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Dive into the research topics where Roberta Angelini is active.

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Featured researches published by Roberta Angelini.


Nature Materials | 2011

Observation of empty liquids and equilibrium gels in a colloidal clay

Barbara Ruzicka; Emanuela Zaccarelli; Laura Zulian; Roberta Angelini; Michael Sztucki; Abdellatif Moussaid; Theyencheri Narayanan; Francesco Sciortino

The relevance of anisotropic interactions in colloidal systems has recently emerged in the context of the rational design of new soft materials. Patchy colloids of different shapes, patterns and functionalities are considered the new building blocks of a bottom-up approach toward the realization of self-assembled bulk materials with predefined properties. The ability to tune the interaction anisotropy will make it possible to recreate molecular structures at the nano- and micro-scales (a case with tremendous technological applications), as well as to generate new unconventional phases, both ordered and disordered. Recent theoretical studies suggest that the phase diagram of patchy colloids can be significantly altered by limiting the particle coordination number (that is, valence). New concepts such as empty liquids—liquid states with vanishing density—and equilibrium gels—arrested networks of bonded particles, which do not require an underlying phase separation to form—have been formulated. Yet no experimental evidence of these predictions has been provided. Here we report the first observation of empty liquids and equilibrium gels in a complex colloidal clay, and support the experimental findings with numerical simulations.


Physical Review Letters | 2010

Competing interactions in arrested states of colloidal clays

Barbara Ruzicka; Laura Zulian; Emanuela Zaccarelli; Roberta Angelini; Michael Sztucki; Abdellatif Moussaid; G. Ruocco

Using experiments, theory and simulations, we show that the arrested state observed in a colloidal clay at high concentrations is stabilized by screened Coulomb repulsion (Wigner glass). Dilution experiments allow us to distinguish this disconnected state, which melts upon addition of water, from a low-concentration gel state, which does not melt. Theoretical modeling and simulations at high concentrations reproduce the measured small angle x-ray scattering static structure factors and confirm the long-range electrostatic nature of the arrested structure. These findings are attributed to the different time scales controlling the competing attractive and repulsive interactions.


Nature Communications | 2014

Glass–glass transition during aging of a colloidal clay

Roberta Angelini; Emanuela Zaccarelli; Flavio Augusto de Melo Marques; Michael Sztucki; Andrei Fluerasu; G. Ruocco; Barbara Ruzicka

Colloidal suspensions are characterized by a variety of microscopic interactions, which generate unconventional phase diagrams encompassing fluid, gel and glassy states and offer the possibility to study new phase and/or state transitions. Among these, glass-glass transitions are rare to be found, especially at ambient conditions. Here, through a combination of dilution experiments, X-ray photon correlation spectroscopy, small angle X-ray scattering, rheological measurements and Monte Carlo simulations, we provide evidence of a spontaneous glass-glass transition in a colloidal clay. Two different glassy states are distinguished with evolving waiting time: a first one, dominated by long-range screened Coulombic repulsion (Wigner glass) and a second one, stabilized by orientational attractions (Disconnected House of Cards glass), occurring after a much longer time. These findings may have implications for heterogeneously charged systems out-of-equilibrium and for applications where a fine control of the local order and/or long term stability of the amorphous materials are required.


Physical Review E | 2008

Arrested state of clay-water suspensions: gel or glass?

Barbara Ruzicka; L. Zulian; Roberta Angelini; Michael Sztucki; Abdellatif Moussaid; G. Ruocco

The aging of a charged colloidal system has been studied by small-angle x-ray scattering, in the exchanged momentum range Q=0.03-5 nm(-1) , and by dynamic light scattering, at different clay concentrations (C(w)=0.6-2.8%) . The static structure factor S(Q) has been determined as a function of both aging time and concentration. This is the direct experimental evidence of the existence and evolution with aging time of two different arrested states in a single system simply obtained only by changing its volume fraction: an inhomogeneous state is reached at low concentrations, while a homogeneous one is found at high concentrations.


Physical Review Letters | 2006

High-frequency dynamics in metallic glasses

T. Scopigno; J.-B. Suck; Roberta Angelini; Francesco Albergamo; G. Ruocco

Using inelastic x-ray scattering we studied the collective dynamics of the glassy alloy Ni33Zr67 in the first pseudo-Brillouin-zone, an energy-momentum region still unexplored in metallic glasses. We determine key properties such as the momentum transfer dependence of the sound velocity and of the acoustic damping, discussing the results in the general context of recently proposed pictures for acoustic dynamics in glasses. Specifically, we demonstrate the existence in this strong glass of well defined (in the Ioffe-Regel sense) acoustic-like excitations well above the boson peak energy.


Physical Review B | 2004

Microscopic dynamics and relaxation processes in liquid Hydrogen Fluoride

Roberta Angelini; P. Giura; D. Fioretto; G. Monaco; G. Ruocco; F. Sette

Inelastic x-ray scattering and Brillouin light scattering measurements of the dynamic structure factor of liquid hydrogen fluoride have been performed in the temperature range


Journal of Chemical Physics | 2007

High frequency dynamics and structural relaxation process in liquid ammonia

P. Giura; Roberta Angelini; Frédéric Datchi; G. Ruocco; F. Sette

T=214\div 283 K


RSC Advances | 2012

Isotopic effect on the aging dynamics of a charged colloidal system

V. Tudisca; Maria Antonietta Ricci; Roberta Angelini; Barbara Ruzicka

. The data, analysed using a viscoelastic model with a two timescale memory function, show a positive dispersion of the sound velocity


Physical Review E | 2008

Phase diagram of a solution undergoing inverse melting

Roberta Angelini; G. Ruocco; S. De Panfilis

c(Q)


Journal of Chemical Physics | 2015

Local structure of temperature and pH-sensitive colloidal microgels

Valentina Nigro; Roberta Angelini; Monica Bertoldo; Fabio Bruni; Valter Castelvetro; Maria Antonietta Ricci; Sarah Rogers; Barbara Ruzicka

between the low frequency value

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Barbara Ruzicka

Sapienza University of Rome

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G. Ruocco

Sapienza University of Rome

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F. Sette

European Synchrotron Radiation Facility

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P. Giura

European Synchrotron Radiation Facility

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Simona Sennato

Sapienza University of Rome

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