Block copolymers highly asymmetric

Usually the discussion of the ODT of highly asymmetric block copolymers in the strong segregation limit starts from a body-centred cubic (bcc) array of the minority phase. Phase transitions were calculated using SOFT accounting for both the translational entropy of the micelles in a disordered micelle regime and the intermicelle free energy [129]. Results indicate that the ODT occurs between ordered bcc spheres and disordered micelles. 

For highly asymmetric block copolymers with a large insoluble block, the copolymer chains can t be directly solubilized in the selective solvent. However, micelles can be obtained from these copolymers by the temporary use of a nonselective solvent which is further eliminated (see Sect. 2.2 for further details on this issue). In principle, all the copolymer chains are aggregated... 

It should be mentioned here that some researchers argued Bates criterion for the ODT of highly asymmetric block copolymers and proposed another method. Han and coworkers" used log G vs log G" plots to determine the ODT temperatures of... 

We will start our discussion with the grafting to approach, which may be characterized as the simplest. Depending on the nature of the surface of the porous membrane that we want to decorate with a brush, we must choose an end-functionalized polymer chain (or a highly asymmetric block copolymer of an amphipathic nature) that may strongly adsorb from its functionalized part on the inner surface. Then in principle we may use the same method as for the case of a flat surface, i.e., dip the membrane in a solution that contains these polymers and then wait for the full formation of the brush. However, it has been shown [21] that self-assembly inside the pores is prohibited when the ratio of pore diameter to chain radius of gyration... 

Segahnan, R. A., Schaefer, K.E. et al. (2003c) Topographic tenaplating of islands and holes in highly asymmetric block copolymer films. Macromolecules, 36(12), 4498-4506. 

Oscillatory Shear Rheometry of Highly Asymmetric Block Copolymers... 

The reasons for inapplicability of TTS to symmetric or nearly symmetric copolymers, discussed in the previous section, are equally applicable to the highly asymmetric block copolymers Vector 4111 and SIS-110. Specifically, it should be very clear from Figure 8.14 that there is no way one can obtain temperature-independent reduced plots for the microphase-separated SIS-110 by shifting logG versus log > (and/or logG" versus log >) plots along the co axis to the data at an arbitrarily chosen reference temperature below 166 °C. Thus, TTS would fail completely for the highly asymmetric SIS-110 ... 

In this section, we present the effect of thermal history on the oscillatory shear rheometry of block copolymers. We will show that the occurrence of a minimum in G in the isochronal dynamic temperature sweep experiment does not necessarily signify OOT for highly asymmetric block copolymers instead, it sometimes reflects imperfect bcc spheres, as determined by SAXS and TEM, due to an insufficient annealing of a specimen. Here, we will show that a minimum in G, observed for an unannealed specimen in the isochronal dynamic temperature sweep experiment, may disappear completely when the specimen is annealed for a sufficiently long time at an elevated temperature below the TmoT of highly symmetric SI diblock copolymer. 

In this chapter we have discussed two as yet unresolved issues, finite molecular weight effect and the phase behavior and phase transitions in highly asymmetric block copolymers. We believe that these issues are fundamental enough to require a fresh look, particularly from a theoretical point of view. We do not think that the currently held mean-field theory can explain every conceivable phase behavior and phase transitions experimentally observed in block copolymers. Additionally, most if not all of the physical theories in the literature are based on certain assumptions which were made, more often than not, for the reason of mathematical simplicity. We have suggested that a new theory for phase behavior and phase transitions in block copolymers be developed by relaxing the assumptions made in the formulation of the currently held mean-field theories. 

Choi S, Vaidya NY, Han CD, Sota N, Hashimoto T (2003) Effects of sample preparation method and thermal history on phase transition in highly asymmetric block copolymers comparison with symmetric block copolymers. Macromolecules 36 7707-7720... 

---