Physics http://hdl.handle.net/2262/86 2013-05-12T21:14:30Z 2013-05-12T21:14:30Z COLEMAN, JONATHAN NESBIT NICOLOSI, VALERIA WANG, JING JING KHAN, UMAR http://hdl.handle.net/2262/66473 2013-05-08T21:52:21Z 2011-01-01T00:00:00Z

Title: Large-Scale Exfoliation of Inorganic Layered Compounds in Aqueous Surfactant Solutions Author: COLEMAN, JONATHAN NESBIT; NICOLOSI, VALERIA; WANG, JING JING; KHAN, UMAR Abstract: Thumbnail image of graphical abstract A method to exfoliate MoS2 in large quantities in surfactant-water solutions is described. The layered material tends to be exfoliated as dispersions of thin, relatively defect-free flakes with lateral sizes of hundreds of nanometers. This method can be extended to a range of other layered compounds. The dispersed flakes can be mixed with nanotubes or graphene to greate functional hybrid materials. Description: PUBLISHED

2011-01-01T00:00:00Z SATTI, AMRO COLEMAN, JONATHAN NESBIT GOUNKO, IOURI MAY, PETER O'NEILL, ARLENE NICOLOSI, VALERIA http://hdl.handle.net/2262/66472 2013-05-08T21:40:44Z 2012-01-01T00:00:00Z

Title: Covalently functionalized hexagonal boron nitride nanosheets by nitrene addition Author: SATTI, AMRO; COLEMAN, JONATHAN NESBIT; GOUNKO, IOURI; MAY, PETER; O'NEILL, ARLENE; NICOLOSI, VALERIA Abstract: Exfoliated h-BN nanosheets were covalently functionalized via a one-step nitrene addition using azide precursor molecules. Functionalized h-BN nanosheets were found to exhibit markedly enhanced dispersability relative to pristine h-BN in a range of organic solvents. Extension of the functionalization methodology allowed the covalent attachment of polymer chains to the surface of h-BN nanosheets. Polymer nanocomposites were prepared using the molecularly-functionalized h-BN nanosheets within a polycarbonate (PC) matrix, while h-BN nanosheets functionalized with poly(bisphenol A-co-epichlorohydrin) (PBCE) chains were employed within a PBCE matrix. In both cases the mechanical properties were studied. Significant increases in moduli, strength and ductility of the functionalized h-BN nanocomposites indicated enhanced reinforcement of the functionalized h-BN filler materials over pristine h-BN. The implications of tuning the surface chemistry of exfoliated nanosheets exactly to the chemis-try of a host polymer matrix are considered. Description: PUBLISHED

2012-01-01T00:00:00Z SATTI, AMRO COLEMAN, JONATHAN NESBIT GOUNKO, IOURI MC GOVERN, IGNATIUS MAY, PETER http://hdl.handle.net/2262/66471 2013-05-08T21:36:33Z 2012-01-01T00:00:00Z

Title: Oxygen radical functionalization of boron nitride nanosheets Author: SATTI, AMRO; COLEMAN, JONATHAN NESBIT; GOUNKO, IOURI; MC GOVERN, IGNATIUS; MAY, PETER Abstract: The covalent chemical functionalization of exfoliated hexagonal boron-nitride nanosheets (BNNSs) is achieved by the solution phase oxygen radical functionalization of boron atoms in the h-BN lattice. This involves a two-step procedure to initially covalently graft alkoxy groups to boron atoms and the subsequent hydrolytic defunctionalisation of the groups to yield hydroxyl-functionalized BNNSs (OH-BNNSs). Characterization of the functionalized-BNNSs using HR-TEM, Raman, UV-Vis, FTIR, NMR, and TGA was performed to investigate both the structure of the BNNSs and the covalent functionalization methodology. OH-BNNSs were used to prepare polymer nanocomposites and their mechanical properties analyzed. The influence of the functional groups grafted to the surface of the BNNSs is investigated by demonstrating the impact on mechanical properties of both non-covalent and covalent bonding at the interface between the nanofiller and polymer matrices. Description: PUBLISHED

2012-01-01T00:00:00Z BLAU, WERNER http://hdl.handle.net/2262/66470 2013-05-08T21:34:49Z 1986-01-01T00:00:00Z

Title: Optical phase conjugation In a soluble polymer Author: BLAU, WERNER Abstract: Degenerate four-wave mixing of picosecond light pulses in polydiacetylene dissolved in toluene has been observed. Phase conjugate reflectivities of over 100% were obtained. The origin of the non-linear interaction was found to be a thermal refractive index change. Description: PUBLISHED

1986-01-01T00:00:00Z BLAU, WERNER http://hdl.handle.net/2262/66469 2013-05-08T21:28:03Z 1987-01-01T00:00:00Z

Title: Resonant third-order hyperpolarizabilities of large organic molecules Author: BLAU, WERNER Abstract: Resonant degenerate four-wave mixing in a number of infrared-absorbing dyeswas studied with 160-psec pulses at 1.064 µm. Hyperpolarizabilities in the range of 10-44 to 10-42 V-2 m5 were observed. A theoretical model based on a two-band system is developed that explains the results and permits the prediction of hyperpolarizabilities from the linear spectroscopic properties. Description: PUBLISHED

1987-01-01T00:00:00Z KELLY, JOHN MOFFAT BLAU, WERNER http://hdl.handle.net/2262/66468 2013-05-08T21:25:34Z 1987-01-01T00:00:00Z

