The thesis relates to synthesis and investigation of nanostructured polymer composites based on oligomers of cyanate esters of bisphenol a (DCBA) or cyclic butylene terephthalate (CBT) and multiwalled carbon nanotubes (MWCNTS). Catalytic effect of mwcnts in process of DCBA polycyclotrimerization as well as in cbt polymerization has been observed. Significant increase in crystallization temperature of nanocomposites based on polybutylene terephthalate (cPBT) with adding of MWCNTS is observed. The effect of processing method of cpbt/mwcnts nanocomposites on its electrical properties has been found. It has been established that the additional heating of the samples (annealing) at temperatures above melting of cPBT leads to reagglomeration of MWCNTS in the system. It is established that reagglomeration of MWCNTS results in increase of conductivity values of nanocomposites due to formation of percolation pathways of MWCNTS through polymer matrix. In the case of polycyanurate matrix (PCN), it is found that addition of small mwcnts contents (0.03-0.06 weight percents) provides increasing tensile strength by 62-94 percents. It has been found that addition of even 0.01 weight percents of MWCNTS provides significant increase in storage modulus of cPBT matrix. This is explained by effective dispersing of small amount of the nanofiller during in situ synthesis of pcn or cpbt matrix that is confirmed by microscopy techniques. It has been established that the properties of the nanocomposites based on heterocyclic esters and MWCNTS can be varied from isolator to conductor and has low percolation thresholds (0.22 and 0.38 weight percents for cPBT and PCN nanocomposites respectively). The conductivity of samples is particularly stable on a very large range of temperature from 300 to 10 degrees Kelvin that make these materials perspective for practical applications in microelectronics, as parts of aircraft and space constructions.

For the commercial success of polymer - multiwalled carbon nanotube (MWNT) composites the production of these materials on industrial scale by melt processing is of significant importance. The complete dispersion of primary MWNT agglomerates in a polymer melt is difficult to achieve, making it an important and challenging technological problem. Hence, it is necessary to understand the process of MWNT agglomerate dispersion in a polymer melt. Based on an intensive literature research on mechanisms and influencing factors on dispersion of other agglomerated nanostructured fillers (e.g. carbon black), the main dispersion steps were evaluated and investigated concerning the agglomerated MWNT.Consequently, systematic investigations were performed to study the effect of the melt infiltration on MWNT agglomerate dispersion and to analyse the corresponding main dispersion mechanisms, namely rupture and erosion. The states of MWNT agglomerate dispersion were assessed by quantifying the agglomerate area ratio and particle size distribution using image analysis of optical transmission micrographs. Additionally, the composite’s electrical resistivity was determined. In the prevailing study, polycarbonates (PC) varying in molecular weight were used to produce composites containing 1 wt% MWNT (Baytubes C150HP) as model systems and a discontinuous microcompounder was applied as melt mixing device. The agglomerate structure of the used MWNT material made them especially suitable for the reported investigations. The step of melt infiltration into the primary nanotube agglomerates plays a crucial role for their dispersion in the PC melt. During melt mixing when low shear rates were applied, better state of MWNT dispersion was obtained in high viscosity matrices because applied shear stresses were high. On the contrary, if high shear rates were applied, similar states of MWNT dispersion were obtained in low and high viscosity matrices although significantly lower shear stresses were applied in the low viscosity matrix as compared to the high viscosity matrix. The results indicate that if the applied shear stress values are compared, with increasing matrix viscosity the agglomerate dispersion gets worsen. This is attributed to the fact that low viscosity matrices can infiltrate relatively faster than high viscosity matrices into the agglomerate making them weaker and reducing the agglomerate strength. Thus, at sufficient shear rates MWNT agglomerates disperse relatively faster in low viscosity matrix. This illustrates a balance between the counteracting effects of viscosity on agglomerate infiltration and agglomerate dispersion. Additionally, the effect of matrix molecular weight on the size of un-dispersed MWNT agglomerates was investigated. Under similar conditions of applied shear stress, the composites based on low molecular weight matrix showed smaller sized un-dispersed primary agglomerates as compared to composites with higher molecular weight matrices. This again highlights the role of matrix infiltration as the first step of dispersion. Following the step of melt infiltration, agglomerate size gets reduced due to the dispersion mechanisms. To analyse the corresponding contributions of different dispersion mechanisms (rupture and erosion), the kinetics of MWNT agglomerate dispersion was investigated. If high mixing speeds are employed dispersion is quite fast and needs less time as compared to low mixing speed. A model is proposed to estimate the fractions of rupture and erosion mechanisms during agglomerate dispersion based on the kinetic study in the discontinuous mixer. Under the employed experimental conditions, at high mixing speeds, the dispersion was found to be governed by rupture dominant mechanism, whereas at low mixing speeds the dispersion was controlled by both mechanisms. As far as electrical resistivity is concerned, for a given content of MWNT as the state of dispersion improves, the resistivity values decrease significantly but only up to a plateau value. The composites produced using low viscosity matrices have lower resistivity values as compared to high viscosity matrices. Additionally, composites were prepared using additives, whereas the additives were found to be useful for improving filler dispersion and electrical conductivity.

