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  • 1
    Electronic Resource
    Electronic Resource
    Aggregating block copolymers as model systems to study polymer brush dynamics (1994)
    Springer
    Il nuovo cimento della Società Italiana di Fisica 16 (1994), S. 747-755 
    Details
    ISSN: 0392-6737
    Keywords: Neutron scattering techniques (including small-angle scattering) ; Polymers, elastomers, and plastics ; Fluctuation phenomena, random processes and Brownian motion ; Conference proceedings
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Summary A-B block copolymers in a selective solvent—good for the B-species and bad for the A-species—form micellar aggregates with a compact A-core with a corona (brush) of B «hairs» reaching into the solvent. Whereas polystyrene(PS)-polyisoprene(PI) in decane forms spherical micelles with a PS core of about 10 nm radius, polyethylene(PE)-polyethylenepropylene(PEP) forms micellar platelets, the shape of which is goverend by the habitus of PE crystallites forming the core. These planar aggregates have large (several hundred nanometers) lateral extension and a core thickness in the range of 10 nm. Both systems are model systems for polymer brushes, either on a spherical surface or planar. Neutron spin-echo experiments allow for the investigation of the dynamics of the brushes which reflects their viscoelastic properties. Results of neutron small-angle and spin-echo investigations are reported. The brush dynamics is explained using a model based on an idea of de Gennes describing the brush properties in terms of scaling relations for osmotic pressure and viscosity of a semi-dilute solution with inhomogeneous density.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02456720
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  • 2
    Electronic Resource
    Electronic Resource
    Dynamics of bicontinuous microemulsion phases with and without amphiphilic block-copolymers (2001)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 115 (2001), S. 9563-9577 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Neutron Spin Echo and Dynamic Light Scattering techniques are used for an extensive investigation of the bicontinuous phase in water/decane microemulsions. The dynamical behavior of different surfactant systems, decyl polyglycol ether (C10E4), C10E4 mixed with polyethylenepropylene/polyethyleneoxide amphiphilic block-copolymers-(PEPx/PEOy), and sodium-bisethylhexylsulfosuccinate (AOT) is investigated under comparable conditions. At scattering wave numbers q large compared to the inverse of the structure length scale, q0=2π/d, always stretched exponential relaxations ∝e−(Γqt)β with Γq∝q3 are found, as predicted theoretically. The relaxation rate increases almost linearly as function of the bicontinuous structure correlation scale—ξ(similar, equals)d/2. The apparent bare bending modulus κ determined by fitting theoretical predictions to the experimental high-q data yields values of about 1.3kBT—as inferred from previous small angle neutron scattering (SANS) studies and from other methods. The effect of increasing rigidity of the surfactant layers by anchoring amphiphilic block-copolymers, predicted theoretically and revealed experimentally in structural investigations, could not be clearly resolved due to its small influence on the dynamics. At structural length scales, the relaxation rate in water–oil contrast shows a minimum corresponding to the maximum of the static structure factor. At length scales much larger than the typical structure length the relaxation is single-exponential with a q2 dependent rate. In this regime we find indications of the additional membrane interaction due to the presence of block-copolymers. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1413509
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  • 3
    Electronic Resource
    Electronic Resource
    Effect of amphiphilic block copolymers on the structure and phase behavior of oil–water-surfactant mixtures (2001)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 115 (2001), S. 580-600 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The effect of amphiphilic diblock copolymers of several molecular weights on the structure and phase behavior of ternary amphiphilic systems (water, oil, and nonionic surfactant) is investigated. Small amounts of amphiphilic block copolymer polyethyleneoxide–polyethylpropylene lead to a dramatic decrease of the amount of total surfactant needed to solubilize given equal volumes of water and oil in a bicontinuous microemulsion. Neutron scattering experiments employing a high-precision two-dimensional contrast variation technique demonstrate that the polymer is distributed uniformly on the surfactant membrane. Based on these observations, we propose a mechanism for the enhancement of swelling behavior, which is due to the variation of the membrane curvature elasticity by polymer mushrooms anchored to the interface. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1377881
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  • 4
    Electronic Resource
    Electronic Resource
    From Rouse dynamics to local relaxation: A neutron spin echo study on polyisobutylene melts (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 6107-6120 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We investigated the single chain motions of monodisperse polyisobutylene chains in the melt by neutron spin echo spectroscopy. Thereby a wide range in momentum space over a large dynamic range was covered. Motional processes from the center of mass diffusion, the Rouse dynamics to the more local relaxation processes which limit the validity of the standard Rouse model, were elucidated. The observed dynamic structure factors were analyzed in terms of relevant theoretical approaches addressing the limiting factors of the Rouse model. We found that other than claimed in the literature effects of local chain stiffness—they were treated in terms of the all rotational states model and a bending force model—cannot account for the experimental observations. It appears that additional damping effects related to an internal viscosity of the chain have to be involved, in order to explain the experimental results. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.479907
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  • 5
    Electronic Resource
    Electronic Resource
