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Université de Fribourg

Pathways and challenges towards a complete characterization of microgels

Scheffold, Frank

In: Nature Communications, 2020, vol. 11, no. 1, p. 4315

Due to their controlled size, sensitivity to external stimuli, and ease-of-use, microgel colloids are unique building blocks for soft materials made by crosslinking polymers on the micrometer scale. Despite the plethora of work published, many questions about their internal structure, interactions, and phase behavior are still open. The reasons for this lack of understanding are the...

Université de Fribourg

Experimental tuning of transport regimes in hyperuniform disordered photonic materials

Aubry, Geoffroy J. ; Froufe-Pérez, Luis S. ; Kuhl, Ulrich ; Legrand, Olivier ; Scheffold, Frank ; Mortessagne, Fabrice

In: Physical Review Letters, 2020, vol. 125, no. 12, p. 127402

We present wave transport experiments in hyperuniform disordered arrays of cylinders with high dielectric permittivity. Using microwaves, we show that the same material can display transparency, photon diffusion, Anderson localization, or a full band gap, depending on the frequency ν of the electromagnetic wave. Interestingly, we find a second weaker band gap, which appears to be related to...

Université de Fribourg

Mapping the unoccupied state dispersions in ${\mathrm{Ta}}_{2}{\mathrm{NiSe}}_{5}$ with resonant inelastic x-ray scattering

Monney, Claude ; Herzog, Marc ; Pulkkinen, Aki ; Huang, Y. ; Pelliciari, Jonathan ; Olalde-Velasco, P. ; Katayama, Naoyuk ; Nohara, Minoru ; Takagi, Hide ; Schmitt, Thorsten ; Mizokawa, Takashi

In: Physical Review B, 2020, vol. 102, no. 8, p. 085148

The transition metal chalcogenide Ta2NiSe5 undergoes a second-order phase transition at Tc=328K involving a small lattice distortion. Below Tc, a band gap at the center of its Brillouin zone increases up to about 0.35 eV. In this work, we study the electronic structure of Ta2NiSe5 in its low-temperature semiconducting phase, using resonant inelastic x-ray scattering (RIXS) at the Ni L3 edge....

Université de Fribourg

Colloidal transformations in ms2 virus particles: driven by ph, influenced by natural organic matter

Watts, Samuel ; Julian, Timothy R. ; Maniura-Weber, Katharina ; Graule, Thomas ; Salentinig, Stefan

In: ACS Nano, 2020, vol. 14, no. 2, p. 1879–1887

Enteric viruses, such as enterovirus, norovirus, and rotavirus, are among the leading causes of disease outbreaks due to contaminated drinking and recreational water. Viruses are difficult to remove from water through filtration based on physical size exclusion—for example by gravity-driven filters—due to their nanoscale size. To understand virus removal in drinking water treatment ...

Université de Fribourg

Accounting for effective interactions among charged microgels

Aguirre-Manzo, L. A. ; Ledesma-Motolinía, Mónica ; Rojas-Ochoa, Luis Fernando ; Trappe, Véronique ; Callejas-Fernández, J. ; Haro-Pérez, Catalina ; González-Mozuelos, P.

In: Physical Review E, 2019, vol. 100, no. 3, p. 032602

We introduce a theoretical approach to describe structural correlations among charged permeable spheres at finite particle concentrations. This theory explicitly accounts for correlations among microions and between microions and macroions and allows for the proposal of an effective interaction among macroions that successfully captures structural correlations observed in poly- N -isopropyl...

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

Colloidal dynamics and elasticity of dense wax particle suspensions over a wide range of volume fractions when tuning the softness by temperature

Yoon, Jiwon ; Scheffold, Frank ; Ahn, Kyung Hyun

In: Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2019, vol. 576, p. 1–8

We report on the colloidal dynamics and rheology of liquid droplet emulsions and solid particle suspensions over a wide range of volume fractions. Diffusing wave spectroscopy and rheometry were utilized to study the micro/macroscale properties of 1-eicosene wax particles dispersed in water. By changing the temperature, the wax droplets change their properties from soft to hard or vice versa,...

Université de Fribourg

Directing single-molecule emission with dna origami-assembled optical antennas

Hübner, Kristina ; Pilo-Pais, Mauricio ; Selbach, Florian ; Liedl, Tim ; Tinnefeld, Philip ; Stefani, Fernando D. ; Acuna, Guillermo P.

In: Nano Letters, 2019, vol. 19, no. 9, p. 6629–6634

We demonstrate the capability of DNA self-assembled optical antennas to direct the emission of an individual fluorophore, which is free to rotate. DNA origami is used to fabricate optical antennas composed of two colloidal gold nanoparticles separated by a predefined gap and to place a single Cy5 fluorophore near the gap center. Although the fluorophore is able to rotate, its excitation and...

Université de Fribourg

Diagram, valence-to-core, and hypersatellite Kβ X-ray transitions in metallic chromium

Zeeshan, Faisal ; Hoszowska, Joanna ; Dousse, Jean-Claude ; Sokaras, Dimosthenis ; Weng, Tsu-Chien ; Alonso-Mori, Roberto ; Kavčič, Matjaz ; Guerra, Mauro ; Sampaio, Jorge Miguel ; Parente, Fernando ; Indelicato, Paul ; Marques, José Pires ; Santos, José Paulo

In: X-Ray Spectrometry, 2019, vol. 48, no. 5, p. 351–359

We report on measurements of the Kβ diagram, valence‐to‐core (VtC), and hypersatellite X‐ray spectra induced in metallic Cr by photon single and double K‐shell ionization. The experiment was carried out at the Stanford Synchrotron Radiation Lightsource using the seven‐crystal Johann‐type hard X‐ray spectrometer of the beamline 6‐2. For the Kβ diagram and VtC transitions, the...

Université de Fribourg

The structural colors of photonic glasses

Schertel, Lukas ; Siedentop, Lukas ; Meijer, Janne-Mieke ; Keim, Peter ; Aegerter, Christof M. ; Aubry, Geoffroy J. ; Maret, Georg

In: Advanced Optical Materials, 2019, p. 1900442

The color of materials usually originates from a combination of wavelength‐dependent absorption and scattering. Controlling the color without the use of absorbing dyes is of practical interest, not only because of undesired bleaching properties of dyes but also regarding minimization of environmental and health issues. Color control without dyes can be achieved by tuning the material's...