Equilibrium self-assembly of colloids with distinct interaction sites: Thermodynamics, percolation, and cluster distribution functions

We calculate the equilibrium thermodynamic properties, percolation threshold, and cluster distribution functions for a model of associating colloids, which consists of hard spherical particles having on their surfaces three short-ranged attractive sites (sticky spots) of two different types, A and B. The thermodynamic properties are calculated using Wertheim's perturbation theory of associating fluids. This also allows us to find the onset of self-assembly, which can be quantified by the maxima of the specific heat at constant volume. The percolation threshold is derived, under the no-loop assumption, for the correlated bond model: In all cases it is two percolated phases that become identical at a critical point, when one exists. Finally, the cluster size distributions are calculated by mapping the model onto an effective model, characterized by a-state-dependent-functionality (f) over bar and unique bonding probability (p) over bar. The mapping is based on the asymptotic limit of the cluster distributions functions of the generic model and the effective parameters are defined through the requirement that the equilibrium cluster distributions of the true and effective models have the same number-averaged and weight-averaged sizes at all densities and temperatures. We also study the model numerically in the case where BB interactions are missing. In this limit, AB bonds either provide branching between A-chains (Y-junctions) if epsilon(AB)/epsilon(AA) is small, or drive the formation of a hyperbranched polymer if epsilon(AB)/epsilon(AA) is large. We find that the theoretical predictions describe quite accurately the numerical data, especially in the region where Y-junctions are present. There is fairly good agreement between theoretical and numerical results both for the thermodynamic (number of bonds and phase coexistence) and the connectivity properties of the model (cluster size distributions and percolation locus).

Development of membranes for purification of liquid effluents from stainless steel pickling

Este trabalho foi desenvolvido no âmbito de um projecto europeu intitulado: “Operational demonstration of innovative and sustainable nitrate elimination in stainless steel pickling by higher power biological denitrification technique” Projecto RESP-CT-2007-00047, tendo em vista o desenvolvimento de membranas para o tratamento de efluente resultante da decapagem do aço inox. Numa fase inicial foram desenvolvidas membranas compostas assimétricas pelo método de polimerização interfacial. Estas membranas foram produzidas utilizando uma membrana comercial de suporte em polietersulfona e os filmes selectivos de poliamiada foram formados por reacção entre 1,3,5-tri(clorocarboni)benzeno (TMC) e várias dinaminas: piperazina (PIP), N-(2-aminoetil)-piperazina (EAP), 1,4-bis(3-aminopropil)-piperazina (DAPP), 6-metil-1,3,5 triazina-2,4 diamina (MTC), Isoforodiamina (IPD) e Dietilenetriamina (DET). A elaboração de membranas de TFC (thin film composite) tinha como objectivo a retenção de sais do efluente resultante da decapagem do aço inox. No entanto, chegou-se a conclusão de que o principal problema do efluente não era a retenção dos sais, mas sim a retenção da matéria orgânica. Assim, já não era necessa´ria a produção de membranas compostas, mas apenas uma membrana suporte simples de microfiltração. Numa segunda fase procedeu-se a preparação da membrana suporte pelo método da inversão de fase, tendo-se testado vários tipos de polímeros: PVC (polyvinyl chloride), PEI (Polyetherimide) e um polímero termoplástico geral. A membrana seleccionada foi a de PEI, com base na sua permeabilidade à água destilada e ao efluente resultante das águas residuais da decapagem do aço inox. Todas as membranas elaboradas durante a realização deste trabalho foram testadas na célula de Berghof a uma pressão de 4bar e com agitação. O principal prâmetro estudado foi a permeabilidade da membrana.

Substrate interaction with recombinant amidase from Pseudomonas aeruginosa during biocatalysis

The interaction of a variety of substrates with Pseudomonas aeruginosa native amidase (E.C. 3.5.1.4), overproduced in an Escherichia coli strain, was investigated using difference FTIR spectroscopy. The amides used as substrates showed an increase in hydrogen bonding upon association in multimers, which was not seen with esters. Evidence for an overall reduction or weakening of hydrogen bonding while amide and ester substrates are interacting with the enzyme is presented. The results describe a spectroscopic approach for analysis of substrate-amidase interaction and in situ monitoring of the hydrolysis and transferase reaction when amides or esters are used as substrates.

