In this research, a low-cost template-based process has been developed to structure the surfaces of polymeric materials rendering them superhydrophobic. This biology-inspired approach was developed using results from the first part of this thesis: the first known detailed study of superhydrophobic aspen leaf surfaces. Aspen leaves, similar to lotus leaves, possess a dual-scale hierarchical surface structure consisting of micro-scale papillae covered by nano-scale wax crystals, and this surface structure was used as a blueprint in the structuring of templates. These distinctive surface features coupled with a hydrophobic surface chemistry is responsible for these leaves’ extreme non-wetting property. Non-wetting is further augmented by the unique high aspect ratio aspen leafstalk geometry. The slender leafstalks offer very little resistance to twisting and bending, which results in significant leaf movement in the slightest breeze, facilitating water droplet roll-off. The structured template surfaces, produced by sand blasting and chemical etching of electrodeposited nanocrystalline nickel sheets, resemble the negative of the superhydrophobic aspen leaf surfaces. Re-usable templates were subsequently employed in a hot embossing technique where they were pressed against softened polymers (polyethylene, polypropylene and polytetrafluoroethylene) thereby transferring their surface structures. The resulting pressed polymer surfaces exhibited features very similar to aspen leaf surfaces. This process increased the water contact angle for all pressed polymers to values above 150 degrees. Additionally, after pressing the water roll-off angle for all polymer surfaces dropped below 5 degrees. The effects of water surfactant concentration, water drop size and temperature on the wetting characteristics of the structured polymers were studied to indicate in which applications these functional surfaces could be most beneficial. Coupling this attractive superhydrophobic surface property with mechanical motion (shaking, bending, or vibrating) could result in superhydrophobic surfaces with superior non-wetting properties suitable for a wide range of applications.

In this research, a low-cost template-based process has been developed to structure the surfaces of polymeric materials rendering them superhydrophobic. This biology-inspired approach was developed using results from the first part of this thesis: the first known detailed study of superhydrophobic aspen leaf surfaces. Aspen leaves, similar to lotus leaves, possess a dual-scale hierarchical surface structure consisting of micro-scale papillae covered by nano-scale wax crystals, and this surface structure was used as a blueprint in the structuring of templates. These distinctive surface features coupled with a hydrophobic surface chemistry is responsible for these leaves’ extreme non-wetting property. Non-wetting is further augmented by the unique high aspect ratio aspen leafstalk geometry. The slender leafstalks offer very little resistance to twisting and bending, which results in significant leaf movement in the slightest breeze, facilitating water droplet roll-off. The structured template surfaces, produced by sand blasting and chemical etching of electrodeposited nanocrystalline nickel sheets, resemble the negative of the superhydrophobic aspen leaf surfaces. Re-usable templates were subsequently employed in a hot embossing technique where they were pressed against softened polymers (polyethylene, polypropylene and polytetrafluoroethylene) thereby transferring their surface structures. The resulting pressed polymer surfaces exhibited features very similar to aspen leaf surfaces. This process increased the water contact angle for all pressed polymers to values above 150 degrees. Additionally, after pressing the water roll-off angle for all polymer surfaces dropped below 5 degrees. The effects of water surfactant concentration, water drop size and temperature on the wetting characteristics of the structured polymers were studied to indicate in which applications these functional surfaces could be most beneficial. Coupling this attractive superhydrophobic surface property with mechanical motion (shaking, bending, or vibrating) could result in superhydrophobic surfaces with superior non-wetting properties suitable for a wide range of applications.

Since the discovery of nanomaterials in early ninety’s, a remarkable progress in the synthesis of nanocomposites has been reported looking for a new better material with improved physical and chemical properties for a variety of applications in almost all fields. The science and technology of nanocomposites has created great excitement and expectations in the last decade too. In addition to that, researches in this area have been focusing on the nanoscale second phase embedded in the polymeric matrix that gives physical and chemical properties that cannot be achieved by ordinary material synthesis methods. Researchers have also discovered that incorporating the right amount of nanoparticles into a polymer matrix pose a remarkable strength and flexibility and that industries should be able to integrate the outcome of their researches widely in high performance applications in the field of biomedical engineering, aerospace, marine, high speed parts in engines, packaging and sports gadgets. With the new methods of synthesis and tools for characterisation, nanocomposite science and technology is now experiencing explosive growth. Taking advantage of the need and the properties of the nanomaterials, through this research a new nano-enhanced composite is developed through addition of nanofiller into epoxy matrix to cater for varied applications. The physical and mechanical properties of the identified nanomaterial reinforced polymer composite were characterised by experimentation in order to ascertain the improvement in tensile, compressive and flexural properties as well as the adhesion of the matrix to the substrate. Also, while addressing potential enhancements like improved mechanical strength, better dimensional stability, higher thermal stability, better abrasion resistance, hard and wear resistance, better chemical properties like better flame retardance, anticorrosive and antioxidation, adequate importance was given to easy and bulk processability and most importantly the commercial viability as well. This nano-enhanced nanocomposite was then optimised. Based on these results, it has been established that epoxy reinforced with 1% percent of nanoclay can significantly improve the mechanical properties without compromising the weight or processability of the composite. Thus, a futuristic and much promising nano-enhanced epoxy composite has been successfully made ready for commercialisation.

