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Wei P.,Shanghai JiaoTong University | Bocchini S.,Center for Space Human Robotics Polito | Camino G.,Polytechnic University of Turin
European Polymer Journal | Year: 2013

This paper addresses the combustion behaviour of polylactide (PLA) nanocomposites based on organomodified montmorillonite clays. It is shown that PLA nanocomposites burn in a very different way compared to virgin PLA. Indeed, nanocomposites burning rate is usually lower respect to PLA, with a rate decrease depending on clay type and concentration. However, an easier ignition is shown by PLA nanocomposites as compared to PLA which is due to a catalytic effect of the clays. It is shown that these peculiar features of nanocomposites burning behaviour may prevent reliable comparison between polymers and nanocomposites based only on a single parameter such as UL 94 test ranking or the Limiting Oxygen Index value (LOI). It is also shown that by an extended use of data provided by the LOI apparatus, the peculiarities of nanocomposites combustion process are easily detected. © 2012 Elsevier Ltd. All rights reserved.


Griffini G.,Polytechnic of Milan | Bella F.,Polytechnic University of Turin | Bella F.,Center for Space Human Robotics Polito | Nisic F.,University of Milan | And 5 more authors.
Advanced Energy Materials | Year: 2015

A new multifunctional coating for photovoltaic cells incorporating light-management, UV-protection, and easy-cleaning capabilities is presented. Such coating consists of a new photocurable fluorinated polymer embedding a luminescent europium complex that acts as luminescent down-shifting (LDS) material converting UV photons into visible light. The combination of this system with ruthenium-free organic dye-sensitized solar cells (DSSCs) gives a 70% relative increase in power conversion efficiency as compared with control uncoated devices, which is the highest efficiency enhancement reported to date on organic DSSC systems by means of a polymeric LDS layer. Long-term (>2000 h) weathering tests in real outdoor conditions reveal the excellent stabilizing effect of the new coating on DSSC devices, which fully preserve their initial performance. This excellent outdoor stability is attributed to the combined action of the luminescent material that acts as UV-screen and the highly photostable, hydrophobic fluoropolymeric carrier that further prevents photochemical and physical degradation of the solar cell components. The straightforward approach presented to simultaneously improve performance and outdoor stability of DSSC devices may be readily extended to a large variety of sensitizer/luminophore combinations, thus enabling the fabrication of highly efficient and extremely stable DSSCs in an easy and versatile fashion. A new multifunctional coating system based on a photocurable fluoropolymer that incorporates luminescent-down shifting, UV-screening, and easy-cleaning functionalities is presented. The use of such coating in organic dye-sensitized solar cell (DSSC) devices allows for significant improvement of the power conversion efficiency of uncoated devices and imparts outstanding long-term device stability in real outdoor operating conditions. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


Bella F.,Center for Space Human Robotics Polito | Bella F.,Polytechnic University of Turin | Mobarak N.N.,National University of Malaysia | Jumaah F.N.,National University of Malaysia | Ahmad A.,National University of Malaysia
Electrochimica Acta | Year: 2014

Renewable energy systems represent a milestone of third millennium applied scientific research. As a viable, economic and environmentally friendly alternative to the solid electrolytes currently used in dye-sensitized solar cells (DSSCs), here we propose a biopolymer derived from seaweeds, which undergoes a process of selective carboxylation to improve its transport properties. Subsequently, a chemometric approach is used to tune the amount of salts and additives, and the highest ever measured ionic conductivity for a biopolymeric solid electrolyte has been reached (5.53 â™ © 2014 Elsevier Ltd. All rights reserved.


