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- Polydimethylsiloxane composites characterization and its applications: a reviewPublication . Ariati, Ronaldo; Sales, Flaminio; Souza, Andrews Victor Almeida; Lima, Rui A.; Ribeiro, J.E.Polydimethylsiloxane (PDMS) is one of the most promising elastomers due its remarkable pro-prieties such as good thermal stability, biocompatibility corrosion resistance, flexibility, low cost, ease of use, chemically inertia, hyperplastic characteristics, and gas permeability. Thus, it can be used in areas like microfluidic systems, biomedical devices, electronic components, membranes for filtering and pervaporation, sensors and coatings. Although pure PDMS has low mechanical properties, such as low modulus of elasticity and strength, it can be improved by mixing the PDMS with other polymers and by adding particles or reinforcements. Fiber-reinforced PDMS has proved to be a good alternative to manufacture flexible displays, batteries, wearable devices, tac-tile sensors, and energy harvesting systems. PDMS and particulates are often used in the sepa-ration of liquids from wastewater by means of porosity followed by hydrophobicity. Waxes as beeswax and paraffin have proved to be materials capable of improving properties such as hy-drophobic, corrosion resistance, thermal and optical properties of PDMS. Finally, blended with polymers such as poly (vinyl chloride-co-vinyl acetate), PDMS became a highly efficient alterna-tive for separation membrane applications. However, to the best of our knowledge there are few works dedicated to the review and comparison of different PDMS composites. Hence, this review will be focused in PDMS composites, their respective applications, and properties. Generally, it will be discussed the combination of elastomer with fibers, particles, waxes, polymers, and others; aiming to be a review able to demonstrate the wide applications of this material and how tailored characteristics can be reached for custom applications.
- Composite material of PDMS with interchangeable transmittance: study of optical, mechanical properties and wettabilityPublication . Sales, Flaminio; Souza, Andrews; Ariati, Ronaldo; Noronha, Verônica Teixeira; Giovanetti, Elder Gulick; Lima, Rui A.; Ribeiro, J.E.Polydimethylsiloxane (PDMS) is a polymer that has attracted the attention of researchers due to its unique properties such as transparency, biocompatibility, high flexibility, and physical and chemical stability. In addition, PDMS modification and combination with other materials can expand its range of applications. For instance, the ability to perform superhydrophobic coating allows for the manufacture of lenses. However, many of these processes are complex and expensive. One of the most promising modifications, which consists of the development of an interchangeable coating, capable of changing its optical characteristics according to some stimuli, has been underexplored. Thus, we report an experimental study of the mechanical and optical properties and wettability of pure PDMS and of two PDMS composites with the addition of 1% paraffin or beeswax using a gravity casting process. The composites’ tensile strength and hardness were lower when compared with pure PDMS. However, the contact angle was increased, reaching the highest values when using the paraffin additive. Additionally, these composites have shown interesting results for the spectrophotometry tests, i.e., the material changed its optical characteristics when heated, going from opaque at room temperature to transparent, with transmittance around 75%, at 70 °C. As a result, these materials have great potential for use in smart devices, such as sensors, due to its ability to change its transparency at high temperatures.
- Fabrico e caracterização mecânica de placas estabilizadoras de fraturas em material compósito poliméricoPublication . Sales, Flaminio; Ribeiro, J.E.; Costa, Romeu Rony Cavalcante daFraturas são eventos com altíssima ocorrência e que, além dos impactos na qualidade de vida, geram enormes gastos por todo o mundo. Para auxiliar nos processos de consolidação óssea após um destes incidentes, são utilizadas placas estabilizadoras de fratura, normalmente, fabricadas em materiais metálicos. Contudo, estes materiais apresentam algumas desvantagens, tais como os efeitos adversos provocados pela corrosão, as falhas por fadiga, as reações alérgicas, o custo, considerado alto e, principalmente, o fenômeno da blindagem óssea: uma redução na densidade dos ossos devido à alta rigidez do implante. Visando contornar tais problemas, o objetivo deste estudo foi fabricar e caracterizar placas estabilizadoras de fratura em material compósito de resina poliuretana (PU) reforçada com fibra de vidro. Para tal, foram concebidas e simuladas diferentes geometrias; o material foi avaliado em tração e, posteriormente, os implantes na flexão em 4 pontos. As simulações numéricas não mostraram diferenças significativas nas propriedades em flexão dos diferentes modelos avaliados, desta forma, o modelo mais utilizado atualmente foi adaptado para o fabrico em compósito. Em tração, a resina PU utilizada demostrou aumento de 102% na tensão máxima atingida quando se empregou 15 Wf% de reforços. Nas placas, a inserção de reforços entre 10 a 25% também aumentou a rigidez estrutural em 126-165%, comparativamente com as amostras de PU pura. Por outro lado, alterações no número de furos, de 4 para 6, reduziram a tensão máxima atingida em 40%. Quanto ao processo utilizado, este apresentou baixo custo, foi altamente customizável e permitiu o desenvolvimento de geometrias complexas. Desta forma, mesmo que os valores de resistência e rigidez ainda precisem aumentar para utilização segura quando implantado, os métodos adotados mostraram-se uma alternativa efetiva para o fabrico e caracterização deste tipo de dispositivo.
- Stress Concentration on PDMS: An evaluation of three numerical constitutive models using digital image correlationPublication . Sales, Flaminio; Souza, Andrews; Oliveira, Fallconny Rodrigues Sensato; Lima, Rui A.; Ribeiro, J.E.The examination of hyperelastic materials’ behavior, such as polydimethylsiloxane (PDMS), is crucial for applications in areas as biomedicine and electronics. However, the limitations of hyperelastic models for specific stress scenarios, with stress concentration, are not well explored on the literature. To address this, firstly, three constitutive models were evaluated (Neo-Hookean, Mooney-Rivlin, and Ogden) using numerical simulations and Digital Image Correlation (DIC) analysis during a uniaxial tensile test. The samples were made of PDMS with stress concentration geometries (center holes, shoulder fillets, and edge notches). Results of ANOVA analysis showed that any of the three models can be chosen for numerical analysis of PDMS since no significant differences in suitability were found. Finally, the Ogen model was chosen to obtain the stress concentration factors for these geometries, a property which characterize how discontinuities change the maximum stress supported by an element. Our study provides new values for variables needed to analyze and design hyperelastic elements and produce a foundation for understanding PDMS stress-strain behavior.