Organic and Inorganic Material-Based Functional Surfaces for Sensors and Biosensors: Synthesis and Design

The aim of this thesis is the realization of integrated optic sensors based on fiber grating devices. In order to obtain chemical and biological sensors, a Long Period Gratings transducer was used as transduction platform. Different organic and inorganic materials were used as sensitive elements at the interface between the LPGs and the external environment. Since the selectivity and sensitivity of a LPGs based sensor depend upon the interface materials, careful study of the sensing materials, as well as of the deposition process was done. Results of this PhD work has been obtained thanks to the integration of interdisciplinary knowledges in different scientific and technological areas, such as optical engineering, biochemistry, polymer materials, synthetic chemistry. Within the framework of the OPTOFER Project, a GPL sensor based on LPGs coated with a-PS thin films was developed and manufactured. This polymeric film was considered for the physical affinity among hydrophobic polystyrene chains and short aliphatic molecules that constitute GPL. Preliminary results have shown good sensitivity of the device in presence of unknown GPL concentrations: the signal is stable and the sensor is characterized by fast response time and reversibility (absence of hysteresis in consecutive gas on/gas off cycles). An accurate study, of both material and interaction between the LPG transducer and the a-PS film, has allowed the development of a device capable to detect clearly GPL concentration between 1000 and 30000 ppm. These sensors have been installed and tested under the railway tunnel of Porta Rufina station, in Benevento. “Relative humidity fiber optic sensors based on Long Period Gratings” is the name of the collaboration agreement with CERN during which have been designed, developed and manufactured humidity sensors resistant to radiation and to cryogenic temperature. LPGs, used as transducers, were coated with thin film of sol-gel synthesized titania, an inorganic oxide that shows different interesting features: 1) hygrosensitive characteristics, 2) ageing and high energy radiation resistance and 3) thermal stability. The sol-gel synthesis and the deposition process optimization has led to the development of humidity sensors with good sensibility and reversibility, and the inorganic nature of the titania coating guarantees the mechanical and thermal stability of the device. Within the framework of the OPTOBACTERIA Project, has been developed a highly- sensitive reflection-type LPG biosensor, useful to detect antibiotic resistance bacteria. The reflection-type LPG was coated by a primary a-PS layer and by a secondary very thin overlay of PMMA-co-MA. a-PS was used as HRI layer in order to tune the LPG to be able to operate within the transition region. PMMA-co-MA has been employed as thin film to provide carboxylic groups on the external surface of the fiber. A standard linkage chemistry has been carried out to anchor the bioreceptors onto the probe surface. Preliminary experimental results demonstrate the capability of the fabricated LPG biosensor to monitor successfully all steps of the biochemical immobilization strategy as well as to detect the β-Lactamase binding to its functionalized surface

Fracture Toughening Mechanisms in Epoxy Adhesives

Fracture toughness is generally considered as the main properties of a polymer or a polymer adhesive system for measuring the material resistance to the extension of cracks. Epoxy adhesives are generally brittle in nature; however, the addition of a second dispersed phase could induce a remarkable increase of damage tolerance performance by an enhancement of the material fracture toughness. The fracture behavior of a filled epoxy resin is strongly affected by the dimensions, the shape, and the chemical nature of the considered filler. The chapter describes the different toughening mechanisms for polymer adhesives with special attention toward innovative nanofiller such as graphene nanoplatelets and hyperbranched polymer nanoparticles

Aromatic hyperbranched polyester/RTM6 epoxy resin for EXTREME dynamic loading aeronautical applications