Influence of growth temperature and carrier flux on the structure and transport properties of highly oriented CrO2 on Al2O3 (0001)

In this work we report on the structure and magnetic and electrical transport properties of CrO2 films deposited onto (0001) sapphire by atmospheric pressure (AP)CVD from a CrO3 precursor. Films are grown within a broad range of deposition temperatures, from 320 to 410 degrees C, and oxygen carrier gas flow rates of 50-500 seem, showing that it is viable to grow highly oriented a-axis CrO2 films at temperatures as low as 330 degrees C i.e., 60-70 degrees C lower than is reported in published data for the same chemical system. Depending on the experimental conditions, growth kinetic regimes dominated either by surface reaction or by mass-transport mechanisms are identified. The growth of a Cr2O3 interfacial layer as an intrinsic feature of the deposition process is studied and discussed. Films synthesized at 330 degrees C keep the same high quality magnetic and transport properties as those deposited at higher temperatures.

The condensation and ordering of models of empty liquids

We consider a simple model consisting of particles with four bonding sites ("patches"), two of type A and two of type B, on the square lattice, and investigate its global phase behavior by simulations and theory. We set the interaction between B patches to zero and calculate the phase diagram as the ratio between the AB and the AA interactions, epsilon(AB)*, varies. In line with previous work, on three-dimensional off-lattice models, we show that the liquid-vapor phase diagram exhibits a re-entrant or "pinched" shape for the same range of epsilon(AB)*, suggesting that the ratio of the energy scales - and the corresponding empty fluid regime - is independent of the dimensionality of the system and of the lattice structure. In addition, the model exhibits an order-disorder transition that is ferromagnetic in the re-entrant regime. The use of low-dimensional lattice models allows the simulation of sufficiently large systems to establish the nature of the liquid-vapor critical points and to describe the structure of the liquid phase in the empty fluid regime, where the size of the "voids" increases as the temperature decreases. We have found that the liquid-vapor critical point is in the 2D Ising universality class, with a scaling region that decreases rapidly as the temperature decreases. The results of simulations and theoretical analysis suggest that the line of order-disorder transitions intersects the condensation line at a multi-critical point at zero temperature and density, for patchy particle models with a re-entrant, empty fluid, regime. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3657406]

Evaluation of intermolecular interactions in thioxanthone derivatives: substituent effect on crystal diversity

A family of 9H-thioxanthen-9-one derivatives and two precursors, 2-[(4-bromophenyl) sulfanyl]-5-nitrobenzoic acid and 2-[(4-aminophenyl) sulfanyl]-5-nitrobenzoic acid, were synthesized and studied in order to assess the role of the different substituent groups in determining the supramolecular motifs. From our results we can conclude that Etter's rules are obeyed: whenever present the -COOH head to head strong hydrogen bonding dimer, R-2(2)(8) synthon, prevails as the dominant interaction. As for -NH2, the best donor when present also follows the expected hierarchy, an NH center dot center dot center dot O(COOH) was formed in the acid precursor (2) and an NH center dot center dot center dot O(C=O) in the thioxanthone (4). The main role played by weaker hydrogen bonds such as CH center dot center dot center dot O, and other intermolecular interactions, pi-pi and Br center dot center dot center dot O, as well as the geometric restraints of packing patterns shows the energetic interplay governing crystal packing. A common feature is the relation between the p-p stacking and the unit cell dimensions. A new synthon notation, R`, introduced in this paper, refers to the possibility of accounting for intra- and intermolecular interactions into recognizable and recurring aggregate patterns.

Phase diagrams of binary mixtures of patchy colloids with distinct numbers and types of patches: Theempty fluid regime

We investigate the effect of distinct bonding energies on the onset of criticality of low functionality fluid mixtures. We focus on mixtures ofparticles with two and three patches as this includes the mixture where "empty" fluids were originally reported. In addition to the number of patches, thespecies differ in the type of patches or bonding sites. For simplicity, we consider that the patches on each species are identical: one species has threepatches of type A and the other has two patches of type B. We have found a rich phase behavior with closed miscibility gaps, liquid-liquid demixing, and negative azeotropes. Liquid-liquid demixing was found to pre-empt the "empty" fluid regime, of these mixtures, when the AB bonds are weaker than the AA or BB bonds. By contrast, mixtures in this class exhibit "empty" fluid behavior when the AB bonds are stronger than at least one of the other two. Mixtureswith bonding energies epsilon(BB) = epsilon(AB) and epsilon(AA) < epsilon(BB), were found to exhibit an unusual negative azeotrope. (C) 2011 American Institute of Physics. [doi:10.1063/1.3561396]

Re-entrant phase behaviour of network fluids: A patchy particle model with temperature-dependent valence

