On the parameters influencing the deposition of polystyrene colloidal crystals

Colloidal crystals of polystyrene particles of 1.0, 1.4 and 2.8 μm diameter have been prepared by vertical deposition. The influence of parameters such as temperature, particle size and concentration as well as dispersion medium has been studied. The size of domain and the crystalline structure of the particle arrays have been analyzed by optical microscopy. The quality of the crystals has been improved (minimizing cracks) by controlling sedimentation (density matching), evaporation (volatility of the medium) and drying (co-solvents)

Electrophoretic deposition of colloidal crystals assisted by hydrodynamic flows

Latex-based colloidal crystals have been grown by electrophoretic deposition. The deposition has been assisted by hydrodynamic von Kármán-like flows, which lead to quantitative improvements. It has been studied the influence of applied voltage, deposition time and flow rate on the number of deposited layers and on the mean domain size. The samples were studied with microscopy and precision weight measurement. It has been found that there is a critical time after which the deposition mechanism changes, and the behavior of the system before and after this critical time is considered. The mean domain size and the deposition time were reduced to non-dimensional forms which show the collapse of the data for different applied voltages and flow rates into one curve

Influence of excesses of volatile elements on structure and composition of solution derived lead-free (Bi0.50Na0.50)1xBaxTiO3 thin films

The preparation of (Bi0.50Na0.50)1−xBaxTiO3 films requires a compositional/structural control, as they determine the functionality of these materials. We report a systematic compositional and structural analysis on (Bi0.50Na0.50)1−xBaxTiO3 films fabricated by chemical solution deposition. The effects of incorporating Na(I) and Bi(III) excesses are analyzed through the comparison of the compositional depth profiles of stoichiometric films (BNBT) and films containing excesses (BNBTxs). Heterogeneous compositional profiles with larger bismuth content close to the substrate and thicker film-substrate interfaces are observed in BNBTxs, unlike stoichiometric films, which show atomic concentrations that correspond to the nominal composition of the precursor solution. Excesses induce structural differences in depth, observing a shift of the region of coexistence of rhombohedral and tetragonal phases (morphotropic phase boundary) toward higher x values and the formation of thick film-substrate interfaces. In contrast, stoichiometric films have homogeneous compositional and structural profiles with the MPB placed close to that described for bulk ceramics.This work was financed by Spanish Project MAT2013-40489-P. D. Pérez-Mezcua acknowledges the financial support of the FPU Spanish program (AP2012-0639). A portion of this research was carried out at the Stanford Synchrotron Radiation Lightsource, a national user facility operated by Stanford University. D. Chateigner acknowledges the Conseil Régional de Basse Normandie for its partial financial of the four-circles X-ray diffractometer.Peer reviewe

Solvent-free formation of cyclodextrin-based pseudopolyrotaxanes of polyethylene glycol: kinetic and structural aspects

Pseudopolyrotaxanes (PPRs) are supramolecular structures consisting of macrocycles able to thread on a linear polymer chain in a reversible, non-covalent way, often referred to in the literature as "molecular necklaces". While the synthesis and reaction mechanisms of these structures in solution have been widely described, their solvent-free production has received little attention, despite the advantages that this route may offer. We propose in this work a kinetic mechanism that describes the PPR formation in the solid phase as a process occurring in two consecutive stages. This mechanism has been used to investigate the spontaneous formation of a PPR that occurs when grinding alpha-Cyclodextrin (alpha-CD) with polyethylene glycol (PEG). In the threading stage, the inclusion of the polymer and subsequent release of the water molecules lodged in the cavity of the macrocycle cause vibrational changes that are reflected in the time-dependence of the FTIR-ATR spectra, while the further assembly of PPRs to form crystals produces characteristic reflections in the XRD patterns, due to the channel-like arrangement of CDs, that can be used to track the formation of the adduct in crystalline form. The effects that working variables have on the kinetics of the reaction, such as temperature, feed ratio, molar mass of the polymer and the introduction of an amorphous block in the polymer structure, have been investigated. The rate constants of the threading step increase with the temperature and the activation energy of the process increases at lower proportions of CD to PEG. This is attributed to the lower degree of covering of the polymer chain with CDs that reduces the hydrogen-bonding driven stabilization between adjacent macrocycles. The formation of crystalline PPR, which takes place slowly at room temperature, is markedly promoted at higher temperatures, with lower proportions of CD favoring both the formation and the growth of the crystals. The molar mass of the polymer does not modify the typical channel-like arrangement of packed PPRs but the conversion into crystalline PPR diminishes when using PEG1000 instead of PEG400. At a microscopic level, the crystals arrange into lamellar structures, in the order of hundreds of nm, embedded in an amorphous-like matrix. The introduction of a polypropylene oxide block in the structure of the polymer (Pluronic L62) renders poorer yields and a considerable loss of crystallinity of the product of the reaction. The methodology here proposed can be applied to the general case of inclusion complexes of CDs with drugs in the solid phase, or to multicomponent systems that contain polymers as excipients in pharmaceutical formulations along with CDs

Photoferroelectric thin films for flexible systems by a three-in-one solution-based approach

