Imbibition in mesoporous silica: rheological concepts and experiments on water and a liquid crystal

We present, along with some fundamental concepts regarding imbibition of liquids in porous hosts, an experimental, gravimetric study on the capillarity-driven invasion dynamics of water and of the rod-like liquid crystal octyloxycyanobiphenyl (8OCB) in networks of pores a few nanometers across in monolithic silica glass (Vycor). We observe, in agreement with theoretical predictions, square root of time invasion dynamics and a sticky velocity boundary condition for both liquids investigated. Temperature-dependent spontaneous imbibition experiments on 8OCB reveal the existence of a paranematic phase due to the molecular alignment induced by the pore walls even at temperatures well beyond the clearing point. The ever present velocity gradient in the pores is likely to further enhance this ordering phenomenon and prevent any layering in molecular stacks, eventually resulting in a suppression of the smectic phase in favor of the nematic phase.Comment: 18 pages, 8 figure

Molecular dynamics simulations of Ibuprofen release from pH-gated silica nanochannels

The iboprufen delivery process from cylindrical silica pores of diameter 3~nm, with polyamine chains anchored at the pore outlets,was investigated by means of massive molecular dynamics simulations. Effects from pH were introduced by considering polyamine chains with different degree of protonation. High, low and intermediate pH environments were investigated. The increment of the acidity of the environment leads to a significant decrease of the pore aperture,  yielding an effective diameter, for the lowest pH case, that is 3.5~times smaller than the one associated to the highest pH one. Using a biased sampling procedure, Gibbs free energy profiles for the ibuprofen delivery process were obtained. The joint analysis of the corresponding profiles, time evolution of the ibuprofen position within the channel, orientation of the molecule and instantaneous effective diameter of the gate, suggests a 3-steps mechanism for ibuprofen delivery. A complementary analysis of the translational mobility of ibuprofen along the axial direction of the channel revealed a sub-diffusive dynamics in the low and intermediate pH cases.Deviations from Brownian diffusive dynamics are discussed and compared with direct experimental results. Fil: Rodriguez, Javier. Comisión Nacional de Energía Atómica; Argentina. Universidad Nacional del Centro de la Provincia de Buenos Aires. Facultad de Ciencias Exactas. Núcleo de Investigación en Educacion Ciencia y Tecnologia; ArgentinaFil: Elola, Maria Dolores. Comisión Nacional de Energía Atómica; Argentin

Activity report 2014

Centro de Física de Materiales (CFM) is a research center focused in Materials Science. Born in 1999 as a joint initiative between Consejo Superior de Investigaciones Científicas (CSIC) and Universidad del Pais Vasco – Euskal Herriko Unibertsitatea (UPV-EHU), the long term goal of CFM is to push forward the frontiers of knowledge in our areas of expertise, by putting together stable teams with a record of excellence in scientific research. CFM is distinguished as a “Basque Excellence Research Center” by the Basque Government (BERC Program).N

Silver electrodeposition on nanostructured gold: from nanodots to nanoripples

Silver nanodots and nanoripples have been grown on nanocavity-patterned polycrystalline Au templates by controlled electrodeposition. The initial step is the growth of a first continuous Ag monolayer followed by preferential deposition at nanocavities. The Ag-coated nanocavities act as preferred sites for instantaneous nucleation and growth of the three-dimensional metallic centres. By controlling the amount of deposited Ag, dots of ∼50 nm average size and ∼4 nm average height can be grown with spatial and size distributions dictated by the template. The dots are in a metastable state. Further Ag deposition drives the dot surface structure to nanoripple formation. Results show that electrodeposition on nanopatterned electrodes can be used to prepare a high density of nanostructures with a narrow size distribution and spatial order.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicada

The toolbox of porous anodic aluminum oxide–based nanocomposites: from preparation to application

Anodic aluminum oxide (AAO) templates have been intensively investigated during the past decades and have meanwhile been widely applied through both sacrificial and non-sacrificial pathways. In numerous non-sacrificial applications, the AAO membrane is maintained as part of the obtained composite materials; hence, the template structure and topography determine to a great extent the potential applications. Through-hole isotropic AAO features nanochannels that promote transfer of matter, while anisotropic AAO with barrier layer exhibits nanocavities suitable as independent and homogenous containers. By combining the two kinds of AAO membranes with diverse organic and inorganic materials through physical interactions or chemical bonds, AAO composites are designed and applied in versatile fields such as catalysis, drug release platform, separation membrane, optical appliances, sensors, cell culture, energy, and electronic devices. Therefore, within this review, a perspective on exhilarating prospect for complementary advancement on AAO composites both in preparation and application is provided