<p>Cilj ove doktorske disertacija&nbsp; bio je razvoj&nbsp; novih, osetljivih, selektivnih i ekonomski<br />isplativih&nbsp; voltametrijskih&nbsp; radnih&nbsp; elektroda&nbsp; za&nbsp; praćenje&nbsp; odabranih&nbsp; analita&nbsp; kako&nbsp; u<br />laboratorijskim tako i pri terenskim uslovima.&nbsp; Ispitivana je&nbsp; mogućnost primene&nbsp; ovih&nbsp; radnih&nbsp; elektroda&nbsp; primenom&nbsp; voltametrijskih&nbsp; metoda&nbsp; kako&nbsp; u&nbsp; model&nbsp; rastvorima&nbsp; tako&nbsp; i&nbsp; u&nbsp; pojedinim realnim sistemima. SW-ASV&nbsp; zasnovana&nbsp; na&nbsp; elektrodama&nbsp; od&nbsp; staklastog&nbsp; ugljenika&nbsp; povr&scaron;inski modifikovanim&nbsp; Bi-MWCNT&nbsp; i&nbsp; BiOCl-MWCNT&nbsp; je&nbsp; primenjena&nbsp; za&nbsp; određivanje&nbsp; jona&nbsp; Pb(II)&nbsp; i Cd(II)&nbsp; pri&nbsp; optimizovanim&nbsp; uslovima&nbsp; merenja.&nbsp; Određivanje&nbsp; ciljnih&nbsp; jona&nbsp; vr&scaron;eno&nbsp; je&nbsp; pri&nbsp; radnom potencijalu&nbsp; od&nbsp; -1,2&nbsp; V&nbsp; (izmeren&nbsp; u&nbsp; odnosu&nbsp; na&nbsp; zasićenu&nbsp; kalomelovu&nbsp; elektrodu)&nbsp; i&nbsp; vremenu<br />elektrodepozicije jona&nbsp; od 120 s. Sva merenja su izvr&scaron;ena u rastvoru acetatnog pufera čija je pH-vrednost iznosila&nbsp; 4,0. Primenjeni koncentracioni opseg ciljnih analita iznosio je&nbsp; od 5 do 50&nbsp; &mu;g&nbsp; dm ^-3 .&nbsp; Primenom&nbsp; ovog&nbsp; tipa&nbsp; elektrode&nbsp; dobijene&nbsp; su&nbsp; vrednosti&nbsp; granice&nbsp; detekcije&nbsp; za&nbsp; jone Pb(II) i Cd(II) 0,57&nbsp; &mu;g dm ^-3i 1,2 &mu;g dm^-3 , redom. Dobijena RSD iznosila je manje od 10% za oba&nbsp; jona.&nbsp; Ova&nbsp; metoda&nbsp; je&nbsp; primenjena&nbsp; i&nbsp; za&nbsp; određivanje&nbsp; ciljnih&nbsp; jona&nbsp; u&nbsp; realnom&nbsp; uzorku&nbsp; porne vode&nbsp; sedimenta&nbsp; a&nbsp; rezultati&nbsp; dobijeni&nbsp; optimizovanom&nbsp; voltametrijskom&nbsp; metodom&nbsp; su&nbsp; u&nbsp; dobroj saglasnosti sa rezultatima koji su dobijeni primenom komparativne GFAAS metode. Bizmut oksihlorid-vi&scaron;ezidne ugljenične nanocevi kompozitni materijal je primenjen za povr&scaron;insko&nbsp; modifikovanje&nbsp; elektrode&nbsp; od&nbsp; staklastog&nbsp; ugljenika&nbsp; za&nbsp; brzo&nbsp; i&nbsp; jednostavno voltametrijsko&nbsp; određivanje&nbsp; tragova&nbsp; Zn(II)-jona&nbsp; primenom&nbsp; SW-ASV&nbsp; metode.&nbsp; BiOClMWCNT/GCE je pokazala linearan analitički odgovor u&nbsp; osegu koncentracija od&nbsp; 2,50 do&nbsp; 80,0 &mu;g&nbsp; dm ^-3sa dobijenom vredno&scaron;ću GD 0,75 &mu;g&nbsp; dm^-3pri akumulacionom vremenu od&nbsp; 120 s&nbsp; i potencijalu&nbsp; elektrodepozicije&nbsp; -1,40&nbsp; V&nbsp; u&nbsp; odnosu&nbsp; na&nbsp; ZKE.&nbsp; Merenja&nbsp; su&nbsp; vr&scaron;ena&nbsp; u&nbsp; acetatnom puferu pH 4,5. Dobijena RSD iznosila je 4,8 %. Upoređene su performanse novodizajnirane BiOCl-MWCNT/GCE elektrode&nbsp; i&nbsp; tradicionalne elektrode na bazi bizmut filma (BiF/GCE), MWCNT/GCE,&nbsp; BiF-MWCNT/GCE&nbsp; i&nbsp; nemodifikovane&nbsp; GC&nbsp; elektrode.&nbsp; Novodizajnirana elektroda je primenjena za&nbsp; detekciju&nbsp; i određivanje&nbsp; Zn(II)-jona&nbsp; u realnim&nbsp; uzorcima kao &scaron;to su<br />dijetetski&nbsp; suplement&nbsp; i&nbsp; pekarski&nbsp; kvasac.&nbsp; Dobijeni&nbsp; rezultati&nbsp; su&nbsp; uporedivi&nbsp; sa&nbsp; deklarisanom vredno&scaron;ću&nbsp; u&nbsp; slučaju&nbsp; dijetetskog&nbsp; suplementa&nbsp; a&nbsp; u&nbsp; slučaju&nbsp; pekarskog&nbsp; kvasca&nbsp; sa&nbsp; rezultatima dobijenih komparativnom FAAS .<br />Elektroda od ugljenične paste je povr&scaron;inski modifikovana pripremljenim kompozitom<br />koji je&nbsp; izgrađen od vi&scaron;ezidnih ugljeničnih nanocevi i čestica&nbsp; Sb₂O_3.&nbsp; Kompozitni&nbsp; materijal&nbsp; je okarakterisan&nbsp; primenom&nbsp; TEM,&nbsp; EDS&nbsp; i&nbsp; XRD&nbsp; mernih&nbsp; tehnika.&nbsp; Sb₂O₃-MWCNT/CPE&nbsp; je okarakterisana primenom ciklične voltametrije a merenja su vr&scaron;ena u rastvoru hlorovodonične kiseline&nbsp; (pH&nbsp; 2,0).&nbsp; Primenom&nbsp; SW-ASV&nbsp; metode&nbsp; ova&nbsp; radna&nbsp; elektroda&nbsp; je&nbsp; upotrebljena&nbsp; za određivanje&nbsp; jona Pb(II) i Cd(II)&nbsp; u&nbsp; koncentracionom opsegu 2,0-40,0&nbsp; &mu;g&nbsp; dm&nbsp; ^-3za&nbsp; Pb(II)-jon&nbsp; i 2,0-40,0&nbsp; &mu;g&nbsp; dm ^-3 za&nbsp; Cd(II)-jon&nbsp; pri&nbsp; čemu&nbsp; su&nbsp; dobijene&nbsp; dobre&nbsp; linearne&nbsp; zavisnosti&nbsp; za&nbsp; oba&nbsp; ciljna jona.