Electrospray Deposition of Polyvinylidene Fluoride (PVDF) Microparticles: Impact of Solvents and Flow Rate

Polymeric microparticles have been shown to have great impacts in the area of drug delivery, biosensing, and tissue engineering. Electrospray technology, which provides a simple yet effective technique in the creation of microparticles, was utilized in this work. In addition, altering the electrospray experimental parameters such as applied voltage, flow rate, collector distance, solvents, and the polymer-solvent mixtures can result in differences in the size and morphology of the produced microparticles. The effects of the flow rate at (0.15, 0.3, 0.45, 0.6, 0.8, and 1 mL/h) and N, N-Dimethylformamide (DMF)/acetone solvent ratios (20:80, 40:60, 60:40, 80:20, 100:0 v/v) in the production of polyvinylidene fluoride (PVDF) microparticles were studied. Scanning electron microscopy (SEM) was used to observe changes in the morphology of the microparticles, and this revealed that a higher acetone to DMF ratio produces deformed particles, while flow rates at (0.3 and 0.45 mL/h) and a more optimized DMF to acetone solvent ratio (60:40 v/v) produced uniform spherical particles. We discovered from the Raman spectroscopy results that the electrosprayed PVDF microparticles had an increase in piezoelectric β phase compared to the PVDF pellet used in making the microparticles, which in its original form is α phase dominant and non-piezoelectric

Light intensity-induced phase transitions in graphene oxide doped polyvinylidene fluoride

The coupling of light with low-frequency functionalities of dielectrics and liquid crystals and an ability to turn “on” and “off” the pyro-, piezo-, or ferro- electric properties of materials on demand by optical means leads to fascinating science and device applications. Moreover, to achieve all-optical control in nano-circuits, the coupling of the light with mechanical degrees of freedom is highly desirable and has been elusive until recently. In this work, we report on the light intensity-induced structural phase transitions in graphene oxide doped piezoelectric polyvinylidene fluoride (PVDF) film observed by micro-Raman spectroscopy. Increasing the laser power results in a steady transformation of the Raman spectrum featured piezoelectric phase to one of non-piezoelectric structure. This effect is accompanied by volumetric change of a PVDF unit cell by a factor of two, useful for a photostriction materials application. Furthermore, we observed the reversible switching of α and phases as a function of the light intensity (laser power between 5.7–31.3 mW). This opens up a new route for multi-functionality control where strain, piezoelectric constants and polarization can be modified by light

Design and Fabrication of a Surface Acoustic Wave Device for Bio/Chemical Applications

In this work, we report on the design and fabrication of a surface acoustic wave device, SAW sensors use piezoelectric materials to generate acoustic waves. With the help of the interdigitated transducers on the piezoelectric material, applying a voltage at the input IDT causes an acoustic wave that propagates through the substrate and at the output is converted to an electrical signal which is readable. To actualize a SAW sensor for bio/chemical sensing applications the following were studied and developed: i) Detection of stable and sensitive sensing materials, ii) Integration of sensing layers and gas testing using a dual QCM sensor, iii) Testing the fabricated SAW device. The synthesis and performance evaluation of electrosprayed multi-walled carbon nanotubes (MWCNTs) sensing layers for gas detection of volatile organic compounds were carried out. MWCNTs are characterized by a hollow structure, large surface area, and several unique properties that make them potentially excellent for gas sensing.However, to improve the sensitivity, stability, and reproducibility effects of the carbon nanotubes, they were doped with PVDF polymer in a minimal concentration such that it utilizes its strong binding effect with interconnected nanotubes and the substrate. We further ensured that the inclusion of the polymer as a binder does not affect the dominance of the MWCNTs on the surface as observed from SEM characterization. The electrospray deposition technique, combined with sonication, was used to ensure the MWCNT was dispersed evenly in the polymer matrix, as MWCNTs tend to aggregate due to their strong Van der Waals forces. The synthesized MWCNT and MWCNT/PVDF films were coated onto a Quartz Crystal Microbalance (QCM) sensor as a chemically interactive sensing material. The QCM sensors are widely used acoustic sensors for practical applications due to their ease of measurement and high sensitivity. The sensing mechanism and the kinetic adsorption of gases on the sensors were studied and the experimental result shows that MWCNT-OH/PVDF sensor revealed a larger sensitivity than that of the MWCNT-OH sensor to tested volatile organic compounds at room temperature

Development of a Flexible Piezoelectrc Materials Platform Based on PVDF Nanocomposites for Microsensor Applications

Piezoelectric flexible substrates are of great importance for acoustic wave microsensor applications due to a number of advantages such as: materials adaptability to any surface, low cost of production and ecologically friendly. In this work, we conduct the rigorous study of synthesis and characterization of Polyvinylidene fluoride (PVDF) and Polyvinylidene fluoride-based nanocomposites to obtain the optimal processing parameter leading to enhanced microsensor performance. PVDF is a known piezoelectric polymer with great properties such as flexibility, high thermal stability, high permittivity, chemically resistant, low acoustic impedance and membrane forming properties. Nanoparticles enhance the functional properties of composites. To enhance the functional properties of PVDF, the polymer was doped with graphene oxide (GO) sheets, barium titanate (BTO) and silicon dioxide (SiO2) nanoparticles. The produced materials were characterized by Raman spectroscopy, X-ray diffraction, scanning electron microscopy and Fourier Transform Infrared Spectroscopy. Mechanical testing using the Deben micro test tensile tester was also done on the samples to observe the tensile properties. We found that GO doped PVDF can lead to phase modulations by light intensity via local soft laser heating and that BTO nps increase the fraction of piezoelectric β phase which can be observed in XRD and stress-strain relation studies. On the contrary, we found that adding paraelectric SiO2 nanoparticles lead to non-piezoelectric phase formation. The current studies described in the thesis shows that optimal doping of PVDF with functional nanomaterials enhances its functionality and leads to flexible piezoelectric composite materials useful for acoustic wave microsensor application