78 research outputs found
Bimetallic Au/Ag nanoparticle loading on PNIPAAm–VAA–CS8 thermoresponsive hydrogel surfaces using ss-DNA coupling, and their SERS efficiency
No full textThermoresponsive hydrogels can be efficiently used as templates for bimetallic noble metal surface loading for the fabrication of plasmonic surfaces with a wide range of applications. Here, we report, for the first time, an easy approach for bimetallic Au/Ag surface loading by modifying poly(N-isopropylacrylamide) (PNIPAAm) hydrogel surfaces with ss-DNA. The advantages of this approach consist of the accuracy and the simplicity by which both gold and silver nanoparticles can be adsorbed by electrostatic interactions on hydrogel templates, without requiring sophisticated chemical treatment for their conjugation or the growth of nanoparticles on a hydrogel surface. The resulting patterns possess the capability of tuning the interparticle distance upon temperature changes, and thus their plasmonic properties. The aforementioned templates have been successfully used as SERS substrates for 5 × 10-7 M adenine detection
Easy-to-fill asymmetric polymeric micro-reservoirs
No full textIn this work, we demonstrate the feasibility of micrometric asymmetric reservoirs made of thermoplastic polymers by using the gas foaming method, which has been recently introduced, and consists in forming bubbles in micro- or nano-metric bulk particles as it is done with carbonated drinks. As this simplicity anticipates, this represents a breakthrough in the area of micro and nano-particles as it responds to the needs of: i) breaking the symmetry of commonly available systems, ii) filling the particles with a multitude of host molecules and solutions, iii) having different shapes, iv) having a wide range of particle dimensions, v) having particles made of a wide range of materials. Here we report the achievement of micrometric spherical particles and of micrometric ellipsoidal particles with eccentric holes, filled with crystal violet or with quantum dots as model host molecules. Raman spectroscopy and optical and electron imaging are utilized to verify the effectiveness of the method. This study should open up the use of micro- and nano-metric reservoirs in a multitude of research areas, from the biomedicine and pharmacology, to electronics, energy and optics
Wettability of graphene by molten polymers
No full textGraphene wetting by polymers is a critical issue to both the success of polymer-aided transfer of large size sheets onto specific substrates and to the development of well performing nanocomposites. Here we show for the first time that high temperature contact angle measurements can be performed to investigate the wettability of CVD graphene by molten polymers. In particular, poly(methyl methacrylate), a widely used polymer support for CVD graphene transfer, has been adopted herein for this proof-of-concept study and the values of contact angle and work of adhesion have been provided in the temperature range 170–200 °C
Thermoplastic polyurethane–graphene nanoplatelets microcellular foams for electromagnetic interference shielding
No full textHighly Efficient Surface-Enhanced Raman Scattering Substrate Formulation by Self-Assembled Gold Nanoparticles Physisorbed on Poly(N-isopropylacrylamide) Thermoresponsive Hydrogels
No full textEmploying thermoresponsive hydrogels as scaffolding material for noble metal surface loading might be useful for the fabrication of surface-enhanced Raman scattering (SERS) surfaces. Here, we report on a new, reproducible, and simple approach to engineer poly(N-isopropylacrylamide) (PNIPAAm) hydrogel surfaces optimized for physisorption of gold nanoparticles (AuNPs). The advantage. of this approach consists of the simple mechanism by which AuNPs are adsorbed on hydrogel templates, without sophisticated chemical treatments for their conjugation with the hydrogel. The resulting PNIPAAm-40 nm AuNP modes demonstrate that this approach gives the capability to tune the interparticle distance and, therefore, to control and modulate SERS affinity upon temperature changing
