A carregar...
6 resultados
Resultados da pesquisa
A mostrar 1 - 6 de 6
- Coolant flow in structured grinding wheels: CFD validation via high-speed imaging and particle trackingPublication . Costa, Sharlane; Souza, Andrews; Neves, Lucas B.; Ribeiro, J.E.; Pereira, Mário; Soares, DelfimEfficient coolant delivery is essential in grinding to control heat generation, minimize tool wear, and preserve workpiece integrity. However, Computational Fluid Dynamics (CFD) models commonly used for coolant system design remain rarely validated due to the extreme speeds and complex multiphase flows involved. This work addresses this gap by combining CFD simulations with targeted experiments to evaluate heat removal effectiveness in internally cooled grinding wheels with three channel inclinations: positive, straight, and negative. Transparent resin prototypes enabled high-speed imaging and particle tracking for flow field validation, while grinding tests measured temperature rise and mechanical loads. Results demonstrate that channel inclination strongly affects fluid acceleration, jet coherence, and penetration into the grinding zone, with the positive inclination producing the highest outlet velocities and reducing temperature rise by up to 67%. Particle tracking confirmed CFD predictions within 16% deviation, validating the model’s reliability. By establishing a direct correlation between coolant jet dynamics, heat dissipation, and process performance, this study demonstrates a methodology for the thermal optimization of internal cooling systems in rotating tools. The approach provides a pathway for improving energy efficiency, extending tool life, and reducing coolant consumption in industrial machining processes.
- A Review of Methods to Modify the PDMS Surface Wettability and Their ApplicationsPublication . Neves, Lucas B.; Afonso, Inês Santos; Nobrega, Glauco; Barbosa, Luiz G.; Lima, Rui A.; Ribeiro, J.E.Polydimethylsiloxane (PDMS) has attracted great attention in various fields due to its excellent properties, but its inherent hydrophobicity presents challenges in many applications that require controlled wettability. The purpose of this review is to provide a comprehensive overview of some key strategies for modifying the wettability of PDMS surfaces by providing the main traditional methods for this modification and the results of altering the contact angle and other characteristics associated with this property. Four main technologies are discussed, namely, oxygen plasma treatment, surfactant addition, UV-ozone treatment, and the incorporation of nanomaterials, as these traditional methods are commonly selected due to the greater availability of information, their lower complexity compared to the new techniques, and the lower cost associated with them. Oxygen plasma treatment is a widely used method for improving the hydrophilicity of PDMS surfaces by introducing polar functional groups through oxidation reactions. The addition of surfactants provides a versatile method for altering the wettability of PDMS, where the selection and concentration of the surfactant play an important role in achieving the desired surface properties. UV-ozone treatment is an effective method for increasing the surface energy of PDMS, inducing oxidation, and generating hydrophilic functional groups. Furthermore, the incorporation of nanomaterials into PDMS matrices represents a promising route for modifying wettability, providing adjustable surface properties through controlled dispersion and interfacial interactions. The synergistic effect of nanomaterials, such as nanoparticles and nanotubes, helps to improve wetting behaviour and surface energy. The present review discusses recent advances of each technique and highlights their underlying mechanisms, advantages, and limitations. Additionally, promising trends and future prospects for surface modification of PDMS are discussed, and the importance of tailoring wettability for applications ranging from microfluidics to biomedical devices is highlighted. Traditional methods are often chosen to modify the wettability of the PDMS surface because they have more information available in the literature, are less complex than new techniques, and are also less expensive.
- Tunable physicochemical properties of PDMS@nanoparticle composites: modifications, mechanisms, and emerging applicationsPublication . Cardoso, B.D.; Nobrega, Glauco; Afonso, Inês Santos ; Souza, Andrews; Neves, Lucas B.; Faria, C.L.; Díaz de Tuesta, Jose Luis; Ribeiro, J.E.; Lima, Rui A.Polydimethylsiloxane@nanoparticles (PDMS@NPs) composites represent a versatile class of advanced elastomers whose physicochemical behavior can be finely tuned through nanoscale interfacial design and nanofiller morphology. Owing to their inherent flexibility, transparency, and chemical stability, PDMS based systems have emerged as model platforms for developing multifunctional materials with optimized mechanical, thermal, electrical, optical, acoustic and wetting properties. This review systematically elucidates the structure property relationships in PDMS@NPs composites and the interaction mechanisms between NPs and polymer chains that enable tunable control over bulk and interfacial behavior, with particular emphasis on how NPs dimensionality and aspect ratio (0D, 1D, and 2D fillers) regulate stress transfer, transport pathways, and functional interconnectivity within the matrix. Three main NP incorporation strategies, (namely, physical mixing of presynthesized NPs, in situ synthesis on cured PDMS, and in situ formation within uncured matrices) are critically compared in terms of interfacial coupling, dispersion stability, and processing scalability. Particular attention is given to how interfacial engineering, nanofiller morphology, and hierarchical architecture govern stress transfer, phonon transport, charge percolation, and optical or surface responses. In addition, a property design prospective is presented that links interphase design and nanofiller morphology to mechanical, thermal, electrical, optical, acoustic and wetting-controlled surface properties. This review further critically examines the limiting factors that reduce the applicability of PDMS@NPs composites, including performance degradation, interface instability, and limited recyclability, as well as long-term stability under mechanical, thermal, optical, and environmental conditions. Emerging directions such as green filler synthesis, recyclable PDMS matrices, dynamic and hi-erarchical interphases, and predictive modeling of morphology-dependent dynamic interfaces are outlined. Overall, this review provides a comprehensive and critical perspective on PDMS@NPs composites as a next generation of soft, functional, and sustainable elastomeric materials, opening new avenues for advances in flexible electronics, soft robotics, biomedical devices, and adaptive coatings.
