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International audience; 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 and MCM-41sil, and a biphenylene-bridged periodic mesoporous organic matrix, PMOBph, were synthetized and used as drug carriers, having comparable pore sizes (∼3 nm) and loading percentages (∼30% w/w). The loaded guest was investigated by attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy, powder X-ray diffraction (XRD), differential scanning calorimetry (DSC), and dielectric relaxation spectroscopy (DRS). DSC and XRD confirmed amorphization of a nap fraction incorporated inside the pores. A narrower glass transition was detected for PMOBph_nap, taken as an indication of the impact of host ordering, which also hinders the guest molecular mobility inside the pores as probed by DRS. While the PMOBph matrix is highly hydrophobic, the unmodified MCM-41 readily adsorbs water, accelerating the nap relaxation rate in the respective composite. In the dehydrated state, the faster dynamics was found for the silylated matrix since guest–host hydrogen bond interactions were inhibited to some extent by methylation. Nevertheless, in all the prepared composites, bulk-like crystalline drug deposits outside pores in a greater extent in PMOBph_nap. The DRS measurements analyzed in terms of conductivity show that, upon melting, nap easily migrates into pores in MCM-41-based composites, while it stays in the outer surface in the ordered PMOBph, determining a faster nap delivery from the latter matrix. On the other side, the mobility enhancement in the hydrated state controls the drug delivery in the unmodified MCM-41 matrix vs the silylated one. Therefore, DRS proved to be a suitable technique to disclose the influence of the ordering of the host surface and its chemical modification on the guest behavior, and, through conductivity depletion, it provides a mean to monitor the guest entrance inside the pores, easily followed even by untrained spectroscopists.

Permanent memory effect (PME) in polymer dispersed liquid crystal (PDLC) allows a greater applicability range than traditional PDLCs. One of the most interesting application could be the possible s...

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. The single calorimetric detection of a broad glass transition step for both ibuprofen composites indicates full drug amorphization, confirmed by the only appearance of an amorphous halo in the powder XRD patterns. Moreover, a gradient profile is disclosed by the heat flux derivative plot in the glass transition, in coherence with the thermogravimetric profile that shows a multi-step decomposition trace for confined ibuprofen in these matrixes. While identical guest dynamics, as probed by dielectric relaxation spectroscopy, were found in both dehydrated composites, a significant molecular population with faster relaxation exists in the hydrated state for the drug inside the unmodified matrix. This was rationalized as the concurrence of true confinement effects, which manifest under nanometer dimensions, and greater water affinity of the unmodified matrix, forcing the drug molecules to be placed mostly in the pore core. Finite size effects are also felt in both dehydrated composites, however guest-host interactions give origin to a dominant population with slowed down mobility that governs the overall guest dynamics. In spite of an inferior number of active sites for drug adsorption in the silylated matrix, a faster Ibuprofen delivery in phosphate buffer (pH = 6.8) was observed when the drug is released from unmodified MCM-41 in the hydrated state. Therefore, our results suggest that a relevant role is played by water molecules, which impair a strong guest adsorption in the host surface more efficiently than the limited surface modification, influence the higher ratio of a faster population in the pore core and facilitate the diffusion of the aqueous releasing media inside pores.

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The pharmaceutical drug naproxen was loaded in three different silica hosts with pore diameters of 2.4 (MCM), 3.2 (MCM), and 5.9 nm (SBA), respectively: napMCM_2.4 nm, napMCM_3.2 nm, and napSBA_5.9 nm. To access the guest physical state in the prepared composites, differential scanning calorimetry (DSC), X-ray diffraction (XRD), and attenuated total reflectance Fourier transform infrared spectroscopy were used. The different techniques provided complementary information on a molecular population that was revealed to be distributed among different environments, namely the pore core, the inner pore wall, and the outer surface. It was found that naproxen is semicrystalline in the higher pore size matrix being able to crystallize inside pores; after melting it undergoes full amorphization. In the case of the lower pore size matrix, naproxen crystallizes outside pores due to an excess of filling while most of the remaining fraction is incorporated inside the pores as amorphous. Crystallinity in these two compo...

