Piezoelectric composites are materials composed of a polymeric matrix and a piezoelectric ceramic fillers, commonly applied in transducers, actuators and sensor applications. Thanks to the combination of the constituent phases, piezocomposites show good mechanical properties and a piezoelectric activity. By choosing a proper combination of particles/polymer matrix, it is possible to tailor the properties of the final material and thus to develop sensors for particular applications. Due to all these aspects, piezoelectric composites are more advantageous compared to other piezoelectric materials, such as bulk ceramics or electroactive polymers. The arrangement of the constituent components in a composite is crucial for the electromechanical coupling of the material. It has been proved that a composite with piezoelectric phase disposed in parallel columns within the matrix has an enhanced piezoelectric behaviour with respect to a composite with piezoelectric filler homogeneously dispersed. A homogeneously dispersed structure is called 0-3, while the columnar one is called 1-3 connectivity. 1-3 composites are commonly achieved through several complex techniques such as rod placement, dice-fill, ultrasonic cutting, laser machining, co-extrusion, tape lamination and fibre insertion method. Electric field structuring is an easier way to produce 1-3 composites, exploiting a phenomenon called dielectrophoresis. In this work were produced two composites via dielectrophoresis, for two different fields of application: health structural monitoring of ball bearings and intravascular cardiac pressure measurements. For the former application, the main requests are high piezoelectric response, good flexibility and high temperature resistance, thus a composite of PZT particles in PDMS matrix was chosen. For the latter, high piezoelectric response and biocompatibility are the main requirements, therefore a composite made of BTOnp in PDMS matrix was selected. For both PZT/PDMS and BTOnp/PDMS, a 0-3 and 1-3 composites were produced. 1-3 composites were prepared by applying an AC electric field on the uncured matrix filled by piezoelectric particles at high temperature. Each sample was then characterized via dielectric and piezoelectric measurement. According to the results, 1-3 connectivity leads to superior piezoelectric behaviour. Then thermal resistance and high temperature XRD analyses were accomplished, in order to understand the composites behaviour in high temperature environment: the results show that PZT/PDMS composites maintain a good piezoelectric response even at 200°C, while BTOnp/PDMS ones completely lose their piezoelectric behaviour at 120°C. In order to improve the degree of alignment of the piezoelectric phase, a study of electric field amplitude and frequency dependence of dielectrophoresis process were carried out. This analysis allowed to select the best parameters for the PZT/PDMS composite. Finally, a conductive ink made of silver nanoparticles in PDMS matrix compatible with the material produced was developed to be used as electrodes.
I compositi piezoelettrici sono materiali composti da una matrice polimerica e un filler ceramico piezoelettrico, spesso utilizzati come trasduttori, attuatori e sensori. Grazie alla presenza delle due diverse fasi, i piezocompositi mostrano buone proprietà meccaniche in combinazione con una notevole attività piezoelettrica. Scegliendo opportunamente le particelle e la matrice polimerica, è possibile selezionare determinate proprietà del materiale finale e quindi sviluppare sensori per applicazioni particolari. I compositi piezoelettrici sono più vantaggiosi rispetto ad altri materiali piezoelettrici, come ceramiche o polimeri elettroattivi . La disposizione dei componenti è cruciale per l'accoppiamento elettromeccanico del materiale. Diversi studi hanno dimostrato che un composito con filler disposto in colonne esibisce un miglior comportamento piezoelettrico rispetto a un composito con filler omogeneamente disperso in matrice. La struttura con particelle omogeneamente disperse si chiama 0-3, mentre la struttura colonnare viene detta connettività 1 -3. I compositi 1-3 sono comunemente ottenuti attraverso diverse tecniche complesse come rod placement, dice-fill, taglio ad ultrasuoni, lavorazione laser, coestrusione, laminazione e inserimento della fibra. La strutturazione del campo elettrico è un modo semplice per produrre 1-3 compositi, sfruttando un fenomeno chiamato dielettroforesi. In questo lavoro sono stati prodotti due compositi tramite dielettroforesi, per due diversi campi di applicazione: monitoraggio strutturale dei cuscinetti a sfera in ambiente ad alta temperatura e misurazioni della pressione sanguigna intravascolare. Per la prima applicazione, le richieste principali sono l'elevata risposta piezoelettrica, la buona flessibilità