Maria Penelope De Santo

Universidade do Estado do Pará

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Co-Authors

R. Barberi

University of Calabria

Federica Ciuchi

University of Calabria

Gia Petriashvili

Georgian Technical University

Giuseppe Lombardo

Vision Engineering (Italy)

Marco Lombardo

Vision Engineering (Italy)

M. A. Matranga

Hewlett-Packard (United Kingdom)

Andro Chanishvili

Georgian Technical University

G. S. Chilaya

Georgian Technical University

Cristina Labate

University of Calabria

Caterina Maria Tone

University of Calabria

Cooperative Institutions

University of Calabria

154

National Research Council

Istituto di Nanotecnologia

Istituto Nanoscienze

Renfe Operadora (Spain)

Institute on Membrane Technology

National Interuniversity Consortium of Materials Science and Technology

Istituto Nazionale per la Fisica della Materia

National Interuniversity Consortium for the Physical Sciences of Matter

Centre National de la Recherche Scientifique

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Ordered interfaces for dual easy axes in liquid crystals

Soft Matter (2010)

Emmanuelle Lacaze Alessandra Apicella Maria Penelope De Santo Delphine Coursault M. Alba

Using nCB films adsorbed on MoS 2 substrates studied by x-ray diffraction, optical microscopy and Scanning Tunneling Microscopy, we demonstrate that ordered interfaces with well-defined orientations of adsorbed dipoles induce planar anchoring locked along the adsorbed dipoles or the alkyl chains, which play the role of easy axes. For two alternating orientations of the adsorbed dipoles or dipoles and alkyl chains, bi-stability of anchoring can be obtained. The results are explained using the introduction of fourth order terms in the phenomenological anchoring potential, leading to the demonstration of first order anchoring transition in these systems. Using this phenomenological anchoring potential, we finally show how the nature of anchoring in presence of dual easy axes (inducing bi-stability or average orientation between the two easy axes) can be related to the microscopical nature of the interface. Introduction Understanding the interactions between liquid crystal (LC) and a solid substrate is of clear applied interest, the vast majority of LC displays relying on control of interfaces. However this concerns also fundamental problems like wetting phenomena and all phenomena of orientation of soft matter bulk induced by the presence of an interface. In LCs at interfaces, the so-called easy axes correspond to the favoured orientations of the LC director close to the interface. If one easy axis only is defined for one given interface, the bulk director orients along or close to this axis [1]. It is well known that, in anchoring phenomena, two major effects compete to impose the anchoring directions of a liquid crystal, first, the interactions between molecules and the interface, second, the substrate roughness whose role has been analyzed by Berreman [2]. The influence of adsorbed molecular functional groups at the interface is most often dominant with, for example in carbon substrates, a main influence of unsaturated carbon bonds orientation at the interface [3]. In common LC displays, there is one unique easy axis, but modifications of surfaces have allowed for the discovery of promising new anchoring-related properties. For instance, the first anchoring bi-stability has been established on rough surfaces, associated with electric ordo-polarization [4] and the competition between a stabilizing short-range term and a destabilizing long-range term induced by an external field, can induce a continuous variation of anchoring orientation [5]. More recently, surfaces with several easy axes have been studied extensively. It has been shown that control of a continuous variation of director pretilt, obtained in several systems [6, 7], is associated with the presence of two different easy axes, one perpendicular to the substrate (homeotropic) and one planar [7, 8]. Similar models can explain the continuous evolution of anchoring between two planar orientations observed on some crystalline substrates [9]. However, in the same time, two easy axes can also lead to anchoring bi-stability [10, 11] or discontinuous transitions of anchoring [9], which is not compatible with the model established to interpret observed control of pretilt. In order to be able to predict if bi-stability or continuous combination of the two easy axes occurs for one given system, it becomes necessary to understand the microscopic origin of the easy axes.