We study a model consisting of particles with dissimilar bonding sites ("patches"), which exhibits self-assembly into chains connected by Y-junctions, and investigate its phase behaviour by both simulations and theory. We show that, as the energy cost epsilon(j) of forming Y-junctions increases, the extent of the liquid-vapour coexistence region at lower temperatures and densities is reduced. The phase diagram thus acquires a characteristic "pinched" shape in which the liquid branch density decreases as the temperature is lowered. To our knowledge, this is the first model in which the predicted topological phase transition between a fluid composed of short chains and a fluid rich in Y-junctions is actually observed. Above a certain threshold for epsilon(j), condensation ceases to exist because the entropy gain of forming Y-junctions can no longer offset their energy cost. We also show that the properties of these phase diagrams can be understood in terms of a temperature-dependent effective valence of the patchy particles. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3605703]

Análise comparativa de soluções adotadas para a reabilitação de pavimentos flexíveis que integram a rede rodoviária nacional

A presente dissertação tem como objetivo efetuar a análise comparativa de soluções adotadas de reabilitação de pavimentos flexíveis que integram a rede rodoviária nacional. No âmbito desta análise apresenta-se o estado da arte respeitante à reabilitação de pavimentos flexíveis, nomeadamente: mecanismos de degradação, famílias de degradações, avaliação da capacidade de carga dos pavimentos, metodologia utilizada no dimensionamento do reforço de pavimentos, sendo também efetuada uma análise comparativa de técnicas de reforço de pavimentos e dos tratamentos antifendas. Neste contexto, apresenta-se um caso de estudo no qual é efetuada uma análise de três soluções possíveis para a reabilitação estrutural do pavimento do IC 20 entre Almada e a Costa de Caparica. É feita a descrição da solução projetada pela EP, SA patenteada em concurso público lançado em 2007, a qual é de certa forma inovadora ao nível do tratamento retardador da reflexão de fendas. Aquela solução técnica é constituída pela aplicação de grelhas de fibra de vidro e grelhas de fibra de carbono, seguidas da colocação de uma camada de desgaste em mistura betuminosa rugosa com betume modificado com baixa percentagem de borracha reciclada de pneus usados (BBr - BBB). Complementarmente, é efetuada a análise da solução do projeto de reabilitação do IC 20, patenteado pela Subconcessionária do Baixo Tejo, que contemplou a aplicação de misturas betuminosas rugosas com betume modificado com média percentagem de borracha reciclada de pneus usados (BBr - BBM). Para além da solução patenteada pela subconcessionária, é analisada a solução do projeto de alterações (variante) apresentado pelo agrupamento de empresas construtoras, que foi adotado na execução da obra realizada no IC 20. A intervenção de reabilitação estrutural contemplou a utilização de uma camada de ligação em AC 16 10/20 (MBAM) e uma camada de desgaste em mistura betuminosa rugosa com betume modificado com média percentagem de borracha reciclada de pneus usados (BBr - BBM). Adicionalmente à caracterização de diferentes soluções de reabilitação de pavimentos flexíveis adotados em Portugal, é efetuada uma análise comparativa dos custos de ciclo de vida (construção, manutenção e conservação) de cada tipo de solução de reabilitação.

Qualidade do processamento sensorial e vinculação infantil

Estudou-se a relação entre a segurança da vinculação e a qualidade do processamento sensorial na primeira infância. Para o efeito, seleccionou-se uma amostra normativa de 40 díades mãe-bebé, com crianças entre os 11 e os 18 meses. Avaliou-se a qualidade da vinculação, observando a díade no procedimento Situação Estranha. Classificaram-se 17 (42,5%) das crianças no grupo de vinculação segura, sendo que as restantes 23 (57,5%) revelaram uma vinculação não segura. A qualidade do processamento sensorial avaliou-se através do Teste de Funções Sensoriais. Constatou-se que a segurança da vinculação infantil associava-se a um score agregando quatro factores ambientais (nível sócio-económico dos pais; existência de internamentos hospitalares; coeficiente de número de irmãos; local onde a criança passa o dia). O Teste de Funções Sensoriais não apresentou valor prognóstico relativamente ao tipo de vinculação. Porém, a boa qualidade no processamento da informação sensorial parece constituir um factor de resiliência no desenvolvimento da vinculação.

Estudo exploratório dos comportamentos interativos mãe – filho(a) e pai – filho(a) aos 15 meses de vida.

