Biomedical subjects

S Jurga

Publications and source records attributed to S Jurga.

10 recordsLinked to original sources

PubMed2005

Nanomechanical properties of silica-coated multiwall carbon nanotubes-poly(methyl methacrylate) composites.

The mechanical properties of polymer composites, reinforced with silica-coated multiwall carbon nanotubes (MWNTs), have been studied using the nanoindentation technique. The hardness and the Young's modulus have been found to increase strongly with the increasing content of these nanotubes in the polymer matrix. Similar experiments conducted on thin films containing MWNTs, but without a silica shell, revealed that the presence of these nanotubes does not affect the nanomechanical properties of the composites. While carbon nanotubes (CNTs) have a very high tensile strength due to the nanotube stiffness, composites fabricated with CNTs may exhibit inferior toughness. The silica shell on the surface of a nanotube enhances its stiffness and rigidity. Our composites, at 4 wt % of the silica-coated MWNTs, display a maximum hardness of 120 +/- 20 MPa, and a Young's modulus of 9 +/- 1 GPa. These are respectively 2 and 3 times higher than those for the polymeric matrix. Here, we describe a method for the silica coating of MWNTs. This is a simple and efficient technique, adaptable to large-scale production, and might lead to new advanced polymer based materials, with very high axial and bending strength.

Journal Article↗

PubMed2004

Low-temperature ordering effects in diblock copolymer melts from lattice simulation.

A lattice simulation of a model diblock copolymer melt is presented. In a series of simulation experiments an 8-8 diblock melt is quenched from an athermal state to 47 lower temperatures. A set of simulation boxes, 30 x 32 x 30, 40 x 32 x 60, 50 x 32 x 30, and 60 x 32 x 30, is used in order to explore the size effects. Energy, specific heat, copolymer end-to-end distance, lamellar spacing, and the degree of interfacial ordering are reported. For all sizes considered, the low-temperature interfacial ordering is noticeable.

Journal Article↗

PubMed2004

Molecular dynamics in solid pyridoxine as studied by 1H NMR.

Spin-lattice relaxation times T1 and T1d as well as NMR second moment were employed to study molecular dynamics of pyridoxine (vitamin B6) in the temperature range 10-350 K. The T1 minimum observed at low temperatures at 200 MHz is attributed to a motion of methyl group. The motion is interpreted in terms of Haupt's theory, which takes into account the tunneling assisted relaxation. At low temperatures, where T1 is temperature independent, occupation of the ground state only is assumed. A motion of proton of the hydroxyl groups or CH2OH groups probably provides additional mechanism of relaxation, in the high-temperature region.

Crystallization↗

PubMed2004

Studies of water penetration into LDPE--calcium lactate composite.

Penetration of water into low-density polyethylene-calcium lactate composite is studied with NMR techniques. The presence of filler speeds up the water uptake by the polymer matrix and facilitates polyethylene degradation. Spatial distribution of absorbed water molecules within the composite visualised with MRI corroborates differences in dynamical behaviour of the absorbed water molecules revealed by T2 measurements.

Absorption↗

PubMed2004

Molecular dynamics of n-dodecylammonium chloride in aqueous solutions investigated by 2H NMR and 1H NMR relaxometry.

Molecular dynamics in n-dodecylammonium chloride/water solutions for concentrations of 34 and 45 wt% was studied by 2H NMR and by 1H NMR dispersion of spin-lattice relaxation in the 2 kHz-90 MHz frequency range. The system exhibits a number of lyotropic liquid crystalline phases, which differ in symmetry and involve motions characterized by a wide frequency scale. The analysis of 2H NMR lineshapes of selectively deuterated DDACl molecules gave us an evidence for local trans-gauche conformational changes in the chains, whereas the dispersion of spin-lattice relaxation times T1 explored by fast field cycling method revealed fast local motions, translational diffusion and collective molecular dynamics of the chains. In particular, we have found that the order director fluctuation mechanism in smectic and nematic phases dominates spin-lattice relaxation below 1 MHz and that local motions and translational diffusion are responsible for the spin-lattice relaxation in the higher Larmor frequency range.

Journal Article↗

PubMed2004

Rheological and NMR studies of polyethylene/calcium carbonate composites.

Rheometry, 13C CP/MAS NMR spectra and 1H spin-lattice relaxation times T1 and T1rho have been employed to study the structure and molecular dynamics in composites of polyethylene (LDPE) with calcium carbonate filler. It has been found that the addition of the filler into the polymer leads to an increase in composite rigidity and a decrease in mobility in its crystalline regions. The presence of the filler affects the crystallization process making the crystal structure less perfect and reduces the size of the crystallites.

Calcium Carbonate↗

PubMed2002

Computer simulation of structure and microphase separation in model A-B-A triblock copolymers.

A set of computer simulations for three symmetric A-B-A triblock copolymer microarchitectures at varying temperatures is reported. By using the cooperative motion algorithm we obtain energy, specific heat, end-to-end distance, and bridging fraction as a function of the reduced temperature. The order-disorder transition temperatures are determined, an outline of a symmetric A-B-A triblock copolymer phase diagram is presented, and the visualization of different microstructures is given. A bicontinuous microstructure is reported at 67% fraction of A component.

Journal Article↗

PubMed1997

Local and global dynamics in the glass-forming di-isobutyl phthalate as studied by 1H NMR.

Spin-lattice relaxation times T1 and T1p as well as 1H NMR spectra have been employed to study the dynamics of the glass-forming di-isobutyl phthalate in the temperature range extending from 100 K, through the glass transition temperature Tg, up to 340 K. Below Tg NMR relaxation is governed by local dynamics and may be attributed to rotation of methyl groups at low temperatures and to motion of isobutyl groups in the intermediate temperature interval. Above Tg the main relaxation mechanism is provided by overall molecular motion. The observed relaxation behavior is explained by motional models assuming asymmetrical distributions of correlation times. The motional parameters obtained from Davidson-Cole distribution, which yields the best fit of the data at all temperatures are given.

Dibutyl Phthalate↗

PubMed1997

Dynamics of glass-forming di-n-butyl phthalate as studied by NMR.

Spin-lattice relaxation times T1 and nuclear Overhauser effect (NOE) enhancement factors for the individual ring carbons in di-n-butyl phthalate (DBF) show that the reorientational correlation function corresponding to the global dynamics in supercooled liquid can be described by a Davidson-Cole distribution. Measurements of proton spin-lattice relaxation times T1 and T1p, as well as 1H NMR spectra at temperatures below the glass transition temperature, Tg, reveal that the same distribution holds also for description of local dynamics in glassy DBF. The activation parameters of the motions detected are derived.

Carbon Isotopes↗

PubMed1995

Molecular dynamics in stiff ionene below glass transition.

Temperature dependences of proton and fluorine second moments and spin-lattice relaxation time T1 below glass transition were measured in glassy "I-Do,Pip-Me-BF4" ionene. The existence of motions of methyl groups and segments linking the cationic centers, namely piperidinium rings and trimethylene groups, for the polymeric part of ionene were established. Isotropic rotation of the counter-ion was evidenced and its limited diffusion suggested. To interpret the proton and fluorine relaxation data, a Davidson-Cole distribution of correlation times was assumed.

Anions↗