Thesis (M.S.)--Worcester Polytechnic Institute. / Keywords: Thermodynamics; Fuel Cell; Proton-exchange membranes; Proton Transport. Includes bibliographical references.

Thesis (Ph. D.)--West Virginia University, 2002. / Title from document title page. Document formatted into pages; contains xv, 217 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 213-217).

Thesis (Ph. D.)--University of Washington, 1999. / Vita. Includes bibliographical references (leaves 75-79).

Thesis--Leyden. / In Periodical Room.

Thesis (Ph. D.)--University of Chicago, Department of Chemistry, August 2002. / Includes bibliographical references. Also available on the Internet.

Thesis (Ph. D.)--West Virginia University, 2006. / Title from document title page. Document formatted into pages; contains xx, 149 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 144-149).

Proefschrift Universiteit van Amsterdam. / Met lit. opg. - Met samenvatting in het Nederlands.

Processos de transferência de H+ de fotoácidos como piranina (POH) em vidros de SiO2, foram atribuídos à presença de água residual no gel. Nestes experimentos, o efeito devido à espécie básica do tampão (HPO4=), todavia não foi investigada. O entendimento de como as reações prototrópicas são mediadas no meio sólido e como a atividade do par ácido - base de Brönsted participa na transferência é o objetivo deste presente estudo. Questões como: o H+ difunde livremente através do gel? A espécie do tampão interage diretamente com o doador de H+, ou água é necessário para intermediar a transferência? Existe um teor limiar de água? Aqui são discutidas. A transferência de H+ da POH foi estudada em monólitos derivados da hidrólise ácida do TEOS contendo diferentes concentrações de tampão fosfato (condições iniciais Si: H2O 1: 16,5). A extensão da transferência de H+ é determinada pelo monitoramento da intensidade de fluorescência devido à base excitada (% PO-*) uma vez que a emissão surge da reação de transferência de H+. Nestes experimentos, géis foram preparados na ausência e presença de tampão fosfato. Até ~ 12 dias, um aumento na transferência de H+ é observada para todas as condições. É também verificado que o aumento na concentração de tampão é paralelo à extensão da reação. Em tempos muito curtos, a atividade da transferência de H+ relativamente baixa é devido à presença de ETOH (hidrólise do TEOS), o qual assim que o sistema envelhece é lixiviado junto com a água do gel. Depois deste envelhecimento inicial, aqueles géis contendo altas concentrações de tampão (50 e 250 mM) mostram uma atividade constante e os demais géis mostram uma queda na transferência de H+. No final do estágio, ~ 50 dias, os géis perderam aproximadamente 80% de sua massa, mas no gel final ainda existe quantia de água residual Si: H2O 1: 7. Com o intuito de explorar a atividade do tampão, misturas secas de KH2PO4 e K2HPO4 na proporção de pHaparente = 6,0 foram trituradas e secas e a fotoacidez do 2 - naftol (NOH) foi investigada. Claramente a baixo teor de água nenhuma reação é observada e somente a emissão devido a NOH* aparece (yem. = 345 nm), adição passo a passo de H2O é seguida pelo aumento na emissão a 413 nm, devido à forma básica (NO-*). Nesta condição, a concentração de água limiar é Xw = 0,44. Por outro lado, para o POH o limite de água para a transferência de H+ é Xw = 0,13. POH e NOH têm pKa no estado excitado (pKa*) de 0,5 e 3,0, respectivamente. Neste estudo, a atividade dos fotoácidos em meio sólido mostra ser dependente do pKa*, da concentração da espécie básica e do teor de água limiar. / H+ transfer processes in SiO2 glasses, from photoacids as piranine (POH), were assigned to the presence of residual water in the gel. In these experiments the effects due to the buffer basic species (HPO4=) were however not investigated. The understanding on how prototropic reactions are mediated in solid media and how the activity of Brönsted acid and base pairs participates in the transfer is the subject of the present study. Questions as: Does the H+ diffuse freely through the gel? Do the buffer species interacts directly with the H+ donors, or water is needed to intermediate the transfer? Is there a threshold in the water content? are here discussed. H+ transfer from POH was studied in monoliths derived from the acid hydrolysis of TEOS having varying concentrations of phosphate buffer (initial conditions Si : H2O 1:16.5). The extent of H+ transfer is determined by monitoring the fluorescence intensity due to the excited base (%PO-*) once this emission arises from the H+ transfer reaction. In these experiments gels were prepared in the absence and presence of phosphate buffer. Up to ~ 12 days an increase in H+ transfer is observed for all conditions. It is also found the increase in buffer concentration parallels the extent of reaction. At very short time the relatively low H+ transfer activity is due to the presence of ETOH (hydrolysis of TEOS), which as the systems age are lixiviated together with water from the gel. After this initial aging, those gels having high buffer concentrations (50 and 250 mM) show a leveled activity, the other gels show a decrease in H+ transfer. At the final stages ~ 50 days the gels lost around 80% of its mass, but in the final gel residual water still amounts to Si:H2O 1:7. In order to further exploit the buffer activity, \"dry\" mixtures of KH2PO4 and K2HPO4 in proportions to pHapp = 6.0 were grinded and dried and the photoacidity of 2-naphtol (NOH) were investigated. Clearly at low water contents no reaction is observed and only the emission due to the NOH* appears (yem = 345 nm), addition step by step of H2O is followed by an increase in the emission at 413 nm, due to the basic form (NO-*). In this situation the threshold water concentration is around Xw = 0.44. By other hand for POH the threshold water for H+ transfer is Xw = 0.13. POH and NOH have excited state pKa\'s (pKa*) of 0.5 and 3.0, respectively. In this study the activity of photoacids in solid media is shown to be dependent on pKa*, on the concentration of basic species and of a threshold water content.

The shear force mechanism has been utilized as a distance regulation method in scanning probe microscopes. However, the origin of shear force is still unclear. One of the most important reasons for the shear-force damping is due to the presence of a water contamination layer at the sample surface in ambient conditions. Understanding the behavior of such mesoscopic fluid-like films is of significance for studies of not only scanning probe microscopy but also other complex surface phenomena, such as nanotribology, lubrication, adhesion, wetting, and the microfluidity of biological membranes. This thesis investigates, in particular, the dynamics of mesoscopic fluids confined between two sliding solid boundaries. When fluids are constrained to nanometer-sized regions, their physical properties can greatly differ from those displayed by bulk liquids. To gain an insight into the fundamental characteristics of the confined fluid films, we exploit the versatile capabilities of the novel shear-force/acoustic near-field microscope (SANM), which is able to concurrently and independently monitor the effects of the fluid-mediated interactions acting on both the microscope's probe and the sample to be analyzed. Two signals are monitored simultaneously during each experimental cycle: the tuning fork signal, which is the oscillation amplitude of the probe and gives access to the shear force; and acoustic signal, which is detected by an acoustic sensor placed under the sample. Systematic experiments are carried out to investigate the effects of probe geometry, environmental humidity, and chemical properties of probe and sample surface (water affinity: hydrophobicity or hydrophilicity) on the probe-sample interactions, expressing the influence of the fluid-like contamination films.

No description available.