Search

Frank Kasper (FK) σ and A15 phases were found in the blend system of asymmetric and symmetric polystyrene-b-poly(methyl acrylate) block copolymers. Bates and co-workers first discovered these complex particle packings in the blend system where the diblock copolymers with a constant chain length of one component which consists of corona chains and variable chain lengths being micelle core. It is significantly important to have discover the formation of these complex phases in different block copolymer systems and also from a different research group, which strongly supports the prediction that the FK and A15 packing. Such complex phases had been found in limited conditions with a low molecular weight BCP with high X (strongly segregated system) and conformationally asymmetric BCP system (flexibility asymmetry between constituent blocks). Discovery of the FK and A15 phases in a high molecular weight diblock copolymer without high X or conformational asymmetry indicates a universal phenomenon of the formation of the complex particle packing in a substantially wide range of polymers. [ABSTRACT FROM AUTHOR]

We investigated surface structures of three kinds of block copolymer (BCP) specimens forming hard spherical microdomains embedded in a soft matrix, by using atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS) and grazing-incidence small-angle X-ray scattering (GISAXS). The three BCP specimens consist of different chemical species such as SEBS (polystyrene- block -poly(ethylene- co -butylene)- block -polystyrene) and MAM (polymethylmethacrylate- block -poly( n -butylacrylate)- block -polymethylmethacrylate). Two of them form spherical microdomains at the thermodynamically equilibrium state (i.e., after fully long time thermal annealing), while the other exhibits spherical microdomains as a frozen state of the non-equilibrium structure (i.e., at the as-cast state using a selective solvent for the solution casting method), which was automatically frozen in by the vitrification of the hard component; the state is far from equilibrium). Nevertheless, such three different BCP specimens (chemically different in the molecular structure and thermodynamically different in the state) showed a common feature of the surface structure, as the outermost surface was completely covered with the single component having a lower value of the surface free energy, as revealed by XPS measurements. This finding significantly indicates that the AFM observation, which implies a coexistence of both BCP components on the free surface, misleads the conclusion. Although such surface coverage is reasonable and well-known, it was further found that the block chains are confined in a thin layer of the outermost region of the specimen. It is striking to find that the block chains are forced to be deformed (compressed) in order to meet the thermodynamic requirement of the surface coverage. [ABSTRACT FROM AUTHOR]

Block copolymers forming glassy spheres in the matrix of rubbery chains can exhibit elastomeric properties. It is well known that the spherical microdomains are arranged in the body-center cubic (bcc) lattice. However, recently, we have found packing in the face-centered cubic (fcc) lattice, which is easily transformed into the bcc lattice upon uniaxial stretching. In the same time, the packing regularity of the spheres in the bcc lattice was found to be enhanced for samples completely recovered from the stretched state. This reminds us that a cycle of stretching-and-releasing plays an important role from analogy of densification of the packing in granules upon shaking. In the current paper, we quantify the enhancement of packing regularity of spherical microdomains in the bcc lattice upon uniaxial stretching of the same elastomeric triblock copolymer as used in our previous work by conducting small-angle X-ray scattering (SAXS) measurements using high brilliant synchrotron radiation. Isotropically circular rings of the lattice peaks observed for the unstretched sample turned into deformed ellipsoidal rings upon the uniaxial stretching, with sharpening of the peaks in the direction parallel to the stretching direction and almost disappearing of the peaks in the perpendicular direction. By quantitatively analyzing the SAXS results, it was found that the packing regularity of the spherical microdomains was enhanced in the parallel direction while it was spoiled in the perpendicular direction under the stretched state. The enhanced regularity of packing was unchanged even if the stretching load was completely removed. [ABSTRACT FROM AUTHOR]