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Testing Adhesives
Published in Gerald L. Schneberger, Adhesives in Manufacturing, 2018
Harold Koski, Gerald L. Schneberger
The viscosity of thixotropic adhesives is usually determined by ASTM Standard D-2556 [1]. Thixotropic materials exhibit a viscosity which is shear-rate dependent. The viscosity is determined at several different shear rates, usually with an electrically driven spindle, disk, T-bar, or coaxial cylinder rotated in the adhesive. A plot of apparent viscosity versus rotational speed is prepared, and from this plot the apparent viscosity associated with the particular rotation speed and spindle shape is obtained.
Introduction
Published in Steven G. Penoncello, Thermal Energy Systems, 2018
Shear-thinning fluids can be further classified as pseudoplastic, thixotropic, or Bingham plastic. A pseudoplastic substance experiences a viscosity decrease with an applied shearing stress. When the applied stress is removed, the fluid reverts back to a more solid-like phase. Tomato ketchup is a good example of a pseudoplastic fluid. Squeezing the ketchup out of its container requires an applied force to make it run. However, once the applied force is removed, the ketchup becomes thicker. A thixotropic substance experiences a decrease in viscosity with an applied shear stress, but its viscosity continues to decrease with time as the shear stress is applied. An example of a thixotropic fluid is spun honey. The more it is stirred, the more liquid-like it becomes. A Bingham plastic behaves like a Newtonian fluid once the initial yield stress of the fluid is exceeded. Bingham plastic fluids include toothpaste, blood, molten chocolate, and mashed potatoes.
Viscometers—Application and Selection
Published in Béla G. Lipták, Analytical Instrumentation, 2018
Thixotropic materials (Curve #5) are usually pseudo-plastics (shear thinning substances), but they exhibit hysteresis. They seem to “remember” their past history and, for example, when reagitated they will require less force than was required during the first agitation. Thixotropic substances include asphalts, lard, silica gel, most paints, glues, and fruit juice concentrates.
Pulsatile flow of thixotropic blood in artery under external body acceleration
Published in Computer Methods in Biomechanics and Biomedical Engineering, 2023
Louiza Cheffar, Abdelhakim Benslimane, Djamel Sadaoui, Adel Benchabane, Karim Bekkour
Whereas many studies have considered Newtonian, non-Newtonian and viscoelastic assumptions, studies regarding the time-dependent thixotropic effect exhibited by physiological systems such as blood are fewer despite its importance in blood flow modeling. However, the concept of thixotropy is well established and the related rheological experimentation has already been extensively investigated (Barnes 1997; de Souza Mendes et al. 2012; Pritchard et al. 2020) given the widespread nature of thixotropic fluid applications. Thixotropic fluids are commonly used in the construction industry (e.g. liquid cements, liquid concrete, drilling fluids), industrial applications (e.g. muds, paints) and the food industry (e.g. liquid dairy products, ketchup). Related applications include some forms of mud flows and debris flows, pasty sewage sludges and some wastewater treatment residues (Benslimane et al. 2016a, 2016b).
Bigels as novel systems for the delivery active compounds from Centella asiatica
Published in Soft Materials, 2023
Agnieszka Kulawik-Pióro, Emilia Osak, Mariola Mendrycka, Zuzanna Trześniewska-Ofiara
The investigated bigels belong to the group of non-Newtonian liquids that are shear thinning with the yield stress. The rheograms of the analyzed bigels presented in the figure have a visible hysteresis loop; moreover, the hysteresis phenomenon does not disappear, which means that none of the received preparations rebuilds the system structure after the disappearance of shear. This confirms the results of Singh and co-workers[59] that bigels have thixotropic properties. A thixotropic system reveals a loss in apparent viscosity over time at a constant shear rate, while the shear stress is removed. Subsequently, the apparent viscosity constantly increases and returns to its primary value. It is assumed that under shearing stress, the bonding between polymer chains is broken down, resulting in a more fluid-like low-viscosity system, while in the absence of mechanical forces, polymer particles rejoin again, and the three-dimensional network rebuilds, restoring the primary structure of the material.[60,61] The thixotropy behavior leads to relatively low viscosity of the product at the time of its application, but also prevents it from running off the skin surface. Also, their pseudoplastic tendency results in the formation of a coherent film covering the skin surface. This property is valuable and critical for a better fortification of the skin surface.[62] Furthermore, Wróblewska et al.[61] claim that the shear thinning phenomenon is considered a relevant parameter for the local application of the semisolid formulation. This facilitates the formation of a thin layer of the gel preparation when it is applied locally, which results in the efficient delivery of active agents at the site of application. Bigels had a similar energy dissipated, which means that the changes to the bigels structure due to the shear rating used were the same in all samples.
Characterization and modelling of the rheological behaviour of blended cements based on mineral additions
Published in European Journal of Environmental and Civil Engineering, 2021
Mohammed Salah Bouglada, Abdelghani Naceri, Mohamed Baheddi, Luiz Pereira-de-Oliveira
Figure 10 presents the torque variation as function of the speed and each binder rheology test is described by zones of hysteresis translating pastes thixotropic behaviours. Thixotropy is defined as a decrease in viscosity when shear is applied, followed by a gradual recovery when shear is removed. This is a reduction in stress at constant shear rate or at constant shear rate at constant shear stress. This effect is time dependent (Tattersall & Banfill, 1983).