Die Deutung von Fließerscheinungen durch molekulare Platzwechsel

Holzmüller, W.

doi:10.1007/bf01499924

Cited by 11 publications

(1 citation statement)

References 5 publications

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“…An early attempt to calculate the molecular mobility in such systems was undertaken by Holzmüller in 1965 in his simple but successful Platzwechseltheorie ͑theory of site exchange͒. 30 He found a nearly Gaussian distribution of activation energies in his calculations, in accord with our observations. We like to stress that a prerequisite for the observation of this distribution are small length and time scales in the experiment which is the case here.…”

Section: A the Ordered Statesupporting

confidence: 77%

Self-diffusion of an asymmetric diblock copolymer above and below the order-to-disorder transition temperature

Fleischer

Rittig

Kärger

et al. 1999

The Journal of Chemical Physics

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Microphase separation in poly(isoprene-b-ethylene oxide) diblock copolymer melts. I. Phase state and kinetics of the order-to-order transitionsThe self-diffusivity of an asymmetric poly͑ethylenepropylene͒-poly͑dimethylsiloxane͒ diblock copolymer ͑PEP-PDMS͒ was investigated using pulsed field gradient NMR both in the ordered and the disordered state. In a temperature range below the order-to-disorder transition temperature, the diblock copolymer forms micelles which order in a simple cubic structure, and at lower temperatures, a noncubic structure is formed. We have found a broad distribution of self-diffusivities. The distribution width increases with decreasing temperature. The self-diffusivity as well as its distribution width changes only slightly at the order-to-disorder transition. In contrast to self-diffusion in symmetric diblock copolymers where single chains diffuse independently, our results are interpreted as a collective diffusion of chains confined to micelles which further cluster to larger aggregates. This behavior cannot be described by existing models of chain dynamics in the melt. The disordered state is characterized by a large temperature range above the order-to-disorder transition where concentration fluctuations dominate. This is revealed in the temperature dependence of the self-diffusivity and its distribution width, in the viscosity and in the inverse intensity of the first-order Bragg reflection in small angle neutron scattering ͑SANS͒.

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Section: A the Ordered Statesupporting

confidence: 77%

Self-diffusion of an asymmetric diblock copolymer above and below the order-to-disorder transition temperature

Fleischer

Rittig

Kärger

et al. 1999

The Journal of Chemical Physics

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Molekulare Beweglichkeit und Strukturänderungen erweichender amorpher Polymere in phänomenologischer und Kinetischer Sicht

Holzmüller

1987

Acta Polymerica

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Neben den verbreiteten phanomenologischen Betrachtungen fur das viskoelastische und viskose Verhalten erweichender Polymere haben sich die auf EYRING zuruckfuhrbaren Barrieretheorien bewahrt. In dieser Arbeit werden nichtlinearc Effekte zur Deutung herangezogen. Dabei wird gezeigt, daB bei der Bildung des frcien Volumens, also bei der Entstehung beweglicher FlieBelemente, eine Lockerung der Struktur erfolgt. Daruber hinaus wird die sich einstellende Sattigung der Zahl der beweglichen Elemente mit wacbsender Temperatur als ein Effekt zweiter Ordnung erklart. Oberhalb des Erweichungs-und Schmclzgebietes herrscht Arrhcniusverhalten. Alle beobachteten FlieBprozesse und Deformationen erweisen sich als Uherlagerungen von rein elastischer Deformation, viskoelastischer Verformung und viskosem FlieBen. Die neuerdings oft diskutierte Hoppingtheorie baut auf der Platzwechseltheorie auf. Im Fall der kautschukelastischen Delinung fuhrt die Berucksichtigung einer nichtlinearen Anderung des elastischen Potentials als Folgc einer HuBeren Beanspruchung zu einer S-formigen Krummung im Zug-Dehnungsverhalten, wobei in Erweiterung der MOONEY-RIvLIN-Beziehuiig die auftretende Sattigung zwanglos erklart wird.MoJcetcympnas no8smnocma u u3aenenufi cmpyxmypbi npu pa3~fizuenuu aaopg5nbcx noJcuaepos c @ e n~a e n~~c~~uuecfiol 14 xunemuuectcol mouetc apeuus

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Developing a hypothesis: Native cellulose elementary fibrils are formed with metastable structure

Stöckmann¹

1972

Biopolymers

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synopsisAny spinning of high-polymeric solutions and any extruding of high-polymeric melts produce fibrillar textures built-up of folded molecules with a predominantly uniform period. Because data strongly suggest extended molecules within native cellulose elementary fibrils, spinning or extruding as potential fibrillar growth mechanisms must be considered unlikely. Among the crystallization conditions known to produce extended chain structures, Crystallization with simultaneous polymerization appears the most plausible mechanism for forming elementary fibrils. The mechanism yields a structure distinguished by uniformity of lateral order along the fibrillar length axis with the lateral order being paracrystalline. Because thermodynamic equilibrium requires a fibrillar structure of alternating crystalline and amorphous regions, a newly grown elementary fibril is hypothesized to be in a thermodynamically unfavorable state. Intermolecular forces "freezing-in" the unfavorable state provide metastability. Whenever the intermolecular cohesion is weakened, a structural transformation of the paracrystalline fibril is predicted, which consists of the creation of distinctly disordered and distinctly well-ordered phases. Because disorder is created, a transforming fibril contracts longitudinally. The transformation must be expected to be gradual, which gives rise to a series of intermediate metastable structures of decreasing free energy levels. With lattice type I, a fibril, however, is believed unable to reach the stable state. The equilibrium structure characterized by coexistence of perfectly ordered crystallites with completely disordered regions is thought associated with lattice type 11.

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Die Deutung von Fließerscheinungen durch molekulare Platzwechsel

Cited by 11 publications

References 5 publications

Self-diffusion of an asymmetric diblock copolymer above and below the order-to-disorder transition temperature

Self-diffusion of an asymmetric diblock copolymer above and below the order-to-disorder transition temperature

Molekulare Beweglichkeit und Strukturänderungen erweichender amorpher Polymere in phänomenologischer und Kinetischer Sicht

Developing a hypothesis: Native cellulose elementary fibrils are formed with metastable structure

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