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Your search keyword '"Ruzicka B"' showing total 6 results
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6 results on '"Ruzicka B"'

1. Observation of empty liquids and equilibrium gels in a colloidal clay.

Author

Angelini, R., Ruzicka, B., Zaccarelli, E., Zulian, L., Sztucki, M., Moussaïd, A., Narayanan, T., and Sciortino, F.

Subjects
*LIQUID-liquid interfaces, *CLAY, *COLLOIDS, *X-ray scattering, *PHASE separation method (Engineering), *CHEMICAL equilibrium, *SUSPENSIONS (Chemistry)
Abstract

The observation of empty liquids and equilibrium gels in a complex colloidal clay has been obtained through dilution experiments, small angle x ray scattering measurements and extensive numerical simulations. We investigate the behaviour of dilute suspensions of a synthetic clay, Laponite, for low concentrations, Cw ≤ 1%, to waiting times significantly longer than those previously studied. A significant evolution takes place on the year timescale and samples undergo a clear phase separation process which terminates at a finite clay concentration Cw = 1%, above which they remain in a homogeneous arrested state. Moreover, the slow aging dynamics peculiar of Laponite suspensions drive an arrest transition through a very slow rearrangement, so that equilibrium gels are formed. The observed features are similar to those predicted in simple models of patchy particles, suggesting that Laponite forms an (arrested) empty liquid at very low concentrations. [ABSTRACT FROM AUTHOR]

Published
2013
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2. Influence of an adsorbing polymer on the aging dynamics of Laponite clay suspensions.

Author

Zulian, L., Ruzicka, B., and Ruocco, G.

Subjects
*POLYMERS, *NUCLEAR reactions, *POLYETHYLENE oxide, *MOLECULAR weights, *CLAY
Abstract

Clay-polymer dispersions in aqueous solutions are of great interest due to their industrial applications and intriguing physical properties. Aqueous solutions of bare Laponite particles age spontaneously, from an ergodic to a non-ergodic state, in a time varying from hours to months depending on Laponite concentration. When a polymer species, such as polyethylene oxide (PEO), is added to the solution, it weakly adsorbs on clay particle surfaces modifying the effective interaction potential between Laponite particles. A dynamic light-scattering study was performed to investigate the effect of polymer on the aging dynamics of the system by varying the polymer concentration at a fixed polymer molecular weight (Mw = 200,000 g/mol). The results show that arresting phenomena between clay particles are hindered when PEO is added and, thus, a slowing of the aging dynamics with increasing PEO concentration is observed. A possible mechanism is progressive coverage of the clay surface by polymers, which grow with increasing PEO concentration. [ABSTRACT FROM AUTHOR]

Published
2008
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3. Ageing dynamics in Laponite dispersions at various salt concentrations.

Author

Ruzicka, B., Zulian, L., and Ruocco, G.

Subjects
*SALT, *DISPERSION (Chemistry), *SALTS, *PHOTONS, *CLAY, *WATER
Abstract

The ageing dynamics of a charged colloidal system, Laponite suspended in water, have been investigated by photon correlation technique. The samples covered a novel and very wide range of clay concentrations (Cw = 0.3-3.1 wt%) and four different NaCl concentrations (Cs = 1 × 10-4 M, 1 × 10-3 M, 2 × 10-3 M and 5 × 10-3 M) and were studied to investigate the phase diagram, which has been a subject of discussion in recent literature. A clear picture of the Laponite phase diagram has been obtained. The measurements show the existence of two different dynamical routes to reach a final arrested state and the presence of a transition line between them in the Cw-Cs plane. [ABSTRACT FROM AUTHOR]

Published
2007
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4. Gel and glass transition in fragile colloidal clays.

Author

Angelini, R., Ruocco, G., and Ruzicka, B.

