Raman spectroscopic studies of the cure of dicyclopentadiene (DCPD)

The cure of polydicyclopentadiene conducted by ring-opening metathesis polymerisation in the presence of a Grubbs catalyst was studied using non-invasive Raman spectroscopy. The spectra of the monomer precursor and polymerised product were fully characterised and all stages of polymerisation monitored. Because of the monomer's high reactivity, the cure process is adaptable to reaction injection moulding and reactive rotational moulding. The viscosity of the dicyclopentadiene undergoes a rapid change at the beginning of the polymerisation process and it is critical that the induction time of the viscosity increase is determined and controlled for successful manufacturing. The results from this work show non-invasive Raman spectroscopic monitoring to be an effective method for monitoring the degree of cure, paving the way for possible implementation of the technique as a method of real-time analysis for control and optimisation during reactive processing. Agreement is shown between Raman measurements and ultrasonic time of flight data acquired during the initial induction period of the curing process. (c) 2004 Elsevier B.V. All rights reserved.

Competitive adsorption of aqueous metal ions on an oxidized nanoporous activated carbon\

<p>Competitive adsorption is the usual situation in real applications, and it is of critical importance in determining the overall performance of an adsorbent. In this study, the competitive adsorption characteristics of all the combinations of binary mixtures of aqueous metal ion species Ca2+(aq), Cd2+(aq), Pb2+(aq), and Hg2+(aq) on a functionalized activated carbon were investigated. The porous structure of the functionalized active carbon was characterized using N-2 (77 K) and CO2 (273 K) adsorption. The surface group characteristics were examined by temperature-programmed desorption, Fourier transform infrared spectroscopy, Raman spectroscopy, acid/base titrations, and measurement of the point of zero charge (pH(PZC)). The adsorption of aqueous metal ion species M2+(aq), on acidic oxygen functional group sites mainly involves an ion exchange mechanism. The ratios of protons displaced to the amount of M2+(aq) metal species adsorbed have a linear relationship for both single-ion and binary mixtures of these species. Hydrolysis of metal species in solution may affect the adsorption, and this is the case for adsorption of Hg2+(aq) and Pb2+(aq). Competitive adsorption decreases the amounts of individual metal ions adsorbed, but the maximum amounts adsorbed still follow the order Hg2+(aq) &gt; Pb2+(aq) &gt; Cd2+(aq) &gt; Ca2+(aq) obtained for single metal ion adsorption. The adsorption isotherms for single metal ion species were used to develop a model for competitive adsorption in binary mixtures, involving exchange of ions in solution with surface proton sites and adsorbed metal ions, with the species having different accessibilities to the porous structure. The model was validated against the experimental data.</p>

Tip-enhanced Raman microscopy: practicalities and limitations

<p>The feasibility of apertureless scanning near-field Raman microscopy, exploiting the local enhancement in Raman scattering in the vicinity of a silver or gold tip, was investigated. Using the finite difference time domain method we calculated the enhancement of electric field strength, and hence Raman scattering, achieved through the resonant excitation of local modes in the tip. By modelling the frequency-dependent dielectric response of the metal tip we were able to highlight the resonant nature of the tip-enhancement and determine the excitation wavelength required for the strongest electric field enhancement, and hence Raman scattering intensity, which occurs for the excitation of modes localized at the tip apex. It is demonstrated that a peak Raman enhancement of 10(7)-fold should be achievable with &lt;5 nm spatial resolution. We show that surface-enhanced Raman scattering from carbon contamination on a silver or gold tip can be significant. However, we find for a tip of radius of curvature 20 nm that the Raman enhancement should decay totally within 20 nm from the tip. Hence withdrawal of the tip by this distance should lead to the disappearance of the tip-enhanced signal, leaving only that from carbon contamination on the tip itself and the intrinsic signal from the sample. Copyright (C) 2003 John Wiley Sons, Ltd.</p>

The lateritic profile of Balkouin, Burkina Faso: geochemistry, mineralogy and genesis

