Polyimide and polyetherimide organic solvent nanofiltration membranes

Integrally asymmetric skinned Lenzing P84 and Matrimid 5218 polymide membranes and Ultem 1000 polyetherimide membranes were prepared. Crosslinking of membranes using aliphatic diamines resulted in marked improvement in chemical stability. This however resulted in a decline in flux with only Lenzing P84 demonstrating good flux in DMF. Further variation of membrane dope parameters and operating conditions allowed for good control of the MWCO of membranes made from Lenzing P84. SEM pictures of Lenzing P84 membranes revealed a significant difference in membranes morphology. The presence of macrovoids increased when using more DMF in the dope solution. These studies demonstrate the possibility of developing OSN membranes using different polyimides and opens up future possibilities for controlling the MWCO of these membranes. Preliminary modelling demonstrates that good control of the MWCO could extend the application of OSN membranes to allow the fraction of molecules in the NF range.

Development of polymeric membranes for forward osmosis

Dissertação apresentada na Faculdade de Ciências e Tecnologia da Universidade Nova de Lisboa para obtenção do grau de Mestre em Engenharia Química e Bioquímica

Influence of commercially available polyimide and formation conditions on the performance and structure of asymmetric polyimide organic solvent nanofiltration membranes

Dissertação apresentada na Faculdade de Ciências e Tecnologia da Universidade Nova de Lisboa para a obtenção do grau de Mestre em Engenharia Química e Bioquímica

Promoção da saúde oral: uma experiência de prevenção de cárie num concelho rural

Resumo: A cárie dentária, um problema que tem atingido populações em grande parte do mundo, é a doença de maior prevalência da cavidade oral, gerando graves consequências económicas e sociais. Esta doença tem sido estudada ao longo do tempo em diferentes países com o emprego de diversos índices, geralmente para o estudo da sua prevalência, a avaliação de medidas preventivas e o adequado planeamento das acções e serviços de saúde oral. O objectivo deste Projecto foi determinar se a escovagem quando realizada na escola com pasta fluoretada, e supervisionada pelos professores, duas vezes por dia, seria ou não eficaz na diminuição das populações microbianas de Streptococcus mutans e Lactobacillus e na consequente diminuição da incidência de cárie dentária. Material e métodos: Foram seleccionadas todas as crianças (universo = 178), com idades compreendidas entre os 5, 6 e 7 anos, residentes no Concelho de Aljustrel e a frequentar o pré-escolar e o primeiro ciclo do ensino básico oficial. Foi realizada a escovagem bi-diária com pasta fluoretada a 500 ppm F-, na escola, segundo o método de Bass modificado, supervisionado pelos professores titulares de turma, que tiveram formação da técnica de escovagem utilizada. Durante os 3 anos de estudo foram realizadas 6 observações dentárias e recolhas salivares para contagem de Streptococcus mutans e Lactobacillus e avaliação da capacidade tampão da saliva. Resultados: O grupo de estudo no início da intervenção apresentava valores dos índices de cárie dentária mais elevados do que os do grupo de controlo (mais 0,109 no CPO-S, 0,0749 no CPO-D, 1,505 no cpo-s e 0,831 no cpo-d), porém sem diferenças de significância estatística. A análise estatística dos resultados não veio confirmar este pressuposto uma vez que o grupo de estudo apresentou um aumento percentual ligeiramente maior do índice CPO-D (12,5%) do que o grupo de controlo (11,6%). Para além deste aspecto, ao contrário do que seria de esperar, não foi possível detectar nenhuma diferença estatisticamente significativa em nenhum dos índices de cárie dentária (cpo-s, cpo-d, CPO-S e CPO-D) entre o grupo de estudo e grupo de controlo entre a 1ª e última observação.Ainda que os resultados do estudo aqui apresentado tenham ficado aquém do esperado, deveria ser efectuada a escovagem diária na escola, uma vez por dia, com pasta fluoretada a 1000 ppm F-, atendendo a que esta medida contribui para a promoção da saúde e prevenção da doença e é facilitadora da construção de estilos de vida saudáveis.-------ABSTRACT: Dental caries, a problem that has affected populations worldwide, is one of the most prevalent diseases of the oral cavity, causing severe economic and social consequences. This disease has been studied over time in different countries with the use of various indices, usually for the knowledge of its prevalence, evaluation of preventive measures and appropriate planning of actions and oral services. The aim of this study was to determine whether toothbrushing when performed in schools, with fluoride toothpaste, and supervised by teachers twice a day, was effective in reducing microbial populations of Streptococcus mutans and Lactobacillus with consequent reduction in the incidence of dental caries. Material and Methods: All children aged 5, 6, and 7 years, from Aljustrel County, attending official pre-school and first cycle of basic educatio were selected. Toothbrushing was performed twice a day with toothpaste with 500 ppm F-,in the school, according to the modified Bass method, supervised by professors in the class, who were trained in the brushing technique used. During the study period were performed 6 observations of the dental status, and were also collected saliva for the count of Streptococcus mutans and Lactobacillus, and assessment of buffering capacity of saliva. Results: The study group at the beginning of the intervention had higher values of dental caries than the control group (more than 0,109 in DMF-S, 0, 0749 in DMF, dmf-s 1,505 and 0,831 in dmf-t) although without statistical significance. The expected results were not confirmed, since the study group had a slightly higher percentage increase of the DMF-T (12,5%) than the control group (11,6%). Apart from that, contrary to what one would expect, we could not detect any statistical significant difference in any of the indices of dental caries (dmf-s, dmf-t and DMF-S, DMF-T) between the study and the control group in all study periods. Although the study results were not has expected, toothbrushing should be performed daily at school, once a day with fluoride toothpaste with 1000 ppm F-, since this measure contributes to health promotion and disease prevention and encourages healthy lifestyles.