The effects of the addition of an aromatic hyperbranched polyester (AHBP) on thermal, mechanical, and fracture toughness properties of a thermosetting resin system were investigated. AHBP filler, synthesized by using a bulk poly-condensation reaction, reveals a glassy state at room temperature. Indeed, according to differential scanning calorimetry measurements, the glass transition temperature (Tg) of AHBP is 95 °C. Three different adduct weight percentages were employed to manufacture the AHBP/epoxy samples, respectively, 0.1, 1, and 5 wt%. Dynamical Mechanical Analysis tests revealed that the addition of AHBP induces a negligible variation in terms of conservative modulus, whereas a slight Tg reduction of about 4 °C was observed at 5 wt% of filler content. Fracture toughness results showed an improvement of both critical stress intensity factor (+18%) and critical strain energy release rate (+83%) by adding 5 wt% of AHBP compared to the neat epoxy matrix. Static and dynamic compression tests covering strain rates ranging from 0.0008 to 1000 s−1 revealed a pronounced strain rate sensitivity for all AHBP/epoxy systems. The AHBP composites all showed an increase of the true peak yield compressive strength with the best improvement associated with the sample with 0.1 wt% of AHBP

Effect of silica nanoparticles on the compressive behavior of RTM6 epoxy resin at different strain rates

RTM6 epoxy resin is considered the main matrix material for high performance aeronautical grade composites which can be subjected to impact loads. Research efforts have been spent to improve the strength and the overall impact properties of these resins. One of the routes followed focuses on the enhancement of the epoxy resin by the addition of rigid nanoparticles with different weight percentages and sizes. The purpose of this work is to study the compressive behavior of RTM6 epoxy resin filled with silica nanoparticles at different strain rates. Two types of epoxy resins, namely neat epoxy resin and epoxy resin filled with silica nanoparticles at 0.1% weight percentage were tested. Quasi-static experiments were performed at strain rates of 0.008, 0.08, and 0.8 /s , while high strain rate experiments were performed at strain rates approx. 1000 /s using the split Hopkinson pressure bar technique. The behavior of both the nanoparticle filled resin and neat resin is compared and discussed. The effect of the silica nanoparticles on the compressive yield strength is also presented

Hydrothermal Aging of an Epoxy Resin Filled with Carbon Nanofillers

The effects of temperature and moisture on flexural and thermomechanical properties of neat and filled epoxy with both multiwall carbon nanotubes (CNT), carbon nanofibers (CNF), and their hybrid components were investigated. Two regimes of environmental aging were applied: Water absorption at 70 °C until equilibrium moisture content and thermal heating at 70 °C for the same time period. Three-point bending and dynamic mechanical tests were carried out for all samples before and after conditioning. The property prediction model (PPM) was successfully applied for the prediction of the modulus of elasticity in bending of manufactured specimens subjected to both water absorption and thermal aging. It was experimentally confirmed that, due to addition of carbon nanofillers to the epoxy resin, the sorption, flexural, and thermomechanical characteristics were slightly improved compared to the neat system. Considering experimental and theoretical results, most of the epoxy composites filled with hybrid carbon nanofiller revealed the lowest effect of temperature and moisture on material properties, along with the lowest sorption characteristics

Environmental effects on mechanical, thermophysical and electrical properties of epoxy resin filled with carbon nanofillers

The aim of this work was to establish the effect of environmental factors (moisture and temperature) on some mechanical, electrical and thermal properties of epoxy-based composites filled with carbon nanofillers: nanotubes (CNT), nanofibers (CNF) and hybrid nanofiller (nanotubes/nanofibers in the ratio 1:1) and to reveal the most environmentally stable NC. First, the nanocomposites (NC) containing different nanofiller contents were prepared to evaluate electrical percolation threshold and to choose NC at certain electrical conductivity for further characterization of the physical properties in initial state and during/after environmental ageing. The environmental ageing consisted of water absorption at 70 °C until equilibrium moisture content reached all samples in 4 weeks and 2) heating at 70 °C for the same time, and 3) freezing at -20 °C for 8 weeks. Two concurrent factors, temperature and moisture, led to post-curing of all materials studied without significant plastization. Some positive nanofiller effects were found for sorption, mechanical and thermophysical characteristics of RTM6 epoxy resin. Based on experimental results, the most environmentally stable NC was epoxy filled with 0.1 wt. % of CNT/CNF hybrid, which had the lowest effect of temperature and moisture on thermal and electrical conductivities, along with the lowest equilibrium water content and diffusivity

