International Conference on Rheology and Fluid Mechanics November 10-11, 2016 Alicante, Spain

Biography:

Talib Dbouk has completed his PhD from the University of Nice Sophia Antipolis (France). He is an Assistant Professor at the Ecole des Mines de Douai (University of Lille, France). His research is focused on conjugate heat transfer and complex flows modeling and simulation including topology optimization. He is teaching graduate students a course entitled “Pinch Analysis and Process Integration” for optimizing energy requirements in an industrial process.

Abstract:

This work addresses a new suspension balance direct-forcing immersed boundary model (SB-DF-IBM), for wet granular flows over obstacles. We mean by “wet granular” term all non-Newtonian flows that are made of non-Brownian particles (rigid spheres) immersed in a Newtonian fluid. This new SB-DF-IBM couples the Suspension Balance Model (SBM) to a Direct-Forcing Immersed Boundary Method (DF-IBM). The mathematical formulation in this contribution is based on a mixed Eulerian–Lagrangian approach. A novel feature of this new formulation is that many Lagrangian particles of the same size of the suspended particles, can be introduced into the continuum medium. This extrapolates the physics from a macroscopic to a microscopic scale, making the SB-DF-IBM behaves as a Dynamic-Scale Model (DSM). This SB-DF-IBM is implemented, as a new solver, in the OpenFOAM ® open-source Computational Fluid Dynamics (CFD) software. Then, a numerical study is conducted on isodense mono-dispersed suspension flows over a stationary cylinder, in both wide and micro-channels, to test the functionality and performances of this SB-DF-IBM. The pressure difference, drag and lift forces are addressed for different initial bulk concentrations between 0% and 50%. Moreover, the effect of a cylindrical obstacle on the suspension flow separation in a microchannel is analyzed. The numerical results are presented and compared to recent experimental measurements from the literature addressing the non-Newtonian response of a suspension flow. As a conclusion, this SB-DF-IBM is a promising tool that can be introduced into different CFD packages for simulating wet granular non-Newtonian flows over obstacles.

Biography:

Valery Kulichikhin has completed his first and second PhD (1980) from the Institute of Chemical Fibers. Till 1986, he was the Leader of laboratory “Theoretical basis of fiber spinning from polymer solutions” in this Institute. Beginning from 1986 till present time, he works as the Head of Polymer Rheology Lab at the Institute of Petrochemical Synthesis, Russian Academy of Sciences. In 2000, he was elected as Corresponding Member of RAS. He has published more than 250 papers in reputed journals and has been serving as an Editorial Board Member of repute.

Abstract:

Fiber spinning processes from polymer solutions are the most difficult for practical realization compared to the melt spinning. They involve necessity to know the shear rheology of solutions (flow through the spinneret channels), the phase state of the initial solutions and their transformation during contact with coagulation bath, the extension rheology in the air gap (dry-wet method) or in liquid medium (wet method), accompanying with transition from non-Newtonian liquid to the gel-like system and, finally, to the solid viscoelastic product. Nevertheless, such polymers as aramides, polyimides, PAN and its copolymers, cellulose and others cannot be processed in fibers from melts, and only spinning from solutions remains the unique way to obtain textile and technical yarns. This lecture is devoted to development of the specific devices allowing combining rheological, optical and structural tests and analysis of the obtained results at extension of solutions PAN in DMSO, aramides in DMAA and cellulose in N-methylmorpholine-N-oxide. In addition, the role of such nanofillers as carbon nanotubes and clay in dopes was considered. The traditional way of removing a solvent from extended solution jet is contact with precipitator in coagulation bath. Due to an interdiffusion, the solvent is going away from the jet and non-solvent is coming into jet resulting in as-spun fiber formation. We have shown that at strong extension the phase transition in solution jet takes place and solvent passed away on periphery of jet/fiber. Calculations based on elaborated models for dilute and concentrated solutions have shown that less than 0.1% of solvent remains in resulting fibers. This process was realized in laboratory spinning stand and prepared fibers were investigated by different methods. The skin-core effect is missed for such fibers with diameter of 5-10 m and their structure is closed to oriented para-crystalline phase. Mechanical characteristics of such fibers are higher than of fibers obtained by traditional methods, and behavior at thermolysis at carbonization is very promising.