Molecular simulation of xenon NMR in fluids and nanocavities

AbstractFluids, especially liquid crystals, enclosed in porous materials exhibit a rich phase behaviour which can be exploited in both the study of the fundamental properties of the fluid itself, as well as its confinement. Nuclear magnetic resonance spectroscopy of xenon dissolved in the confined fluid is a sensitive and noninvasive method to study these systems. The purpose of this thesis is to develop and validate computational methods which can be used to interpret, as well as predict the structure and ¹²⁹Xe NMR of the fluid.The work used a combination of classical simulations of coarse-grained molecular models with quantum-chemical parameterisation for the pairwise-additive potential energies and the ¹²⁹Xe nuclear shielding tensors. More specifically, Monte Carlo molecular simulation was used to study the structure and phase behaviour of a uniaxial liquid crystal in a cylindrical nanocavity. Next, a small number of xenon atoms was added to the simulation and the nuclear shielding of ¹²⁹Xe was computed from the simulated configurations. Finally, the factors contributing to the maximum of the chemical shift of ¹²⁹Xe in water were studied with a semianalytical cavity model, which was parameterised using a combination of molecular dynamics simulations and quantum-chemical calculations.It was found that planar anchoring of liquid-crystal molecules at the walls of a cylindrical cavity promotes orientational order well above the isotropic-nematic phase transition temperature and the sharp isotropic-nematic transition of the bulk liquid crystal is replaced by a gradual paranematic-nematic transition. At lower temperatures the formation of translationally ordered phases is hindered by the packing of molecules at the wall.The ¹²⁹Xe shielding computed from the simulations corresponds qualitatively to earlier experimental results for xenon dissolved in a liquid crystal enclosed in the small cavities of controlled pore glass. The gradual change of orientational order at the paranematic-nematic transition is hard to observe in the isotropic shielding, especially in very small pores, but the transition reveals itself in the anisotropic part of the shielding.The semianalytical cavity model qualitatively reproduces the maximum of the ¹²⁹Xe chemical shift in water. The extremum is interpreted as arising from the interplay of the variation in water density and the collisions of the Xe solute with its nearest water molecule neighbours. The interpretation suggests the chemical shift maximum could be observed also in other solvents.Original papersOriginal papers are not included in the electronic version of the dissertation.Karjalainen, J., Lintuvuori, J., Telkki, V.-V., Lantto, P., & Vaara, J. (2013). Constant-pressure simulations of Gay–Berne liquid-crystalline phases in cylindrical nanocavities. Physical Chemistry Chemical Physics, 15(33), 14047. https://doi.org/10.1039/c3cp51241jKarjalainen, J., Vaara, J., Straka, M., & Lantto, P. (2015). Xenon NMR of liquid crystals confined to cylindrical nanocavities: a simulation study. Physical Chemistry Chemical Physics, 17(11), 7158–7171. https://doi.org/10.1039/c4cp04868gPeuravaara, P., Karjalainen, J., Zhu, J., Mareš, J., Lantto, P., & Vaara, J. (2018). Chemical shift extremum of 129Xe(aq) reveals details of hydrophobic solvation. Scientific Reports, 8(1). https://doi.org/10.1038/s41598-018-25418-4Self-archived versionOsajulkaisutOsajulkaisut eivät sisälly väitöskirjan elektroniseen versioon.Karjalainen, J., Lintuvuori, J., Telkki, V.-V., Lantto, P., & Vaara, J. (2013). Constant-pressure simulations of Gay–Berne liquid-crystalline phases in cylindrical nanocavities. Physical Chemistry Chemical Physics, 15(33), 14047. https://doi.org/10.1039/c3cp51241jKarjalainen, J., Vaara, J., Straka, M., & Lantto, P. (2015). Xenon NMR of liquid crystals confined to cylindrical nanocavities: a simulation study. Physical Chemistry Chemical Physics, 17(11), 7158–7171. https://doi.org/10.1039/c4cp04868gPeuravaara, P., Karjalainen, J., Zhu, J., Mareš, J., Lantto, P., & Vaara, J. (2018). Chemical shift extremum of 129Xe(aq) reveals details of hydrophobic solvation. Scientific Reports, 8(1). https://doi.org/10.1038/s41598-018-25418-4Rinnakkaistallennettu versioAcademic dissertation to be presented with the assent of the Doctoral Training Committee of Technology and Natural Sciences of the University of Oulu for public discussion in the Auditorium L5, Linnanmaa, on May 28th, 2021, at 12 o’clock noon.Abstract Fluids, especially liquid crystals, enclosed in porous materials exhibit a rich phase behaviour which can be exploited in both the study of the fundamental properties of the fluid itself, as well as its confinement. Nuclear magnetic resonance spectroscopy of xenon dissolved in the confined fluid is a sensitive and noninvasive method to study these systems. The purpose of this thesis is to develop and validate computational methods which can be used to interpret, as well as predict the structure and ¹²⁹Xe NMR of the fluid. The work used a combination of classical simulations of coarse-grained molecular models with quantum-chemical parameterisation for the pairwise-additive potential energies and the ¹²⁹Xe nuclear shielding tensors. More specifically, Monte Carlo molecular simulation was used to study the structure and phase behaviour of a uniaxial liquid crystal in a cylindrical nanocavity. Next, a small number of xenon atoms was added to the simulation and the nuclear shielding of ¹²⁹Xe was computed from the simulated configurations. Finally, the factors contributing to the maximum of the chemical shift of ¹²⁹Xe in water were studied with a semianalytical cavity model, which was parameterised using a combination of molecular dynamics simulations and quantum-chemical calculations. It was found that planar anchoring of liquid-crystal molecules at the walls of a cylindrical cavity promotes orientational order well above the isotropic-nematic phase transition temperature and the sharp isotropic-nematic transition of the bulk liquid crystal is replaced by a gradual paranematic-nematic transition. At lower temperatures the formation of translationally ordered phases is hindered by the packing of molecules at the wall. The ¹²⁹Xe shielding computed from the simulations corresponds qualitatively to earlier experimental results for xenon dissolved in a liquid crystal enclosed in the small cavities of controlled pore glass. The gradual change of orientational order at the paranematic-nematic transition is hard to observe in the isotropic shielding, especially in very small pores, but the transition reveals itself in the anisotropic part of the shielding. The semianalytical cavity model qualitatively reproduces the maximum of the ¹²⁹Xe chemical shift in water. The extremum is interpreted as arising from the interplay of the variation in water density and the collisions of the Xe solute with its nearest water molecule neighbours. The interpretation suggests the chemical shift maximum could be observed also in other solvents

