Liquid crystals are versatile materials, with outstanding anisotropic properties which can be a model for turbulence, a guide for the self assembling of nanoparticles or quantum dots. The guided self assembling control can be applied to the development of miniaturized devices for the optics, photonics and microfluidics. Their birefringence and their optical properties allow the LC employment in technological applications such as displays, sensors, lasers, gratings.
A special class of liquid crystal are biocompatible and then can be used in biological sensing.
Nanoconfinement of liquid crystals (LC) and anisotropic fluids dynamics
The structure and response of complex and anisotropic fluids such as LC can be very different in the bulk, where molecules interact with each other and with external fields (e.g. electromagnetic field), and at the interfaces where molecule-surface interactions may become dominant. For instance, a surface may enhance or inhibit the LC order (e.g., orientational order in nematic LC) or even induce a new type of order (e.g. positional smectic-like order) compared to the bulk. When a LC is confined to a length scale comparable with the coherence length of the order that is being induced or altered, the liquid may undergo a structural transition and show a different mechanical or electro-optical response.
The viscoelastic description of anisotropic fluids is conventionally done at fixed topologies. The research in nematic electrooptics has been strongly stimulated by the demonstration of fast coherent switching between two topologically distinct textures by means of the electrically controlled biaxial order reconstruction in nematics (BORN). Thermotropic nematics consist of rigid molecular core units, which can build a nematic phase with uniaxial order, usually described by using the scalar order parameter S and the director n (average molecular orientation). Nevertheless, uniaxial nematics under strong external constraints can induce a local and/or transient biaxial order at nanometric scale and the (n,S) description is no longer adequate. This is the case of BORN, which requires a tensorial description of the nematic material. The BORN allows the dynamical reconstruction of the long axis of the nematic order tensor Q in a perpendicular direction with respect to a starting one. This means that a nematic texture can locally be reconstructed in a perpendicular direction without any rotation of n. This allows to connect nematic textures with different topologies.
Furthermore nematic and smectic LC confined between solid surfaces can be studied using the Surface Force Apparatus (SFA) and Atomic Force Microscope (AFM). By accurately measuring the surface forces generated by nanometer films with non homogeneous boundary conditions, we could reveal a structural transition towards a partial biaxial phase and measure the complex mechanical response of a smectic LC.
Defect pattern self-assembly and guided nanoparticle (NP) assembly in thin liquid crystal films.
We propose a bottom-up approach to create patterns and templates by dispersing or conjugating functional NPs with an anisotropic LC materials that can self-assemble into ordered and aligned structures over multiple length scales. Periodic patterns of topological defects can be created in thin films of layered materials such as smectic LC and cholesteric LC. The interaction of NPs with the core of the defects determines both a regular spatial distribution and alignment of NPs.
The dispersion of gold NPs in a chiral nematic LC shows that Au NP’s presence, besides affecting LC order, influences its electric properties: ion conductivity results importantly reduced, and beyond a threshold value of the applied field electrophoresis phenomena are induced.
Furthermore quantum dots can be dispersed in the LC medium: they accumulate in the topological defects and their position can be tuned by laser light by means of the holographic control of the command surfaces or by electric field. This result can be applied to the development of miniaturized devices for the optics, photonics and microfluidics.
Technological applications of liquid crystals: displays, sensors, lasers, gratings
Nematic and cholesteric LC are very attractive materials for the development of optical and electro-optical devices. In particular, due to their helicoidal supramolecular structure, cholesteric LC may be considered as one-dimensional photonic structures. Cholesteric materials possess several unique properties: 100 % selective reflection of circularly polarized light and the ability to change their selective reflection wavelength changing external or internal factors (electric, and electromagnetic fields, temperature, local order). In the years, cholesteric liquid crystals have been used to develop different devices as luminescent displays, mirror-less lasers, paper-like mirrors and temperature sensors at the microscale.
