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M Cohen A Stuart - One of the best experts on this subject based on the ideXlab platform.
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rheology of a reversible supramolecular polymer studied by comparison of the effects of temperature and chain Stoppers
Journal of Chemical Physics, 2007Co-Authors: W Knoben, N A M Besseling, M Cohen A StuartAbstract:The rheology of a reversible supramolecular polymer is studied by comparing the effects of an increase in temperature and the addition of chain Stoppers. The dependence of the zero-shear viscosity and the terminal relaxation time on temperature is exponential, and the activation energy for viscous flow can be calculated. Above a critical stopper fraction, power laws describe the stopper dependence of the viscosity and relaxation time. A simple model for the effect of the addition of chain Stoppers on the average degree of polymerization adequately describes the results. A comparison of flow curves at several temperatures and stopper fractions reveals considerable differences between solutions with the same zero-shear viscosity. These are mainly associated with differences in the terminal relaxation time. A mechanism of shear-induced alignment and subsequent elongation of chains is proposed, with which the experimental results are consistent.
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chain Stoppers in reversible supramolecular polymer solutions studied by static and dynamic light scattering and osmometry
Macromolecules, 2006Co-Authors: W Knoben, N A M Besseling, M Cohen A StuartAbstract:The effect of the addition of chain Stoppers to solutions of hydrogen-bonded reversible supramolecular polymers was studied by vapor pressure osmometry and static and dynamic light scattering. Vapor pressure osmometry showed that within the range of concentrations studied the average degree of polymerization is independent of the overall monomer concentration and roughly inversely proportional to the mole fraction of chain Stoppers, in agreement with theoretical predictions. The correlation length as measured by static light scattering has a maximum at the overlap concentration in solutions without chain Stoppers. In the presence of a fixed fraction of chain Stoppers, the results coincide with those without chain Stoppers at low and high concentrations, but there is a plateau in the correlation length at intermediate concentrations. From the data, information about the association constant and the persistence length of the chains is obtained. The effectiveness of the chain stopper is discussed, and the re...
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dynamics of reversible supramolecular polymers independent determination of the dependence of linear viscoelasticity on concentration and chain length by using chain Stoppers
Physical Chemistry Chemical Physics, 2005Co-Authors: W Knoben, N A M Besseling, Laurent Bouteiller, M Cohen A StuartAbstract:The linear viscoelasticity of solutions of a hydrogen bonded reversible supramolecular polymer in the presence of a chain stopper was studied by rheometry and by dynamic light scattering using probe particles. The use of chain Stoppers enabled the independent variation of the degree of polymerisation and the monomer concentration, and the effect of both parameters on rheology was investigated. Scaling exponents were obtained for the chain length and concentration dependence of the zero-shear viscosity and the terminal relaxation time, and these were compared to theoretical values. The results indicate that the reversible supramolecular polymer is semiflexible, and that both breaking and reptation of chains contribute to the stress relaxation. The parameters from macroscopic rheometry were compared to microscopic values obtained from probe particle diffusion. The particles probe the macroscopic viscoelastic parameters if their size is large compared to the correlation length in the system and to the (persistence) length of the polymer chains.
W Knoben - One of the best experts on this subject based on the ideXlab platform.
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rheology of a reversible supramolecular polymer studied by comparison of the effects of temperature and chain Stoppers
Journal of Chemical Physics, 2007Co-Authors: W Knoben, N A M Besseling, M Cohen A StuartAbstract:The rheology of a reversible supramolecular polymer is studied by comparing the effects of an increase in temperature and the addition of chain Stoppers. The dependence of the zero-shear viscosity and the terminal relaxation time on temperature is exponential, and the activation energy for viscous flow can be calculated. Above a critical stopper fraction, power laws describe the stopper dependence of the viscosity and relaxation time. A simple model for the effect of the addition of chain Stoppers on the average degree of polymerization adequately describes the results. A comparison of flow curves at several temperatures and stopper fractions reveals considerable differences between solutions with the same zero-shear viscosity. These are mainly associated with differences in the terminal relaxation time. A mechanism of shear-induced alignment and subsequent elongation of chains is proposed, with which the experimental results are consistent.
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chain Stoppers in reversible supramolecular polymer solutions studied by static and dynamic light scattering and osmometry
Macromolecules, 2006Co-Authors: W Knoben, N A M Besseling, M Cohen A StuartAbstract:The effect of the addition of chain Stoppers to solutions of hydrogen-bonded reversible supramolecular polymers was studied by vapor pressure osmometry and static and dynamic light scattering. Vapor pressure osmometry showed that within the range of concentrations studied the average degree of polymerization is independent of the overall monomer concentration and roughly inversely proportional to the mole fraction of chain Stoppers, in agreement with theoretical predictions. The correlation length as measured by static light scattering has a maximum at the overlap concentration in solutions without chain Stoppers. In the presence of a fixed fraction of chain Stoppers, the results coincide with those without chain Stoppers at low and high concentrations, but there is a plateau in the correlation length at intermediate concentrations. From the data, information about the association constant and the persistence length of the chains is obtained. The effectiveness of the chain stopper is discussed, and the re...
