Investigating the rheology of 2D titanium carbide (MXene) dispersions for colloidal processing: Progress and challenges

Among 2D materials, MXenes (especially their most studied member, titanium carbide) present a unique opportunity for application via colloidal processing, as they are electrically conductive and chemically active, whilst still being easily dispersed in water. And since the first systematic study of colloidal MXene rheology was published in 2018 (Rheological Characteristics of 2D Titanium Carbide (MXene) Dispersions: A Guide for Processing MXenes by Akuzum, et al.), numerous works have presented small amounts of rheological data which together contribute to a deeper understanding of the topic. This work reviews the published rheological data on all MXene-containing formulations, including liquid crystals, mixtures and non-aqueous colloids, which have been used in processes such as stamping, patterning, 2D and 3D printing. An empirical model of aqueous titanium carbide viscosity has been developed, and recommendations are made to help researchers more effectively present their data for future rheological analysis. Graphic abstract

Numerical analysis of slot die coating of nanocellulosic materials

Nanocellulosic coatings as a food packaging material are of commercial interest due to their nontoxic nature, renewability, and excellent barrier properties. Complex shear-thinning rheology poses challenges in designing and sizing equipment to pump, mix, and process the suspension and actual coating process. This study aims to determine the effectiveness of computational fluid dynamics (CFD) in predicting nanocellulosic suspension flow in light of existing rheological data. We employ and compare three distinct rheological models to characterize the rheology and flow of nanocellulose suspensions through a slot die coater, where the model parameters are established from existing slot rheometry measurements. A volume-of-fluid (VoF) based finite volume method is employed to simulate the flow in a slot die operated in an unconventional metering mode. Results with the Casson model predict the presence of unyielded regions in the flow, which was not captured using the power law model. These stagnation regions will incur coatability issues stemming from flow intermittencies and lead to potential defects in the coating layer, including fracture. The results suggest that a rheological model that includes yield stress should be considered while modeling such flows. A need for better rheological data to model nanocellulosic flows, especially at high consistencies and shear rates, is also highlighted.

A torsion-based rheometer for measuring viscoelastic material properties

ABSTRACTRheology and the study of viscoelastic materials is an integral part of engineering and the study of biophysical systems however the cost of a rheometer is only feasible for colleges, universities and research laboratories. Even if a rheometer can be purchased it is bulky and delicately calibrated limiting its usefulness to the laboratory itself. The design presented here is less than a tenth of the cost of a professional rheometer and portable making it the ideal solution for high school students as a way to introduce viscoelasticity at a younger age as well as for use in the field for obtaining preliminary rheological data.

Stress Relaxation and Creep of a Polymer-Aluminum Composite Produced through Selective Laser Sintering

This article discusses the rheological properties (stress relaxation and creep) of polymer-aluminum composite specimens fabricated through the selective laser sintering (SLS) from a commercially available powder called Alumide. The rheological data predicted using the Maxwell–Wiechert and the Kelvin–Voigt models for stress relaxation and creep, respectively, were in agreement with the experimental results. The elastic moduli and dynamic viscosities were determined with high accuracy for both models. The findings of this study can be useful to designers and users of SLS prints made from the material tested.

Dough Rheological Behavior and Microstructure Characterization of Composite Dough with Wheat and Tomato Seed Flours

The rheological and microstructural aspects of the dough samples prepared from wheat flour and different levels of tomato seed flour (TSF) were investigated by rheology methods through the Mixolab device, dynamic rheology and epifluorescence light microscopy (EFLM). The Mixolab results indicated that replacing wheat flour with TSF increased dough development time, stability, and viscosity during the initial heating-cooling cycle and decreased alpha amylase activity. The dynamic rheological data showed that the storage modulus G’ and loss modulus G” increased with the level of TSF addition. Creep-recovery tests of the samples indicated that dough elastic recovery was in a high percentage after stress removal for all the samples in which TSF was incorporated in wheat flour. Using EFLM all the samples seemed homogeneous showing a compact dough matrix structure. The parameters measured with Mixolab during mixing were in agreement with the dynamic rheological data and in accordance with the EFLM structure images. These results are useful for bakery producers in order to develop new products in which tomato seed flour may be incorporated especially for wheat flours of a good quality for bread making and high wet gluten content. The addition of TSF may have a strength effect on the dough system and will increase the nutritional value of the bakery products.

Assessment of the Tumbling-Snake Model against Linear and Nonlinear Rheological Data of Bidisperse Polymer Blends

We have recently solved the tumbling-snake model for concentrated polymer solutions and entangled melts in the academic case of a monodisperse sample. Here, we extend these studies and provide the stationary solutions of the tumbling-snake model both analytically, for small shear rates, and via Brownian dynamics simulations, for a bidisperse sample over a wide range of shear rates and model parameters. We further show that the tumbling-snake model bears the necessary capacity to compare well with available linear and non-linear rheological data for bidisperse systems. This capacity is added to the already documented ability of the model to accurately predict the shear rheology of monodisperse systems.