Embedding orthogonal memories in a colloidal gel through oscillatory shear

Abstract

It has recently been shown that in a broad class of disordered systems oscillatory shear training can embed memories of specific shear protocols in relevant physical parameters such as the yield strain. These shear protocols can be used to change the physical properties of the system and memories of the protocol can later be read out. Here we investigate shear training memories in colloidal gels, which include an attractive interaction and network structure, and discover that such systems can support memories both along and orthogonal to the training flow direction. We use oscillatory shear protocols to set and read out the yield strain memories and confocal microscopy to analyze the rearranging gel structure throughout the shear training. We find that the gel bonds remain largely isotropic in the shear-vorticity plane throughout the training process suggesting that structures formed to support shear along the training shear plane are also able to support shear along the orthogonal plane. Orthogonal memory extends the usefulness of shear memories to more applications and should apply to many other disordered systems as well.

Shear-induced memory effects in boehmite gels

“…The imprint of the shear protocol may subsequently be read out by a strain sweep from small to large amplitudes 14 . Similar memory effects have been identified in colloidal gels 15 , where shear history significantly affects the microstructural and mechanical properties [16][17][18] , which constitutes the subject of the present article. Indeed, depending on its intensity, mechanical shear may either enhance or compete with the attractive interactions driving the formation of clusters, which play a key role in the solid-like behavior of the sample upon flow cessation 19,20 .…”

Tuning local microstructure of colloidal gels by ultrasound-activated deformable inclusions

“…The structure of such networks, which coarsens with time, 11 dictates whether and how the network may support shear stresses in the linear regime 8,12 and governs their rheological behaviour for larger deformation. [13][14][15] Oscillatory shear induces unique structures in complex fluids 16 and in particular in colloidal gels, [17][18][19] providing additional control over their microstructure and rheological properties. 18 For instance, shear-induced crystallisation also imparts remarkable acoustic 20 or photonic properties for advanced material applications.…”

Real Space Analysis of Colloidal Gels: Triumphs, Challenges and Future Directions

“…The ability to encode structural or mechanical properties into a gel through specific shear conditions as a form of "memory" was recently explored by Schwen et al [220] using a custom biaxial shear stage [216] on a confocal microscope. By using many shear cycles at a given strain to "train" the gel, strain memories were embedded, such that a reversible structural rearrangement (such that the image difference before and after strain was small) in response to further strains below the training strain amplitude was observed: In effect, a new yield strain is set for the gel at the training strain.…”