María Teresa Viciosa

• Researcher at Technical University of Lisbon

Aceclofenac (ACF), a non-steroidal anti-inflammatory drug, was obtained in its amorphous state by cooling from melt. The glass transition was investigated using dielectric and calorimetric techniques, namely, dielectric relaxation spectroscopy (DRS), thermally stimulated depolarization currents (TSDC), and conventional and temperature-modulated dif...

Hybrid solid-like materials prepared from the incorporation of liquid-like ionic conductors into nanoporous matrices could represent an advantage for a variety of electronic applications. Aiming to obtain such materials, three composites of the polymorphic ionic liquid crystal (ILC) 1-hexadecyl-2-methylpyridinium bromide ([C16-2-Pic][Br]), loaded i...

To investigate the impact of the surface functionalization of mesoporous silica nanoparticle (MSN) carriers in the physical state, molecular mobility and the release of Fenofibrate (FNB) MSNs with ordered cylindrical pores were prepared. The surface of the MSNs was modified with either (3-aminopropyl) triethoxysilane (APTES) or trimethoxy(phenyl)si...

A rational design of drug delivery systems requires in-depth knowledge not only of the drug itself, in terms of physical state and molecular mobility, but also of how it is distributed among a carrier and its interactions with the host matrix. In this context, this work reports the behavior of simvastatin (SIM) loaded in mesoporous silica MCM-41 ma...

Random copolymers of 2-(2-methoxyethoxy)ethyl methacrylate (MEO2MA) and oligo(ethylene glycol) methacrylate (OEGMA) have a temperature-induced phase transition in aqueous solutions, which can be tuned for different temperatures from ca. 20 °C–90 °C by changing their monomer ratio. Here, we explore a novel approach combining UV–Vis measurements (lig...

Natural deep eutectic systems (NADES), which have applications as solvents for both engineering and life sciences, are mainly composed of sugars, aminoacids or organic acids. In this work NADES composed by glucose, urea and proline (G:U:P in a molar ratio of 1:1:1) and proline and glucose (P:G 5:3) were prepared and added in different mass fraction...

The thermal behavior of carvedilol and loratadine was studied by differential scanning calorimetry (DSC). The glass-forming ability, the tendency for crystallization from the glass (glass stability) and from the metastable and equilibrium melt was investigated by DSC. This technique was also used to characterize the glass transition of carvedilol a...

The analysis of the thermal behavior of efavirenz showed a high glass-forming ability and good glass stability of this glass-forming liquid at room temperature. No polymorphic forms were formed either by cold crystallization or by recrystallization from solvent acetone. The determination of the dynamic fragility by the differential scanning calorim...

Studies of the impact of chirality on the amorphous states are scarce. Here, we present combined dielectric relaxation spectroscopy (DRS) experiments and molecular dynamics (MD) simulations investigations of the homochiral and racemic ibuprofen in the liquid, undercooled liquid and glassy states. The influence of chirality is particularly investiga...

This study of the thermal behaviour of two glass formers showed that rofecoxib has a good ability to vitrify while celecoxib displays a moderate glass forming ability. On the other hand, celecoxib forms an instable glass while rofecoxib displays moderate glass stability. The α-relaxation of the two amorphous drugs was studied by differential scanni...

A thermoresponsive, biocompatible and water soluble copolymer was synthetized via RAFT from 2-(2-methoxyethoxy)ethyl methacrylate (MEO2MA) and oligo (ethylene glycol) methacrylate (OEGMA) in the molar ratio of 9:1. The thermal behavior of the bulk material was investigated through thermogravimetric analysis and differential scanning calorimetry, re...

The amorphization of the readily crystallizable therapeutic ingredient and food additive, menthol, was successfully achieved by inclusion of neat menthol in mesoporous silica matrixes of 3.2 and 5.9 nm size pores. Menthol amorphization was confirmed by the calorimetric detection of a glass transition. The respective glass transition temperature, Tg...

Thermoresponsive microgels with an upper critical solution temperature (UCST) response (i.e., showing volume expansion at higher temperature) are highly desirable for a variety of applications, but quite uncommon, in particular if they are to work in physiological conditions. Here we present a novel UCST-type microgel showing a remarkable transitio...

The slow molecular mobility in the amorphous solid state of 3 active pharmaceutical drugs (cimetidine, nizatidine, and famotidine) has been studied using differential scanning calorimetry and the 2 dielectric-related techniques of dielectric relaxation spectroscopy and thermally stimulated depolarization currents. The glass-forming ability, the gla...

The pharmaceutical drug naproxen was loaded in three different silica hosts with pore diameter of 2.4 nm (MCM), 3.2 nm (MCM) and 5.9 nm (SBA), respectively, napMCM_2.4nm, napMCM_3.2nm and napSBA_5.9nm. To access the guest physical state in the prepared composites, differential scanning calorimetry (DSC), X-Ray diffraction (XRD) and attenuated total...