Biography:

Iván Santamaría Holek has completed his PhD from University of Barcelona and Post-doctoral studies from National University of Mexico. He is Titular Professor at the National University of Mexico since 2008. He has published more than 53 papers in reputed journals and has been serving as an Editorial Board Member of the Open Journal of Physical Chemistry.

Abstract:

In this talk I will discuss the role of confinement forces in the obtention of the viscosity and the diffusion coefficients as a function of particle concentration for suspensions of solid particles at arbitrary volume fractions. In addition, I will also discuss the connection between the mentioned rheological properties with the mesoscopic dynamics of the suspended particles by showing their implications on the Stokes-Einstein relation. A generalization of this relation valid at arbitrary volume fractions is proposed. I will particularize the results to spherical particles and give a clue on its generalization to particles of arbitrary shapes. The generalization of the Stokes-Einstein relation leads to the existence of effective temperatures in these systems. This is briefly discussed in these systems and in the context of active micro-rheology in colloidal and molecular glasses. Comparison between theoretical calculations and experimental results is remarkably good in all cases.

Biography:

Masami Kageshima has completed his PhD from University of Tokyo in 1996 and has pursued his research in surface/interface physics based on his cutting-edge techniques of probe microscopy instrumentation. His past publications include works on nanometer-scale physics of various solid surfaces, low-dimension systems, and atom/molecule manipulation that have been highly evaluated for their originality and technical sophistication. After that he extended his research interest into microscopic aspects of soft-matter physics including biophysics and has worked on single biopolymer chains, interfacial fluids, etc. He is currently a Physics Professor at Kansai Medical University.

Abstract:

Viscoelastic response of hydrated 2-methacryloyloxyethyl phosphorylcholine (MPC), a bio-compatible phospholipid polymer and a potential lubricant for artificial joint, under sub-nanometer oscillatory shear was studied while shear amplitude and normal loading force were varied by using atomic force microscopy (AFM). An AFM cantilever having a borosilicate glass colloidal probe with a diameter of 20 μm was employed. Shear motion with a typical frequency of 30 kHz was induced by using a home-built AFM apparatus via magnetic torque exerted from an electromagnet onto magnetic spheres attached to the cantilever. A Si substrate with physisorbed MPC layer was moved toward the probe in water while the normal force between the probe and the sample was measured through the cantilever’s flexural deflection. The approaching motion was halted several times to sweep the shear oscillation amplitude typically between 0.5 nm and 0.02 nm; although this amplitude range shifted lower as the contact area increased with compression. The relaxation time derived from the viscoelastic response measured during these amplitude sweeps exhibited a characteristic dependence on the shear amplitude; the dependence was not marked in the low amplitude regime, i.e., a quasi-Newtonian behavior, whereas it turned to a negative dependence in high amplitude regime. The boundary between these two regimes became sharper as the probe was compressed harder to the sample, a feature obviously different from the one known for macroscopic non-Newtonian fluid. The present result may provide knowledge for understanding microscopic origin of non-Newtonian dynamics

Biography:

Masami Kageshima has completed his PhD from University of Tokyo in 1996 and has pursued his research in surface/interface physics based on his cutting-edge techniques of probe microscopy instrumentation. His past publications include works on nanometer-scale physics of various solid surfaces, low-dimension systems, and atom/molecule manipulation that have been highly evaluated for their originality and technical sophistication. After that he extended his research interest into microscopic aspects of soft-matter physics including biophysics and has worked on single biopolymer chains, interfacial fluids, etc. He is currently a Physics Professor at Kansai Medical University.