Anchoring

Homeotropic alignment

Soft matter

10.1039/c0sm00727g

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Citations (10)

NMR Diffusiometry Spectroscopy, a Novel Technique for Monitoring the Micro-Modifications in Bitumen Ageing

Applied Sciences (2020)

Paolino Caputo Dilshad Shaikhah Michele Porto Valeria Loise Maria Penelope De Santo

In the past three decades, several conventional methods have been employed for characterizing the bitumen ageing phenomenon, such as rheological testing, ultraviolet testing, gel permeation chromatography (GPC), gas chromatography (GC), atomic force microscopy (AFM), X-ray scattering, and Fourier transform infrared spectroscopy (FTIR). Nevertheless, these techniques can provide only limited observations of the structural micro-modifications occurring during bitumen ageing. In this study, Fourier transform nuclear magnetic resonance self-diffusion coefficient (FT-NMR-SDC) spectroscopy, as a novel method, was employed to investigate and compare the microstructural changes between virgin bitumen (pristine bitumen) and aged bitumen. The virgin bitumen was aged artificially using two standard ageing tests: Rolling Thin-Film Oven Test (RTFOT) and Pressure Ageing Vessel (PAV). For a comprehensive comparison and an assessment of the validity of this method, the generated samples were studied using various methods: rheological test, atomic force microscopy, and optical microscopy. Significant differences were obtained between the structure and ageing patterns of virgin and aged bitumen. The results indicate that the modification of maltenes to asphaltenes is responsible for the ageing character. When compared with the other methods’ findings, FT-NMR-SDC observations confirm that the asphaltene content increases during ageing processes.

Asphaltene

Gel permeation chromatography

10.3390/app10165409

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Polar diffraction gratings made by spatially periodic photopoling Langmuir–Blodgett films

Applied Physics Letters (2002)

L. M. Blinov S. P. Palto S. G. Yudin Maria Penelope De Santo G. Cipparrone

Polar diffraction gratings have been prepared by spatially periodic photopoling Langmuir–Blodgett films consisting of azobenzene compounds. The gratings were made by film irradiation with two left circularly polarized Ar-ion laser beams under strong electric field from a corona discharge. Therefore, simultaneously with the spatial modulation of the linear refractive index, the local polar order of the film becomes periodically modulated (through symmetry, the latter is related to the modulation of second-order optical nonlinearity χ(2)). The local polarity is shown by an electrostatic force microscopy technique: an image of the polar grating is recorded without any trace of periodicity in the film topography.

Azobenzene

Diffraction efficiency

10.1063/1.1431399

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Citations (17)

OPTICAL ANISOTROPY AND FOUR POSSIBLE ORIENTATIONS OF A NEMATIC LIQUID CRYSTAL ON THE SAME FILM OF A PHOTOCHROMIC CHIRAL SMECTIC POLYMER

Journal of Nonlinear Optical Physics & Materials (2000)

L. M. Blinov R. Barberi Mikhail V. Kozlovsky В. В. Лазарев Maria Penelope De Santo

Spin coated films of a chiral comb-like liquid crystalline copolymer containing azobenzene chromophores in its side chains are optically isotropic in their twisted smectic-like glassy state. In contact with a nematic liquid crystal (5CB, E7, MBBA) they provide a degenerate planar orientation. When irradiated by unpolarized UV light, they orient the same nematics homeotropically. Treated with linearly polarized UV light they orient nematics homogeneously with the director along the electric vector of the exciting light. After a combined irradiation first with unpolarized UV light and then with linearly polarized visible light, the films again provide a homogeneous liquid crystal orientation, this time with the director perpendicular to the visible light electric vector. The phenomena observed are related to the light induced optical anisotropy. Two main processes are responsible for the anisotropy (1) a UV light depletion of trans-isomers of the azobenzene chromophores from the chosen direction and (2) a reorientation of the chromophores by polarized visible light.

Chromophore

Azobenzene

Visible spectrum

MBBA

10.1142/s0218863500000029

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Citations (3)

Dielectric Characterisation of an Orthoconic Antiferroelectric Liquid Crystal Mixture

Molecular Crystals and Liquid Crystals (2012)

L. Marino Emanuela Bruno Maria Penelope De Santo Federica Ciuchi Simeone Marino

Dielectric properties of the orthoconic smectic liquid crystalline mixture W-129, which presents both antiferroelectric and ferroelectric smectic C phases, have been studied in the frequency range from 10 mHz to 100 kHz in planar aligned cells. Some important relaxation modes were detected in SmCa* and SmC* phases. Dielectric increments, distribution parameters and relaxation frequencies of these modes have been evaluated at different temperatures. From the study of dielectric spectra a great variety of relaxation responses emerges that could indicate the presence of different SmCa* subphases.