Since the discovery of nanomaterials in early ninety’s, a remarkable progress in the synthesis of nanocomposites has been reported looking for a new better material with improved physical and chemical properties for a variety of applications in almost all fields. The science and technology of nanocomposites has created great excitement and expectations in the last decade too. In addition to that, researches in this area have been focusing on the nanoscale second phase embedded in the polymeric matrix that gives physical and chemical properties that cannot be achieved by ordinary material synthesis methods. Researchers have also discovered that incorporating the right amount of nanoparticles into a polymer matrix pose a remarkable strength and flexibility and that industries should be able to integrate the outcome of their researches widely in high performance applications in the field of biomedical engineering, aerospace, marine, high speed parts in engines, packaging and sports gadgets. With the new methods of synthesis and tools for characterisation, nanocomposite science and technology is now experiencing explosive growth. Taking advantage of the need and the properties of the nanomaterials, through this research a new nano-enhanced composite is developed through addition of nanofiller into epoxy matrix to cater for varied applications. The physical and mechanical properties of the identified nanomaterial reinforced polymer composite were characterised by experimentation in order to ascertain the improvement in tensile, compressive and flexural properties as well as the adhesion of the matrix to the substrate. Also, while addressing potential enhancements like improved mechanical strength, better dimensional stability, higher thermal stability, better abrasion resistance, hard and wear resistance, better chemical properties like better flame retardance, anticorrosive and antioxidation, adequate importance was given to easy and bulk processability and most importantly the commercial viability as well. This nano-enhanced nanocomposite was then optimised. Based on these results, it has been established that epoxy reinforced with 1% percent of nanoclay can significantly improve the mechanical properties without compromising the weight or processability of the composite. Thus, a futuristic and much promising nano-enhanced epoxy composite has been successfully made ready for commercialisation.

Since the discovery of nanomaterials in early ninety’s, a remarkable progress in the synthesis of nanocomposites has been reported looking for a new better material with improved physical and chemical properties for a variety of applications in almost all fields. The science and technology of nanocomposites has created great excitement and expectations in the last decade too. In addition to that, researches in this area have been focusing on the nanoscale second phase embedded in the polymeric matrix that gives physical and chemical properties that cannot be achieved by ordinary material synthesis methods. Researchers have also discovered that incorporating the right amount of nanoparticles into a polymer matrix pose a remarkable strength and flexibility and that industries should be able to integrate the outcome of their researches widely in high performance applications in the field of biomedical engineering, aerospace, marine, high speed parts in engines, packaging and sports gadgets. With the new methods of synthesis and tools for characterisation, nanocomposite science and technology is now experiencing explosive growth. Taking advantage of the need and the properties of the nanomaterials, through this research a new nano-enhanced composite is developed through addition of nanofiller into epoxy matrix to cater for varied applications. The physical and mechanical properties of the identified nanomaterial reinforced polymer composite were characterised by experimentation in order to ascertain the improvement in tensile, compressive and flexural properties as well as the adhesion of the matrix to the substrate. Also, while addressing potential enhancements like improved mechanical strength, better dimensional stability, higher thermal stability, better abrasion resistance, hard and wear resistance, better chemical properties like better flame retardance, anticorrosive and antioxidation, adequate importance was given to easy and bulk processability and most importantly the commercial viability as well. This nano-enhanced nanocomposite was then optimised. Based on these results, it has been established that epoxy reinforced with 1% percent of nanoclay can significantly improve the mechanical properties without compromising the weight or processability of the composite. Thus, a futuristic and much promising nano-enhanced epoxy composite has been successfully made ready for commercialisation.

