The Graphene term has become synonymous with layered carbon sheets having thicknesses ranging from the monolayer to stacks of about ten layers. For bulk volume production, graphite chemical exfoliation is the preferred solution. For this reason, much interest has congregated around different processes to oxidize and peel off graphite to obtain graphene oxide (GO) and its counterpart, reduced GO (rGO). The community at-large has quickly adopted those processes and has been intensively using the resulting (r)GO as active materials for a myriad of applications. Yet, partially given the absence of comparative studies in synthesis methodologies, a lack of understanding persists on how to best tailor these carbon materials for a given application. In this dissertation, the effect of using different chemical oxidation-reduction strategies for graphite, namely the impact on the structure and chemistry of GOs and rGOs is systematically discussed. Added to this, it is demonstrated that the drying step of the powdered materials cannot be neglected. Its influence is demonstrated in studies such as the optimization of capacitance of rGOs touted as electrochemical energy storage materials (Chapter 4). It is concluded that, in order to maximize the performance of GO and rGO materials for any particular application, there must be a judicious choice of their synthesis steps. Obvious as it may be for anyone working in Chemistry, this point has been surprisingly overlooked for too long by the vast majority of those working with these carbon materials.

Over the last decade, two dimensional (2D) materials have attracted considerable attention from both the scientific and engineering community due to their unique properties. One important advance of 2D materials is that they can be exfoliated into nanosheets suspended in a liquid phase and that this allows the formulation of 2D nanomaterials inks. Such inks can be deposited as functional components through low-cost inkjet printing techniques. Many 2D materials based inks have been produced over the years. This thesis investigates the use of inkjet printing to deposit 2D materials such as graphene oxide (GO) and black phosphorus (BP).GO, a derivative of graphene, has been widely used to produce graphene-based conductors via inkjet printing owing to its good stability in readily available solvents such as water. In this work, highly conductive reduced graphene oxide (rGO) films with bulk conductivity in excess of 2 × 10^4 Sm-1 have been prepared by inkjet printing a GO aqueous ink, with mean flake size 35.9 micro metre, through a 60 micro metre inkjet printing nozzle followed by a reduction step. Experimental results showed that individual GO flakes up to 200 micro metre diameter can be successfully printed with no instances of nozzle blocking or poor printing performance. The mechanism by which this occurs is believed to be GO sheet folding during drop formation followed by elastic unfolding during drop impact and spreading. In addition, the influence of GO flake size on rGO film conductivity has been investigated. It was found that the rGO film conductivity increased about 60% when the mean flake size of the GO flakes in the ink increases from 0.68 micro metre to 35.9 micro metre. The drying behaviour of printed GO droplets has been studied on eight GO aqueous inks in which the mean flake size of GO was varied over a range from 0.68 to 35.9 micro metre. It was found that the coffee ring effect (inhomogeneous drying of a droplet to leave a ring like deposit) of dried droplets of the GO ink weakened and disappeared when the flake size increasing. It was found that, with a printed deposit around 340 micro metre in diameter, the coffee ring effect (CRE) was suppressed with the mean flake size > 10.3 micro metre. The critical flake size for CRE suppression reduced to 5.97 and 3.68 micro metre when the substrate temperature was 40 and 50 °C, respectively. It was further found that the CRE weakened with decreasing printed drop size, with the critical flake size reducing to 1.58 micro metre with a printed drop diameter of 30 micro metre.The interaction between BP nanometre thickness flakes and humid atmospheres was investigated using an inkjet printed BP sensor. The BP sensor showed was very sensitive to changes in humidity with a response time of a few seconds and the effect is reproducible in minutes. However, long term exposure to humid air with a relative humidity (RH) > 11% leads to a significant chemical change in the BP films, with Fourier transform infra-red spectroscopy (FTIR) indicating partial hydrolysis of the BP to form phosphate and phosphonate ions. Low temperature heat treatment of BP films under dry conditions after exposure to elevated RH leads to a partial recovery of the impedance response and reversion to a chemical state similar to that before exposure to a humid environment. The recovery of BP properties is most complete after exposure to lower humidity environments (RH < 11%), although exact replication of the original impedance response and FTIR spectrum was not possible.

