232 research outputs found
Fractal dimension in mass spectra from herbal extracts: Hypothesis for a new method of phytocomplex characterization
No full textIn order to optimize the quality control of phytochemical products, we propose a non-conventional method of analysis of complex systems, called fractal analysis, applied to ESI (Electrospray Ionisation) mass spectra. The ESI spectra obtained with phytochemical commercial products (Mattoli et al., J. Mass Spectrom. 41: 1534, 2006; Mattoli et al., Metabolomics 7:437, 2011) were submitted to fractal analysis using the “box counting” method. Subsequent cluster analysis permitted to determine a distinctive fractal dimension (DB) for single plant extracts, as well as for mixtures of plant extracts contained in commercial herbal products. On several replicates obtained with different batches, DB tended to display a normal distribution around a mean value, which might be suggested as a typical reference tag for that product. The fractal approach permitted to characterize the repeatability of the instrumental measure too. Changes in DB following thermal treatment of samples, to simulate ageing, indicated the ability of the method also to identify appropriate conditions of storage and to suggest stability control interventions. In conclusion, evaluation of mass spectra DB might be proposed as a new promising technique to be used as a summary measurement of the complexity of the overall composition of a phytochemical product
Functional Materials for Two‐Photon Polymerization in Microfabrication
No full textDirect laser writing methods based on two-photon polymerization (2PP) are powerful tools for the on-demand printing of precise and complex 3D architectures at the micro and nanometer scale. While much progress was made to increase the resolution and the feature size throughout the years, by carefully designing a material, one can confer specific functional properties to the printed structures thus making them appealing for peculiar and novel applications. This Review summarizes the state-of-the-art of functional resins and photoresists used in 2PP, discussing both the range of material functions available and the methods used to prepare them, highlighting advantages and disadvantages of different classes of materials in achieving certain properties
Electrically responsive photonic crystals: A review
No full textTunable photonic crystals (TPCs) represent an important class of intelligent materials, which can be used as optically active components and as functional technology to change an object's colour. Among these smart structures, electrically responsive photonic crystals are the most promising for real technological applications. Up to now, to transform the electrical stimulus into an optical response several strategies have been adopted that can be classified into (1) electrochemical processes, (2) reorientation of liquid crystal molecules, (3) electrophoretic organization of colloidal suspension and (4) indirect electrically induced modification of the photonic structures. In this review article, these approaches are systematically summarized and analysed with a particular emphasis on the chemistry of materials
Bending actuation of a composite liquid crystal elastomer via direct Joule heating
No full textIn this work a new bi-layered composite actuator based on a polysiloxane-based monodomain nematic Liquid Crystal Elastomer (LCE) and on a conductive PEDOT:PSS thin layer is proposed. The basic idea is to integrate electroconductive properties in the LCE and to validate the feasibility of direct actuation of the LCE by Joule heating of the conductive (and compliant) PEDOT: PSS layer. The fabrication of the actuator is achieved by depositing a thin conductive polymer layer by drop casting a PEDOT: PSS waterborne solution after having increased the LCE surface wettability with an air plasma treatment. The excellent stability of PEDOT: PSS and its mechanical properties, better matched with LCE ones compared to metals or inorganic nanoparticles used in other approaches, allowed to develop an all-organic reliable actuating composite based on thermoresponsive properties of LCE. Thermal actuation via direct Joule heating of the composite has been verified and prototypes of LCE/PEDOT:PSS bending actuators have been preliminary tested
Conformable on-skin devices for thermo-electro-tactile stimulation: Materials, design, and fabrication
No full textConformable electronics is an emerging and innovative research field investigating functional materials and electronic devices capable of adhering and conforming to non-planar surfaces such as human skin. Conformable devices find applications of high economical and scientific interest in healthcare, human-machine interfaces, wearable electronics, robotics, and the internet of things. Compared to the more widely used rigid and bulky electrodes often employed in wearable platforms, the former offers multiple advantages such as imperceptibility, low cost, and the possibility of continuous use, being able to follow the multiple deformations of curvilinear living tissues. In recent years, much attention has been paid to the development of soft and skin-wearable sensors, but an additional area of great interest is certainly that of conformable electrodes capable of providing some kind of stimulation. This review provides an overview of the most attractive and innovative conformable devices developed to stimulate the human body through thermal, electrical, mechanical, and optical stimuli. In particular, it focuses on the functional materials employed, the fabrication techniques involved, and the design solutions proposed to improve the performance of conformable stimulation devices
