Disordered block copolymers

Dynamic light scattering has traditionally been applied to polymer solutions, and DLS results for block copolymer solutions are discussed in Chapters 3 and 4. A number of recent papers have described the application of the technique to disordered block copolymer melts (Anastasiadis et al. 1993a,6 Boudenne et al. 1996 Floudas et al. 1995 Fytas et al. 1993 Jian et al. 1994a Stepanek and Lodge 1996 Vogt et al. 1994). Due to the limited range of dynamic time-scales that can... 

Mansky P, Russell TP, Hawker CJ, Mays J, Cook DC, Satija SK (1997) Interfacial segregation in disordered block copolymers Effect of tuneable surface potential. Phys Rev Lett 79(2) 237-240... 

Dielectric loss e" measured at 10°C for a PI12/PVE60 miscible blend with Mp = 1.2 x W, Mpvp = 6 X lO, and Wp, = 17 wt% (circles). Dotted and solid curves, respectively, indicate the results of fitting with Havriliak-Negami empirical equation without and with the mode broadening due to the concentration fluctuation. (Data taken, with permission, from Hirose, Y., O. Urakawa, and K. Adachi. 2004. Dynamics in disordered block copolymers and miscible blends composed of poly(vinyl ethylene) and polyisoprene. /. Polym. Sci. Part B Polym. Phys. 42 4084-4094.)... 

Hirose, Y., O. Urakawa, and K. Adachi. 2004. Dynamics in disordered block copolymers and miscible blends composed of poly(vinyl ethylene) and polyisoprene. /. Polym. Sci. Part B Polym. Phys. 42 4084r-4094. 

Solvents or homopolymers added to block copolymers bring about additional effects, especially, when the homopolymer is the same as one of the blocks [82-84]. Macroscopic phase separation, micelle formation and/or different mesophases can occur [65]. Disordered block copolymers, where the blocks are compatible, will not be considered here. 

Experiments of Roe et al. [26] and Hashimoto et al. [27] demonstrated that scattering experiments on disordered block copolymers may also be used to determine x I parameters, using the RPA theory of Leibler [9]. In a subsequent paper, Fredrickson and Helfand showed that fluctuation corrections to the RPA are important in block copolymer melts [28]. When available, x parameters obtained from block copolymer melts are reported after fluctuation corrections have been incorporated, k values obtained from block copolymers are often [29,30] but not always [31] larger than those obtained in homopolymer blends. 

Fig. 16. Phase diagram of a mixture containing polystyrene (M = 2400) and styrene/butadiene diblock copolymer (27 % styrene, M = 28000). Liquid phases L, and Lj represent mixtures of disordered block copolymer and polystyrene. Mesophase M, consists of ordered microdomains of the block copolymer swollen with polystyrene. Mesophase Mj probably contains aggregates of block copolymer micelles within the medium of polystyrene. The features on the lower right, drawn in broken lines, are more speculative. (From Roe and Zin...

Mansky, P., Russell, T.P. etoL (1997b) Interfacial segregation in disordered block copolymers effect of tunable surface potentials. Physics Review Letters, 79(2), 237 240. 

It should be clear that the disordered PS-Wocfe-PI chain does not possess the properties of a neat PS or neat PI chain, but it has new properties influenced by the chain connectivity. For instance, the friction coefficient of a disordered PS-fi/t)cA -PI chain would not be the same as the friction coefficient of neat PS chain or the friction coefficient of neat PI chain. It is reasonable to surmise that the friction coefficient of a disordered PS-h/ocfe-PI chain depends not only on its composition but also on chain connectivity (the junction effect) between the two chains. On the basis of the considerations presented above, we conclude that the stronger molecular weight dependence of zero-shear viscosity for disordered SI diblock copolymers a M for M > M ) displayed in Figure 8.34 is attributable to the presence of the styrene-isoprene (S-I) junction, which originates from the difference in the monomeric friction coefficients between PS and PI blocks. At present, however, we do not have theoretical guideline as to how the junction effect can be incorporated into the description of the dynamics of disordered block copolymers. 

Effect of Block Length Ratio on the Linear Dynamic Viscoelasticity of Disordered Block Copolymers... 

Figure 8.42 gives log G versus log G" plots for two disordered block copolymers, CII and BIT It is of great interest to observe in Figure 8.42 that log G versus log G"... 

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. 

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