Control system for actuation and sensing in digital microfluidics devices

Digital Microfluidics (DMF) is a second generation technique, derived from the conventional microfluidics that instead of using continuous liquid fluxes, it uses only individual droplets driven by external electric signals. In this thesis a new DMF control/sensing system for visualization, droplet control (movement, dispensing, merging and splitting) and real time impedance measurement have been developed. The software for the proposed system was implemented in MATLAB with a graphical user interface. An Arduino was used as control board and dedicated circuits for voltage switching and contacts were designed and implemented in printed circuit boards. A high resolution camera was integrated for visualization. In our new approach, the DMF chips are driven by a dual-tone signal where the sum of two independent ac signals (one for droplet operations and the other for impedance sensing) is applied to the electrodes, and afterwards independently evaluated by a lock-in amplifier. With this new approach we were able to choose the appropriated amplitudes and frequencies for the different proposes (actuation and sensing). The measurements made were used to evaluate the real time droplet impedance enabling the knowledge of its position and velocity. This new approach opens new possibilities for impedance sensing and feedback control in DMF devices.

Digital microfluidic devices: the role of the dielectric layer

Digital microfluidics (DMF) is a field which has emerged in the last decade as a re-liable and versatile tool for sensing applications based on liquid reactions. DMF allows the discrete displacement of droplets, over an array of electrodes, by the application of voltage, and also the dispensing from a reservoir, mixing, merging and splitting fluidic operations. The main drawback of these devices is due to the need of high driving volt-ages for droplet operations. In this work, alternative dielectric layers combinations were studied aiming the reduction of these driving voltages. DMF chips were designed, pro-duced and optimized according to the theory of electrowetting-on-dielectric, adopting different combinations of parylene-C and tantalum pentoxide (Ta2O5) as dielectric ma-terials, and Teflon as hydrophobic layer. With both devices’ configurations, i.e., Parylene as single dielectric, and multilayer chips combining Parylene and Ta2O5, it was possible to perform all the fluidic opera-tions in the microliter down to hundreds of nanoliters range. Multilayer chips presented significant reduction on driving voltages for droplet op-erations in silicone oil filler medium: from 70 V (parylene only) down to 30 V (parylene/Ta2O5) for dispensing; and from 50 V (parylene only) down to 15 V (parylene/Ta2O5) for movement. Peroxidase colorimetric reactions were successfully performed as proof-of-concept, using multilayer configuration devices.