Microphase Separation Transition Research Articles

Homogeneous block copolymer systems under shear flow

Effects of shear flow are investigated in melts of diblock copolymers in the homogeneous disordered phase near the microphase separation transition point. Simple approximate expressions are given for the anisotropic scattering intensity in nonlinear regimes under shear. A non-Newtonian effect and a normal stress effect are also examined, which are caused by deformations of the critical fluctuations in shear. An explicit expression is also found for the critical part of the complex shear modulus. This paper is a generalization of recent work by Fredrickson and Larson.

Fluctuation effects in the theory of microphase separation in block copolymers

The effect of composition fluctuations on the microphase separation transition in diblock copolymers is investigated. Such fluctuation corrections, which were neglected in the mean field treatment of Leibler, are found to be significant for the molecular weights usually encountered. The analysis is facilitated by reducing the block copolymer Hamiltonian to a form previously studied by Brazovskii. Our principal results are the following: (i) A symmetric diblock copolymer is predicted to undergo a first order phase transition at a larger value of χN than the second order transition found by Leibler. The Flory interaction parameter is denoted χ and N is the number of statistical segments per chain. The location of the transition is predicted to be at (χN)t=10.495+41.022 N−1/3, where the peak in the scattering function attains its maximum value of 0.12328 N1/3. (ii) We find windows in composition, with finite width, through which it is possible to pass from the disordered phase to each of the ordered microphases (lamellar, hexagonal, and body-centered-cubic) by changing temperature. (iii) All the results of Leibler are recovered in the limit of block copolymers with infinite molecular weight.

Viscoelasticity of homogeneous polymer melts near a critical point

The anomalous contribution to the shear stress caused by critical fluctuations in homogeneous polymer melts is investigated. Mean field expressions for the critical contributions to the stress tensor, dynamic shear modulus, and nonlinear steady shear viscosity are derived. These expressions are applied to the case of a homogeneous diblock copolymer near its microphase separation transition. The low frequency scaling behavior of the storage modulus is found to be G′(ω)∼ω2a−5/2, while the loss modulus is predicted to scale like G″(ω)∼ωa−3/2. The dimensionless parameter a is defined by a=2(χN)s−2χN, where χN is the product of the Flory interaction parameter and the number of Kuhn segments per chain, and (χN)s is the value of χN on the spinodal computed by Leibler. The linear steady shear viscosity is also found to be singular as a→0. A comparison is made between the present theoretical predictions and the recent experiments of Bates on 1,4/1,2 polybutadiene block copolymers.

Microphase separation transition in block copolymer melts

AbstractThe microphase separation transition (MST) in block copolymer melts has been studied using synchrotron SAXS. The results indicate that the MST occurs in the range of molecular weights and Flory‐Huggins interaction parameters x predicted by the theory of Leibler (Ref. 5). Studies of the MST as a function of molecular weight for constant composition can be used to determine the temperature dependence of x. The observed change of macrolattice constants with temperature is somewhat different from theoretically predicted values.

Block copolymers near the microphase separation transition. 3. Small-angle neutron scattering study of the homogeneous melt state

Block copolymers near the microphase separation transition. 3. Small-angle neutron scattering study of the homogeneous melt state

Block copolymers near the microphase separation transition. 2. Linear dynamic mechanical properties

Block copolymers near the microphase separation transition. 2. Linear dynamic mechanical properties

Block copolymers near the microphase separation transition. 1. Preparation and physical characterization of a model system

Preparation et caracterisation moleculaire d'un modele des copolymeres bisequences polybutadiene-1,4/polybutadiene-1,2