Nanographene oxide particles (NGO) were produced via oxidative exfoliation of graphite. Three different sizes of NGO (300 nm, 200 nm and 100 nm) have been separated by using probe sonication and sucrose density gradient centrifugation. There is great interest in functionalized NGO as a nanocarrier for in vitro and in vivo drug delivery, in order to improve dispersibility and stability of the nanocarrier platforms in physiological media. In this study, the NGO particles were covalently functionalized with zero generation polyamidoamide (PAMAM-G0) and with gelatin via noncovalent interaction. Spectroscopic techniques have been used to discriminate the chemical states of NGO prior and after functionalization. The X-ray photoelectron spectroscopy (XPS) revealed a clear change in the chemical state of NGO after functionalization, for both covalent and noncovalent approaches. Raman spectroscopy gave obvious insight after oxidation of graphite and functionalization of NGO particles depending on the variation of intensity ratios between D, G and 2D bands. The Fourier transform infrared spectroscopy (FTIR) exhibited the presence of oxygen containing functional groups distributed onto graphene sheets after oxidation of graphite. Furthermore, the FTIR is complementary with the XPS which performed a strong reduction in the oxygen contents after functionalization. UV visible spectroscopy was used to understand the binding capacity of gelatin coated NGO particles. The Microscopy tools, scanning electron microscopy (SEM) and atomic force microscopy (AFM) are used to estimate the dimensions of NGO particles (thickness and lateral width). The nanohybrid systems (NGO-PAMAM and Gelatin-NGO) loaded with carboplatin (CP) were sought for anticancer activity investigation in HeLa and neuroblastoma cancer cells respectively. Mesenchymal stem cells (hMSCs) were used as a model of normal cells. On HeLa cells, the pristine NGO particles with average widths of 200 nm and 300 nm showed a cytotoxic effect at low (50 g.ml−1) and high (100 g.ml−1) concentrations. While the pristine NGO sample with an average width of 100 nm revealed no significant cytotoxicity at 50 g.ml−1, and only recorded a 10% level at 100 g.ml−1. The mesenchymal stem cells showed less than 35% viability for all size distributions. After functionalization with PAMAM, the carrier was found to be able to deliver carboplatin to the cancer cells, by enhancing the drug anticancer efficiency. Moreover, the carboplatin loaded NGO carrier shows no significant effect on the viability of hMSCs even at high concentration (100 g.ml−1). On neuroblastoma cells, the cell viability assay validated gelatin-NGO nanohybrids as a useful nanocarrier for CP release and delivery, without obvious signs of toxicity. The nano-sized NGO (200 nm and 300 nm) did not enable CP to kill the cancer cells efficiently, whilst the CP loaded gelatin-NGO 100 nm resulted in a synergistic activity through increasing the local concentration of CP inside the cancer cells.

abstract: Thiol functionalization is one potentially useful way to tailor physical and chemical properties of graphene oxides (GOs) and reduced graphene oxides (RGOs). Despite the ubiquitous presence of thiol functional groups in diverse chemical systems, efficient thiol functionalization has been challenging for GOs and RGOs, or for carbonaceous materials in general. In this work, thionation of GOs has been achieved in high yield through two new methods that also allow concomitant chemical reduction/thermal reduction of GOs; a solid-gas metathetical reaction method with boron sulfides (BxSy) gases and a solvothermal reaction method employing phosphorus decasulfide (P4S10). The thionation products, called "mercapto reduced graphene oxides (m-RGOs)", were characterized by employing X-ray photoelectron spectroscopy, powder X-ray diffraction, UV-Vis spectroscopy, FT-IR spectroscopy, Raman spectroscopy, electron probe analysis, scanning electron microscopy, (scanning) transmission electron microscopy, nano secondary ion mass spectrometry, Ellman assay and atomic force microscopy. The excellent dispersibility of m-RGOs in various solvents including alcohols has allowed fabrication of thin films of m-RGOs. Deposition of m-RGOs on gold substrates was achieved through solution deposition and the m-RGOs were homogeneously distributed on gold surface shown by atomic force microscopy. Langmuir-Blodgett (LB) films of m-RGOs were obtained by transferring their Langmuir films, formed by simple drop casting of m-RGOs dispersion on water surface, onto various substrates including gold, glass and indium tin oxide. The m-RGO LB films showed low sheet resistances down to about 500 k&#937;/sq at 92% optical transparency. The successful results make m-RGOs promising for applications in transparent conductive coatings, biosensing, etc. / Dissertation/Thesis / Ph.D. Chemistry 2013

