Solid state H NMR study of molecular dynamics and domain sizes in PBT with the fullerene derivates: Decylamine-C60 and tetracyanoethylene oxide-C60

The solid-state ¹H NMR on-resonance and off-resonance techniques have been performed to study molecular dynamics and domain sizes in heterogenous nanocomposites based on poly(butylene terephthalate) and nanoparticles C₆₀ modified by n-decylamine (DA) or tetracyanoethylene oxide (TCNEO), respectively. The spin-lattice off-resonance relaxation times in the rotating frame T_1ρ^off as well as the second moment M₂ of the absorption line were analysed as a function of temperature. To determine the size of heterogeneities and characterize the morphology of the nanocomposites, the ¹H NMR spin-diffusion experiment designed by Goldman-Shen [1,2] was performed. The results from the measurements allow us to investigate the spin-diffusion phenomenon and relaxation behavior of the new nanocomposites.     

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.     

Chain dynamics of bilayer n-decylammonium chloride studied by deuteron NMR spectroscopy

N-decylammonium chloride is a polymorphic solid which exhibits a variety of layered phases. The molecular dynamics and phase transitions in these phases have been studied using²H NMR of selectively deuterated n-decylammonium in the chain positions 1 and 6 and in the ammonium group. Measurements were performed over the temperature range of the interdigitated phase I, the non-interdigitated monoclinic phase , the tetragonal phase , and the monotropic phase , obtained upon cooling the sample from the -phase. In phase I, below 321 K, the hydrocarbon chain is rigid except for ND₃ rotation about its own symmetry axis. In phase , between 321 K and 325 K, a fast motion of the hydrocarbon chains is assigned to an exchange between two pairwise nonequivalent positions. The chains are slightly tilted in this phase. In phase above 325 K the chains rotate freely around their long axes experiencing additional transgauche conformational dynamics. In the non-interdigitated phase the spectra can be interpreted by assuming a reorientation between two variously occupied potential wells about the axis determined by the C-N bond, which is believed to be parallel to the normal bilayer axis.     

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.     

Mood Disorder Detection in Adolescents by Classification Trees,Random Forests and XGBoost in Presence of Missing Data

We apply tree-based classification algorithms, namely the classification trees, with the use of the rpart algorithm, random forests and XGBoost methods to detect mood disorder in a group of 2508 lower secondary school students. The dataset presents many challenges, the most important of which is many missing data as well as the being heavily unbalanced (there are few severe mood disorder cases). We find that all algorithms are specific, but only the rpart algorithm is sensitive; i.e., it is able to detect cases of real cases mood disorder. The conclusion of this paper is that this is caused by the fact that the rpart algorithm uses the surrogate variables to handle missing data. The most important social-studies-related result is that the adolescents’ relationships with their parents are the single most important factor in developing mood disorders—far more important than other factors, such as the socio-economic status or school success.     

1H and 13C NMR studies of molecular dynamics in the biocopolymer of glycolide and epsilon-caprolactone

Copolymers of glycolide and epsilon-caprolactone were studied using differential scanning calorimetry and solid-state NMR. The variation of the T1 relaxation time with temperature reflects local disorder and can be quantified in terms of the distribution of correlation times predicted by the Davidson-Cole model. T, relaxation is dominated by trans-gauche isomerisation, with an activation energy of 34-35 kJ mol(-1).     

Studies of gelation process investigated by fast field cycling relaxometry and dynamical rheology: the case of aqueous low methoxyl pectin solution

The Fast Field Cycling Relaxometry and the dynamical rheology were applied to study the gelation process in aqueous low methoxyl pectin solution in the presence of divalent cations from the calcium chloride. The model-free approach to the analysis of 1H NMRD data was used to separate the information on the static and dynamic behaviour of the system provided by the dispersion profiles of the systems tested. Mechanical spectroscopy was applied as a complementary method to probe the network formation. The structural changes were most pronounced for the concentration of calcium chloride between 10 and 15 mM (the static parameter beta was found to vary from 0.936 x 10(7) to 1.27 x 10(7) 1/s2) revealing the sol-gel transition on visual inspection. The presence of the gel network was confirmed by the rheological measurements. All mechanical spectra exhibited the gel like character, and the solid like response was more evident at higher concentrations of calcium cations. The mean correlation time increased with increasing salt concentration, but remained unchanged for the concentrations above 15 mM. The dynamical changes were most significant at the phase transition from the sol to the gel state.     

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.     

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.