Abstract:

Starch derivatives find application in cement-based construction materials. In the case of ceramic tile adhesives (CTA’s), specific kinds of modified starches are instrumental in imparting good anti-slip behavior. Using cement pastes as model systems, the influence of starch ether concentration on suspension rheological properties have been examined using focused beam reflectance measurements (FBRM) and controlled shear rate rheometry with a specialized geometry for construction materials. FBRM provides information on changes in cement particle size distributions as a function of starch ether concentration, which in turn can be correlated to relevant rheological parameters, in this instance the yield value in particular. The results can best be interpreted as polymer bridging flocculation being the mechanism by which such specific starch derivatives are responsible for the origin of anti-slip properties in CTA’s.

Biography:

Nariman Ashrafi is an Assistant Professor of Mechanical Engineering at the University of IAU Science and Research Branch, Iran. He received his PhD in Mechanical Engineering from University of Western Ontario of Canada. His current research focuses on non-Newtonian fluid dynamics and nonlinear mechanics.

Abstract:

To analyze the drilling process, the pseudoplastic flow between coaxial cylinders is investigated. Here, the inner cylinder is assumed to rotate and, at the same time, slide along its axis. A numerical scheme based on the spectral method is used to derive a low-order dynamical system from the conservation of mass and momentum equations under mixed boundary conditions. It is found that the Azimuthal stress develops far greater than other stress components. All stress components increase as pseudoplasticity is decreased. The flow loses its stability to the vortex structure at a critical Taylor number. The emergence of the vortices corresponds to the onset of a supercritical bifurcation. The Taylor vortices, in turn, lose their stability as the Taylor number reaches a second critical number corresponding to the onset of a Hopf bifurcation. The rotational and axial velocities corresponding to the optimum drilling conditions are evaluated.

Biography:

Anh V Nguyen is a prospective PhD at University of Rome “Tor Vergata”, Italy. His research interests are computational fluid dynamics, numerical simulations of multiphase flows, particle flows and experiments in fluids and fluid mechanics. He completed his Master’s study at Ritsumeikan University, Japan in the field of Fluid Mechanics.

Abstract:

Statement of the Problem: The purpose of this research is to numerically investigate blood flows over an aortic bileaflet mechanical heart valve employed in the human heart through valve implantation surgery. The modeled valve used in the simulation is a St. Jude Medical valve with three sinuses Valsava grafts (Fig. (a)). Many previous studies of bileaflet mechanical heart valves have been done but there is still lack in investigations of hemolysis of the blood at the closure of the valve leaflets as well as at the highly turbulent flows due to high viscous shear stresses of the flow in the ascending aorta.

Methodology & Theoretical Orientation: The computational method is a fluid-structure integration (FSI) algorithm that couples direct numerical simulation (DNS) and immersed boundary method (IBM). The FSI model is used to model blood flow through the aortic valve to investigate physiological characteristics of the blood flow in silico. Boundary conditions and flow geometry are set with the same physiological condition as the real model of the prosthetic heart valve that is used in reality (Fig. (b)).

Findings: Physical parameters of hemodynamics in the aortic prosthesis in a number of cardiac cycles were obtained. The results indicate that there are strong turbulences occurring in the flow field downstream after the heart valve (Fig. (c)), especially in the sinuses of Valsava. Hemolysis takes place frequently in the trailing edges of the leaflets that affects quality of blood pumping into the ascending aorta.

Conclusion & Significance: Shear-induced effects play an important role in blood damage as well as platelets damage in the systolic phase of cardiac cycle. The closing phase of cardiac cycle also generates blood damage at the trailing edges of the leaflets as well as at the hinge regions of the leaflets.

Biography:

Somaris E Quintana has a Master’s in Formulation and Technology of Products and student of PhD of Food Science. She has experience in design of new products, complex fluids and rheology. Her principal investigations are in extraction of isolated protein, design and standardization of complex fluids, foods emulsions and hydrocolloids for applications in foods industry. She has experience in research group of Complex Fluid Engineering and Food Rheology at University of Cartagena University and teaching on the areas of rheology and unit operations.

Abstract:

Statement of the Problem: Food systems present different behavior depending on process condition; the rheological behavior of smoothies will be influenced by chemical composition, size, shape and arrangement of these particles comprising the dispersed phase, which influence the texture and flavor. The purpose of this study is to evaluate the rheological behavior of smoothies with tropical fruit, squash (Cucurbita moschata) and dietary fiber of pineapple (Ananas comosus).

