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Effect of Polymer Dissolution Temperature and Conditioning Time on the Morphological and Physicochemical Characteristics of Poly(Vinylidene Fluoride) Membranes Prepared by Non-Solvent Induced Phase Separation

Publication . Cardoso, V. F.; Botelho, Gabriela; Morão, António; Nunes-Pereira, João; Lanceros-Mendez, Senentxu

This work reports on the production of poly(vinylidene fluoride) (PVDF) membranes by non-solvent induced phase separation (NIPS) using N,N-dimethylformamide (DMF) as solvent and water as non-solvent. The influence of the processing conditions in the morphology, surface characteristics, structure, thermal and mechanical properties were evaluated for polymer dissolution temperatures between 25 and 150 C and conditioning time between 0 and 10 min. Finger-like pore morphology was obtained for all membranes and increasing the polymer dissolution temperature led to an increase in the average pore size ( 0.9 and 2.1 m), porosity ( 50 to 90%) and water contact angle (up to 80 ), in turn decreasing the PVDF content ( 67 to 20%) with the degree of crystallinity remaining approximately constant ( 56%). The conditioning time did not significantly affect the polymer properties studied. Thus, the control of NIPS parameters proved to be suitable for tailoring PVDF membrane properties.

2021Journal article

Open access

Antimicrobial and Antibiofilm Properties of Fluorinated Polymers with Embedded Functionalized Nanodiamonds

Publication . Nunes-Pereira, João; Costa, Pedro; Fernandes, Liliana; Carvalho, Estela O.; Fernandes, Margarida M.; Carabineiro, S.A.C.; Buijnsters, Josephus; Rial Tubio, Carmen; Lanceros-Mendez, Senentxu

Environmentally resilient antimicrobial coatings are becoming increasingly required for a wide range of applications. For this purpose, nanocomposite thin films of poly(vinylidene fluoride) (PVDF) filled with several types of functionalized nanodiamonds (NDs) were processed by solvent casting. The effects of ND inclusion and functionalization in their morphological, structural, optical, thermal, and electrical properties were evaluated taking into account the type of the nanofiller and a concentration up to 2 wt %. The morphology, structure, and thermal features of the polymer matrix are governed by the processing conditions, and no noticeable changes occurred due to the presence of the ND fillers. The polymer crystallized mainly in the α phase with a crystallinity of ≈60%. In turn, the optical transmittance from 200 to 800 nm and the dielectric constant effectively depended on the ND type and content. The inclusion of the ND particles effectively provided antimicrobial properties to the films, which depended on the ND functionalization. This study thus shows that the incorporation of functionalized NDs into PVDF allows the development of antimicrobial coatings with tailorable optical and dielectric properties, which could be of great importance to face nowadays pandemic crisis scenario.

2020Journal article

Restricted access

Comparative Evaluation of Dielectric Materials for Plasma Actuators Active Flow Control and Heat Transfer Applications

Publication . Rodrigues, Frederico; Nunes-Pereira, João; Abdollahzadehsangroudi, Mohammadmahdi; Pascoa, Jose; Lanceros-Mendez, Senentxu

Dielectric Barrier Discharge (DBD) plasma actuators are simple devices with great potential for active flow control applications. Further, it has been recently proven their ability for applications in the area of heat transfer, such as film cooling of turbine blades or ice removal. The dielectric material used in the fabrication of these devices is essential in determining the device performance. However, the variety of dielectric materials studied in the literature is very limited and the majority of the authors only use Kapton, Teflon, Macor ceramic or poly(methyl methacrylate) (PMMA). Furthermore, several authors reported difficulties in the durability of the dielectric layer when the actuators operate at high voltage and frequency. Also, it has been reported that, after long operation time, the dielectric layer suffers degradation due to its exposure to plasma discharge, degradation that may lead to the failure of the device. Considering the need of durable and robust actuators, as well as the need of higher flow control efficiencies, it is highly important to develop new dielectric materials which may be used for plasma actuator fabrication. In this context, the present study reports on the experimental testing of dielectric materials which can be used for DBD plasma actuators fabrication. Plasma actuators fabricated of poly(vinylidene fluoride) (PVDF) and polystyrene (PS) have been fabricated and evaluated. Although these dielectric materials are not commonly used as dielectric layer of plasma actuators, their interesting electrical and dielectric properties and the possibility of being used as sensors, indicate their suitability as potential alternatives to the standard used materials. The plasma actuators produced with these nonstandard dielectric materials were analyzed in terms of electrical characteristics, generated flow velocity and mechanical efficiency, and the obtained results were compared with a standard actuator made of Kapton. An innovative calorimetric method was implemented in order to estimate the thermal power transferred by these devices to an adjacent flow. These results allowed to discuss the ability of these new dielectric materials not only for flow control applications but also for heat transfer applications.

2021Conference object

Restricted access