Polyelectrolyte multilayer capsules fabricated by layer-by-layer (LbL) self-assembly technique consistsing of core-shell structure have emerged as potential drug delivery systems along with their applications in micro-reactors, cosmetics, vaccines and antimicrobial coatings. Various ligands and stimuli responsive entities can be incorporated into the core and shell of the capsules for targeted delivery and/or controlled release applications. Though multilayer capsules have been studied extensively as delivery systems, their utility for encapsulation of hydrophobic drugs and multiple drugs have not been explored in detail so far. Application of traditional polyelectrolyte capsules has several limitations, which renders them inapplicable for encapsulation of multiple drugs, hydrophobic drugs and also for releasing drugs on demand without addition of the external photothermal agents such as metal nanoparticles into the shells of the capsules. Thus, in this thesis, an attempt has been made to develop novel multifunctional multilayered capsules to overcome the above mentioned limitations. We have formulated two novel methods to functionalize the core with cyclodextrin molecules and the shell of the capsules with two-dimensional material, graphene oxide (GO). The properties such as high surface area along with π bonds, broad NIR-absorption, superior photothermal conversion and antimicrobial activity of graphene oxide has been explored and it has been demonstrated that 2-D graphene oxide is unique compared to the regular polyelectrolytes. By functionalizing the shell of capsules with GO as one of the layer material, a simple and efficient way for encapsulating multiple drugs into core and shell of the capsules is achieved by utilizing the large surface area and amphiphilic nature of GO. Based on the unique optical absorption and photothermal conversion properties of GO, we have demonstrated a facile route for near-infrared (NIR)-laser triggered release with low laser power. In the second part, functionalization of the hollow core of the capsules has been functionalized using cylodextrin (CD)-incorporated CaCO3 porous sacrificial templates, where both CD-CaCO3 and CD-modified capsules are used as high efficient carriers for hydrophobic drugs. In the third part, synergistic antimicrobial therapy was achieved using composite graphene oxide/polymer LbL films by combining the intrinsic antimicrobial activity and photothermal conversion ability of graphene oxide and the results depicted superior antimicrobial activity towards E. coli. These composite films also can be used as efficient antimicrobial coatings on biomedical devices or implants. The thesis has been divided into five chapters based on the individual works. In Chapter 1, a brief review on the history of LbL self-assembly, mechanism of self-assembly along with factors affecting the process have been discussed. Followed by a brief discussion about the fabrication of multilayered hollow capsules (core-shell structure), their applications in drug delivery and fabrication of multifunctional multilayered capsules through core and shell have been discussed. Finally, recent developments in LbL self-assembly and multilayered hollow capsules using carbon based materials (fullerenes, carbon nanotubes and graphene oxide) and their biomedical applications have been presented. Chapter 2 deals with the study on fabricating multifunctional multilayered capsules for facile encapsulation of multiple drugs into the capsules, which is achieved by functionalizing the capsules with graphene oxide (GO) as one of the layer materials. The GO composite capsules exhibited unique permeability properties compared to traditional multilayered capsules made of two polyelectrolytes. Multiple drugs could be simultaneously encapsulated in the capsules in a simple and effective manner. These capsules were found to exhibit a “core-shell” loading property for encapsulation of dual drugs into the core and shell of the capsules respectively. In addition, the graphene oxide composite capsules showed excellent biocompatibility towards MCF-7 cells. This study is the first one that demonstrates the potential of hybrid polyelectrolyte capsules without the use of micelles or polymer-drug conjugates for multi-drug encapsulation. Chapter 3 deals with the development of a facile route for near-infrared (NIR)-light triggered release of encapsulated drugs from the multilayered capsules via incorporation of graphene oxide (GO) into layer-by-layer (LbL) assembled capsules without addition of any external additives such as metal