Cauda V.,Center for Space Human Robotics Polito | Stassi S.,Center for Space Human Robotics Polito | Stassi S.,Polytechnic University of Turin | Bejtka K.,Center for Space Human Robotics Polito | Canavese G.,Center for Space Human Robotics Polito
ACS Applied Materials and Interfaces | Year: 2013

The dimensional confinement and oriented crystallization are both key factors in determining the piezoelectric properties of a polymeric nanostructured material. Here we prepare arrays of one-dimensional polymeric nanowires showing piezoelectric features by template-wetting two distinct polymers into anodic porous alumina (APA) membranes. In particular, poly(vinylidene fluoride), PVDF, and its copolymer poly(vinylidene fluoride-trifluoroethylene), PVTF, are obtained in commercially available APA, showing a final diameter of about 200 nm and several micrometers in length, reflecting the templating matrix features. We show that the crystallization of both polymers into a ferroelectric phase is directed by the nanotemplate confinement. Interestingly, the PVDF nanowires mainly crystallize into the β-phase in the nanoporous matrix, whereas the reference thin film of PVDF crystallizes in the α nonpolar phase. In the case of the PVTF nanowires, needle-like crystals oriented perpendicularly to the APA channel walls are observed, giving insight on the molecular orientation of the polymer within the nanowire structure. A remarkable piezoelectric behavior of both 1-D polymeric nanowires is observed, upon recording ferroelectric polarization, hysteresis, and displacement loops. In particular, an outstanding piezoelectric effect is observed for the PVDF nanowires with respect to the polymeric thin film, considering that no poling was carried out. Current versus voltage (I-V) characteristics showed a consistent switching behavior of the ferroelectric polar domains, thus revealing the importance of the confined and oriented crystallization of the polymer in monodimensional nanoarchitectures. © 2013 American Chemical Society.


Bocchini S.,Center for Space Human Robotics Polito | Frache A.,Polytechnic University of Turin
Express Polymer Letters | Year: 2013

Polylactide (PLA) based nanocomposites of organically modified montmorillonite and micro-talc based microcomposites were prepared with different compositions and were UV-light irradiated under artificial accelerated conditions representative of solar irradiation. The chemical modifications resulting from photo-oxidation were followed by infrared (IR) and ultraviolet (UV)-visible spectroscopies. The infrared analysis of PLA photooxidation shows the formation of a band at 1847 cm-1 due to the formation of anhydrides. The filler addition provokes an increase of anhydride formation rate dependent on filler nature, amount and dispersion degree on the matrix. The main factors that influence oxidation rate are the total extension of polymer/filler interfacial area and the presence of transition metal impurities of clays. © BME-PT.


Stassi S.,Center for Space Human Robotics Polito | Stassi S.,Polytechnic University of Turin | Canavese G.,Center for Space Human Robotics Polito
Journal of Polymer Science, Part B: Polymer Physics | Year: 2012

This work presents a comprehensive investigation of the piezoresistive response of a composite material based on conductive nickel filler in a silicone-insulating matrix. In the absence of a deformation, the prepared composite shows no electric conductivity, even though the metal particle content is well above the expected percolation threshold. Upon samples deformation (compressive or tensile stress), the composite exploits a variation of electrical resistance up to nine orders of magnitude. This huge variation can be explained with the quantum tunnelling mechanism where the probability of an electron to tunnel from a particle to the next one is exponentially proportional to the thickness of the insulating layer between them and strongly enhanced by the morphology of the nickel particles, showing spiky nanostructured tips. Two different conduction theoretical models are proposed and compared with the experimental results. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012 A huge piezoresistive response upon compressive or tensile stress is achieved in a composite material based on nickel conductive filler in a polydimethylsiloxane (PDMS) insulating matrix. The conduction mechanism, enhanced by the spiky nanostructured morphology of the particles inside the composite, is based on a quantum tunneling effect as confirmed by theoretical models. The huge variation in resistance upon a small deformation of the composite material makes it a good candidate for sensor applications. Copyright © 2012 Wiley Periodicals, Inc.


