Jan Jurga

The influence of filler modification on its aggregation and dispersion behaviour in silica/PBT composite

In this work, highly dispersed silica is obtained using a precipitation technique from emulsion medium. The selected emulsifier, applied in the process, allows production of silica with almost ideally spherical particles. To examine the tendency to aggregation, the silica powder is treated with commercially available silane coupling agents: 3-mercaptopropyltrimethoxysilane (A-189), N-2-(aminoethyl)-3-aminopropyltrimethoxy silane (A-1120) and 3-methacryloxypropyltrimethoxysilane (A-174). The silica microstructure is characterised by scanning electron microscopy (SEM). Size distribution of primary particles, aggregates and agglomerates structures is determined using dynamic light scattering (DLS) method. Surface treatment of silica generally enhances powder dispersibility. The pristine spherical silica and silica modified with silanes are introduced to poly(butylene terphthalate) (PBT). Dispersion of nanosize precipitated silica particles in PBT matrix is studied by SEM technique. For the visualisation of silica particles covered by polymer layer, the composite fracture surfaces are etched by air-plasma. The agglomerates of untreated silica are not efficiently destroyed during the extrusion process, whereas surface treatment by selected silanes leads to a significant reduction of agglomerate number. However, a large number of small, strongly bonded aggregates still occupied the composite structure.

Two-dimensional spectral–spatial EPR imaging with the rapid scan and modulated magnetic field gradient

A new method for fast spectral-spatial electron paramagnetic resonance imaging (EPRI) is presented. To reduce the time of projections acquisition we propose to combine rapid scan of Zeeman magnetic field using high frequency sinusoidal modulation with simultaneously applied magnetic field gradients, whose amplitude is modulated at low frequency. The correctness of the method is confirmed by studies carried out on a phantom consisting of two LiPc samples. The spectral-spatial images from the acquired data are reconstructed using iterative algorithms. The proposed method allows to acquire the spectral-spatial image with 800 projections at 200ms.

The Instrument Set for Generating Fast Adiabatic Passage

The design and construction of a high-performance, low-cost, and easy to assemble adiabatic extension set for homebuilt and commercial spectrometers is described. Described apparatus set was designed for the fast adiabatic passage generation and is based on direct digital synthesizer DDS. This solution gives generator high signal to noise ratio, phase stability even during frequency change which is only possible in expansive commercial high-end hardware. Critical synchronization and timing issues are considered and solutions are discussed. Different experimental conditions and techniques for the measurements are briefly discussed. The proposed system is very flexible and might be used for the measurement of low-frequency nuclear magnetic resonance.

Effect of Heat Treatment on Phase Behaviour and Molecular Dynamics of Mineral-Filled PPS

Abstract Investigation concerning the structure and molecular dynamics of a nanocomposite made up of poly(p-phenylene sulfide) and silicon dioxide (SiO2) has been conducted by means of atomic force microscopy (AFM) and nuclear magnetic resonance (NMR). AFM and NMR studies of samples PPS in the neat and composite forms show that during annealing the fragmentation of big agglomerates of PPS take place. Between agglomerates and smaller aggregates there exist repulsion forces which are probably the source of fragmentation in the polymer network. The work has also proved that inside agglomerates and smaller aggregates of PPS dipolar magnetic interaction exist, whereas the electrostatic one occurs between them.

Analysis of Uniformity of Magnetic Field Generated by the Two-Pair Coil System

In this paper we use a simple analysis based on properties of the axial field generated by symmetrical multipoles to reveal all possible distributions of two coaxial pairs of circular windings, which result in systems featuring zero octupole and 32 pole magnetic moments (six-order systems). Homogeneity of magnetic field of selected systems is analyzed. It has been found that one of the derived systems generates homogenous magnetic field whose volume is comparable to that yielded by the eight-order system. The influence of the current distribution and the windings placement on the field homogeneity is considered. The table, graphs and equations given in the paper facilitate the choice of the most appropriate design for a given problem. The systems presented may find applications in low field electron paramagnetic resonance imaging, some functional f-MRI (nuclear magnetic resonance imaging) and bioelectromagnetic experiments requiring the access to the working space from all directions.