Methodology & Theoretical Orientation: Smoothies were standardized considering the percentages of squash pulp (P), xanthan gum (XG), lactose-free skim milk (M), using design surface center response of one blocks in central points and one center points on each block. pH and the percentage of dietary fiber of pineapple (Ananas comosus) was kept constant. The rheological characterization was carried out in controlled-stress (ARES, Rheometric Scientific, UK) rheometer, using coaxial cylinder geometry. Viscous flow test was determined at 25ºC in a shear rate range of 10 s^-2-10 s^-1, were taken 3 minutes at each shear rate order to obtaining the steady state regime.

Findings: The samples with amount of xanthan gum around 0.2% (M4, M5, M6, M7 and M8) were stabilized until 8 days. The smoothies presented a shear thinning behavior fitted to the Ostwald de Waele model, where apparent viscosity decreased over the shear-rate range.

Conclusion & Significance: The viscous flow behavior of the smoothies investigated is strongly influenced by the amount and concentration of xanthan gum and the nature of the phases.

Biography:

Helena Svihlova is a PhD student at Mathematical Institute at Charles University in Prague. Her area of interest is computational fluid mechanics with application in biomechanics, especially flow in diseased valves and arteries.

Abstract:

Stenotic heart valve diseases are among the leading causes of death worldwide. A stenosis in the cardiovascular system is a reduction in cross-sectional area of a structure acrosswhich blood flows. Because of the stenosis in valve, theheartmust pump out more blood and this leads to increaseof the pressure at the beginning of the valve. In order to compute this pressure, we can use the information about velocity field obtained from the modern imaging techniques such as 4D magnetic resonance. The "gold standard" of ascertaining pressure difference is Gorlin formula based on Bernoulli equation improved by empirical constant. There were some attempts to prove the concept using Bernoulli equation. The standard methodology is however based on several unrealistic assumptions. We used two techniques to obtain the pressure directly from the Navier-Stokes equations when the velocity field is considered to be known or at least approximated. The first technique is to derive the gradient of pressure directly from the Navier-Stokes equations. This leads to a Poisson equation and was investigated. The second technique was suggested in and leads to a Stokes problem where the unknowns are the pressure and some correction vector. In both cases, we fix the value of the pressure at the outlet boundary which represents the pressure measured in the aorta. The results confirming that the second technique provides more accurate estimation of the pressure.

Biography:

Bo An has his expertise in Fluid Mechanics. He graduated as a Bachelor from Northwestern Polytechnical University in 2010. He got his Master’s degrees from Northwestern Polytechnical University and Universidad Politécnica de Madrid in 2013 and 2015 respectively. Now he is working on fluid control, lattice Boltzmann method, ice accretion and linear stability.

Abstract:

Considering the present work, the flow inside 2D lid driven triangular and trapezoidal cavities is investigated based on the lattice Boltzmann method. It is important to notice that the steady fluidic characteristics are the only concerns in the present work. The numerical cases were tested in many enclosures of different geometries. The equilateral triangular cavity was the first geometry to be studied, the simulation was performed at Reynolds number 500 and the numerical prediction was compared with previous work done by other scholars. Several isosceles triangular cavities were studied at different initial conditions, Reynolds numbers ranging from 100 to 3000. A series of trapezoidal cavities with different top/base ratios were also studied at low Reynolds numbers. Compared with the lid driven condition, for each trapezoidal geometry, the driven velocity was also tested on the base line, regardless of the geometry studied, the top lid was always moving from left to right and the driven velocity remained constant. Results were also compared with previous works performed by other scholars, the agreement is very good.

Biography:

Ke Zhang received her PhD degree in Polymer Science and Engineering from Inha University, Korea in 2011. She is currently a Lecturer at Harbin Institute of Technology, China. Her research interests include polymer-induced turbulent drag reduction, electro-rheology, and magneto-rheology. She has published more than 30 papers in reputed journals and international conferences.

