Liquid Crystals (LC) are anisotropic functional materials with applications in a variety of soft matter technologies ranging from displays to organic electronics, elastomeric actuators etc. (see, e.g.[1]). These applications are, however, often based on empirical knowledge, as the understanding and prediction of properties of LC and of their interaction with surfaces still presents various fundamental unsolved problems. Computer simulations at various resolutions ranging from atomistic to mesoscale can be precious in this respect. 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 LC computer simulations (see, e.g.[2]). While these approaches are still very valuable in understanding the general properties of complex LC, like LC Elastomers [3], 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. This is essential, e.g., for applications in organic electronics, like organic solar cells [4] and in interpreting detailed spectroscopic data. Atomistic scale molecular dynamics simulations can now start to meet the challenge and we present some recent applications to nematic and smectic liquid crystal systems [5,6] as well as to solutes in LC where we compare with detailed NMR data [7]. We also tackle the problem of predicting alignment and anchoring strength of LC close to a solid interface, considering in detail thin films of 5CB on crystalline (cristobalite) and amorphous silica surfaces of increasing roughness [8].

[1] J.P.F.Lagerwall, G. Scalia, Current Applied Physics 12, 1387-1412 (2012)

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

(Kluwer, Dordrecht, 2000)

[3] G. Skacej, C. Zannoni, Molecular simulations elucidate electric field actuation in swollen liquid crystal elastomers, PNAS, 109, 10193–10198 (2012); Molecular simulations shed light on Supersoft Elasticity in Polydomain Liquid Crystal Elastomers, Macromolecules, 8824-8832 (2014)

[4] J. Idé, R. Méreau, L. Ducasse , F. Castet, H. Bock, Y. Olivier, J. Cornil, D. Beljonne, G. D’Avino, O. M. Roscioni, L.Muccioli, C. Zannoni, Charge dissociation at interfaces between discotic liquid crystals: the surprising role of column mismatch, J.Am. Chem.Soc., 136, 2911 (2014)

[5] 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)

[6] 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)

[7] A. Pizzirusso, M. E. Di Pietro, G. De Luca, G. Celebre, M. Longeri, L. Muccioli, C. Zannoni, Order and conformation of biphenyl in cyanobiphenyl liquid crystals. A combined atomistic molecular dynamics and 1H-NMR study, ChemPhysChem, 15, 1356–1367 (2014).

[8] O. M. Roscioni, L. Muccioli, R. G. Della Valle, A. Pizzirusso, M. Ricci, C. Zannoni, Langmuir, 29, 8950 (2013).

http://claudiozannoni.fci.unibo.it