Title: Base-specific photocleavage of DNA induced by nanosecond U.V. pulsed laser radiation or methylene blue sensitisation Author: KELLY, JOHN MOFFAT; BLAU, WERNER Abstract: Excitation of DNA in neutral solution either with short-duration, intense pulses of excimer laser (248 nm) radiation or with low intensity red-ligh (633 nm) sensitisation by methylene blue causes cleavage of the DNA backbone selectively at guanine. Description: PUBLISHED

1987-01-01T00:00:00Z BLAU, WERNER http://hdl.handle.net/2262/66467 2013-05-08T21:22:45Z 2006-01-01T00:00:00Z

Title: Blue-green small-signal gain and saturation in a luminescent polymer gain medium Author: BLAU, WERNER Abstract: The authors study the optical gain and saturation behavior in a blue-green-emitting luminescent polymer gain medium. Based on the results of amplified spontaneous emission measurements, the gain coefficients, the gain-length product, and the corresponding small-signal gain are determined. By the use of the variable stripe length method, large net gain coefficients of up to 106±6 cm −1 have been measured under nanosecond photopumping. The large gain has favorable implications for the development of short wavelength lasers and amplifiers. Their study shows that a small-signal gain of 19 dB is achievable with a very compact optical amplifier with a 400 m length. Description: PUBLISHED

2006-01-01T00:00:00Z BLAU, WERNER http://hdl.handle.net/2262/66466 2013-05-08T21:20:45Z 1986-01-01T00:00:00Z

Title: Near-infrared dye having a large ultrafast third-order susceptibility Author: BLAU, WERNER Abstract: Efficient degenerate four-wave mixing of 160-psec infrared light pulses at λ = 1.064 µm in solutions of a new dye that absorbs between 1.0 and 1.6 µm is reported. A Kerr-like third-order susceptibility of X(3)xyyx = 8 ± 3) × 10-12 esu with a decay time of less than 50 psec is observed in various solvents. Description: PUBLISHED

1986-01-01T00:00:00Z COLEMAN, JONATHAN NESBIT O'NEILL, ARLENE KHAN, UMAR http://hdl.handle.net/2262/66460 2013-05-08T18:09:21Z 2012-01-01T00:00:00Z

Title: Preparation of high concentration dispersions of exfoliated MoS 2 with increased flake size Author: COLEMAN, JONATHAN NESBIT; O'NEILL, ARLENE; KHAN, UMAR Abstract: Solvent exfoliation of inorganic layered compounds is likely to be important for a range of applications. However, this method generally gives dispersions of small nanosheets at low concentrations. Here we describe methods, based on sonication of powdered MoS2 in the solvent N-methyl-pyrrolidone, to prepare dispersions with significantly increased lateral nanosheet size and dispersed concentration. We find the concentration to scale linearly with starting MoS2 mass allowing the definition of a yield. This yield can be increased to ~40% by controlling the sonication time, resulting in concentrations as high as 40 mg/ml. We find the nanosheet size to increase initially with sonication time reaching ~700 nm (for a concentration of ~7.5 mg/ml). At longer sonication times the nanosheets size falls off due to sonication induced scission. The nanosheets produced by such methods are relatively thin and have no observable defects. We can separate the dispersed nanosheets by size using controlled centrifugation. This allows us to produce dispersions with mean flake size of up to ~2µ m. However, such large flakes are noticeably thicker than the standard nanosheets. We demonstrate that such nanosheets can be mixed with polymers to form composites. While standard nanosheets result in no improvement in composite mechanical properties, addition of size-selected nanosheets results in significant improvements in composite modulus and strength. Description: PUBLISHED

2012-01-01T00:00:00Z COLEMAN, JONATHAN NESBIT SANVITO, STEFANO http://hdl.handle.net/2262/66459 2013-05-08T18:00:07Z 2012-01-01T00:00:00Z

Title: Solvent Exfoliation of Transition Metal Dichalcogenides: Dispersibility of Exfoliated Nanosheets Varies Only Weakly between Compounds Author: COLEMAN, JONATHAN NESBIT; SANVITO, STEFANO Abstract: We have studied the dispersion and exfoliation of four inorganic layered compounds, WS2, MoS2, MoSe2 and MoTe2 in a range of organic solvents. The aim was to explore the relationship between the chemical structure of the exfoliated nanosheets and their dispersability. Sonication of the layered compounds in solvents generally gave few-layer nanosheets with lateral dimensions of a few hundred nanometers. However the dispersed concentration varied greatly from solvent to solvent. For all four materials the concentration peaked for solvents with surface energy close to 70 mJ/m2, implying that all four layered compounds have surface energy close to this value. Inverse gas chromatography measurements showed MoS2 and MoSe2 to have surface energies of ~75 mJ/m2, in good agreement with dispersability measurements. However, this method suggested MoTe2 to have a considerably larger value of surface energy (~120 mJ/m2). While surface energy based solubility parameters are perhaps more intuitive for 2-dimensional materials, Hansen solubility parameters are probably more useful. Our analysis shows the dispersed concentration of all four layered materials to show well-defined peaks when plotted as a function of Hansen’s dispersive, polar and H-bonding solubility parameters. This suggests that we can associate Hansen solubility parameters of ~ P  18 MPa1/2, ~ D  8.5 MPa1/2 and ~ H  7 MPa1/2 with all four types of layered material. Knowledge of these properties allows the estimation of the Flory-Huggins parameter, , for each combination of nanosheets and solvent. We found that the dispersed concentration of each material falls exponentially with  as predicted by solution thermodynamics. This work shows that solution thermodynamics and specifically solubility parameter analysis can be used as a framework to understand the dispersion of 2-dimensional materials. Finally, we note that in good solvents such as cyclohexylpyrrolidone, the dispersions are temporally stable with >90% of material remaining dispersed after 100 h. Description: PUBLISHED

2012-01-01T00:00:00Z