Ανάπτυξη νέας τεχνικής επιφανειακής ενίσχυσης της σκέδασης raman (SERS) για ποσοτικές μετρήσεις ενεργών ουσιών σε πολύ μικρές συγκεντρώσεις
No full textLaser Raman spectroscopy plays an increasing important role in polymer science, biophysics/biochemistry and life science. Based on vibrational transitions, it has long been regarded as a valuable non-destructive tool for the identification of chemical and biological samples as well as the elucidation of molecular structure, surface processes and interface reactions. Spontaneous Raman scattering is however an inherently weak process characterized by extremely small cross sections. Even so, the Raman signal can be highly enhanced when the analyte is placed on or near either to nano-rough noble-metal substrates or to nano-structured colloidal clusters of noble metals. This nano-enhanced scattering process is known as Surface Enhanced Raman Scattering, SERS. With SERS, extremely small amounts of substances can be detected; even single molecule detection has been reported. This constitutes a challenge of applying SERS to extremely low concentration measurements. Nevertheless, the quantitative evaluation by means of SERS was proved difficult, due largely to lack of nano-sized noble metal structures with analytically suitable stability and reproducibility. The commonly used SERS substrates are nanostructured colloids or roughened surfaces of mainly silver and gold undergoing visible or NIR excitation. A note is made of the fact that the Raman scattering geometry that is actually largely used is the backscattering geometry. For solids this is better achieved via a microscope objective, while for liquids via a macro lens. However, the best scattering geometry for Raman light collection from liquids and nanostructured colloids is the right angle scattering; that is, the scattered light is collected at 90° from the excitation light. Having all above in mind, in order to perform quantitative SERS measurements we have designed and developed an oscillating cell making use of the right angle Raman scattering geometry. Originally, the development of the oscillating or “shaking” cell allows large sample sectional surface monitoring, better mixing and homogeneity giving rise to SERS signal reproducibility. In addition, the application of the advantageous for nanocolloidal solutions right angle Raman scattering collection geometry enables SERS measurements at extremely low concentrations. We demonstrated the use this new surface enhanced Raman scattering excitation/collection configuration to monitor the level of the antitumor drugs mitoxantrone and doxorubicin as well as the antibiotic ciprofloxacin at very low concentrations performing fast SERS & SERRS measurements. We have also quantified the concentration of the active agents in aqueous solutions as well as in artificial tears by a partial least-squares (PLS) chemo metric regression algorithm. All above reveal the potential of this technique in the monitoring of the controlled release of active agents from polymeric matrices as well as in the quantitative analysis of drugs in corporal fluids. The only need is to add in a test tube containing 0.5 mL of a nanocolloidal noble metal solution³ about 25-100 μL of a sampling fluid. Finally, in an attempt to detect “living” cells by SERS, to identify DNA components released in a cell culture medium as a “touch mark” of cell death and to perform even single molecule detection, a home-made micro-incubator was designed to allow Raman measurements of neuron cells under the microscope. Commercial micro incubators feature higher optical path between coverslips than the required (<1-1,5 cm) for typical micro-Raman systems even bearing long working distance objectives. It was at that sense a prerequisite to design, construct and optimize a micro-incubator to fit a conventional micro-Raman configuration. The designed micro incubator meets well-defined stable conditions (temperature, culture solution and atmosphere).