&nbsp; Optimalna&nbsp; procedura&nbsp; uključuje&nbsp; primenu&nbsp; Sb2O3-MWCNT/CPE&nbsp; u&nbsp; 0,01&nbsp; mol dm ^-3<br />hlorovodoničnoj kiselini uz vreme elektrodepozicije jona iz rastvora od 120&nbsp; s&nbsp; na&nbsp; potencijaluod&nbsp; -1,2&nbsp; V,&nbsp; pri&nbsp; čemu&nbsp; su&nbsp; dobijene&nbsp; vrednosti&nbsp; za&nbsp; GD&nbsp; 1,1&nbsp; &mu;g&nbsp; dm ^-3 Cd(II)&nbsp; i&nbsp; 1,6&nbsp; &mu;g&nbsp; dm ^-3 Pb(II). Optimizovana&nbsp; metoda&nbsp; zasnovana&nbsp; na&nbsp; ovom&nbsp; tipu&nbsp; voltametrijskog&nbsp; senzora&nbsp; je&nbsp; uspe&scaron;no primenjena&nbsp; za&nbsp; određivanje&nbsp; jona&nbsp; Cd(II)&nbsp; u&nbsp; obogaćenom&nbsp; uzorku&nbsp; česmenske&nbsp; vode,&nbsp; gde&nbsp; su&nbsp; se dobijene vrednosti u&nbsp; saglasnosti sa očekivanom. Elektroda od ugljenične paste povr&scaron;inski je&nbsp; modifikovana primenom&nbsp; Sb₂O₃-MWCNT nanokompozitnog&nbsp; materijala&nbsp; i&nbsp; primenjena&nbsp; za&nbsp; direktno&nbsp; voltametrijsko&nbsp; određivanje imidakloprida&nbsp; u&nbsp; model&nbsp; rastvorima.&nbsp; U&nbsp; cilju&nbsp; postizanja&nbsp; &scaron;to&nbsp; boljih&nbsp; analitičkih&nbsp; performansi optimizovani su eksperimentalni uslovi merenja kao &scaron;to su pH-vrednost rastvora pomoćnog elektrolita&nbsp; i&nbsp; kondicioniranje&nbsp; povr&scaron;ine&nbsp; voltametrijskog&nbsp; senzora.&nbsp; Kao&nbsp; optimalna&nbsp; pH-vrednost pomoćnog elektolita (Britton-Robinsonovog pufera) odabrana je pH 7,0, a ponavljanje ciklusa cikliranja najmanje 4 puta povoljno utiče na stabilnost&nbsp; voltametrijskih signala. Optimizovana metoda primenjena je za SW direktno katodno određivanje imidakloprida u koncentracionom intervalu od 1,41 do 32,77 &mu;g cm ^-3 uz dobijeni korelacioni faktor od 0,9995. Na osnovu dobijenih rezultata može se zaključiti da su razvijene analitičke metode pre svega&nbsp; osetljive,&nbsp; selektivne,&nbsp; reproduktivne&nbsp; i&nbsp;&nbsp; jednostavne&nbsp; &scaron;to&nbsp; omogućava&nbsp; njihovu&nbsp; primenu&nbsp; za veliki broj uzoraka.&nbsp; Merenjima u model i realnim rastvorima dokazana je mogućnost njihove primene&nbsp; u&nbsp;&nbsp; komplikovanim&nbsp; matriksima,&nbsp; pri&nbsp; različitim&nbsp; pH&nbsp; vredostima&nbsp; pri&nbsp; čemu&nbsp; su&nbsp; dobijeni<br />rezultati koji su u saglasnosti sa rezultatima primenjenih komparativnih metoda. Naravno, za dobijanje&nbsp; reprezentativnih&nbsp; rezultata&nbsp; neohodno&nbsp; je&nbsp; izvr&scaron;iti&nbsp; optimizaciju&nbsp; uslova&nbsp; merenja&nbsp; &scaron;to podrazumeva sam odabir supstrat-elektrode, odabir povr&scaron;inskog modifikatora i optimizaciju eksperimentalnih uslova merenja.</p> / <p>The&nbsp; aim of this&nbsp; Ph.D. thesis&nbsp; was the development of new, sensitive, selective and economically&nbsp; viable&nbsp; voltametric&nbsp; working&nbsp; electrode&nbsp; for&nbsp; continuous&nbsp; monitoring&nbsp; of&nbsp; different target&nbsp; analytes.&nbsp; The&nbsp; use&nbsp; of&nbsp; these&nbsp; advantaged&nbsp; working&nbsp; electrodes&nbsp; was&nbsp; investigated&nbsp; using voltametric methods both in model solutions and in certain real systems.SW-ASV&nbsp; based on glassy carbon&nbsp; electrode surface modified with&nbsp; Bi- MWCNT and BiOCl-MWCNT&nbsp; were&nbsp; applied&nbsp; for&nbsp; determination&nbsp; of&nbsp; Pb(II)&nbsp; and&nbsp; Cd(II)&nbsp; ions.&nbsp; Voltametric determination&nbsp; of&nbsp; Pb(II)&nbsp; and&nbsp; Cd(II)&nbsp; ions&nbsp; was&nbsp; performed&nbsp; at&nbsp; working&nbsp; potential&nbsp; of&nbsp; -1.2&nbsp; V (measured against the saturated calomel electrode) and time of electrodeposition of 120 s. All measurements were performed in acetate buffer solution pH 4.0. Concentration range of targetanalites were&nbsp; 5-50 &mu;g&nbsp; dm -3 . Using this type of electrode,&nbsp; obtained&nbsp; detection limits for&nbsp; Pb(II) and Cd(II) ions&nbsp; were&nbsp; 0.57&nbsp; &mu;g&nbsp; dm -3 and 1.2&nbsp; &mu;g&nbsp; dm -3 , respectively, with RSD lower than 10%.This&nbsp; method&nbsp; was&nbsp; applied&nbsp; for&nbsp; target&nbsp; ions&nbsp; determination&nbsp; in&nbsp; sediment&nbsp; pore&nbsp; water&nbsp; sample,&nbsp; and obtained results are comparable with those who are obtained using GFAAS method. Bismuth oxychloride-multiwalled carbon nanotubes composite material was applied for&nbsp; surface&nbsp; modification&nbsp; of&nbsp; the&nbsp; glass-carbon&nbsp; electrode&nbsp; for&nbsp; quick&nbsp; and&nbsp; simple&nbsp; voltametric determination&nbsp; of&nbsp; Zn(II)&nbsp; ions&nbsp; using&nbsp; the&nbsp; SW-ASV&nbsp; method.