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Daniel Bonn - One of the best experts on this subject based on the ideXlab platform.

  • carbopol from a simple to a Thixotropic yield stress fluid
    Journal of Rheology, 2018
    Co-Authors: M Dinkgreve, Mina Fazilati, Morton M. Denn, Daniel Bonn
    Abstract:

    There is an ongoing discussion in the literature about the flow Behavior of the widely used model yield-stress fluid Carbopol. Some papers show that it is indeed the simple model yield-stress fluid that many people believe it to be. However, other authors report rheological hysteresis in the flow curve, transient shear banding that persists for a very long time, and the breaking of fore-aft symmetry in a falling ball experiment. Such Behaviors have in the past been associated with Thixotropic yield stress fluids, which are very different from simple ones. We present experiments that suggest that both types of Behavior may be found in the same type of Carbopol, depending on the preparation: After strong stirring for a long time, the system becomes slightly Thixotropic. Flow visualization experiments with fluorescently labeled Carbopol elucidate the difference between the simple and Thixotropic Behavior of the systems: The stirring breaks the polymers into smaller fragments, some of which are so small that ...

Hongfei Liu - One of the best experts on this subject based on the ideXlab platform.

Tobias Robert - One of the best experts on this subject based on the ideXlab platform.

  • straightforward synthetic protocol to bio basedunsaturated poly ester amide s from itaconic acidwith Thixotropic Behavior
    Polymers, 2020
    Co-Authors: Lazaros Papadopoulos, Marcel Kluge, Dimitrios N Bikiaris, Tobias Robert
    Abstract:

    In the field of polymer chemistry, tremendous efforts have been made over the last decade to replace petrochemical monomers with building blocks from renewable resources. In this respect, itaconic acid has been used as an alternative to acrylic acid or maleic acid in unsaturated polyesters for thermal or UV-curing applications. However, examples of poly(ester amide)s from itaconic acid are scarce. Under standard polycondensation reactions, the presence of free amines leads to aza-Michael addition reactions at the α,β-unsaturated double bond of the itaconic acid and isomerization reactions to mesaconic acid. Both reactions make the resulting materials useless as UV-curing polymer resins. To avoid these undesired side reactions, we herein report the use of preformed, well-defined diols containing internal amide bonds. The resulting unsaturated poly(ester amide) resins were analyzed before and after UV-induced crosslinking. Viscosity measurements revealed a strong Thixotropic Behavior induced by the amide groups, which is usually not detected in structurally similar polyester resins.

Marcel Kluge - One of the best experts on this subject based on the ideXlab platform.

  • straightforward synthetic protocol to bio basedunsaturated poly ester amide s from itaconic acidwith Thixotropic Behavior
    Polymers, 2020
    Co-Authors: Lazaros Papadopoulos, Marcel Kluge, Dimitrios N Bikiaris, Tobias Robert
    Abstract:

    In the field of polymer chemistry, tremendous efforts have been made over the last decade to replace petrochemical monomers with building blocks from renewable resources. In this respect, itaconic acid has been used as an alternative to acrylic acid or maleic acid in unsaturated polyesters for thermal or UV-curing applications. However, examples of poly(ester amide)s from itaconic acid are scarce. Under standard polycondensation reactions, the presence of free amines leads to aza-Michael addition reactions at the α,β-unsaturated double bond of the itaconic acid and isomerization reactions to mesaconic acid. Both reactions make the resulting materials useless as UV-curing polymer resins. To avoid these undesired side reactions, we herein report the use of preformed, well-defined diols containing internal amide bonds. The resulting unsaturated poly(ester amide) resins were analyzed before and after UV-induced crosslinking. Viscosity measurements revealed a strong Thixotropic Behavior induced by the amide groups, which is usually not detected in structurally similar polyester resins.

Jinjun Zhang - One of the best experts on this subject based on the ideXlab platform.

  • modeling the Thixotropic Behavior of waxy crude
    Industrial & Engineering Chemistry Research, 2013
    Co-Authors: Houxing Teng, Jinjun Zhang
    Abstract:

    Waxy crude shows viscoelastic, yielding, and Thixotropic Behaviors below the gelation point. In this paper, to depict those complex rheological Behaviors a new Thixotropic model is proposed. In the model, the total shear stress is considered to be a combination of an elastic stress and a viscous stress. The elastic stress, assumed to be structure- and strain-dependent, is described by a nonlinear damping function together with a structural parameter. The evolution of structural parameter is described by a new kinetic equation, whose breakdown term is assumed to be dependent on energy dissipation rate rather than on shear rate. The proposed model is validated respectively by the test of stepwise increases in shear rate and the hysteresis loop test for waxy crude and further validated by predicting the transient flow curve of hysteresis loop test with the model parameters obtained from the test of stepwise increases in shear rate. The results showed that the model’s capability of fitting experimental data a...