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Aggregating block copolymers as model systems to study polymer brush dynamics (1994)

Monkenbusch, M. ; Schneiders, D. ; Richter, D. ; [et al.]

Springer

Il nuovo cimento della Società Italiana di Fisica 16 (1994), S. 747-755

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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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Neutron spin echo studies on the segmental diffusion behavior in the different chain sections of high molecular weight poly(dimethylsiloxane) melts (1994)

Ewen, B. ; Maschke, U. ; Richter, D. ; [et al.]

Weinheim : Wiley-Blackwell

Acta Polymerica 45 (1994), S. 143-147

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ISSN: 0323-7648

Keywords: Chemistry ; Polymer and Materials Science

Source: Wiley InterScience Backfile Collection 1832-2000

Topics: Chemistry and Pharmacology , Physics

Notes: Using neutron spin echo spectroscopy, the dynamics of high molecular weight poly(dimethylsiloxane) in the melt (T=473 K) was investigated. In order to decide whether the lateral constraints are uniform or nonuniform with respect to the contour of a test chain, chains were labeled either completely or partially by a corresponding proton-deuterium exchange. It was found that the central and the terminal chain sequences experience the same amount of lateral confinement, which-in the framework of the reptation or tube model-can be characterized by a tube diameter dt of about 70 Å. Nearly the same dt value is obtained from the plateau modulus of rheological measurements, too. Thus, these experiments show unambiguously that the lateral constraints, responsible for the reptational chain dynamics, are quite homogeneous, even in the case of extremely large tube dimensions.

Additional Material: 4 Ill.