Madalena Dionísio

• Universidade NOVA de Lisboa

Ionic liquid crystals (ILCs), a class of soft matter materials whose properties can be tuned by the wise pairing of the cation and anion, have recently emerged as promising candidates for different applications, combining the characteristics of ionic liquids and liquid crystals. Among those potential uses, this review aims to cover chromogenic ILCs...

1-Dodecyl-2-methylpyridinium bromide ([C12-2-Pic][Br]) and 1-hexadecyl-2-methylpyridinium bromide ([C16-2-Pic][Br]) are two ionic liquid crystals presenting thermotropic smectic phases above 80 °C. Aiming to take advantage of the liquid crystalline properties at lower temperatures, lyotropic aqueous systems were prepared from these two organic salt...

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...

Thyroid diseases affect a considerable portion of the population, with hypothyroidism being one of the most commonly reported thyroid diseases. Levothyroxine (T4) is clinically used to treat hypothyroidism and suppress thyroid stimulating hormone secretion in other thyroid diseases. In this work, an attempt to improve T4 solubility is made through...

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...

The impact of the alkyl size moiety in the mesomorphic and conductivity properties was evaluated in 2-picolinium ([Cn-2-Pic]+, n = 6 (n-hexyl), 12 (n-dodecyl) and 16 (n-hexadecyl)) organic salts. While the lengthier chains imprint crystalline order, the shortest [C6-2-Pic][Br] easily bypasses crystallisation, vit-rifying on cooling. Furthermore, bo...

Polyhydroxyalkanoates (PHA) are biopolymers with potential to replace conventional oil-based plastics. However, PHA high production costs limit their scope of commercial applications. Downstream processing is currently the major cost factor for PHA production but one of the least investigated aspects of the PHA production chain. In this study, the...

Novel ionic liquid crystals based on pyridinium and methylpyridinium cations with a dodecyl chain and bromide as anion have been prepared and characterised. [C12Pyr][Br] and [C12-n-Pic][Br] (n = 2, 3 or 4) were studied in order to understand the influence of the methyl group position in the mesomorphic behaviour. Neat microwave-assisted reactions w...

Composites of lithium ferrite, LiFe5O8 (LFO) particles, dispersed in the biopolymer poly(l-lactic acid) (PLLA) were prepared by solvent casting in concentrations from 0 to 19.5 wt%, which were characterized by thermal analysis (TGA/DSC), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), attenuated...

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...

Aiming to evaluate how the release profile of naproxen (nap) is influenced by its physical state, molecular mobility, and distribution in the host, this pharmaceutical drug was loaded in three different mesoporous silicas differing in their architecture and surface composition. Unmodified and partially silylated MCM-41 matrices, respectively MCM-41...

Aiming to rationalize the release profile of an incorporated pharmaceutical drug in terms of its mobility, driven by guest-host interactions, the poorly water-soluble Ibuprofen drug was loaded in a mesoporous inorganic silica matrix with unmodified (MCM-41) and modified surface (MCM-41sil) by post-synthesis silylation, both having pore sizes ∼ 3 nm...

One of the most current trends in applied electrochemistry is the development of solid ionic conductors with electrical, mechanical, and optical properties tailored for a specific functional application. Moreover, particular interest exists in materials with low environmental impact and low cost where matters such as sustainability and recyclabilit...

Deep Eutectic Solvents (DES) composed by lithium, sodium or potassium iodide salts combined to ethylene glycol (EG), glycerol (Gly) or poly(ethyleneglycol) (PEG) as Hydrogen Bond Donors (HBD) have been developed. All prepared ESs were characterized by thermal analysis (DSC and TGA), dielectric relaxation spectroscopy (DRS) in order to evaluate its...

We report the cryoprotective potential of FucoPol, a fucose-containing bacterial exopolysaccharide produced by Enterobacter A47. In vitro cryopreservation assays of Vero, Saos-2, HFFF2 and C2C12 cell lines exposed to a validated non-cytotoxic 2.5 mg/ml FucoPol concentration demonstrated a consistent post-thaw metabolic viability increase. Calorimet...