Abstract:

It is well-known that the skin frictional drag of turbulent flow can be remarkably decreased when tiny amounts of polymers are added. Recently, polymers as turbulent drag additives have been successfully applied in different fields, such as firefighting, oil transportation and farm irrigation. However, they present less resistant to high shear and extensional rates under turbulent flows. In this study, the effect of Reynolds number (Re), temperature, polymer molecular weight, and distribution as well as concentration on the drag reduction (DR) efficiency of copolymers was investigated in a rotating disk apparatus. To explore the regularity of mechanical degradation, DR efficiency was also analyzed as the function of time by using different models such as a simple exponential decay function, stretched-exponential model, and Brostow equation.

Biography:

Fred J Molz received his BS in Physics from Drexel University in 1966, an MSCE in 1968, and a PhD in Hydrology from Stanford University in 1970. He came to Clemson University in 1995, from Auburn University, as a Professor and DOE Distinguished Scientist in the Department of Environmental Engineering and Earth Sciences. His past research interests have involved computer simulation of reactive plutonium transport in variably saturated soils and radionuclide transport in plants. Recently, he began working with Boris Faybishenko, a soil physicist at the Lawrence Berkeley National Lab, on problems involving nonlinear dynamics and deterministic chaos in microbial systems.

Abstract:

Complexity is a term being used in many different ways. However, a quantitative definition suggested by a distinguished scientist, Warren Weaver (1948), corresponds to the modern requirements for a mathematical model that can potentially display deterministic chaotic dynamics. We call such models “Organized Complex Systems”, and categorize these systems by levels equal to the number of dependent variables in the mathematical model -- the minimum being 3 for the system to exhibit deterministic chaos. Examples of Level 3 and Level 4 mathematical models are presented. Weaver was also an early proponent of Shannon information theory, ultimately resulting in the idea that information, its transmission and decoding are fundamental to an improved understanding of living systems. Our own studies and a review of several recent publications, suggest that information flow from the DNA molecule and transmission throughout a cell is the basis for the open system processes of life. It is now known that only irregular and non-periodic signals can transmit information, so we conjecture that such signals, which are produced by chaotic dynamics, are common in biological systems. It is conjectured further that the formation of a strange attractor in system space represents mathematically the emergence of the system being simulated. If the system behaves within the boundaries of the attractor, such systems may be viewed as “Sustainable”. These concepts are illustrated by a very recent paper in Biology Today that shows in detail how the Venus fly trap decodes and separates wind-borne information from insect-borne information.

Biography:

Nina Stoppe has completed her PhD in 2015 at the Christian Albrechts University, Kiel. Since graduation, she works as a Post-doctoral Research Assistant in the Department of Soil Science.

Abstract:

Soils are multifunctional key resources for human beings–they provide food and water, renewable resources, construction grounds and habitats for animals and plants. At the same time, they regulate local and global cycles of substances and water and therefore affect climate. Nowadays soil degradation and the loss of beneficial soil functions, which are intertwined with soil structure and convenient pore geometry, are severe problems. As soil structure possesses many valuable functions, the quantification of structural stability is an important field of research. As a basic understanding of soil behavior requires knowledge of the processes at the microscale (i.e. particle scale), rheological investigations of natural soils receive growing attention and useful insights have been gained in recent years to understand the microstructural deformation behavior of soils. Several homogenized soil materials were analyzed with a modular compact rheometer MCR 300 (Anton Paar, Germany) and a profiled parallel-plate measuring system. Amplitude sweep tests (AST) with controlled shear deformation were conducted to investigate the viscoelastic properties of the studied soils under oscillatory stress. The gradual depletion of microstructural stiffness during AST can be characterized by the well-known rheological parameters G′, G″ and tan δ but also by the dimensionless area parameter integral z, which quantifies the elasticity of microstructure. Depending on soil texture, various physicochemical features significantly affect the elasticity of soil microstructure, such as soil organic matter, concentration of Ca²⁺, K⁺ and Na⁺, content of CaCO₃ and pedogenic iron oxides. Especially under consideration of the combined effects of these features, the rheological behavior of soils becomes explainable.