nanoparticles (NPs) or carbon nanotubes (CNTs) into the shells of the capsules. Till now, there is no report on light-responsive drug delivery system by utilizing the NIR-optical absorption properties of GO. Here, graphene oxide (GO) plays a dual role, serving as a structural component of LbL capsules as well as strong NIR-light absorbing agent, which efficiently converts absorbed light into heat. Upon NIR-laser irradiation, the microcapsules were opened in “point-wise fashion” due to local heating caused by laser irradiation. The rupturing mechanism of the capsules has been clearly demonstrated using confocal fluorescence microscopy and high resolution transmission electron microscopy. The light-triggering ability of these capsules has been applied successfully to release the encapsulated anticancer drug, doxorubicin. Chapter 4 deals with simple and versatile simple routes for encapsulation of model hydrophobic drug. Encapsulation of hydrophobic drugs in pharmaceutical industries is always a big challenge due to limited number of available drug carrier systems and poor aqueous solubility of hydrophobic drugs. Here, by combining the special properties of cyclodextrins (CDs) with biodegradable inorganic calcium carbonate microparticles, the hybrid CD-CaCO3 mesoporous microparticles have been prepared for the first time. These CD-CaCO3 microparticles were utilized as sacrificial templates to prepare CDs-modified LbL capsules. We have demonstrated that both the hybrid CD-CaCO3 microparticles and CDs-modified capsules are potential carriers for encapsulation of model hydrophobic drugs (self-fluorescent coumarine and nile red dyes) with high loading efficiency using supramolecular host-guest interaction between entrapped CDs and hydrophobic dye molecules. Compared with other inorganic drug carrier systems (mesoporous silica), CaCO3 porous particles have better biocompatibility, biodegradability and cost-effective and without use of any organic solvents. Both these hybrid CD-CaCO3 microparticles and CDs-modified capsules can be good candidates for encapsulation of hydrophobic drugs without involving extreme chemical conditions for fabrication. Chapter 5 deals with development of facile synergistic method for killing pathogenic bacteria by combining the intrinsic antimicrobial activity of graphene oxide (GO) and unique photothermal conversion property of GO into a single material. We fabricated composite LbL films of graphene oxide (GO) and poly(allylamine hydrochloride) (PAH) films. Antimicrobial activity of these GO composite films has been studied using Escherichia coli (E. coli) cells by varying number of deposited layers on glass slides (20 to 80 layers) and results suggest that by increasing the number of deposited layers, antimicrobial activity is also increased gradually. Based on the unique optical properties of GO, photothermal therapy have been carried out for killing of E. coli using GO composite films by varying number of deposited layers (20 to 80 layers) by irradiation of NIR-pulse laser at 1064 nm wavelength (Nd:YAG, 10 ns pulse, 10 Hz). The photothermal results revealed the enhanced antimicrobial activity compared to GO composite films alone without NIR-laser irradiation. The synergistic photothermal killing ability along with intrinsic antimicrobial activity of GO films results in much faster killing compared to films alone.

Nanotechnology refers to the use of the materials or particles ranging from a few nanometers (nm) to 100 nanometers (nm) in a wide range of applications. Use of nanomaterials in cement composite to enhance the mechanical properties, fracture toughness and other functionalities has been studied for decades. In this regard, one of the carbon-based nanomaterials, Graphene Oxide (GO), has received attentions from researchers for its superior mechanical properties (e.g. tensile strength, yield strength, and Young's modulus). Although GO is not lucrative in increasing electrical conductivity (EC) of cement paste compared to that of graphene- another derivative of GO, reduced graphene oxide (rGO), might be a solution to increase EC. Another derivative of GO is the solution to the problem. In this research, the compressive strength and flexural strength of GO-cement composite (GOCC) and rGO-cement composite (rGOCC) have been investigated with 0.01% and 0.05% GO and rGO content. GOCC-0.05% showed 27% increase in compressive strength compared to the control cement paste after 28 days (d) of hydration. GOCC-0.01% showed only 3.4% increase in compressive strength compared to the control. rGOCC-0.05% showed 21% increase in compressive strength and 15.5% increase in Modulus of Rupture (MOR) compared to the control cement paste after 28 d of hydration. On the other