Linear Viscoelasticity of Disordered Block Copolymers

Owing to the presence of microdomain structures, the rheological behavior of block copolymers in an ordered state (at odt) is much more complicated than that in the disordered state (at T For instance, block copolymers with lamel- 

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Molecular Theory for the Linear Viscoelasticity of Disordered Block Copolymers... 

Since the first theoretical attempts in the 1970s (Hall and DeWames 1975 Hansen and Shen 1975a, 1975b Stockmayer and Kennedy 1975 Wang and DiMarzio 1975) to describe the chain dynamics of disordered block copolymers, little progress has been made. The molecular theory for the linear viscoelasticity of disordered block copolymers is still in its infancy. In this section, we present first the currently held linear viscoelasticity theory for unentangled disordered block copolymer and then an extended version for disordered, entangled block copolymer. 

At present there is no comprehensive theory predicting the linear viscoelasticity of disordered entangled block copolymers. As shown in Chapter 7, which discusses the dynamics of miscible polymer blends, the inclusion of the intermolecular interactions (perhaps via segmental interaction parameter) between the constituent blocks in a block copolymer would be very important to the development of a comprehensive molecular theory predicting the linear viscoelasticity of disordered block copolymers. 

Ren, J., SUva, A. S., and Krishnamoorti, R., Linear viscoelasticity of disordered polystyrene-polyisoprene block copolymer based layered-silicate nanocomposites. Macromolecules, 33, 3739-3746 (2000). 

Theory for block copolymer rheology is still in its infancy. There are no models that can predict the rheological behaviour of a block copolymer from microscopic parameters. Fredrickson and Helfand (1988) considered fluctuation effects on the low frequency linear viscoelastic properties of block copolymers in the disordered melt near the ODT. They found that long-wavelength transverse momentum fluctuations couple only to compositional order parameter fluctua-... 

In this section, we present the effect of block composition (block length ratio) on the linear dynamic viscoelasticity of disordered PS- /ocfc-poly(a-methylstyrene) (PaMS) copolymers and also SI diblock copolymers in the disordered state. Table 8.3 gives a summary of the molecular characteristics for seven PS- tocA -PaMS copolymers, and Figure 8.38 gives thermograms of differential scanning calorimetry (DSC) for the seven... 

The order-disorder transition temperature (ODT) of the block copolymer was determined using a temperature scan under isochronal conditions, which involves measuring the dynamic storage modulus (G ) at a constant frequency (co = 0.2 rad/s) with temperature increasing from 130°C to 240°C in the linear viscoelastic regime. 

At present, there is no comprehensive theory for the chain dynamics of disordered, entangled block copolymers. Using the concept of the tube model, Kim and Han (1992) modified on an ad hoc basis the Stockmayer-Kennedy theory to interpret their experimental results for the linear viscoelastic behavior of disordered, entangled PS-block-PaMS copolymers. They used the expression... 

We have presented experimental observations for the linear dynamic viscoelasticity of low-molecular-weight SI diblock copolymers in the disordered state. We have shown that the log G versus log G" plot is very useful for investigating the effects of molecular weight and block length ratio on the linear dynamic viscoelasticity of block copolymers. The experimental results were compared with currently held theory for disordered, unentangled AB-type and ABA-type block copolymers. 

Wu L, Cochan EW et al (2004) Consequences of block number on the order — disorder transition and viscoelastic properties of linear (AB)n multiblock copolymers. Macromolecules 37 3360-3368... 

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