This study reports on the geochemical and mineralogical characterization of a lateritic profile cropping out in the Balkouin area, Central Burkina Faso, aimed at obtaining a better understanding of the processes responsible for the formation of the laterite itself and the constraints to its development. The lateritic profile rests on a Paleoproterozoic basement mostly composed of granodioritic rocks related to the Eburnean magmatic cycle passing upwards to saprolite and consists of four main composite horizons (bottom to top): kaolinite and clay-rich horizons, mottled laterite and iron-rich duricrust. In order to achieve such a goal, a multi-disciplinary analytical approach was adopted, which includes inductively coupled plasma (ICP) atomic emission and mass spectrometries (ICP-AES and ICP-MS respectively), X-ray powder diffraction (XRPD), scanning electron microscopy with energy dispersive spectrometry (SEM-EDS) and micro-Raman spectroscopy.<br/><br/>The geochemical data, and particularly the immobile elements distribution and REE patterns, show that the Balkouin laterite is the product of an in situ lateritization process that involved a strong depletion of the more soluble elements (K, Mg, Ca, Na, Rb, Sr and Ba) and an enrichment in Fe; Si was also removed, particularly in the uppermost horizons. All along the profile the change in composition is coupled with important changes in mineralogy. In particular, the saprolite is characterized by occurrence of abundant albitic plagioclase, quartz and nontronite; kaolinite is apparently absent. The transition to the overlying lateritic profile marks the breakdown of plagioclase and nontronite, thus allowing kaolinite to become one of the major components upwards, together with goethite and quartz. The upper part of the profile is strongly enriched in hematite (+ kaolinite). Ti oxides (at least in part as anatase) and apatite are typical accessory phases, while free aluminum hydroxides are notably absent. Mass change calculations emphasize the extent of the mass loss, which exceeds 50 wt% (and often 70 wt%) for almost all horizons; only Fe was significantly concentrated in the residual system.<br/><br/>The geochemical and mineralogical features suggest that the lateritic profile is the product of a continuous process that gradually developed from the bedrock upwards, in agreement with the Schellmann classic genetic model. The laterite formation must have occurred at low pH (? 4.5) and high Eh (? 0.4) values, i.e., under acidic and oxidizing environments, which allowed strongly selective leaching conditions. The lack of gibbsite and bohemite is in agreement with the compositional data: the occurrence of quartz (�� amorphous silica) all along the profile was an inhibiting factor for the formation of free aluminum hydroxides.

In-situ Monitoring of Solid Oxide Electrolysis Cells

<p>High temperature co-electrolysis of steam and carbon dioxide using a solid oxide cell (SOC) has been shown to be an efficient route to produce syngas (CO + H-2), which can then be converted to synthetic fuel. Optimization of co-electrolysis requires detailed understanding of the complex reactions, transport processes and degradation mechanisms occurring in the SOC during operation. Thermal imaging, Raman spectroscopy and Diffuse Reflectance Infrared Fourier Transform Spectroscopy are being developed to probe in-situ both the reactions occurring during operation and any associated changes within the structure of the electrodes and electrolyte. Here we discuss the challenges in designing experimental apparatus suitable for high temperature operation with optical spectroscopic access to the areas of the SOC that are of interest. In particular, issues with sealing, temperature gradients, signal strength and cell configuration are discussed and final designs are presented. Preliminary results obtained during co-electrolysis operation are also presented.</p>

Tailoring Alphabetical Metamaterials in Optical Frequency: Plasmonic Coupling, Dispersion, and Sensing

