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Projeto de investigação
Center of Physics and Engineering of Advanced Materials
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Publicações
Observing short-range orientational order in small-molecule liquids
Publication . Gradišek, Anton; Apih, Tomaž; Beira, Maria J.; Cruz, Carlos; Fernandes, Susete N.; Godinho, Helena M.; Sebastião, Pedro J.; DCM - Departamento de Ciência dos Materiais; CENIMAT-i3N - Centro de Investigação de Materiais (Lab. Associado I3N); Nature Publishing Group
Local molecular ordering in liquids has attracted a lot of interest from researchers investigating crystallization, but is still poorly understood on the molecular scale. Classical nucleation theory (CNT), a macroscopic thermodynamic description of condensation, has shortcomings when dealing with clusters consisting of tens of molecules. Cluster formation and local order fluctuations in liquid media are difficult to study due to the limited spatial resolution of electron- and photon-imaging methods. We used NMR relaxometry to demonstrate the existence of dynamic clusters with short-range orientational order in nominally isotropic liquids consisting of elongated molecules. We observed clusters in liquids where the local ordering is driven by polar, steric, and hydrogen-bond interactions between the molecules. In the case of a liquid crystal, measuring the local orientational order fluctuations allowed us to observe the size of these clusters diverging when approaching the phase transition from the isotropic to the nematic phase. These fluctuations are described in terms of rotational elasticity as a consequence of the correlated reorientations of the neighbouring molecules. Our quantitative observations of the dynamic clusters in liquids, numbering about ten or fewer molecules, indicate that this is a general phenomenon in various types of liquids.
Impact of nanoconfinement on the physical state and conductivity mechanisms of a 2-picolinium ionic liquid crystal
Publication . Santos, Andreia F. M.; Teresa Viciosa, M.; Matos, Inês; Sotomayor, João C.; Figueirinhas, João L.; Godinho, Maria H.; Branco, Luís C.; Dias, C. J.; Dionísio, Madalena; DQ - Departamento de Química; LAQV@REQUIMTE; DCM - Departamento de Ciência dos Materiais; CENIMAT-i3N - Centro de Investigação de Materiais (Lab. Associado I3N); Elsevier
Hybrid solid-like materials prepared from the incorporation of liquid-like ionic conductors into nanoporous matrices could represent an advantage for a variety of electronic applications. Aiming to obtain such materials, three composites of the polymorphic ionic liquid crystal (ILC) 1-hexadecyl-2-methylpyridinium bromide ([C16-2-Pic][Br]), loaded in the mesoporous inorganic silica SBA-15 (∼6.8 nm in pore diameter), were prepared at guest–host weight fractions of ∼ 40, 60 and 80% (w/w) and investigated by different techniques: ATR-FTIR, BET, TGA, XRD and DSC. Complete amorphisation was achieved for the 40 and 60% composites, while the 80% preparation was stabilised in the low-T morph of native C16, being in the liquid state at room temperature. Furthermore, through Dielectric Relaxation Spectroscopy, the ionic conductivity of the three hybrid materials was characterised, allowing to deconvolute this property in a pure ohmic contribution (conductivity I) and the overlapping of ac − dc transition with interfacial polarisation resulting from the coexistence of the ionic liquid and the quasi-insulating inorganic matrix (conductivity II). From –20 to 20 °C, the conductivity and the corresponding charge migration are faster in all composites relative to the neat ILC, as deduced from the inferior radii of Nyquist arcs. The 60% preparation stood out from the other materials, exhibiting direct conductivity unaffected by electrode polarisation over a larger T-range, leading to the assumption of a nearly continuous silica-mediated charge migration pathway, which is never reached for the 40% composite, while, in the 80% preparation, some C16 deposits on the outer surface of the pores. Incorporation into the silica matrix proved to be a good strategy for the production of cost-efficient materials with long-term stabilisation of the ionic liquid in a single phase over a large range of temperatures, enabling the prediction of flow and conductive properties.