hand, rGOCC-0.01% showed 7% increase in compressive strength and 0.35% increase in MOR after 28 d. GOCC-0.05% showed increasing trends in compressive strength after 28 d indicating continuation of hydration. Similarly, rGOCC-0.05% also showed increasing trends in compressive and flexural strength after 28 d, possibly due to the reason described earlier. Microstructural investigation on GOCC-0.05% and GOCC-0.01% by X-ray Diffraction (XRD) illustrated that the crystallite sizes of tobermorite-Å and jennite, which are mineralogical counterpart of disordered Calcium-Silicate-Hydrate (C-S-H), increases from 3 d to 28 d, representing the crystallite growth due to continued hydration. However, the crystallite size of GOCC-0.05% was smaller than that of GOCC-0.01% at both 3 d and 28 d, indicating finer nucleated grains. According to Hall-Petch equation, mechanical strength increases with decreasing particle size. Finer particles or grains can increase the strength in cement composites in several other ways: (1) GO acted as heterogeneous nucleation sites because of reactive functional groups. Activation energy was decreased by these "defects" in the cement paste, and consequently, numerous nuclei of C-S-H. with high surface area were formed, (2) because of finer grains, cracks are forced to move along a tortuous path, which makes the structure difficult to fail, and strength increased consequently (3) Finer grains of GOCC-0.05% created compacted hydration products decreasing porosity which can indirectly increase the strength. The above reasons, separately or in conjunction, might increase the strength of GOCC-0.05% and proved that GO is responsible for increasing heterogeneous nucleation sites during cement hydration. Early age hydration (EAH) characteristics were investigated for rGOCC specimens with 0.1% and 0.5% rGO content. Scanning Electron Microscope (SEM), Energy Dispersive X-ray analysis (EDX), and X-ray Diffraction (XRD) were employed to study the EAH characteristics. SEM/EDX, and XRD analysis were performed after 15 min, 1 h, 3 h and 24 h of hydration. (EAH) study on rGOCC-0.1% showed that at 15 min hydration, numerous precipitates of, possibly, C-S-H formed along the grain boundary (GB) of unhydrated cement grains. This served as visual confirmation of Thomas and Scherer's Boundary Nucleation and Growth (BNG) model that hydration of cement grains was initiated by the short burst of nucleation of C-S-H embryos along GB. EDX on rGOCC-0.1% and rGOCC-0.5% showed that Ca/Si ratio in C-S-H was ~2.0. This finding indicated that C-S-H structure in this study was concurrent with that of impure jennite. XRD analysis also evidently showed that jennite was present, possibly possessing a short range ordered (SRO) structure, referring to local crystalline structure in a very short area. After consulting Chen's work, it would be appropriate to say that C-S-H found in this study resembled more as C-S-H (II), which is disordered jennite. It was also observed that as expected with cement with nanomaterials, with continuing hydration, pore spaces were filled with hydration products such as C-S-H, ettringite, CH, sulfoaluminates etc,. Lastly, Electrical resistivity (ER) testing on 9 sets of rGOCC specimens was conducted. The specimen includes 0.5%, 1%, 5% rGO content, and the control conditioned in both oven dry (OD) and saturated surface dry (SSD). ER increased with the increase of rGO content from 0.5% and 1% compared to that of the control. However, the ER of rGOCC-5% was significantly decreased, showing 93% reduction compared to the control, which can be interpreted as a threshold value for sensing applications to be explored. As expected, large reduction of ER value occurred on the specimens with the SSD condition. This reduction can be attributed to the ionic conduction though the pore solution of the composites. As the rGO content increased, so did the potential nucleation sites for hydration (as can be seen in SEM images), which might block the number of contact points among the rGO, resulting in low conduction and high resistivity. However, as rGO content increased to 5%, the contact areas/points increased to a degree that could trump the nucleation seeding sites, resulting in decreased ER. The ER measured with the rGOCC specimens was comparable to that of cement composites incorporating carbon fibers (CF), and steel fibers, but higher content of rGO are required to have a similar ER range of those fiber cement composites. This might be due to smaller sizes of rGO sheets and lower aspect ratio compared to other nanofibers causing drastic reduction of electron tunneling mechanism compared to other fibers.

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No description available.