Antiferroelectricity

10.1080/15421406.2011.653717

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Citations (7)

A laser spectroscopy based method for the detection of acidic compounds in solution

Sensors and Actuators B Chemical (2017)

Gia Petriashvili Maria Penelope De Santo R. Barberi

Cuvette

Solvatochromism

10.1016/j.snb.2017.01.066

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Citations (3)

Temperature tunable omnidirectional lasing in liquid crystal blue phase microspheres

OSA Continuum (2019)

Gia Petriashvili Andro Chanishvili Tsisana Zurabishvili Ketevan Chubinidze Nino Ponjavidze

In this work, we demonstrate micro resonators made of liquid crystal blue phase (BP) microspheres, embedded in a polymer/water matrix. The omnidirectional 3D lasing from BPII and BPI microspheres and the temperature-controlled laser tuning within the range of 55 nm from the BPI microspheres were observed for the first time. The potential applications of BPs microlasers range from temperature-controllable, omnidirectional, coherent light micro sources to informational displays and micro sensing devices.

Glass microsphere

10.1364/osac.2.003337

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Citations (10)

Petrophysical Characterizations of Carbonate Reservoir Rocks

AGU Fall Meeting Abstracts (2019)

T. Lipovetsky Behzad Ghanbarian L. Moriconi Elizabeth M. Pontedeiro Amir Raoof

Petrophysics

Source

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Multiscale Investigation of the Depth-Dependent Mechanical Anisotropy of the Human Corneal Stroma

Investigative Ophthalmology & Visual Science (2015)

Cristina Labate Marco Lombardo Maria Penelope De Santo Janice Dias Noël Ziebarth

To investigate the depth-dependent mechanical anisotropy of the human corneal stroma at the tissue (stroma) and molecular (collagen) level by using atomic force microscopy (AFM).Eleven human donor corneas were dissected at different stromal depths by using a microkeratome. Mechanical measurements were performed in 15% dextran on the surface of the exposed stroma of each sample by using a custom-built AFM in force spectroscopy mode using both microspherical (38-μm diameter) and nanoconical (10-nm radius of curvature) indenters at 2-μm/s and 15-μm/s indentation rates. Young's modulus was determined by fitting force curve data using the Hertz and Hertz-Sneddon models for a spherical and a conical indenter, respectively. The depth-dependent anisotropy of stromal elasticity was correlated with images of the corneal stroma acquired by two-photon microscopy.The force curves were obtained at stromal depths ranging from 59 to 218 μm. At the tissue level, Young's modulus (ES) showed a steep decrease at approximately 140-μm stromal depth (from 0.8 MPa to 0.3 MPa; P = 0.03) and then was stable in the posterior stroma. At the molecular level, Young's modulus (EC) was significantly greater than at the tissue level; EC decreased nonlinearly with increasing stromal depth from 3.9 to 2.6 MPa (P = 0.04). The variation of microstructure through the thickness correlated highly with a nonconstant profile of the mechanical properties in the stroma.The corneal stroma exhibits unique anisotropic elastic behavior at the tissue and molecular levels. This knowledge may benefit modeling of corneal behavior and help in the development of biomimetic materials.

Indentation

Microkeratome

10.1167/iovs.15-16875

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Citations (30)

Direct Oxidation of Cyclohexene with Inert Polymeric Membrane Reactor

Organic Process Research & Development (2009)

Maria Giovanna Buonomenna Giovanni Golemme Maria Penelope De Santo Enrico Drioli

In this work, the use of PVDF flat membranes as contactors for direct solvent-free biphasic oxidation of cyclohexene to adipic acid has been reported. The oxidation has been carried out using 30% H2O2 and ammonium molybdate ((NH4)6Mo7O24) in the presence of succinic acid. The effect of different membranes as interfaces between the organic phase, containing cyclohexene, and the aqueous phase, with the oxidant and catalyst, has been studied and related to conversion and selectivity.

Ammonium molybdate

Adipic acid

Succinic acid

10.1021/op900022t

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Citations (18)