Novel, High-Resolution, Subtractive Photoresist Formulations for 3D Direct Laser Writing Based on Cyclic Ketene Acetals
No full textDirect laser writing (DLW) is an innovative technology based on two-photon polymerization processes which allow the 3D printing of architectures with arbitrary complexity at the (sub)micrometer scale. While most of the research interest in this field relies on additive manufacturing, subtractive approaches can be extremely helpful in nano/microfabrication, allowing the preparation of expendable scaffolds, replaceable parts, and for the protection of fragile structures. In this study, we show that the simple addition of 2-methylene-1,3-dioxepane, a cyclic ketene acetal compound, to a series of different acrylate-based photoresists results in functional formulations that allow the 3D-printing of degradable poly(ester-co-acrylate) microstructures via DLW. These latter could be degraded reliably under mild conditions compatible with other photoresists and materials of common use in the fabrication of MEMS, thus opening new opportunities to design novel fabrication procedures. In addition, the possibility of using different acrylate mixtures without affecting the degradability, allows the users to choose between a broad range of properties for the printed structures to fit their needs, without affecting the degradability. Finally, the authors show the potential of these photoresists in the fabrication of shadowing masks on 3D objects and their selective degradation employing a photobase
A Simple Approach for Flexible and Stretchable Anti-icing Lubricant-Infused Tape
No full textUnwanted icing has major safety and economic repercussions on human activities, affecting means of transportation, infrastructures, and consumer goods. Compared to the common deicing methods in use today, intrinsically icephobic surfaces can decrease ice accumulation and formation without any active intervention from humans or machines. However, such systems often require complex fabrication methods and can be costly, which limits their applicability. In this study, we report the preparation and characterization of several slippery lubricant-infused porous surfaces (SLIPSs) realized by impregnating with silicone oil a candle soot layer deposited on double-sided adhesive tape. Despite the use of common household items, these SLIPSs showed anti-icing performance comparable to other systems described in the literature (ice adhesion < 20 kPa) and a good resistance to mechanical and environmental damages in laboratory conditions. The use of a flexible and functional substrate as tape allowed these devices to be stretchable without suffering significant degradation and highlights how these systems can be easily prepared and applied anywhere needed. In addition, the possibility of deforming the substrate can “allow” the application of SLIPS technology in mechanical ice removal methodologies, drastically incrementing their performance
Model validation of a mercury sensor, based on the resistivity variation of a thin gold film
No full textNowadays, the awareness of the importance of mercury as a global pollutant increases the need for new tools helping support citizens' health safeguard. With this in mind, the authors developed a microfabricated sensor to monitor elemental gaseous mercury (Hg 0) in the air, and they presented it in a previous work. A deep understanding of the physical phenomena concerning the processes involved was necessary to improve the performance and to develop an "optimised sensor". This paper presents a simple physical model, developed to quantitatively estimate the sensitivity of a mercury sensor. The sensor is based on the resistivity variation induced by the adsorption of mercury onto a thin gold film. The model provided the design criteria for a new version of the mercury sensor. The paper describes the model validation, which was carried out through a series of experiments on new sensors, as well as the new design, microfabrication process, and technical features of the mercury sensor. The sensor consists of a miniaturized system, which includes the sensing element, the electrical routes, and a digital temperature sensor integrated onto a small SIM-card-shape substrate. Conventional IC technologies and materials were used throughout the sensor fabrication process, in order to produce a low-cost microsystem, which could be used as a disposable sensor
Bending actuation of a composite liquid crystal elastomer via direct Joule heating
No full textIn this work a new bi-layered composite actuator based on a polysiloxane-based monodomain nematic Liquid Crystal Elastomer (LCE) and on a conductive PEDOT:PSS thin layer is proposed. The basic idea is to integrate electroconductive properties in the LCE and to validate the feasibility of direct actuation of the LCE by Joule heating of the conductive (and compliant) PEDOT:PSS layer. The fabrication of the actuator is achieved by depositing a thin conductive polymer layer by drop casting a PEDOT:PSS waterborne solution after having increased the LCE surface wettability with an air plasma treatment. The excellent stability of PEDOT:PSS and its mechanical properties, better matched with LCE ones compared to metals or inorganic nanoparticles used in other approaches, allowed to develop an all-organic reliable actuating composite based on thermoresponsive properties of LCE. Thermal actuation via direct Joule heating of the composite has been verified and prototypes of LCE/PEDOT:PSS bending actuators have been preliminary tested. © 2012 IEEE
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