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Periodic Report Summary 1 - SOFTEVA (Drying of complex fluids on soft substrates)

The objective of SOFTEVA project is to describe the deposition of colloidal suspensions on soft materials on two main aspects:
* the coating uniformity
* the measurement of stresses induced by drying.
Two types of soft materials are in the scope of this project: elastomers for which no solvent exchange occurs with the aqueous colloidal suspension and hydrogels making posssible solvent exchange.
The project has also the ambition to study two different types of colloidal suspensions: concentrated silica nanoparticles that enables the development of large stresses and continous films and micron size particles used in a very dilute regime.
The work performed since the beginning of the project consists in the following.
1. experimental and theoretical investigation of the drying of silica nanoparticles on thin elastomeric sheets
2. experimental and theoretical investigation of the absorption of a water drop containing microspheres on a swelling hydrogel.

Regarding item 1. a paper has been published in EuroPhysics Letter entitled "Self-crumpling elastomers: bending induced by the drying stimulus of a nanoparticle suspension" and is mentioned in the previous report. In the mean time, we have published a second paper in Physical Review Letter entitled "Effect of the polydispersity of a colloidal drop on the drying induced stress as measured by the buckling of a floating sheet". In this paper, we study the stress developed during the drying of a colloidal drop of silica nanoparticles. In particular, we use the wrinkling instability of a thin floating sheet to measure the net stress applied by the deposit on the substrate and we focus on the effect of the particle polydispersity. In the case of a bidisperse suspension, we show that a small number of large particles substantially decreases the expected stress, which we interpret as the formation of lower hydrodynamic resistance paths in the porous material. As colloidal suspensions are usually polydisperse, we show for different average particle sizes that the stress is effectively dominated by the larger particles of the distribution and not by the average particle size.
A patent application has been submitted by Princeton University on the use of polydisperse suspensions to reduce drying stresses.

Regarding item 2, we published the paper (submitted in the previous report) entitled "Homogeneous deposition of particles by absorption on hydrogels" in EuroPhysics Letter.
In addition to this paper, a second paper has been published in Langmuir (Tuning the receding contact angle on hydrogels by addition of particles) where we investigate experimentally the effect of adsorbed particles on hydrogels on the depinning of contact lines. In our experiments, a water drop containing polystyrene microspheres is deposited on a swelling hydrogel, which leads to the drop absorption and particle deposition. Two regimes are observed: a decreasing drop height with a pinned contact line followed by a receding contact line. We show that increasing the particles concentration increases the duration of the first regime and significantly decreases the total absorption time. The adsorbed particles increase the pinning force at the contact line. Finally, we develop a method to measure the receding contact angle with the consideration of the hydrogel swelling.

François Boulogne has also the opportunity to write an opinion paper resulting of a workshop on soft interfaces in Leiden (The Netherlands).
He co-advised a PhD student in Princeton who worked on the deposition of quantum dots in a capillary tube, which led to a publication in Langmuir.
In addition, he developed a collaboration on the drying of whisky drops ("Controlled uniform coating from the interplay of Marangoni flows and surface-adsorbed macromolecules" published in Physical Review Letters), which has been reported in several popular science media, including an interview in Science et Vie, a french science magazine.

A paper entitled "Coffee-stain growth dynamics on dry and wet surfaces" has been submitted. In this paper we argue that the suppression of the diverging evaporating flux at the contact line has a weak effect on the coffee stain.

References (cited in the previous report):

- F. Boulogne, A. Sauret, B. Soh, E. Dressaire, H. Stone, "Mechanical tuning of the evaporation rate of liquid on crossed fibers", Langmuir, vol. 31, no. 10, 2015, pp. 3094-3100.
- A. Sauret, F. Boulogne, B. Soh, E. Dressaire, H. Stone, "Wetting of fibrous arrays: liquid morphology on two randomly oriented fibers", The European Physical Journal E, 2015
- A. Sauret, F. Boulogne, D. Cébron, E. Dressaire, H. Stone, "Wetting morphologies on an array of fibers of different radii", Soft Matter, vol. 11, 2015, pp. 4034-4040.
- A. Sauret, F. Boulogne, J. Cappello, E. Dressaire, H. Stone, "Damping of liquid sloshing by foams", Physics of Fluids, vol. 27, no. 2, 2015.
- J. Cappello, A. Sauret, F. Boulogne, E. Dressaire, H. Stone, "Damping of liquid sloshing by foams: from everyday observations to liquid transport", Journal of Visualization, vol. 18, no. 2, 2015, pp. 269-271
- F. Boulogne, H. A. Stone, "Self-crumpling elastomers: bending induced by the drying stimulus of a nanoparticle suspension", EPL, vol. 108, 2014, pp. 19001.

References (published since the previous report):

- F. Boulogne, F. Ingremeau, J. Dervaux, L. Limat, H. A. Stone, "Homogeneous deposition of particles by absorption on hydrogels", EPL, vol. 112, no. 4, 2015, pp. 48004.
- Y. L. Kong, F. Boulogne, H. Kim, J. Nunes, J. Feng, H. A. Stone, "Deposition of quantum dots in a capillary tube", Langmuir, vol. 31, no. 45, 2015, pp. 12560-12566.
- B. Andreotti, O. Baumchen, F. Boulogne, K. E. Daniels, E. R. Dufresne, H. Perrin, T. Salez, J. H. Snoeijer, R. W. Style, "Solid Capillarity: When and How does Surface Tension Deform Soft Solids?", Soft Matter, vol. 12, 2016, pp. 2993-2996.
- F. Boulogne, Y. L. Kong, J. K. Nunes, H. A. Stone, "Effect of the polydispersity of a colloidal drop on the drying induced stress as measured by the buckling of a floating sheet", Physical Review Letters, vol. 116, 2016, pp. 238001.
- F. Boulogne, F. Ingremeau, L. Limat, H. A. Stone, "Tuning the receding contact angle on hydrogels by addition of particles", Langmuir, vol. 32, no. 22, 2016, pp. 5573-5579.
- H. Kim, F. Boulogne, E. Um, I. Jacobi, E. Button, H. A. Stone, "Controlled uniform coating from the interplay of Marangoni flows and surface-adsorbed macromolecules", Physical Review Letters, vol. 116, 2016, pp. 124501.

Submitted papers:

- F. Boulogne, F. Ingremeau and H. A. Stone, "Coffee-stain growth dynamics on dry and wet surfaces", Submitted.

Reported by

UNIVERSITE PARIS DIDEROT - PARIS 7
France

Subjects

Life Sciences
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