Tailoring optical properties of artificial metamaterials, whose optical properties go beyond the limitations of conventional and naturally occurring materials, is of importance in fundamental research and has led to many important applications such as security imaging, invisible cloak, negative refraction, ultrasensitive sensing, transformable and switchable optics. Herein, by precisely controlling the size, symmetry and topology of alphabetical metamaterials with U, S, Y, H, U-bar and V shapes, we have obtained highly tunable optical response covering visible-to-infrared (Vis-NIR) optical frequency. In addition, we show a detailed study on the physical origin of resonance modes, plasmonic coupling, the dispersion of electronic and magnetic surface plasmon polaritons, and the possibility of negative refraction. We have found that all the electronic and magnetic modes follow the dispersion of surface plasmon polaritons thus essentially they are electronic- and magnetic-surface-plasmon-polaritons-like (ESPP-like and MSPP-like) modes resulted from diffraction coupling between localized surface plasmon and freely-propagating light. Based on the fill factor and formula of magnetism permeability, we predict that the alphabetical metamaterials should show the negative refraction capability in visible optical frequency. Furthermore, we have demonstrated the specific ultrasensitive surface enhanced Raman spectroscopy (SERS) sensing of monolayer molecules and femtomolar food contaminants by tuning their resonance to match the laser wavelength, or by tuning the laser wavelength to match the plasmon resonance of metamaterials. Our tunable alphabetical metamaterials provide a generic platform to study the electromagnetic properties of metamaterials and explore the novel applications in optical frequency.

Better understanding of mechanochemical reactions: Raman monitoring reveals surprisingly simple 'pseudo-fluid' model for a ball milling reaction

Quantitative monitoring of a mechanochemical reaction by Raman spectroscopy leads to a surprisingly straightforward second-order kinetic model in which the rate is determined simply by the frequency of reactive collisions between reactant particles.<br/>

Use of water in aiding olefin/paraffin (liquid + liquid) extraction via complexation with a silver bis(trifluoromethylsulfonyl)imide salt

<p>This paper describes the extraction of C₅���C₈ linear <em>��</em>-olefins from olefin/paraffin mixtures of the same carbon number <em>via</em> a reversible complexation with a silver salt (silver bis(trifluoromethylsulfonyl)imide, Ag[Tf₂N]) to form room temperature ionic liquids [Ag(olefin)<em>_x</em>][Tf₂N]. From the experimental (liquid��+��liquid) equilibrium data for the olefin/paraffin mixtures and Ag[Tf₂N], 1-pentene showed the best separation performance while C₇ and C₈ olefins could only be separated from the corresponding mixtures on addition of water which also improves the selectivity at lower carbon numbers like the C₅ and C₆, for example. Using infrared and Raman spectroscopy of the complex and Ag[Tf₂N] saturated by olefin, the mechanism of the extraction was found to be based on both chemical complexation and the physical solubility of the olefin in the ionic liquid ([Ag(olefin)<em>_x</em>][Tf₂N]). These experiments further support the use of such extraction techniques for the separation of olefins from paraffins.</p>

Raman spectra of SiC nanorods with different excitation wavelengths

<p>With increasing excitation wavelength from 514 to 782 nm, a significant difference in the Raman spectra of SiC nanorods was observed as compared to bulk material. The intensity ratio of the LO mode to that of the IF mode increases with the excitation wavelength increasing. This has been identified as resonant Raman scattering caused by Fr��hlich interaction.</p>

Comparative Raman Study of Carbon Nanotubes Prepared by D.C. Arc Discharge and Catalytic Methods

The Raman spectra of carbon nanotubes prepared by catalytic (C-CNT) and d.c. arc discharge (D-CNT) methods are reported. A previously unnoticed third-order Raman peak at ca. 4248 cm-1 was observed in the Raman spectrum of D-CNT. The Raman features of D-CNT and C-CNT are similar to those of highly oriented pyrolytic graphite (HOPG) and active carbon, respectively. The data also suggest that the increase in disorder in D-CNT compared with HOPG is due to structural defects in D-CNT. �� 1997 by John Wiley &amp; Sons, Ltd.