A number of polymer dispersed liquid crystal (PDLC) films based on dimethacrylate monomers were synthesised by polymer-induced phase separation (PIPS) using polyethylene glycol p-(1,1,3,3-tetramethylbutyl)-phenyl ether (TX-100) as an additive up to total solution weight of 10% aiming to modify the initial anchorage force of the liquid crystal (LC) molecules to the polymeric matrix. The effects of the addition of this additive to the PDLC films were studied resorting to electro-optical studies. Using a fitting model, several parameters were correlated such as the permanent memory effect (PME), the voltage required to achieve 90% of maximum transmittance (E90), the average elastic constant (K) and the rotational viscosity of the director (γ). The use of TX-100 results on an increase on the PME and γ, and decrease on the E90 and K.

Permanent memory effect in polymer dispersed liquid crystal (PDLC) films prepared by thermal polymerization induced phase separation (PIPS) were studied. New trimethylolpropane trimethacrylate (TMP3MA)/poly(propylene glycol) methacrylate (PPGMA375)/E7/AIBN and pentaerythritol tetraacrylate (PE4A)/poly(propylene glycol) acrylate (PPGA475)/E7/AIBN PDLC films showed 86% permanent memory effect with E90 = 6 V/μm and memory state contrast of 70% and full permanent memory effect with E90 = 3 V/μm and total memory state contrast, respectively. These materials with two stable states (opaque and transparent) seem to be promising for the development of a new class of optical memories as they can be used for electrically write information, optically read the written information and they can be thermally erased back to the initial scattered state.

BACKGROUND Polymer dispersed liquid crystal (PDLC) films have a range of applications varying from switchable windows to new optical memory devices. They switch from an opaque state, when liquid crystal molecules are randomly dispersed, to a transparent state, when liquid crystal molecules are aligned, simply by applying a small voltage. On some PDLC films, the transparent state is retained even when the voltage is switched off; this is called permanent memory effect (PME). This process is totally reversible, returning to the initial opaque state either through heating or applying a higher frequency electric field when using a two frequency liquid crystal. RESULTS In this work, the impact on the electro-optical response of PDLC films as a result of adding an additive was studied. This performance is affected by several factors, the most important being the anchorage force. This anchorage force is modified with the addition of an additive such as TX-100. As a result, it was verified that the addition of TX-100, increased the PME up to 98.7% and decreased the voltage required to achieve 90% of maximum transmittance to 2 V µm−1. CONCLUSIONS The addition of a surfactant, as TX-100 in this case, was shown to be a valuable method to control the PME in PDLC systems in particular those prepared by PIPS from the oligomer polyethylene glycol dimethacrylate and the monomer triethylene glycol dimethacrylate in mixture with the nematic LC E7. This new advance on liquid crystal field also allows development of a new memory device based on a write–read–erase cycle. © 2015 Society of Chemical Industry

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 = −54.3 °C, is in good agreement with the one predicted by the composition dependence of the Tg values determined for menthol:flurbiprofen therapeutic deep eutectic solvents (THEDESs). Nonisothermal crystallization was never observed for neat menthol loaded into silica hosts, which can indicate that menthol rests as a full amorphous/supercooled material inside the pores of the silica matrixes. Menthol mobility was probed by dielectric relaxation spectroscopy, which allowed to identify two relaxation processes in both pore sizes: a faster one associated with mobility of neat-like menthol molecules (α-process), and a slower, dominant one due to the hindered mobil...

It has been reported that the length of the molecular chain and the rigidity of molecules influence the structure of the polymer network in PDLC films and hence the electro-optical properties of the composites. Herein, a series of new aromatic monomeric monomethacrylates, bismethacrylates and monovinylbenzene derivatives with a mesogenic core were successfully synthesized under microwave irradiation. The microwave assisted synthesis resulted in decreased reaction times, reduced solvent requirement, increased operational simplicity, and in most cases, improved yields and selectivity.