Indianapolis / In this thesis, cellulose nanofiber (CNF) reinforced polylactic acid (PLA) filaments were produced for 3D printing applications using melt extrusion. The use of CNF reinforcement has the potential to improve the mechanical properties of PLA, making it a more suitable material for various 3D printing applications. To produce the nanocomposites, a master batch with a high concentration of CNFs was premixed with PLA, and then diluted to final concentrations of 1, 3, and 5 wt% during the extrusion process. The dilution was carried out to assess the effects of varying CNF concentrations on the morphology and mechanical properties of the composites. The results showed that the addition of 3 wt.% CNF significantly enhanced the mechanical properties of the PLA composites. Specifically, the tensile strength increased by 77.7%, the compressive strength increased by 62.7%, and the flexural strength increased by 60.2%. These findings demonstrate that the melt extrusion of CNF reinforced PLA filaments is a viable approach for producing nanocomposites with improved mechanical properties for 3D printing applications. In conclusion, the study highlights the potential of CNF reinforcement in improving the mechanical properties of PLA for 3D printing applications. The results can provide valuable information for researchers and industries in the field of 3D printing and materials science, as well as support the development of more advanced and sustainable 3D printing materials.

Clean and affordable energy, especially solar energy, is becoming more and more important as our annual total energy consumption keeps rising. However, to make solar energy more affordable and accessible, the cost for fabrication, transportation and assembly of all components need to be reduced. As a crucial component for solar cells, transparent conductive electrode (TCE) can determine the cost and performance. A light weight, easy-to-fabricate and cost-effective new generation TCE is thus needed. While indium-doped tin oxide (ITO) has been the most widely used material for commercial applications as TCEs, its cost has gone up due to the limited global supply of indium. This is not only due to the scarcity of the element itself, but also the massive production of various opto-electronic devices such as TVs, smartphones and tablets. In order to reduce the cost for fabricating large area solar cells, substitute materials for ITO should be developed. These materials should have similar optical transmittance in the visible wavelength range, as well as similar electrical conductivity (sheet resistance) to ITO. This work starts with synthesizing ITO-replacing nano-materials, such as copper nanowires (CuNWs), derivative zinc oxide (ZnO) thin films, reduced graphene oxide (rGO) and so on. Further, we applied various deposition techniques, including spin-coating, spray-coating, Mayer-rod coating, filtration and transferring, to coat transparent substrates with these materials in order to fabricate TCEs. We characterize these materials and analyze their electrical/optical properties as TCEs. Additionally, these fabricated single-material-based TCEs were tested in various lab conditions, and their shortcomings (instability, rigidity, etc.) were highlighted. In order to address these issues, we hybridized the different materials to combine their strengths and compared the properties to single-material based TCEs. The multiple hybridized TCEs have comparable optical/electrical metrics to ITO. The doped-ZnO TCEs exhibit high optical transmittance over 90% in the visible range and low sheet resistance under 200Ω/sq. For CuNW-based composite electrodes, ~ 85% optical transmittance and ~ 25Ω/sq were observed. Meanwhile, the hybridization of materials adds additional features such as flexibility or resistance to corrosion. Finally, as a proof of concept, the CuNW-based composite TCEs were tested in dye-sensitized solar cells (DSSCs), showing similar performance to ITO based samples.

We report the synthesis of ultra-high aspect ratio copper nanowires (CuNW) and fabrication of CuNW-based transparent conductive electrodes (TCE) with high optical transmittance (> 80%) and excellent sheet resistance (R-s < 30 Omega/sq). These CuNW TCEs are subsequently hybridized with aluminum-doped zinc oxide (AZO) thin-film coatings, or platinum thinfilm coatings, or nickel thin-film coatings. Our hybrid transparent electrodes can replace indium tin oxide (ITO) films in dye-sensitized solar cells (DSSCs) as either anodes or cathodes. We highlight the challenges of integrating bare CuNWs into DSSCs, and demonstrate that hybridization renders the solar cell integrations feasible. The CuNW/AZO-based DSSCs have reasonably good open-circuit voltage (V-oc = 720 mV) and short-circuit current-density (J(sc) = 0.96 mA/cm(2)), which are comparable to what is obtained with an ITO-based DSSC fabricated with a similar process. Our CuNW-Ni based DSSCs exhibit a good open-circuit voltage (V-oc = 782 mV) and a decent short-circuit current (J(sc) = 3.96 mA/cm2), with roughly 1.5% optical-to-electrical conversion efficiency.