The slow molecular mobility of the active pharmaceutical drug fenofibrate is studied by differential scanning calorimetry (DSC) and thermally stimulated depolarization currents (TSDC). The general kinetic features of the secondary relaxations and of the main relaxation, in particular their distribution of relaxation times, were determined by TSDC....

It was demonstrated that the combination of the almost water insoluble active pharmaceutical ingredient (API) ibuprofen with the biocompatible 1-ethanol-3-methylimidazolium [C2OHMIM] cation of an ionic liquid (IL) leads to a highly water miscible IL-API with a solubility increased by around 5 orders of magnitude. Its phase transformations, as cryst...

Inclusion complexes (ICs) composed of α-cyclodextrin (α-CD) and poly(d,l-lactic acid) (PDLLA), with 10/24 (IC1) and 15/46 (IC2) (% w/w) of PDLLA incorporated/initial PDLLA weight percentage, were prepared and characterized mainly by dielectric relaxation spectroscopy (DRS). Bulk PDLLA was also analyzed for comparison. DRS was revealed to be a suita...

Statins have been widely used as cholesterol-lowering agents. However, low aqueous solubility of crystalline statins and consequently reduced biovailability, requires seeking for alternative forms and formulations to ensure an accurate therapeutic window. The objective of the present study was to evaluate the stability of amorphous simvastatin by p...

Amorphous S-flurbiprofen was obtained by the melt quench/cooling method. Dielectric measurements performed in the isochronal mode, conventional and temperature modulated differential scanning calorimetry (TMDSC) studies showed a glass transition, recrystallization and melting. The different parameters characterizing the complex molecular dynamics o...

The paper investigates the influence of the crystalline structure in the dynamical behavior of semicrystalline Triton X-100 allowing enlightening the reason for the detection/nondetection of the α'-process. The work was preceded by the study of the full amorphous material for which dielectric relaxation spectroscopy (DRS) identified multiple relaxa...

The thermal and dielectric properties of ionic liquid 1-butyl-3-methylimidazolium bromide (BmimBr) were measured in the glassy, supercooled liquid and equilibrium liquid states, covering the temperature range from −120 to 100 °C. From thermally stimulated depolarization current (TSDC) data we determined the glass transition temperature, that was in...

The phase transformations of the surfactant Triton X-100 were investigated by differential scanning calorimetry (DSC), polarized optical microscopy (POM), and dielectric relaxation spectroscopy (DRS). In particular, crystallization was induced at different cooling rates comprised between 13 and 0.5 K min(-1). Vitrification was detected by both DSC...

The Thermally Stimulated Depolarization Current (TSDC) technique has been used to study the molecular mobility of diglycidyl ether of bisphenol-A (DGEBA) in the temperature range from −160 °C up to 10 °C. The molecular mobility in the glassy state and in the supercooled liquid was then characterized. Two secondary relaxations were detected, one of...

Molecular mobility of a series of tri-ethylene glycol dimethacrylate (TrEGDMA) samples polymerized with different amounts of ethyl acetate up to 40% (w/w) as diluent was investigated by dielectric relaxation spectroscopy. In the first measuring scan, the samples show three secondary relaxation processes: a c process related to the twisting motions...

The isothermal cold-crystallization of the glass-former low-molecular-weight compound, ethylene glycol dimethacrylate (EGDMA), was monitored by real-time dielectric relaxation spectroscopy (DRS) and differential scanning calorimetry (DSC). The alpha-relaxation associated with the dynamic glass transition as detected by DRS was followed at different...

The crystallization induced by different thermal treatments of a low molecular weight glass former, ethylene glycol dimethacrylate (EGDMA), was investigated by dielectric relaxation spectroscopy (DRS) and differential scanning calorimetry (DSC). The fully amorphous material, dielectrically characterized for the first time, exhibits three relaxation...

In the present work we revisit the previously published study by Thermally Stimulated Depolarisation Currents (TSDC) of the slow molecular mobility in the amorphous solid state of 4,4′-methylenebis(N,N-diglycidylaniline), MBDA (H. P. Diogo, J. J. Moura Ramos, J. Mol. Liq. 129(2006)138–146) in order to add two important points dealing with recent us...

The data treatment in Thermally Stimulated Depolarisation Currents (TSDC) is generally based on the Debye decay function. Due to the nonexponentiality of the main relaxation in molecular glasses and amorphous polymers, this usual methodology has been criticized and the alternative use of the Kohlrausch function (stretched exponential) was suggested...

Electric field driven anchoring breakage in poly(triethylene glycol dimethacrylate)/nematic E7 composites was studied using dielectric spectroscopy and transmittance measurements. The transmittance hysteresis observed on increasing and decreasing an applied electric field, associated with different alignment states of the liquid crystal (LC), was m...

