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wizyta

od 2020-09-20

Dr Marcin Wachowicz  | 2000-10 <> 2006-01

Doktorant


Zainteresowania naukowe:
Ciekłe kryształy, mieszaniny polimerowe; 1H i 2H NMR, mikroskopia polaryzacyjna

Publikacje                Magistrowie           Seminaria


4.

Wachowicz M., Jurga S., Vilfan M.

Collective and local molecular dynamics in the lyotropic mesophases of decylammonium chloride: 1H and 2H NMR study The collective and individual dynamics of decylammonium chloride (DACl) molecules in water environment were investigated as a function of surfactant concentration and temperature. In the presence of water the DACl forms a variety of self-assembled structures, ranging from isotropic micellar systems to lyotropic liquid crystalline phases of hexagonal, nematic, and lamellar types. In order to characterize the complex molecular dynamics that occur in the DACl-water system, we applied H-1 and H-2 NMR techniques that cover the whole frequency range between 1 kHz and 30 MHz. The slow molecular dynamics were studied by H-1 NMR fast-field-cycling T-1 measurements and pulse-frequency dependence of H-2 NMR transverse relaxation time, performed by means of the Carr-Purcell-Meiboom-Gill sequence. We detected a well-expressed contribution of order director fluctuations, i.e., layer undulations, with characteristic omega(L)(-1) frequency dependence of T-1(-1) in the lamellar phase. Its presence indicates a relatively weak impact of interactions between neighboring DACl layers. The frequency dependence of proton T-1(-1) in the hexagonal phase exhibits a different type of frequency dispersion, T(1)(-1)similar toomega(L)(-1.32). The increase in the exponent is explained with the quasi-one-dimensional character of fluctuations in elongated cylinders. Further, the T-1 and T-2 relaxation times of deuterons selectively attached to the C2 and C7 segments of the hydrocarbon chains of DACl were measured at a Larmor frequency of 30.7 MHz, providing quantitative information about local molecular dynamics.

Physical Review E - Statistical, Nonlinear and Soft Matter Physics, 70, 031701 (2004)

DOI: 10.1103/PhysRevE.70.031701   (Pobrane:  2020-10-23)


3.

Wachowicz M., Wolak_J., Gracz H., Stejskal E.O., Jurga S., McCord E.F., White J.L.

Length scales which perturb chain packing in amorphous polymers Direct spectroscopic probes of individual chain conformation and free volume are used to measure the increasing perturbation in the local glass-transition temperature of one polymer chain with decreasing length scale of mixing in binary polyolefin blends. Solid-state 2H and 129Xe NMR experiments reveal a compositional miscibility window in side-chain concentration for polyisobutylene (PIB)/poly- (ethylene-co-butene) (PEB) blends. A combination of pulsed-field gradient and chemical shift data for xenon gas absorbed in these polymer blends indicates that the presence of polymer chains within a radius of ~35 nm of a different chain structure will perturb the intermolecular packing contribution to the total conformational energy of that chain, thereby changing its Tg

Macromolecules, 37(12), 4573-4579 (2004)

DOI: 10.1021/ma049263u   (Pobrane:  2020-08-10)


2.

Wolak_J., Jia X., Gracz H., Stejskal E.O., White J.L., Wachowicz M., Jurga S.

Polyolefin miscibility: solid-state NMR investigation of phase behaviour in saturated hydrocarbon blends Chain-level mixing in polyolefins is investigated for blends of polyisobutylene (PIB) and polyethylene-co-1-butene (PEB). Previous reports suggest that PIB exhibits unusual mixing behavior in certain saturated blends relative to other polyolefins, even though it is immiscible with most. Variable-temperature H-1, H-2, C-13, and Xe-129 NMR experiments are used to characterize local PIB chain dynamics in blends with PEB in which the concentration of 1-butene comonomer units is 23 or 66 wt %. Results from 1D and 2D solid-state C-13 exchange experiments, H-1 relaxation measurements, and H-2 line shape analysis indicate that local conformational dynamics of the PIB CH2 group in the polymer backbone increase significantly in blends with PEB copolymers containing 66 wt % butene comonomer (PEB-66). Even though the PEB-66 is a higher Tg polymer than PIB, PIB exhibits a lower effective Tg when the blend is formed relative to its pure state. Similar perturbations are not observed in the PIB/PEB-23 blend, indicating that this blend is not miscible at the chain level. These results are directly relevant to the length scale of glass transitions in polyolefins, indicating that local interchain packing plays an important role in the conformational dynamics that occur within a chain, and are suggestive of local configurational entropy contributions to mixing. Although H-1 spin-diffusion experiments could not reveal quantitative length scales of mixing in the these blends due to insufficient contrast between the constituents, Xe-129 NMR experiments showed that the PIB/PEB-66 blend was homogeneous on a 50 nm length scale. In agreement with the heterogeneous morphology indicated by the dynamic NMR experiments, Xe-129 NMR showed two resolved peaks for the PIB/PEB-23 blend, indicative of phase separation on a 50 nm length scale. The compilation of all the data, most of which was obtained at natural abundance, indicates that the PIB/PEB-66 blend exhibits intimate chain-level mixing on a length scale much shorter than R-g (ca. 8 nm). More importantly, the data show that reduced chain packing constraints occur in the miscible blend and suggest that local entropic contributions are the driving force for miscibility.

Macromolecules, 36(13), 4844-4850 (2003)

DOI: 10.1021/ma0301449   (Pobrane:  2020-08-10)


1.

Wachowicz M., Fojud Z., Jurga S.

Fast field cycling proton NMR relaxation in decylammonium chloride/water system We have investigated the dispersion of the proton spin-lattice relaxation times in decylammonium chloride/water systems, which exhibit different liquid crystalline phases of isotropic (micelles), lamellar (layers), hexagonal (layers rolled up into cylinders), and of nematic structures. The measurements were performed in the frequency range from 3·10^3 to 1.6·10^7 Hz and in the temperature range from 10°C to 85°C. The analysis of relaxation dispersion curves gave us information on local collective molecular dynamics of the alkylammonium chains.

Molecular Physics Reports, 33, 176-178 (2001)

WWW: http://www.ifmpan.poznan.pl/mol/
ISSN: 1505-1250   (Pobrane:  2021-01-07)


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