Flow-Induced Structure and Viscoelastic Properties of Poly(styrene-block-2-vinylpyridine)s Solutions near the Order–Disorder Transition

Abstract

ABSTRACT:Flow effects on the structure and the related viscoelastic properties of lamellar forming poly(styreneblock-2-vinylpyridine)s (SP) and DP in which S in SP replaced by deutrated chains are studied by small angle neutron scattering (SANS) and viscoelastic measurements under shear flows near the order-disorder transition (ODT). A distinctive feature of this sample is that both components have quite similar viscoelastic properties. In the quiescent ordered states, SANS intensities showed strong anisotropy denoting flow-induced alignment of lamellar structure at high shear rates ( _ ) in a limited range of concentration. When the lamellae are well aligned, first normal stress difference was proportional to _ 2 and reduced steady state compliance J eR became practically the same as those of components. The viscosity behaviors in the quiescent ordered and disordered states were also the same as those of components. In the disordered states, on the other hand, J eR was higher than those of components. Under steady shear flows, however, SANS intensities are isotropic and became lower and J eR became almost the same as those of components denoting the suppression of fluctuation effects. Block copolymers possess different microphaseseparated structure in the ordered states, such as sphere, cylinder, co-continuous and lamella, depending on the molecular structure and compositions of components. In the disordered states but near the order-disorder transition (ODT), there exist composition fluctuations of component polymers in the block copolymer liquids. Both the microphase separated structure and the composition fluctuations affect the rheological properties of block copolymers, therefore, structure and the related viscoelastic properties of the block copolymers have been extensively studied both in the ordered and the disordered states. General results of rheological properties for variety of block copolymers are summarized in review articles.

A Separation Method of Responses from Large Scale Motions and Chain Relaxations for Viscoelastic Properties of Symmetric Poly(styrene-<i>b</i>-2-vinylpyridine)s in the Ordered State

“…Therefore, apparent η 0 and J e of SP solutions can be obtained in the ordered states, which also became practically the same as those of corresponding components solutions. 27,28) Above results may mean that terminal relaxation behaviors of diblock copolymer chains are similar with homopolymers near the ODT. That is, existence of lamellar interface does not affect the relaxation of whole chains in weak segregation regime, at least in solutions.…”

“…[20][21][22][23][24][25] Takahashi et al studied viscosity 26) , flow-induced structure and related viscoelastic properties 27,28) of poly(styrene-b-2-vinylpyridine)s (SPs) in common good solvents. Since polystyrene (PS) and poly(2-vinylpyridine) (P2VP) have the same Kuhn segment length [29][30][31] , the same glass transition temperature and almost the same viscoelastic properties at melt states and in common good solvents, 32,33) comparison between the data for diblocks and component homopolymers , respectively.…”

Viscoelastic Properties of Low Molecular Weight Symmetric Poly(styrene-<i>b</i>-2-vinylpyridine)s in the Ordered and Disordered States under Steady Shear Flow

“…[29][30][31] Corresponding structural changes under the flow are examined by small angle neutron scattering (SANS) using deutrated SP (DP). 30,31,[36][37][38] In the disordered states 30) , no fluctuation effect was observed on G" and shear stress σ so that the η 0 values obtained by dynamic and steady flow measurements are practically the same as those for components' solutions. 32,39) To further examine the viscoelastic properties of block copolymers, it is very interesting and essential to study SP diblocks in comparison with components for more wider range of χN in melt states, where stronger fluctuation effects are expected as shown by a previous study.…”

Hysteresis Behavior in Shear Rate Dependence of First Normal Stress Difference of Diblock Copolymers in Ordered State near Order-Disorder Transition

“…That is, N 1 is proportional to shear rate _ at low _ but N 1 become proportional to _ 2 at high _ . 1,4 An exceptional behavior was observed for DP and SP solutions just above ODT concentration, C ODT . There was no apparent change in the _ dependence of N 1 ; _ dependence of N 1 was slightly lower than _ 2 in the whole range of tested shear rate.…”

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KEY WORDSPoly(styrene-block-isoprene)s / Poly(styrene-block-2-vinylpyridine)s / FlowInduced Alignment / Lamellae / First Normal Stress Difference / [doi:10.1295/polymj.PJ2006158] In previous papers, [1][2][3][4][5] we reported viscoelastic properties and flow-induced structure of symmetric poly(styrene-block-2-vinylpyridine)s (SP) and poly-(styrene-d 8 -block-2-vinylpyridine)s (DP) in a common good solvent, -chloronaphtharene (-CN) and poly(styrene-block-isoprene)s (SI) and poly(styrened 8 -block-isoprene)s (DI) in dioctyl phthalate (DOP) near the order-disorder transition (ODT). Note that viscoelastic properties of components of DP and SP are almost the same.

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