The materials described in this work result from the self-assembly of liquid crystals and ionic liquids into droplets, stabilized within a biopolymeric matrix. These systems are extremely versatile gels, in terms of composition, and offer potential for fine tuning of both structure and function, as each individual component can be varied. Here, the...

Herein we report the synthesis of novel ionic liquids (ILs) and organic salts by combining ibuprofen as anion with ammonium, imidazolium, or pyridinium cations. The methodology consists of an acid–base reaction of neutral ibuprofen with cation hydroxides, which were previously prepared by anion exchange from the corresponding halide salts with Ambe...

Multi‐colored intrinsically electrochromic based Deep Eutectic Solvents (IEDES) have been firstly developed. IEDES composed by the suitable mixing between viologen salt derivatives as HBA and ethylene glycol (EG), glycerol (Gly) and poly(ethylene glycol) (PEG) as HBD have been prepared and characterized by thermal and electrochemical studies. A det...

Different feeding strategies, namely, exponential feeding and DO-stat mode, were implemented for the production of poly(3-hydroxybutyrate), P(3HB), by Cupriavidus necator DSM 428 with used cooking oil (UCO) as the sole carbon source. With the exponential feeding strategy, a cell dry mass of 21.3 ± 0.9 g L ⁻¹ was obtained, with a polymer content of...

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 development of chloride free Deep Eutectic Solvents (DES) based on lithium acetate, triflate, bistriflimide, and sodium triflate combined with glycerol, ethylene glycol, and polyethylene glycol (PEG400) as suitable electrolytes was successfully applied in electrochromic devices (ECD). Reversible ECD incorporating selected DES as electrolyte and...

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...

Jonas Gruber, Ana C. A. Roque, and co-workers report a tunable gas-sensing gel in article number 1700803. The gel is generated by cooperative self-assembly of liquid crystals, biopolymers, and ionic liquid. Thin films react to stimuli by generating optical and electrical signals. Compared to metal oxide semiconductor based gas sensors, the system i...

The cooperative assembly of biopolymers and small molecules can yield functional materials with precisely tunable properties. Here, the fabrication, characterization, and use of multicomponent hybrid gels as selective gas sensors are reported. The gels are composed of liquid crystal droplets self-assembled in the presence of ionic liquids, which fu...

In the last two decades, it has been observed an increasing low enrolment of students in chemistry teaching courses in secondary schools. On the one hand, because of the a negative connotation of chemistry, associated with the potentially toxic and pollutant chemical industry, and on the other hand, that the teaching of this subject is exclusively...

The relaxation behavior of a series of solvent free polyurethane model networks with variable cross-link density prepared based on different commercial diols and a diisocyanate containing component are studied by differential scanning calorimetry (DSC), dynamic-mechanical analysis (DMA) and dielectric relaxation spectroscopy (DRS). A systematic dec...

(B.Sc. thesis upload for documentation purposes only) Cryopreservation allows organisms to survive at sub-zero temperatures by making use of biological agents able to control crystal growth and avoid lethal damage. Artificial cryopreservation has been widely optimized and used in the food industry and for medical applications, most recently to prov...

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 main goal of this work was the preparation and study of a composite material by dispersing lithium ferrite particles in a polymeric matrix. The matrix selected was styrene-b-isoprene-b-styrene (SIS) copolymer. Lithium ferrite (LiFe5O8) is an attractive material for several potential technological applications, due to its physical properties LiF...

A therapeutic deep eutectic system (THEDES) is here defined as a deep eutectic solvent (DES) having an active pharmaceutical ingredient (API) as one of the components. In this work, THEDESs are proposed as enhanced transporters and delivery vehicles for bioactive molecules. THEDESs based on choline chloride (ChCl) or menthol conjugated with three d...

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...