e la resistenza alle alte temperature, quindi é stato scelto un composito di particelle PZT in PDMS. Per la seconda applicazione elevate prestazioni e biocompatibilità sono i requisiti principali, pertanto è stato selezionato un composito costituito da nanoparticelle di BTOnp in matrice PDMS. Sia per PZT / PDMS che per BTOnp/ PDMS sono stati prodotti compositi 0-3 e 1-3. I compositi 1-3 sono stati preparati applicando un campo elettrico alternato sul composito non polimerizzato ad alte temperature. Ciascun campione è stato poi caratterizzato tramite spettroscopia dielettrica e piezoelettrica. Secondo i risultati, la connettività 1-3 conferisce un comportamento piezoelettrico superiore. Quindi sono state eseguite analisi di resistenza termica e XRD ad alta temperatura, al fine di comprendere il comportamento dei compositi in ambiente con temperature elevate: i risultati mostrano che i compositi PZT/PDMS mantengono una buona risposta piezoelettrica anche a 200 ° C, mentre quelli BTOnp/ PDMS perdono completamente la loro comportamento piezoelettrico a 120 ° C. Al fine di migliorare il grado di allineamento della fase piezoelettrica, è stato condotto uno studio sulla dipendenza del processo di dielettroforesi dall’ampiezza e dalla frequenza del campo elettrico. Questa analisi ha permesso di trovare i parametri di processo ottimali per il composito PZT / PDMS. Infine, è stato sviluppato un inchiostro conduttivo di nanoparticelle d'argento in matrice PDMS compatibile con il sensore da utilizzare come elettrodi.
Piezoelectric composites structured via dielectrophoresis for sensor applications
D'AMBROGIO, GIULIA
2018/2019
Abstract
Piezoelectric composites are materials composed of a polymeric matrix and a piezoelectric ceramic fillers, commonly applied in transducers, actuators and sensor applications. Thanks to the combination of the constituent phases, piezocomposites show good mechanical properties and a piezoelectric activity. By choosing a proper combination of particles/polymer matrix, it is possible to tailor the properties of the final material and thus to develop sensors for particular applications. Due to all these aspects, piezoelectric composites are more advantageous compared to other piezoelectric materials, such as bulk ceramics or electroactive polymers. The arrangement of the constituent components in a composite is crucial for the electromechanical coupling of the material. It has been proved that a composite with piezoelectric phase disposed in parallel columns within the matrix has an enhanced piezoelectric behaviour with respect to a composite with piezoelectric filler homogeneously dispersed. A homogeneously dispersed structure is called 0-3, while the columnar one is called 1-3 connectivity. 1-3 composites are commonly achieved through several complex techniques such as rod placement, dice-fill, ultrasonic cutting, laser machining, co-extrusion, tape lamination and fibre insertion method. Electric field structuring is an easier way to produce 1-3 composites, exploiting a phenomenon called dielectrophoresis. In this work were produced two composites via dielectrophoresis, for two different fields of application: health structural monitoring of ball bearings and intravascular cardiac pressure measurements. For the former application, the main requests are high piezoelectric response, good flexibility and high temperature resistance, thus a composite of PZT particles in PDMS matrix was chosen. For the latter, high piezoelectric response and biocompatibility are the main requirements, therefore a composite made of BTOnp in PDMS matrix was selected. For both PZT/PDMS and BTOnp/PDMS, a 0-3 and 1-3 composites were produced. 1-3 composites were prepared by applying an AC electric field on the uncured matrix filled by piezoelectric particles at high temperature. Each sample was then characterized via dielectric and piezoelectric measurement. According to the results, 1-3 connectivity leads to superior piezoelectric behaviour. Then thermal resistance and high temperature XRD analyses were accomplished, in order to understand the composites behaviour in high temperature environment: the results show that PZT/PDMS composites maintain a good piezoelectric response even at 200°C, while BTOnp/PDMS ones completely lose their piezoelectric behaviour at 120°C. In order to improve the degree of alignment of the piezoelectric phase, a study of electric field amplitude and frequency dependence of dielectrophoresis process were carried out. This analysis allowed to select the best parameters for the PZT/PDMS composite. Finally, a conductive ink made of silver nanoparticles in PDMS matrix compatible with the material produced was developed to be used as electrodes.| File | Dimensione | Formato | |
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https://hdl.handle.net/10589/152102