[Show abstract][Hide abstract] ABSTRACT: A novel scheme for solar energy harvesting based on the pyro-electric effect has been demonstrated. The proposed harvester is based on an optical system focusing solar radiation onto a ferroelectric crystal (i.e. lithium niobate). The face exposed to the heating source is coated with a nanocomposite material (i.e. carbon black and graphene particles) that greatly improves the adsorption of solar radiation. The solar energy focused onto the crystal through a simple optical system allows one to induce a thermal gradient able to generate electric charges. Experiments have been carried out indoor as well as outdoor (in Pozzuoli, Naples, Italy, on December). Results show that two configurations appear to be preferable: (a) pyro-electric element with carbon black-based coating and a Fresnel lens (surface of about 100 cm2); (b) pyro-electric element with graphene-based coating and a Fresnel lens (surface of about 600 cm2). In both experimental arrangements the maximum temperature variation reached locally onto the lithium niobate substrate is relatively high with peaks greater than 250 °C. The maximum electrical power peak is of about 90 μW and about 50 μW for (a) and (b) respectively. The results of this first investigation are encouraging for further development of more efficient harvesting devices.
Applied Energy 12/2014; 136:357-362. · 5.26 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Highly sensitive detection of biomolecules is of paramount interest in many fields including biomedicine, safety and eco-pollution. Conventional analyses use well-established techniques with detection limits ~1 pM. Here we propose a pyro-concentrator able to accumulate biomolecules directly onto a conventional binding surface. The operation principle is relatively simple but very effective. Tiny droplets are drawn pyro-electro-dynamically and released onto a specific site, thus increasing the sensitivity. The reliability of the technique is demonstrated in case of labelled oligonucleotides diluted serially. The results show the possibility to detect very diluted oligonucleotides, down to a few hundreds of attomoles. Excellent results are shown also in case of a sample of clinical interest, the gliadin, where a 60-fold improved detection limit is reached, compared with standard ELISA. This method could open the way to a mass-based technology for sensing molecules at very low concentrations, in environmental as well as in diagnostics applications.
[Show abstract][Hide abstract] ABSTRACT: In this work we introduce an easy multiscale approach for the fabrication of polymer microlens arrays through a self-assembling process driven by the electrohydrodynamic (EHD) pressure. This method represents a simple alternative to the conventional soft lithography techniques. A thin layer of liquid polymer is deposited on a micro-engineered ferroelectric crystal and can be self-assembled and cross-linked in a single step process as a consequence of the pyro-electric effect activated by simply heating the substrate. Although the EHD instability induced by the pyroelectric effect was discovered in principle few years ago, here we demonstrate a systematic investigation for fabrication of microlens arrays in a multiscale range (i.e. between 25 ???m to 200 ???m diameter) with high degree of uniformity. By controlling the polymer instability driven by EHD, we report on two different micro-optical shapes can be obtained spontaneously, i.e. spherical or toroidal. Here we show how the geometrical properties and the focal length of the lens array are modulated by controlling two appropriate parameters. Such microlenses can be useful also as polymer patterned arrayed microstructures for optical data interconnections, OLEDs efficient light extraction, concentrating light in energy solar cells, imaging and 3D display solutions and other photonics applications.
IEEE Journal of Selected Topics in Quantum Electronics 11/2014; · 3.47 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Here, we report on a single step approach for fabricating free-standing polymer membranes reinforced with arrayed self-assembled carbon nanotubes (CNTs). The CNTs are self-assembled spontaneously by electrode-free DC dielectrophoresis based on surface charge templates. The electrical charge template is generated through the pyroelectric effect onto periodically poled lithium niobate ferroelectric crystals. A thermal stimulus enables simultaneously the self-assembly of the CNTs and the cross-linking of the host polymer. Examples of thin polydimethylsiloxane membranes reinforced with CNT patterns are shown.