&nbsp; BiOCl-MWCNT/GCE&nbsp; showed&nbsp; a linear&nbsp; analytical&nbsp; response&nbsp; in&nbsp; a&nbsp;&nbsp; concentration&nbsp; from&nbsp; 2.50&nbsp; to&nbsp; 80.0&nbsp; &mu;g&nbsp; dm -3 with&nbsp; a&nbsp; value&nbsp; of detection limit 0.75 &mu;g dm -3 at a acumulation time of 120 s and an electrodeposition potential of&nbsp; -1.40 V vs. saturated&nbsp; calomel electrode.&nbsp; Measurements were carried out in acetate buffer pH 4.5. The obtained&nbsp; value of the RSD&nbsp; was&nbsp; 4.8%. The performance of the newly designed BiOCl-MWCNT/GCE&nbsp; electrode,&nbsp; traditional&nbsp; bismuth-based&nbsp; electrode&nbsp; (BiF/GCE), MWCNT/GCE,&nbsp; BiF-MWCNT/GCE&nbsp; and&nbsp; unmodified&nbsp; GC&nbsp; electrodes&nbsp; were&nbsp; compared.&nbsp; The applied electrode shows very good electroanalytic properties when determining this target ion. Obtained results are in good agreement with declared value in case of dietetic suplement, and in the brewer&rsquo;s yeast sample results were comparable with FAAS results. Carbon&nbsp; paste&nbsp; electrode&nbsp; surface&nbsp; modified&nbsp; with&nbsp; new&nbsp; composite&nbsp; material&nbsp; based&nbsp; on multiwalled carbon nanotubes and&nbsp; Sb2O3&nbsp; particles. The composite is characterized by TEM, EDS and&nbsp; XRD measurment. Sb2O3- MWCNT/CPE was characterized by cyclic voltammetry and measurements were carried out in a&nbsp; hydrochloric acid&nbsp; solution&nbsp; (pH 2.0). Using the SWASV&nbsp; method,&nbsp; this&nbsp; working&nbsp; electrode&nbsp; was&nbsp; used&nbsp; to&nbsp; determine&nbsp; Pb(II),&nbsp; Cd(II)&nbsp; ions&nbsp; in&nbsp; the concentration range&nbsp; from&nbsp; 2.0&nbsp; to 40.0&nbsp; &mu;g dm -3 for Pb(II) and 2.0-40.0&nbsp; &mu;g dm -3 for Cd(II) ions. Newly&nbsp; designed&nbsp; sensor&nbsp; showed&nbsp; good&nbsp; linear&nbsp; dependences&nbsp; for&nbsp; both&nbsp; target&nbsp; ions.&nbsp; The&nbsp; most optimal&nbsp; procedure&nbsp; involving&nbsp; application&nbsp; of&nbsp; Sb2O3-MWCNT/CPE&nbsp; in&nbsp;&nbsp; .01&nbsp; mol&nbsp; dm -3 hydrochloric&nbsp; acid,&nbsp; with&nbsp; electroposition&nbsp; time&nbsp; of&nbsp; target&nbsp; ions&nbsp; 120&nbsp; s&nbsp; at&nbsp; a&nbsp; electrodeposition potential&nbsp; of&nbsp; -1.2&nbsp; V.&nbsp; Obtained&nbsp;&nbsp; values&nbsp; of&nbsp;&nbsp;&nbsp; LOD&nbsp; 1,1&nbsp; &mu;g&nbsp; dm -3 for&nbsp; Cd(II)&nbsp; and&nbsp; for&nbsp; 1,6&nbsp; &mu;g&nbsp; dm -3 Pb(II)&nbsp; ions.&nbsp; An&nbsp; optimized&nbsp; method&nbsp; based&nbsp; on&nbsp; this&nbsp; type&nbsp; of&nbsp; voltametric&nbsp; sensor&nbsp; has&nbsp; been successfully&nbsp; applied&nbsp; for&nbsp; determination&nbsp; of&nbsp; Cd(II)&nbsp; ion&nbsp; in&nbsp; a&nbsp; spiked&nbsp; tap&nbsp; water&nbsp; sample.&nbsp; Results obtained during this measurment were in tune with expected results. CPE&nbsp; was&nbsp; surface&nbsp; modified&nbsp; using&nbsp; Sb2O3-MWCNT&nbsp; nanocomposite&nbsp; material&nbsp; and tested&nbsp; for&nbsp; direct&nbsp; voltametric&nbsp; determination&nbsp; of&nbsp; imidacloprid&nbsp; in&nbsp; model&nbsp; solutions.&nbsp; In&nbsp; order&nbsp; to achieve the best analytical performance, experimental conditions of measurement such as the pH value of the supporting electrolyte and conditioning of the voltametric sensor surface havebeen&nbsp; optimized.&nbsp; As&nbsp; an&nbsp; optimum&nbsp; pH&nbsp; value&nbsp; of&nbsp; the&nbsp; supporting&nbsp; electrolyte&nbsp; (Britton-Robinson buffer), a pH 7.0 was selected, and the repeating cycles of the cycling process at least 4 times favorably&nbsp; influenced&nbsp; the&nbsp; stability&nbsp; of&nbsp; the&nbsp; voltametric&nbsp; signals.&nbsp; The&nbsp; optimized&nbsp; method&nbsp; was applied for the SW direct cathodic determination&nbsp; of&nbsp; imidacloprid in the concentration range from 1.41 to 32.77 &mu;g cm -3&nbsp; with obtained correlation factor of 0.9995. Based on results it can be concluded that developed analytical methods are sensitive, selective, reproducibile and simple, which can enable their application for various number of samples. Measurements in the model and real solutions have demonstrated the possibility of their&nbsp; application&nbsp; in&nbsp; complicated&nbsp; matrices,&nbsp; at&nbsp; different&nbsp; pH,&nbsp; whereby&nbsp; obtained&nbsp; results&nbsp; are&nbsp; in accordance&nbsp; with&nbsp; the&nbsp; results&nbsp; of&nbsp; the&nbsp; applied&nbsp; comparative&nbsp; methods.&nbsp; For&nbsp; obtainig&nbsp; of representative&nbsp; results&nbsp; it&nbsp; is&nbsp; necessary&nbsp; to&nbsp; optimize&nbsp; conditions&nbsp; of&nbsp; measurment&nbsp; which&nbsp; include: selection of substrat electrode, surface modifier and optimization of experimental condition.</p>