This thesis investigates pool boiling heat transfer from bare and graphene-coated NiCr wires in a saturated liquid of FC 770, a fluorocarbon fluid. Of particular interest was the effect of graphene-oxide platelets, dip-coated onto the heater surface, in enhancing the nucleate boiling heat transfer (BHT) rates and the critical heat flux (CHF) value. In the course of the pool boiling experiment, the primary focus was on the reduction mechanism of graphene oxide. The transition from hydrophilic to hydrophobic behavior of the graphene oxide-coated surface was captured, and the attendant effects on surface wettability, porosity and thermal activity were observed. A parametric sensitivity analysis of these surface factors was performed to understand the CHF and BHT enhancement mechanisms. In the presence of graphene-oxide coating, the data indicated an increase of 50% in CHF. As the experiment continued, a partial reduction of graphene oxide occurred, accompanied by (a) further enhancement in the CHF to 77% larger compared to the bare wire. It was shown that the reduction of graphene oxide progressively altered the porosity and thermal conductivity of the coating layer without changing the wettability of FC 770. Further enhancement in CHF was explained in terms of improved porosity and thermal activity that resulted from the partial reduction of graphene-oxide. An implication of these results is that a graphene-oxide coating is potentially a viable option for thermal management of high-power electronics by immersion cooling technology. / Master of Science

In the last three decades carbon nanomaterials such as fullerenes, carbon nanotubes and graphene have attracted significant attention from the scientific community due to their unique electronic, optical, thermal, mechanical and chemical properties. Among them carbon nanotubes and graphene have been used in numerous applications for future nanoelectronics, biochemical sensors and energy harvesting technologies due to their unique properties including exceptionally high electronic conductivity and mechanical strength. Carbon nanotubes are cylindrical structures and considered to be large mesoscopic molecules with high aspect ratios. Graphene is a single atomic layer of crystalline graphite and prepared by stripping layers off the graphite using Scotch tape. Apart from this scotch tape method, chemical ex-foliation and reduction of graphite oxide produces large amounts of reduced graphene oxide which has similar properties as graphene. This thesis reports on the biosensors made of reduced graphene oxide and single walled carbon nanotubes based on their electronic properties. We also demonstrate the changes in electronic properties of single walled carbon nanotubes due to interactions with dendrimer molecules. Finally, the yielding and flow behaviour of graphene oxide nematic gel are discussed. Chapter 1 gives a general introduction about the preparation and characterization along with the electronic properties of the systems studied in this thesis, namely graphene oxide, reduced graphene oxide and single walled carbon nanotubes. We have also discussed about the experimental techniques such as Raman, UV-visibe and infrared spectroscopy, atomic force and scanning tunneling microscopy and different types of rheometers used in this thesis work. In Chapter 2, we discuss top-gated field effect transistor characteristics of the devices made of reduced graphene oxide monolayer by dielectrophoresis. Raman spectrum of RGO flakes shows a single 2D band at 2687 cm 1, characteristic of a single layer graphene. The two probe current - voltage measurements of RGO flakes, deposited in between the patterned electrodes using a.c. dielectrophoresis show ohmic behavior with a resistance of 37kΩ. The temperature dependence of the resistance (R) of RGO measured between temperatures 305K to 393K yields the temperature coefficient of resistance of -9.5 10 4/K. Ambipolar nature of graphene flakes is observed upto a doping level of 6 1012/cm2 and carrier mobility of 50cm2/V-sec. The source - drain current characteristics shows a tendency of current saturation at high source - drain voltage which is analyzed quantitatively by a diffusive transport model. In Chapter 3, We demonstrate the detection of glucose molecules by using reduced graphene oxide (RGO) and aminophenylboronic acid (APBA) complex with detection limit of 5 nM. APBA functionalized RGO (APBA-RGO) flakes, prepared by stirring the aqueous GO suspension in the presence of APBA molecules at 100◦C, were used as conducting channel in our field effect transistor (FET) devices. The APBA-RGO complex formation was confirmed by atomic force microscopy (AFM), x - ray photoelectron, Raman and UV-visible spectroscopic studies. Detection of glucose molecules was carried out by monitoring the changes in electrical conductance of the APBA-RGO flake in the FET device. FET devices made of non-covelently functionalized APBA-RGO complex (nc-APBA-RGO) exhibited enhanced sensitivity over the devices made of covalently functionalized APBA-RGO complex (c-APBA-RGO). Change in normalized conductance in the FET devices made of nc-APBA-RGO flakes ( 85%) is 4 times more than that of in the devices made of c-APBA-RGO flakes in response to aqueous glucose solution with different concentrations. Specificity of APBA-RGO complex to glucose was proved from the observation of negligible change in electrical conductance of the FET devices made of nc-APBA-RGO complex after exposure to 10 mM lactose solution. Chapter 4 reports unipolar resistive