Chromonic materials and their interaction with surfaces
Chromonics are a LC class of soft matter in which the aggregates are reversibly self-assembled by non-amphiphilic molecules. This term includes drugs, dyes and DNA nucleotides, such as guanosine derivatives, all biocompatible materials.
Their anisotropic optical properties can be used for enhancing optical images. In fact chromonics are not toxic to many microbial species and they do not alter the antibody-antigen binding, important conditions for using them in biological sensing. The interaction of chromonics with surfaces and the alignment that surfaces induce, is subject of the present task.
The dynamics of nematic LC subject to an external electric field can be described by nonlinear equations that recall the convective motion of fluids and plasmas. This results in a number of features which can be studied in the framework of turbulence, such as the generation of vortical motion. In particular, the presence of a multiplicative cascade of structures on smaller and smaller scales can be observed, and its dependence on the experimental parameters reveal a rich variety of phenomena, which are typical of complex flows.
The study of electroconvective turbulence is mostly based on the analysis of experimental observations produced in the Licryl laboratory under a broad range of experimental conditions. Subsequently, advanced data analysis techniques are applied, so that the similarities with the ordinary turbulence can be established, and the turbulence characteristics pointed out. The main results are the characterization of intermittency in nematic LC electroconvection and the study of the sweeping effect in nematic LC electroconvective turbulence: the analysis of the space-time autocorrelation function has allowed the evaluation of the effect of large-scale structure decorrelation on turbulence, also providing the first experimental evidence of such phenomenon.
- Coursault, D.; Zappone, B.; Coati, A.; …. Lacaze, E. “Self-organized arrays of dislocations in thin smectic liquid crystal films” Soft Matter DOI: 10.1039/C5SM02241J (2016)
- Gryn I., Lacaze E., Carbone L., Giocondo M., Zappone B. Electric-Field-Controlled Alignment of Rod-Shaped Fluorescent Nanocrystals in Smectic Liquid Crystal Defect Arrays, Adv. Funct. Mat. in press DOI: 10.1002/adfm.201602729
- Kasyanyuk D., Pagliusi P., Mazzulla A., Reshetnyak V., Reznikov Y., Provenzano C., Giocondo M., Vasnetsov M., Yaroshchuk O., Cipparrone G. Light manipulation of nanoparticles in arrays of topological defects, Scientific Reports 6, 20742 (2016) DOI: 10.1038/srep20742
- Provenzano C., Mazzulla A., Chiaravalloti F., Audia B., Cipparrone G. Topological defects and electro-convective flows in anisotropic fluids: A microfluidic platform for nano-objects tunable structuring. Appl. Phys. Lett. Vol. 109, 7, Article number 071901 (2016) DOI: 10.1063/1.4960635
- D. Coursault, J.-F. Blach, J. Grand, A. Coati, A. Vlad, B. Zappone, D. Babonneau, E. Lacaze et al. “Tailoring Anisotropic Interactions between Soft Nanospheres Using Dense Arrays of Smectic Liquid Crystal Edge Dislocations” ACS Nano 9, 11678-11689 (2015) DOI: 10.1021/acsnano.5b02538
- I. Gryn, E. Lacaze, R. Bartolino, B. Zappone “Controlling the self-assembly of periodic defect patterns in smectic liquid crystal films with electric fields“, Advanced Functional Materials, 25, 142-149, (2014) DOI: 10.1002/adfm.201402875
- D. Coursault, B. H. Ibrahim, L. Pelliser, B. Zappone, A. de Martino, E. Lacaze and B. Gallas “Modeling the optical properties of self-organized thin films of 8CB molecules” Optics Express, 22, 23182–23191, (2014) DOI: 10.1364/OE.22.023182
- Infusino M., De Luca A., Ciuchi F., Ionescu A., Scaramuzza N., Strangi G. Optical and electrical characterization of a gold nanoparticle dispersion in a chiral liquid crystal matrix J. Mat.Sci. 49, 4, 1805-1811, (2014) DOI 10.1007/s10853-013-7868-6
- Petriashvili G, De Santo MP, Chubinidze K, Hamdi R, Barberi R Visual micro-thermometers for nanoparticles photo-thermal conversion. Optics Express, 22, 14705-14711 DOI: 10.1364/OE.22.014705, (2014).
