Towards an accurate understanding of shear thickness

Shear thickeners are colloidal suspensions that have a viscosity that increases – sometimes very suddenly – with the intensity of the shear to which they are subjected. The researchers demonstrated experimentally that if this phenomenon arises mainly from the intrinsic roughness of the colloids, it can be greatly amplified by the presence of the bonds hydrogen (Hydrogen is a chemical element with symbol H and atomic number 1.).

what or what kitchen (kitchen) He has never experienced this contradictory and embarrassing behavior of cornstarch “rejecting” itself mixed (A mixture is the union of two or more components of solid, liquid or gaseous…) ? When the starch corn (Maize (also called Indian corn in Canada) is a tropical plant…) It is actually highly concentrated inWater (Water is a chemical compound found everywhere on Earth, essential to everyone…)The mixture becomes almost solid when the spatula is too fast. This rheological behavior, called shear thickening, is not very common in complex fluids, where we often observereflect (In mathematics, the inverse of the x element of a group endowed with a law…)subordinate Materials (A substance is a substance of natural or artificial origin that forms man to …) which becomes liquid under the cut (paints when spread, for example). This increase in the viscosity of cornstarch is due to the interactions between the cornstarch molecules that make up it suspension (The verb to suspend particles in chemistry, suspension refers to dispersion…).

However, the exact microscopic scenario associated with this sudden increase in viscosity is still poorly understood, especially because the starch particles have the double drawback of being insufficient for individual characterization and chemical aging during time (Time is a concept developed by humans to understand…). Since this phenomenon is also found in other types of colloidal suspensions, which are chemically significantly different from cornstarch, different microscopic origins of the shear thickness have been suggested in the literature, from which experiments with contradictory results have sometimes been unsuccessful to separate completely.

Scanning electron micrographs (the scale corresponds to 200 nm) show two types of colloids used, the coarseness Different (In mathematics, the difference is defined in the algebraic theorem of…) The resulting aggregation of SiO2 nanoparticles with radii of 25 nm (top) and 10 nm (bottom). Red circles highlight some of these primary nanoparticles. Credit: LPENSL (CNRS/ENS de Lyon)

By a new series of experiments on the comment silica (Silica is made up of silicon dioxide, a chemical compound that goes into…) (SiO2), with exact size and roughness, a team of researchers from Laboratoire de physical (Physics (from Greek φυσις, nature) is etymologically…) Ecole Normale Supérieure de Lyon (LPENSL, CNRS (The National Center for Scientific Research, better known by the acronym CNRS, is the largest…) / ENS de Lyon), from the CNRS-MIT International Joint Multiscale Materials Laboratory Science (Science (Latin science, “knowledge”) is, according to the dictionary…) energy and environment)2, CNRS/MIT) and MIT Strictly Relative Contributions to Friction Shear Thickness Mechanical (In everyday parlance, mechanics is the field of machines, engines, vehicles, organs, etc.) between particles on the one hand and their physical and chemical interactions on the other hand.

By comparing the behavior of fairly coarse particle suspensions and the chemical treatment of space (Surface generally refers to the surface layer of an object. The term A…) Worker (In mathematics and logic, a variable is represented by a symbol. It is…)it illustrates on the one hand the necessary role of particle roughness to induce shear thickening and on the other hand exacerbation of this phenomenon by the presence of physico-chemical reactions (usually hydrogen bonds) up to a mechanical response close to that of a steel.

By varying the proportion of particles in the suspension capable of forming hydrogen bonds, the physicists have also succeeded in continuously controlling the intensity of the shear thickness observed. This opens the way for many applications, for example editing (Installation is an industrial activity consisting of the manufacture of products…) Cement with better controlled rheological properties or design flexible and shock-absorbing materials such as bulletproof vests. These results have been published in the journal Physical Review Research.

To obtain these results, the researchers performed rheological measurements on four types of fumed silica colloidal solutions (agglomerated SiO2 nanoparticles) in Polypropylene (Equal spaced polypropylene (or polypropylene), abbreviated PP (or PPi) and formula…) Glycol, particles vary in coarseness and hydrophobicity, but all have a size You know? (Average is a statistical measure that characterizes the elements of a set of…) 300 nanometers (nm).

The control (The word control can have several meanings. It can be used as a synonym for checking, or…) The roughness is caused by the manufacturing process of silica particles produced by a conglomerate (A agglomeration is an urban agglomeration based on the continuity of the built environment….) at height temperature (Temperature is a physical quantity measured with a thermometer and …) of SiO2 nanoparticles whose size (10 and 25 nm in the described experiments) is precisely determined by the fabrication process. Aggregates are obtained in more complex shapes because the nanoparticles that make up them are small (see figure). This zigzag enables them to develop significant friction in the event of contact between them, and the contact they extend and thus their efficacy in increasing viscosity can also be controlled by modifying the water resistance of their surface by chemical treatment.

It is interesting to note that the results obtained using these colloids of complex shapes are not well described by current theories and thus raise some number (The notion of number in linguistics is addressed in the article “Number …) Essential questions that have yet to be answered.

Contacts:

– Tipo Defox – Responsible for Research (Scientific research identifies in the first place all actions taken with a view to …)Physics Laboratory of ENS de Lyon – thibaut.divoux at ens-lyon.fr
– Telecommunications (Contact with man (communication within oneself, communication between people, etc.) INP – inp.com at cnrs.fr