Biography:

Suresh Kumar Yatirajula has completed his Master of Technology from Indian Institute of Technology, Madras, India by working on ‘Rheology of Aqueous CTAB/NaSal Wormlike Micelles’ and is now pursing Doctoral thesis on ‘Studies on Self Assembling Polymer (SAP) Application in Enhanced Oil Recovery Application’ at Department of Chemical Engineering from Indian School of Mines, Dhanbad, India. He is also working as an Assistant Professor at the same university currently. He has presented two papers at international conferences including 9^th World Congress of Chemical Engineering, Seoul, South Korea.

Abstract:

Linear and nonlinear rheological responses of self-assembling polymer (SAP) systems are of great interest in chemical flooding for enhanced oil recovery (EOR) application. The motivation of these extended polymolecular assemblies with improved mechanical and thermal stability as well as tolerance to elevated salinity and hardness; superior viscoelastic properties and pronounced pseudoplastic shear thinning behavior due to network interlocking effect for EOR. The formation of these self-assemblies relies on noncovalent interactions that hold them together. The performance of two self-assembly systems derived from a xanthan gum (SAP-XG) and partially hydrolyzed polyacrylamide (SAP-HPAM). The present work is concerned with experimental results of rheological characteristic of SAP in aqueous, aqueous salt solutions and brain aqueous solutions with systematically changing experimental conditions such as polymer concentration, surfactant concentration, salt content, temperature and aging time. Rheological properties of SAP systems in both linear and nonlinear regions have been investigated by means of techniques, small amplitude oscillatory shear (SAOS) and large amplitude oscillatory shear (LAOS), respectively. Loss and storage modulus, with in linear viscoelastic range, were confirmed to be higher than the conventional base polymer. In LAOS test protocols and the associated materials measure provide a rheological figure print of the yielding behavior of a SAP (with Lissajous curves) that can be closely represented with in the domain of a Pipkin diagram defined by the amplitude and angular frequency.

Biography:

Nariman Ashrafi is an Assistant Professor of Mechanical Engineering at the University of IAU Science and Research Branch, Iran. He received his PhD in Mechanical Engineering from University of Western Ontario of Canada. His current research focuses on non-Newtonian fluid dynamics and nonlinear mechanics.

Abstract:

The squeeze flow of a nonlinear viscoelastic flow is studied. In particular, the flow of an upper-convected Maxwell fluid between two approaching disks is analyzed. The momentum and continuity equations together with constitutive relations are solved by a low-order method. Both no slip and slip boundary conditions are considered. Next, stress components are evaluated and flow stability is investigated. It is observed that, as the disks approach, velocity increased the developed stresses, which are interrelated to velocity gradients through the constitutive relation, and are altered exponentially. This analysis is applicable to many industrial instances such as lubrication as well as natural joints.

Biography:

Luis A García-Zapateiro received his BS in Food Engineering from University of Cartagena, Colombia in 2005, his MSc degree in Formulation and Product Technology, applications in the Chemical Industry, Agri-Food and Pharmaceutical and his PhD degree in Processes and Chemical Products from University of Huelva (UHU), Spain, in 2007 and 2013, respectively. He has worked in the Department of Chemical Engineering in the research group of the complex fluid from University of Huelva (Spain). He has been a Director, Head of Department of Unit Operations and Professor of Food Engineering. Currently, he works as Head of Department of Postgraduate Faculty of Engineering of the University of Cartagena (Colombia), and also is the Director of the research group, IFCRA. His main expertise is in food product design, complex fluid and rheology. His investigations are in vegetable oils, estolides, lubricant and biodegradable greases. In the food product area, he has performed research in emulsions, hydrocolloids from tropical fruit, isolated proteins from fish and vegetable seeds such as beans.