The structural and electronic properties of covalently and non-covalently functionalized graphene are investigated by means of first-principles density-functional-theory. The electronic characteristics of non-covalently functionalized graphene by a planar covalent organic framework (COF) are investigated. The aromatic central molecule of the COF acts as an electron donor while the linker of the COF acts as an electron acceptor. The concerted interaction of donor acceptor promotes the formation of planar COF networks on graphene. The distinctive electronic properties of covalently functionalized fluorinated epitaxial graphene are attributed to the polar covalent C–F bond. The partial ionic character of the C–F bond results in the hyperconjugation of C–F σ-bonds with an sp2 network of graphene. The implications of resonant-orbital-induced doping for the electronic and magnetic properties of fluorinated epitaxial graphene are discussed. Isolation of single-walled carbon nanotubes (SWNTs) with specific chirality and diameters is critical. Water-soluble poly [(m- phenyleneethynylene)- alt- (p- phenyleneethynylene)], 3, is found to exhibit high selectivity in dispersing SWNT (6,5). The polymer’s ability to sort out SWNT (6,5) appears to be related to the carbon–carbon triple bond, whose free rotation allows a unique assembly. We have also demonstrated the important role of dispersion forces on the structural and electronic stability of parallel displaced and Y-shaped benzene dimer conformations. Long-range dispersive forces play a significant role in determining the relative stability of benzene dimer. The effective dispersion of SWNT depends on the helical pitch length associated with the conformations of linkages as well as π-π stacking configurations. We have revisited the constructing schemes for a large family of stable hollow boron fullerenes with 80 + 8n (n = 0,2,3,...) atoms. In contrast to the hollow pentagon boron fullerenes the stable structures constitute 12 filled pentagons and 12 additional hollow hexagons. Based on results from density-functional calculations, an empirical rule for filled pentagons is proposed along with a revised electron counting scheme. We have also studied the relative stability of various boron fullerene structures and structural and electronic properties of B80 bucky ball and boron nanotubes. Our results reveal that the energy order of fullerenes strongly depends on the exchange-correlation functional employed in the calculation. A systematic study elucidates the importance of incorporating dispersion forces to account for the intricate interplay of two and three centered bonding in boron nanostructures.