A detailed dielectric characterization of n-ethylene glycol dimethacrylate monomers with n = 2 and 4 is provided. Besides the α relaxation associated to the glass transition, two secondary relaxation processes were detected: the γ process assigned to the twisting motions within the ethylene glycol moiety, and the β process related with hindered rot...

Temperature modulated differential scanning calorimetry (TMDSC) is used to study the kinetics of the free radical isothermal polymerization of triethyleneglycol dimethacrylate (TEGDMA). Azo-bis-isobutironitrile was used as initiator. The polymerization’s temperature is lower than the final glass transition temperature of the polymer network. The me...

Ethylene and 10-undecen-1-ol copolymers, prepared using a nickel complex as catalyst, were studied using differential scanning calorimetry (DSC), X-ray diffraction, and dielectric relaxation spectroscopy. The behavior exhibited by copolymers containing incorporated 10-undecen-1-ol amounts within 0.5 and 4.6 mol % was compared with neat polyethylene...

A detailed dielectric characterization of the relaxation modes found in a poly(L-lactic acid), PLLA, film containing 0.4 mass% of water is provided. The sub-glass relaxation process is a superposition of two processes, one highly influenced by water with activation energy of 50 kJ mol–1, and another one, with longer relaxation times and lower inten...

The dielectric properties of methylacrylate (MA)/tri-ethyleneglycol dimethacrylate (TrEGDMA) copolymers at different compositions, ranging from 0 to 100, were measured between −120 and 150 °C over the frequency range 0.1 Hz–1 MHz. In the given frequency range, three relaxation processes were detected by dielectric relaxation spectroscopy in homo po...

The properties of the amorphous component in poly(l-lactic acid), PLLA, depend on its crystalline structure, where the nanoconfinement effects may be monitored using dielectric relaxation spectroscopy. In this work this technique is used to monitor isothermal crystallization in PLLA by probing the evolution of the loss peak with crystallization tim...

The molecular dynamics during the formation of a polymer dispersed liquid crystal (PDLC) was followed by dielectric relaxation spectroscopy in the frequency range from 10(-1) to 2 x 10(6) Hz and over the temperature range from 158 to 273 K. The composite was produced by thermal polymerization induced phase separation of a mixture of triethyleneglyc...

Isothermal dielectric loss spectra of neutralized and nonneutralized chitosan were acquired in successive runs from –130°C up to increasing final temperatures, in a frequency range between 20 Hz and 1 MHz. Essentially, three relaxation processes were detected in the temperature range covered: (i) a β-wet process, detected when the sample has a high...

Dielectric relaxation spectroscopy was used to monitor the development of crystallinity in poly( L ‐lactic acid) (PLLA) at 80 °C. The continuous shifting of the main loss peak towards lower frequencies was modelled considering the evolution of three relaxation processes: the α‐process of the bulk‐like (non‐restricted) amorphous phase, the α‐process...

The dielectric behavior of the tri-ethylene glycol dimethacrylate monomer was investigated by dielectric relaxation spectroscopy after isothermal polymerization at different temperatures and compared with the unreacted monomer. The relaxation process associated with the monomer glass transition slightly deviates to lower frequencies/higher temperat...

Neutralized and nonneutralized chitosan films subject to different thermal treatments were studied by dielectric relaxation spectroscopy from -130 to +150 degrees C in the frequency range between 20 Hz and 1 MHz. Two main relaxation processes, both arrhenian type, were detected: process I at temperatures below 0 degrees C with a mean activation ene...

Di-, tri- and tetra-ethylene glycol dimethacrylate monomers were investigated by dielectric relaxation spectroscopy in the frequency range from 20 Hz to 1 MHz and in the temperature region comprised between −120 and +25 °C. A rather intense relaxation process associated with the glass transition is found for all the monomers in the temperature regi...

The pressure and temperature behaviours of the structural relaxation time in glass-forming systems can be well described by a new equation, based on the Adam-Gibbs model, where the configurational entropy has been written in terms of the excess heat capacity and the molar thermal expansion. An experimental check of this equation was performed on th...

To study the influence of a polymeric substrate, hydroxypropylcellulose (HPC), on the dynamics of the nematic mixture E7, the real (ε′) and imaginary (ε″) parts of the complex dielectric permittivity of the unaligned composite system (polymeric substrate covered with liquid crystal) were measured as a function of frequency and temperature, and comp...

The analysis of the low frequency dielectric loss of electrically aged LDPE shows an increase with electrical ageing. This could be further verified by extending the frequency range down to 10-5 Hz in order to measure the changes at the expected peak maximum. TSDC results are however inconclusive whether the measured current is due to dipoles or sp...