[Show abstract][Hide abstract] ABSTRACT: A lthough electrospinning (ES) allows the production of unsurpassed nanoscale polymer fibers, the major draw-backs are the nozzle-clogging and single-jet spinneret, respectively. This is a real limitation in terms of usable polymers and for patterning active organics. Nowadays the micro-engineering of smart materials could represent a new route for many fields of technology ranging from the production of electronic and photonic devices 1−3 to regener-ative medicine and tissue engineering. 4−7 An enormous technological interest is related to the possibility of patterning fibers directly in well-ordered patterns avoiding the deposition of nonwoven submicrometer mats often occurring in ES. 8,9 In the past decade several attempts have been made using field-induced 10−13 and near-field ES, 14,15 but only very recently, with the introduction of mechano ES, 16 has the production of well-ordered fiber patterns been achieved. Nevertheless, some drawbacks related to the complexity of the setup, the operating temperature, and the selection of usable materials for problems related to nozzle clogging still persist. Moreover, high temperature can cause deterioration of the optical and electronic properties of active organic materials eventually embedded in the functionalized fibers. On the other side, interfering effects due to closeness of multiple electrified nozzles ban working with multiple spinnerets. Here we introduce a revolutionary nozzle-free approach, the tethered pyro-electrodynamic spinning (TPES) operating in wireless modality, i.e., without electric circuit, electrodes, and voltage supply. This novel approach definitively simplifies the ES apparatus extending the nanofiber spinning also to active organic polymers preserving at the same time all the properties of conventional systems. Fiber drawing from the liquid polymer is driven through the pyroelectric charge generated into a ferroelectric crystal (i.e., LiNbO 3) able to induce the electro-hydrodynamics (EHD) pressure required for polymer manip-ulation without wires. The approach is highly flexible, simple, compact, and cost-effective when compared with classical ES, and last but not least, it allows working safely, avoiding the use of high-voltage equipment at kVolts scale. For the first time, in situ observation of fiber drawing is provided allowing real-time adjustments and full control of the process. Moreover the TPES adds to the capabilities of conventional ES the chance of printing polymer fibers even in the case of multiple drops opening the way to the multijetting spinneret modality for multiplexing and speeding up the fabrication process. Printing of micro-and nanofibers directly from a polymer drop with unprecedented order, direct writing of sharp/straight edges, and easy multijets electrospinning are demonstrated and reported. Experimental fabrication of patterns embedded with active molecules ensures that functionalized patterns preserve their functionalities after the TPES process. Results regarding the use of smart patterns for keeping alive and viable cultured cells are discussed. This study opens the way to innovative optogenesys analysis, guiding light for generating or trans-porting optical/electronic signals from and to cells. 17−21 The setup proposed in this work, unlike the conventional ES, is electrode-free and nozzle-free, Figure 1a,b. The method allows polymer nanofibers to be printed directly from a polymer drop overpassing the viscosity border of nozzle clogging in conventional inkjet systems. 22 The drop reservoir is placed directly on a flat substrate (base) while an electric field,
Chemistry of Materials 06/2014; · 8.54 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: In the recent years many commercial applications such as optoelectronics, photonic and biomedical devices, as well as image processing require the fabrication of adaptive and adjustable micro-lens array. A lot of attempts have been conducted in order to support the growing interest in the production of lens arrays for sensors or optical communications devices for parallel data transmission. Several fabrication techniques and a large variety of process have been proposed for polymer based microlenses and their incorporation into technological devices with a large area of application, but, the preparation of moulds, masks or metal layers with very accurate dimensions and shapes is generally required. Here we present the application of a pyro-electrohydrodynamic (Pyro-EHD)-dispenser for the fabrication of polymer microlens arrays overpassing the viscosity limit of the conventional ink-jet printing systems and working in a nozzle-less modality. The results regarding the fabrication procedure and the characterization of polymer micro-lens arrays of different shapes and heights are examined.
[Show abstract][Hide abstract] ABSTRACT: In the case of light emitting semiconducting polymers, different techniques have been used for the fabrication of electroluminescent devices. Experiments and characterizations have been carried out at different operating voltages and for voltage dependent emission color also combining the processability of organic materials with efficient luminescence displayed by inorganic nanocrystals (NCs). In fact, the experimental perspective to disperse emitting colloidal NCs into polymers has allowed to further engineer hybrid organic-inorganic materials introducing innovative functionalities as for instance photoluminescence conversion capabilities. This has proved of great interest for novel applications such as the fabrication of photonic crystals and, notably, of innovative solar cells showing enhanced efficiency. Here we report on the fabrication of novel active micro-optical elements made by a mixture of rod-shaped inorganic NCs dispersed into poly-dimethylsiloxane.