Η φασματοσκοπία Raman θεωρείται αξιόπιστη μέθοδος χαρακτηρισμού της μοριακής δομής της ύλης. Τελευταία δε καταβάλλεται μεγάλη προσπάθεια να αναδειχθεί και ως μη επεμβατική τεχνική ανίχνευσης ουσιών φαρμακευτικού και βιολογικού ενδιαφέροντος. Επειδή όμως το φαινόμενο Raman είναι ασθενές και τα όρια ανίχνευσης των ουσιών αυτών ιδιαίτερα χαμηλά, η συμβατική φασματοσκοπία Raman ανταποκρίνεται με μεγάλη δυσκολία στις απαιτήσεις μιας μη επεμβατικής τεχνικής. Τα τελευταία χρόνια με την ανακάλυψη της επιφανειακής ενίσχυσης της σκέδασης Raman (Surface Enhanced Raman Scattering) και την ανάπτυξη της ομώνυμης τεχνικής SERS αυξήθηκε η πιθανότητα του φαινομένου κατά τάξεις μεγέθους. Στο πλαίσιο αυτό, έχουν αναφερθεί και μελέτες SERS με ανίχνευση σκέδασης Raman ακόμη και από ένα μόνο μόριο (single molecule detection).Προϋπόθεση όμως ανάπτυξης φαινομένου SERS είναι η γειτνίαση της εξεταζόμενης ουσίας με νανοσωματίδια αργύρου (Ag) ή χρυσού (Au). Τα νανοσωματίδια αυτά χρησιμοποιούνται κυρίως είτε υπό μορφή κολλοειδών διαλυμάτων είτε υπό την μορφή νανοδομημένων επιφανειών. Μια επιπλέον παράμετρος που πρέπει να συνυπολογισθεί ώστε η μέθοδος αυτή να χαρακτηριστεί αναλυτική είναι η δυνατότητα πραγματοποίησης με SERS ποσοτικών μετρήσεων. Στην παρούσα εργασία ως “υπόστρωμα” εμφάνισης του φαινομένου SERS χρησιμοποιήθηκαν κολλοειδή διαλύματα Au και Ag (~2 mL), στα οποία προστίθεντο 25-100 μL διαλύματος της προς ανίχνευσης ουσίας. Η χρησιμοποίηση της γεωμετρίας σκέδασης 90ο, της πλέον ενδεδειγμένης για λήψη φασμάτων Raman από υγρά και κολλοειδή διαλύματα νανομετρικής κλίμακας (10-100 nm), έδωσε τη δυνατότητα ανίχνευσης συγκεντρώσεων ουσιών-στόχων ακόμη και της τάξης των fg/mL. Επιπλέον, η χρησιμοποίηση μιας κυψελίδας με συνεχή ταλάντωση σε κάθετη ως προς το επίπεδο σκέδασης διεύθυνση (oscillating or shaking cell), επέτρεψε την πραγματοποίηση ποσοτικών μετρήσεων SERS σε συγκεντρώσεις της τάξης των (sub)-ng & (sub)-pg/mL. Η διάταξη αυτή φωταψίας δείγματος και συλλογής σκεδαζόμενης ακτινοβολίας εφαρμόστηκε σε αντικαρκινικά φάρμακα (Novantrone® & Doxorubicin), αντιβιοτικό (Ciproxin®) και βάσεις του DNA. Στην περίπτωση του αντιβιοτικού με ενεργή ουσία το Ciprofloxacin ελήφθησαν ποσοτικά αποτελέσματα σε διαλύματα τεχνητών δακρύων της τάξης των ng/mL, κάτω από την συνολική κλίμακα της μέσης ανασταλτικής πυκνότητας (minimum inhibitory concentration range) του φαρμάκου. Στόχος και φιλοδοξία είναι η τεχνική αυτή να αναδειχθεί ως μια ταχεία μη επεμβατική αναλυτική μέθοδος μέτρησης φαρμακευτικών ή/και βιολογικών ουσιών σε σωματικά υγρά (π.χ. σίελος, δάκρυα, …), για την μελέτη της φαρμακοκινητικής, την έγκαιρη διάγνωση ασθενειών καθώς και τη μελέτη ελεγχόμενης αποδέσμευσης ενεργών ουσιών από πολυμερικές μήτρες σε πολύ μικρές συγκεντρώσεις. Επιπλέον, έγινε προσπάθεια μελέτης/ανίχνευσης μορίων Ε18 primary rat cortical cells με την χρήση του SERS σε συνθήκες προσομοίωσης ηλεκτροχημικού εμφυτεύματος. Για τον λόγο αυτό σχεδιάστηκε και αναπτύχθηκε ένας μικρο-επωαστής (micro-incubator) που επιτρέπει αφ’ ενός μεν τη συντήρηση των κυττάρων σε περιβάλλον κατάλληλο για τη μελέτη τους (layer of Neurobasal-culture medium with a 95% air & 5% CO₂ gas flow at 37°C), αφ’ ετέρου δε την προσαρμογή του σε χώρο υποδοχής δείγματος ενός φασματοφωτόμετρου μικρο-Raman για τη λήψη φασματοηλεκτροχημικών μετρήσεων Raman/SERS. Το κύριο σημείο ενδιαφέροντος στο οποίο εστιάσαμε στην παρούσα εργασία αναφέρεται στην διερεύνηση ανίχνευσης βασικών/θεμελιωδών μορίων των κυττάρων στo θρεπτικό υγρό του πειράματος για την ταχεία εκτίμηση ενδεχόμενης αποδέσμευσης DNA που θα αντικατόπτριζε την κατάσταση των κυττάρων
Damage arrest mechanisms in nanoparticle interleaved composite interfaces
No full textThe effectiveness of carbonaceous nanoparticles in arresting and delaying damage in nanocomposites has been attributed to multiscale toughening mechanisms. To explore their application in joined interfaces of composites, this study investigates the use of carbon nanotube (CNT) interleaved films for co-cured joining of composite parts and their consequent effects on the interfacial fracture toughness. Carbon nanotubes dispersed in a thermoset resin into thin films of two discrete thicknesses (200 μ and 500 μ) and three concentrations of CNT dispersion were chosen for this study (0.5% wt., 1% wt., and 2% wt.). The films were semi-cured in the oven before being incorporated as interleaves in the composite laminate interface. Fracture toughness of the interface in mode I loading conditions was determined through double cantilever beam (DCB). Micrographs of the fracture surfaces reveal a slip-and-stick based crack jump and arrest phenomena in mode I when nanoparticles are added to the interleaved interface. The thickness of the interleaves has a more significant effect on mode I toughening mechanisms than the concentration of the nanoparticles.Aerospace Structures & Computational Mechanic