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dynamics of reversible supramolecular polymers independent determination of the dependence of linear viscoelasticity on concentration and chain length by using chain Stoppers
Physical Chemistry Chemical Physics, 2005Co-Authors: W Knoben, N A M Besseling, Laurent Bouteiller, M Cohen A StuartAbstract:The linear viscoelasticity of solutions of a hydrogen bonded reversible supramolecular polymer in the presence of a chain stopper was studied by rheometry and by dynamic light scattering using probe particles. The use of chain Stoppers enabled the independent variation of the degree of polymerisation and the monomer concentration, and the effect of both parameters on rheology was investigated. Scaling exponents were obtained for the chain length and concentration dependence of the zero-shear viscosity and the terminal relaxation time, and these were compared to theoretical values. The results indicate that the reversible supramolecular polymer is semiflexible, and that both breaking and reptation of chains contribute to the stress relaxation. The parameters from macroscopic rheometry were compared to microscopic values obtained from probe particle diffusion. The particles probe the macroscopic viscoelastic parameters if their size is large compared to the correlation length in the system and to the (persistence) length of the polymer chains.
N A M Besseling - One of the best experts on this subject based on the ideXlab platform.
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rheology of a reversible supramolecular polymer studied by comparison of the effects of temperature and chain Stoppers
Journal of Chemical Physics, 2007Co-Authors: W Knoben, N A M Besseling, M Cohen A StuartAbstract:The rheology of a reversible supramolecular polymer is studied by comparing the effects of an increase in temperature and the addition of chain Stoppers. The dependence of the zero-shear viscosity and the terminal relaxation time on temperature is exponential, and the activation energy for viscous flow can be calculated. Above a critical stopper fraction, power laws describe the stopper dependence of the viscosity and relaxation time. A simple model for the effect of the addition of chain Stoppers on the average degree of polymerization adequately describes the results. A comparison of flow curves at several temperatures and stopper fractions reveals considerable differences between solutions with the same zero-shear viscosity. These are mainly associated with differences in the terminal relaxation time. A mechanism of shear-induced alignment and subsequent elongation of chains is proposed, with which the experimental results are consistent.
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chain Stoppers in reversible supramolecular polymer solutions studied by static and dynamic light scattering and osmometry
Macromolecules, 2006Co-Authors: W Knoben, N A M Besseling, M Cohen A StuartAbstract:The effect of the addition of chain Stoppers to solutions of hydrogen-bonded reversible supramolecular polymers was studied by vapor pressure osmometry and static and dynamic light scattering. Vapor pressure osmometry showed that within the range of concentrations studied the average degree of polymerization is independent of the overall monomer concentration and roughly inversely proportional to the mole fraction of chain Stoppers, in agreement with theoretical predictions. The correlation length as measured by static light scattering has a maximum at the overlap concentration in solutions without chain Stoppers. In the presence of a fixed fraction of chain Stoppers, the results coincide with those without chain Stoppers at low and high concentrations, but there is a plateau in the correlation length at intermediate concentrations. From the data, information about the association constant and the persistence length of the chains is obtained. The effectiveness of the chain stopper is discussed, and the re...
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dynamics of reversible supramolecular polymers independent determination of the dependence of linear viscoelasticity on concentration and chain length by using chain Stoppers
Physical Chemistry Chemical Physics, 2005Co-Authors: W Knoben, N A M Besseling, Laurent Bouteiller, M Cohen A StuartAbstract:The linear viscoelasticity of solutions of a hydrogen bonded reversible supramolecular polymer in the presence of a chain stopper was studied by rheometry and by dynamic light scattering using probe particles. The use of chain Stoppers enabled the independent variation of the degree of polymerisation and the monomer concentration, and the effect of both parameters on rheology was investigated. Scaling exponents were obtained for the chain length and concentration dependence of the zero-shear viscosity and the terminal relaxation time, and these were compared to theoretical values. The results indicate that the reversible supramolecular polymer is semiflexible, and that both breaking and reptation of chains contribute to the stress relaxation. The parameters from macroscopic rheometry were compared to microscopic values obtained from probe particle diffusion. The particles probe the macroscopic viscoelastic parameters if their size is large compared to the correlation length in the system and to the (persistence) length of the polymer chains.
Laurent Bouteiller - One of the best experts on this subject based on the ideXlab platform.
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Chain stopper engineering for hydrogen bonded supramolecular polymers.
