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Digitale Medien

Investigation of the interface between polymers: a comparison of scattering and reflectivity techniques (1991)

Stamm, M.

Copenhagen : International Union of Crystallography (IUCr)

Applied crystallography online 24 (1991), S. 651-658

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ISSN: 1600-5767

Quelle: Crystallography Journals Online : IUCR Backfile Archive 1948-2001

Thema: Geologie und Paläontologie , Physik

Notizen: With the techniques of small-angle X-ray scattering (SAXS) and small-angle neutron scattering (SANS) the interfacial region between polymers forming a two-phase structure can be investigated. Various approaches are possible including the classical Porod analysis as well as the Fourier transform, sandwich or contrast-matching techniques. Their application for the determination of the interface width and profile between polymer phases is discussed. As an alternative method X-ray and neutron reflectometry from polymer layer systems has recently been introduced. It allows an accurate determination of various interfacial parameters provided a flat and smooth interface with sufficient contrast between the materials can be prepared. The techniques are compared and discussed with respect to the information which is obtained on the interfacial region of polymers.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1107/S0021889891000821

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Digitale Medien

Comparison of the behaviour of polymers in supercritical fluids and organic solvents via small-angle neutron scattering (2000)

Melnichenko, Y.B. ; Kiran, E. ; Heath, K.D. ; [weitere]

Copenhagen : International Union of Crystallography (IUCr)

Applied crystallography online 33 (2000), S. 682-685

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ISSN: 1600-5767

Quelle: Crystallography Journals Online : IUCR Backfile Archive 1948-2001

Thema: Geologie und Paläontologie , Physik

Notizen: Small-angle neutron scattering has been used to study the effect of temperature and pressure on the phase behaviour of semidilute solutions of polymers dissolved in organic and supercritical solvents. Above the theta temperature (TΘ), these systems exhibit a "good solvent" domain, where the molecules expand beyond the unperturbed dimensions in both organic solvents and in CO2. However, this transition can be made to occur at a critical "theta pressure" (PΘ) in CO2 and this represents a new concept in the physics of polymer-solvent systems. For T 〈 TΘ, and P 〈 PΘ, the system enters the "poor solvent" domain, where diverging concentration fluctuations prevent the chains from collapsing and allow them to maintain their unperturbed dimensions.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1107/S0021889899013229

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Digitale Medien

Study on interdiffusion of polystyrenes of high molecular weight by SANS (1991)

Brautmeier, D. ; Stamm, M. ; Lindner, P.

Copenhagen : International Union of Crystallography (IUCr)

Applied crystallography online 24 (1991), S. 665-671

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ISSN: 1600-5767

Quelle: Crystallography Journals Online : IUCR Backfile Archive 1948-2001

Thema: Geologie und Paläontologie , Physik

Notizen: The interdiffusion coefficient Dint of polystyrenes of different molecular weights has been measured. The small-angle neutron scattering (SANS) intensity from a sandwich-like sample consisting of alternating deuterated and protonated films is determined as a function of time and analysed with respect to Dint. In the symmetrical case both components have the same molecular weight and interdiffusion coefficients may be scaled according to the reptation theory D ̃M−2. The WLF (Williams–Landel–Ferry) temperature behaviour is observed. In the asymmetrical case using low- and high-molecular-weight polystyrenes, the interdiffusion is dominated by the faster-moving species. The fast-mode diffusion theory best describes the result. The influence of a non-zero Flory-Huggins interaction parameter χ between deuterated and non-deuterated material has been taken into account showing a significant slowing down for the high-molecular-weight material.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1107/S0021889890013024

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