switching in ultrathin films of chemically produced graphene (reduced graphene oxide) and multiwalled carbon nanotubes. The two - terminal devices with yield > 99% are made at room temperature by forming continuous films of graphene of thickness 20 nm on indium tin oxide coated glass electrode, followed by metal (Au or Al) deposition on the lm. These memory devices are non - volatile, rewritable with ON/OFF ratios up to 105 and switching times up to 10 s. The devices made of MWNT films are rewritable with ON/OFF ratios up to 400. The resistive switching mechanism is proposed to be nanogap formation. In the first part of Chapter 5, we study the interactions between SWNT and PETIM dendrimer by measuring the quenching of inherent fluorescence of the dendrimer. Also, the dendrimer - nanotube binding results in the increased electrical resistance of the hole-doped SWNT due to charge transfer interaction between the dendrimer and the nanotube. This charge transfer interaction was further corroborated by observing a shift in frequency of the tangential Raman modes of SWNT. Experimental studies were supplemented by all atom molecular dynamics simulations to provide a microscopic picture of the dendrimer - nanotube complex. The complexation was achieved through charge - transfer and hydrophobic interactions, aided by multitude of oxygen, nitrogen and n-propyl moieties of the dendrimer. We also studied the effect of acidic and neutral pH conditions on the binding affinities. In the second part, we show that SWNT decorated with sugar functionalized PETIM dendrimer is a very sensitive platform to quantitatively detect carbohydrate recognizing proteins, namely, lectins. The changes in electrical conductivity of SWNT in field effect transistor device due to carbohydrate - protein interactions forms the basis of this study. The mannose sugar attached PETIM dendrimers undergo charge - transfer interactions with the SWNT. The changes in the conductance of the dendritic sugar functionalized SWNT after addition of lectins in varying concentrations were found to follow the Langmuir type isotherm, giving the concanavalin A (Con A) - mannose affinity constant to be 8.5 106 M-1. The increase in the device conductance observed after adding 10 nM of Con A is same as after adding 20 µM of a non - specific lectin peanut agglutinin, showing the high specificity of the Con A - mannose interactions. The specificity of sugar-lectin interactions was characterized further by observing significant shifts in Raman modes of the SWNT. Chapter 6 reports the metal to semiconductor transition in metallic single-wall carbon nanotubes (SWNT) due to the wrapping of mannose attached poly (propyl ether imine) dendrimer (DM) molecule. Scanning tunneling spectroscopic (STS) measurements and ionic liquid top gated field effect transistor (FET) characteristics of the nanotube-dendrimer complex gives a band gap of 0.42eV, close to the E11 energy gap between the first van Hove singularities of 1.7nm diameter semiconducting nanotubes. The absence of Breit-Wigner-Fano (BWF) component in G band in the Raman spectrum of the nanotube-dendrimer complex corroborates the semiconductor nature of the tubes after wrapping with the dendrimer molecules. Dendrimer molecule breaks the symmetry in metallic SWNT by wrapping around it through the charge transfer interactions. In the first part of Chapter 7, we demonstrate a rigidity percolation transition and the onset of yield stress in a dilute aqueous dispersion of graphene oxide platelets (aspect ratio 5000) above a critical volume fraction of 3.75x10-4 with a percolation exponent of 2.4 ± 0.1.The viscoelastic moduli of the gel at rest measured as a function of time indicates the absence of structural evolution of the 3D percolated network of disks. However, a shear-induced aging giving rise to a compact jammed state and shear rejuvenation indicating a homogenous flow is observed when a steady shear stress (σ ) is imposed in creep experiments. We construct a shear diagram (σ vs volume fraction ϕ) and the critical stress above which shear rejuvenation occurs is identified as the yield stress σ y of the gel. The minimum steady state shear rate ƴm obtained from creep experiments agrees well with the end of the plateau region in a controlled shear rate flow curve, indicating a shear localization below ƴm. A steady state shear banding in the plateau region of the flow curve observed in particle velocimetry measurements in a couette geometry confirms that the dilute suspensions of GO platelets form a thixotropic yield stress fluid (TYSF). In the second part, we report that the creep experiments on a nematic liquid crystalline suspension of Graphene Oxide platelets which was established recently as a TYSF exhibit two characteristic timescales Tc and Tf marking the onset of yielding, and a final steady state of flow respectively. We show that both Tc and Tf exhibit a power law dependence on the applied stress σ which can be linked to the steady state flow behaviour of a TYSF. The smooth transition from Andrade creep to the onset of flow with ƴ~ t 0.7 at a critical strain ƴc for different applied stresses, is well captured by the master curve for the creep compliance, obtained through a simple scaling of the creep times with either Tc or Tf . We propose that the absence of diverging timescales for onset of flow as σ→ yield stress σy from above, is a characteristic feature of TYSF. The thesis concludes with a summary of the main results and a brief account of the scope of future work described in Chapter 8.