Dissertation (Ph.D.)--Worcester Polytechnic Institute. / Keywords: Surface roughness; Surface forces; Van der Waals forces. Includes bibliographical references.

The surface roughness of a few asperities and their influence on the work of adhesion is of scientific interest. Macroscale and nanoscale adhesion data have given seemingly inconsistent results. Despite the importance of bridging the gap between the two regimes, little experimental work has been done, presumably due to the difficulty of the experiment needed to determine how small amounts of surface roughness might influence adhesion data lying in between the two scales. To investigate the role of few-asperity contacts in adhesion, the pull-off force was measured between different sized AFM (Atomic-Force Microscope) tips that had different roughnesses and sample surfaces that had well-controlled material properties. The spring constant of the cantilever, the deflection of the cantilever, and the radius of the cantilever tip were measured before each experiment. There were seventeen tips of four different types, with radii from 200 nm to 60 ìm. The samples were unpatterned amorphous silicon dioxide die with two types of surface conditions: untreated and treated with a few angstroms of vapor deposited diphenylsiloxane. We observed that the pull-off force was independent of the radius of the AFM tip, which was contrary to all continuum-mechanics model predictions. To explain this behavior, we assumed that the interactions between the AFM tip and sample were additive, material properties were constant, and that the AFM tip, asperities, and sample surfaces were of uniform density. Based on these assumptions, we calculated a simple correction due to the measured Root Mean Square (RMS) surface roughness of the AFM tips. The simple correction for the RMS surface roughness resulted in the expected dependence of the pull-off force on radius, but the magnitudes were higher than expected. Commercial and heat-treated AFM tips had minimal surface roughness and result in magnitudes that were more reliable. The relative uncertainty for the pull-off force was estimated to be 10% and the work of adhesion was estimated to be 15%. In this thesis, we derive how the cantilever and tip parameters contribute to the measured pull-off force, show how the corrected results compare with theory, and demonstrate how the AFM probes were calibrated. Although much work is still needed, the work presented here should expand the understanding of adhesion between the nanoscale and macroscale.

Orientador: Regina Maria Puppin-Rontani / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Odontologia de Piracicaba / Made available in DSpace on 2018-08-18T00:24:32Z (GMT). No. of bitstreams: 1 Paula_AndreiaBolzande_D.pdf: 4070151 bytes, checksum: 59b6aec78bd6931d2430106db002b0dc (MD5) Previous issue date: 2011 / Resumo: O avanço da Odontologia Estética tem sido impulsionado pela introdução de novos materiais restauradores, tais como os nanoparticulados, os quais têm demonstrado bom desempenho mecânico e excelentes propriedades ópticas. Entretanto, deve-se considerar que os materiais restauradores estão constantemente sujeitos aos desafios térmicos, mecânicos e químicos na cavidade bucal que podem acarretar danos a estes materiais, num processo denominado degradação. Dessa forma, os objetivos nesta tese, composta por 2 capítulos, foram: (1) avaliar a morfologia e a rugosidade de superfície de materiais nanopartículados quando submetidos a biodegradação e abrasão por escovação e (2) avaliar os efeitos do armazenamento em diferentes soluções simuladoras da dieta ácida na rugosidade e dureza de superfície de materiais restauradores. No capítulo 1, vinte espécimes obtidos de cada material (Vitremer, Ketac N100, TPH Espectrum e Filtek Z350) foram divididos em dois grupos de armazenamento (n=10): umidade relativa e bioflime de S. mutans. Após sete dias, todos os espécimes foram lavados em ultrassom para a mensuração da rugosidade de superfície (Ra) e avaliação em microscopia eletrônica de varredura. Seguidamente, o teste de abrasão por escovação foi conduzido no grupo biodegradado e os espécimes reavaliados. Os dados foram submetidos aos testes ANOVA 3 fatores para medidas repetidas e Tukey (p<0.05). Após a biodegradação o ketac N100 apresentou os maiores valores de Ra. Quando as amostras biodegradadas foram submetidas à abrasão por escovação, o compósito Z350 apresentou os menores valores de Ra. No capítulo 2, foram