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Université de Fribourg

Inclined layer convection in a colloidal suspension with negative Soret coefficient at large solutal Rayleigh numbers

Italia, Matteo ; Croccolo, Fabrizio ; Scheffold, Frank ; Vailati, Alberto

In: The European Physical Journal E, 2014, vol. 37, no. 10, p. 1–6

Convection in an inclined layer of fluid is affected by the presence of a component of the acceleration of gravity perpendicular to the density gradient that drives the convective motion. In this work we investigate the solutal convection of a colloidal suspension characterized by a negative Soret coefficient. Convection is induced by heating the suspension from above, and at large solutal...

Université de Fribourg

Diffusing wave microrheology of highly scattering concentrated monodisperse emulsions

Kim, Ha Seong ; Şenbil, Nesrin ; Zhang, Chi ; Scheffold, Frank ; Mason, Thomas G.

In: Proceedings of the National Academy of Sciences, 2019, vol. 116, no. 16, p. 7766–7771

Motivated by improvements in diffusing wave spectroscopy (DWS) for nonergodic, highly optically scattering soft matter and by cursory treatment of collective scattering effects in prior DWS microrheology experiments, we investigate the low-frequency plateau elastic shear moduli G′p of concentrated, monodisperse, disordered oil-in- water emulsions as droplets jam. In such experiments, the...

Université de Fribourg

Entropic, electrostatic, and interfacial regimes in concentrated disordered ionic emulsions

Kim, Ha Seong ; Scheffold, Frank ; Mason, Thomas G.

In: Rheologica Acta, 2016, vol. 55, no. 8, p. 683–697

We develop a free energy model that describes two key thermodynamic properties, the osmotic pressure Π and the linear elastic shear modulus G′p (i.e. plateau storage modulus), of concentrated monodisperse emulsions which have isotropic, disordered, droplet structures, and are stabilized using ionic surfactants. This model effectively incorporates the concept of random close packing or...

Université de Fribourg

Numerical study of Anderson localization of terahertz waves in disordered waveguides

Lapointe, Clayton P. ; Zakharov, Pavel ; Enderli, F. ; Feurer, T. ; Skipetrov, S. E. ; Scheffold, Frank

In: EPL (Europhysics Letters), 2014, vol. 105, no. 3, p. 34002

We present a numerical study of electromagnetic wave transport in disordered quasi–one-dimensional waveguides at terahertz frequencies. Finite element method calculations of terahertz wave propagation within LiNbO3 waveguides with randomly arranged air-filled circular scatterers exhibit an onset of Anderson localization at experimentally accessible length scales. Results for the average...

Université de Fribourg

Light induced inverse-square law interactions between nanoparticles: “mock gravity” at the nanoscale

Luis-Hita, J. ; Marqués, M. I. ; Delgado-Buscalioni, R. ; Sousa, N. de ; Froufe-Pérez, Luis S. ; Scheffold, Frank ; Sáenz, J. J.

In: Physical Review Letters, 2019, vol. 123, no. 14, p. 143201

The interaction forces between identical resonant molecules or nanoparticles, optically induced by a quasimonochromatic isotropic random light field, are theoretically analyzed. In general, the interaction force exhibits a far-field oscillatory behavior at separation distances larger than the light wavelength. However, we show that the oscillations disappear when the frequency of the random...

Université de Fribourg

High-quality photonic crystals with a nearly complete band gap obtained by direct inversion of woodpile templates with titanium dioxide

Marichy, Catherine ; Muller, Nicolas ; Froufe-Pérez, Luis S. ; Scheffold, Frank

In: Scientific Reports, 2016, vol. 6, p. 21818

Photonic crystal materials are based on a periodic modulation of the dielectric constant on length scales comparable to the wavelength of light. These materials can exhibit photonic band gaps; frequency regions for which the propagation of electromagnetic radiation is forbidden due to the depletion of the density of states. In order to exhibit a full band gap, 3D PCs must present a threshold...

Université de Fribourg

Crossover between entropic and interfacial elasticity and osmotic pressure in uniform disordered emulsions

Mason, Thomas G. ; Scheffold, Frank

In: Soft Matter, 2014, vol. 10, no. 36, p. 7109–7116

We develop a simple predictive model of the osmotic pressure Π and linear shear elastic modulus G′p of uniform disordered emulsions that includes energetic contributions from entropy and interfacial deformation. This model yields a smooth crossover between an entropically dominated G′p ∼...

Université de Fribourg

Photonic hyperuniform networks obtained by silicon double inversion of polymer templates

Muller, Nicolas ; Haberko, Jakub ; Marichy, Catherine ; Scheffold, Frank

In: Optica, 2017, vol. 4, no. 3, p. 361–366

Hyperuniform disordered networks belong to a peculiar class of structured materials predicted to display isotropic complete photonic bandgaps for a refractive index contrast larger than 3. The practical realization of such photonic designer materials is challenging, however, as it requires control over a multi-step fabrication process on optical length scales. Here we report the direct-laser...

Université de Fribourg

Silicon hyperuniform disordered photonic materials with a pronounced gap in the shortwave infrared

Muller, Nicolas ; Haberko, Jakub ; Marichy, Catherine ; Scheffold, Frank

In: Advanced Optical Materials, 2014, vol. 2, no. 2, p. 115-119

The mesoscale fabrication of silicon hyperuniform disordered materials with a broad and pronounced photonic gap in the shortwave infrared is reported. Due to their unique structure and their high refractive index, these fascinating materials are predicted to possess a complete photonic bandgap in the absence of any long-range order.

Université de Fribourg

Linear-to-branched micelles transition: a rheometry and diffusing wave spectroscopy (DWS) study

Oelschlaeger, C. ; Schopferer, M. ; Scheffold, Frank ; Willenbacher, N.

In: Langmuir, 2009, vol. 25, no. 2, p. 716–723

The frequency-dependent shear modulus of aqueous wormlike micellar solutions of cetylpyridinium chloride (CPyCl) and sodium salicylate (NaSal) has been measured over a broad frequency range from 10⁻² to 10⁶ rad/s using diffusing wave spectroscopy (DWS) based tracer microrheology as well as mechanical techniques including rotational rheometry and oscillatory squeeze flow. Good agreement...