SANS Investigations of Topological Constraints in Networks Made from Triblock Copolymers

Westermann, Stephan; Urban, Volker S.; Pyckhout‐Hintzen, Wim; Richter, D.; Straube, E.

doi:10.1021/ma9602381

Cited by 26 publications

(37 citation statements)

References 24 publications

(60 reference statements)

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“…However, a standard application of the approximation is not appropriate here. One must take care to modify the standard RPA expression often used to analyse scattering experiments, before applying it to the system with quenched disorder [8,9]. The modifications arise from the fact that the density variables fluctuate about some non-zero mean determined by the disorder, which effectively correlates fluctuations associated with different wave vectors, necessitating an average over quenched disorder.…”

Section: Introductionmentioning

confidence: 99%

Microphase separation in cross-linked polymer blends

2009

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Abstract.We investigate the behaviour of randomly cross-linked (co)polymer blends using a combination of replica theory and large-scale molecular dynamics simulations. In particular, we derive the analogue of the random phase approximation for systems with quenched disorder and show how the required correlation functions can be calculated efficiently. By post-processing simulation data for homopolymer networks we are able to describe neutron scattering measurements in heterogeneous systems without resorting to microscopic detail and otherwise unphysical assumptions. We obtain structure function data which illustrate the expected microphase separation and contain system-specific information relating to the intrinsic length scales of our networks.

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Section: Introductionmentioning

confidence: 99%

Microphase separation in cross-linked polymer blends

2009

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“…In a recent paper, studies on polyisoprene homopolymer systems randomly cross-linked by peroxides were extended to the case of a HDH isotopic triblock copolymer with a deuterated middle block connected to two equally sized protonated wings. 10 There, the end-to-end distance of the labeled path was much longer than the average strand length between two cross-links. With respect to the homopolymer studies, this HDH system has the advantage that the labeled path may be firmly embedded into the macroscopic network, and no direct scattering contributions from labeled dangling chains ends, as is the case for fully labeled paths, will occur.…”

Section: Introductionmentioning

confidence: 99%

On the Length Scale Dependence of Microscopic Strain by SANS

Westermann¹,

Pyckhout‐Hintzen²,

Richter³

et al. 2001

Macromolecules

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We present a SANS study on the length scale dependence of chain deformation patterns in dense cross-linked elastomers. Three different polyisoprene networks of long primary block-copolymer chains of the HDH-type were analyzed. The total length of the primary chains is identical, while the length of the deuterated middle block was varied in order to cover several length scale regimes of interest. The scattering data are analyzed in the frame of the tube model of rubber elasticity in combination with the random phase approximation (RPA), which is used in order to account for the interchain correlations. We show experimentally that for the longest labeled path the rubber elastic response is dominated by both cross-link and entanglement contributions, whereas it is of clear phantomlike chain behavior if the labeled middle block of the chain is shorter than the distance between two successive entanglements, i.e., the tube diameter. We further propose schemes to quantify nonaffine deformations on various length scales and chain scissioning processes during the radical cross-linking process.

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“…These two types of structure factor may be written in terms of single chain structure factors, subjected only to tube constraints in deformed tubes A more intuitive and much simpler treatment of the scattering in undeformed and deformed melts follows the approach which was used in the description of permanent networks of long-labeled paths 34 or centerlabeled chains. 29 This approach is expected to be applicable with good accuracy for the scattering properties immediately after deformation because in the case of rapidly applied deformations a very network-like behavior should occur. For a description of the scattering during the arm relaxation process, the time evolution of correlations in the system must be taken into account approximately by the following considerations:…”

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confidence: 99%

“…Therefore, selective information like unrelaxed cross-bar configurations can be input. Details about the structure of the correlation functions in eq 14 are given in ref 29. The calculation of the bare structure factors in eq 15 is straightforward using the elementary Debye-like contributions (see e.g.…”

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confidence: 99%

Arm Relaxation in Deformed H-Polymers in Elongational Flow by SANS

Heinrich¹,

Pyckhout‐Hintzen²,

Allgaier³

et al. 2002

Macromolecules

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We present a small-angle neutron scattering (SANS) investigation of the relaxation process of branched polymer melts under deformation. The selected model polymer is an H-shaped polyisoprene having deuterium-labeled blocks at the dangling tips of the arms. The melt is step strained in a strain rig especially built for that purpose, where the sample temperature and its deformation conditions are precisely controlled. Uniaxial extensions to values of 2 and 3 are performed at a temperature above the polymer glass transition temperature T g. The sample is then allowed to relax during a given time before being quenched to below its Tg in order to freeze the chains conformation to perform the SANS experiments. Very large anisotropies in S(q) develop on time scales corresponding to the relaxation of the dangling arms. The experimental structure function is then compared to theoretical ones obtained by the random phase approximation applied to the tube model. While theory describes well the scattering for short times, it seems not to be able to describe the increase of intensity in the direction parallel to the strain at higher times, even when highly nonaffine processes such as arm retraction and branch point withdrawal are taken into account.

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SANS Investigations of Topological Constraints in Networks Made from Triblock Copolymers

Cited by 26 publications

References 24 publications

Microphase separation in cross-linked polymer blends

Microphase separation in cross-linked polymer blends

On the Length Scale Dependence of Microscopic Strain by SANS

Arm Relaxation in Deformed H-Polymers in Elongational Flow by SANS

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