For the commercial success of polymer - multiwalled carbon nanotube (MWNT) composites the production of these materials on industrial scale by melt processing is of significant importance. The complete dispersion of primary MWNT agglomerates in a polymer melt is difficult to achieve, making it an important and challenging technological problem. Hence, it is necessary to understand the process of MWNT agglomerate dispersion in a polymer melt. Based on an intensive literature research on mechanisms and influencing factors on dispersion of other agglomerated nanostructured fillers (e.g. carbon black), the main dispersion steps were evaluated and investigated concerning the agglomerated MWNT.Consequently, systematic investigations were performed to study the effect of the melt infiltration on MWNT agglomerate dispersion and to analyse the corresponding main dispersion mechanisms, namely rupture and erosion. The states of MWNT agglomerate dispersion were assessed by quantifying the agglomerate area ratio and particle size distribution using image analysis of optical transmission micrographs. Additionally, the composite’s electrical resistivity was determined. In the prevailing study, polycarbonates (PC) varying in molecular weight were used to produce composites containing 1 wt% MWNT (Baytubes C150HP) as model systems and a discontinuous microcompounder was applied as melt mixing device. The agglomerate structure of the used MWNT material made them especially suitable for the reported investigations. The step of melt infiltration into the primary nanotube agglomerates plays a crucial role for their dispersion in the PC melt. During melt mixing when low shear rates were applied, better state of MWNT dispersion was obtained in high viscosity matrices because applied shear stresses were high. On the contrary, if high shear rates were applied, similar states of MWNT dispersion were obtained in low and high viscosity matrices although significantly lower shear stresses were applied in the low viscosity matrix as compared to the high viscosity matrix. The results indicate that if the applied shear stress values are compared, with increasing matrix viscosity the agglomerate dispersion gets worsen. This is attributed to the fact that low viscosity matrices can infiltrate relatively faster than high viscosity matrices into the agglomerate making them weaker and reducing the agglomerate strength. Thus, at sufficient shear rates MWNT agglomerates disperse relatively faster in low viscosity matrix. This illustrates a balance between the counteracting effects of viscosity on agglomerate infiltration and agglomerate dispersion. Additionally, the effect of matrix molecular weight on the size of un-dispersed MWNT agglomerates was investigated. Under similar conditions of applied shear stress, the composites based on low molecular weight matrix showed smaller sized un-dispersed primary agglomerates as compared to composites with higher molecular weight matrices. This again highlights the role of matrix infiltration as the first step of dispersion. Following the step of melt infiltration, agglomerate size gets reduced due to the dispersion mechanisms. To analyse the corresponding contributions of different dispersion mechanisms (rupture and erosion), the kinetics of MWNT agglomerate dispersion was investigated. If high mixing speeds are employed dispersion is quite fast and needs less time as compared to low mixing speed. A model is proposed to estimate the fractions of rupture and erosion mechanisms during agglomerate dispersion based on the kinetic study in the discontinuous mixer. Under the employed experimental conditions, at high mixing speeds, the dispersion was found to be governed by rupture dominant mechanism, whereas at low mixing speeds the dispersion was controlled by both mechanisms. As far as electrical resistivity is concerned, for a given content of MWNT as the state of dispersion improves, the resistivity values decrease significantly but only up to a plateau value. The composites produced using low viscosity matrices have lower resistivity values as compared to high viscosity matrices. Additionally, composites were prepared using additives, whereas the additives were found to be useful for improving filler dispersion and electrical conductivity.

