Publications

Abstract Vanillin is a naturally occurring phenolic aldehyde that is world-wide known for its flavouring properties. This work reports an extensive experimental and computational study of its thermodynamic properties. The vapour pressures of crystalline and liquid phases of vanillin were measured in the following temperature ranges T = (321.0-350.7) K and (324.9-382.3) K respectively, using a static method based on diaphragm capacitance gauge. Additionally, the crystalline vapour pressures were also measured in the temperature interval T = (303.1-325.2) K, using a Knudsen mass-loss effusion technique. The standard molar enthalpies, entropies and Gibbs energies of sublimation and of vaporization, at selected reference temperatures, were derived from the vapour pressure measurements. The enthalpies of vaporization and of sublimation, at T = 298.15 K, were also determined using Calvet microcalorimetry and the standard (p degrees = 10(5) Pa) molar enthalpy of formation, in the crystalline phase, at T = 298.15 K, was derived from its standard massic energy of combustion measured by static-bomb combustion calorimetry. From the experimental results, the standard molar enthalpy of formation in the gaseous phase, at T = 298.15 K, was calculated and compared with the values estimated by employing quantum chemical calculations. To analyse the thermodynamic stability of vanillin, the standard Gibbs energies of formation in crystalline and gaseous phases were calculated. The molar enthalpy of fusion determined using DSC is compared with indirect results determined using Calvet microcalorimetry and vapour pressure measurements. (C) 2018 Elsevier Ltd.

Abstract Er3+/Yb3+ codoped NaGdF4 upconversion phosphor is synthesized by thermal decomposition route. The phase confirmation of synthesized sample is further confirmed by x-ray diffraction analysis. Particle size and elemental composition of phosphor is analyzed by field emission scanning electron microscopy (FESEM) and energy dispersive x-ray (EDX), respectively. The upconversion emission is measured by exciting the sample with 976 nm diode laser source. The fluorescence intensity ratio (FIR) of two close levels H-2(11/2) and S-4(3/2) is taken into account to study thermometry ability of sample for the temperature range of 301-506 K at a constant laser power (17.60 W cm(-2)). The sensor sensitivity of phosphor is found to 5.107 x 10(-3) K-1 at 301 K.

Abstract This work presents an extended study of the thermal behavior of the alkyl and dialkylpyridinium derivatives of the bis(trifluoromethylsulfonyl)imide ionic liquid series, using high resolution power compensation differential scanning calorimetry (DSC) equipment. Temperatures, enthalpies, entropies, and the heat capacity change associated with the glass transition, as well as cold crystallization, solid-solid transitions, and melting, are used to evaluate their ability to form a glass and crystallize. The effects of the cation isomerization and the alkyl chain length increase were used to investigate the nature of the irregular thermal behavior of ionic liquids in general and to establish the link between their thermal properties and nanostructuration. The observed V-shape profile of the melting temperatures versus the alkyl side-chain length is interpreted as a consequence of the balance between the initial decrease of the magnitude of the electrostatic interaction and the regular increase of the dispersive van der Waals forces. The observed differentiation between the thermal behavior below and above the critical alkyl size, CAS, is analyzed and compared with the regular behavior of both the n-alkanes and the n-alkanols. Above the CAS, the entropy and enthalpy profiles present trends similar to those observed in the alkane and alcohol series, contrasting with those observed in the molten salts-like region. These results and evidence are a strong support to the interpretation of the effect of the ILs nanostructuration in the physical-chemical properties. We found a great similarity between the thermal behavior of the imidazolium and pyridinium cation core, highlighting the strong ability of ILs to form a nanostructured network with distinguishable polar and nonpolar domains in the liquid phase.