- Optimization of parameters for modifying surface wettability and thermal conductiv- ity of PDMSPublication . Neves, Lucas B.; Ribeiro, J.E.; Barbosa, Luiz Gustavo de Moura da SilvaO polidimetilsiloxano (PDMS) tem atraído significativa atenção em diversas áreas devido às suas excelentes propriedades, mas sua hidrofobicidade inerente apresenta desafios em aplicações que exigem controle da molhabilidade. Este estudo fornece uma visão abrangente das principais estratégias para modificar a molhabilidade das superfícies de PDMS, focando nos métodos tradicionais e seu impacto no ângulo de contato e outras características relacionadas. Quatro técnicas principais foram estudadas, sendo elas o tratamento com plasma de oxigênio, a adição de surfactantes, o tratamento com UV-ozônio e a incorporação de nanomateriais, sendo a aplicada neste estudo a adição de surfactantes. Esses métodos são escolhidos entre os demais devido a sua ampla disponibilidade de literatura, menor complexidade e custo-benefício em comparação com técnicas mais novas. O tratamento com plasma de oxigênio melhora a hidrofilicidade do PDMS ao introduzir grupos funcionais polares através da oxidação. A adição de surfactantes possui uma abordagem versátil para alterar a molhabilidade, sendo a escolha e a concentração dos surfactantes fundamentais para obter as propriedades desejadas da superfície. O tratamento com UV-ozônio aumenta com eficácia a energia da superfície por meio da indução de oxidação e geração de grupos funcionais hidrofílicos. A incorporação de nanomateriais nas matrizes de PDMS possibilita modificações promissoras na molhabilidade, permitindo propriedades de superfície que são ajustáveis através da dispersão controlada e interações interfaciais. Os efeitos das nanopartículas e dos nanotubos melhoram significativamente o com- portamento de molhamento e a energia da superfície. Adicionalmente, esse estudo aborda os desafios da recuperação hidrofóbica no PDMS, especialmente considerável para dispositivos microfluídicos comerciais que se tem a exigência do armazenamento e distribuição prolongados. Um estudo comparando três surfactantes não iônicos (Triton X-100, Brij L4 (BL4) e Polietileno Óxido (PEO)) apresenta que a seleção de surfactantes deve considerar a eficiência, estabilidade e durabilidade do comportamento hidrofílico. Diversos tipos e concentrações de surfactantes e a suas temperaturas de cura foram testados, revelando que 2,5% de PEO curado a 80°C atingiu um ângulo de contato de 12,8° imediatamente após a cura. Análises de condutividade térmica indicaram que 0,5% de TX-100 a 80°C era ideal inicialmente, enquanto 2,5% de BL4 a 25°C apresentou melhor desempenho após três semanas. Análises estatísticas, incluindo o método Taguchi e a Análise Relacional de Grey, validam ainda mais a influência de vários parâmetros na molhabilidade e condutividade térmica.
- Progress in Nanofluid Technology: From Conventional to Green Nanofluids for Biomedical, Heat Transfer, and Machining ApplicationsPublication . Cardoso, Beatriz D.; Souza, Andrews; Nobrega, Glauco; Afonso, Inês Santos ; Neves, Lucas B.; Faria, Carlos; Ribeiro, J.E.; Lima, Rui A.Nanofluids (NFs), consisting of nanoparticles (NPs) suspended in base fluids, have attracted growing interest due to their superior physicochemical properties and multifunctional potential. In this review, conventional and green NF technology aspects, including synthesis routes, formulation, and applications, are discussed. Conventional NFs, involving NPs synthesized using physical and chemical approaches, have improved NP morphology control but are likely to cause environmental and safety concerns. In contrast, green NFs that are plant extract, microorganism, and biogenic waste-based represent a sustainable and biocompatible alternative. The effect of key parameters (e.g., NP size, shape, concentration, dispersion stability, and base fluid properties) on the performance of NFs is critically examined. The review also covers potential applications: in biomedical engineering (e.g., drug delivery, imaging, theranostics, and antimicrobial therapies), in heat transfer (e.g., solar collectors, cooling electronics, nuclear reactors), and precision machining (e.g., lubricants and coolants). Comparative insights regarding green versus conventionally prepared NFs are provided concerning their toxicity, environmental impact, scalability, and functional performance across various applications. Overall, this review highlights the new promise of both green and conventional NFs and provides key opportunities and challenges to guide future developments in this field.
- Recent Advances of PDMS In Vitro Biomodels for Flow Visualizations and Measurements: From Macro to Nanoscale ApplicationsPublication . Souza, Andrews; Nobrega, Glauco; Neves, Lucas B.; Barbosa, Filipe; Ribeiro, J.E.; Ferrera, Conrado; Lima, Rui A.Polydimethylsiloxane (PDMS) has become a popular material in microfluidic and macroscale in vitro models due to its elastomeric properties and versatility. PDMS-based biomodels are widely used in blood flow studies, offering a platform for improving flow models and validating numerical simulations. This review highlights recent advances in bioflow studies conducted using both PDMS microfluidic devices and macroscale biomodels, particularly in replicating physiological environments. PDMS microchannels are used in studies of blood cell deformation under confined conditions, demonstrating the potential to distinguish between healthy and diseased cells. PDMS also plays a critical role in fabricating arterial models from real medical images, including pathological conditions such as aneurysms. Cutting-edge applications, such as nanofluid hemodynamic studies and nanoparticle drug delivery in organ-on-a-chip platforms, represent the latest developments in PDMS research. In addition to these applications, this review critically discusses PDMS properties, fabrication methods, and its expanding role in micro- and nanoscale flow studies.