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Ralph H Colby - One of the best experts on this subject based on the ideXlab platform.

  • Linear Viscoelasticity and cation conduction in polyurethane sulfonate ionomers with ions in the soft segment multiphase systems
    Macromolecules, 2018
    Co-Authors: Shih Wa Wang, Ralph H Colby
    Abstract:

    PEO-based polyurethane sulfonate ionomers with various PEO chain lengths and sodium counterions were synthesized and characterized by both Linear Viscoelasticity (LVE) and dielectric relaxation spectroscopy (DRS). Since p-phenylene diisocyanate is a small hard segment, the ionomers were found to be single phase with only one DSC Tg which increases with both ion content and hard segment content. An electrode polarization model was used to simultaneously determine the temperature dependence of conducting ion concentration and their mobility, which show Arrhenius and Vogel–Fulcher–Tammann (VFT) temperature dependences, respectively. The polymer dipole relaxation probed by DRS was found to be between 103 and 106 times faster than the mechanical segmental relaxation observed in LVE data near Tg, suggesting that most polymer modes need to wait for the ions to rearrange. The dielectric relaxation, mechanical relaxation, and ionic conductivity all show good correlation with DSC Tg and are related to ion rearrange...

  • Linear Viscoelasticity and Cation Conduction in Polyurethane Sulfonate Ionomers with Ions in the Soft Segment–Single Phase Systems
    2018
    Co-Authors: Shih Wa Wang, Ralph H Colby
    Abstract:

    PEO-based polyurethane sulfonate ionomers with various PEO chain lengths and sodium counterions were synthesized and characterized by both Linear Viscoelasticity (LVE) and dielectric relaxation spectroscopy (DRS). Since p-phenylene diisocyanate is a small hard segment, the ionomers were found to be single phase with only one DSC Tg which increases with both ion content and hard segment content. An electrode polarization model was used to simultaneously determine the temperature dependence of conducting ion concentration and their mobility, which show Arrhenius and Vogel–Fulcher–Tammann (VFT) temperature dependences, respectively. The polymer dipole relaxation probed by DRS was found to be between 103 and 106 times faster than the mechanical segmental relaxation observed in LVE data near Tg, suggesting that most polymer modes need to wait for the ions to rearrange. The dielectric relaxation, mechanical relaxation, and ionic conductivity all show good correlation with DSC Tg and are related to ion rearrangement. Lower ion content creates lower Tg, lower activation energy for conducting ions, and higher ion mobility, as sodium cations interact strongly with both PEO and the urethane linkage

  • Linear Viscoelasticity and fourier transform infrared spectroscopy of polyether ester sulfonate copolymer ionomers
    Macromolecules, 2014
    Co-Authors: Quan Chen, Hanqing Masser, Huaisuen Shiau, Siwei Liang, James Runt, Paul C Painter, Ralph H Colby
    Abstract:

    Fourier transform infrared spectroscopy (FTIR) and Linear Viscoelasticity (LVE) were used to characterize amorphous copolyester ionomers synthesized via condensation of sulfonated phthalates with mixtures of poly(ethylene glycol) with M = 600 g/mol and poly(tetramethylene glycol) with M = 650 g/mol. The copolymer ionomers exhibited microdomain separation, as confirmed in previous X-ray scattering measurements. Since PEO has superior ion solvating ability compared with PTMO, the ions near the interface reside preferentially in the PEO microdomain. FTIR measurements were used to quantify fractions of ions in different association states, in turn quantifying the fractions in the PEO-rich domains, in the PTMO-rich domains, and at the interface between these domains. FTIR shows that the structure of the interfacial ion aggregates is quite different for the copolymers with different counterions; at the interface Na+ aggregates into open string structures while Li+ aggregates into denser sheets of ions, as depic...