Effect of fullerene derivates on thermal and crystallization behavior of PBT/decylamine-C 60 and PBT/TCNEO-C 60 nanocomposites

The paper describes the process of the preparation of new nanocomposites based on poly(butylene terephthalate) and C60 nanoparticles modified by decylamine (DA) and tetracyanoethylene oxide (TCNEO), respectively. Thermal and crystallization properties of new synthesized nanocomposites were investigated by means of thermal differential scanning calorimetry (DSC). The experimental results demonstrate the effect of fullerene derivates, DA-C60 and TCNEO-C60, on the melting and crystallinity processes of nanocomposites. The morphology of new nanocomposites was investigated by SEM.

Molecular dynamics of poly(ethylene 2,6-naphthalate)-polycarbonate composite by nuclear magnetic resonance

The aim of the work was to examine molecular dynamics of a series of poly(ethylene 2,6-naphthalate)-polycarbonate blends with changing weight ratio of copolymers by off-resonance nuclear magnetic resonance technique. It was shown that this technique provides information about the correlation times of the internal motions. The spectral density function amplitudes were estimated on the basis of the dispersion of the spin-lattice relaxation time off-resonanceTlpoff. The measurements were performed for two series of blends which had been injection moulded with and without compatibilizer. The new polymer materials were also characterized using differential scanning calorimetry. Samples obtained after injection moulding and annealing became amorphous, which indicates that a reaction of transesterification process between the two polymers occurred.

Two-dimensional imaging by the continuous-wave EPR

To be able to perform a two-dimensional study of free radical distribution by the continuous-wave electron paramagnetic resonance method in the X-band, special coils producing a magnetic gradient of 8 G/mm have been designed and constructed. The EPR spectra recorded for this gradient were subjected to the procedure of deconvolution in order to elicit information on the concentration of the radical distribution. The data obtained were used as the source file of the program reconstructing the image. The reconstruction was based on the iterative simultaneous algebraic reconstruction technique (Andersen A.H., Kak A.C.: Ultrason. Imag. 6, 81–94, 1984). The quality of the generated images depends on the angle of the sample axis to the gradient direction set by a goniometer and on the deconvolution procedures applied. The first tests on artificially generated phantoms indicated a dependence of the obtained images on the magnetic field gradients applied. The determined spatial distribution of radicals has confirmed their uniform distribution in the sample. The preliminary tests were performed for diphenyl-picrylhydrazyl. Having proved the reliability of the method, analogous measurements were also performed for plyphenylene sulphide PPS-V1 and indicated a homogeneous distribution of radicals in the whole volume of the sample. The images obtained confirmed the uniform distribution of the radicals.

Two-dimensional EPR imaging with the rapid scan and rotated magnetic field gradient

A new method for fast 2D Electron Paramagnetic Resonance Imaging (EPRI) is presented. To reduce the time of projections acquisition we propose to combine rapid scan of Zeeman magnetic field using high frequency sinusoidal modulation with simultaneously applied magnetic field gradient, whose orientation is changed at low frequency. The correctness of the method is confirmed by studies carried out on a phantom consisting of two LiPc samples. The images from the acquired data are reconstructed using iterative algorithms. The proposed method allows to reduce the image acquisition time up to 10 ms for 2D EPRI, and to detect the sinogram with infinitesimal angular step between projections.

Overmodulation of projections as signal-to-noise enhancement method in EPR imaging.

A study concerning the image quality in electron paramagnetic resonance imaging in two‐dimensional spatial experiments is presented. The aim of the measurements was to improve the signal‐to‐noise ratio (SNR) of the projections and the reconstructed image by applying modulation amplitude higher than the radical electron paramagnetic resonance linewidth. Data were gathered by applying four constant modulation amplitudes, where one was below 1/3 (Amod = 0.04 mT) of the radical linewidth (ΔBpp = 0.14 mT). Three other modulation amplitude values were used in this experiment, leading to undermodulated (Amod < 1/3 ΔBpp), partially overmodulated (Amod ~ 1/3 ΔBpp) and fully overmodulated (Amod > > 1/3 ΔBpp) projections. The advantages of an applied overmodulation condition were demonstrated in the study performed on a phantom containing four shapes of 1.25 mM water solution of 2, 2, 6, 6‐tetramethyl‐1‐piperidinyloxyl. It was shown that even when the overmodulated reference spectrum was used in the deconvolution procedure, as well as the projection itself, the phantom shapes reconstructed as images directly correspond to those obtained in undermodulation conditions. It was shown that the best SNR of the reconstructed images is expected for the modulation amplitude close to 1/3 of the projection linewidth, which is defined as the distance from the first maximum to the last minimum of the gradient‐broadened spectrum. For higher modulation amplitude, the SNR of the reconstructed image is decreased, even if the SNR of the measured projection is increased. Copyright