H��bridos org��nicos-inorg��nicos para aplica����es de baixo custo em ��ptica integrada

O objectivo desta tese �� a utiliza����o de materiais h��bridos org��nicos-inorg��nicos, designados por di-ureiasis modificados pela adi����o de tetra-prop��xido de zirc��nio (Zr(i-OPr)4) estabilizado com ��cido metacr��lico (CH2=C(CH3)COOH), obtidos pela via sol-gel, para aplica����es em dispositivos ��pticos integrados de baixo custo. A estrutura local dos di-ureiasis com diferentes concentra����es de prop��xido de zirc��nio (20 a 80 % mol) foi estudada por difrac����o de raios-X, espalhamento de raios X a baixos ��ngulos, microscopia de for��a at��mica, resson��ncia magn��tica nuclear dos n��cleos dos ��tomos de 29Si e 13C, espectroscopia no infravermelho por transformada de Fourier, espectroscopia de Raman por transformada de Fourier e termogravimetria. A influ��ncia dos par��metros de s��ntese, concentra����o de tetra prop��xido de zirc��nio e r��cio tetra prop��xido de zirc��nio: ��cido metacrilico na estrutura e propriedades das amostras em mon��lito e filmes finos (depositados pela t��cnica de deposi����o por rota����o do substrato) foram avaliadas, permitindo obter amostras transparentes, fotopolimeriz��veis e est��veis termicamente at�� aos 100 ��C. Foram determinadas as propriedades dos guias planares em substratos de vidro borosilicato e sil��cio oxidado (1<WSiO2< 5��m) relevantes para aplica����o em ��ptica integrada tais como : ��ndice de refrac����o (1,4774-1,5149 a 1550 nm), espessura (6-10 ��m), perdas por propaga����o (~1,5 dB/cm) e rugosidade (~5,0 nm). Posteriormente o processo de escrita laser directa permitiu a grava����o de dispositivos para ��ptica integrada de que s��o exemplos: guias de onda em canal com di��metros modais de 2,5 ��m (monomodo) e de 15-20 ��m (multimodo) e contraste de valor do ��ndice de refrac����o de 2x10-3; divisores de pot��ncia ��ptica com geometria em Y com r��cios de divis��o de ~50:50; filtros ��pticos baseados em redes de Bragg com valores de rejei����o do sinal ��ptico de 10 dB (mon��litos) e 24 dB (filmes finos); cavidades ��pticas do tipo Fabry-Perot com valores de rejei����o de ~5 dB e gama espectral livre de 16,5 e 35,5 GHz. A actua����o termo-��ptica de uma estrutura do tipo Mach-Zhender sim��trica conduziu a uma atenua����o do sinal ��ptico de 7,5 dB.

Desenvolvimento de Anticorpos Pl��sticos para um Biomarcador do Cancro

O trabalho descrito compreende o desenvolvimento de um anticorpo pl��stico (MIP, do ingl��s Molecularly Imprinted Polymer) para o antig��nio carcinoembrion��rio (CEA, do ingl��s Carcinoembriogenic Antigen) e a sua aplica����o na constru����o de dispositivos port��teis, de tamanho reduzido e de baixo custo, tendo em vista a monitoriza����o deste biomarcador do cancro do colo-retal em contexto Point-of-Care (POC). O anticorpo pl��stico foi obtido por tecnologia de impress��o molecular orientada, baseada em eletropolimeriza����o sobre uma superf��cie condutora de vidro recoberto por FTO. De uma forma geral, o processo foi iniciado pela electropolimeriza����o de anilina sobre o vidro, seguindo-se a liga����o por adsor����o do biomarcador (CEA) ao filme de polianilina, com ou sem mon��meros carregados positivamente (Cloreto de vinilbenziltrimetilam��nio, VB). A ��ltima fase consistiu na electropolimeriza����o de o-fenilenodiamina (oPD) sobre a superf��cie, seguindo-se a remo����o da prote��na por clivagem de liga����es pept��dicas, com o aux��lio de tripsina. A efici��ncia da impress��o do biomarcador CEA no material polim��rico foi controlada pela prepara����o de um material an��logo, NIP (do ingl��s, Non-Imprinted Polymer), no qual nem a prote��na nem o mon��mero VB estavam presentes. Os materiais obtidos foram caracterizados quimicamente por t��cnicas de Infravermelho com Transformada de Fourier (FTIR, do ingl��s, Fourier Transform Infrared Spectroscopy) e microscopia confocal de Raman. Os materiais sensores preparados foram entretanto inclu��dos em membranas polim��ricas de Poli(cloreto de vinilo) (PVC) plastificado, para constru����o de sensores (biomim��ticos) seletivos a CEA, tendo-se avaliado a resposta anal��tica em diferentes meios. Obteve-se uma boa resposta potenciom��trica em solu����o tamp��o de ��cido 4-(2-hidroxietil)piperazina-1-etanosulf��nico (HEPES), a pH 4,4, com uma membrana seletiva baseada em MIP preparada com o mon��mero carregado VB. O limite de dete����o foi menor do que 42 pg/mL, observando-se um comportamento linear (versus o logaritmo da concentra����o) at�� 625 pg/mL, com um declive ani��nico igual a -61,9 mV/d��cada e r2>0,9974. O comportamento anal��tico dos sensores biomim��ticos foi ainda avaliado em urina, tendo em vista a sua aplica����o na an��lise de CEA em urina. Neste caso, o limite de dete����o foi menor do que 38 pg/mL, para uma resposta linear at�� 625 pg/mL, com um declive de -38,4 mV/d��cada e r2> 0,991. De uma forma geral, a aplica����o experimental dos sensores biomim��ticos evidenciou respostas exatas, sugerindo que os biossensores desenvolvidos prossigam estudos adicionais tendo em vista a sua aplica����o em amostras de indiv��duos doentes.