  • structure and Linear Viscoelasticity of flexible polymer solutions comparison of polyelectrolyte and neutral polymer solutions
    Rheologica Acta, 2010
    Co-Authors: Ralph H Colby
    Abstract:

    The current state of understanding for solution conformations of flexible polymers and their Linear viscoelastic response is reviewed. Correlation length, tube diameter, and chain size of neutral polymers in good solvent, neutral polymers in θ-solvent, and polyelectrolyte solutions with no added salt are compared as these are the three universality classes for flexible polymers in solution. The 1956 Zimm model is used to describe the Linear Viscoelasticity of dilute solutions and of semidilute solutions inside their correlation volumes. The 1953 Rouse model is used for Linear Viscoelasticity of semidilute unentangled solutions and for entangled solutions on the scale of the entanglement strand. The 1971 de Gennes reptation model is used to describe Linear viscoelastic response of entangled solutions. In each type of solution, the terminal dynamics, reflected in the terminal modulus, chain relaxation time, specific viscosity, and diffusion coefficient are reviewed with experiment and theory compared. Overall, the agreement between theory and experiment is remarkable, with a few unsettled issues remaining.

  • miscible polymer blend dynamics double reptation predictions of Linear Viscoelasticity in model blends of polyisoprene and poly vinyl ethylene
    Macromolecules, 2004
    Co-Authors: Sanat K Kumar, Jai A Pathak, Ralph H Colby
    Abstract:

    Predictions of the Linear viscoelastic complex shear modulus in model miscible blends of polyisoprene (PI) and poly(vinyl ethylene) (PVE) are compared with literature data. Using ideas of chain connectivity, the effective monomer relaxation times of PI and PVE in the blend were calculated using PI self-composition φPI,s = 0.40 and PVE self-composition φPVE,s = 0.80, determined in our earlier analysis of segmental dynamics in PI/PVE blends. The reptation times of PI and PVE were then determined from their effective monomer relaxation times in the blend, assuming a common tube for both components (thus specifying the blend plateau modulus). The component reptation times and effective terminal dispersion widths from fits to the pure component polymers were input along with the blend plateau modulus to the des Cloizeaux “double reptation” model of polymer dynamics to make predictions of blend Linear Viscoelasticity with no adjustable parameters. The calculated frequency dependence of the complex modulus of PI...

J M Franco - One of the best experts on this subject based on the ideXlab platform.

  • rheological and mechanical properties of oleogels based on castor oil and cellulosic derivatives potentially applicable as bio lubricating greases influence of cellulosic derivatives concentration ratio
    Journal of Industrial and Engineering Chemistry, 2011
    Co-Authors: R Sanchez, J M Franco, C Valencia, M A Delgado, C Gallegos
    Abstract:

    Abstract Nowadays the lubricating market is demanding new biodegradable or more environmentally acceptable products based on renewable resources as a consequence of progressively more strict environmental regulations. In this framework, this study deals with the design of gel-like dispersions potentially applicable as environmentally friendly lubricating greases. These dispersions were formulated using castor oil and ethyl cellulose/α-cellulose or ethyl cellulose/methyl cellulose blends. In particular, the influence of cellulosic derivatives concentration ratio on the Linear Viscoelasticity and mechanical stability of the resulting oleogel formulations was studied. The modification of ethyl cellulose/α-cellulose or ethyl cellulose/methyl cellulose weight ratios allows obtaining some formulations with suitable rheological characteristics and mechanical stability for potential lubricating applications. An important decrease in the values of the Linear Viscoelasticity functions down to a minimum value was found by increasing ethyl cellulose/α-cellulose or ethyl cellulose/methyl cellulose weight ratios ( W ) up to a critical value, which depends on both nature of the cellulosic derivatives employed and temperature. Above this critical value, the Linear viscoelastic functions increase with W , at temperatures in the range 0–75 °C, and continuously decrease at higher temperatures, i.e. 125 °C. Thermal susceptibility is significantly dampened by reducing ethyl cellulose concentration. Gel-like dispersions formulated with ethyl cellulose/methyl cellulose blends showed appropriate mechanical stabilities to be used as bio-lubricating greases.