Abstract Twelve surface-active ionic liquids (SAILs) and surface-active derivatives, based on imidazolium, ammonium, and phosphonium cations and containing one, or more, long alkyl chains in the cation and/or the anion, were synthetized and characterized. The aggregation behavior of these SAILs in water, as well as their adsorption at solution/air interface, were studied by assessing surface tension and conductivity. The CMC values obtained (0.03-6.0 mM) show a high propensity of these compounds to self-aggregate in aqueous media. Their thermal properties were also characterized, namely the melting point and decomposition temperature by using DSC and TGA, respectively. Furthermore, the toxicity of these SAILs was evaluated using the marine bacteria Aliivibrio fischeri (Gram-negative). According to the EC50 values obtained (0.3-2.7 mg L-1), the surface-active compounds tested should be considered "toxic" or "highly toxic". Their ability to induce cell disruption of Escherichia coli cells (also Gram-negative), releasing the intracellular green fluorescent protein (GFP) produced, was investigated. The results clearly evidence the capability of these SAILs to act as cell disruption agents.

Abstract The Knudsen mass-loss effusion method was used to determine the sublimation vapour pressures, at different temperatures, of ortho and para aminophenols in the temperature intervals T = (321.1 to 343.3) K and T= (337.2 to 359.2) K, respectively. The vapour pressures of crystalline meta-aminophenol were measured using the referred to above technique, between (321.4 and 343.3) K, and a static method, based on capacitance diaphragm manometers, between (354.4 and 391.8) K. The latter technique was also used to measure the liquid vapour pressures of this isomer over the temperature range T = (370.0 to 423.3) K. The experimental results enabled the determination of the standard (p(0) = 0.1 MPa) molar enthalpies, entropies and Gibbs energies of sublimation, at T = 298.15 K, of the three compounds, and of vaporization of the meta isomer. The standard enthalpies of formation in the gaseous phase were calculated using quantum chemical calculations and also by combining literature results of enthalpies of formation in the crystalline phase with the sublimation enthalpies results determined in this work. Gas-phase absolute entropies and heat capacities of the three compounds studied were also calculated using theoretical methods. The standard Gibbs energies of formation in crystalline and gaseous phases were determined and used to evaluate the thermodynamic stability of the three isomers in standard conditions. DSC analysis enabled the determination of the temperature and molar enthalpies of fusion of the compounds studied. (C) 2018 Elsevier Ltd.

Abstract A storytelling approach has been seen as a powerful way to teach science and arouse interest and promote positive attitudes toward learning science in the early years. The purpose of our study was to determine how middle school students - Key Stage 3 (KS3) aged 12-14 in Portuguese schools - experienced learning chemistry through storytelling and how they, in turn, experienced creating stories using a storytelling approach with pre-school children. We aimed to perceive the appropriation of concepts of chemistry by the pre-school children through their drawings, the results collected during the pedagogical intervention and the recordings of the discussions between the pre-school children, the students and the pre-school teachers. The KS3 students were also given a self-assessment questionnaire as a way of assessing the pedagogical dynamics and the drive and motivation to learn chemistry. The study involved 53 children: 16 from KS3 and 37 from pre-school. The intervention took place during the KS3 students' chemistry classes and during the pre-schoolers' storytelling moment, a weekly 1 hour activity that took place at their kindergarten. We found that the use of a storytelling approach complemented with hands-on activities, as a strategy to teach acid-base content to KS3 students, contributed to their learning. Moreover, it was an important experience, which motivated them to write their stories and to prepare the activities for the pre-schoolers. We also found that the interaction of the older students with the pre-schoolers was profitable for both parts, since this type of activity promotes the acquisition of knowledge. During the storytelling moment and the hands-on activities with the pre-schoolers, we were able to witness that the younger students understood the concepts, enjoyed the interaction and felt captivated to learn science, through the questions they posed, the informal conversations and the drawings they made. This study showed us that the use of stories and hands-on activities is an effective strategy in motivating young people to learn chemistry.

Abstract Museums and exhibitions usually attempt to evaluate visitors' obtained knowledge through the use of traditional evaluation methods such as questionnaires. These are intrusive and may not provide correct results, especially due to the fact that visitors are usually not interested in being evaluated and may consider such questionnaires as intelligence tests. This paper proposes methods of design and creation of automatic evaluation techniques that make use of Virtual Reality (VR) in order to evaluate users' obtained knowledge after playing through a VR museum game experience. This Analysis System is non-intrusive (its methodology does not impact users' immersion and engagement), valid (can draw conclusions regarding users' obtained knowledge), and replicable (designed techniques can be used in a variety of experiences). Results indicate that the designed assessment techniques can be used to automatically evaluate the knowledge obtained by users throughout the experience, as well as some considerations to keep in mind when designing game experiences with these techniques.