Abstract:

Statement of the Problem: The physicochemical properties of vegetables and fruits can change due to the storage condition, the operations and the thermic treatment applied. So in the food industry, i.e. 20ºC are used in storage and 60ºC in processes such as pasteurization and others. During pumping, in-pipe flow, mixing and stirring of liquid-like foods, shear rates in the range of 10–1000 s^-1 may be experienced. Therefore, rheological experiments should preferably be done within the frequency and stress range that encompasses most applications. The purpose of this study is to describe the effect of thermic treatment on the viscoelastic properties of squash (Cucurbita moschata) pulp.

Methodology & Theoretical Orientation: Rheological measurements were carried out by using a stress-controlled rheometer Haake Mars 60 (TA Instruments, England), using roughened plate-plate geometries (diameter 35 mm, gap 1 mm, roughness 0.5 mm). Prior to measurement, all samples were allowed to stand for 600 seconds to relaxation of the same, the temperature of the samples was assured by Peltier system installed in the inferior plate of the rheometer. Oscillatory stress sweeps between 0.001 to 1000 Pa were performed to determine the linear viscoelastic range at a frequency of 1 Hz. Then, a frequency sweep between 0.01 and 100 Hz was performed to determine the mechanical spectra. All the rheological tests were performed at temperatures of 20, 40, 60, 80 and 100ºC.

Findings: The behavior of storage modulus G’ (elastic behavior) is higher and loss modulus G’’ (viscous modulus) in the frequency range of temperatures applied. According to this, the viscous and elastic properties of squash pulp are significantly different for temperatures of 20, 40, 60, 80 and 100ºC. On the other hand, no significant differences were found for 40 and 60ºC. So the lineal viscoelastic behavior of squash pulps is similar to mango, cherry and borojó, and is influenced by the temperature.

Conclusion & Significance: The present work has evaluated the viscoelastic properties of squash pulp. Product has shown a weak behavior, with storage modulus higher than loss modulus in the evaluated frequency.

Biography:

Anna Berkovich has her interests is laying in the field of polymer nanocomposites, nanoparticle dispersions in polymer solutions and mixes. She has a big practice in carbon nanotubes dispersion stabilization. The other area of interests is the fiber formation process and chemistry of thermally induced reactions during fiber carbonization process.

Abstract:

The combined concentrated solutions of cellulose and acrylonitrile copolymers, containing carboxyl groups, in N-methylmorpholine-N-oxide (MMO) were prepared first time using solid-phase activation of powders with subsequent heating to the melting point of MMO. The rheological measurements at 120 and 135°Ð¡ were performed to estimate the effect of the phase state of the considered combined solutions and the observed morphological transformations on the flow patterns. The addition of PAN to cellulose solutions has practically no effect on solution viscosity at 120°Ð¡, but the situation changes drastically during heating of systems to 135°C. This effect can be explained by suppression of the nonlinear elastic reaction of cellulose solutions by PAN macromolecules. With the use of IR spectroscopy, it was previously found that, at temperatures above 130°Ð¡ in PAN solutions in MMO, the cyclization of nitrile groups with the formation of polyconjugated segments in macromolecules occurs and is accompanied by decrease in viscosity and viscoelasticity. The recorded structural–rheological features of the combined-solution behavior raises a question: Are the observed chemical transformations in PAN macromolecules mainly responsible for changes in the mechanism of the combined-solution flow, or is the flow limited by specific interactions arising between macromolecules of cellulose and the PAN copolymer in an MMO solution? The evolution of the viscoelastic and viscous properties over time was examined in the 25% solution PAN carried out at 120 and 135^oC. It was found that the parameters characterizing the viscosity as well as the elasticity of the solution decreased over time. This can be the case only if chemical reactions did not lead to interchain crosslinking but to a change in the chain conformations due to the cyclization discussed above. Degradation of PAN at such temperatures is excluded. Therefore, the rheological data also indicated that the PAN/MMO solutions are “Living Systems” at elevated temperatures due to partial cyclization of nitrile groups. Thermolysis of the hybrid fibers with a minor PAN content demonstrates a decrease of intensity of the main heat effect at the cellulose carbonization that indicates the strong interaction between PAN and cellulose. In other words, PAN can be considered as the catalyst of the cellulose pyrolysis.