Deep eutectic solvents (DES) can be formed by bioactive compounds or pharmaceutical ingredients. A therapeutic DES (THEDES) based on ibuprofen, a non-steroidal anti-inflammatory drug (NSAID), and menthol was synthesized and its thermal behavior was analyzed by differential scanning calorimetry (DSC). A controlled drug delivery system was developed...

Olive oil distillate (OOD), biodiesel fatty acids-byproduct (FAB) and used cooking oil (UCO) were tested as inexpensive carbon sources for the production of polyhydroxyalkanoates (PHA) with different composition using twelve bacterial strains. OOD and FAB were exploited for the first time as alternative substrates for PHA production. UCO, OOD and F...

Lithium ferrite (LiFe5O8) is an attractive material for technological applications due to its physical properties, which are significantly dependent on the preparation method and raw materials. In this work, LiFe5O8 crystallites were obtained by controlled heat-treatment process at 1100 °C, of a homogeneous mixture of Li2O-Fe2O3 powders, prepared b...

The thermal behavior and transport properties of several ion jellys (IJs), a composite that results from the combination of gelatin with an ionic liquid (IL), were investigated by dielectric relaxation spectroscopy (DRS), differential scanning calorimetry (DSC), and pulsed field gradient nuclear magnetic resonance spectroscopy (PFG NMR). Four diffe...

The molecular mobility of ibuprofen confined to a mesoporous silica host (MCM-41) of 3.6 nm pore diameter is investigated by dielectric relaxation spectroscopy. It is confirmed that crystallization is suppressed; therefore, depending on the temperature, the guest exists in the glassy and supercooled state inside of the pores. A detailed relaxation...

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...

The dynamical behavior of three low molecular weight glass formers confined to nanostructured mesoporous silica (100 % Si) with pore sizes ranging from 2.8 to 8.6 nm, is probed by Dielectric Relaxation Spectroscopy (DRS). The confined guests embrace different classes of materials: a surfactant, Triton X-100, a liquid crystal, E7 nematic mixture and...

A fat-containing waste produced from the margarine manufacturing process was tested as a low cost carbon source for cultivation of different polyhydroxyalkanoates (PHAs) producing bacterial strains, including Cupriavidus necator, Comamonas testosteroni and several Pseudomonas strains. The margarine waste was mainly composed of free fatty acids (76w...

In this work, blends of starch and poly-ε-caprolactone (PCL) doped with different concentrations of 1-butyl-3-methylimidazolium acetate ([BMIM]Ac) or 1-butyl-3-methylimidazolium chloride ([BMIM]Cl) were studied. The blends were characterized by mechanical analysis, infra-red spectroscopy (FTIR), differential scanning calorimetry (DSC) and dielectri...

The relaxation properties of polymethacrylates of the n-alkyl series with n = l, 2 and 4 (poly(methyl methacrylate) (PMMA), poly(ethylmethacrylate) (PEMA) and poly(n-butyl methacrylate) (PnBMA)) have been measured and analyzed in order to relate their properties to the size of the lateral side chains. The n-alkyl series has been regarded as a model...

Because of the strong tendency of Triton X-100 to crystallize, inclusion in a SBA-15 matrix of 5.7 nm in pore diameter was used as a means to suppress crystallization. Clear evidence that Triton X-100 exists under confinement in the amorphous and supercooled state is given by X-ray diffraction supported by differential scanning calorimetry and diel...

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...

Analysis of AC electrical conductivity of deoxyribonucleic acid (DNA) thin films, irradiated with ultraviolet (UV) light, revealed that electrical conduction arises from DNA chain electron hopping between base-pairs and phosphate groups. The hopping distance calculated from correlated barrier hopping model equals the distance between DNA base-pairs...

The properties of the light flexible device, ion jelly, which combines gelatin with an ionic liquid (IL) were recently reported being promising to develop safe and highly conductive electrolytes. This article aims for the understanding of the ion jelly conductive mechanism using dielectric relaxation spectroscopy (DRS) in the frequency range 10(-1)...