Advances in patterned polymer nanoestructures in-situ polymerization and polymer infiltration in AAO templates

Tesis inédita de la Universidad Complutense de Madrid, Facultad de Ciencias Químicas, Departamento de Química-Física, leída el 19-04-2017Las plantillas porosas de alúmina (AAO) son sistemas ordenados, formados por una matriz de poros cilíndricos uniformemente dimensionados. Estas plantillas han sido ampliamente empleadas en nuestro grupo para la obtención de nanoestructuras poliméricas como nanorods, nanofibras y nanotubos mediante el proceso infiltración de polímeros (nanomoldeo). Asimismo, numerosos trabajos han demostrado que las propiedades del polímero en confinamiento dentro de los nanoporos cambian con respecto a las propiedades del mismo polímero en masa. Sin embargo, cuando se trata de infiltrar polímeros termoestables o el proceso de infiltración debe llevarse a cabo a alta temperatura y/o durante un tiempo relativamente largo, de horas a días, el polímero se puede degradar y es conveniente buscar otro método. Esta tesis doctoral plantea la polimerización in situ de un monómero dentro de los poros de la plantilla AAO (nanoreactor) como método alternativo para producir nanoestructuras poliméricas. Una vez polimerizado el polímero puede extraerse para el estudio de sus propiedades y para su uso en distintas aplicaciones. Esta tesis está basada en el empleo de plantillas AAO y comprende dos aspectos importantes, su empleo como nanoreactores y nanomoldes. Los objetivos de esta tesis son: el estudio de las reacciones de polimerización de diferentes monómeros en las nanocavidades y la preparación de nuevas nanoestructuras poliméricas nunca reportadas en la literatura, mediante la infiltración de polímeros en AAO. El primer objetivo además plantea la modelización de la polimerización en confinamiento estudiando las diferencias respecto al bulk. Para alcanzar estos objetivos se prepararon plantillas de alúmina mediante el proceso de doble anodización. El empleo de distintas condiciones de anodización (temperatura, naturaleza y concentración del electrolito, voltaje y tiempo) permitió la elaboración de plantillas de distintos tamaños de diámetro y longitud de poro, entre 15-400 nanómetros y 0.7-100 micras, respectivamente...Anodic aluminium oxide templates (AAO) are ordered systems, formed by a matrix of uniformly sized cylindrical pores. These templates have been widely used in our group to obtain polymer nanostructures such as nanorods, nanofibers and nanotubes through the process of polymer infiltration (nanomolding). Also, numerous studies have shown that the properties of the polymer in confinement inside the nanopores change acoording to the properties of the same polymer in bulk. However, when we need to infiltrate thermosetting polymers or the infiltration process must be carried out at high temperature and / or for a relatively long time, from hours to days, the polymer may be degraded and it is required to use other method. This doctoral thesis proposes the in situ polymerization of a monomer within the pores of the AAO template (nanoreactor) as an alternative method to produce polymer nanostructures. Once it polymerized, the polymer can be extracted for the study of its properties and can be the use in different applications. This thesis is based on the use of AAO templates and comprises two important aspects, their use as nanoreactors and nanomolds. The objectives of this thesis are: the study of the reactions of polymerization of different monomers in the nanocavities and the preparation of new polymer nanostructures never reported in the literature, by the polymer infiltration process in AAO. The first objective also proposes the modelling of the polymerization in confinement by studying the differences with respect to the bulk. To achieve these objectives, alumina templates were prepared by the double anodization process. The use of different anodizing conditions (temperature, nature and concentration of electrolyte, voltage and time) allowed the development of templates of different sizes of pore diameter and pore length, between 15-400 nanometers and 0.7-100 microns, respectively...Depto. de Química FísicaFac. de Ciencias QuímicasTRUEunpu