Binary blends of diblocks

Self-consistent field theory has been applied to analyse the phase behaviour of binary blends of diblocks by Shi and Noolandi (1994,1995), Matsen (1995a) and Matsen and Bates (1995). Mixtures of long and short diblocks were considered by Shi and Noolandi (1994) and Matsen (1995a), whilst Shi and Noolandi (1995) and Matsen and Bates (1995) calculated phase diagrams for blends of diblocks with equal degrees of polymerization but different composition. 

Winey KI, Thomas EL, Fetters LJ (1991) Ordered morphologies in binary blends of diblock copolymer and homopolymer and characterization of their intermaterial dividing surfaces. J Chem Phys 95(12) 9367-9375... 

Sakurai S, Umeda H, Furukawa C, Me H, Nomura S, Lee HH, Kim JK (1998) Thermally induced morphological transition from lamella to gyroid in a binary blend of diblock copolymers. J Chem Phys 108 4333-4339... 

Figure 16 Transmission electron micrographs of binary blends of diblock copolymers with microsphere SV500-M at/= 0.5 (a) with S4V-100 (b) with S4V-200.

With the discussion above in mind, it is now possible to provide a similar semi quantitative framework in which to view the results obtained on ternary systems (homopolymer A, homopolymer B, diblock AB) and on binary blends of one homopolymer and a diblock copolymer. Of particular importance is the need for an explanation of the fact that the diblock copolymer may serve either as an emulsifying agent (9,25) or as a homogenizing agent (1, 4 ) in ternary blends. 

In binary blends of A homopolymer and AB diblock copolymer, the interplay between microphase separation and macrophase separation is controlled mainly by the relative length of the chains, in addition to the composition of the mixture. Homopolymers shorter than the corresponding block tend to be solubilized within the corresponding domain of a microphase-separated structure. As the homopolymer molecular weight increases to approach that of the corresponding... 

Binary blends of block copolymers can also macrophase separate if the mismatch in molecular weights is sufficient. In the other limit, blends of diblocks of... 

Macrophase separation after microphase separation has been observed in an AB block copolymer/homopolymer C blend (Hashimoto et al 1995). Blends of a PS-PB starblock copolymer (75wt% PS) and PVME homopolymer were prepared by solvent casting. Binary blends of PS and PVME exhibit a lower critical solution temperature (LCST), i.e. they demix at high temperatures. The initial structure of a 50% mixture of a PS-PB diblock and PVME shown in Fig. 6.20(a) consists of worm-like micelles. Heating led to macrophase separation as evident... 

Until recently, very little quantitative information was available on blends of block copolymers. The literature is summarized in Table 6.3. Hoffman et al. (1970) reported microscopic demixing of blends of PS-PB diblocks, with two maxima in the domain size distribution, but with no evidence tor macrophase separation. These findings must be treated with caution in the light of more recent results. Hadziioannou and Skoulios (1982) used SAXS and SANS to investigate the morphology of binary blends of PS-PI diblocks, and binary PS-PI/PS-PI-PS or PS-PI/PI-PS-PI blends or blends of the two types of triblock. They found that the blends were microphase separated, and that the sharpness of the interface was not reduced in blends compared to neat copolymers. The transition between a lamellar and a cylindrical structure was shown to depend primarily on blend composition. In contrast, the transition from a lamellar to a disordered phase at... 

Fig. 6.35 Calculated constant y N ( = 12) phase diagram for a binary blend of a diblock and homopolymer with equal degree of polymerization (/ = 1) as a function of the volume fraction of homopolymer, 0h, and the composition of the diblock (/) (Matsen 1995ft). For clarity, only the largest biphasic regions are indicated.

Fig. 6.46 Calculated phase diagram cube for binary blends of symmetric diblocks (equal degrees of polymerization) with xN = 20 (Shi and Noolandi 1995). The diblock compositions are denoted /,/2 and the blend composition as cf>.

The distribution of chains in a lamellar film formed by a binary blend of symmetric PS-PMMA diblocks has been probed using neutron reflectivity by Mayes et al. (1994). The microphase self-assembled parallel to the substrate, giving a lamellar stack, as for pure diblocks (see Section 2.5.1). By blending mixtures of unlabelled and selectively labelled long and sort diblocks, it was determined that short diblock copolymer chains are localized at the PS-PMMA interface, while the longer chains are selectively located at the domain centres. These results... 

The morphological feature is in accordance with that of binary blends of iPP and true diblock iPP-b-EPR copolymers (63). For the immiscible blends showing phase separation, the EP domains have no ability to affect the lamellar or crystalline morphology of iPP. It follows that the strength of iPP lamellae is essentially independent of the addition of EP copolymers although the magnitude of bulk stress is reduced by the addition of EP copolymers with a lower modulus. 

Since the 1980s, phase behaviors of A-homopolymer/A-B diblock copolymer binary systems have been investigated experimentally [14—22] and theoretically [23-25], where the EG /Si CsEOn systems that we focus on in this study are also their counterpart. The phase behaviors of binary blends of homopolymer and block copolymer are affected not only by o, , and ( NAE but also by a= where... 

Fig. 15 Mean-field phase diagram of supramolecular diblock copolymer model with equivalent block lengths. Labeled phases are Dis (hranogeneous disordered), Lam (lamellar), and 2 phase (coexisting A-rich and B-rich homogtaieons phases). The values of N indicate the diblock copolymer length. Solid dots denote Ltfshitz points (LS). The horizontal dashed line on the l denotes 1//N = 1/4, the macrophase separation transition for a binary blend of polymers. The horizontal dashed line on the right signifies 1//A1 = 0.095, the order-disorder transition for a symmetric diblock copolymer. Reprinted with permission from [97]. Copyright 2007 American Chemical Society...

Fig. 11.11 Melting points of symmetric binary blends and diblock copolymers for three E/JEc values. The blends contain the chain length 16 monomers in parallel to the block length of diblock copolymers. The straight lines are drawn to guide eyes (Ma et al. 2011) (Reprinted with permission)...

H. Frielinghaus, N. Hermsdorf, K. Ahndal, K. Mortensen, L. Messe, L.J. Corvazier, P.A. Fairclough, A.J. Ryan, P.D. Olmsted, I.W. Hamley, Micro- vs. macro-phase separation in binary blends of poly(styrene)-poly(isoprene) and poly(isoprene)-poly(ethylene oxide) diblock copolymers. Europhysics Letters 53 (2001) 680-686, http //dx.doi.org/10.1209/ ephi2001-00205-7. 

Nojima S, Wang D, Ashida T. Ringed spheruhte in binary blends of poly(e-caprolactone) and e-caprolactone-butadiene diblock copolymer. Polym J 1991 23 1473-1482. 

Dudowicz J, Freed KF (1993) Relation of effective interaction parameters for binary blends and diblock copolymers lattice cluster theory predictions and comparison with experiment. Macromolecules 26 213—220... 

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