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...

Aiming to develop new dielectric polymers containing CN and F groups with strong dipole moments, a novel copolymer of acrylonitrile (AN) and 2,2,2-trifluoroethyl acrylate (ATRIF) was synthesized in acetonitrile by free radical process as well as the respective homopolymer (poly(ATRIF)). The copolymer’s composition and microstructure were analyzed b...

The molecular mobility of condensed matter confined to nanometer dimensions can be dramatically changed from those of the bulk state in such a way that, when the guest is a drug, it can be advantageously used in pharmaceutical applications. We show by dielectric relaxation spectroscopy that the molecular mobility of the important ibuprofen drug emb...

A reformulation of the Sinanoglu–Reisse semi-empirical approach to describe the cavity formation process in liquids is proposed. The energy of cavity formation is regarded as a strictly potential energy corrected for short range order effects in the liquid state. Deviations from the Corresponding States Principle quantified by the Pitzer acentric f...

A new method to calculate the enthalpy and entropy of cavity formation in liquids is proposed. The reference cavity formation process is identified with the vaporization of liquid in the absence of order and Corresponding States Principle is used to eliminate the order contribution to vaporization enthalpy. The proposed method agrees very well with...

This work brings together dynamical and structural information at a molecular level for cellulose acetate being an original contribution to the general description of polysaccharide properties. In particular, it allowed reinterpreting the secondary relaxation mechanisms that are still controversial in the literature; a compilation of data provided...

Dipole moment techniques have been applied to the study of the n-alkane environmental influence on the conformational equilibrium of trans-1,2-dibromocyclohexane. Both the Debye and the Onsager theories have been used in order to calculate the dipole moment from the dielectric constants of the liquid solutions, and the results have been obtained in...

The nematic liquid crystalline mixture E7 was confined with similar filling degrees to molecular sieves with constant composition but different pore diameters (from 2.8 to 6.8 nm). Fourier transform infrared analysis proved that the E7 molecules interact via the cyanogroup with the pore walls of the molecular sieves. The molecular dynamics of the s...

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...

Reported herein is the architecture for a nonvolatile n‐type memory paper field‐effect transistor. The device was built via the hybrid integration of natural cellulose fibers (pine and eucalyptus fibers embedded in resin with ionic additives), which act simultaneously as substrate and gate dielectric, using passive and active semiconductors, respec...

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...

This chapter introduces the general dielectric properties of materials. In electrical or dielectric measurements, the material to be characterized is usually placed between two conducting electrodes, where an electric field can be created within it by application of a voltage. The extent to which a material responds to an applied electric field can...

We present a new concept for the design of a polymeric conducting material that combines the chemical versatility of an organic salt (ionic liquid) with the morphological versatility of a biopolymer (gelatin); the resulting 'ion jelly' can be applied in electrochemical devices, such as batteries, fuel cells, electrochromic windows or photovoltaic c...

The molecular mobility of amorphous ibuprofen has been investigated by broadband dielectric relaxation spectroscopy (DRS) covering a temperature range of more than 200 K. Four different relaxation processes, labeled as alpha, beta, gamma, and D, were detected and characterized, and a complete relaxation map was given for the first time. The gamma-p...

Specimens of poly(l-lactic acid) (PLLA) with 0.43 ≤ χc ≤ 0.65 were dielectric characterized. The relaxation process associated to the dynamic glass transition shifts to higher frequencies/lower temperatures with the increase of crystallinity. From the VFT temperature dependence of relaxation times, the glass transition and Vogel temperatures were e...

Broadband dielectric spectroscopy (10(-2)-10(9) Hz) was employed to investigate the molecular dynamics of the liquid crystalline mixture E7 confined in both untreated and lecithin-treated 20 nm Anopore membranes. Because E7 does not crystallize, it was possible to cover a temperature range of more than 200 K, providing an exhaustive dielectric char...

