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Visit of Prof. Claudio Zannoni

from: Dipartimento di Chimica Industriale "Toso Montanari", Università di Bologna, Bologna, IT 02/02/2016 - 15.00 - Room A51 - DCB

Computer simulations of liquid crystals in the bulk and close to interfaces 

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]. 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 we 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], crystalline and glassy silica with different roughness [8] as well as soft self assembled monolayers [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 (2012) and Macromolecules, 47, 8824 (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 (2014)

[6] D. Vanzo, M. Ricci, R. Berardi and C. Zannoni, Wetting behaviour of nematic nanodroplets on planar surfaces, Soft Matter, published on line (2016)
[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] O. Roscioni, L. Muccioli, C. Zannoni, Liquid crystals anchoring on soft surfaces: from planar to homeotropic ordering for 5CB on SAM,
to be submitted (2016) 


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