Desenvolvimento e aplica����o de um biossensor para monitoriza����o de creatinina, um biomarcador associado a doen��as emergentes

Este trabalho descreve o desenvolvimento de um material sensor para creatinina por impress��o molecular em estrutura polim��rica (MIP) e a sua aplica����o no desenvolvimento de um dispositivo de natureza potenciom��trica para a determina����o da mol��cula alvo em fluidos biol��gicos. A creatinina �� um dos biomarcadores mais utilizados no acompanhamento da doen��a renal, j�� que �� um bom indicador da taxa de filtra����o glomerular (TFG). Os materiais biomim��ticos desenhados para intera����o com a creatinina foram obtidos por polimeriza����o radicalar, recorrendo a mon��meros de ��cido metacr��clico ou de vinilpiridina e a um agente de reticula����o apropriado. De modo a aferir o efeito da impress��o da creatinina na resposta dos materiais MIP �� sua presen��a, foram tamb��m preparados e avaliados materiais de controlo, obtidos sem impress��o molecular (NIP). O controlo da constitui����o qu��mica destes materiais, incluindo a extra����o da mol��cula impressa, foi realizado por Espectroscopia de Raman e de Infravermelho com Transformada de Fourrier. A afinidade de liga����o entre estes materiais e a creatinina foi tamb��m avaliada com base em estudos cin��ticos. Todos os materiais descritos foram integrados em membranas selectivas de el��trodos seletivos de i��o, preparadas sem ou com aditivo i��nico lip��filo, de carga negativa ou positiva. A avalia����o das caracter��sticas gerais de funcionamento destes el��trodos, em meios de composi����o e pH diferentes, indicaram que as membranas com materiais impressos e aditivo ani��nico eram as ��nicas com utilidade anal��tica. Os melhores resultados foram obtidos em solu����o tamp��o Piperazine-N,N���-bis(2- ethanesulfonic acid), PIPES, de pH 2,8, condi����o que permitiu obter uma resposta quasi-Nernstiana, a partir de 1,6��10-5 mol L-1. Estes el��trodos demonstraram ainda uma boa selectividade ao apresentaram uma resposta preferencial para a creatinina quando na presen��a de ureia, carnitina, glucose, ��cido asc��rbico, albumina, cloreto de c��lcio, cloreto de pot��ssio, cloreto de s��dio e sulfato de magn��sio. Os el��trodos foram ainda aplicados com sucesso na an��lise de amostras sint��ticas de urina, quando os materiais sensores eram baseados em ��cido metacrilico, e soro, quando os materiais sensores utilizados eram baseados em vinilpiridina.