicating the onset of the negative wake.
Abstract: Experiments were performed using visual and PIV techniques in order to study the appearance of a negative wake as well as its influence upon the deformation and breakup of droplets rising in viscoelastic fluids. In this report, Newtonian and viscoelastic drops were injected through different viscoelastic fluids; the deformation of the droplets was then followed and analyzed. In the case of Newtonian drops traveling through a viscoelastic fluid, a tail appears which later breaks into satellite droplets; a negative wake is present on the sides of the tail. The viscoelastic drops also exhibit a tail which is more resistant to rupture and the negative wake appears after the tail; additionally, a bump appears at the tip of the tail which enhances its elongation and determines the onset of breakup.
TL;DR: In this paper, a squeeze mode MR damper is analyzed using the Navier-Stokes equations and the shear stress of MR fluid is characterized by a non-convex constitutive relation, which is capable of capturing the solid-like to liquid-like switching.
Abstract: Magneto-Rheological (MR) fluid is a controllable material upon the applied magnetic field, and various MR dampers with different structures are designed to take advantage of this unique property. In the current paper, the squeeze mode MR damper is analyzed. The two-dimensional MR fluid squeeze flow in the damper is simulated using the Navier-Stokes’ equations. The shear stress of MR fluid is characterized by a non-convex constitutive relation, which is capable of capturing the solid-like to liquid-like switching. The two-dimensional velocity field and pressure distribution of MR fluid are obtained, from which the damping force of the MR damper is obtained. The unique hysteresis characteristic of the force versus velocity relation of the MR damper is captured. Further, the dependence on the loading rate and the field strength of the hysteresis characteristic is studied in the current paper.
TL;DR: In this article, the effects of component pair miscibility and mixing sequence on the phase structure of ternary blends of polycarbonate (PC), styrene-acrylonitrile (SAN), and poly(methyl methacrylate) (PMMA), and their composites with multi-walled carbon nanotubes (MWCNTs) were investigated.
Abstract: In this study, the effects of component pair miscibility and mixing sequence on the phase structure of ternary blends of polycarbonate (PC), styrene-acrylonitrile (SAN), and poly(methyl methacrylate) (PMMA), and their composites with multi-walled carbon nanotubes (MWCNTs) were investigated. SAN phase was surrounded by a layer of PMMA in the PC matrix and the thickness of the shell was dependent on the content of acrylonitrile (AN) in SAN (24% vs. 32%). It was established that the miscibility between SAN and PMMA affects the shell thickness on the merging of SAN and PMMA domains, which were separately dispersed at the early stage of kneading section in a twin-screw extruder. Consequently, the PMMA shell around the SAN was thinner in the SAN24, which is miscible with PMMA. When the pre-compounded composites of SAN/PMMA/MWCNT were mixed with PC through a 2-step blending, shell formation was promoted only with SAN32, which is immiscible with PMMA at a processing temperature. Additionally, it was established during the 2-step blending that the MWCNTs pre-dispersed in SAN and PMMA were transferred to the PC phase. This migration behavior of MWCNTs was prevented by introducing viscous impact modifiers. The change in electrical resistivity of the composites was explained using the observed phase morphology.
TL;DR: An analytical solution for examining the effect of a fluid's elasticity on the performance of MHD micropumps is found in this article, where the test fluid is assumed to be an incompressible viscoelastic fluid obeying the Oldroyd-B model.
Abstract: An analytical solution is found for examining the effect of a fluid’s elasticity on the performance of MHD micropumps. The test fluid is assumed to be an incompressible viscoelastic fluid obeying the Oldroyd-B model. The flow generated by the Lorentz force is assumed to be laminar, unidirectional, and two-dimensional. The effects of relaxation and retardation times are investigated on the volumetric flow rate. It is concluded that by a decrease in the relaxation time, the pulsatile nature of micropump can be eliminated in its transient phase. At sufficiently low relaxation times, the flow is predicted to monotonically reach its steady value at a much shorter time. By an increase in the retardation time, the pulsatile nature of micropump in its transient phase can also be eliminated and the flow will be more continuous in its steady conditions.
TL;DR: In this article, a review classifies various droplet-based micro-extraction techniques as either a static or continuous method and discusses the advantages and drawbacks of each method and the extraction performance and types of analyses that can be used.
Abstract: Over the last few decades, droplets have been used for enrichment of target compounds from various types of samples including water, body fluids, soils, and food. Leveraging the high surface area-to-volume ratio, droplets are excellent means of rapidly concentrating the target compounds. The droplet-based microextraction technologies reported so far can be categorized as static and continuous. For a static method, droplets are exposed to a given amount of sample while for a continuous method the sample is continuously fed by a flow and the droplets can either remain static or move with the sample flow. Both the extraction performance and types of analyses that can be used depend on whether the method is static or continuous microextraction. This review classifies various droplet-based microextraction techniques as either a static or continuous method and discusses the advantages and drawbacks of each.
