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Projeto de investigação
Study of NMR superoaramagnetic relaxation effects in magnetic ionic liquids
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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.
Dynamical processes and order behind the pronounced 1H NMR paramagnetic relaxation enhancement induced in [P6,6,6,14]3[GdCl6]-based ionic liquid mixtures
Publication . Beira, Maria J.; Silva, Gonçalo M.C.; Eusébio, Tiago M.; Figueirinhas, João L.; Cordeiro, Rui; Cruz, Carlos; Corvo, Marta C.; Almeida, Pedro L.; Rosatella, Andreia A.; Afonso, Carlos A.M.; Filipe, Eduardo J.M.; Parella, Teodor; Cabrita, Eurico J.; Sebastião, Pedro J.; CENIMAT-i3N - Centro de Investigação de Materiais (Lab. Associado I3N); DCM - Departamento de Ciência dos Materiais; Faculdade de Ciências e Tecnologia (FCT); UCIBIO - Applied Molecular Biosciences Unit; DQ - Departamento de Química; Elsevier
NMR relaxometry is a technique that allows the molecular dynamics study of chemical compounds across a broad time scale, ranging from slow translational diffusion or collective motions to fast rotations. The present work is a 1H NMR relaxometry and diffusometry study of systems based on [P6,6,6,14][Cl] and [P6,6,6,14]3[GdCl6] ionic liquids, complemented by X-ray diffractometry measurements. The use of the X-ray profiles enabled the determination of an almost temperature independent interdigitated disposition of the cations that is at the origin of local order fluctuations. This structure also affects the paramagnetic relaxation enhancement, which is very significant for these systems and is achieved at very low metal concentrations (around 1mM). The present study provides a comprehensive analysis that is consistent for all the analyzed systems and across the different experimental techniques, despite the experienced technical challenges related to extremely short relaxation times. Additionally, the Electrochemical Impedance Spectroscopy profiles of the neat [P6,6,6,14][Cl] sample were explained by an analogous equivalent circuit model that allowed for a global analysis consistent with the diffusometry and X-ray diffractometry results. The representation of the real and imaginary parts of the impedance allowed for a visual deconvolution of the contributions of the different circuit blocks considered in the model.
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Fundação para a Ciência e a Tecnologia
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OE
Número da atribuição
COVID/BD/152743/2022