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See detailApplication of the Storing Matter technique to organic samples: fundamentals, applications, and evaluation of the analytical potential
Becker, Nora UL

Doctoral thesis (2011)

SIMS is a sensitive surface analysis method that is commonly used for a wide range of applications in various domains. Its major drawback is the so-called matrix effect, which is due to a change of the ... [more ▼]

SIMS is a sensitive surface analysis method that is commonly used for a wide range of applications in various domains. Its major drawback is the so-called matrix effect, which is due to a change of the ionization efficiency as a function of the chemical environment of the considered atom or molecule and which makes quantitative analysis very difficult. The Storing Matter technique was developed in order to circumvent the matrix effect while still keeping an excellent sensitivity: in a first step, the sample surface is sputtered by an ion beam and the emitted matter is deposited at sub-monolayer level onto a dedicated collector. Then the collector is transferred under UHV conditions to a SIMS instrument where the deposit is analyzed. If the deposit coverage is in the sub-monolayer range, all the deposited particles are surrounded by the same matrix, i.e. the collector material. The main goal of this work was the study and setup of experimental conditions for the application of the Storing Matter technique to organic samples. In this case, it is particularly important that molecular information is preserved. The key parameters of the technique were studied in detail and the optimal conditions with regard to high ionization efficiency and low fragmentation could be defined. [less ▲]

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See detailInfluence of Al2O3 nanoparticles on the isothermal cure of an epoxy resin
Sanctuary, Roland UL; Krüger, Jan-Kristian UL; Baller, Jörg UL et al

in Journal of Physics : Condensed Matter (2009), 21

The influence of Al2O3 nanoparticles on the curing of an epoxy thermoset based on diglycidyl ether of bisphenol A was investigated using temperature-modulated differential scanning calorimetry (TMDSC) and ... [more ▼]

The influence of Al2O3 nanoparticles on the curing of an epoxy thermoset based on diglycidyl ether of bisphenol A was investigated using temperature-modulated differential scanning calorimetry (TMDSC) and rheology. Diethylene triamine was used as a hardener. TMDSC not only allows for a systematic study of the kinetics of cure but simultaneously gives access to the evolution of the specific heat capacities of the thermosets. The technique thus provides insight into the glass transition behaviour of the nanocomposites and hence makes it possible to shed some light on the interaction between the nanoparticles and the polymer matrix. The Al2O3 fillers are shown to accelerate the growth of macromolecules upon isothermal curing. Several mechanisms which possibly could be responsible for the acceleration are described. As a result of the faster network growth chemical vitrification occurs at earlier times in the filled thermosets and the specific reaction heat decreases with increasing nanoparticle concentration. Rheologic measurements of the zero-shear viscosity confirm the faster growth of the macromolecules in the presence of the nanoparticles. [less ▲]

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See detailInteractions between silica nanoparticles and an epoxy resin before and during network formation.
Baller, Jörg UL; Becker, Nora UL; Ziehmer, Markus UL et al

in Polymer (2009), 50(14), 3211-3219

In polymer nanocomposites, interactions between filler particles and matrix material play a crucial role for their macroscopic properties. Nanocomposites consisting of varying amounts of silica ... [more ▼]

In polymer nanocomposites, interactions between filler particles and matrix material play a crucial role for their macroscopic properties. Nanocomposites consisting of varying amounts of silica nanoparticles and an epoxy resin based on diglycidyl ether of bisphenol A (DGEBA) have been studied before and during network formation (curing). Rheology and mainly temperature modulated differential scanning calorimetry (TMDSC) have been used to investigate interactions between the silica nanoparticles and molecules of the epoxy oligomer or molecules of the growing epoxy network. Measurements of the complex specific heat capacity before curing showed that interactions between the nanoparticles and DGEBA molecules are very weak. An expression for an effective specific heat capacity of the silica nanoparticles could be deduced. Examination of the isothermal curing process after addition of an amine hardener yielded evidences for a restricted molecular mobility of the reactants in the cause of network formation. These restrictions could be overcome by increasing the curing temperature. No evidences for an incorporation of the silica nanoparticles into the epoxy network, i.e. for a strong chemical bonding to the network, were found. Interactions between the silica nanoparticles and the epoxy resins under study are assumed to be of a physical nature at all stages of network formation. [less ▲]

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