Université de Fribourg

Interplay of coarsening, aging, and stress hardening impacting the creep behavior of a colloidal gel

Calzolari, D. C. E. ; Bischofberger, Irmgard ; Nazzani, Francesco ; Trappe, Véronique

In: Journal of Rheology, 2017, vol. 61, no. 4, p. 817–831

We explore the dynamical and mechanical characteristics of an evolving gel in diffusing wave spectroscopy (DWS) and rheometry, aiming to assess how the gel evolution impacts the creep response of the system. Our gel is formed by inducing the aggregation of thermosensitive colloids by a variation in temperature. We find experimental evidence that the long time evolution of this gel is due to...

Université de Fribourg

Impact of volume transition on the net charge of poly-$N$-isopropyl acrylamide microgels

Braibanti, Marco ; Haro-Pérez, Catalina ; Quesada-Pérez, M. ; Rojas-Ochoa, Luis Fernando ; Trappe, Véronique

In: Physical Review E, 2016, vol. 94, no. 3, p. 032601

We explore the electrostatic properties of poly-N-isopropyl acrylamide microgels in dilute, quasi-de-ionized dispersions and show that the apparent net charge of these thermosensitive microgels is an increasing function of their size, the size being conveniently varied by temperature. Our experimental results obtained in a combination of light scattering, conductivity, and mobility...

Université de Fribourg

Viscoelasticity of nematic liquid crystals at a glance

Giavazzi, Fabio ; Crotti, Stefano ; Speciale, Antonio ; Serra, Francesca ; Zanchetta, Giuliano ; Trappe, Véronique ; Buscaglia, Marco ; Bellini, Tommaso ; Cerbino, Roberto

In: Soft Matter, 2014, vol. 10, no. 22, p. 3938–3949

Polarised microscopy is shown to be a powerful alternative to light scattering for the determination of the viscoelasticity of aligned nematic liquid crystals. We perform experiments in a wide range of temperatures by using an adapted version of the recently introduced differential dynamic microscopy technique, which enables us to extract scattering information directly from the microscope...

Université de Fribourg

Hydrophobic hydration of poly-N-isopropyl acrylamide: a matter of the mean energetic state of water

Bischofberger, Irmgard ; Calzolari, D. C. E. ; Rios, Paolo De Los ; Jelezarov, I. ; Trappe, Véronique

In: Scientific Reports, 2014, vol. 4, p. -

The enthalpically favoured hydration of hydrophobic entities, termed hydrophobic hydration, impacts the phase behaviour of numerous amphiphiles in water. Here, we show experimental evidence that hydrophobic hydration is strongly determined by the mean energetics of the aqueous medium. We investigate the aggregation and collapse of an amphiphilic polymer, poly-N-isopropyl acrylamide (PNiPAM), in...

Université de Fribourg

Unexpected Decoupling of Stretching and Bending Modes in Protein Gels

Gibaud, Thomas ; Zaccone, Alessio ; Gado, Emanuela Del ; Trappe, Véronique ; Schurtenberger, Peter

In: Physical Review Letters, 2013, vol. 110, no. 5, p. 058303

We show that gels formed by arrested spinodal decomposition of protein solutions exhibit elastic properties in two distinct frequency domains, both elastic moduli exhibiting a remarkably strong dependence on volume fraction. Considering the large difference between the protein size and the characteristic length of the network we model the gels as porous media and show that the high and low...

Université de Fribourg

Ultra-long range correlations of the dynamics of jammed soft matter

Maccarrone, S. ; Brambilla, G. ; Pravaz, O. ; Duri, Agnès ; Ciccotti, M. ; Fromental, J.-M. ; Pashkovski, E. ; Lips, A. ; Sessoms, David ; Trappe, Véronique ; Cipelletti, Luca

In: Soft Matter, 2010, vol. 6, no. 21, p. 5514-5522

We use photon correlation imaging, a recently introduced space-resolved dynamic light scattering method, to investigate the spatial correlation of the dynamics of a variety of jammed and glassy soft materials. Strikingly, we find that in deeply jammed soft materials spatial correlations of the dynamics are quite generally ultra-long ranged, extending up to the system size, orders of magnitude...

Université de Fribourg

Unexpected spatial distribution of bubble rearrangements in coarsening foams

Sessoms, David A. ; Bissig, Hugo ; Duri, Agnès ; Cipelletti, Luca ; Trappe, Véronique

In: Soft Matter, 2010, vol. 6, no. 13, p. 3030-3037

Foams are ideal model systems to study stress-driven dynamics, as stress-imbalances within the system are continuously generated by the coarsening process, which, unlike thermal fluctuations, can be conveniently quantified by optical means. However, the high turbidity of foams generally hinders the detailed study of the temporal and spatial distribution of topological bubble rearrangement events,...

Université de Fribourg

Arrested fluid-fluid phase separation in depletion systems: Implications of the characteristic length on gel formation and rheology

Conrad, J. C. ; Wyss, H. M. ; Trappe, Véronique ; Manley, S. ; Miyazaki, K. ; Kaufman, L. J. ; Schofield, A. B. ; Reichman, D. R. ; Weitz, D. A.

In: Journal of Rheology, 2010, vol. 54, no. 2, p. 421-438

We investigate the structural, dynamical, and rheological properties of colloid-polymer mixtures in a volume fraction range of Φ=0.15–0.35. Our systems are density-matched, residual charges are screened, and the polymer-colloid size ratio is ~0.37. For these systems, the transition to kinetically arrested states, including disconnected clusters and gels, coincides with the fluid-fluid phase...

Université de Fribourg

Rheology and structural arrest of casein suspensions

Dahbi, Louisa ; Alexander, M. ; Trappe, Véronique ; Dhont, J.K.G. ; Schurtenberger, Peter

In: Journal of Colloid and Interface Science, 2010, vol. 342, no. 2, p. 564-570

The rheology of milk powder suspensions is investigated up to very high concentrations, where structural arrest occurs. The main component of the milk powder investigated is casein, so that the suspensions can be regarded as casein suspensions. Four concentration regimes are identified. For effective casein volume fractions less than 0.54 the concentration dependence of the zero-shear viscosity...

Université de Fribourg

Multiple dynamic regimes in concentrated microgel systems

Sessoms, David A. ; Bischofberger, Irmgard ; Cipelletti, Luca ; Trappe, Véronique

In: Philosophical Transactions of the Royal Society A, 2009, vol. 367, no. 1909, p. 5013-5032

We investigate dynamical heterogeneities in the collective relaxation of a concentrated microgel system, for which the packing fraction can be conveniently varied by changing the temperature. The packing fraction-dependent mechanical properties are characterized by a fluid–solid transition, where the system properties switch from a viscous to an elastic low-frequency behaviour. Approaching this...