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Stimuli-responsive materials capable of reversible changes in physicochemical properties or morphology in response to external influences are increasingly being used in various "smart" devices, such as sensors, actuators, soft robotics, protective coatings etc. A representative of such materials in the field of dispersed systems are electrorheological fluids. Typically, they are suspensions revealing transition from viscous behavior to viscoelastic one under an electric field due to the polarization of the dispersed particles with the formation of an extended structure. The formation of a percolation network of particles leads to the appearance and growth of the yield stress. The driving force behind the effect is the difference in the electrical characteristics (permittivity and conductivity) of the filler and the dispersion medium, while maintaining a low value of the conductivity of the suspension. Therefore, various dielectric liquids are used as dispersion media, often both synthetic (silicone, mineral, etc.) and natural (olive, corn, etc.) oils. Recent development of electrorheology shows a trend towards the low-concentrated fluids exhibiting a contrasting change in rheological behavior with high yield stress in an electric field at minimum filler content [1].
The natural polysaccharides, cellulose and chitin are the most abundant biopolymers in the earth. Cellulose is the main component of the cell wall of plants, while chitin is the main structural component of fungi and crustacean shells. In nature, these polymers are found mainly as a component of composite materials in the form of fibrous structures with high crystallinity, such as protein matrices. An individual fiber consists of alternating crystalline and amorphous regions. The latter can be destroyed by chemical methods, thus cellulose and chitin particles are isolated in the form of highly anisometric nanocrystals. Chitosan is produced by deacetylation of chitin. Typically, the definition of chitin or chitosan refers to the balance of amino and acetamide groups in the particles structure. The boundary is conventional: the deacetylation degree of chitin is less than 50%, and that of chitosan is more than 50%.
The present study considers the electrorheological behavior of suspensions filled by cellulose, chitin [2] and chitosan [3] in low molecular weight polydimethylsiloxane (silicon oil) in the range of electric field strengths up to 7 kV/mm. The key role of the supramolecular structure of particles in low-concentrated electrorheological fluids is shown. It is noteworthy that chitosan forms a solution in an acetic acid aqueous medium, which opens up opportunities for producing highly porous particles by spraying followed by freeze-drying. Thus, novel highly porous fillers with high sedimentation stability in silicon oil suspension have been developed. The sedimentation ratio remains higher than 90% for at least a month. Such fluids reveal high values of the yield stress up to 600 Pa under an electric field at a filler concentration of only 1 wt% [3]. Typically, similar rheological characteristics are observed in suspensions with a filler content at least an order of magnitude higher.
The mechanism of the electrorheological effect for fluids with various types of polysaccharide fillers was analyzed in terms of electrical properties. The temperature dependences of the dielectric spectra made it possible to reveal the contribution of conductivity along with polarization. One of the ways to increase the electrorheological effect is to regulate the electrical properties of the filler, and a promising technique is to produce composite particles. Thus, the combination of two approaches, such as the formation of a developed highly porous structure of the filler and the incorporation of electrosensitive nanoparticles into it, will allow the development of novel effective materials. Silver nanoparticles could be reduced in solution by chitosan from silver nitrate. Thus, chitosan acts as a reductant and prevents the strong aggregation of nanoparticles during synthesis. It is possible to produce a chitosan-silver composite with the most optimal properties for specific applications by varying some parameters, such as the concentration of chitosan and silver, the molecular weight of chitosan, temperature, recovery time, etc [4].
The report discusses the prospects for creating low-concentrated electrorheological fluids with polysaccharide fillers and environmentally friendly material that comply with the principles of green chemistry as well.
The work was partially supported by the Russian Science Foundation, grant 22-73-10081.

References
1.        Kuznetsov N.M., Kovaleva V. V., Belousov S.I., Chvalun S.N. // Mater. Today Chem. 2022. V. 26. P. 101066. https://doi.org/10.1016/j.mtchem.2022.101066
2.        Kovaleva V.V., Kuznetsov N.M., Istomina A.P., et al. // Carbohydr. Polym. 2022. V. 277. P. 118792. https://doi.org/10.1016/j.carbpol.2021.118792
3.        Kuznetsov N.M., Zagoskin Y.D., Vdovichenko A.Y., et al. // Carbohydr. Polym. 2021. V. 256. №September 2020. P. 117530. https://doi.org/10.1016/j.carbpol.2020.117530
4.         Kuznetsov N.M., Zagoskin Y.D., Bakirov A. V, et al. // Polym. Adv. Technol. 2022. №June. P. 1–15. https://doi.org/10.1002/pat.5817

stimuli-responsive materials,smart materials,electrorheological fluids,dispersed systems,polysaccharides,chitin,chitosan,cellulose