Beilstein Journal of Organic Chemistry, 2010Co-Authors: Thomas Pinault, Bruno Andrioletti, Laurent BouteillerAbstract:Supramolecular polymers are linear chains of low molar mass monomers held together by reversible and directional non-covalent interactions, which can form gels or highly viscous solutions if the self-assembled chains are sufficiently long and rigid. The viscosity of these solutions can be controlled by adding monofunctional compounds, which interact with the chain extremities: chain Stoppers. We have synthesized new substituted ureas and thioureas and tested them as chain Stoppers for a bis-urea based supramolecular polymer. In particular, the bis-thiourea analogue of the bis-urea monomer is shown not to form a supramolecular polymer, but a good chain stopper, because it is a strong hydrogen bond donor and a weak acceptor. Moreover, all substituted ureas tested reduce the viscosity of the supramolecular polymer solutions, but the best chain stopper is obtained when two hydrogen bond acceptors are placed in the same relative position as for the monomer and when no hydrogen bond donor is present.
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anions as efficient chain Stoppers for hydrogen bonded supramolecular polymers
Langmuir, 2009Co-Authors: Thomas Pinault, Bruno Andrioletti, Caroline Cannizzo, Guylaine Ducouret, Francois Lequeux, Laurent BouteillerAbstract:The chain length of hydrogen-bonded supramolecular polymers and thus their rheological properties can be controlled by the presence of so-called chain Stoppers: these monofunctional monomers are able to interact with the monomers and break the polymer chains. In this letter, we show that the use of anions, strong hydrogen bond competitors, instead of precisely designed complementary units is a very simple approach to tuning the rheology of a bisurea-based hydrogen-bonded supramolecular polymer. All of the anions tested were able to break the supramolecular chains, resulting in a dramatic drop in the viscosity of the solutions and were found to be more efficient than a previously described organic stopper. A careful study of the rheological properties of bisurea solutions in the presence of H2PO4,N(C4H9)4 showed that the presence of this ion does not modify the nature of the bisurea supramolecular assembly. For a molar fraction of stopper of only 10−5, the viscosity of bisurea solutions decreases by a fact...
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dynamics of reversible supramolecular polymers independent determination of the dependence of linear viscoelasticity on concentration and chain length by using chain Stoppers
Physical Chemistry Chemical Physics, 2005Co-Authors: W Knoben, N A M Besseling, Laurent Bouteiller, M Cohen A StuartAbstract:The linear viscoelasticity of solutions of a hydrogen bonded reversible supramolecular polymer in the presence of a chain stopper was studied by rheometry and by dynamic light scattering using probe particles. The use of chain Stoppers enabled the independent variation of the degree of polymerisation and the monomer concentration, and the effect of both parameters on rheology was investigated. Scaling exponents were obtained for the chain length and concentration dependence of the zero-shear viscosity and the terminal relaxation time, and these were compared to theoretical values. The results indicate that the reversible supramolecular polymer is semiflexible, and that both breaking and reptation of chains contribute to the stress relaxation. The parameters from macroscopic rheometry were compared to microscopic values obtained from probe particle diffusion. The particles probe the macroscopic viscoelastic parameters if their size is large compared to the correlation length in the system and to the (persistence) length of the polymer chains.
Carlos Pinho - One of the best experts on this subject based on the ideXlab platform.
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PRESSURE DROP IN A SPOUTED BED OF CORK Stoppers
Revista de Engenharia Térmica, 2018Co-Authors: Ana Magalhães, Carlos PinhoAbstract:The spouted bed is a particular type of fluidized bed which is well suited for the handling of large size particles like cork Stoppers. It is commonly used for the drying of granulates and the present work is the first part of a study concerning the drying of cork Stoppers in a laboratory scale spouted bed reactor. The study considers two Stoppers size, one the port wine stopper and another small size stopper. The choice of these smaller sizes was imposed by the small dimensions of the reactor. In this preliminary set of experiments the fluid-dynamics regime of the particular two phase flow was characterized. For different experimental situations covering several air flows and temperatures typical of cork drying operations the evolution of pressure drop was evaluated and a correlation for the minimum spouting velocity was obtained.
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spouted bed drying of cork Stoppers
Chemical Engineering and Processing, 2008Co-Authors: Ana Magalhães, Carlos PinhoAbstract:Abstract The spouted bed is commonly used to dry granular particles as it displays some special characteristics which render it capable of performing cyclic operations, with particles that are very difficult to fluidize under a different type of bed. Information on the characteristic drying rates of cork Stoppers is still very limited in the technical and scientific literature, and until now no published data was found on the spouted bed drying of cork Stoppers. The characterization of the drying performance of Port wine cork Stoppers was carried out in a laboratory scale spouted bed. Characteristic drying curves were determined with 29 mm × 21 mm cork Stoppers under several operating conditions. Values for the effective diffusivity were obtained in the range of 1.36 × 10−9 to 4.44 × 10−9 m2/s, with the temperature dependence represented by an Arrhenius-type relationship. The activation energy obtained was 28.72 kJ/mol.