  • use of chitin chitosan and acylated derivatives as thickener agents of vegetable oils for bio lubricant applications
    Carbohydrate Polymers, 2011
    Co-Authors: R Sanchez, J M Franco, G B Stringari, C Valencia, C Gallegos
    Abstract:

    This work deals with the development of new gel-like formulations prepared from natural resources, which could be potentially applicable as environmentally friendly lubricating greases. In particular, the use of chitin, chitosan and acylated derivatives as thickener agents of vegetable oils, which may represent an alternative to the traditional metallic soaps or polyurea derivatives, was explored. Biopolymers used to obtain oleogels were chemically and thermally characterized. Oleogels thermal and rheological behaviours were studied by means of TGA and DSC tests, and Linear Viscoelasticity measurements, respectively. Moreover, some lubricant performance properties were evaluated. The evolution of Linear Viscoelasticity functions with frequency was very similar to that found for standard lubricating greases. In general, Linear Viscoelasticity functions increased with biopolymer concentration, whilst they decreased when acylated chitosan or soybean oil were used in the oleogel formulation. The use of acylated chitosan with a degree of acylation of around 0.3 provides oleogels with very similar rheological properties than those shown by traditional lubricating greases, as a consequence of reducing the biopolymer polarity. However, chitin and chitosan-based oleogels show higher thermal stabilities than formulations containing acylated chitosan. In general, oleogel samples studied exhibited values of the friction coefficient comparable to those found for standard lithium greases. However, most of these oleogels generally display a quite poor mechanical stability in rolling elements.

  • development of new green lubricating grease formulations based on cellulosic derivatives and castor oil
    Green Chemistry, 2009
    Co-Authors: R Sanchez, J M Franco, C Valencia, M A Delgado, C Gallegos
    Abstract:

    Environmentally friendly lubricating greases may be produced by solely replacing the mineral base oil for vegetable oil. However, the substitution of traditional metallic soaps by biodegradable and renewable thickeners is, up to now, much less considered. This work is focused on the development of new oleogels, using castor oil and cellulose derivatives, which could be potentially used as biodegradable lubricating greases. Thermal and thermo-rheological behaviours of these materials were characterised by means of TGA analysis and SAOS measurements, in order to evaluate the evolution of oleogel microstructure with temperature. Moreover, both roll-stability and leakage tendency standard tests, usually performed in the grease industry, were used to evaluate the mechanical resistance of each sample. The evolution of biogrease Linear Viscoelasticity functions with frequency is quite similar to that found for traditional lithium lubricating greases. However, the influence of temperature on biogreases Linear Viscoelasticity functions is less important than that found for traditional greases. In general, the biogrease samples studied show both slightly lower mechanical stability and higher leakage tendency than traditional lubricating greases. The use of a blend of ethyl and methyl cellulose as thickener provides a mechanical stability comparable to that found for commercial greases.

  • Linear Viscoelasticity of tomato sauce products influence of previous tomato paste processing
    European Food Research and Technology, 2002
    Co-Authors: C Valencia, A Ciruelos, A Latorre, J M Franco, M C Sánchez, Crı´spulo Gallegos
    Abstract:

    Tomato paste is used as an ingredient for the manufacture of tomato sauce products. This work deals with the influence that some tomato paste processing variables (finisher screen opening and breaking temperature) and tomato variety exert on the Linear viscoelastic properties of tomato sauce products. Four tomato varieties (two commercial varieties, one with a lower content of polygalacturonase enzyme, and one with a low content in pectin methylesterase enzyme) have therefore been used. Dynamic viscoelastic tests and particle size distribution (PSD) measurements have been carried out. From the experimental results obtained, we may conclude that the dependence of the Linear viscoelastic properties of tomato sauce on the above-mentioned variables is very complex. Nevertheless, the evolution of the viscoelastic characteristics of these products is mainly related to their mean volume diameter and tomato paste water insoluble solids content (WIS). This solid content is mainly controlled by tomato variety and tomato paste processing conditions.

  • Rheology of food, cosmetics and pharmaceuticals
    Current Opinion in Colloid and Interface Science, 1999
    Co-Authors: Críspulo Gallegos, J M Franco
    Abstract:

    The major recent advances in the theology of food, cosmetics and pharmaceuticals have been developed in the fields of emulsions and gels. Concerning emulsion theology, this review has been specially focused on the problem of wall slip, processing and modelling of its non-Linear Viscoelasticity behaviour. Concerning the theology of gels, the most relevant contributions have been made on the improvement of gel strength by acidification of several protein dispersions.

