Static and dynamic scattering at the microphase separation transition in block copolymers

Hoffmann, Alexander; Koch, T.; Schuler, M.; Stickel, F.; Stühn, Bernd

doi:10.1007/bfb0116458

Cited by 3 publications

(2 citation statements)

References 16 publications

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“…There have been speculations that relate such a length scale dependence to the cooperative nature of the glass transition.17 A continuation of our measurements to lower frequencies could help to test these ideas as there are two length scales available in the polyisoprene system on which relaxational dynamics may be studied. About 20 K above Tt both normal and segmental modes display a temperature dependence which is in accordance with the WLF description C^T-TJ log vma = log vQ + C^+T_T (10) vmax = wmai/2x is the position of the maximum in <"( ), and log »o, Ci, and C2 are the WLF parameters. We use the glass transition temperature Tt = 204 K as the reference temperature.…”

Section: ¡7supporting

confidence: 78%

Dielectric normal mode spectroscopy in the ordered and disordered states of diblock copolymers

Stuehn¹,

Stickel²

1992

Macromolecules

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Section: ¡7supporting

confidence: 78%

Dielectric normal mode spectroscopy in the ordered and disordered states of diblock copolymers

Stuehn¹,

Stickel²

1992

Macromolecules

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“…The scattered intensity I(q) at scattering vector q is related to the correlation of concentration fluctuations S(q) /(<?) = VKS(q) (7) where V denotes the volume of a polymer chain and K is Table II. Characteristic Temperatures and the Position q* of the Maximum in S(q) (in the scattering contrast factor given as the square of the electron density difference between isoprene and styrene.…”

Section: Resultsmentioning

confidence: 99%

Effect of the disorder-to-order transition in diblock copolymers on the segmental dynamics: a study using depolarized photon correlation spectroscopy

Hoffmann¹,

Koch²,

Stuehn³

1993

Macromolecules

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Depolarized light scattering has been applied to study the anisotropy fluctuations in a series of polystyrenelpolyisoprene diblock copolymers. This method is selective for the dynamica of the polystyrene block. The molecular weights of the block copolymers (10500-20800) were chosen such that the microphase separation transition (MST) occurs at temperatures which are experimentally acceeeible with photon correlation spectroscopy. Small-angle X-ray scattering (SAXS) was used to identify the disordered regime, the fluctuationcontrolled transition regime, and the ordered state. The relaxation time spectrum in the disordered state is similar to that of bulk polystyrene. Concentration fluctuations increasingly broaden the spectrum and lead to a bimodal shape. Close to the MST the spectrum becomes dominated by a slow, nearly single exponential contribution. Comparison with the SAXS results suggests that this splitting of the relaxation time spectrum can be related to chain stretching.

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Computer simulations of asymmetric block copolymers

Hoffmann¹,

Sommer²,

Blumen³

1997

The Journal of Chemical Physics

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We simulate dense diblock copolymer melts using the lattice bond-fluctuation method. Letting the lengths NA and NB of the A- and B-subchains vary (with NA+NB=N) we study the dependence of the static and dynamic properties on f=NA/N. Changes in the A-B interaction parameter allow to mimic large temperature variations. Thus at low T we find, depending on f, lamellar, hexagonal or micellar structures, as evident from the appearance of Bragg-reflexes in the collective structure factor S(q); for high temperatures S(q) is well approximated by a generalized Leibler form. The single chain statics reveals non-mean-field behavior even well above the order-disorder transition (ODT). Near the ODT the copolymer chains are, as a whole, stretched whereas the blocks contract slightly; the maximal contraction occurs near the spinodal Tsp. We evaluate the mean repulsive energy felt by the monomers and its dependence on the monomer’s position along the chain. From the variance of the repulsive energy we calculate cv, the specific heat per chain; cv is continuous both near Tsp and near the ODT. Surprisingly, cv scales with ε2Nf(1−f ), where ε is the microscopic energy parameter of the simulations. As dynamical features we compute D, the diffusion coefficient of single chains and the rotational relaxation times τ of the end-to-end vector: D scales with εf(1−f ), whereas the τ-times show complex f-dependencies, facts which stress that the diffusional motion and the rotational relaxation behave differently.

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Static and dynamic scattering at the microphase separation transition in block copolymers

Cited by 3 publications

References 16 publications

Dielectric normal mode spectroscopy in the ordered and disordered states of diblock copolymers

Dielectric normal mode spectroscopy in the ordered and disordered states of diblock copolymers

Effect of the disorder-to-order transition in diblock copolymers on the segmental dynamics: a study using depolarized photon correlation spectroscopy

Computer simulations of asymmetric block copolymers

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