Indiana University-Purdue University Indianapolis (IUPUI) / This study represents a cost-effective method to advance the physical and mechanical properties of carbon fiber-reinforced polymer (CFRP) prepreg composite materials, where electrospun multiwalled carbon nanotubes (CNTs)/epoxy nanofibers fabricated and deposited in between the layers of traditional CFRP prepreg composite. CNT-aligned epoxy nanofibers were uniformly formed by an optimized electrospinning method. Electrospinning is considered one of the most flexible, low-cost, and globally recognized methods for generating continuous filaments from submicron to tens of nanometer diameter. Nanofilaments were incorporated precisely on the layers of prepreg to accomplish increased adhesion and interfacial bonding, leading to increased strength and enhancements in more mechanical properties. As a result, the modulus of the epoxy and CNT/epoxy nanofibers were revealed to be 3.24 GPa and 4.84 GPa, leading to 49% enhancement. Furthermore, interlaminar shear strength (ILSS) and fatigue performance at high-stress regimes improved by 29% and 27%, respectively. Barely visible impact damage (BVID) energy improved considerably by up to 45%. The thermal and electrical conductivities were also increased considerably because of the highly conductive CNT networks present in between the CFRP layers. The newly introduced approach was able to deposit high content uniform CNTs at the ply interface of prepregs to enhance the CFRP properties, that has not been achieved in the past because of the randomly oriented high viscosity CNTs in epoxy resins.

This study represents a cost-effective method to advance the physical and mechanical properties of carbon fiber-reinforced polymer (CFRP) prepreg composite materials, where electrospun multiwalled carbon nanotubes (CNTs)/epoxy nanofibers fabricated and deposited in between the layers of traditional CFRP prepreg composite. CNT-aligned epoxy nanofibers were uniformly formed by an optimized electrospinning method. Electrospinning is considered one of the most flexible, low-cost, and globally recognized methods for generating continuous filaments from submicron to tens of nanometer diameter. Nanofilaments were incorporated precisely on the layers of prepreg to accomplish increased adhesion and interfacial bonding, leading to increased strength and enhancements in more mechanical properties. As a result, the modulus of the epoxy and CNT/epoxy nanofibers were revealed to be 3.24 GPa and 4.84 GPa, leading to 49% enhancement. Furthermore, interlaminar shear strength (ILSS) and fatigue performance at high-stress regimes improved by 29% and 27%, respectively. Barely visible impact damage (BVID) energy improved considerably by up to 45%. The thermal and electrical conductivities were also increased considerably because of the highly conductive CNT networks present in between the CFRP layers. The newly introduced approach was able to deposit high content uniform CNTs at the ply interface of prepregs to enhance the CFRP properties, that has not been achieved in the past because of the randomly oriented high viscosity CNTs in epoxy resins.

One of the aim of this study is to prepare conductive polymer nanocomposites of polypropylene to obtain better mechanical and electrical properties. Composite materials based on conductive fillers dispersed within insulating thermoplastic matrices have wide range of application. For this purpose, conductive polymer nanocomposites of polypropylene with nano dimentional conductive fillers like carbon black, carbon nanotube and fullerene were prepared. Their mechanical, electrical and thermal properties were investigated. Polypropylene (PP)/carbon black (CB) composites at different compositions were prepared via melt blending of PP with CB. The effect of CB content on mechanical and electrical properties was studied. Test samples were prepared by injection molding and compression molding techniques. Also, the effect of processing type on mechanical and electrical properties was investigated. Composites become semiconductive with the addition of 2 wt% CB. Polypropylene (PP) / Carbon Nanotube (CNT) and Polypropylene / Fullerene composites were prepared by melt mixing. CNT&rsquo / s and fullerenes were surface functionalized with HNO3 : H2SO4 before composite preparation. The CNT and fullerene content in the composites were varied as 0.5, 1.0, 2.0 and 3.0 % by weight. For the composites which contain surface modified CNT and fullerene four different compatibilizers were used. These were selected as TritonX-100, Poly(ethylene-block-polyethylene glycol), Maleic anhydride grafted Polypropylene and Cetramium Bromide. The effect of surface functionalization and different compatibilizer on mechanical, thermal and electrical properties were investigated. Best value of these properties were observed for the composites which were prepared with maleic anhydride grafted polypropylene and cetramium bromide. Another aim of this study is to built and characterize transistors which have polyethylene as dielectric layers. While doing this, polyethylene layer was deposited on gate electrode using vacuum evaporation system. Fullerene , Pentacene ve Indigo were used as semiconductor layer. Transistors work with low voltage and high on/off ratio were built with Aluminum oxide - PE and PE dielectrics.