Subjects
*SUPERCOOLED liquids, *COLLOIDAL suspensions, *COLLOIDS, *GLASS transitions, *CLAY
Abstract

DynamicLightScattering(DLS)measurements were performed on colloidal suspensions ofLaponite atdiffer- ent concentrations in the range Cw = (1.5 3.0)%. The slowing down of the dynamics induced by aging was monitored byfollowingthetemporal evolution of autocorrelation functionsatdifferentconcentrations towards the gel and glass transition. Exploiting analogies with supercooled liquids approaching their glass transitions, an Angell plot for the structural relaxation times was drawn. Finally, the fragility ofLaponite suspensions at differentconcentrations, in differentsolvents, attwosaltconcentrationsand with theaddition of a polymerwas reported and discussed. [ABSTRACT FROM AUTHOR]

Published
2019
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5. Neutron diffraction study of aqueous Laponite suspensions at the NIMROD diffractometer

Author

Maria Antonietta Ricci, L. Zulian, Fabio Bruni, Barbara Ruzicka, Roberta Angelini, Valentina Tudisca, Alan K. Soper, Ernesto Scoppola, Valentina, Tudisca, Bruni, Fabio, Ernesto, Scoppola, Roberta, Angelini, B., Ruzicka, L., Zulian, A. K., Soper, Ricci, Maria Antonietta, Tudisca, V, Bruni, F, Scoppola, E, Angelini, R, Ruzicka, B, Zulian, L, Soper, A, and Ricci, M

Subjects
Models, Molecular, Length scale, Mesoscopic physics, Time Factors, Materials science, business.industry, Scattering, Silicates, Neutron diffraction, Molecular Conformation, Water, colloid, soft matter, SANS, laponite, aging, out of equilibrium sistems, phase transitions, gel, glass, Small-angle neutron scattering, Condensed Matter::Soft Condensed Matter, Neutron Diffraction, Colloid, FIS/01 - FISICA SPERIMENTALE, Optics, Suspensions, Chemical physics, Nimrod, LAPONITE DISPERSIONS, GELS, SUSPENSIONS, POLYMER, STATES, CLAY, business, Monte Carlo Method, Diffractometer
Abstract

The process of dynamical arrest, leading to formation of different arrested states such as glasses and gels, along with the closely related process of aging, is central for both basic research and technology. Here we report on a study of the time-dependent structural evolution of two aqueous Laponite clay suspensions at different weight concentrations. Neutron diffraction experiments have been performed with the near and intermediate range order diffractometer (NIMROD) that allows studies of the structure of liquids and disordered materials over a continuous length scale ranging from 1 to 300 angstrom, i.e., from the atomistic to the mesoscopic scales. NIMROD is presently a unique diffractometer, bridging the length scales traditionally investigated by small angle neutron scattering or small angle x-ray scattering with that accessible by traditional diffractometers for liquids. Interestingly, we have unveiled a signature of aging of both suspensions in the length scale region of NIMROD. This phenomenon, ascribed to sporadic contacts between Laponite platelets at long times, has been observed with the sample arrested as gel or as repulsive glass. Moreover, water molecules within the layers closest to Laponite platelets surface show orientational and translational order, which maps into the crystalline structure of Laponite.

Published
2014
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6. Isotopic effect on the aging dynamics of a charged colloidal system

Author

Roberta Angelini, Maria Antonietta Ricci, Barbara Ruzicka, Valentina Tudisca, Tudisca, V, Ricci, Maria Antonietta, Angelini, R, and Ruzicka, B.

Subjects
Interaction potentials, General Chemical Engineering, Experimental techniques, Isotopic substitution, Mineralogy, Dynamical behaviors, Colloid, Master curve, Dynamic light scattering, Stretching parameters, Water molecule, Molecule, CLAY, Colloidal system, Isotopic effects, GELS, Aqueous solution, Chemistry, Dynamics (mechanics), Relaxation (NMR), General Chemistry, Solvent, Colloidal gels, LAPONITE DISPERSIONS, Deuterium, Chemical physics, Aging behavior, Aging dynamics, Laponite suspensions
Abstract

A dynamic light scattering (DLS) investigation of the isotopic H/D substitution on water molecules in aqueous Laponite suspensions is reported for two Laponite weight concentrations (C-w = 1.5% and C-w = 3.0%). Increasing the deuterium percentage results in a slowing down of the dynamics for both concentrations, although the aging behavior of the suspensions is not qualitatively modified by the isotopic substitution. A scaling law for the isotopic effect is found. The relaxation times and the stretching parameters collapse on two distinct master curves, indicating that the two previously found dynamical behaviors of colloidal gels and glasses are preserved. These results may facilitate a large variety of experimental techniques and further theoretical investigations about the role of the solvent in determining the interaction potential.

Published
2012
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