Dissertação apresentada à Escola Superior de Educação de Lisboa para obtenção do grau de Mestre em Intervenção Precoce

Solution enthalpies of 1,4-dioxane: Study of solvent effects through quantitative structure-property relationships

Solution enthalpies of 1,4-dioxane have been obtained in 15 protic and aprotic solvents at 298.15 K. Breaking the overall process through the use of Solomonov's methodology the cavity term was calculated and interaction enthalpies (Delta H-int) were determined. Main factors involved in the interaction enthalpy have been identified and quantified using a QSPR approach based on the TAKA model equation. The relevant descriptors were found to be pi* and beta, which showed, respectively, exothermic and endothermic contributions. The magnitude of pi* coefficient points toward non-specific solute-solvent interactions playing a major role in the solution process. The positive value of the beta coefficient reflects the endothermic character of the solvents' hydrogen bond acceptor (HBA) basicity contribution, indicating that solvent molecules engaged in hydrogen bonding preferentially interact with each other rather than with 1,4-dioxane. (C) 2013 Elsevier B.V. All rights reserved.

How patchy can one get and still condense? The role of dissimilar patches in the interactions of colloidal particles

We investigate the influence of strong directional, or bonding, interactions on the phase diagram of complex fluids, and in particular on the liquid-vapour critical point. To this end we revisit a simple model and theory for associating fluids which consist of spherical particles having a hard-core repulsion, complemented by three short-ranged attractive sites on the surface (sticky spots). Two of the spots are of type A and one is of type B; the interactions between each pair of spots have strengths [image omitted], [image omitted] and [image omitted]. The theory is applied over the whole range of bonding strengths and results are interpreted in terms of the equilibrium cluster structures of the coexisting phases. In systems where unlike sites do not interact (i.e. where [image omitted]), the critical point exists all the way to [image omitted]. By contrast, when [image omitted], there is no critical point below a certain finite value of [image omitted]. These somewhat surprising results are rationalised in terms of the different network structures of the two systems: two long AA chains are linked by one BB bond (X-junction) in the former case, and by one AB bond (Y-junction) in the latter. The vapour-liquid transition may then be viewed as the condensation of these junctions and we find that X-junctions condense for any attractive [image omitted] (i.e. for any fraction of BB bonds), whereas condensation of the Y-junctions requires that [image omitted] be above a finite threshold (i.e. there must be a finite fraction of AB bonds).

Shear-induced lamellar phase of an ionic liquid crystal at room temperature

The phase behaviour of a number of N-alkylimidazolium salts was studied using polarizing optical microscopy, differential scanning calorimetry and X-ray diffraction. Two of these compounds exhibit lamellar mesophases at temperatures above 50 degrees C. In these systems, the liquid crystalline behaviour may be induced at room temperature by shear. Sheared films of these materials, observed between crossed polarisers, have a morphology that is typical of (wet) liquid foams: they partition into dark domains separated by brighter (birefringent) walls, which are approximately arcs of circle and meet at "Plateau borders" with three or more sides. Where walls meet three at a time, they do so at approximately 120 degrees angles. These patterns coarsen with time and both T1 and T2 processes have been observed, as in foams. The time evolution of domains is also consistent with von Neumann's law. We conjecture that the bright walls are regions of high concentration of defects produced by shear, and that the system is dominated by the interfacial tension between these walls and the uniform domains. The control of self-organised monodomains, as observed in these systems, is expected to play an important role in potential applications.

Criticality of colloids with distinct interaction patches: The limits of linear chains, hyperbranched polymers, and dimers

We use a simple model of associating fluids which consists of spherical particles having a hard-core repulsion, complemented by three short-ranged attractive sites on the surface (sticky spots). Two of the spots are of type A and one is of type B; the bonding interactions between each pair of spots have strengths epsilon(AA), epsilon(BB), and epsilon(AB). The theory is applied over the whole range of bonding strengths and the results are interpreted in terms of the equilibrium cluster structures of the phases. In addition to our numerical results, we derive asymptotic expansions for the free energy in the limits for which there is no liquid-vapor critical point: linear chains (epsilon(AA)not equal 0, epsilon(AB)=epsilon(BB)=0), hyperbranched polymers (epsilon(AB)not equal 0, epsilon(AA)=epsilon(BB)=0), and dimers (epsilon(BB)not equal 0, epsilon(AA)=epsilon(AB)=0). These expansions also allow us to calculate the structure of the critical fluid by perturbing around the above limits, yielding three different types of condensation: of linear chains (AA clusters connected by a few AB or BB bonds); of hyperbranched polymers (AB clusters connected by AA bonds); or of dimers (BB clusters connected by AA bonds). Interestingly, there is no critical point when epsilon(AA) vanishes despite the fact that AA bonds alone cannot drive condensation.