ABSTRACT
The rheological studies of Lactic Acid (LA)-based Natural Deep Eutectic Solvents (NADES) are provided in the present investigation. Those mechanisms were also studied in which three distinct Hydrogen Bond Acceptors (HBAs) of Choline Chloride (ChCl), Betaine (Be), and ß-Alanine (ß-Al), after being added to a specific Hydrogen Bond Donor (HBD) at a predefined mole-to-mole ratio of 1:1, affected the rheological properties of the prepared NADES. The alterations in the rheology-related characteristics in association with the mechanical and physical properties indicate the tolerance of the material under various operational conditions in the field and show their potential utilization as environmentally suitable and feasible solvents for industrial applications. In the present research, the viscoelastic properties of the three samples of NADES were assessed along with their shear flow properties. The backward and forward temperature change in the Apparent Viscosity (AV) pattern related to the NADES system was described by a rheogram. Furthermore, the density was determined and compared with the AV while considering the temperature-related factor. On a further note, the viscoelastic characteristics were utilized in describing and investigating the network disturbance on the level of the microstructure of NADES upon frequency sweep. A series of experiments were carried out using Thermogravimetry Analysis (TGA) to investigate the thermo-physical properties to optimize them. The rheological properties of shear flow measurements were analyzed using the Bingham model that is best suited for the AV developed with the shear rate with the dynamic yield stress of three systems. The Bingham model was used to determine the lowest stress necessary to disturb the network structure and commence the flow of LA-based NADES. Overall, the viscoelastic behavior of the LA-based NADES revealed the dissimilarity between their strength and viscosity. In addition, shear flow investigations demonstrated that LA-based NADES systems exhibit non-Newtonian properties and substantial shear-thinning effects equivalent to those of alternative IL sorbents. Assessing the rheological properties of LA-based NADES is crucial for a better understanding the key challenges associated with high viscosity. Defining the transport yield stress requirements for NADES systems under different conditions benefits their future development and potentially opens the door to more challenging applications.
ABSTRACT
The rheological characterization for a series of Malic Acid based Hydrogen Bond Donor Natural Deep Eutectic Solvents (NADES) is studied in this work for their potential usage as sorbents for CO2 capture. Three different NADES combinations were synthesized based on B-Alanine, Betaine and Choline Chloride as Hydrogen Bond Acceptors. The work provides insights on the rheological behaviors of Malic Acid-based NADES at temperature ranges from 25 to 105 °C and shear rates from 0.01 to 1000 s-1, which shows the impact of altering the Hydrogen Bond Acceptor in a NADES system. All Malic Acid-based systems showed non-Newtonian, shear thinning behaviors and diverse viscoelastic flow behavior ranging from as low as 3 × 102 up to 4 × 107 mPa stress requirements showing viscous liquids to solid-like gel structures. The different NADES combinations showed strong temperature dependence behavior, where the density at different temperatures dropped from 1.42 to 1.37 g/cm3 for B-Alanine: Malic Acid. This behavior fits on the Bingham model revealed that the yield stress for all Malic Acid-NADES decreased with increasing temperature as expected for the shear thinning materials. The differences in the yield stress magnitudes of approximately 7 × 102 to 6 × 106 mPa in the case of B-Alanine: Malic Acid for example was attributed to the changes in the nature and the numbers of the interaction forces between the Hydrogen Bond Acceptor and Hydrogen Bond Donor of the NADES and the molecular weight. The viscoelasticity of these NADES systems demonstrated the fundamental differences between the ways the different Hydrogen Bond Acceptor interacts with the Hydrogen Bond Donor. The Linear Viscoelastic Region (LVR) was set to 0.1%-10% according to the type of NADES under a frequency range of 0.1-100 rad/s. The hole theory was used as a theoretical approach to describe the structural differences behind the flow behaviors.