Tuning the 1H NMR Paramagnetic Relaxation Enhancement and Local Order of [Aliquat]+-Based Systems Mixed with DMSO
Publication . Cordeiro, Rui; Beira, Maria J.; Cruz, Carlos; Figueirinhas, João L; Corvo, Marta C; Almeida, Pedro L; Rosatella, Andreia A.; Afonso, Carlos A. M.; Daniel, Carla I.; Sebastião, Pedro J.; CENIMAT-i3N - Centro de Investigação de Materiais (Lab. Associado I3N); LAQV@REQUIMTE; DQ - Departamento de Química; MDPI - Multidisciplinary Digital Publishing Institute
Understanding the behavior of a chemical compound at a molecular level is fundamental, not only to explain its macroscopic properties, but also to enable the control and optimization of these properties. The present work aims to characterize a set of systems based on the ionic liquids [Aliquat][Cl] and [Aliquat][FeCl4] and on mixtures of these with different concentrations of DMSO by means of 1H NMR relaxometry, diffusometry and X-ray diffractometry. Without DMSO, the compounds reveal locally ordered domains, which are large enough to induce order fluctuation as a significant relaxation pathway, and present paramagnetic relaxation enhancement for the [Aliquat][Cl] and [Aliquat][FeCl4] mixture. The addition of DMSO provides a way of tuning both the local order of these systems and the relaxation enhancement produced by the tetrachloroferrate anion. Very small DMSO volume concentrations (at least up to 1%) lead to enhanced paramagnetic relaxation without compromising the locally ordered domains. Larger DMSO concentrations gradually destroy these domains and reduce the effect of paramagnetic relaxation, while solvating the ions present in the mixtures. The paramagnetic relaxation was explained as a correlated combination of inner and outer-sphere mechanisms, in line with the size and structure differences between cation and anion. This study presents a robust method of characterizing paramagnetic ionic systems and obtaining a consistent analysis for a large set of samples having different co-solvent concentrations.
An indium-oxide electrode with discontinuous Au layers for plasmonic devices
Publication . Vygranenko, Yuri; Lavareda, Guilherme; André, Vânia; Brogueira, Pedro; Amaral, Ana; Fernandes, Miguel; Fantoni, Alessandro; Vieira, M.; CTS - Centro de Tecnologia e Sistemas; UNINOVA-Instituto de Desenvolvimento de Novas Tecnologias; DCM - Departamento de Ciência dos Materiais
In this contribution we report on a low cost plasmonic electrode for light-sensing applications. The electrode combines a conducting nonstoichiometric indium oxide (InOx) layer with an ultrathin (∼5 nm) discontinuous Au layer. The InOx and Au layers were deposited on glass substrates by plasma enhanced reactive thermal evaporation and thermal evaporation, respectively. Several device configurations with one or two Au layer(s) sandwiched between InOx layers were fabricated and characterized. The morphological and structural properties of both Au and InOx layers were analyzed using AFM and XRD techniques. In particular, the effect of thermal annealing (673 K, 15 min) on the surface morphology of Au layers grown on bare glass and InOx-coated substrate was investigated. It has been also found that the oxide film grown above an underlying nanostructured Au layer is amorphous, while a reference InOx film on glass is nanocrystalline with a smooth surface. The electrical properties of InOx grown on the Au surface are worsened due to Au-induced structural disorder. The observed difference in transmission spectra of the glass/InOx/Au and glass/Au/InOx structures indicates the difference in the morphology of the metal layer. Thus, the optical and morphological properties of the InOxelectrode can be varied in a wide range by incorporating several Au layers.
Ionic Liquid Crystals as Versatile Functional Materials
Publication . Santos, Andreia Filipa Magalhães Seixas Lopes dos; Branco, Luís; Andrade, Maria Madalena; Godinho, Maria Helena
Ionic liquid crystals (ILCs) have emerged as a promising approach to develop versatile soft
materials, exhibiting liquid crystalline behaviour. As they combine characteristics of both liquid
crystals and ionic liquids, it is possible to tune their physicochemical and self-assembly prop-
erties by the wise pairing of cation and anion, allowing the design of new functional and re-
sponsive materials. It is known that the rigidity of the cation linked to the flexibility of the alkyl
moiety are main requirements for the formation of ionic liquid crystals. In this thesis, a new
series of ILCs based on pyridinium and picolinium cations was synthesised through sustainable
methods and further characterised by thermal (TGA and DSC), microscopic (POM) and spec-
troscopic (NMR, ATR-FTIR, XRD and DRS) techniques. Moreover, the influence of the methyl
group position (
ortho-,
meta- and
para-) and the alkyl chain length (C6, C12 and C16) on their
mesomorphism and conductive behaviour is provided, revealing smectic phases for all mate-
rials with the exception of C6-substituted ionic liquid. Furthermore, it is presented multiple ways
of exploring the selected organic salts:
i) fundamental studies regarding modifications at mo-
lecular level;
ii) lyotropic aqueous mesophases and shear-induced foams;
iii) enhancement of
the performance by incorporating in porous silica matrices;
iv) stimuli-responsive formulations
using ionic liquid crystals as additives for fuel dyes.
These synthesised organic salts acted as model compounds to evaluate the correlation
between chemical structure, phase transitions and conductivity behaviour, guiding also the
future design of sustainable electronic and smart materials.
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Entidade financiadora
Fundação para a Ciência e a Tecnologia
Programa de financiamento
6817 - DCRRNI ID
Número da atribuição
UID/CTM/04540/2019