Cellular internalization of large therapeutic agents such as proteins or nucleic acids is a challenging task because of the presence of the plasma membrane. One strategy to facilitate intracellular drug uptake is to induce transient pores in the cell membrane through physical delivery strategies. Physical approaches are attractive as they offer more generic applicability compared with viral or biochemical counterparts. Pulsed laser light can induce the endothermic carbon-steam reaction in carbon-nanoparticle suspensions to produce explosive photoacoustic effects in the surrounding medium. In this study, for the first time, these photoacoustic forces were used to transiently permeabilize the cell membrane to deliver macromolecules into cells. Intracellular delivery using this method was demonstrated in multiple cell types for uptake of small molecules, proteins and DNA. At optimized conditions, uptake was seen in up to 50% of cells with nearly 100% viability and in 90% of cells with ≥90% viability, which compared favorably with other physical methods of drug delivery. Cellular bioeffects were shown to be a consequence of laser-carbon interaction and correlated with properties of the carbon and laser, such as carbon concentration and size, laser pulse duration, wavelength, intensity and exposure time. Similar results were observed using two different lasers, a femtosecond Ti: Sapphire laser and a nanosecond Nd: YAG laser. Uptake was also shown in murine skeletal muscles in vivo with up to 40% efficiency compared to non-irradiated controls. This synergistic use of nanotechnology with advanced laser technology could provide an alternative to viral and chemical-based drug and gene delivery.

Segmental chain dynamics in polymer blends is a very important topic, not only from a fundamental point of view but also from technological applications. Because of the difficulties in the commercialization of new polymers, industries have turned increasingly towards blending of polymers to optimise their end use (mechanical, rheological) properties. The design of tailor-made materials would be enormously facilitated by the understanding of the blending phenomena at a molecular level. The key question to address is to understand the dynamics of each component of the blend modified by blending? The thesis has systematically studied the effect of multiwalled carbon nanotubes on the chain dynamics, demixing temperature, structural properties and evolution of morphology in a classical miscible polymer blend system (PVDF/PMMA). The thesis comprises of six chapters, Chapter 1 is an introductory chapter that outlines the fundamentals of polymer blends, crystallisation in polymer blends and the basics of dielectric spectroscopy. As one of the rationales of this work is to systematic study whether phase separated in these blends can be used as a tool to develop membrane for water purification. This chapter also gives an overview of the reported studies of ultrafiltration membrane fabrication, factors affecting membrane morphology and flux. In Chapter 2, the materials and methodology used to carry out experiments and the experimental procedures are discussed. Chapter 3 discusses the effect of concentration of PMMA and amine functionalized multiwalled carbon nanotubes (MWNTs) on the crystallisation induced phase separation using FTIR, XRD, POM and shear rheology. Electron microscopy and selective etching confirmed the localisation of MWNTs in the PVDF phase of the blends. Blends with MWNTs facilitated in heterogeneous nucleation manifesting in an increase in crystallisation temperature. The crystallisation induced phase separation in PVDF/PMMA blends was observed to influence the interconnected network of MWNTs in the blends. Chapter 4 discuss the effect of concentration of PMMA and MWNTs on the miscibility and the segmental relaxations was probed in situ by DSC and dielectric relaxation spectroscopy (DRS). The dynamic heterogeneity in the blends as manifested by the presence of an extra relaxation at a higher frequency at or below the crystallisation induced phase separation temperature was also discussed. We found that PVDF/PMMA blend (PVDF ≥ 80 wt%) exhibits three distinct relaxations; αc corresponding to crystalline PVDF, αβ segmental relaxation of PMMA and αm of amorphous miscibility whereas all relaxations overlap and constitute a single broad relaxation in PVDF/PMMA blend (PVDF ≤ 70 wt%). This confirms that there is a certain composition width in this blend wherein three distinct relaxations can be traced. This could due to many reasons like the width of crystal-amorphous interphase in the crystal lamellae, crystal size and morphology is strongly contingent on the concentration of PMMA. Relaxations are not very distinct in presence of MWNTs due to defective spherulites that shift the relaxations towards a higher frequency. Chapter 5 has attempted to tune the microporous morphology of PVDF membranes using crystallisation induced phase separation in PVDF/PMMA blends. As PVDF/PMMA is a melt-miscible blend, the samples were allowed to crystallise and the amorphous PMMA phase, which isolates in the interlamellar or inter-spherulitic regions in the blends, was etched out to generate microporous structures. The pore sizes can be tuned by varying the PMMA concentration in the blends. We observed that 60/40 PVDF/PMMA blends showed larger pores as compared to 90/10 PVDF/PMMA blends. We further modified PVDF membranes by sputtering silver on the surface. The bacterial cell viability was distinctly suppressed (99 %) in silver sputtered membranes. The ICP analysis suggests that slow Ag+ ions release from the sputtered membrane surface assisted in developing antibacterial surface. Our findings open new avenues in designing water filtration membranes and also help in understanding the crystallisation kinetics for tuning pore size in membranes. Chapter 6 summarises the important results of this work. MWNTs act as hetero nucleating agent and specifically interact with PVDF thereby influences the dynamics of PVDF chains. MWNTs can also restrict the amorphous segmental mobility and can influence the intermolecular cooperativity and coupling. The crystallisation induced phase separation in various blends can result in various crystalline morphologies depending on the PVDF concentration. By selectively etching PMMA from the phase-separated blends, microporous morphology can be generated

Interest in effects of carbonaceous particles in the atmosphere has recently taken an upswing due to knowledge of how these particles affect our environment. Carbonaceous aerosols are characterized by their dark color, giving them the ability to absorb both incoming and outgoing radiation of all wavelengths in the atmosphere. If these particles are deposited on snow or ice they blacken the surface, with an increased rate of melting as a consequence. These particles play a significant role in climate change and it is important to characterize the particles in order to determine their environmental impact and their origin. In this thesis, two non-destructive dielectric measurement approaches for characterizing carbonaceous particles at microwave frequencies were explored: measurements with an impedance analyzer and measurements using a cavity resonator. Measurements were carried out on quartz filters containing concentrations of carbon normally found in snow in northern Scandinavia. To validate the carbon concentration on the filters a field trip to northern Sweden was conducted. Snow samples were collected and analyzed in regards of carbon content, confirming that the amount of carbon on the filters were accurate. The impedance analyzer showed great uncertainty and the results were not precise enough to determine the credibility of the approach. Measurements with the cavity resonator showed some promising results due to its extreme sensitivity but require adjustments to distinguish different particle types from each other. Thus, it is expected that the use of a cavity resonator operating at microwave frequencies will become an applicable method for characterizing carbonaceous particles in the future.

