In this work, we developed and characterized composites prepared by dispersing conductive carbon black (CB) at different concentrations in an azobenzene-based photomobile polymer (azo-PMP) matrix. This polymer can move under UV-blue light because its azobenzene moieties undergo a reversible photoisomerization from trans to cis configuration and this nanoscopic structural movement induces a macroscopic movement in the film. We studied the possibility to modify the photomobile properties of azo-PMP by introducing different concentrations of CB (from 0wt.% up to 1wt.%) and we investigated morphology, optical properties and photomobile behaviour at different wavelengths. Optical analysis by polarized light shows that the films with CB concentrations up to 0.1wt.% are quite homogeneous and still present birefringence properties. Photoresponsivity measurements at wavelengths in the range 457-747nm were studied to investigate how the presence of the CB affects the photomobile response inside and outside the absorption spectral region of azo-polymers. Choosing appropriately the CB concentration, we demonstrated that it is possible to enlarge the usable spectral bandwidth of the samples in visible region towards the visible and near infrared spectral region.
Films based on a composite of a liquid crystal polymer (LC-POL) with acrylic backbone and carbon black (CB) were manufactured and characterized to develop a new smart material able to move under light. In detail, the effect of 0.1wt% of CB, a high absorption and thermal conductive filler, on morphological, optical and photomobile properties was investigated and compared with pristine LC-POL films. To study photomobile behaviuor the films were irradiated with 457nm-laser at different powers and the responses to these stimuli were compared in terms of bending angle and response time. The work shows that the presence of CB induces photomobile properties in an inactive LC polymer matrix and the mechanical response under light is fast and reversible.
Azobenzene-based photo-mobile polymer (PMP) samples were mechanically coupled with foils of piezoelectric material (PZM) and placed under a solar simulator. The solar simulator used a short arc xenon lamp as a light source with an AM1.5 filter o mimic the absorption spectrum of earth’s atmosphere. This setup, commonly used for testing solar cells (at a power density of 1000W/m2), was used to verify the energy generation capabilities of a PMP-PZM system. As shown in previous works, the movement of the PMPs can be attributed to a narrow spectrum of light near the UV range while heat or light outside of that narrow band can prove detrimental to the motion. Thus, to verify operation under "natural light" various methods filters are employed to the solar simulator light. The output of the PZM was loaded with a constant resistance and the voltage across the load was measured using a high impedance buffer amplifier to eliminate any other loading effects. While it was shown that any optical filters that removed the UV component lead to completely stopping the PMP motion, the system was capable of operating in direct sunlight and generated measurable energy on the load. Peak voltage of over 4V was achieved and discharged an average of 710nJ over a 50s period. This result could be significantly improved, but was limited by the mechanical capabilities of the shutter.
In the last decade, smart materials have been developed in the fields of optical machines, sensors, motors, robots, and energy harvesting. This is due to their capability to respond to external stimuli or environmental changes. Among smart materials, photo-mobile polymers (PMPs) based on liquid crystals are the most promising in the field of photo-responsive actuators. These polymers are made with a mixture of liquid crystals containing azobenzene moieties that can undergo photoisomerization from trans to cis under UV light. This process leads to a macroscopic bending of the PMPs, which transforms light into mechanical energy. To enhance the PMPs' actuation, a novel liquid crystal nanocomposite is proposed. In our work, the nanocomposites are prepared with different concentrations of ZnO nanoparticles (NPs) embedded in the cross-linked polymer matrix. We have demonstrated that ZnO NPs improve the actuation and mechanical properties of the PMP, and the main aim of this assay is to optimize such effect as a function of the nanoparticles concentration. We also show the lowest and highest amounts of ZnO needed to enhance the bending behavior of the PMP. Optical, mechanical, and thermal analyses were performed to characterize the PMPs. Spectral characterization in UV/vis range of the bare and doped films, optical and atomic force microscopy, were used to comprehend the role of ZnO nanoparticles and their distribution among the liquid crystals. To study the dynamic response of the PMPs and their mechanical properties, lasers at different wavelengths were used.
Development of novel plasmonic nanopatterns is of great interest for various applications, including chemical and biological analysis. Systems based on gold nanoelements have been designed and tested in several research works for the study and detection of various kinds of biological analytes, giving appreciable results. Plasmonic properties associated to the nanostructure can be tuned by changing the size and the shape of the nanoparticles or the periodicity or, more in general, the geometry of the nanopattern. These features are key to many applications aiming at signal enhancement and low threshold sensing. In this work we present a study of periodic arrangements of novel plasmonic metamolecular unit cells made of triangular nanoelements. Nanostructures analyzed were fabricated using electron beam lithography technique (EBL) that allows to create patterns with high accuracy and repeatability. Morphological analysis was realized by Scanning Electron Microscopy (SEM) and their plasmonic properties were studied and compared using experimental set-up for Surface Plasmon Resonance (SPR) and Surface Enhanced Raman Spectroscopy (SERS) measurements. We tested the sensing performance of our nanostructures by analyzing the SARS-CoV-2 (COVID-19) Spike Antibody (3525) getting its molecular fingerprint. Our results suggest that these plasmonic patterns are promising to develop highly sensitive nanosensors for the detection of biological analytes.
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