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 out to determine the HPLC detection wavelength and to characterize the absorptivity constants of E7 constituents. The technique developed is applied in the case of equilibrium solubility studies for E7 in supercritical carbon dioxide (scCO2). The results indicate unambiguously that scCO2 can fractionate the mixture towards the E7 components. The four single component peaks of the E7 mixture were distinctively separated by this method, which enabled the determination of the solubility of E7 constituents in the scCO2.

This paper presents a transformerless electronic converter topology for PDLC applications. In order to meet the PDLC ON/OFF state requirements, the converter must be able to supply an AC @1 kHz signal with different voltage levels, which correspond to different transparency levels. The converter will be connected directly to the electrical socket outlet and will use three conversion stages (AC - DC, DC - DC, DC - AC) to meet the PDLC's requirements. The AC - DC conversion stage will be composed by a single-phase diode rectifier, the DC - DC conversion stage will use a Buck-Boost converter and, in the DC - AC conversion stage, it will be used the Boost Inverter topology. Simulation and experimental results will be presented to show the system's performance.

The construction of a diode laser polarimeter apparatus by undergraduate students is described. The construction of the modular apparatus by undergraduate students gives them an insight into how it works and how the measurement of a physical or chemical property is conducted. The students use the polarimeter to obtain rotation angle values for the acid hydrolysis of sucrose, which are in good agreement with values obtained by a commercial instrument and those reported in the literature. The kinetic constant of the classic chemical reaction of the sucrose inversion in various experimental conditions is also obtained.

Heterosupramolecular assemblies based on modified transparent nanostructured TiO2 (anatase) membranes are described. Exposure of these heterosupramolecular assemblies to visible light causes them to turn blue. Furthermore, if a negative potential is applied to the nanostructured TiO2 membrane this blue color persists for hours. Because only those areas which have been irradiated are blue, and because the lifetime of the blue colored state depends on the potential applied to the nanostructured TiO2 membrane, applications are foreseen for these photoelectrochromic materials.

Reaction of Re2{μ-O2CC(CH3)3}4Cl2 with [(CO)5M–CN]Na (M = Cr, Mo, W) leads to tetranuclear complexes of formula Re2{μ-O2CC(CH3)3}4[–NC–M(CO)5]2 (M = Cr, Mo, W). These complexes were characterized by 1H-, 13C-, and 95Mo-NMR, IR and Raman spectroscopy, elemental analysis and examined by cyclic voltammetry. The applied methods show the donor capabilities of the [(CO)5M–CN]− ligands which shift electron density towards the Re centers weakening the Re–Re quadruple bond. The Re–Re bond lengths and the ν(Re–Re) force constants are estimated based on the FT-IR and Raman examinations. Photochemical examinations and TG/MS experiments have also been conducted. The latter method shows that the product complexes decompose around 100 °C, by first loosing their carbonyl substituents; as do the Cr, Mo, W precursor compounds. The dirhenium tetrapivalate unit decomposes only at higher temperatures in a distinct second step.

Reacting transition metal complexes in low oxidation states, containing one or two cyanide ligands, with methyltrioxorhenium(VII) leads to bridged mixed metal compounds in good yields. The Re(VII) core is then surrounded by five or six ligands, respectively. The strength of these CN bridges and thus the stability of the newly generated bimetallic compound strongly depends on the donor strength of the ligands surrounding of the Cr/Mo/W or Fe moiety. The stability of the mixed metal molecules is reflected in the temperature dependent behavior of their 17 O-NMR spectra, in their IR (ReO) stretching frequencies and force constants, as well as several other spectroscopic data. UV–vis absorption spectra show the appearance of charge transfer bands. In the case of the mixed Mo/Re complexes the 95 Mo-NMR spectroscopy is also a helpful tool to examine the donor capability of the Mo moiety. The described compounds also show photosensitivity.

PDLCs have been prepared by two general methods: one in which the system remains heterogeneous during the process, and another in which the system becomes heterogeneous. The first case includes the solvent induced phase separation (SIPS): the LC is mechanically dispersed in solution of a polymer. After evaporation of the solvent, the composite structure obtained is stabilised because of the polymer morphology, but is poorly controlled due to a coalescence of droplets during the preparation process. The second case is called thermally induced phase separation (TIPS) or polymerisation induced phase separation (PIPS)1.

