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The potential of spectrofluorometry and fluorescence microscopy for the characterization and quantification of different functionalities like OH and NH2 groups at plasma-chemically modified polymer surfaces is assessed using traditional reactive dyes such as dansyl derivatives and a sophisticated VIS-excitable chromogenic and fluorogenic pyrylium label showing binding-induced spectral and intensity changes in absorption and emission. Aiming at an improved fluorometric surface analysis, based upon these measurements, several sources of uncertainty inherent to fluorescence measurements are illustrated ranging from environment-dependent dye absorption and emission features over spectral correction and nonspecific adsorption to the critical influence of label choice on the measured background. Solutions to these drawbacks are given thereby underlining the potential of fluorometry for surface analysis.
Nanoparticulate networks as fillers for polymer based nanocomposites offer an optimized, surfactant free distribution of the inorganic component. Additionally, their non-aggregated but interconnected nanoparticulate subunits can lead to new properties owing to special inherent solid state properties and/or spacial restrictions to the polymeric parts. In particular, polymer nanocomposites based on poly(methyl methacrylate) (PMMA) or poly(hydroxyethyl methacrylate) (PHEMA), filled with different nanoparticulate networks of AlOOH were synthesized using two advanced synthesis techniques. An ex situ method, in which a preformed AlOOH-gel was solvent exchanged by methyl methacrylate (MMA) and an in situ method, in which the AlOOH scaffold was prepared within hydroxyethyl methacrylate (HEMA), have been used to produce the materials described here through polymerization. On the MMA based composites the particles were removed by etching, yielding porous polymers. Promising for a broad variety of crystallisable networks within polymers, the phase transition of amorphous AlOOH within PMMA towards crystalline boehmite was performed using a hydrothermal method. The materials were characterized using transmission electron microscopy, X-ray diffraction, gel permeation chromatography, differential scanning calorimetry, IR-spectroscopy, UV/Vis spectroscopy and hardness measurements. Special material properties were investigated using thermogravimetry, thermomechanical analysis and dynamic mechanical analysis. Furthermore, interactions between PMMA segments and the AlOOH network were detailed studied using dielectric spectroscopy.
Plasma-chemical bromination has been shown to be well-suited for highly selective and efficient C–Br-functionalization of polyolefin surfaces and has now been applied to graphitic materials, including highly oriented pyrolytic graphite (HOPG), natural graphite, carbon nanotubes, and graphitized carbon fibres. In contrast to the radical substitution of hydrogen by bromine at hydrogen-terminated sp3-hybridized carbon, bromination of all-carbon bound sp2-hybridized carbon in graphene requires addition to aromatic double bonds. The related change of sp2 to sp3 hybridization of the carbon atoms involved helps to explain experimental results of a loss in surface planarity on brominated HOPG. Bromine concentrations of up to 50 bromine atoms per 100 C-atoms were achieved in elemental bromine vapour under low-pressure plasma conditions using low-energetic inductively coupled radio-frequency plasma excitation. The time scale of the bromination progress was found to increase with the specific surface area of the material. The results of plasma-chemical bromination are compared to that of wet-chemical electrophilic addition reactions, which achieved 28 Br per 100 C for MWCNT. The resulting C–Br bonds from plasma-chemical processing of graphitic materials were shown to be well-suited for hydroxyl functionalization and for grafting of organic molecules by nucleophilic substitution with 1,6-diaminohexane and (3-aminopropyl)triethoxysilane.