[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: Liquid handling at micron- and nano-scale is of paramount importance in many fields of application such as biotechnology and biochemistry. In fact, the microfluidics technologies play an important role in lab-on-a-chip devices and, in particular, the dispensing of liquid droplets is a required functionality. Different approaches have been developed for manipulating, dispensing and controlling nano-droplets under a wide variety of configurations. Here we demonstrate that nano-droplets can be drawn from liquid drop or film reservoirs through a sort of milking effect achieved by the absorption of IR laser radiation into a pyroelectric crystal. The generation of the pyroelectric field induced by the IR laser is calculated numerically and a specific experiment has been designed to visualize the electric field stream lines that are responsible for the liquid milking effect. The experiments performed are expected to open a new route for the visualization, measure and characterization procedures in the case of electrohydrodynamic applications.
Measurement Science and Technology 03/2013; 24(4):045203. · 1.44 Impact Factor
[show abstract][hide abstract] ABSTRACT: We report on tuning the optical whispering gallery modes (WGMs) in a poly dimethyl siloxane-based (PDMS) microsphere resonator by more than 1 THz. The PDMS microsphere system consists of a solid spherical resonator directly formed with double stems on either side. The stems act like tie-rods for simple mechanical stretching of the microresonator, resulting in tuning of the WGMs by one free spectral range. Further investigations demonstrate that the WGM shift has a higher sensitivity (0.13 nm/μN) to an applied force when the resonator is in its maximally stretched state compared to its relaxed state.
[show abstract][hide abstract] ABSTRACT: The investigation of a method for fabricating microlenses by a nozzle-free inkjet printing approach is reported. The new method, based on a pyroelectrohydrodynamic mechanism, is also able to dispense viscous liquids and to draw liquid phase drops directly from the reservoir. Specifically, by dispensing optical grade polymer dissolved in different solvent mixtures, microlenses were printed with a pattern defined directly through this deposition method. The reliability of the microlenses and the tunability of their focal properties were demonstrated through profilometric and inteferometric analyses.
[show abstract][hide abstract] ABSTRACT: A digital holographic characterization of Bessel beams produced by
polymeric microaxicons is reported. Both intensity and phase of the beam
can be numerically reconstructed in whichever point starting from a
single acquired hologram. Optical parameters such as the full width at
half maximum, the focal length and the depth of focus of the axicon lens
are experimentally measured. The Bessel beam exiting from the axicon,
with a very large depth of focus with respect to that of a Gaussian
beam, is successfully exploited for optical trapping of micrometric
[show abstract][hide abstract] ABSTRACT: The pyroelectric functionality of a Lithium Niobate (LN) substrate is
used for non-contact manipulation of polymeric material. In this work we
introduced a novel approach for fabricating a wide variety of soft
solid-like microstructures, thus leading to a new concept in 3D
lithography. A relatively easy to accomplish technique has been
demonstrated for curing different transient stages of polymer fluids by
rapid cross-linking of PDMS. The method is twofold innovative thanks to
the electrode-less configuration and to the rapid formation of a wide
variety of 3D solid-like structures by exploiting polymer instabilities.
This new and unique technique is named "pyro-electrohydrodynamic (PEHD)
lithography", meaning the generation of structures by using forces
produced by electric fields generated by the pyroelectric effect. The
fabrication of polymer wires, needles, pillars, cones, or microspheres
is reported, and practical proofs of their use in photonics are
[show abstract][hide abstract] ABSTRACT: We present a quick, simple and accurate digital holographic characterization of the Bessel beams produced by polymeric microaxicons. This technique allows the numerical reconstruction of both intensity and phase of the beam at whichever point starting from a single acquired hologram. From these data, it is possible to go back to the axicon structure, and to gather information about their characteristics. In particular, the focal length and the depth of focus of the axicon lens are experimentally measured, and the full width at half maximum of the beam is obtained too. The depth of focus, very large for a Bessel beam with respect to a Gaussian one, is successfully exploited for optical trapping of micrometric objects.
Measurement Science and Technology 01/2012; 23(6). · 1.44 Impact Factor
[show abstract][hide abstract] ABSTRACT: Here the pyroelectric functionality of a Lithium Niobate (LN) substrate
is used for non-contact manipulation of liquids. In this work we
introduced the use of a pyro-electrohydrodynamc (PEHD) dispenser for the
manipulation of high viscous polymer materials leading to the
fabrication of arrays of microlenses. The set-up used for the experiment
is described and the fabricated microlenses are analyzed by means of the
Digital Holography (DH) set-up in transmission mode and through
profilometric analysis. PMMA based ink was employed for the realization
of optical quality microsctructures whose geometrical properties and,
hence, the focal lengths were controlled by modifying the printing
configuration of the PEHD method. The profilometric results are in
agreement with those calculated using the digital holography technique.
[show abstract][hide abstract] ABSTRACT: In liquids realm, surface tension and capillarity are the key forces driving the formation of the shapes pervading the nature. The steady dew drops appearing on plant leaves and spider webs result from the minimization of the overall surface energy [Zheng Y, et al. (2010) Nature 463:640-643]. Thanks to the surface tension, the interfaces of such spontaneous structures exhibit extremely good spherical shape and consequently worthy optical quality. Also nanofluidic instabilities generate a variety of fascinating liquid silhouettes, but they are however intrinsically short-lived. Here we show that such unsteady liquid structures, shaped in polymeric liquids by an electrohydrodynamic pressure, can be rapidly cured by appropriate thermal treatments. The fabrication of many solid microstructures exploitable in photonics is demonstrated, thus leading to a new concept in 3D lithography. The applicability of specific structures as optical tweezers and as novel remotely excitable quantum dots-embedded microresonators is presented.
Proceedings of the National Academy of Sciences 09/2011; 108(37):15106-11. · 9.74 Impact Factor
[show abstract][hide abstract] ABSTRACT: Destabilization of liquid film by electro-hydro-dynamics (EHD) pressure is achieved through the pyroelectric effect on a polar dielectric crystal. We show that by destabilizing the liquid film, periodical self-assembled multi-jets are obtained. The multi-jets operate simultaneously and could be exploited to dispense liquids with nanolitre drops. Such multiple self-assembled liquid jets have significant potential applicability for high-throughput liquid transfer by this novel pyro-EHD ink-jet approach. Since the method avoids the use of nozzles and electrodes, it is especially suitable for highly viscous liquids. Here we present and discuss the new multi-jet process and the results obtained with a liquid polymer (PDMS).
Lab on a Chip 08/2011; 11(19):3294-8. · 5.70 Impact Factor
[show abstract][hide abstract] ABSTRACT: Manipulation of micro-sized objects in lab-on-a-chip and microfluidic environments is essential for different experiments and procedures ranging from chemical to biological applications and for experimental biotechnologies. For example polymeric particles, useful as targets for encapsulating or for being covered by drug vaccines, can be manipulated and controlled with the aim of releasing them to specific sites. Here we show a novel ElectroHydroDynamic tool able to control and manipulate dielectric micro-targets by a touch-less approach. This approach allows one to manipulate liquids and nano-particles simultaneously for specific delivery applications (i.e. decoration and coating). Thus a sort of EHD micro-robot is proposed. This flexible tool provides a new and powerful way to operate various tasks as demonstrated by the experiments reported here.
Lab on a Chip 08/2011; 11(18):3148-52. · 5.70 Impact Factor
[show abstract][hide abstract] ABSTRACT: We report on the application of polymeric micro-axicons for optical trapping. Bessel beams with great depth of focus generated by these structures are interferometrically characterized and used as optical tweezers in different situations.