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...

Dielectric Relaxation Spectroscopy (10-1 Hz to 106 Hz) was used in order to get relevant information regarding the different modes of motion, from supercooled liquid down to the glassy state, present in the glass-forming Ibuprofen. This pharmaceutical drug easily avoids crystallization on cooling from the melt, forming a glass below the dielectric...

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 combination of broadband dielectric (10{-2}Hz-10{9}Hz) and specific heat (10{-3}Hz-2 x 10{3}Hz) spectroscopy is employed to study the molecular dynamics of the glass-forming nematic liquid crystal E7 in a wide temperature range. In the region of the nematic phase the dielectric spectra show two relaxation processes which are expected theoreticall...

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...

In the present work a simple but selective reversed‐phase high performance liquid chromatographic method (HPLC) was developed for the analysis of the nematic liquid crystal mixture E7 to determine precisely the composition of the liquid crystal mixture used in PDLC film preparation. Ultraviolet absorption spectrophotometry experiments were carried...

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...

It is well known that the properties of polymeric materials depend strongly upon their chemical structure. Other more specific factors that may be related to the chemical structure also determine the macroscopic behaviour of such materials, namely the relative position of the different segments of the polymeric chain, the molecular architecture (mo...

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...

Dielectric experiments are often performed in non-isothermal conditions. Thus, there is a difference between the temperature of the sample and the sensor temperature. In this work we propose and compare three temperature calibration methods based on the detection of transitions or relaxations: i) the melting of high-purity metallic standards (indiu...

The contact angle goniometer described herein is an inexpensive and easy-to-handle instrument that provides experimental results in good agreement with published values. The goniometer method proposed here to measure the cmc of a surfactant is accurate and simple, suitable for an undergraduate student experiment in surface chemistry. The results ar...

To study the influence of PEO on the relaxation process of PMMA, the real and imaginary parts of the permittivity, ε‘ and ε‘ ‘, of PEO/PMMA blends (with PEO contents up to 25 wt %) were measured as a function of frequency and temperature, and the results obtained were compared with those of pure PMMA. It is shown that the presence of PEO broadens t...

The glass transition relaxation of different blends of poly(vinyl acetate) and poly(ethyl methacrylate) have been investigated by dielectric relaxation spectroscopy in the frequency range from 20 Hz to 1 MHz. The obtained results suggest that the poly(vinyl acetate)-rich blends show immiscibility between the two components, whereas the poly(ethyl m...

In the present work we report a study of the molecular relaxation processes in tetrachloro-m-xylene in the solid state. The techniques of dielectric relaxation spectroscopy and thermally stimulated discharge currents were used in order to identify and characterise the different relaxation processes and it was found that a solid rotator phase appear...

This paper reports on a modification of the dielectric properties of cork which occurs as a consequence of heating above 60° C or evacuation for several days. This phenomenon was observed using different experimental techniques (thermally stimulated currents, dielectric relaxation spectroscopy, isothermal depolarization experiments and differential...

In the work described in this paper the dielectric properties of solid solutions of p-nitroaniline in poly(methyl methacrylate), poly(ethyl methacrylate) and poly(n-butyl methacrylate) were measured in the frequency range from 20 to 106 Hz and the results obtained were compared with those of the pure polymers. It is shown that the presence of the s...

In the present paper we examine the dielectric properties of solid solutions of p-nitroaniline in a poly(vinyl acetate) matrix in the frequency range from 16 to 105 Hz and the results are compared with those for pure poly(vinyl acetate). It is shown that the presence of the solute increases the activation energy of the α relaxation process of the p...

In the present paper the dielectric properties of solid solutions of 4-nitroaniline in a poly(methyl methacrylate) matrix have been measured in the frequency range 20-106 Hz and the obtained data have been compared with those for pure poly(methyl methacrylate). It is shown that the presence of the solute has a strong influence on the relaxation pro...