Institute for Complex Systems - Sapienza - CNR

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ISC Sapienza Nicoletta Gnan
Nicoletta Gnan Profile Page
Nicoletta Gnan
9 months ago

Activities

Modeling Microgels

Microgels are soft particles individually made by cross-linked polymer networks which are widely used as a colloidal model system thanks to their swelling properties and their responsivity to external control parameters such temperature or pH. Their internal architecture affects the effective interactions between microgels, especially at high densities, where the polymeric nature of the particle becomes important due to strong interpenetration and entanglements. To go beyond the simple models available so far we have recently synthesized microgels in-silico using different preparation protocols. The aim of the research is to design and investigate numerically, coarse-grained microgels with properties comparable to the experimental ones. This work is done within the ERC project MIMIC whose main objectives are

 

  • To synthesize coarse-grained microgel particles with the correct swelling behaviour and elasticity;
  • To obtain accurate effective interactions between monomer-resolved microgel particles;
  • To predict the structure, dynamics, and rheology of bulk microgel suspensions, based on these effective potentials, and compare the results with experiments and existing theories;

N. Gnan, L. Rovigatti, M. Bergman, E. Zaccarelli, Macromol. 50 (21), 8777 (2017)

F. Camerin, N. Gnan, L. Rovigatti, E. Zaccarelli arXiv preprint arXiv:1807.07893 (2018)

L. Rovigatti, N. Gnan, ., Ninarello, E. Zaccarelli arXiv preprint arXiv:1808.04769 (2018)

N Gnan, E Zaccarelli arXiv preprint arXiv:1806.04788 (2018)

 

Complex Effective Interactions:

Colloidal particles can be treated as super- atoms moving in a continuum (solvent) in the framework of statistical mechanics. They interact with effective potentials that can be tuned arbitrarily by changing the properties of the particle (e.g. shape, architecture, heterogenous surface) or by varying externally the conditions of the solutions in which they are suspended. In this way, they experience effective interactions mediated by the solvent and show phenonema that are not found in atomic or molecular systems.The simplest way to control the interactions between colloids is to add smaller particles (cosolute) in the solution, which originate so-called depletion interactions. By tuning the properties of the co-solutes, unusual effects can be found. For instance novel effective interactions can be found when co-solute particles are  (I) close to a critical point (ii) close to percolation (iii) close to the liquid- nematic transition. My research focuses on investigating novel mechanisms to induce effective interactions in colloidal solutions by means of numerical simulations.

N. Gnan et al. Soft Matter 8 (2012)

N. Gnan et al., Nat. Comm.. 5,  3267 (2014)

L. Rovigatti, N.Gnan et al. Soft Matter 11 (4), 692 (2015)

N. Gnan. et al. Soft Matter 12, 9649 (2016)

N. Gnan et al. Soft Matter 13, 6051 (2017)

 

 

Patchy Colloids

Soft matter provides a ideal breeding ground to understand self-assembly at the micro-scale thanks to the advances in the synthesis of particles with specific properties. Such particles play the role of "building blocks” able to assemble in targeted structures through complex processes. Among this arsenal of colloidal building blocks, patchy particles,  i.e. particles with  directional and selective interactions,  have become one of the favourite model systems for scientists since they allow to go beyond spherical interactions, providing valence to colloids, and to develop  effective bottom-up approaches to fully control their self-assembly for relevant condensed-matter physics problems. Patchy particles can give rise to a plethora of states: crystals with open structures, arrested and equilibrium gels, nematic phases, polymerized fluids, tubes, lamellae etc. Besides studying the non-trivial phase behavior of these kind of particles, I am interested in their self-assembly in confined environments such close to a wall or a slit pore or in between larger particles. Patchy particles are also promising candidates as model systems to investigate naturally occurring systems that self-assemble into structures thanks to their anisotropic interactions. An example are globular proteins that behave as short-range attractive colloids, having a metastable gas-liquid critical point and being able to form, besides the crystal phase, also metastable kinetically arrested gels and glasses. However it is also known that the surface of proteins is covered by heterogeneous interacting sites, each with its own bonding strenght, that makes the interaction anisotropic and selective. In this respect, special models of patchy particles have shown to correctly reproduce the liquid-gas phase behaviour of globlular proteins. Yet, different proteins own different parameters such as number of patches, interaction strengths and patches position, that are essential to know for developing the corresponding patchy model.

N. Gnan, et al., JCP 137 (8), 084704 (2012)

M.K. Quinn, N. Gnan et al., PCCP 17 (46), 31177-31187 (2015)

N. Gnan et al. Soft Matter 13, 6051 (2017)

 

Active Matter:

Active matter comprises all those systems that self-propel taking energy from their environment. Notable examples of active systems are abundant in nature: motile cells, living bacteria, flocks of birds and school of fishes are just few examples; moreover  current technologies allow to realise non-living active systems such as gold-capped janus particles that propel by catalyzing hydrogen peroxide dissociation in solution or granular tapered rods that becomes motile thanks to an underlying vibrated plate. Differently from equilibrium systems, the non-equilibrium nature of active matter leads to a plethora of fascinating phenomena including accumulations close to obstacles, swarming, coherent turbulent-like motion, non-Newtonian rheology, violation of the fluctuation-dissipation theorem. Another remarkable example is the so called “motility induced phase separation” (MIPS) which has received in the last few years great attention in the active matter community. Recently I have contributed to the development of the multidimensional unified colored noise approximation (MUCNA) which maps  the active particle system into an equilibrium system with complex many-body interactions. MUCNA  is the only currently available theory that allows to derive a microscopic expression for the system free-energy, which determines formally the full thermodynamic properties of the system. It has been demonstrated that this free energy contains truly non-equilibrium terms which are directly linked to the particle velocities;  configurations with low velocities corresponding to denser particle arrangements, are favoured and hence particles tends to phase separate. Thus MUCNA is able to predict motility-induced phase separation; at the mean field level the theory predicts a gas-liquid phase separation at low densities in purely repulsive systems.

C. Maggi, U.M.B. Marconi, N. Gnan, R. Di Leonardo, Sci. Rep. 5, 10742 (2015)

U.M.B. Marconi, N. Gnan, et al. Sci. Rep. 6, 23297 (2016)

 

Here you can download a brief CV with a complete list of my publications

Contact Info

Nicoletta Gnan
...
+390649913459
Researcher

I am at the Department of Physics ,Fermi Building, room 103, of 'Sapienza' University of Rome.

Here you can find a map of our locations at and near Sapienza.

Research



This user has no published articles.