Este trabalho estuda o fluxo de etileno glicol (MEG) sobre duas superfícies sólidas com constituições químicas diferentes: borossilicato e dióxido de estanho (SnO 2 ). O alinhamento intermolecular, determinado como polarização e anisotropia, mostrou dependência da natureza química do sólido. A razão entre as tensões interfaciais dinâmicas foi 1.09 ± 0.07, devendo ser maior para MEG/borossilicato do que para MEG/SnO 2 . A razão da capilaridade foi 0.92 ± 0.06, sendo menor para MEG/borossilicato. Medidas estáticas do ângulo de contato mostraram valores menores para borossilicato do que para SnO 2 . Os mapas de polarização e anisotropia apresentaram valores mais altos para MEG/SnO 2 , o que pode ser explicado pela alta tensão interfacial do MEG/borossilicato. Estes resultados são compatíveis com interações de volume mais fortes em MEG/SnO 2 e com contribuições de superfície mais fortes em MEG/borossilicato. Isto pode ser atribuído ao borossilicato ser mais eletronegativo, favorecendo mais as pontes de hidrogênio com o MEG.This work studied ethylene glycol (MEG) flowing on two different solid surfaces, borosilicate and thin dioxide (SnO 2 ). Intermolecular alignment, determined as polarization and anisotropy, showed dependence on the solid chemical nature. The ratio between dynamic surface tensions was found 1.09 ± 0.07, being stronger for MEG/borosilicate than for MEG/SnO 2 . The capillary ratio found was 0.92 ± 0.06, being smaller for MEG/borosilicate. Static contact angle measurements gave lower values for borosilicate than for SnO 2 . Both polarization and anisotropy maps presented higher values for MEG/SnO 2 , which can be explained by MEG/borosilicate higher interfacial interaction. The results obtained are compatible with stronger bulk phenomena for MEG/SnO 2 and with stronger interfacial phenomena for MEG/borosilicate. This may be due to borosilicate being more electronegative, yielding more efficiently hydrogen bonds with MEG.

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Recebido em 6/4/05; aceito em 4/10/05; publicado na web em 18/4/06 ATMOSPHERIC PASSIVE MONITORING OF SO 2 , NO 2 AND O 3 IN URBAN AREAS AND IN THOSE UNDER INDUSTRIAL INFLUENCE AS AN ENVIRONMENTAL CHEMISTRY EXPERIMENT FOR UNDERGRADUATE STUDENTS. This study is a result of undergraduate student participation in the Environmental Chemistry discipline provided by the Chemistry Institute/UFBA. The students were involved in the development of passive samplers, a project of the LAQUAM (Environmental Analytical Chemistry Laboratory). The students' residences and other neighborhoods were used to create a passive sampling network, allowing the measurement of atmospheric levels of pollutants in urban areas and in those under industrial influence. The assembly of the passive samplers, including impregnation of filters and chemical analysis were part of the students' practice tasks. The results were analyzed taking into consideration the Brazilian legislation.Keywords: passive sampling; air pollutants; environmental chemistry. INTRODUÇÃOA disciplina optativa "Química Ambiental", oferecida para alunos de Química no IQ/UFBA, aborda no seu conteúdo teórico a química das diferentes esferas ambientais. Para a parte prática da disciplina não é definido um programa específico, e sim, a participação dos alunos em um projeto de pesquisa ou estudo de caso que esteja sendo desenvolvido por uma equipe do IQ na área de meio ambiente, devendo ser examinado sob os aspectos químicos, integrando-os à obediência à legislação, aos efeitos sobre o meio ambiente e à saúde humana. Esta disciplina sempre foi oferecida, em semestres alternados para um número de alunos entre 4 -6, porém teve seu módulo (de 10 alunos) ultrapassado neste semestre, devido ao interesse despertado entre os estudantes quanto aos temas ambientais.Este trabalho apresenta o resultado da participação dos alunos dessa disciplina no referido semestre, junto à equipe do LAQUAM (Laboratório de Química Analítica Ambiental do Departamento de Química Analítica do IQ/UFBA) no monitoramento atmosférico de SO 2 , NO 2 e O 3 utilizando amostradores passivos, em áreas urbanas e com influência industrial.A técnica de monitoramento atmosférico mais difundida e aplicada é a ativa, principalmente através do uso de monitores contí-nuos que consistem de tecnologia complicada e cara. No entanto, o uso de amostradores passivos, dispositivos capazes de fixar gases ou vapores da atmosfera, sem envolver bombeamento artificial, tem se mostrado uma alternativa simples e de custo muito baixo. Aliado a isso, a experiência da equipe do LAQUAM no desenvolvimento de amostradores passivos 1-8 motivaram este trabalho, o qual produziu dados ambientais de importância e antes ainda não levantados simultaneamente em tal extensão espacial na região, para os gases medidos.Dióxido de enxofre (SO 2 ) é emitido para a atmosfera principalmente pela queima de combustíveis fósseis para aquecimento e produção de energia, e por fontes industriais como fundição de minéri-os não-ferrosos, além de outros processos, tais como...

