Filippo Cellini

Mechanochromic polyurethane strain sensor

In this Letter, we study the mechanical and optical response of a thermoplastic polyurethane blended with 0.5 wt. % of bis(benzoxazolyl)stilbene dye. The mechanochromic behavior of the material is characterized in a uniaxial stress-relaxation test by simultaneously acquiring the applied force, mechanical deformation, and fluorescence emission. To offer insight into the stress-strain response of the polymer-dye blend, we adapt a classical nonlinear constitutive behavior for elastomeric materials that accounts for stress-induced softening. We correlate the fluorescent response with the mechanical strain to demonstrate the possibility of accurate strain sensing for a broad range of deformations during both loading and unloading.

Energy harvesting from fluid-induced buckling of ionic polymer metal composites:

In this article, we assess the feasibility of energy harvesting from mechanical buckling of ionic polymer metal composites induced by a steady fluid flow. Specifically, we consider an underwater energy harvester composed of a paddle wheel, a slider-crank mechanism, and two ionic polymer metal composites clamped at both their ends. To enhance electromechanical transduction, the electrodes of the ionic polymer metal composites are split into three parts via a selective platinum deposition process. The system is installed in a water tunnel and experiments are performed to elucidate the influence of both the flow speed and the shunting resistance on energy harvesting. To provide a theoretical interpretation of the experimental results, the classical post-buckling theory of inextensible elastic beams is adapted to predict mechanical deformations and a lumped-circuit model is utilized to estimate the harvested power.

Ionic polymer metal composites with polypyrrole-silver electrodes

Ionic polymer metal composites (IPMCs) are a class of soft active materials that are finding increasing application in robotics, environmental sensing, and energy harvesting. In this letter, we demonstrate the fabrication of IPMCs via in-situ photoinduced polymerization of polypyrrole-silver electrodes on an ionomeric membrane. The composition, morphology, and sheet resistance of the electrodes are extensively characterized through a range of experimental techniques. We experimentally investigate IPMC electrochemistry through electrochemical impedance spectroscopy, and we propose a modified Randles model to interpret the impedance spectrum. Finally, we demonstrate in-air dynamic actuation and sensing and assess IPMC performance against more established fabrication methods. Given the simplicity of the process and the short time required for the formation of the electrodes, we envision the application of our technique in the development of a rapid prototyping technology for IPMCs.

Underwater energy harvesting from a turbine hosting ionic polymer metal composites

In this study, we explore the possibility of energy harvesting from fluid flow through a turbine hosting ionic polymer metal composites (IPMCs). Specifically, IPMC harvesters are embedded in the blades of a small-scale vertical axis water turbine to convert flow kinetics into electrical power via low-frequency flow-induced IPMC deformations. An in-house fabricated Savonius–Darrieus hybrid active turbine with three IPMCs is tested in a laboratory water tunnel to estimate the energy harvesting capabilities of the device as a function of the shunting electrical load. The turbine is shown to harvest a few nanowatt from a mean flow of for shunting resistances in the range 100–. To establish a first understanding of the energy harvesting device, we propose a quasi-static hydroelastic model for the bending of the IPMCs and we utilize a black-box model to study their electromechanical response.

In situ temperature sensing with fluorescent chitosan-coated PNIPAAm/alginate beads

The interest in the development of non-contact temperature sensors for particle image velocimetry (PIV) is continuously growing. The integration of thermochromic tracers in PIV represents a critical step forward in experimental fluid mechanics, which would enable detailed full-field analysis of thermal and environmental flows. In this paper, interpenetrated polymer networks (IPN) PNIPAAm/alginate loaded with Nile Red (NR) fluorescent dye are used to develop beads for simultaneous non-contact temperature sensing and flow tracing in fluids. The novel IPN beads are coated with chitosan to properly modulate particle permeability in water. The thermochromic response of the fluorescent tracers is studied through fluorescence spectroscopy, evidencing an increase in the NR fluorescence emission up to twenty times above the lower critical solution temperature of PNIPAAm. These findings confirm the potential of fluorescent chitosan-coated PNIPAAm/alginate beads for in situ temperature in PIV.

Flow velocity and temperature sensing using thermosensitive fluorescent polymer seed particles in water

ABSTRACT Particle image velocimetry (PIV) is an experimental technique that uses microscale particles as tracers to measure the velocity of a fluid flow. In this paper, we seek to extend this technique to simultaneously measure fluid temperature as well, by employing a novel class of thermosensitive polymer particles. Towards this aim, we designed a process to encapsulate highly fluorescent thermosensitive NBD-AE-co-poly(N-isopropylacrylamide) polymers into optically transparent poly(dimethylsiloxane) particles. These novel PIV particles enable direct measurement of water velocity while serving as temperature probes that increase their fluorescence intensity when the temperature rises above 32 °C. To demonstrate the ability of the particles to simultaneously serve as flow tracers and temperature sensors in water, we examine the flow velocity and temperature in the wake of a heated cylinder in a cross flow. Our results indicate the possibility of extending PIV to afford the spatial and temporal resolution of fluid velocity and temperature gradients in water, with potential application to the study of convection problems from life sciences to engineering.

A Mechatronics-Based Platform for In Situ Strain Measurement Through Mechanochromic Polymers

Mechanochromic polymers are a new class of active materials, whose fluorescence emission is controlled by their mechanical deformation. In this paper, we present a mechatronics-based platform for fluorescence detection and on-site testing of mechanochromic polymers. We envision the use of this technology in the development of new sensing systems, with applications in soft robotics and environmental engineering.

Harvesting energy from a water flow through ionic polymer metal composites' buckling

This study seeks to investigate the feasibility of energy harvesting from mechanical buckling of ionic polymer metal composites (IPMCs) induced by a steady fluid flow. In particular, we propose a harvesting device composed of a paddle wheel, a slider-crank mechanism, and two IPMCs clamped at both their ends. We test the system in a water tunnel to estimate the effects of the flow speed and the shunting resistance on power harvesting. The classical post-buckling theory of inextensible rods is utilized, in conjunction with a black-box model for IPMC sensing, to interpret experimental results.

Simultaneous sensing of fluid velocity and temperature using particle tracers embedding nitrobenzofurazan functionalized thermosensitive hydrogels

Particle image velocimetry is an experimental technique for measuring the velocity field of a moving fluid by tracking small particles dispersed within the flow. To extend this technique to the study of fluid temperature, we propose a novel tracer particle which enables direct measurement of the velocity, while acting as a temperature sensor by increasing its fluorescence intensity when the local fluid temperature rises above 32°C. Thermoresponsive tracers are prepared by incorporating nitrobenzofurazan functionalized hydrogels within optically transparent polydimethylsiloxane microspheres. We demonstrate the application of the tracers in the study of forced thermal convection in water around a heated cylinder in an open channel.

Highly compressible fluorescent particles for pressure sensing in liquids

Pressure sensing in liquids is important for engineering applications ranging from industrial processing to naval architecture. Here, we propose a pressure sensor based on highly compressible polydimethylsiloxane foam particles embedding fluorescent Nile Red molecules. The particles display pressure sensitivities as low as 0.0018 kPa–1, which are on the same order of magnitude of sensitivities reported in commercial pressure-sensitive paints for air flows. We envision the application of the proposed sensor in particle image velocimetry toward an improved understanding of flow kinetics in liquids.