Σκοπός της παρούσας Πτυχιακής Εργασίας είναι ανάπτυξη μιας διαδικασίας παρασκευής νανοσύνθετων εποξικής ρητίνης/ πολλαπλών νανοσωληνίσκων άνθρακα (MWCNT) σε ένα εύρος περιεκτικοτήτων από 0.1 έως και 1 % κατά βάρος (κ.β) MWCNT. Τα εμποτισμένων δοκίμια έναντι αυτών της καθαρής ρητίνης παρουσίασαν ενισχυμένες μηχανικές ιδιότητες όπως αντοχή σε εφελκυσμό και αυξημένο μέτρο ελαστικότητας. Η αύξηση αυτή μπορεί να αποδοθεί στο υψηλό λόγο μήκους /διαμέτρου καθώς και στην μεγάλη ελεύθερη επιφάνεια των νανοσωληνίσκων (CNTs). Επίσης από τα πειράματα δυναμικής ανάλυσης παρατηρήθηκε αύξηση της θερμοκρασίας υαλώδους μετάβασης με την αύξηση της περιεκτικότητας των CNTs. Στα πλαίσια της ίδιας εργασίας μελετήθηκαν οι ηλεκτρικές ιδιότητες καθώς και οι αισθητήριες ιδιότητες των MWCNT και εξερευνήθηκε η χρήση τους ως νανοαισθητήρες για την παρακολούθηση βλάβης στην εμποτισμένη εποξική ρητίνη. Για τον σκοπό αυτό πραγματοποιήθηκαν πειράματα φόρτισης-αποφόρτισης μονοαξονικού εφελκυσμού με ταυτόχρονη παρακολούθηση της ηλεκτρικής αντίστασης του δοκιμίου. Από την παραπάνω διαδικασία παρατηρήθηκε πως όσο μεγαλύτερη είναι η περιεκτικότητα CNTs στην ρητίνη, τόσο μεγαλύτερη είναι η ευαισθησία της ηλεκτρικής αντίστασης στις αλλαγές του εφαρμοζόμενου φορτίου. Σημειώνεται επίσης πως η εμποτισμένη σε CNTs εποξική ρητίνη παρουσιάζει ηλεκτρική αγωγιμότητα παρουσιάζοντας σε περιεκτικότητα 1% κ.β συμπεριφορά αγωγού, γεγονός που οφείλεται στην αγώγιμη φύση των CNTs. Από τις μετρήσεις ηλεκτρικής αγωγιμότητας παρατηρήθηκε πως το «κατώφλι» αγωγιμότητας επιτυγχάνεται σε περιεκτικότητα 0.3% κ.β MWCNT ενώ, επιβεβαιώνεται η ισχύς της θεωρίας «διήθησης» : σ~ (V-Vc)t δίνοντας τιμή «κρίσιμου» εκθέτη t ίση με 2.05. / The goal of the present study is the development of a manufacturing process of epoxy resin compounds with several multi-wall carbon nanotube (MWCNT) contents per weight. Enhanced mechanical properties of the doped specimens epoxy against the neat epoxy testpieces e.g. tensile strength and modulus of elasticity was achieved and attributed to the high surface area and high aspect ratio of the nanotubes. Moreover the dynamic properties of the nano-doped epoxy polymers were investigated and the relation of glass transition temperature with increasing CNT content was found to be inverse. Another goal of the present work was to use the electrical/sensing properties of MWCNTs as a nano-sensor for the damage detection within the doped matrix material. Therefore loading-unloading tensile tests were performed, along with on-line conductivity monitoring for the nano-doped epoxy polymers. It was noted that all the nano-doped samples were more sensitive to load changes and thus resistance changes. The higher the CNT content per weight was, the higher the sensitivity in load changes. The conductive nature of CNTs has produced conductive epoxy polymers, which exhibit “percolation threshold” at the content of 0.3% wt. MWCNT and enhanced sensing properties. The measurements of electrical conductivity confirm the validity of “percolation” theory: σ~ (V-Vc)t with the critical exponent t equal to 2.05.