Carboxylic acid anions which form ion pairs with transition metal cations can be oxidized by electron transfer mechanisms promoted by irradiation at the ion pair charge transfer (IPCT) band. The overall quantum yield of the photochemical redox reaction of the ion pair in the presence of various carboxylic acid anions must be corrected for each species present and for the fraction of light absorbed by each reactive ion pair. These calculations require the knowledge of the acid—base equilibria of the organic substrate and the characteristic constants of the ion pair (molar absorptivities and thermodynamic association constants which provide the variation in the concentration of each ion pair over the pH range). It is shown that the variation in the overall quantum yield of the photochemical redox reaction of the ion pair as a function of pH is due to the variation in the concentration of the reactive species present in solution.

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 and DRS techniques with a glass transition temperature of ∼212 K (measured on heating by DSC) allowing classifying Triton X-100 as a glass former. A fully amorphous material was obtained by cooling at a rate ≥10 K min(-1), while crystallization was observed for lower cooling rates. The temperature of the onset of melt-crystallization was found to be dependent on the cooling scan rate, being higher the lower was the scan rate. In subsequent heating scans, the material undergoes cold-crystallization except if cooled previously at a rate ≤1 K min(-1). None of the different thermal histories led to a 100% crystalline material because always the jump typical of the glass transformation in both heat flux (DSC) and real permittivity (DRS) is observed. It was also observed that the extent/morphology of the crystalline phase depends on the degree of undercooling, with higher spherulites developing for lower undercooling degree (24 K ≤ T(m) - T(cr) ≤ 44 K) in melt-crystallization and a grain-like morphology emerging for T(m) - T(cr) ≈ 57 K either in melt- or cold-crystallization. The isothermal cold- and melt-crystallizations were monitored near above the calorimetric glass transition temperature by POM (221 K) and real-time DRS (T(cr) = 219, 220, and 221 K) to evaluate the phase transformation from an amorphous to a semicrystalline material. By DRS, the α-relaxation associated with the dynamic glass transition was followed, with the observation that it depletes upon both type of crystallizations with no significant changes either in shape or in location. Kinetic parameters were obtained from the time evolution of the normalized permittivity according to a modified Avrami model taking in account the induction time. The reason the isothermal crystallization occurs to a great extent in the vicinity of the glass transition was rationalized as the simultaneous effect of (i) a high dynamic fragile behavior and (ii) the occurrence of catastrophic nucleation/crystal growth probably enabled by a preordering tendency of the surfactant molecules. This is compatible with the estimated low Avrami exponent (1.12 ≤ n ≤ 1.6), suggesting that relative short length scale motions govern the crystal growth in Triton X-100 coherent with the observation of a grainy crystallization by POM.

Spectrophotometric measurements in the region of the ion pair charge transfer band of the Co(Sepulchrate) 3+ I − system were used to assess the role played by the adducts between the complex cation and iodide anion in the photochemical behaviour of the system. No clear evidence was obtained for the presence or absence of 1:2 or higher adducts and the association constant and molar absorptivity of the 1:1 adduct (ion pair) could not be determined with a satisfactory accuracy. Nevertheless, reliable values were evaluated for the fraction of the exciting light absorbed by the ion pair in the photochemical experiments, and these values were used to correct the previously reported quantum yields, which were based on the total amount of light absorbed by the solutions. The “true” quantum yields for the ion pair are discussed in relation to the proposed reaction mechanism.

This paper describes a Stand-Alone Energy System Supported by Totally Renewable Hydrogen Production. The system was conceived for off-grid operation and is composed by solar panels, a wind turbine, a fuel-cell, an electrolyzer, hydrogen tanks and power electronics converters. The basic control strategy for the overall system considers the pressurized hydrogen gas storage as the energy buffer. The basic logic is that the exceeding renewable energy (solar and wind) is used to accumulate hydrogen, while the fuel cell uses this hydrogen to produce electrical energy when there is insufficient solar/wind energy.

