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"Angew Chem" from Professor Peng Feng's team at Beijing Forestry University: significant progress in non-equilibrium fluids
2019-12-30 Source: Polymer Technology

In the long river of time, everything flows. Generally, liquids that satisfy Newton's law of flow are called Newtonian fluids, such as water, alcohol, and the like. But in reality, non-Newtonian fluids are everywhere in our lives, such as shear thinning fluids (viscosity decreases with increasing shear rate), and the most common are sap, pulp, blood, paint, and polysaccharide solutions. In addition, another relatively rare type of non-Newtonian fluid is shear thickening fluid (viscosity becomes abnormally larger with increasing shear rate). This type of fluid is usually based on particle suspensions, such as starch paste, Nanocellulose concentrated solution and polyvinyl chloride plastisol. Compared with shear-thinning fluids, shear-thickening fluids can undergo liquid-solid transitions under external forces to buffer external energy, so they are mostly used in military body armor, tank armor, damping reducers, and motion cushioning materials. In a broad sense, everything changes; but on a limited time scale, the rheological properties of fluids under external force fields have always been distinct and difficult to transform. How to spontaneously change these two distinct non-Newtonian properties over time on a limited and observable scale has been a problem that has puzzled scientists.

Figure 1 Schematic diagram of non-equilibrium non-Newtonian fluid and molecular structural formula

The team of Professor Peng Feng from Beijing Forestry University has been working on the separation and utilization of lignocellulosic biomass components for many years. Based on a lot of research on the rheological properties of starch paste, pulp and nanocellulose concentrated solution, they have recently cooperated with Chinese science Yang Yang's research group at the University of Technology cooperated to develop a new class of non-equilibrium non-Newtonian fluid materials. Although nano-bio-based suspensions are often used to prepare shear thickeners, there are problems such as difficult modification, poor transparency, and easy phase separation. To this end, they used hydrophobically associated polymers to replace nano-based suspensions, and controlled the molecular weight of the polymer and the degree of hydrophobic modification to achieve intermolecular cross-linking of the hydrophobic polyelectrolyte under high shear rate induction to achieve shear thickening. the goal of. At the same time, by using dissipation-control instead of classical thermal equilibrium-control, the pH of the system is controlled by the urea-urease reaction, which further induces the conformational changes of the polymer clusters over time, achieving the ability of non-Newtonian fluids. Spontaneously switches between two distinct phenomena, shear thinning and shear thickening (Figure 1).

Figure 2 Oscillation behavior of non-equilibrium non-Newtonian fluid and rheological characteristics over time

Due to the use of heat dissipation mechanics, the internal assembly structure and macroscopic properties of polymer non-Newtonian fluids change with time, rather than appearing as a normal thermodynamic equilibrium stimulus response. Specifically, the system must rely on continuous input of external energy to show shear thickening performance. Once the energy supply or energy consumption is lost, the system immediately exhibits shear thinning behavior. As shown in Figure 2, over time, we can observe two distinct fluid characteristics: oscillating thinning and oscillating into gel. If the use concentration of urea buffer (chemical energy) is further controlled, the time during which the nonlinear mechanical properties under the shear field (physical energy) exist briefly can be effectively controlled.

This article is published online in "Biocatalytic Feedback-Controlled Non-Newtonian Fluids" in one of the most influential comprehensive journals in the field of international chemistry, "Angewandte Chemie International Edition" (IF = 12.257). The author is Hao Xiang , a young teacher in the School of Materials, Beijing Forestry University, the first corresponding author is his co-instructor, Professor Peng Feng , School of Materials, Beijing Forestry University, and the Beijing Key Laboratory of Forest Biomass Chemistry, School of Materials, Beijing Forestry University is the first unit.

This work was funded by special funds for basic scientific research business expenses of the Central University of Beijing Forestry University and projects from the National Natural Science Foundation of China.

Article link: http://onlinelibrary.wiley.com/doi/10.1002/anie.201914398

Copyright and Disclaimer: Original article from China Polymer Network. For reprinting of publications or media, please contact the email address : info@chevronsz.com , and please indicate the source.
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