i9OliveFluids: Development of innovative olive mill wastewaters for metalworking fluids

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Optimizing parameters to improve PDMS surface wettability and the thermal conductivity analysis

Publication . 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.

2025Artigo científico

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Fundação para a Ciência e a Tecnologia

Número da atribuição

2024.05919.BDANA