Percorrer por autor "Barbosa, Luiz G."
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- Optimizing parameters to improve PDMS surface wettability and the thermal conductivity analysisPublication . Neves, Lucas B.; Afonso, Inês S.; 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.
- 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.