Effects of 1D and 2D nanofillers in basalt/poly(lactic acid) composites for additive manufacturing

In this work, basalt microfiber reinforced poly(lactic acid) (PLA) composites filled with talc nanoplatelets (2D) and sepiolite nanofibers (1D) were prepared at different compositions and tested to assess the effects of filler geometry. Thermal analysis results show that crystallinity of amorphous PLA can be enhanced up to 24% by adding basalt and talc. Thermal stability of PLA is increased by basalt microfibers whereas talc and sepiolite prompted early degradation in binary composites. In ternary systems, i.e. PLA/basalt/talc and PLA/basalt/sepiolite, thermal stability was further increased. Mechanical tensile and flexural properties were remarkably increased for a specific composition basalt (30 wt%) and talc (10 wt%) with a final enhancement of 176% and 261% for modulus and 46% and 43% for strength respectively in tensile and bending configuration. For the composition, the coefficient of thermal expansion is significantly reduced up to 54% of the corresponding pristine PLA value. The increase of thermal conductivity is mainly related to the presence of 1D sepiolite, with a variation of ~54% for the 10 wt% PLA/sepiolite binary system. Finally, a significant increment of impact property was observed by unnotched Charpy impact tests for talc (+97%) and basalt (+140%) composites.Peer reviewe

Thermal and Mechanical Characterization of an Aeronautical Graded Epoxy Resin Loaded with Hybrid Nanoparticles

Synthesized silica nanoparticles (SiO2) were coated with a thin polydopamine (PDA) shell by a modified one-step procedure leading to PDA coated silica nanoparticles (SiO2@PDA). Core-shell (CSNPs) characterization revealed 15 nm thickness of PDA shell surrounding the SiO2 core (~270 nm in diameter). Different weight percentages of CSNPs were employed as filler to enhance the final properties of an aeronautical epoxy resin (RTM6) commonly used as matrix to manufacture structural composites. RTM6/SiO2@PDA nanocomposites were experimentally characterized in terms of thermal stability and mechanical performances to assess the induced effects by the synthesized CSNPs on pristine matrix. Thermal stability was investigated by thermogravimetry and data were modelled by the Doyle model and Kissinger methods. An overall enhancement in thermal stability was achieved and clearly highlighted by modelling results. Dynamic Mechanical Analysis has revealed an improvement in the nanocomposite performances compared to the neat matrix, with an increase in the glassy (+9.5%) and rubbery moduli (+32%) as well as glass transition temperature (+10 °C). Fracture Toughness tests confirmed the positive effect in damage resistance compared to unloaded resin with an impressive variation in critical stress intensity factor (KIC) and critical strain energy (GIC) of about 60% and 138%, respectively, with the highest SiO2@PDA content

Chapter Fracture Toughening Mechanisms in Epoxy Adhesives

Fracture toughness is generally considered as the main properties of a polymer or a polymer adhesive system for measuring the material resistance to the extension of cracks. Epoxy adhesives are generally brittle in nature; however, the addition of a second dispersed phase could induce a remarkable increase of damage tolerance performance by an enhancement of the material fracture toughness. The fracture behavior of a filled epoxy resin is strongly affected by the dimensions, the shape, and the chemical nature of the considered filler. The chapter describes the different toughening mechanisms for polymer adhesives with special attention toward innovative nanofiller such as graphene nanoplatelets and hyperbranched polymer nanoparticles

Chapter Fracture Toughening Mechanisms in Epoxy Adhesives

Fracture toughness is generally considered as the main properties of a polymer or a polymer adhesive system for measuring the material resistance to the extension of cracks. Epoxy adhesives are generally brittle in nature; however, the addition of a second dispersed phase could induce a remarkable increase of damage tolerance performance by an enhancement of the material fracture toughness. The fracture behavior of a filled epoxy resin is strongly affected by the dimensions, the shape, and the chemical nature of the considered filler. The chapter describes the different toughening mechanisms for polymer adhesives with special attention toward innovative nanofiller such as graphene nanoplatelets and hyperbranched polymer nanoparticles