Association constants for the ion pairs formed between [Co(Sep)]3+ and the anions fluoride, chloride, bromide, iodide, perchlorate, and oxalate were obtained from the chemical shifts of the 59Co resonance that occur upon addition of such anions to solutions of the cobalt complex. The usefulness of 59Co NMR to obtain formation constants, in order to calculate the "true" quantum yields for the ion pairs, is discussed. Key words: association constant, cobalt sepulchrate, ion pair, 59Co NMR, quantum yield.

A number of liquid crystal monomers based on methacrylate derivatives were synthesised by novel mild and solventless procedures under microwave irradiation. Their photo- and thermo assisted homo- and co-polymerizations with glycidyl methacrylate were investigated. The resulting polymers were characterised by NMR, GPC, DSC, and SEM to determine their structures and properties. The effects of the structures of the monomers on the electro-optical properties were correlated.

The preparation of transparent nanostructured TiO2 (anatase) membranes is described. Detailed characterization shows these membranes to be 50 μm thick nanoporous-nanocrystalline structures with associated values for porosity and surface roughness of 50% and 5000, respectively. Modification of these membranes by coadsorption of a ruthenium complex, bis[(4,4‘-dicarboxy-2,2‘-bipyridine)(4,4‘-dimethyl-2,2‘-bipyridine)ruthenium(II)] dichloride (I), and of a viologen, 1-ethyl-1‘-[(4-carboxy-3-hydroxyphenyl)methyl]-4,4‘-bipyridinium perchlorate (II), is also described. Detailed studies show that visible-light-induced electron transfer by electronically excited I to the conduction band of the nanostructured TiO2 membrane is followed by membrane mediated electron transfer to coadsorbed II. Detailed studies also show that, as a consequence of the rectifying properties of the semiconducting membrane, charge separation is long-lived. The possible significance of these findings for the development of a practical water...

The construction of a low-cost apparatus for gas adsorption on solids and prior heat treatment of the adsorbent are discussed. The equilibrium pressure of the gas in a calibrated volume at a constant temperature is related to the extent of the gas adsorption. By means of the adsorption results, the solid surface-area calculation is performed using both BET and Langmuir isotherms. This apparatus provides surface-area values in good agreement with both values obtained by a commercial instrument and those reported in the literature, within the experimental error.

The Co(Sep) 3+ complex (Sep = sepulchrate = 1,3,6,8,10,13,16,19-octaazabicyclo[6.6.6]eicosane) forms ion pairs with citrate in aqueous solution at pH 4.0, 5.6 and 8.5, where the forms CIT − , CIT 2− and CIT 3− (CIT = citrate) predominate respectively. Irradiation in the ion pair charge transfer band for the three pH values leads to the decarboxylation of citrate with the production of CO 2 and Co(Sep) 2+ . In the presence of colloidal platinum, CO 2 and H 2 are evolved. The quantum yields for formation of CO 2 , Co(Sep) 2+ and H 2 were obtained and are discussed in terms of their dependence on pH.

The first part of this work presents the construction of an inexpensive and easy to handle contact angle goniometer. The instrument provides contact angles that are within ±2° of the values obtained by a commercial apparatus and are in good agreement with values reported in the literature. In the second part of this work, the contact angle method is used to measure the critical micelle concentration (cmc) of two common surfactants in aqueous solutions: SDS (sodium dodecylsulfate) and Triton X-100 ([polyoxyethyleneglycol]9-10 p-tert-octyl phenol). The cmc values obtained by the contact angle method are consistent with those reported in literature and also with those obtained by surface tension measurements using a simplified Du Nuoy tensiometer.

Unsupported transparent nanoporous-nanocrystalline TiO2 membranes are prepared which are 20 µm thick anatase structures and have an associated surface roughness of ca. 1100. Visible-light induced charge injection by the adsorbed ruthenium complex, [bis(4,4′-dicarboxy-2,2′-bipyridine)(4,4′-dimethyl-2,2++′-bipyridine)ruthenium(ii)] dichloride 1, has been demonstrated for these membranes. Also demonstrated has been blue-light induced reduction of the adsorbed viologen, 1-ethyl-1′-[4-carboxy-3-hydroxyphenyl)methyl]-4,4′-bipyridini++um perchlorate 2.