Papers by Dietmar Schwahn
Physical Review Letters, 1996
The structure factor of a poly(ethylene-propylene)-poly(dimethylsiloxane) diblock copolymer has b... more The structure factor of a poly(ethylene-propylene)-poly(dimethylsiloxane) diblock copolymer has been measured by small-angle neutron scattering as a function of temperature and pressure. The conformational compressibility exhibits a pronounced maximum at the order-disorder phase transition. The phase boundary shows an unusual shape. With increasing pressure it first decreases and then increases. Its origin is an increase, respectively, of the entropic and of the enthalpic part of the Flory-Huggins interaction parameter. The Ginzburg parameter describing the limit of the mean-field approximation is not influenced by pressure. [S0031-9007(96)01379-8] PACS numbers: 61.25.Hq, 61.12.Ex
Crossover from mean field to three-dimensional Ising critical behavior in a three-component microemulsion system
Physical review. E, Statistical physics, plasmas, fluids, and related interdisciplinary topics, 1996
... The data are found exclusively in the crossover region between the universality class of thre... more ... The data are found exclusively in the crossover region between the universality class of three-dimensional Ising and ... The phenomenon of critical density fluctuations in mi-celles and microemulsions with droplet structure can be treated analogously to simple fluids. ...
Fractal structures of a poly(N-isopropylacrylamide) gel studied by small-angle neutron scattering over a Q-range from 10 −5 to 0.1 Å −1
Physica B, 2000
We report the microscopic structures observed in the poly(N-isopropylacrylamide) (NIPAAM) gel ove... more We report the microscopic structures observed in the poly(N-isopropylacrylamide) (NIPAAM) gel over a wide temperature range from swollen to collapsed phases. We employed pinhole (SANS) and double crystal (DSANS) small-angle neutron scattering diffractometers in order to cover wider length scales. We will discuss the observed power-law q-behaviors, based on the mass and surface fractals.
Proton motion of poly(gamma-benzylL-glutamate) in benzyl alcohol during gelation as measured by quasielastic neutron scattering
Aps Meeting Abstracts, Mar 1, 2004
We demonstrate that macromolecules in miscible polymer blends may behave as poor, theta and good ... more We demonstrate that macromolecules in miscible polymer blends may behave as poor, theta and good polymeric solvents for each other. We construct a conceptual phase diagram, indicating the range of validity of the random phase approximation, outside of which molecules contract or expand beyond their unperturbed dimensions, contrary to common assumptions. Similarly, the concentration fluctuation correlation length collapses onto a master curve for polymeric, liquid and supercritical solvents, indicating that macromolecules behave universally in these media over a wide range of thermodynamic variables.
Deviation of early stage of spinodal decomposition from the Cahn-Hilliard-Cook theory observed in an isotopic polymer blend
Physica B, 1997
The early stage of spinodal decomposition was studied by small-angle neutron scattering in the cr... more The early stage of spinodal decomposition was studied by small-angle neutron scattering in the critical mixture of the isotopic blend deutero-polystyrene/polystyrene (d-PS/PS) of equal molecular volume of 1.42 × 10 6 cm 3/mol. The time evolution of this process is described by the dynamical structure factor. The observed time evolution of the fluctuation modes is a non-exponential. The analysis of the data has shown that the non-exponential behavior was attributed to a time-dependent increase of the “range” of the Onsager coefficient.
Physica B Condensed Matter, Apr 1, 1998
Thermal composition fluctuations were studied by SANS in two d-PB/PS binary polymer mixtures as a... more Thermal composition fluctuations were studied by SANS in two d-PB/PS binary polymer mixtures as a function of temperature and pressure. The difference between both blends is related to the microstructure. The structure factor at scattering vector Q=0 was analyzed by a crossover function from which the critical temperature, the Ginzburg number and the entropic term of the Flory-Huggins interaction parameter were obtained. Our experiments show that Gi is influenced by the microstructure and is connected to the packing of the polymers.