Francesco Mainardi - One of the best experts on this subject based on the ideXlab platform.

  • A generalization of the Becker model in Linear Viscoelasticity: creep, relaxation and internal friction
    Mechanics of Time-Dependent Materials, 2019
    Co-Authors: Francesco Mainardi, Enrico Masina, Giorgio Spada
    Abstract:

    We present a new rheological model depending on a real parameter ν ∈ [ 0 , 1 ] $\nu \in [0,1]$ , which reduces to the Maxwell body for ν = 0 $\nu =0$ and to the Becker body for ν = 1 $\nu =1$ . The corresponding creep law is expressed in an integral form in which the exponential function of the Becker model is replaced and generalized by a Mittag–Leffler function of order ν $\nu $ . Then the corresponding non-dimensional creep function and its rate are studied as functions of time for different values of ν $\nu $ in order to visualize the transition from the classical Maxwell body to the Becker body. Based on the hereditary theory of Linear Viscoelasticity, we also approximate the relaxation function by solving numerically a Volterra integral equation of the second kind. In turn, the relaxation function is shown versus time for different values of ν $\nu $ to visualize again the transition from the classical Maxwell body to the Becker body. Furthermore, we provide a full characterization of the new model by computing, in addition to the creep and relaxation functions, the so-called specific dissipation Q − 1 $Q^{-1}$ as a function of frequency, which is of particular relevance for geophysical applications.

  • erratum on modifications of the exponential integral with the mittag leffler function
    Fractional Calculus and Applied Analysis, 2018
    Co-Authors: Francesco Mainardi, Enrico Masina
    Abstract:

    In this paper we survey the properties of the Schelkunoff modification of the Exponential integral and we generalize it with the Mittag-Leffler function. So doing we get a new special function (as far as we know) that may be relevant in Linear Viscoelasticity because of its complete monotonicity properties in the time domain. We also consider the generalized sine and cosine integral functions

  • on transient waves in Linear Viscoelasticity
    Wave Motion, 2017
    Co-Authors: Ivano Colombaro, Andrea Giusti, Francesco Mainardi
    Abstract:

    Abstract The aim of this paper is to present a comprehensive review of method of the wave-front expansion, also known in the literature as the Buchen–Mainardi algorithm. In particular, many applications of this technique to the fundamental models of both ordinary and fractional Linear Viscoelasticity are thoroughly presented and discussed.

  • An historical perspective on fractional calculus in Linear Viscoelasticity
    Fractional Calculus and Applied Analysis, 2012
    Co-Authors: Francesco Mainardi
    Abstract:

    The article provides an historical survey of the early contributions on the applications of fractional calculus in Linear viscoelasticty. The period under examination covers four decades, since 1930’s up to 1970’s, and authors are from both Western and Eastern countries. References to more recent contributions may be found in the bibliography of the author’s book. This paper reproduces, with Publisher’s permission, Section 3.5 of the book: F. Mainardi, Fractional Calculus and Waves in Linear Viscoelasticity , Imperial College Press-London and World Scienific-Singapore, 2010.

  • an historical perspective on fractional calculus in Linear Viscoelasticity
    Fractional Calculus and Applied Analysis, 2012
    Co-Authors: Francesco Mainardi
    Abstract:

    The article provides an historical survey of the early contributions on the applications of fractional calculus in Linear viscoelasticty. The period under examination covers four decades, since 1930’s up to 1970’s, and authors are from both Western and Eastern countries. References to more recent contributions may be found in the bibliography of the author’s book.

Chixing Zhou - One of the best experts on this subject based on the ideXlab platform.

  • polymer chain topological map as determined by Linear Viscoelasticity
    Journal of Rheology, 2011
    Co-Authors: Jianye Liu, Chixing Zhou
    Abstract:

    The characteristics of van Gurp–Palmen (vGP) plot for long-chain branching polymer with well-defined topological structures, including symmetric star, asymmetric star, H-shaped, and comb polymers, have been calculated by “branch-on-branch” constitutive model. It is indicated that there is only one characteristic transition in the vGP plot for nearly symmetric star polymers, but more for other chain topologies, which were deeply dependent on the topology and the molecular parameters such as side-arm length, backbone length, and number of side arms. The theoretically calculated characteristic transition points were used to construct a topology map. A feasible protocol to distinguish the topological structures of branched polymer was put forward to quantify the chain structure qualitatively and quantitatively. Such a method has been successfully proved by its application on the available data in the literature.