Proc. SPIE 9130, Micro-Optics 2014, 91300Q, Brussels, Belgium; 05/2014
[Show abstract][Hide abstract] ABSTRACT: In this work we present a direct printing of microlenses using high viscous polymer materials. In particular the pyro-electric effect activated onto a Lithium Niobate crystal is exploited for the fabrication on demand of microlens array.
2014 Fotonica AEIT Italian Conference on Photonics Technologies (Fotonica AEIT); 05/2014
[Show abstract][Hide abstract] ABSTRACT: Novel and intriguing lithographic approaches based on instabilities of liquid polymers and electro-hydro-dynamic at nanoscale have been developed. The unusual fabrication methods were aimed at fabricating 3D polymeric microstructures. A variety of microstructures were fabricated and tested for applications in different fields 1. LIQUID NANO DISPENSER A new opto-nanofluidic approach named Pyro-EHD is presented for dispensing liquid nano-pico-droplets through pyroelectric effect activated by hot tip source or an IR laser into a dielectric crystal using a non-invasive simple and powerful electrode-less configuration. The manipulation of small amounts of liquids at micro to nanometer scale is of great interest in many fields of technology: biotechnology, patterning by deposition of inorganic, organic and biological inks and photnics [1-4]. We show a new and simple system where the liquid actuation and dispensing has been achieved through electrode-less configurations using polar dielectric crystals such as Lithium Niobate (LN) crystal and by exploiting the pyroelectric effect [5,6]. The technique presented allows one to avoid the use of high-voltage power supplies and electrical circuits, and moreover there is no need to design and fabricate nanocapillary nozzles. The functionalization of the lithium niobate (LN) is obtained by micro-engineering the ferroelectric domains and by inducing the pyroelectric effect through the use of appropriate heat sources such as a IR laser beam . The set-up consists basically of a polished 500-µm thick z-cut LN substrate (from Crystal Technology, Inc.) placed over a microscope glass slide at a specific distance fixed by appropriate spacers (Figure 1). A liquid drop or film is first deposited on the glass slide and successively the upper surface of the LN wafer is placed in contact with an heated-tip that can be scanned in order to induce point-wise thermal stimuli. The heated-tip is in axis with the droplet reservoir on the microscope glass slide. A conventional heated soldering tip was used as heated-tip-source. LN reacts to the thermal-stimuli by building-up an electric potential across the z-cut LN crystal's surfaces because of the pyroelectric effect, that consists in the spontaneous polarization change ∆Ps following to a temperature gradient ∆T. At equilibrium, the crystal Ps is fully screened by the external screening charge and no electric field exists . When the heating source locally heats the crystal, a sudden surface charge density σ immediately appears given by neglecting losses, where Pc is the material-specific pyroelectric coefficient (Pc= -8.3 x 10 -5C/°C/m2 for LN @ 25°C). The electric field exerts an attractive force on the liquid . When the liquid starts to deform under the action of the electric field, two evolutions are possible. Case (I): if the liquid volume and the separation distance D between the two Invited Paper
Proc. SPIE 8982, Optical Components and Materials XI, 89820N (March 7, 2014), San Francisco; 03/2014
[Show abstract][Hide abstract] ABSTRACT: Hypodermic needle injection is still the most common method of drug delivery despite its numerous limitations and drawbacks, such as pain, one-shot administration, and risk of infection. Seeking a viable, safe, and pain-free alternative to the over 16 billion injections per year has therefore become a top priority for our modern technological society. Here, a system that uses a pyroelectric cartridge in lieu of the syringe piston as a potential solution is discussed. Upon stimulation, the cartridge electro-draws, at room temperature, an array of drug-encapsulated, biodegradable polymer microneedles, able to deliver into hypodermic tissue both hydrophobic and hydrophilic bioactive agents, according to a predefined chrono-programme. This mould-free and contact-free method permits the fabrication of biodegradable polymer microneedles into a ready-to-use configuration. In fact, they are formed on a flexible substrate/holder by drawing them directly from drop reservoirs, using a controlled electro-hydrodynamic force. Tests of insertion are performed and discussed in order to demonstrate the possibility to prepare microneedles with suitable geometric and mechanical properties using this method.