The present thesis titled “Molecular Modulation of Material Properties: Stud- ies on Nanoparticles, Nanoassemblies and Low Molecular Mass Gelator” deals with the preparation, characterization, and investigations into the properties of gold nanoparticles coated with novel thiols. The coverage of nanoparticle surfaces with these thiols renders them with special characteristics that will be of interest in biological and sensor applications. Also, a novel low molecular mass tetrameric sugar-based hydrogelator was synthesized and its gelation properties were studied in detail. Chapter 1 gives a general introduction and an overview about Nanomaterials, with emphasis towards nanoparticles of gold, which form the basis of this work. It delves with the history of research in noble metal nanoparticles, their interesting electronic and optical properties, the present methods of synthesis of high quality nanoparticles of noble metals, numerous potential applications of these novel materials, as well as the challenges in their real-life applications, and ends with the future outlook of this field of research. Chapter 2 describes the synthesis and characterization of three cationic lipid-like disulfides whose molecular structures are shown in Fig. 2.1. Gold nanoparticles capped with these molecules were then synthesized in small size dispersion by a simple one-phase protocol. These particles exhibited remarkably different solubility properties that were dictated by the molecular structure of the capping agent. The nanoparticles were characterized by a variety of techniques like UV-visible spec- troscopy, Transmission Electron Microscopy (TEM), proton Nuclear Magnetic Resonance (1H NMR), Fourier Transform Infra-red (FTIR) spectroscopy, and Zeta Potential measurements. These nanoparticles were then examined for their interactions (structural formula) Figure 1: Chemical Structures of the cationic lipid-like thiols used for nanoparticle preparation with dipalmitoyl phosphatidyl choline (DPPC) vesicles as model biological membranes. TEM, UV-vis, and Differential Scanning Calorimetry (DSC) were employed to probe the interactions. It was found that the capping agent of the nanoparticle had a strong bearing upon the interactions of the nanoparticles with DPPC vesicles. Chapter 3 describes the assembly of hydrophilic cationic nanoparticles upon elec- trostatic interaction with a variety of anionic surfactants. The chemical structures of some of the anions employed in the study, as well as a schematic of cationic nanopar- ticle are shown in Fig. 2. Upon ion pairing with long-chain anionic surfactants, the hydrophilic cationic nanoparticles were completely hydrophobized. They could then be phase-transferred to organic layer. TEM showed that nanoparticles assemble in to a variety of mesostructures upon ion-pairing with anions. The aggregate formation was found to depend critically upon length of the hydrophobic alkyl chain as well as the head-group of the anion. Isothermal Titration Calorimetry (ITC) was employed to probe the interactions of these nanoparticles with anions. It was found that the anions that resulted in nanoparticle precipitation displayed exothermic interactions with the nanoparticle. Chapter 4 deals with the synthesis of -thiolated metal chelator derivatives whose structures are shown in Fig. 3. The molecules are based on well-known chelators viz. iminodiacetic acid and bis-(2-pyridylmethyl)amine. While the first one is carboxylic acid-based chelator, the second one is pyridine-based. Nanoparticles coated with these chelators were synthesized in a size-controlled manner. These nanoparticles exhibited pH-controlled reversible assembly. However, while S-IDA based nanoparticles aggregated at low pH values, the S-BPA based nanoparticles aggregated in high pH regimes. Mixed monolayer protected gold nanoparticles were synthesized by employing S-BPA and C12H25SH as capping agents. It resulted in the formation of nanoparticles in low size-dispersion. These nanoparticles were characterized by 1H NMR spectroscopy to infer the ratio of the two capping agents on the nanoparticle surface. These nanoparticles demonstrated metal-ion induced aggregation. It was found that the nanoparticles could differentiate Cu2+ ions from other ions, and immediately formed aggregates in presence of Cu2+ ions. Chapter 5 describes the synthesis of novel mono-thiolated “Gemini” surfactants for nanoparticle synthesis. Gemini surfactants with different spacers were prepared. These surfactants had a 12-n-12 kind of molecular structure as shown in the Fig. 4. Upon preparation of nanoparticles with these thiols, the resulting material was soluble in water in the case of rigid thiols like D2S and DBPS Chapter 6 deals with the synthesis and hydrogelation properties of a low molecular mass hydrogelator based on an azobenzene based tetrameric sugar derivative (Fig. 5). The pKa of carboxylic acids in the molecule were determined using 13C NMR. The trans-to-cis isomerization of the compound was probed by time-dependent UV-vis studies. The sugar derivative exhibited pronounced hydrogelation capacity, gelling water at micromolar concentration. The gel formed was characterized extensively (structural formula) Figure 2: Schematic of cationic nanoparticles and molecular structures of the anions employed for nanoparticle assembly (structural formula) Figure 3: Chemical structures of metal-chelator containing thiols employed for the pH-controlled and metal-ion mediated nanoparticle assembly (structural formula) Figure 4: Schematic of cationic nanoparticles and molecular structures of the anions employed for nanoparticle assembly (structural formula) Figure 5: Chemical Structure of azobenzene-based tetrameric sugar derivative exhibit- ing pronounced hydrogelation using melting temperature analysis, UV-vis, FT-IR, circular dichroism spectroscopy and scanning electron microscopy. The resultant gel exhibited impressive tolerance to the pH variation of the aqueous phase and gelated water in the pH range of 4 to 10. While UV-vis and CD spectroscopy indicated that pronounced aggregation of the azobenzene chromophores in the gelator was responsible for gelation, FT-IR studies showed that hydrogen bonding is also a contributing factor in the gelation process. The melting of gel was found to depend upon the pH of the aqueous medium in which gel was formed. The gel showed considerable photostability to UV irradiation indicating tight intermolecular packing inside gelated state that render azobenzene groups in the resultant aggregate refractory to photoisomerization. The electron micrographs of the aqueous gels thus formed showed the existence of spongy globular aggregates in such gelated materials. Addition of salts to the aqueous medium led to a delay in the gelation process and also caused remarkable morphological changes in the microstructure of the gel. Appendix A describes the employment of ligand-free palladium nanoparticles towards efficient catalysis of Heck and Suzuki reactions in aqueous medium. Hexadecyl trimethylammonium bromide was employed as the surfactant to achieve solubilization of organic compounds in aqueous medium. UV-vis and TEM investigations into the formation of nanoparticles in the reaction media were undertaken. These studies indicate that the nanoparticles were formed by reduction of potassium tetrachloropalladinate by methyl acrylate used as one of the reactants. TEM investigation indicated the formation of nanoparticle assemblies upon solvent drying. Efficient and catalytic synthesis of a number of organic compounds could be achieved in high yield.