Effect of organic Matter on RO Membrane Scaling in Wastewater Desalination
Acta Crystallographica Section A Foundations and Advances, 2014
J Polym Sci B Polym Phys, 1996
Quasielastic neutron scattering has been used to study the motion of protons in two solutions of ... more Quasielastic neutron scattering has been used to study the motion of protons in two solutions of poly(y-benzyl L-glutamate) (PBLG) and deuterated benzyl alcohol (DBA) as they are brought from the high temperature (cholesteric and isotropic) phase towards the gel. Quasielastic neutron scattering results demonstrate that, in both the isotropic and cholesteric phases, the local rotational dynamics of the polymer are continuous in the high temperature phases, but become more constrained as the system approaches and enters the gel phase. The results also show that the energetics of the rotational motion of the protons below the gelation threshold are independent of the initial phase and the protons are not rendered immobile in the gel phase. 0 1996 John Wiley & Sons, Inc. Keywords: liquid crystalline polymer quasielastic neutron scattering gelation rotational dynamics and poly(y-benzyl L-glutamate)
Journal of Applied Crystallography, Jun 1, 2003
The role of the double-hydrophilic block copolymers (poly(ethylene glycol)-block-poly(methacrylic... more The role of the double-hydrophilic block copolymers (poly(ethylene glycol)-block-poly(methacrylic acid)) on the morphogenesis of calcium carbonate (CaCO3) was studied by applying contrast variation small-angle neutron scattering (SANS). The scattering function for ternary systems can be expressed by only partial scattering functions of the single species, as derived on the assumption of incompressibility. We demonstrate the feasibility of this formula by means of contrast variation SANS, and the decomposed partial scattering functions give their detailed information. Especially the partial scattering function of polymer shows a Q −2.7 monotonic slope at low Q (0.002Å < Q < 0.02Å; Q is the modulus of the scattering vector), which is a clear evidence that the distribution of the polymer in CaCO3 has a mass fractal dimension. This result is confirmed by time-resolved SANS experiments with CaCO3 contrast, where a Q −2.5 slope was observed at the early stage of the reaction in the same Q range.
Le Journal de Physique Colloques, 1977
R b 6 . -Par diffusion des neutrons thermiques on a examine les cinetiques d'agglomeration dans l... more R b 6 . -Par diffusion des neutrons thermiques on a examine les cinetiques d'agglomeration dans les alliages Cu-Ni. Pour optimatiser les conditions de l'expkrience on a utilisi: les isotopes 6 5 C~ et 62Ni. L'tvolution dans le temps de I'intensitk diffuse 1 400 O C a 6te mesurCe pour 8 alliages Cu-Ni de compositions comprises entre 30 et 80 at. % de nickel. La relaxation de la matrice null dans le cas d'un alliage A 56,5 at. % de nickel a ete aussi etudiee A 320, 340, 425 et 450 OC. Ces mesures ont ete
Le Journal De Physique Iv, Dec 1, 1993
Early state of spinodal decomposition in a symmetric isotrope mixture d-PS/PS has been studied wi... more Early state of spinodal decomposition in a symmetric isotrope mixture d-PS/PS has been studied with SANS at two temperatures well below T,. Nonexponential time behaviour was found according to internal relaxation modes of the polymer. The data could satisfactorily be described by an ansata from Akcasu which includes internal relaxation modes approximately and is an extension of the Cahn-Hilliard-Cook theory for polymer blends. The interaction range for the Onsager coefficient was found increasing with time and larger than the radius of gyration.
Exponential and non-exponential relaxation and early state of spinodal decomposition in polymer blends by SANS
Progress in Colloid & Polymer Science, 1993
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The Temperature Dependence of the Chemical Potential of Tetradecyldimethylaminoxide Micelles in D2O - A SANS Study
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Neutron-scattering studies of an electron-irradiated /sup 62/Ni-- 41. 4-at. %-/sup 65/Cu alloy
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Double Crystal Diffractometer (DKD)
Neutronenkleinwinkelstreuung an der Leigierung Al-Zn oberhalb des kritischen Punktes /
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In Dynamics of Ordering Processes in Condensed Matter
Polymer Motion in Dense Systems
The SiO2-Al2O3 System. Part I-Later Stage Spinodal Decomposition and Metastable Immiscibility
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Papers by Dietmar Schwahn