    Methyl rotational potentials and transferable pair potentials in toluene (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 98 (1993), S. 5653-5661 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The crystal structure of α-phase toluene at 5 K has been refined from high resolution neutron powder diffraction data and the charge distribution in the molecule calculated ab initio. From these data, methyl rotational potentials of the two inequivalent methyl groups have been calculated for various parametrizations of transferable pair potentials and compared with potentials derived from tunneling and librational transitions. The results demonstrate that the inclusion of Coulomb interactions is necessary to reproduce the equilibrium orientations of the methyl groups. However, none of the model pair potentials yield the very strong sixfold contribution of the rotational potential of methyl group 1. The best approximation to the experimentally determined values is obtained with the pair potential parameters of Kitaigorodskii [Acta Crystallogr. 18, 585 (1965)]. However, by the inclusion of existing results on p-xylene, the average agreement obtained with the parametrization of Claverie [Acta Crystallogr. Part A 31, 448 (1975)] is equally good. Overall, it was found that general improvements can be made if the repulsive parts of the model pair potentials are softened. The presence of two inequivalent methyl groups in toluene which are influenced in different ways by the various contributions to the interaction provides a rigorous test of the modeling techniques.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.464914
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  • 6
    Electronic Resource
    Electronic Resource
    Methyl rotation in acetamide: the transition from quantum mechanical tunneling to classical reorientation studied by inelastic neutron scattering (1989)
    Springer
    The European physical journal 76 (1989), S. 77-88 
    Details
    ISSN: 1434-6036
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Quasielastic and inelastic incoherent neutron scattering has been used to study in detail the transition from quantum mechanical tunneling motion to classical reorientation of the methyl groups in rhombohedral acetamide CH3CONH2. The temperature dependence of the low temperature quasielastic and inelastic scattering due toE a E b and AE transitions of the tunneling methyl groups has been investigated with μeV resolution and — together with the higher temperature quasielastic scattering-compared with theoretical predictions. Microscopic theories are capable to describe most of the experimental observations at low temperatures. A heuristic theoretical approach accounts well for the high temperature results.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01323489
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  • 7
    Electronic Resource
    Electronic Resource
    Coupling the methyl group in acetamide to phonons: a consistent view of tunnelling and lattice dynamics (1994)
    Springer
    The European physical journal 94 (1994), S. 69-77 
    Details
    ISSN: 1434-6036
    Keywords: 63.20 ; 63.70
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Inelastic neutron spectra of acetamide-h5 and acetamide-h2 have been measured at different temperatures below 40K and with high energy resolution in the energy range up to 15 meV. A lattice dynamical model on the basis of atom-atom potentials and electric charges obtained from first principles calculations describes the spectra well if soft internal molecular modes are included. The model is used to reproduce the temperature dependence of the tunnelling transition of the methyl group. For this purpose the density of states is split into that of an isolated rotor in a static field and that of the phonon bath. The effects of the rotor-phonon coupling are evaluated in second order perturbation theory. The broadening of tunnelling lines comes out correctly when the atom atom potentials taken from literature are scaled down by 20%. To get the shift right the strength of the coupling to the lattice needed to be different for the A type symmetry state from that for the E type state. The coupling with the low frequency phonons appears to be very weak.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01307656
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  • 8
    Electronic Resource
    Electronic Resource
    Dynamical aspects of self-organized (macro) molecular systems investigated by neutron spin-echo spectroscopy (1997)
    Springer
    Colloid & polymer science 106 (1997), S. 112-117 
    Details
    ISSN: 1435-1536
    Keywords: Neutron spin-echo ; relaxation dynamics ; molecular aggregates ; microemulsions ; block copolymers
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Neutron spin-echo (NSE) spectroscopy is a tool to close the gap between light scattering and more conventional neutron spectroscopies. It may also be viewed as an augmentation of small-angle scattering with inelastic, dynamical information. Using a microemulsion system as example for a system of molecular aggregates and a block-copolymer system forming macromolecular aggregates, it is shown what type of dynamics is observable by NSE-spectroscopy. The lamellar phase of a SDS-pentanol-water microemulsion allows for the investigation of different layer modes (undulation, peristaltic mode) the dynamics of which are determined by elastic properties of the interface layers and by the friction due to fluid flow between the layers. Platelet-like aggregates of polyethylene-polyethylenebutylene (PE-PEP) copolymers formed upon cooling a decane solution exhibit a polymeric brush of PEP-hairs on their surface. The fluctuation dynamics of this brush determined by a balance of solvent friction and entropie restoring forces has been observed by NSE spectroscopy. Besides, the direct dynamical information the NSE data allow for the separation of static scattering due to the average structure from the scattering contributions due to mobile fluctuating parts of the sample.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01189503
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  • 9
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    Frozen concentration fluctuations in a poly(N-isopropyl acrylamide) gel studied by neutron spin echo and small-angle neutron scattering (2002)
    Springer
    Details
    Publication Date: 2002-12-01
    Print ISSN: 0947-8396
    Electronic ISSN: 1432-0630
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Published by Springer
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  • 10
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    Neutron spin-echo investigation of the microemulsion dynamics. in bicontinuous, lamellar and droplet phases (2002)
    Springer
    Details
    Publication Date: 2002-12-01
    Print ISSN: 0947-8396
    Electronic ISSN: 1432-0630
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Published by Springer
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