Liquids and Soft Matter Group
Our interest is the experimental research of Liquids and Soft Matter (i.e. all those physical systems whose properties are intermediate between the liquid and solid states). Some relevant examples are: glasses, liquid crystals, polymers, colloids, gels, membranes, etc.. All of these materials, although they belong to very different matter classes, share an important common physical characteristic: the molecules self-organize on spatial mesoscopic lengths (from nanometers to micrometers), realizing ordered structures that generate a coherent dynamics.
At the Dpt. of Physics and Astronomy (DIFA) and at the Lab. European for Non-Linear Spectroscopy (LENS), we study the structure and dynamics of these materials by experimental techniques of different types (for example, laser, dielectric and neutron spectroscopy) to measure their properties (eg. molecular vibrations and structural relaxation processes) under variable thermodynamic conditions (temperature and pressure). The data are interpreted by means of theoretical models and numerical simulations. These studies represent the state of the art in soft matter research; they are innovative, both for the experimental and theoretical aspects.
for contact:
E. Guarini, guarini@fi.infn.it and R.Torre, renato.torre@unifi.it
Italian
Il nostro interesse è la ricerca sperimentale dei Liquidi e della Materia Soffice, ovvero di quei sistemi fisici le cui proprietà sono intermedie tra lo stato liquido e quello solido. Alcuni esempi particolarmente significativi sono: i vetri, i cristalli liquidi, i polimeri, i colloidi, i gel, le membrane, ecc. Tutti questi materiali, nonostante abbiano una tipologia molto diversificata, condividono un'importante caratteristica fisica comune: le molecole, che le compongono, si auto-organizzano su lunghezze spaziali mesoscopiche (dai nanometri ai micrometri) realizzando strutture ordinate e dinamiche coerenti.
Al Dip. di Fisica ed Astronomia (DIFA) e al Lab. Europeo di Spettroscopie Non-Lineari (LENS) studiamo la struttura e la dinamica dei questi materiali tramite tecniche sperimentali di diverso tipo (ad esempio spettroscopia laser, dielettrica e neutronica) per misurare le proprietà (ad esempio le vibrazioni molecolari e processi di rilassamento strutturale) al variare delle condizioni termodinamiche (temperatura e pressione). I dati vengono interpretati mediante modelli teorici e simulazioni numeriche. Questi studi sono innovativi, sia per le tecniche sperimentali utilizzate che per gli aspetti teorici, e rappresentano lo stato dell’arte in questo settore della ricerca.
.... un piccolo video per mostrare l'esistenza dell' Acqua Metastabile : L' acqua che non congela ...subito.
New Researches and Highlights
Protein Self-Assembling Dynamics
Multi-length scale structural investigation of lysozyme self-assembly
S. Catalini, ...., R. Mezzenga and Renato Torre. iScience 25 (2022) 104586
Probing Globular Protein Self-Assembling Dynamics by Heterodyne Transient Grating Experiments
S. Catalini, A. Taschin, P. Bartolini, P. Foggi and Renato Torre. Appl. Sci. 9 (2019) 405
Self-assembling phenomena of biomolecules are characterized by different steps, in which the conformational rearrangements and intermolecular associations drive the formation of stable structures of increasing complexity (e.g. amyloid fibrils, hydrogel networks, ...). Protein-based hydrogels have recently received great attention since they can be the key to develop novel biomaterials. In fact, hydrogels have the capability to retain inside their matrix a great amount of water (up to 97%), which make these materials similar to biological tissues. Protein hydrogels are therefore of great interest in many fields spanning from the medical to the nanotechnological. We undertaken a systematic study of self-assembling phenomena taking place in biologic samples by means of different spectroscopic investigation, e.g HD-TG, OKE of THz measurements as a function of the environmental conditions.
Transport phenomena at the nanoscale investigated by pulsed x-ray
Hard X-ray transient grating spectroscopy on bismuth germanate
Jérémy R. Rouxel et al.
Nature Photonics, https://doi.org/10.1038/s41566-021-00797-9
To date, the modeling and understanding of transport phenomena at the nanoscale remains an open problem in materials science. The poor understanding of these phenomena is strongly due to the lack of experimental investigations capable of probing the transport processes on such a reduced length scale. This requires the use of short wavelength radiation, and in particular X-rays. We achieved, as members of an international consortium of researchers, that succeeded in creating and using a 4-wave X-ray mixing technique with a sub-picosecond time and sub-micrometric spatial resolutions. This first demonstration of hard X-ray transient grating spectroscopy (XTG) opens the way to exciting and novel developments. Indeed, hard X-ray TG is uniquely suited to investigate nanoscale transport phenomena in bulk and nanostructured materials.