The effective incorporation of (multi)functional oxides into next-generation flexible electronics systems requires novel fabrication technologies that enable the direct integration of crystalline oxide layers in them. Unfortunately, this is considerably challenging due to the thermal incompatibility between the crystallization temperatures of metal oxides (>600 degrees C) and the thermal stability of the flexible polymer substrates conventionally used (<400 degrees C). Here, it is shown that BiFeO(3)thin films can be grown on flexible plastic by solution processing involving three different but complementary strategies to induce the crystallization of the perovskite phase at a lower temperature limit of 325 degrees C. This "three-in-one" approach is based on the synthesis of tailored metal precursors i) with a molecular structure resembling the crystalline structure of the oxide phase, which additionally allows both ii) photochemical and iii) internal combustion reactions taking place in the thin films. The flexible BiFeO(3)thin films obtained from a specifically designed molecular complex withN-methyldiethanolamine yield a large remnant polarization of 17.5 mu C cm(-2), also showing photovoltaic and photocatalytic effects. This result paves the way for the direct integration of an interesting class of oxides with photoferroelectric properties in flexible devices with multiple applications in information and communication technology, and energy

Obtaining of repair lime mortars by mixing aerial lime and nanosilica

This work deals with the effect of the nanosilica addition on the performance of aerial lime mortars. Several lime mortars were prepared and modified upon the addition of 3, 6, 10 and 20 wt.% of nanosilica. The presence of nanosilica increased the water demand of the fresh mixtures and reduced the appearance of superficial cracks after the spreading of the mortars onto a porous stone. Setting time underwent a delay when the amount of nanosilica ranged from 3 to 10 wt.%. However, samples with 20 wt.% of nanosilica showed a shortened setting time compared to plain lime mortars. Nanosilica reacted with Ca(OH)2 particles, yielding C-S-H compounds and, acting as a nanofiller, nanosilica also caused a pore blockage in the mesoporous range. These facts resulted in an increase in both compressive strength and durability after undergoing freezing-thawing processes. Overall, the addition of nanosilica clearly improves several characteristics of the aerial lime mortars in order to prepare enhanced mixtures to be used for restoration works

Solidification/stabilization of toxic metals in calcium aluminate cement matrices

The ability of calcium aluminate cement (CAC) to encapsulate toxic metals (Pb, Zn and Cu) was assessed under two curing conditions. Changes in the consistency and in the setting time were found upon the addition of the nitrates of the target metals. Both Pb and Cu caused a delay in CAC hydration, while Zn accelerated the stiffening of the mortar. Compressive strengths of the metal-doped mortars, when initially cured at 60ºC/100% RH, were comparable with that of the free-metal mortar. Three different pore size distribution patterns were identified and related to the compounds identified by XRD and SEM. Sorbent capacities of CAC for the toxic metals were excellent: a total uptake was achieved for up to 3 wt.% loading of the three metals. In this way, CAC mortars were perfectly able to encapsulate the toxic metals, allowing the use of CAC for waste management as proved by the leaching tests

Tradición, versatilidad e innovación en la cal: un material de excelencia

Actas revisadas por pares de los trabajos presentados en las VI Jornadas FICAL organizadas por el Grupo de Investigación MIMED del Departamento de Química de la Facultad de Ciencias, celebradas en la Universidad de Navarra del 28 al 30 de mayo de 2018

Treatment of toxic metal aqueous solutions: encapsulation in a phosphate-calcium aluminate matrix

Polyphosphate-modified calcium aluminate cement matrices were prepared by using aqueous solutions polluted with toxic metals as mixing water to obtain waste-containing solid blocks with improved management and disposal. Synthetically contaminated waters containing either Pb or Cu or Zn were incorporated into phosphoaluminate cement mortars and the effects of the metal’s presence on setting time and mechanical performance were assessed. Sorption and leaching tests were also executed and both retention and release patterns were investigated. For all three metals, high uptake capacities as well as percentages of retention larger than 99.9% were measured. Both Pb and Cu were seen to be largely compatible with this cementitious matrix, rendering the obtained blocks suitable for landfilling or for building purposes. However, Zn spoilt the compressive strength values because of its reaction with hydrogen phosphate anions, hindering the development of the binding matrix

Assessment of the interaction of polycarboxylate superplasticizers in hydrated lime pastes modified with nanosilica or metakaolin as pozzolanic reactives

Two polycarboxylate ether copolymers were assessed as superplasticizers (SPs) for hydrated lime pastes modified with two reactive compounds, nanosilica (NS) and ceramic metakaolin (MK). Characterization of the molecular structure of the SPs by Size Exclusion Chromatography, XRD, FTIR and MALDI-TOF (Matrix Assisted Laser Desorption Ionization Time-of-Flight) mass spectrometry was performed. The structures of the polymers were seen to be star- and worm-like shapes. A close relationship was found between the molecular architecture and the flowability of the pastes, being the star-shaped plasticizer the most efficient. Zeta potential assessment allowed us to elucidate a steric hindrance as the main action mechanism for these polymers. The large specific surface area of nanosilica led to a large SPs consumption as compared with metakaolin with lower surface area. However, SPs in MK-lime samples were attached favourably on the C-S-H and aluminate hydrates, so that the dispersing action was greater with respect to NS-lime suspensions