  • long chain branching polylactide structures and properties
    Polymer, 2010
    Co-Authors: Wei Yu, Ruogu Liao, Runming Li, Chixing Zhou
    Abstract:

    Long chain branching (LCB) of polylactide (PLA) was successfully prepared by the successive reactions of the end hydroxyl groups of PLA with pyromellitic dianhydride (PMDA) and triglycidyl isocyanurate (TGIC) together. The topological structures of the LCB generated from functional group reactions as well as free radical reactions were investigated thoroughly by gel permeation chromatography (GPC) and rheology. Qualitative information about the branching structures could be readily obtained from Linear Viscoelasticity, non-Linear oscillatory shear experiments and strain hardening in elongational experiments. For quantitative information on chain structure, Linear Viscoelasticity combined with branch-on-branch (BOB) dynamic model was used to predict exact compositions and chain topologies of the products, which were reasonably explained by the suggested mechanism of functional group reactions. It was found out that the tree-like LCB structure generated in these reactions contributed remarkably to the enhancement of strain hardening under elongational flow, which improves the foaming ability substantially.

  • Linear Viscoelasticity of polymer blends with co continuous morphology
    Polymer, 2010
    Co-Authors: Wei Zhou, Chixing Zhou
    Abstract:

    The co-continuous morphology of polymer blends has received much attention not only because of its potential promotion of mechanical or electrical properties of polymer blends, but also due to its importance in phase separation by spinodal decomposition. Compared to the recent advances in the characterization of co-continuous structure, the rheology of co-continuous blends has not been understood clearly. In this work, a rheological model is suggested to correlate the Linear Viscoelasticity and the structural information of co-continuous blends. The dynamic modulus of co-continuous blends is composed of the contribution from components and the interface. The interfacial contribution, which is most important in the rheology of blends, is calculated from a simplified co-continuous structure. This model has been compared satisfactorily with available experimental results, which proves a reasonable connection between the co-continuous structure and Linear Viscoelasticity of blends.

Enrico Masina - One of the best experts on this subject based on the ideXlab platform.

  • A generalization of the Becker model in Linear Viscoelasticity: creep, relaxation and internal friction
    Mechanics of Time-Dependent Materials, 2019
    Co-Authors: Francesco Mainardi, Enrico Masina, Giorgio Spada
    Abstract:

    We present a new rheological model depending on a real parameter ν ∈ [ 0 , 1 ] $\nu \in [0,1]$ , which reduces to the Maxwell body for ν = 0 $\nu =0$ and to the Becker body for ν = 1 $\nu =1$ . The corresponding creep law is expressed in an integral form in which the exponential function of the Becker model is replaced and generalized by a Mittag–Leffler function of order ν $\nu $ . Then the corresponding non-dimensional creep function and its rate are studied as functions of time for different values of ν $\nu $ in order to visualize the transition from the classical Maxwell body to the Becker body. Based on the hereditary theory of Linear Viscoelasticity, we also approximate the relaxation function by solving numerically a Volterra integral equation of the second kind. In turn, the relaxation function is shown versus time for different values of ν $\nu $ to visualize again the transition from the classical Maxwell body to the Becker body. Furthermore, we provide a full characterization of the new model by computing, in addition to the creep and relaxation functions, the so-called specific dissipation Q − 1 $Q^{-1}$ as a function of frequency, which is of particular relevance for geophysical applications.

  • erratum on modifications of the exponential integral with the mittag leffler function
    Fractional Calculus and Applied Analysis, 2018
    Co-Authors: Francesco Mainardi, Enrico Masina
    Abstract:

    In this paper we survey the properties of the Schelkunoff modification of the Exponential integral and we generalize it with the Mittag-Leffler function. So doing we get a new special function (as far as we know) that may be relevant in Linear Viscoelasticity because of its complete monotonicity properties in the time domain. We also consider the generalized sine and cosine integral functions