Echeverria, C, Fernandes SN, Almeida PL, Godinho MH.
2016.
Effect of cellulose nanocrystals in a cellulosic liquid crystal behaviour under low shear (regime I): Structure and molecular dynamics. European Polymer Journal. 84:675-684.
AbstractIn the field of cellulosic liquid crystals, attempts to establish the relationship between structure/properties have been developed. Above a critical concentration in an aqueous solution, hydroxypropylcellulose self-assembles in order to form cholesteric liquid crystal phases (LC-HPC). In this work we aim to understand how the incorporation of a low content of cellulose nanocrystals (CNC) within LC-HPC/H2O (50 wt%), could influence the behaviour of the system when subjected to low shear rates, where the cholesteric phase still persists. The analysis of the deuterium spectrum and the T2 (transversal relaxation) values confirm that the mobility of LC-HPC at low shear rates is restricted due to CNC, and consequently so is the flow of the cholesteric polydomains. These effects are more evident in the LC-HPC sample containing 2 wt% of CNC; besides needing more strain units to induce some degree of order, the achieved degree of order is recovered faster when compared to the reference sample.
Duczinski, R, Polesso BB, Bernard FL, Ferrari HZ, Almeida PL, Corvo MC, Cabrita EJ, Menezes S, Einloft S.
2020.
Enhancement of CO2/N2 selectivity and CO2 uptake by tuning concentration and chemical structure of imidazolium-based ILs immobilized in mesoporous silica. Journal of Environmental Chemical Engineering.
AbstractImidazolium-based ionic liquids (ILs) with different cation alkyl chain ([i-C5mim] or [C4mim]) and inorganic anions ([Cl−], [Tf2N−], [PF6−] and [DCA−]) were synthesized and immobilized in commercial mesoporous silica. The synthesized supported ILs (SILs) were characterized using NMR, FTIR, TGA, BET, SEM and TEM. CO2 sorption capacity, reusability and CO2/N2 selectivity were assessed by the pressure-decay technique. The effects of IL concentration, cation and anion chemical structure in CO2 sorption capacity and CO2/N2 separation performance were evaluated. Tests evidenced that the presence of branching on the cation alkyl side chain increases CO2/N2 selectivity. The immobilization of the IL [i-C5TPIm][Cl] on mesoporous silica in different concentrations (50, 20, 10 and 5 %) revealed that lower IL concentration results in higher CO2 sorption capacity. Immobilization of ILs containing fluorinated anions at low concentrations in the mesoporous silica support may promote the improvement of the CO2/N2 selectivity without interfering on CO2 sorption capacity of the original support. CO2 sorption capacity value shown by sample SIL-5 % - [i-C5TPIm][Tf2N] (79.50 ± 0.70 mg CO2 g-1) was close to the value obtained for the pristine mesoporous silica (81.70 ± 2.20 mg CO2 g-1) and the selectivity (4.30 ± 0.70) was more than twice of the one obtained for the support alone (2.32 ± 0.4). Recycle tests demonstrated that the ILs immobilized in mesoporous silica samples are stable, providing a new option to be used in CO2 capture processes.
Neves, CS, Granadeiro CM, Cunha-Silva L, Ananias D, Gago S, Feio G, Carvalho PA, Eaton P, Balula SS, Pereira E.
2013.
Europium Polyoxometalates Encapsulated in Silica Nanoparticles Characterization and Photoluminescence Studies. European Journal of Inorganic Chemistry. :2877-2886., Number 16
AbstractThe incorporation of europium polyoxometalates into silica nanoparticles can lead to a biocompatible nanomaterial with luminescent properties suitable for applications in biosensors, biological probes, and imaging. Keggin-type europium polyoxometalates Eu(PW11)x (x = 1 and 2) with different europium coordination environments were prepared by using simple methodologies and no expensive reactants. These luminescent compounds were then encapsulated into silica nanoparticles for the first time through the water-in-oil microemulsion methodology with a nonionic surfactant. The europium polyoxometalates and the nanoparticles were characterized by using several techniques [FTIR, FT-Raman, 31P magic angle spinning (MAS) NMR, and TEM/energy-dispersive X-ray spectroscopy (TEM-EDS), AFM, dynamic light scattering (DLS), and inductively coupled plasma MS (ICP-MS) analysis]. The stability of the material and the integrity of the europium compounds incorporated were also examined. Furthermore, the photoluminescence properties of the Eu(PW11)x@SiO2 nanomaterials were evaluated and compared with those of the free europium polyoxometalates. The silica surface of the most stable nanoparticles was successfully functionalized with appropriate organosilanes to enable the covalent binding of oligonucleotides.