In this paper, the kinetics and morphology of viscoelastic microphase separation of diblock copolymers are investigated in detail. It is found that for a symmetric system (f=0.5), taking into account the bulk modulus differences between the two blocks, the classical randomly oriented lamellar morphology is not observed. Instead, we find that droplets of the lower bulk modulus soft block disperse in a matrix of higher bulk modulus hard block. In the case of off-critical system (f=0.4), since an inherent composition asymmetry exists between the two blocks, the viscoelastic microphase separated morphology is also different from that normally observed, whether there is an apparent difference in the bulk moduli between two blocks. However, when a bulk modulus difference exists between the two blocks, the morphology is further altered. Addition of random thermal noise to both the critical (f=0.5=and the off-critical system (f=0.4=weakens the suppression of concentration fluctuations, but no fundamental structural transformation is caused by the noise. Since the abnormal morphology is observed on slow approach to the equilibrium state, we conclude that the viscoelastic effect may be largely responsible for the observed deviations between the experimentally measured and the mean-field theoretically calculated phase diagrams.

Simulations of phase separation under oscillatory shear flow have been performed based on the time-dependent Ginzburg-Landau (TDGL) equation. To calculate the stress tensor, the expression proposed by Kawasaki was used. The results of the simulations have been confronted directly with experimental results on a LCST blend of PRMSAN/PMMA to evaluate the potential of the simulations. The effect of quench depth, shear amplitude, and shear frequency on the morphology development as well as on the corresponding rheological properties has been investigated. The results show that the characteristic rheological behavior of phase-separating systems can be attributed to the interfacial relaxation, which is changing during the process of phase separation. The strength of the concentration fluctuations and the interfacial volume fraction are key factors determining the contribution of interfacial relaxation to the global rheological behavior of the blend. In the low frequency range, the oscillatory shear cannot affect the critical point, but it can accelerate the coagulation and growth of the blend morphology. The simulations qualitatively agree with the experimental findings.

As the temperature decreases, thermally sensitive spherical poly (N-isopropylacrylamide) (PNIPAM) microgels with a lower critical solution temperature (LCST～32 ℃) swell in a dispersion, leading to a possible volume-concentration induced sol-gel transition if the microgel concentration is sufficiently high. In such a formed gel, polymer chains inside each microgel were chemically cross-linked, but individual microgels were physically close-packed into a three-dimensional network. Such hybrid gels can be used as model systems for studying the sol-gel transition, which avoids several problems, such as chain entanglements, phase separation, and vitrification, normally occurring in a gelling process. The sol-gel transition of such hybrid gels was studied by the change of viscoelastic modulus G¢ and G¢¢. As expected, the sol-gel transition depends on the polymer concentration, frequency, and shear stress. The gelation point could be roughly estimated by the method of Winter and Chambon. Our results showed that the temperature dependence of G″ and tan σ(=G″/G′) had a minimum, which corresponded to the sol-gel transition, providing a better way to determine the sol-gel transition temperature.