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Evaluation of the conductor-like screening model for real solvents for the prediction of the water activity coefficient at infinite dilution in ionic liquids

Publication . Kurnia, Kiki A.; Pinho, Simão; Coutinho, João A.P.

Ionic liquids (ILs) have attracted great attention, from both industry and academia, as alternative fluids for very different types of applications. The large number of cations and anions allow a wide range of physical and chemical characteristics to be designed. However, the exhaustive measurement of all these systems is impractical, thus requiring the use of a predictive model for their study. In this work, the predictive capability of the conductor-like screening model for real solvents (COSMO-RS), a model based on unimolecular quantum chemistry calculations, was evaluated for the prediction water activity coefficient at infinite dilution, gamma(infinity)(w), in several classes of ILs. A critical evaluation of the experimental and predicted data using COSMO-RS was carried out. The global average relative deviation was found to be 27.2%, indicating that the model presents a satisfactory prediction ability to estimate gamma(infinity)(w) in a broad range of ILs. The results also showed that the basicity of the ILs anions plays an important role in their interaction with water, and it considerably determines the enthalpic behavior of the binary mixtures composed by Its and water. Concerning the cation effect, it is possible to state that generally gamma(infinity)(w) increases with the cation size, but it is shown that the cation-anion interaction strength is also important and is strongly correlated to the anion ability to interact with water. The results here reported are relevant in the understanding of ILs-water interactions and the impact of the various structural features of its on the gamma(infinity)(w) as these allow the development of guidelines for the choice of the most suitable lLs with enhanced interaction with water.

2014Journal article

Restricted access

Síntese e caracterização de polímeros condutores com aplicações em células solares

Publication . Ribeiro, Clementina da Conceição Soares; Dias, Rolando

Neste trabalho foi realizada a síntese de PEDOT (Poli (3,4-etilenodioxitiofeno)) através de três tipos de polimerização a partir do monómero EDOT (3,4-etilenodioxitiofeno): Polimerização oxidativa de EDOT, polimerização oxidativa de EDOT:PSS (Poli (4- ácido estirenossulfónico)) e eletropolimerização de EDOT. Também foi feita interpenetração de PEDOT num hidrogel de ácido acrílico através de diversos métodos, nomeadamente a síntese de PEDOT:PSS com interpenetração simultânea em hidrogel de ácido acrílico inicialmente seco, síntese de PEDOT:PSS em simultâneo com a polimerização de hidrogel de ácido acrílico, interpenetração de PEDOT:PSS seco em hidrogel de ácido acrílico seco e interpenetração de PEDOT:PSS em hidrogel de ácido acrílico. O método que se verificou funcionar de forma mais adequada foi o de síntese de PEDOT:PSS com interpenetração simultânea em hidrogel de ácido acrílico inicialmente seco. A interpenetração de PEDOT:PSS em hidrogel de ácido acrílico mostrou ser também parcialmente viável. Estes testes tiveram como objetivo avaliar a síntese de materiais híbridos, nomeadamente hidrogéis estimuláveis pela corrente elétrica. Procedeu-se também à caraterização dos materiais obtidos através de, espetroscopia UV (Ultravioleta), análise microscópica, testes de condutividade do material, e voltametria cíclica (CV). Na fase final do trabalho foram estudadas duas aplicações práticas dos materiais sintetizados. Procedeu-se à construção de DSC’s (células solares sensibilizadas por corante) com aplicação de PEDOT no contra elétrodo e comprovou-se também o efeito electrocrómico do polímero através de voltametria cíclica. No último caso foi realizada a eletropolimerização de EDOT num vidro FTO (Óxido de Estanho Dopado com Flúor). Neste trabalho são também apresentadas as curvas I-V das DSC’s elaboradas e são analisados os valores obtidos nos testes que lhes foram efetuados. Pretendeu-se desta forma comparar o desempenho das DSC’s produzidas com soluções já padronizadas.

2015Master thesis

Open access

Electrochemical activity of sulfur networks synthesized through RAFT polymerization

Publication . Almeida, Carlos M.F.; Costa, Hugo Davide; Kadhirvel, Porkodi; Queiroz, Ana; Dias, Rolando; Costa, Mário Rui

Novel results concerning the inverse vulcanization of sulfur using reversible addition–fragmentation chain transfer (RAFT) polymerization are here reported. It is shown that RAFT polymerization can be used to carry out this cross-linking process, with the additional possibility to extend the reaction time from a few minutes as with classical free radical polymerization (FRP) to several hours. Higher control on viscosity and processability of the synthesized networks, as well as, the implementation of semibatch feed policies during cross-linking are important advantages of the RAFT process here explored comparatively to the FRP inverse vulcanization. Using cyclic voltammetry, it was assessed the electrochemical activity of the synthesized sulfur-rich polymer networks. It is shown that the fundamental electrochemical activity of the elemental sulfur was preserved in the produced materials. Testing of electrochemical cells assembled with lithium in the anode and different sulfur based materials in the cathode, including the synthesized RAFT networks, is also shown. The results here presented highlight the new opportunities introduced by reversible-deactivation radical polymerization mechanisms on the control of the synthesis process and in the design of such advanced materials and show also that many potential derivatizing possibilities can be achieved.

2016Journal article

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Impact of the cation symmetry on the mutual solubilities between water and imidazolium-based ionic liquids

Publication . Martins, Mónia A.R.; Neves, Catarina M.S.S.; Kurnia, Kiki A.; Luís, Andreia; Santos, Luís M.N.B.F.; Freire, Mara G.; Pinho, Simão; Coutinho, João A.P.

Aiming at the evaluation of the impact of the ionic liquids (ILs) cation symmetry on their phase behaviour, in this work, novel mutual solubilities with water of the symmetric series of [C(n)C(n)im][NTf2] (with n=1-5) were determined and compared with their isomeric forms of the asymmetric [C(n)C(1)im][NTf2] group. While the solubility of isomeric ILs in water was found to be similar, the solubility of water in ILs follows the same trend up to a maximum cation alkyl side chain length. For n >= 4 in [C(n)C(n)im][NTf2] the solubility of water in the asymmetric ILs is slightly higher than that observed in the symmetric counterparts. The thermodynamic properties of solution and solvation derived from the experimental solubility data of ILs in water at infinite dilution, namely the Gibbs energy, enthalpy and entropy were used to evaluate the cation symmetry effect on the ILs solvation. It is shown that the solubility of ILs in water is entropically driven and highly influenced by the cation size. Accordingly, it was found that the ILs solubility in water of both symmetric and asymmetric series depends on their molecular volume. Based on these findings, a linear correlation between the logarithm of the solubility of ILs in water and their molar volume is here proposed for the [NTf2]-based ILs at a fixed temperature.

2014Journal article

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Study of the encapsulation efficiency and release profiles of alginate microspheres containing α-tocopherol

Publication . Vieira, Dalila; Amaral, Joana S.; Barreiro, M.F.

Vitamin E, a lipophilic natural antioxidant comprising different vitamers (α, β, γ and δ-tocopherols and tocotrianols), is frequently used in food supplements and added in different products, such as foodstuffs and cosmetics, to prevent lipid oxidation processes. Due to solubility and stability issues, α-tocopherol is generally administrated as succinate or acetate derivatives, which have lower bioavailability. In this work, alginate microspheres containing α-tocopherol were produced and evaluated for encapsulation efficiency and release profiles at different pH conditions during 24h. In vitro release tests showed that alginate microspheres maintain its integrity under simulated gastric conditions. By the contrary, under simulated intestinal conditions, an almost complete release is achieved during 24h, with a major portion (70%) being released after 2h.

2014Conference object

Open access