Random Laser and Innovative Radiation Sources
Distinct design for a random laser based on a composite material consisting of an elastomeric liquid crystal with embedded TiO2 nanoparticles. Random lasing action can be controlled by an external, non-contact light stimulus; this induces a rearrangement of the elastomeric liquid crystals which moves the laser body in and out of the focal plane of a pump laser, pushing its emissionabove or below the lasing threshold.
Perspectives and recent advances in super-resolution spectroscopy: Stochastic and disordered-based approaches
A. Boschetti, L. Pattelli, R. Torre, D.S. Wiersma,
Applied Physics Letters, 120 (2022) 250502.
Spectral super-resolution spectroscopy using a random laser
A. Boschetti, A. Taschin, P. Bartolini, A. Kumar Tiwari, L. Pattelli, R. Torre and D. S. Wiersma
Nature Photonics 4, pages177–182 (2020)
Remote control of liquid crystal elastomer random laser using external stimuli
A-K. Tiwari, L. Pattelli, Renato Torre and D.-S. Wiersma.
Dynamics of Liquid Water: recent experimental investigations
Modification of local and collective dynamics of water in perchlorate
solution, induced by pressure and concentration
C. Calvagna , ..., and Renato Torre
Journal of Molecular Liquids 337 (2021) 116273
Pressure Effects on Water Dynamics by Time-Resolved Optical Kerr Effect
A.Taschin, P. Bartolini, S. Fanetti, A.Lapini, M.Citroni, R.Righini, R.Bini and Renato Torre
J. Phys. Chem. Lett. 11 (2020) 3063
Vibrational Spectroscopy and Dynamics of Water
Perakis, F.; Marco, L.; Shalit, A.; Tang, F.; Kann, Z. R.; Kuhne, T. D.; Torre, R.; Bonn, M.; Nagata, Y.
Chem Rev 116 (2016), 7590–7607.
Optical Kerr Effect of Liquid and Supercooled Water: The Experimental and Data Analysis Perspective.
A. Taschin, P. Bartolini, R. Eramo, R. Righini, and R. Torre.
Journal of Chemical Physics,141 (2014) 084507.
Evidence of two distinct local structures of water from ambient to supercooled conditions.
A.Taschin,P. Bartolini, R. Eramo, R. Righini, and R. Torre,
The liquid and supercooled states of water show a series of anomalies whose nature is debated. A key role is attributed to the formation of structural aggregates induced by critical phenomena occurring deep in the supercooled region; the nature of the water anomalies and of the hidden critical processes remains elusive. We used a time-resolved optical Kerr effect investigation of the vibrational dynamics and relaxation processes in supercooled bulk water.
Recently, we presented an overview of time-resolved vibrational spectroscopic studies of liquid water from ambient conditions to the supercooled state. The structure and dynamics of the complex hydrogen-bond network formed by water molecules are discussed, as well as the dissipation mechanism of vibrational energy throughout this network. A broad range of water investigations are addressed:infrared and Raman spectroscopy, femtosecond pump−probe, photon-echo, optical Kerr effect, sum-frequency generation, and two-dimensional infrared spectroscopic studies. By comparison of the complementary aspects probed by various linear and nonlinear spectroscopic techniques, a coherent picture of water dynamics and energetics emerges.
Polymer-coated gold nanoparticle dynamics & Bayesian analysis of neutron data
Model-free description of polymer-coated gold nanoparticle dynamics in aqueous solutions obtained by Bayesian analysis of neutron spin echo data
Alessio De Francesco, Luisa Scaccia, R. Bruce Lennox, Eleonora Guarini, Ubaldo Bafile, Peter Falus, and Marco Maccarini
Neutron spin echo study of the nanosecond dynamics of polyethylene glycol (PEG) functionalized gold nanoparticles of different molecular weights dissolved in D2O combined with a description of time correlation functions in terms of exponential terms and a Bayesian analysis of the statistical significance of the exponential representation allow to disentangle the translational diffusion of the nanoparticles from the internal dynamics of the polymers grafted to them. By comparing the results of PEGcoated nanoparticles with those obtained in PEG2000 solutions, it is possible to show that the polymer corona relaxation follows a pure exponential decay in agreement with the behavior predicted by coarse grained molecular dynamics simulations and theoretical models. In particular, a fine-structure analysis of the dynamical complexity of the system is made possible on a well-grounded statistical basis according to the available data without the risk of overparametrizations. This approach is an effective tool that can be used in general to provide an unbiased interpretation of neutron spin echo data or whenever spectroscopic techniques yield time relaxation data curves.