Effect of dwell stage in the cure cycle on toughening of epoxy using thermoplastic multilayers
No full textEpoxies with high cross-linking densities are brittle and hence have a low fracture toughness. However, different methods are known to increase fracture toughness. Numerous approaches are known to incorporate a second phase into the epoxy matrix, such as rubber, inorganic nanoparticles or thermoplastics, referred to as bulk resin modification. These tougheners usually form specific morphologies during the curing phase of epoxy, resulting in improved fracture toughness of the system. Unfortunately, for some tougheners, the addition of second phase into the epoxy system also results in a reduction in overall modulus and limitation in end-use temperature of the system. In the case of thermoplastic tougheners, the second phase is created by diffusion and dissolution, followed by reaction induced phase separation, leading to a morphology in the micrometer range. However, the influence of the curing history beyond phase separation, using two dwell cure cycles with varying dwell time/degree of cure, on the interphase dimension and final morphology for PEI having a contrasting phase behaviour (UCST), is not well understood. The research presented in this work aims to understand the interphase formation, to later attain the desired droplet size and interphase morphology for improved material toughness. This aim is achieved by analyzing the influence of dwell time by considering two main cases for each selected 1st dwell temperature (120-180˚C): (i) wait until the onset of phase separation (OPS) before increasing the temperature to 200°C (second dwell), (ii) wait until 80% degree of cure (80% DOC) before the second dwell. At all processing temperatures, a distinct gradient morphology (Fig. 1a ) was clearly observed for both cases (OPS and 80% DOC). The SEM micrographs revealed the formation of a larger interphase region (71 μm) for the OPS case as compared to the 80% DOC case (56 μm). Figure 1b shows the interphase thickness as a function of 1st dwell temperature for both OPS and 80% DOC cases. It can be seen that the interphase thickness increased with 1st dwell temperature for both cases, until 160˚C after which it slightly decreased for a 1st dwell temperature of 180˚C. This work highlights, i) the importance of the curing process beyond phase separation to control interphase dimension and final morphology and, ii) the influence of both these parameters on the toughness enhancement.Aerospace Manufacturing Technologie
Measurement of damage growth in ultrasonic spot welded joint
No full textUltrasonic spot welding is a joining technique for thermoplastic composites with great potential regarding processing speed and cost. To investigate the damage tolerance and possible inherent damage arresting behavior of multi-spot welded joints, a technique is necessary to measure damage growth in the joints under cyclic loading. Visual inspection is not possible because the damage is not located on the outside surface and conventional techniques such as C-scan are not practical during a fatigue test because the specimen would have to be removed from the setup. This paper details a methodology for quantifying damage growth rates in singlespot welded joints using surface strain measurements made by Digital Image Correlation. This represents the first step towards developing a methodology for quantifying damage progression behavior in complex multi-spot welded joints.Structural Integrity & CompositesAerospace Structures & Computational Mechanic
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