Percorrer por autor "Neves, Lucas B."
A mostrar 1 - 8 de 8
Resultados por página
Opções de ordenação
- Applications and properties of PDMS: From biomicrofluidics to transparent face masksPublication . Lima, Rui A.; Maia, Renata; Souza, Andrews; Barbosa, Filipe; Carvalho, Denise; Carvalho, Violeta; Neves, Lucas B.; Faria, Carlos; Miranda, Inês; Sousa, Paulo; Zille, Andrea; Teixeira, Senhorinha; Minas, Graça; Machado, Lúcio; Ribeiro, J.E.Polydimethylsiloxane (PDMS) is a versatile silicone elastomer widely used in biomedical engineering due to its exceptional properties, including flexibility, chemical stability, optical transparency, biocompatibility, and ease of manufacturing. This chapter explores the unique characteristics of PDMS and its applications in biomicrofluidics and sustainable product development. PDMS is a hyperelastic material with excellent optical transparency, thermal stability, and gas permeability, making it ideal for various applications such as microfluidics, biomodels, blood analogues, implants, and organs-on-chip platforms. Its biocompatibility minimizes adverse tissue reactions, making it suitable for medical implants and skin treatments. However, its hydrophobic nature can limit certain applications, particularly in bioflow transport phenomena. To address this, surface modification techniques, such as oxygen plasma treatment, have been developed to enhance its wettability and expand its usability. In biomicrofluidics, PDMS is extensively used to create microfluidic devices that study blood cell deformability, aiding in the diagnosis of diseases like cancer, diabetes, and malaria. These devices, featuring contractions and bifurcations, provide valuable insights into microscale blood rheology and flow phenomena, improving our understanding of blood flow behavior and validating numerical simulations. The chapter also highlights the innovative use of PDMS in the production of sustainable transparent face masks. By incorporating recycled PDMS and textile fabrics, these masks feature a transparent window that allows visibility of the user’s lips, making them ideal for individuals who rely on lip-reading. The masks meet European Directive EN 14683:2019 standards, achieving level 2 certification for general public use. They offer excellent breathability, bacterial filtration efficiency, and optical transparency, while also promoting sustainability by reusing PDMS at the end of its life cycle. In conclusion, PDMS is a highly adaptable material with significant potential in biomedical applications and sustainable product development. Despite its hydrophobic nature, advancements in surface modification techniques continue to enhance its functionality, making it a valuable resource for innovative solutions in healthcare and beyond.
- 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.
- 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.
- Optimizing parameters to improve PDMS surface wettability and the thermal conductivity analysisPublication . Neves, Lucas B.; Afonso, Inês Santos; Barbosa, Luiz G.; Lima, Rui A.; Ribeiro, J.E.Due to its remarkable characteristics, Polydimethylsiloxane (PDMS) is widely used in microfluidic devices. However, despite its advantageous physical and chemical properties, its hydrophobic nature poses a challenge when pumping aqueous solutions through microchannels using only capillary forces. Various methods have been proposed to increase the hydrophilicity of PDMS; however, many struggle with hydrophobic recovery within a short time, whereas most commercial devices require long-term stability for storage and distribution. Incorporating surfactants into PDMS has become a promising technique for reducing hydrophobicity and regulating its recovery over time. However, selecting the right surfactant requires a thorough evaluation of its effectiveness, stability, and long-term durability in maintaining hydrophilicity. In this study, three non-ionic surfactants with different critical micelle concentrations and chemical compositions were compared: Triton X-100, Brij L4 (BL4), and Polyethylene Oxide (PEO). For this purpose, different surfactant concentrations, curing temperatures, and types of surfactants were compared. Short- and long-term experiments were conducted, where deionized water droplets were placed on the surface of PDMS mixed with surfactants to access wettability. Additionally, the influence of surfactants on thermal conductivity was analysed, using a Hot Disk 5501 sensor. The Taguchi method results identified the optimal sample as 2.5% PEO cured at 80°C, which achieved a contact angle of 12.8° immediately after curing and maintained superior wettability both at 0 hours and after 3 weeks of curing. For the initial thermal conductivity (0 h), the optimal sample was 0.5% TX-100 at 80°C, and after 3 weeks, BL4 2.5% at 25°C. To identify the best overall sample considering both tests, the Grey Relational Analysis method was applied. Additionally, an ANOVA statistical analysis was performed to evaluate the percentage of influence of each parameter, both in the Taguchi method, in individual tests, and in the Grey Relational Analysis combining both methods.
- 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.
- 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.