Dynamics of simulated "Boltzmann" quantum fluids
Quantum simulation techniques like ring polymer molecular dynamics (RPMD) allow studies of the Kubo velocity autocorrelation function (KVAF) of a moderately quantum fluid as para-hydrogen. By applying an exponential mode analysis we find that the dynamical processes establishing the time behavior of the KVAF display the same nature as those already observed in high-density classical fluids. This result permitted us to demonstrate that the exponential mode decomposition is a unique tool to identify which dynamical processes lead to one of the most notable properties of quantum fluids: the large value of the mean kinetic energy (KE) per particle <K> and the importance of the zero-temperature quantum effects in determining it.
It is evident that longitudinal modes (labelled as C2 in the figure) have a net predominance in the dynamical origin of both the zero-point part <K>0 and the total kinetic energy <K>. As it can be observed, <K>0 and <K> are not the sum of positive contributions, but result from a cancellation of effects. In particular, <K>0 is practically accounted for by C2 alone, owing to the opposite trends of the transverse modes contribution (C3) and of diffusive processes (R1), nearly compensating each other. The negative contribution of R1 may be related to the fact that this fast decaying diffusive mode contrasts the particles’ confinement, which becomes less effective as the temperature is raised and counteracts the general trend of the KE. The temperature behavior of the R1 component is consistent with a diffusion process: R1 is found to become more negative as T grows; thus the more diffusion grows with T, the larger will be the reduction of confinement (and of <K>0) brought about by R1 with its negative sign.
Our study highlighted that longitudinal sound waves are the most relevant dynamical processes contributing to the manifestation of the Heisenberg effect at the origin of the large zero point and total KE values of a molecule in a quantum fluid.
Dynamical Origin of the Total and Zero-Point Kinetic Energy in a Quantum Fluid
Eleonora Guarini, Martin Neumann, Ubaldo Bafile, Stefano Bellissima, and Daniele Colognesi
Phys. Rev. Lett. 123, 135301 (2019).
Shear dynamics of liquid silver
The propagation of compression waves in a liquid is a well-established phenomenon, responsible for the travelling of sound in it. More debated is the case of shear waves, which are in principle not allowed to propagate in an ideal liquid. This is an important issue relating to the innermost nature of the liquid state. We therefore decided to combine neutron and numerical techniques to examine the existence of shear excitations in liquid silver and the conditions under which it is possible to detect them.
Ab initio molecular dynamics (AIMD) simulations can probe the dynamics at larger wavevectors Q than those accessible experimentally, and their good agreement with neutron scattering data at smaller Qs makes it possible to investigate the dynamic structure factor S(Q,w) of liquid Ag in a broader Q range with confidence. Doing so, we found that a transverse component clearly sets on at wavevectors above the maximum reached by the measurements (Q ~ 16 nm-1).
Neutron scattering and ab initio simulation: essential and inseparable tools for studying liquids dynamics such as shear waves in silver . E. Guarini, F. Barocchi, A. De Francesco, F. Formisano, A. Laloni, U. Bafile, B. G. del Rio, D. J. González, L. E. González. Scientific Highlight in the ILL Annual Report 2020, Spectroscopy, p. 58-59 (2021). Phys. Rev. E 102, 054210 (2020)
Searching for a second excitation in the inelastic neutron scattering spectrum of a liquid metal: a Bayesian analysis. Alessio De Francesco, Ubaldo Bafile, Alessandro Cunsolo, Luisa Scaccia, and Eleonora Guarini. Sci. Rep 11, 13974 (2021).
Dynamics of liquid methanol and the role of hydrogen bond
Switching off hydrogen-bond driven excitation modes in liquid methanol
Stefano Bellissima, Miguel Angel González, Ubaldo Bafile, Alessandro Cunsolo, Ferdinando Formisano, Simone De Panfilis, and Eleonora Guarini
Hydrogen bonding plays an essential role on intermolecular forces, and consequently on the thermodynamics of materials defined by this elusive bonding character. It determines the property of a vital liquid as water as well as many processes crucial for life. The longstanding controversy on the nature of the hydrogen bond (HB) can be settled by looking at the effect of a vanishing HB interaction on the microscopic properties of a given hydrogen-bonded fluid. This task suits the capabilities of computer simulations techniques, which allow to easily switch off HB interactions. We used molecular dynamics to study the microscopic properties of methanol, a prototypical HB liquid. Fundamental aspects of the dynamics of methanol at room temperature were contextualised only very recently and its rich dynamics was found to have striking analogies with that of water. Most importantly, the computational ability to switch on and off hydrogen bonds permitted us to identify which, among four characteristic modes, have a pure HB-origin. This clarifies the role of hydrogen bonds in liquid dynamics, disclosing new research opportunities and unexplored interpretation schemes.