Avviso di Videoconferenza: Claudio Zannoni "Modelling liquid crystals in the bulk and close to their boundaries"

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Data evento
Data inizio evento: 
02/02/2015 - 15:00
Data fine evento: 
02/02/2015 - 16:00
Data pubblicazione evento
Pubblicato il: 
28/01/2015

AVVISO DI VIDEOCONFERENZA

 

 LUNEDI’ 2 FEBBRAIO 2015,

   ore 15:00, Sala del Consiglio (I piano)

del DIPARTIMENTO DI SCIENZE CHIMICHE E FARMACEUTICHE
Università di Trieste, Edificio C11, Via Giorgieri 1

 

il  Prof. CLAUDIO ZANNONI

del Dipartimento di Chimica Industriale “Toso Montanari” , Università di Bologna

In collegamento dall’Università Ca’ Foscari di Venezia terrà una videoconferenza dal titolo:

 

Modelling liquid crystals in the bulk and close to their boundaries

 

Liquid Crystals (LC) are anisotropic fluids characterized by long range orientational order and pair correlations. Mesoscale models, based on the drastic simplification of representing molecules as simple rigid objects such as spherocylinders or ellipsoids or even spins on a lattice have been the cornerstone of the first generation of liquid crystal (LC) theories and computer simulations (see, e.g.[1]). While these approaches are still very valuable in obtaining the general properties of complex LC, like LC elastomers [2] one of the most important current challenges is to relate a realistic molecular structure to physical observables and predict properties such as morphologies, order parameters, and phase-transition temperatures.

Atomistic molecular dynamics (MD) simulations now start to make this possible [3-5], also allowing the test of classical theories (e.g. Maier-Saupe or Onsager) for bulk LC [5]. However, for most practical applications LC are not used in bulk but in thin films where the LC is aligned with the help of surface interactions, so it is somewhat surprising that surface effects are still described only empirically, while little is known on their molecular origin. In the talk we shall show that computer simulations at coarse grain [4] and atomistic resolution [5] start to shed some light on the interfacial behavior of liquid crystals and show examples for the prediction of the alignment and anchoring of nematics (5CB in particular) at the interface with different solid surfaces e.g. silicon [7] or crystalline and glassy silica with different roughness (see figure)[8]. Simulations show in various cases that molecular organizations at the interface differ radically from those in the bulk, showing either discontinuities [7] or broad distributions of orientations [8] rather than the simple Dirichlet type boundary conditions assumed by many continuum type theories [9].

 

[1] P. Pasini and C. Zannoni (Eds.), Advances in the Computer Simulations of Liquid Crystals (Kluwer, 2000)

[2] G. Skacej, C. Zannoni, Molecular simulations elucidate electric field actuation in swollen liquid crystal elastomers, PNAS 109, 10193–10198 (2012) and Macromolecules, published on line (2014).

[3]G. Tiberio, L. Muccioli, R. Berardi and C. Zannoni, Towards “in silico” liquid crystals. Realistic transition temperatures and physical properties for n-cyanobiphenyls via Molecular Dynamics simulations,  ChemPhysChem 10, 125 (2009)

[4] M.F. Palermo, A.Pizzirusso, L.Muccioli, C.Zannoni, An atomistic description of the nematic and smectic phases of 4-n-octyl-4'cyanobiphenyl (8CB), J.Chem.Phys. 138, 204901 (2013)

[5] Y. Olivier, L. Muccioli, C. Zannoni, Quinquephenyl: the simplest rigid rod-like nematic liquid crystal. Or is it? An atomistic simulation, ChemPhysChem 15, 1345–1355 (2014)

[6] D. Vanzo, M. Ricci, R. Berardi and C. Zannoni, Wetting behaviour of nematic nanodroplets  on planar surfaces,  to be published (2014)

[7] A. Pizzirusso, R. Berardi, L. Muccioli, M. Ricci and C. Zannoni, Predicting surface anchoring. Molecular organization across a thin film of 5CB liquid crystal on silicon,  Chemical Science 3, 573 (2012)

[8] O. Roscioni, L. Muccioli, R. Della Valle, A. Pizzirusso, M. Ricci and C. Zannoni, Predicting the anchoring of liquid crystals at a solid surface: 5-cyanobiphenyl on cristobalite and glassy silica surfaces of increasing roughness,  Langmuir 29, 8950 (2013)

[9] G. Barbero and L.R. Evangelista, Adsorption Phenomena and Anchoring Energy in Nematic Liquid Crystals (CRC – Taylor & Francis, 2006)

E-mail: claudio.zannoni@unibo.it

Ultimo aggiornamento: 27-04-2015 - 16:57
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