Abstract The goal of this paper is to understand the way multimedia and virtual reality are being integrated into the communication practices of science centers and represented by their directors or responsible personnel, from the perspective of the social representations theory. Through a three-phase, mixed-methods approach, we focused on the 21 institutions of the Portuguese network of science centers (Rede de Centros Ciencia Viva). Phase I consisted of a documentary analysis of the science centers websites and Facebook pages, in order to draw a preliminary map of the activities, scientific areas, multimedia and virtual reality devices of the centers. In phase II, we surveyed 16 directors or responsible personnel of the science centers via an online questionnaire, to corroborate the results obtained in the documentary analysis and also to identify the role of multimedia in science centers and which of them had virtual reality activities. Phase III consisted of semi-structured interviews with six directors or responsible personnel of six science centers from North to South of Portugal to explore their social representations, as well as to obtain in-depth information about the role of multimedia, virtual reality and visitors in the science communication strategy of the centers. Data were analyzed with the support of Excel, SPSS, and NVivo. Results showed that exhibitions are the most common kind of activities, followed by laboratories and workshops. Physical-natural sciences were represented in more than 75% of the science centers; mathematics, robotics, and informatics were present in less than 50% of the centers; social sciences and arts were underrepresented. Whereas projection devices and computers were used in more than 80% of the centers, virtual reality devices, tablets, and touch screens were used in less than 15%. Results of phase II, besides corroborating data from phase I, showed that the integration of multimedia seems to be associated with different degrees of interactivity allowed for the visitor. Virtual reality devices were mainly used to demonstrate their immersive capability rather than to explore the specificities of the science contents. As for the social representations, we found that multimedia was associated with the integration of image and sound and anchored to learning purposes and young audiences. Virtual reality was defined as "simulation" and "reality that does not exist", therefore objectifying the concept of interactivity. It was perceived as a means to attract more audience. Though a central role was assigned to the visitor, contextualization seemed to be the more frequently adopted model of science communication. The findings suggest that, though multimedia plays a central role in the centers, it does not meet up the promise of allowing for higher levels of interactivity and public engagement and that virtual reality became the ultimate technology for making sense of interactivity and extension of reality. This study urges for a framework to promote a balanced integration of the multimedia with the activities of science centers to support the adoption of bidirectional models of science communication, in which evaluation is essential. This line of research is being explored in a science communication project (I SEA) by a multidisciplinary team. Based on the affordances and social representations of virtual reality, the main goal is to develop a non-obtrusive method of evaluation of science communication in non-formal spaces.

Abstract A series of pyridyl analogues of rosamines was prepared by employing two methodologies: (i) the conventional-heating condensation of a pyridinecarboxaldehyde with 3-(diethylamino)phenol in propionic acid, and (ii) the novel ohmic-heating assisted condensation under "on water" conditions, followed by oxidation. The 4-pyridyl substituted rosamine was further converted into the N-methylpyridinium derivative through N-alkylation using methyl iodide. The influence of the position and cationization of the nitrogen atom of the pyridyl ring in the physicochemical properties of fluorophores was investigated by H-1, C-13, N-15 NMR spectral analysis, UV/Vis and fluorescence spectroscopy, single-crystal X-ray diffraction (4-pyridyl and N-methylpyridinium derivatives) and thermal-behavior analysis. Curiously, for ethanolic solutions of 4-pyridyl and N-methylpyridinium derivatives an extinction of color and fluorescence over time was observed. This phenomenon was further studied and the data revealed that it is the result of nucleophilic addition of ethoxide ion to the central 9-position of the xanthene. The kinetics of the process is slower for the 4-pyridyl rosamine, which emphasizes the importance of the charge in the N-methylpyridinium analogue in the reactivity of the molecule towards a nucleophile agent. This phenomenon is reversible, meaning that the compounds can be rapidly recovered by decreasing the pH, opening new avenues in the sensing applications of this class of rosamines.