confeccionados espécimes (5mm-diâmetro; 2mm-espessura), dos materiais utilizados no Capítulo 1, os quais foram divididos em 4 grupos (n=30). Após 24h, foram realizados os procedimentos de acabamento e polimento e os testes de dureza Knoop (KHN) e rugosidade de superfície. Seguidamente, cada grupo foi dividido em 3 subgrupos (n=10) de acordo com o meio de armazenagem: saliva artificial, suco de laranja e Coca-Cola®. A rugosidade de superfície e dureza Knoop dos espécimes foram reavaliadas após 30 dias de armazenamento e os dados submetidos aos testes ANOVA 3 fatores para medidas repetidas e Tukey (p<0,05). Os compósitos apresentaram menor Ra e maior KHN que os materiais ionoméricos em todas as situações estudadas. Após a degradação química, a diminuição significativa da KHN foi observada para todos os materiais, enquanto o aumento da Ra foi observado nos materiais ionoméricos armazenados em Coca-Cola® e suco de laranja. O compósito Z350 apresentou valores similares de KHN após a erosão qualquer que fosse a solução de armazenamento. Para os outros materiais, a Coca-cola e o suco de laranja provocaram maiores reduções nos valores de KHN. Com base nos resultados obtidos pode-se concluir que nanopartículas incorporadas aos materiais estudados exerceram influência significativa para a obtenção de maior resistência frente à degradação biomecânica. No entanto, a presença de nanopartículas não influenciou na resposta à erosão quanto à rugosidade e dureza Knoop / Abstract: Esthetic Dentistry has increasingly advanced with the introduction of new restorative dental materials, such as nanofilled materials, which have demonstrated better mechanical behavior and excellent optical properties. However, restorative materials are constantly subjected to thermal, mechanical and chemical challenges in the oral cavity that leads to damage of these materials in a process called degradation. The objectives of this dissertation were to evaluate: (1) the morphology and surface roughness of nanofilled materials subjected to biodegradation and brushing and (2) the effects of storage in different acid diet simulating solutions on roughness and surface hardness of resin based restorative materials. In the study 1, twenty specimens obtained from each material (Vitremer, Ketac N100, TPH Espectrum e Filtek Z350) were divided into two storage groups (n=10): relative humidity (control) and Streptococcus mutans biofilm (biodegradation). After 7 days of storage, roughness values (Ra) and micrographs by Scanning Electron Microscopy (SEM) were obtained. In a second experimental phase, the specimens previously subjected to biodegradation were abraded via toothbrushes (mechanical degradation). Next, these specimens were washed, dried, and reassessed by roughness and SEM. The data were submitted to repeated measures three-way ANOVA and Tukey's tests (p<0.05). After biodegradation, Ketac N100 presented the highest Ra values. Concerning bio plus mechanical challenges the nano composite Filtek Z350 exhibited the best resistance to cumulative challenges proposed. In the study 2, disc-shaped specimens (5mm-diameter; 2mm-thick) of the same materials used on study 1 were obtained according to the manufacturers' instructions, thereby forming four groups (n=30). After 24h, polishing procedures were performed and initial hardness(KHN) and roughness(Ra) measurements were realized. Next, each group was divided into three subgroups (n=10) according to storage media: artificial saliva, orange juice and Coca-Cola®. After 30 days of storage, the specimens were reevaluated about Ra and KHN. Data were tested for significant differences by three-way ANOVA and Tukey (p<0.05). It was observed that composites presented lower roughness values and higher hardness values than ionomeric materials under all storage conditions. After erosion, KHN of all experimental samples dropped significantly, while only the Ra of ionomeric materials increased, depending on the media, with a markedly negative impact of Coca-Cola® and orange juice. There was not difference among storage media for Filtek Z350 regarding to KHN values. Based on the results it can be concluded that nanofillers incorporated into the studied materials was important to obtain greater resistance against biomechanics degradation. However, the presence of nanofillers did not influence the surface roughness and Knoop hardness when the tested materials underwent to erosion / Doutorado / Materiais Dentarios / Doutor em Materiais Dentários