Bella F.,Center for Space Human Robotics Polito | Bella F.,Polytechnic University of Turin | Bongiovanni R.,Polytechnic University of Turin
Journal of Photochemistry and Photobiology C: Photochemistry Reviews | Year: 2013

Dye-sensitized solar cells (DSSCs) have attracted large attention due to their easy fabrication, low cost and high conversion efficiency. One of the major problems limiting the long-term stability of these devices is the volatilization of the liquid electrolytes traditionally used. To solve this problem and improve technological perspectives of DSSCs, many recent studies have been addressed to the preparation of quasi-solid electrolytes, in which a polymer network is able to effectively retain the redox mediator and its additives. In this context, photoinduced polymerization is increasingly proving to be the most effective method of preparation of these polymer electrolytes, since it is a rapid, economic, functional and environmentally friendly process, besides being easily transferable to the industrial scale. This review focuses on the techniques adopted for the preparation of UV-cured quasi-solid electrolytes, on the expedients designed to overcome the inhibition phenomena typical of some photoinitiated mechanisms, and on the evaluation of photoelectric performance obtained in presence of these photopolymer electrolytes. © 2013 Elsevier B.V.


Battezzato A.,Center for Space Human Robotics Polito
Mechanism and Machine Theory | Year: 2014

The current paper deals with the kinetostatic analysis and consequent optimization of an underactuated mechanism, whose aim is to constitute an exoskeleton device, designed to enhance the force of the human finger with whom it is coupled. Given an exoskeleton architecture, optimal from the point of view of the simplicity, the geometric parameters are further optimized, to let the transmitted forces be as similar as possible to the specific force profile, set as a reference for the device. In particular, extra-vehicular activity (EVA) for astronauts is recognized as a possible field for hand exoskeletons, since EVA gloves are very demanding in terms of strength and fatigue. Thus, the force profile for a specific EVA glove is provided as an example, and different optimized devices are obtained from the stochastic optimization process. Their kinetostatic performances are hence analyzed and discussed, thanks to a properly defined performance index. Finally, a verification of the actual encumbrance of the synthesized structure is performed, with respect to EVA-specific constraints. © 2014 Elsevier Ltd.


Feil F.,Ludwig Maximilians University of Munich | Cauda V.,Center for Space Human Robotics Polito | Bein T.,Ludwig Maximilians University of Munich | Brauchle C.,Ludwig Maximilians University of Munich
Nano Letters | Year: 2012

The diffusion dynamics of terrylene diimide (TDI) dye molecules and dye-labeled double-strand DNA were studied in micrometer long silica filaments containing collinear, oriented mesopores using single molecule fluorescence microscopy. TDI was used as a stable and hydrophobic probe molecule for single molecule structural analysis. We used template-free mesoporous silica filaments with 4 nm pore diameter and chemical functionalization with one or two types of trialkoxysilane groups to enhance the affinity between the host system and the guest molecules. Insights about the mesoporous structure as well as the translational and orientational diffusion dynamics of the guest molecules observed along micrometer long trajectories could be obtained. Additionally, the stability of DNA oligomers (15 base pairs, bp, about 5.3 nm long) within the mesopores was examined, showing no degradation of the oligonucleotide upon incorporation into the mesopores. Diffusion of both guest molecules could be controlled by exposure to vapors of water or chloroform; the latter both induced a reversible on-off control of the translational movement of the molecules. © 2011 American Chemical Society.


Calignano F.,Center for Space Human Robotics Polito
Materials and Design | Year: 2014

Selective laser melting (SLM) process allows fabricating strong, lightweight and complex metallic structures. To successfully produce metallic parts by SLM, additional structures are needed to support overhanging surfaces in order to dissipate process heat and to minimize geometrical distortions induced by internal stresses. However, these structures are often massive and require additional post-processing for their removal. A minimization of support structures would therefore significantly reduce manufacturing and finishing efforts and costs. This study investigates the manufacturability of overhanging structures using optimized support parts. An experimental study was performed to identify the optimal self-supporting overhanging structures using Taguchi L36 design. Experimental results revealed that with optimized supports it is possible to build non-assembly mechanism with overhang surfaces. However, it is necessary to correctly orientate the part in the SLM machine in order to build it with a minimal support structure so to obtain the best trade-off between production time, cost, and accuracy. © 2014 Elsevier Ltd.

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