TL;DR: In this paper, the authors developed a new numerical method which converted creep data to dynamic moduli without relying on viscoelastic spectra of relaxation or retardation times, which is an improvement of the previous ones (Kwon et al., 2016) in the reduction of artificial waviness in the terminal regime.
Abstract: We developed a new numerical method which converts creep data to dynamic moduli without relying on viscoelastic spectra of relaxation or retardation times. This algorithm is an improvement of the previous ones (Kwon et al., 2016) in the reduction of artificial waviness in the terminal regime as well as the noise due to measurement errors. The method is the application of the point-wise polynomial regression which reduces the polynomial order dramatically compared with previous method in order to suppress the waviness.
TL;DR: In this paper, the end-block length dependence of the hydrogel relaxation dynamics was investigated using PEO-based ABA triblock copolymer solutions in an aqueous solvent.
Abstract: End-block length dependence of the hydrogel relaxation dynamics was investigated using PEO-based ABA triblock copolymer solutions in an aqueous solvent. Both ends of PEO were capped with hydrophobic poly(isopropyl glycidyl ether-co-ethyl glycidyl ether) exhibiting a lower critical solution temperature (LCST) behavior, resulting in the transition between sol and gel with temperature. Despite the nearly identical hydrophobicity of the end-blocks, the sol-to-gel transition temperature is found to be significantly dependent on the end-block length. Particularly, a small increment of the end-block length leads to significantly slower relaxation dynamics which is attributed to the thermodynamic barrier of end-block extraction. Hydrogels with an appropriate relaxation time show excellent injectability and self-healing ability, yet extremely slow relaxation dynamics result in brittle hydrogels. These results are discussed in terms of current understanding of the hydrogel relaxation dynamics and particular attention is paid to the issue of the chain dynamics between aggregated cores.
TL;DR: In this paper, the authors proposed a control methodology for gloss defect on high-gloss injection-molded surfaces based on the maximum replication factor (RFmax), an index representing the effect of the molding conditions on the surface gloss.
Abstract: A Gloss defect on high-gloss injection-molded surfaces are difficult to control. This paper proposes a control methodology for a gloss defect. The maximum replication factor (RFmax) is an index representing the effect of the molding conditions on the surface gloss. As RFmax increases, the surface gloss is stabilized due to the maximized replication of the mold surface. The process window of the influencing parameters for obtaining a stable surface gloss is predicted by the range of RFmax. The predicted process window suggests specific molding conditions for controlling the gloss defect. Experiments show that the surface gloss is stabilized, and the gloss defect owing to the fluctuation of the filling conditions is suppressed in the predicted process window for poly(acrylonitrile-co-butadiene-co-styrene) and polycarbonate. The novel methodology can be applied to optimize injection-molding technologies, such as sequence valve gating and rapid heat cycle molding.
TL;DR: In this paper, a numerical algorithm based on a combination of the lattice Boltzmann method (LBM) and the improved smoothed profile method (iSPM) has been proposed to study the motion of one, two and many circular particles in a non-Newtonian fluid.
Abstract: In the present work, a numerical algorithm based on a combination of the lattice Boltzmann method (LBM) and the improved smoothed profile method (iSPM) has been proposed to study the motion of one, two and many circular particles in a non-Newtonian fluid. At first, the velocity profile of the non-Newtonian fluid at various power law indexes (n) was analyzed and the findings were compared with the numerical results of the previous works. Then, the motion of one circular cylinder and the hydrodynamic interactions between two particles in a shear flow were investigated. It was observed that Reshear, p had no important impact on the rotation of a single cylinder. In the two particles interaction, increasing the shear rate caused the particles to tumble on each other more closely and during a longer time. Therefore, the effective viscosity of a particulate suspension was considered for different Reynolds numbers and solid volume fractions, showing a satisfactory agreement with the previously published data. The results, therefore, showed that inertia increased the particles contribution to the effective viscosity of the suspension.
TL;DR: In this article, a mold-type slit rheometer has been used to measure the viscosity of acrylonitrile butadiene styrene (ABS) in an injection molding machine.