High-density polyethylene (HDPE) and polypropylene (PP) were studied to identify tailor-made materials for walls of pipelines and ducts for crude paraffinic oil that inhibit paraffin depositions. The interfacial interaction was investigated from 50 to 70 degrees C and as a function of the n-C(36)H(74) paraffin concentration added to the paraffinic crude oil. The static and the dynamic interfacial tensions were observed, respectively, by traditional contact angle measurements and by fluorescence depolarization of the natural fluorescent probes of the crude oil, flowing at a high rate. The static interaction showed a low dependence on the n-paraffin content for both surfaces. For PP, it decreased slightly as the n-paraffin concentration increased, evidencing an increase in the liquid-liquid interaction. The dynamic interfacial tension with PP clearly decreased as temperature and n-paraffin concentration increased, the latter effect being attributed to the PP methyl groups hindering the interaction between the n-paraffin and the PP main chain. For the flow on HDPE, the interaction proved to be highly dependent on the n-paraffin concentration and temperature. It increased as n-paraffin was added and temperature decreased. The former effect is attributed to the alignment of the n-paraffin chains within the high rate flowing liquid and the similar molecular geometry of the n-paraffin and the linear polymer surface (almost without branches), which increases the number of sites available for interaction. PP proved to be more suitable for transportation of crude oil rich in paraffins with more than 36 carbon atoms, while HDPE was more suitable for those with smaller paraffinic chains.

Steady-state fluorescence depolarization has proven, in the past few years, to be a method sensitive to adhesion of thin liquid films flowing without boundaries on solid substrates of different chemical constitutions. This work extends our prior preliminary assessment of the efficiency of the method and the influence of experimental variables. Ten thin films of ethylene glycol (MEG) were mapped over 102 mm2 by polarized laser-induced fluorescence (PLF−FI) while flowing on substrates. The interfacial tension, ΓSL, was varied either by changing the chemical constitution of the substrate (borosilicate, tin dioxide, poly(vinyl alcohol) (PVA), and linear alkylbenzene sulfonate (LAS)) or by addition of tensoactives to MEG (sodium dodecyl sulfate (SDS) and poly(ethylene oxide) (PEO)). Contact angle measurements were employed to classify interfaces according to their static ΓSL, that is, their wetting efficiencies. PLF−FI experimental variables, such as laser power, film thickness, and impinging velocity profile, did not alter the data within the range studied, except for flow rates over 220 cm s-1. Average polarization (P av) increased from 10.5% to 13.5% upon decreasing adhesion by varying the chemical constitution of the solid. When surfactants were dissolved in the liquid flow, polarization ranged from 5.4% to 3.8% while for surfactant as substrate it increased. Simple multivariate principal component analysis (PCA) was applied to downstream polarization averages (P down) for each map. The two principal components accounted for 95.6% of the variance, ordering the maps according to decreasing adhesion and gathering them into three groups:  dissolved surfactants, liquid films flowing at the highest flow rate, and solid surfaces of different chemical composition. Hierarchic cluster analysis (HCA) showed that, as adhesion decreased, similarity among the polarization maps increased.