Order-disorder temperature block copolymer melt

Fig. 2.5 Schematic showing the variation of inverse scattering intensity and domain spacing (as determined from SAXS or SANS) across the order-disorder transition of a block copolymer melt. The mean field transition temperature has been identified operationally as the point where, on heating, the inverse intensity crosses over to a linear dependence on T (after Sakamoto and Hashimoto 1995).

X = A + BIT, where A and B are constants). Thus S(q )should change linearly with 1/7. t his was indeed observed by Hashimoto etal. (1983b) at high temperatures however, at a temperature associated with the transition from the homogeneous disordered phase to the ordered phase, a deviation from linear behaviour was found. Such deviations are now ascribed to the effects of composition fluctuations (Bates et al. 1988 Lodge et al. 1996), and the crossover from linear to non-linear dependence of S(q ) on 1/7 does not correspond to the order disorder transition, rather the mean-field to non-mean-field transition (see Section 2.2.1 for block copolymer melts). 

Fig. 10. Schematic phase diagram of a semi-infinite block copolymer melt for the special case of a perfectly neutral surface (Hj=0). Variables chosen are the surface interaction enhancement parameter (-a) and the temperature T rescaled by chain length (assuming X l/T the ordinate hence is proportional to %c/%). While according to the Leibler [197] mean-field theory a symmetric diblock copolymer transforms from the disordered phase (DIS) at Tcb oc n in a second-order transition to the lamellar phase (LAM), according to the theory of Fredrickson and Helfand [210] the transition is of first-order and depressed by a relative amount of order N 1/3. In the second-order case, the surface orders before the bulk at a transition temperature T (oc l / ) as soon as a is negative [216], and the enhancement...

Grason, G.M. The Packing of Soft Materials Molecular Asymmetry, Geometric Frustration and Optimal Lattices in Block Copolymer Melts. Phys. Rep. 2006,433,1-64. Hammond, M.R. Cochran, E. Fredrickson, G.H. Kramer, E.J. Temperature dependence of order, disorder, and defects in laterally confined di-block copolymer cylinder monolayers. Mlacromolecules 2005, 38,657 6585. 

Microdomain stmcture is a consequence of microphase separation. It is associated with processability and performance of block copolymer as TPE, pressure sensitive adhesive, etc. The size of the domain decreases as temperature increases [184,185]. At processing temperature they are in a disordered state, melt viscosity becomes low with great advantage in processability. At service temperamre, they are in ordered state and the dispersed domain of plastic blocks acts as reinforcing filler for the matrix polymer [186]. This transition is a thermodynamic transition and is controlled by counterbalanced physical factors, e.g., energetics and entropy. 

Hydrogenated SBCs are often used to modify polyolefins such as polypropylene, polybutylene and polyethylene. One of the unique characteristics of strongly phase-separated block copolymers such as high molecular weight (>50 000) SEBS and SEPS is their response to shear in the melt. These polymers retain their phase-separated structure well above the Tg of the polystyrene because their order-disorder transition temperatures are above processing temperatures. This phase separation strongly inhibits flow in the absence of shear resulting in infinite viscosity at zero shear rates. The application of shear... 

For most BC the phase diagram is characterized by the presence of an upper critical solution temperature, UCST, also known as an order-disorder transition temperature or a microphase separation temperature. Below UCST the block copolymers phase separate, while above it, an isotropic melt is obtained. Owing to the chemical... 

The WSL approach for the description of the order-disorder transition, ie, the transition between the microphase-separated block copolymer and the disordered melt, where the two blocks mix with each other, has been developed (74,88,89) using the random phase approximation. This transition is ofl en called the microphase separation transition (MST), and Toot is the temperature at which the order-disorder transition occurs. In this picture the system is described by a so-called order parameter, which is related to the space-dependent volume fraction or segment density of one of the components, say, component A. Again, the system is considered to be incompressible. The order parameter is then given by the deviation of the local segment density from the mean composition value. 

Because of the liquid-crystal-like order, the viscosity of the block copolymer is usually high and is non-Newtonian with reference to dependance on shear rate. As the repulsive interaction energy or the Flory-Huggins interaction parameter increases, the temperature dependence of viscosity decreases. For styrene-diene polymers, the activation energy of flow in the melt state is similar to that of polystyrene. As the interaction gets smaller the distinction between melt state and disordered state disappears. 

Consider now a block copolymer composed of two chemically dissimilar blocks each of which is noncrystalline. The same factors that are involved in homopolymer mixing will still be operative so that phase separation would be a priori expected. However, since the sequences in the block copolymer are covalently linked, macrophase separation characteristic of binary blends is prevented. Instead, microphase separation and the formation of separate domains will occur. The linkages at the A-B junction points further reduce the mixing entropy. There has to be a boundary between the two species and the junction point has to be placed in this interphase. The interphase itself will not be sharp and will be composed of both A and B units. Mixing of the sequences, and homogeneity of the melt, will be favored as the temperature is increased. There is then a transition temperature between the heterogeneous and homogeneous melt, known as the order-disorder transition. 

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