Abstract: Authors designed and built a mold-type slit rheometer. The slit rheometer has a vertical flow channel and interchangeable cores with various slit thicknesses. It is installed in an injection molding machine like a general mold. The melt is supplied by the plasticizing unit of the injection molding machine. The melt temperature supplied by the plasticizing unit varies by the plasticizing conditions and the shear heating effect in the nozzle and the sprue. In this study, the effects of the plasticizing conditions and the shear heating in the nozzle and the sprue were examined, and the influence of the melt temperature variation on the viscosity measurement was analyzed experimentally and numerically. A temperature sensor was designed to measure the melt temperature in the sprue. Its tip is fully immersed in the melt to have a higher sensitivity. Two resins with different thermal sensitivities were used to examine the effect of resin on the melt temperature variation. To check the shear heating effect in the nozzle and the sprue, two sets of the nozzle and the sprue with different orifice sizes were used. The numerical analysis was done by commercial software (Moldex3D) to check the melt temperature from the nozzle to the slit channel. The viscosity of long-fiber reinforced polypropylene (PP) was measured with various slit channel thicknesses to verify the reproducibility. The standard deviation of the viscosity values against the Cross model fitting curve was 3.01 Pa·s. The viscosity of acrylonitrile butadiene styrene (ABS) measured using the slit rheometer was compared with values obtained from a capillary rheometer and commercial database.
TL;DR: In this article, a new concept of adding choker bars inside different dies (namely, T-die, fishtail die, and coat-hanger die) is proposed.
Abstract: Bubble growth inside the die is one of the critical issues in the PVC foam extrusion process. Burning and clogging might have occurred when bubble growth exceeds the critical size, leading to non-uniform outlet velocity and pressure profile inside the die. Therefore, a design modification for die geometry is necessary. This study aims to suppress the bubble generation by making the pressure inside the die greater than the bubble nucleation pressure and to make the velocity distribution uniform at the die exit. A new concept of adding choker bars inside different dies (namely, T-die, fishtail die, and coat-hanger die) is proposed. Three choker bars consecutively placed one after another inside the dies slit sections were numerically simulated to observe and discuss the effects of the proposed geometric shape on the outlet velocity profile in the non-isothermal generalized Newtonian flow. The results show that the velocity distributions at the exit of the die were nearly uniform in all three dies. Among the dies, the fishtail die shows the best outlet velocity uniformity. The pressure values inside all dies are found to be higher than the nucleation pressure except at the last 0.5 mm near the die outlet. This confirmed that the bubble growth could only begin near the 0.5 mm die outlet region in all dies.
TL;DR: In this paper, the authors proposed a numerical method to calculate molecular weight distribution from linear viscoelastic data, which consists of three components: (1) a visco-elastic model of a monodisperse polymer as a function of molecular weight; (2) the mixing rule connecting the data of polydisperse polymers through molecular weight distributions; and (3) an algorithm which calculates the molecular value distribution from the chosen mixing rule.
Abstract: We suggest a numerical method to calculate molecular weight distribution from linear viscoelastic data. The calculation method consists of three components: (1) a viscoelastic model of a monodisperse polymer as a function of molecular weight; (2) the mixing rule connecting viscoelastic data of monodisperse and polydisperse polymers through molecular weight distribution; (3) an algorithm which calculates the molecular weight distribution from the chosen mixing rule. Since we cannot measure the relaxation modulus of all monodisperse samples, we need an accurate monodisperse model for any molecular weight. It is known that a dynamic test is more reliable than a relaxation test, while the mixing rule needs relaxation modulus. Hence, we should have a smart numerical method that can convert dynamic data to relaxation modulus with the minimum conversion error. If we use the numerical method, then we have to generate numerical data from the model. Then it takes quite a long time. On the other hand, if we have a monodisperse model with the analytical relaxation spectrum, then calculation time can be reduced dramatically. Since the conversion from relaxation modulus to dynamic modulus suffers from smaller errors than the reverse conversion because of ill-posedness of the interconversion, the analytical conversion can be implemented more quickly at an acceptable level of errors. This paper proposes a new method satisfying the requirements.
TL;DR: In this article, a mixture of glycinate and glutamate-based surfactants was found to produce a relatively rigid foam compared to that of single component only when the mixture was diluted with tap water and not deionized water.
Abstract: Surfactants are mainly used as mixtures to obtain the foam properties which are suitable for use and purpose. In this study, it was found that a mixture of glycinate- and glutamate-based surfactants produced a relatively rigid foam compared to that of single component only when the mixture was diluted with tap water and not deionized water. When the surfactant mixtures were diluted with deionized water, the foam hardness was linearly dependent on the weight fraction of the glycinate based surfactant. Meanwhile, the mixtures diluted with tap water produced foam which could withstand vertical loads. We observed the rheological behavior of the air-water interface to understand the ideal and nonideal mixing effect of amino acid-based surfactants. It was confirmed that the synergistic effect on the interfacial modulus and the foam texture was due to the divalent ions of tap water. However, the interaction by the divalent ions did not affect the foam stability. It is worth to noting that the existence of divalent ions is one of the important factors that should be considered to control the foam quality as well as interfacial rheology.