Is It Worth the Effort to Reinforce Polymers With Carbon Nanotubes?

Carbon nanotubes (CNTs) show exceptional properties that render them attractive for incorporation in a new generation of high‐performance engineering composites with tailored properties. While a great deal of work has been done toward using CNTs as a reinforcing agent in polymer composites, the full potential of CNTs has yet to be reached. In this work, two case studies were proposed in order to analyze the effectiveness of CNTs and carbon fibers (CFs) as reinforcing agents. Micromechanics models for the stiffness and strength of hybrid composites, comprising CNTs and CFs are derived by considering the concept of effective fiber. In addition, the 2009 prices of commercially available CNTs are reviewed. The strongest, the stiffest, and the cheapest CFs commercially available are compared with single walled CNTs (SWCNTs) and multiwalled CNTs (MWCNTs). The simulated results from the micromechanics models show that the use of CFs makes the acquisition of composites with maximum tensile strengths of 4.18 GPa possible. Analysis of the cost versus property relation showed that CNTs are the most viable strengthening option for achieving composites with strengths of up to 11.61 GPa. It is also shown that CFs are the most viable stiffening option, making composites with Young's moduli of up to 383 GPa possible at the expense of the material's toughness. Moreover, it is shown that, in order to achieve CNT's true potential, several challenges have to be faced. CNTs have to be produced with higher purity, longer lengths, better integrity, in larger amounts, and at lower cost. Moreover, issues such as orientation of the CNTs, their concentration, interfacial adhesion, distribution, and dispersion have to be overcome.

     

Adsorption of dicarboxylic acids onto nano‐structured silver surfaces – surface‐enhanced Raman scattering studies of pH‐dependent adsorption geometries

Understanding and shaping adsorption orientations of molecular compounds on nano‐structured metallic surfaces is an important issue across many areas of contemporary research including the design of nano‐structured surfaces and catalytic processes. Here, we used surface‐enhanced Raman spectroscopy to study these orientations on nano‐structured silver surfaces using dicarboxylic acids (maleic acid and fumaric acid) as model substances. Results revealed a clear pH dependence of the observed adsorption geometries of dicarboxylic acids correlating well with the dissociation states of the two acidic groups. Our data demonstrate the potential of the technique and contribute to an improved understanding of adsorption orientations of molecules at the interface between nano‐structured metal surfaces and a liquid phase. Copyright © 2012 John Wiley & Sons, Ltd.     

Raman spectroscopy of synthetic organic pigments used in 20th century works of art

Raman microscopy allows a non‐destructive characterisation of inorganic and organic painting materials such as pigments and organic dyestuffs. The objectives of this study are the more recent organic pigments typically present in paintings and other art works from the 20th century. More than 20 organic synthetic pigments from different chemical classes could be identified by Raman spectroscopy using different excitation wavelengths (457.9, 476.5, 487.9, 514.5, 632.8, and 1064 nm). To evaluate the performance for real paint samples, varying paint mixtures of the Hansa Yellow pigment PY 3 and the binding medium Mowilith, a polyvinyl acetate (PVAC) compound, were characterised; PY 3 was determined at a 1 wt% level in the binder. In addition, commercial tube paints containing the quinacridone violet PV 19 were studied. The pigment was clearly identified in all of these more complex oil and acrylic paints. Finally, alizarin (PR 83) and a green copper phthalocyanine pigment (PG 7) could unambiguously be identified by Raman microscopy in the painting ‘Woman with mandolin in yellow and red’ of Max Beckmann dating 1950. The discovery of a red naphthol AS pigment by Raman spectroscopy in a sample from the ‘Three field workers’ by Georg Baselitz (1964/1965) demonstrated that in some cases complementary chromatographic methods are needed for a comprehensive identification of the organic pigments. Copyright © 2008 John Wiley & Sons, Ltd.     

Biopolymer-assisted self-assembly of ZnO nanoarchitectures from nanorods

We have investigated three-dimensional (3-D) architectures–microspheres and radial structures–based on biopolymer-assisted self-assembly from one-dimensional ZnO nanorods. The developed method is simple, rapid and cost-effective and can be used for self-assembly of different complex superstructures. A possible model of 3-D architectures self-assembled with biopolymer assistance is presented using minimum energy considerations. Scanning electron microscopy, X-ray diffraction, energy dispersive X-ray spectroscopy, transmission electron microscopy, micro–Raman spectroscopy and cathode luminescence investigations show that the novel 3-D architectures are built from high-purity ZnO nanorods with a wurtzite structure. The resulting radial structures show an intense ultraviolet (UV) cathode luminescence emission suggesting applications as UV light emitting diodes or lasers. Their structural characteristics endow them with a broad area of applications and offer a possibility to be used as fundamental low-dimensional building units. These building units open opportunities for the self-assembly of multifunctional nanostructured systems with applications in bioscience and nanomedicine, electronics and photonics.     

Particle packed columns and monolithic columns in high-performance liquid chromatography-comparison and critical appraisal

The review highlights the fundamentals and the most prominent achievements in the field of high-performance liquid chromatography (HPLC) column development over a period of nearly 50 years. After a short introduction on the structure and function of HPLC columns, the first part treats the major steps and processes in the manufacture of a particle packed column: synthesis and control of particle morphology, sizing and size analysis, packing procedures and performance characterization. The next section is devoted to three subjects, which reflect the recent development and the main future directions of packed columns: minimum particle size of packing, totally porous vs. core/shell particles and column miniaturization. In the last section an analysis is given on an alternative to packed columns-monolithic columns, which have gained considerable attraction. The challenges are: improved packing design based on modeling and simulation for targeted applications, and enhanced robustness and reproducibility of monolithic columns. In the field of miniaturization, particularly in chip-based nano-LC systems, monoliths offer a great potential for the separation of complex mixtures e.g. in life science.     

Microcantilever biosensors based on conformational change of proteins

Microcantilevers (MCLs) hold a position as a cost-effective and highly sensitive sensor platform for medical diagnostics, environmental analysis and fast throughput analysis. MCLs are unique in that adsorption of analytes on the microcantilever (MCL) surface changes the surface characteristics of the MCL and results in bending of the MCL. Surface stress due to conformation change of proteins and other polymers has been a recent focus of MCL research. Since conformational changes in proteins can be produced through binding of anylates at specific receptor sites, MCLs that respond to conformational change induced surface stress are promising as transducers of chemical information and are ideal for developing microcantilever-based biosensors. The MCL can also potentially be used to investigate conformational change of proteins induced by non-binding events such as post-translational modification and changes in temperature or pH. This review will provide an overview of MCL biosensors based on conformational change of proteins bound to the MCL surface. The models include conformational change of proteins, proteins on membranes, enzymes, DNA and other polymers.     

Hydrogen doppler spectroscopy using 15N ions

The energy spread of atomic and molecular ion beams from the 4 MV Dynamitron tandem accelerator at the Ruhr-Universität Bochum has been studied and in part minimized. Using the E_R = 6.40 MeV narrow resonance in ¹H(¹⁵N,!%)¹²C with an ¹⁵N energy spread of 4.55 keV, the Doppler broadening for several hydrogen-bearing gases was found to be in good agreement with expectation: e.g. for NH₃ gas a rotational-vibrational Doppler width of 10.41 - 0.25 keV was observed (theory = 10.4 keV). Studies of the vibrational Doppler widths of H-bonds on a Si 𘜄¢ surface were performed using a 4?%-ray detection system together with UHV-chambers for sample preparation, transport, and analysis. The results showed that further improvements in the experimental set-ups are needed for such investigations.