Abstract Carbon nanotubes (CNTs) have extraordinary mechanical and electrical properties. Together with their small dimensions and low density, they are attractive candidates for building blocks in future nanoelectromechanical systems and for many other applications. The extraordinary properties are however only attained by perfectly crystalline CNTs and quickly deteriorate when defects are introduced to the structure. The growth technique affects the crystallinity where in general CNTs grown by arc-discharge are close to perfectly crystalline, while CVD-grown CNTs have large defect densities. Mechanical deformation also affects these properties, even without introducing defects. When CNTs are bent they behave similarly to drinking straws, i.e. they buckle or ripple and their bending stiffness drops abruptly. In this thesis, the mechanical behaviour of individual CNTs and vertically aligned carbon nanofibers (VACNFs) has been studied by performing force measurements inside electron microscopes. Cantilevered CNTs, and VACNFs, were bent using a force sensor, yielding force-deflection curves while their structure was imaged simultaneously. We have found that CNTs grown by arc-discharge have a high enough crystallinity to possess a Young’s modulus close to the ideal value of 1 TPa. CVD-grown CNTs possess a Young’s modulus that is about one order of magnitude smaller, due to their large defect density. The VACNFs are yet another order of magnitude softer as a result of their cup-stacked internal structure.  We also found that a high defect density will increase the critical strain for the rippling onset and the relative post-rippling stiffness. Multi-walled CNTs with a small inner diameter are less prone to ripple and have a larger relative post-rippling stiffness. Our findings show large variations in the onset of rippling and the bending stiffness before and after rippling. These variations open up possibilities of tailoring the mechanical properties for specific applications. / Baksidetext Carbon nanotubes (CNTs) have extraordinary mechanical and electrical properties. Together with their small dimensions and low density, they are attractive candidates for building blocks in nanoelectromechanical systems (NEMS), and many other applications.  In this thesis the mechanical behaviour of individual CNTs and vertically aligned carbon nanofibers has been studied by performing force measurements inside electron microscopes. We have found that the mechanical behaviour is very sensitive to the defect density and the internal structure of the CNTs. The extraordinary properties are only attained by defect free CNTs and quickly deteriorate if defects are introduced to the structure. Mechanical deformations also alter these properties. Single-walled CNTs behave similarly to drinking straws when bent, i.e. they buckle, while the inner tubes of multi-walled CNTs prevent buckling. Instead a more distributed rippling pattern is created for multi-walled CNTs. Both these deformation behaviours will cause an abrupt drop in the bending stiffness, which is detrimental for many applications. The findings in this work will have implications for the design of future NEMS. / <p>Artikel 2 Image formation mechanisms tidigare som manuskript, nu publicerad: urn:nbn:se:kau:diva-16425 (MÅ 150924)</p>

Discovery of grapheme has paved way for experimental realization of many physical phenomena such as massless Dirac fermions, quantum hall effect and zero-field conductivity. Search for other two dimensional (2D) materials led to the discovery of boron nitride, transition metal dichalcogenides(TMDs),transition metal oxides(MO2)and silicene. All of these materials exhibit different electronic and transport properties and are very promising for nanodevices such as nano-electromechanical-systems(NEMS), field effect transistors(FETs),sensors, hydrogen storage, nano photonics and many more. For practical utility of these materials in electronic and photonic applications, varying the band gap is very essential. Tuning of band gap has been achieved by doping, functionalization, lateral confinement, formation of hybrid structures and application of electric field. However, most of these techniques have limitations in practical applications. While, there is a lack of effective method of doping or functionalization in a controlled fashion, growth of specific sized nanostructures (e.g., nanoribbons and quantum dots),freestanding or embedded is yet to be achieved experimentally. The requirement of high electric field as well as the need for an extra electrode is another disadvantage in electric field induced tuning of band gap in low dimensional materials. Development of simpler yet effective methods is thus necessary to achieve this goal experimentally for potential application of these materials in various nano-devices. In this thesis, novel methods for tuning band gap of few 2D materials, based on strain and stacking, have been proposed theoretically using first principles based density functional theory(DFT) calculations. Electronic properties of few layered nanomaterials are studied subjected to mechanical and chemical strain of various kinds along with the effect of stacking pattern. These methods offer promising ways for controlled tuning of band gap in low dimensional materials. Detailed methodology of these proposed methods and their effect on electronic, structural or vibrational properties have also been studied. The thesis has been organized as follows: Chapter1 provides a general introduction to the low dimensional materials: their importance and potential application. An overview of the systems studied here is also given along with the traditional methods followed in the literature to tune their electronic properties. The motivation of the current research work has also been highlighted in this chapter. Chapter 2 describes the theoretical methodology adopted in this work. It gives brief understanding of first principles based Density Functional Theory(DFT) and various exchange and correlation energy functionals used here to obtain electronic, structural, vibrational