[Show abstract][Hide abstract] ABSTRACT: Stable chains of carbon-based nanoparticles were formed directly in polymer matrixes through an electrode-free approach. Spontaneous surface charges were generated pyroelectrically onto functionalized ferroelectric crystals, enabling the formation of electric field gradients that triggered the dipole-dipole interactions responsible for the alignment of the particles, while embedded in the polymer solution. The phenomenon is similar to the dielectrophoretic alignment of carbon nanotubes reported in the literature. However, here the electric fields are generated spontaneously by a simple heat treatment that, simultaneously, aligns the particles and provides the energy necessary for curing the host polymer. The result is a polymer sheet reinforced with well-aligned chains of carbon-based particles, avoiding the invasive implementation of appropriate electrodes and circuits. Because polymers with anisotropic features are of great interest for enhancing the thermal and/or the electrical conductivity, the electrode-free nature of this technique would improve the scaling down and the versatility of those interconnections that find applications in many fields, such as electronics, sensors, and biomedicine. Theoretical simulations of the interactions between the particles and the charge templates were implemented and appear in good agreement with the experimental results. The chain formation was characterized by controlling different parameters, including surface charge configuration, particle concentration, and polymer viscosity, thus demonstrating the reliability of the technique. Moreover, micro-Raman spectroscopy and scanning electron microscopy were used for a thorough inspection of the assembled chains.
[Show abstract][Hide abstract] ABSTRACT: In the present work, the pyro-electrohydrodynamic technique was used for the realization of tunable-size microlens arrays. Poly(methyl methacrylate) dissolved in different solvent mixtures was used as the polymeric material for the realization of the microstructures. By controlling the experimental parameters and in particular, the volume of the drop reservoir, graded-size square arrays of tens of microlenses with focal length in the range 1.5-3 mm were produced. Moreover, the optical quality and geometrical features were investigated by profilometric and interferometric analysis.
[Show abstract][Hide abstract] ABSTRACT: We present a laser-assisted system for dispensing liquid micro-droplets by near infrared illumination of a pyroelectric crystal functionalized with gold nanorods embedded into polyvinyl alcohol. The non-invasive near infrared source resonates with the plasmon oscillations of the gold nanorods, providing a controlled thermal stimulus able to generate the pyroelectric effect. The resulting electric field interacts electro-hydrodynamically with a liquid reservoir leading to precise drawing of micro-litre droplets. This laser-assisted electro-hydrodynamic technique may open the way to the development of more compact and non-invasive nano-dispensing devices. V C 2013 AIP Publishing LLC. [http://dx.doi.org/10.1063/1.4825337] Lab-on-a-chip systems are of great interest in biotechno-logical and chemical applications, thanks to their possibility of producing the desired products faster and in greater yield and purity compared to conventional techniques. 1 Basically two main classes of microfluidic approaches have been developed during the last decades. The continuous flow microsystems 2 usually consist of a network of micrometre-sized channels, thus suffering from various drawbacks, including large dead volumes and obstruction of channels. Moreover, they make use of valves and pumps, which increases complexity, cost and fragility of the system. On the other hand, the so-called "digital microfluidics" (Ref. 3) con-fine the reactions into single droplets, even with high mono-dispersivity. 4 A significant advantage of droplet-based systems is that they are compatible with wall-free structures, so that the operations can conveniently performed on the sur-face of a planar substrate. Surface microfluidics are simpler to fabricate and assemble and, lacking fixed microchannels, they can be reconfigured more easily. A number of techni-ques have been proposed for the actuation of microfluidic droplets, including the use of thermocapillary effects, 5 elec-trochemical gradients, 6 photochemical effects, 7 and dielec-trophoresis. 8 More recently, the same authors developed an innovative platform for actuating microdroplets through pyroelectric activation of the dielectrophoresis, with addi-tional advantages in terms of versatility. 9,10 In this frame-work, precise and reliable droplet dispensers are highly desirable and different techniques have been presented in lit-erature. Some of these rely on fluid interface instabilities, 11 or on atomic force probes. 