- Tone, C.M., De Santo, M.P., Ciuchi, F. The role of surface energy in guanosine nucleotide alignment: An intriguing scenario, Colloids and Surfaces B: Biointerfaces, 119, 99-105 (2014) DOI 10.1016/j.colsurfb.2014.04.
- Pucci D., Mendiguchia B.S., Tone C.M. , Szerb E.I., Ciuchi F. , Gao M. , Ghedini M., Crispini A. Unconventionally shaped chromonic liquid crystals formed by novel silver(i) complexes, J. Mater.Chem.C, 2014, 2, 8780 (2014) DOI: 10.1039/C4TC01736F
- Carbone, F., Sorriso-Valvo, L. Experimental analysis of intermittency in electrohydrodynamic instability EPJE 37, 61, pp. 1-11 (2014) DOI: 10.1140/epje/i2014-14061-x
Other Selected Publications:
- Hamdi R, Lombardo G, De Santo MP, Barberi R Biaxial coherence length In a nematic π-cell. EPJ E, vol. 36, N 115. DOI:1140/epje/i2013-13115-y (2013).
- Petriashvili G, Japaridze K, Devadze L, Zurabishvili C, Sepashvili N, Ponjavidze N, De Santo MP, Matranga MA, Hamdi R, Ciuchi F, Barberi R Paper like cholesteric interferential mirror. Optics Express, vol. 21, p. 20821-20830, DOI: 10.1364/OE.21.020821, (2013).
- Tone, C.M., De Santo, M.P., Buonomenna, M.G., Golemme, G., Ciuchi, F. Dynamical homeotropic and planar alignments of chromonic liquid crystals, Soft Matter 8, 8478-8482 (2012) DOI:10.1039/c2sm26021b
- Ruths and B. Zappone, ” Direct nanomechanical measurement of an anchoring transition in a nematic liquid crystal subject to hybrid anchoring conditions“, Langmuir 28, 8371-8383, (2012) DOI: 10.1021/la204746d
- D. Coursault, J. Grand, B. Zappone, H. Ayeb, G. Lévi, N. Félidj and E. Lacaze, “Linear self-assembly of nanoparticles within liquid crystal defect arrays“, Advanced Materials 24, 1461–1465, (2012) DOI: 10.1002/adma.201103791
- Mazzulla A, Petriashvili G, Matranga MA, De Santo MP, Barberi R Thermal and electrical laser tuning in liquid crystal blue phase I. Soft Matter, 8, 4882-4885, DOI: 10.1039/c2sm25197c (2012).
- B. Zappone, C. Meyer, L. Bruno and E. Lacaze, “Periodic lattices of frustrated focal conic defect domains in smectic liquid crystal films“, Soft Matter, 8, 4318–4326, (2012) DOI: 10.1039/c2sm07207f
- Carbone, F., Vecchio, A., Sorriso-Valvo, L. Spatio-temporal dynamics, patterns formation and turbulence in complex fluids due to electrohydrodynamics instabilities European Physical Journal E 34 (8), 75, (2011) DOI: 10.1140/epje/i2011-11075-x
- Carbone, F., Sorriso-Valvo, L., Versace, C., Strangi, G., Bartolino, R. Physical Review Letters Anisotropy of spatiotemporal decorrelation in electrohydrodynamic turbulence 106 (11), 114502 (2011) DOI: 10.1103/PhysRevLett.106.114502
- Ayeb H, Lombardo G, Ciuchi F, Hamdi R, Gharbi A, Durand G, Barberi R Surface order reconstruction in nematics. Phys. Lett., vol. 97, 104104. DOI:10.1063/1.3455885 (2010).