and magnetic properties of the concerned materials. Chapter 3 deals with finding the origin of a novel experimental phenomenon, where electromechanical oscillations were observed on an array of buckled multiwalled carbon nanotubes (MWCNTs)subjected to axial compression. The effect of structural changes in CNTs in terms of buckling on electronic properties was studied. Contribution from intra-as well as inter-wall interactions was investigated separately by using single-and double-walled CNTs. Chapter 4 presents a method to manipulate electronic and transport properties of graphene bilayer by sliding one of the layers. Sliding caused breaking of symmetry in the graphene bilayer, which resulted in change in dispersion in the low energy bands. A transition from linear dispersion in AA stacking to parabolic dispersion in AB stacking is discussed in details. This shows a possibility to use these slid bilayers to tailor graphene based devices. Chapter 5 develops a method to tune band gap of bilayers of semiconducting transition metal dichalcogenides(TMDs) by the application of normal compressive strain. A reversible semiconductor to metal(S-M) transition was reported in this chapter for bilayers of TMDs. Chapter 6 shows the evolution of S-M transition from few layers to the bulk MoS2 under various in-plane and out of plane strains. S-M transition as a function of layer number has been studied for different strain types. A comparison between the in-plan and normal strain on modifying electronic properties is also presented. Chapter 7 discusses the electronic phase transition of bulk MoS2 under hydrostatic pressure. A hydrostatic pressure includes a combined effect of both in-plane and normal strain on the structure. The origin of metallic transition under pressure has been studied here in terms of electronic structure, density of states and charge analysis. Chapter 8 studies the chemical strain present in boron nitride nanoribbons and its effect on structural, electronic and magnetic properties of these ribbons. Properties of two achiral (armchair and zig-zag) edges have been analyzed in terms of edge energy and edge stress to predict stability of the edges. Chapter9 summarizes and concludes the work presented in this thesis.

La thèse concerne les synthèse et caractérisation de composites polymères nanostructurés à base d’esters de cyanates de bisphénol a (DCBA) ou à base d’oligomères cycliques de butylène téréphtalate (CBT) et de nanotubes de carbone multi-parois (MWCNTS). L’effet catalytique des nanotubes de carbone sur la polycyclotrimerisation de DCBA et aussi sur la polymérisation du CBT est observé. L’augmentation de la température de cristallisation a été fixée pour tous les échantillons de nanocomposites à base de polybutylène téréphtalate (cPBT). L’effet de la méthode de mise en forme de cPBT/MWCNTS sur ses propriétés thermiques et électriques a été établi. Il est observé que le traitement thermique additionnel des échantillons (recuit) à des températures inférieures à celle de la fusion du cPBT cause la réagglomération des MWCNTS dans le système. Il est établi que l’ajout de très bas taux de MWCNTS (0.03-0.06 pour cent en masse) dans la matrice de polycyanurate (PCN) augmente les valeurs de résistance à la flexion (64-94 pour cent). De même l’ajout de 0.01 pourcent de MWCNTS en masse dans le CBT augmente considérablement le module d'élasticité des nanocomposites cPBT. Cet effet a été expliqué par la dispersion efficace de cette faible quantité de nanocharges pendant la synthèse in situ de la matrice de cPBT et est confirmée par les clichés en microscopie. Il est déterminé que les propriétés électriques des nanocomposites à base d’esters hétérocycliques et MWCNTS peuvent varier de matériaux isolants aux matériaux conducteurs. Les seuils de percolation des deux systèmes sont très bas (0.22 et 0.38 pourcent pour nanocomposites à base de cPBT et PCN respectivement). La conductivité des composites conducteurs est particulièrement stable sur un large domaine de température ce qui laisse présager des applications intéressantes dans le domaine de la microélectronique et pour des pièces d’avion et de navettes spatiales. / The thesis relates to synthesis and investigation of nanostructured polymer composites based on oligomers of cyanate esters of bisphenol a (DCBA) or cyclic butylene terephthalate (CBT) and multiwalled carbon nanotubes (MWCNTS). Catalytic effect of mwcnts in process of DCBA polycyclotrimerization as well as in cbt polymerization has been observed. Significant increase in crystallization temperature of nanocomposites based on polybutylene terephthalate (cPBT) with adding of MWCNTS is observed. The effect of processing method of cpbt/mwcnts nanocomposites on its electrical properties has been found. It has been established that the additional heating of the samples (annealing) at temperatures above melting of cPBT leads to reagglomeration of MWCNTS in the system. It is established that reagglomeration of MWCNTS results in increase of conductivity values of nanocomposites due to formation of percolation pathways of MWCNTS through polymer matrix. In the case of polycyanurate matrix (PCN), it is found that addition of small mwcnts contents (0.03-0.06 weight percents) provides increasing tensile strength by 62-94 percents. It has been found that addition of even 0.01 weight percents of MWCNTS provides significant increase in storage modulus of cPBT matrix. This is explained by effective dispersing of small amount of the nanofiller during in situ synthesis of pcn or cpbt matrix that is confirmed by microscopy techniques. It has been established that the properties of the nanocomposites based on heterocyclic esters and MWCNTS can be varied from isolator to conductor and has low percolation thresholds (0.22 and 0.38 weight percents for cPBT and PCN nanocomposites respectively). The conductivity of samples is particularly stable on a very large range of temperature from 300 to 10 degrees Kelvin that make these materials perspective for practical applications in microelectronics, as parts of aircraft and space constructions.