12 Other approaches involve elec-trohydrodynamic jetting through appropriate nozzles. 13 These electric field based methods provide droplets with rel-atively high resolution but require the arrangement of appro-priate electrodes and high voltage circuits and the fabrication of micrometric nozzles. Recently, the same authors have developed a pyro-electrohydrodynamic (P-EHD) approach for different applications, including liquid printing in the attolitre volume range, 14 fabrication of solid photonic micro-structures, 15 manipulation of dielectric micro-targets. 16 In those works, the electric field, responsible for the electrode-free and nozzle-free manipulation of liquids, polymers, and solids, was activated onto lithium niobate (LN) and lithium tantalate (LT) crystals by resistive sources (e.g., hot tip of a soldering iron) that were contact-dependent, or by CO 2 lasers that avoided contact thanks to the absorption of those crys-tals in the far infrared (IR) region but sacrificing the com-pactness and making difficult the beam alignment due to invisibility to the naked eye. Here, we propose a laser-assisted EHD (LA-EHD) tech-nique based on the successful combination of a near infrared (NIR) source with the plasmon resonance of gold nanorods (GNRs) patterned onto the surface of a LN crystal. This sys-tem exhibits additional advantages compared to the elec-trode-and nozzle-free pyro-EHD configuration developed previously by the same authors. 14 The stimulation of the pyro-EHD effect is performed optically by a compact laser source launched in fibre. Such fibre-based setup favours the integrability and makes the light addressing easier thanks to its visibility to the naked eye when the light hits the target. In this context, a portable system could be fabricated for bio-sensing applications where on site drawing of very little amounts of liquids is needed. More versatile dispensing modes (serial and multiple) are possible by simply modulat-ing the distance between fibre and crystal and therefore by lens-free manipulation of the beam expansion. Moreover, additional versatility and precision are provided here by the possibility of patterning the heat source onto the pyroelectric crystal. In fact, the thermal gradient is ensured by the effi-cient photothermal conversion of the GNRs during the plas-mon resonance induced by laser illumination, so that the pyroelectric effect can be generated with high precision and selectivity by near field excitation through an appropriately addressed small beam or alternatively by a largely expanded beam illuminating a pattern of GNRs. The selectivity offered by the patterning approach reduces the stress induced to the crystal and provides, at the same time, better control over the
[Show abstract][Hide abstract] ABSTRACT: Very interesting effects can be observed in maneuvering nematic liquid crystal (NLC) droplets onto functionalized polar lithium niobate (LN) crystal surfaces, covered with thin films of Polydimethylsiloxane (PDMS). It has been discovered that pyroelectric effect is able to drive a reversible fragmentation process in liquid crystal drops, starting from nanoliter drops and obtaining pico/femtoliter droplets. These small droplets are patterned according to the geometry of the substrate and aligned along the electric field lines. This novel approach for manipulating different classes of liquids by exploiting the pyroelectric effect, where the strong electric fields generated allow to manipulate liquids in 2D on a substrate or even in 3D, has been recently discovered and exploited for different purposes. In particular, manipulation of liquid crystals by a thermal stimulus could be suitable for applications such as spatial modulation of the wettability (i.e. wettability patterning), or, in principle, a dynamical optical element able to switch from a diffuser (fragmentation) state to a microlens array. Moreover, the biocompatibility of some kinds of nematic or cholesteric liquid crystals makes them suitable as biomaterials for applications in biology and tissue engineering.
[Show abstract][Hide abstract] ABSTRACT: Nanoparticles are drawing tremendous attention due to their great potential as building blocks in nanoelectronics and photonics. In particular, it is highly desirable to control their orientation and assembly: incorporating nanowires into thin polymer films is interesting to obtain materials with anisotropic optical, thermal and structural features that can be potentially used as conductive films for semiconductor packaging and electromechanical connections in liquid crystal displays [1, 2]. The most of these approaches for manipulating and chaining conductive nanoparticles often require voltages by external electrodes and, usually, report the growth velocity as a function of electric potential and electrode spacing [1, 3].
The European Conference on Lasers and Electro-Optics; 05/2013