Ramon J. Albalak

Thermal annealing of roll-cast triblock copolymer films

Abstract Polystyrene—polybutadiene—polystyrene triblock copolymers were roll-cast from toluene solutions to form globally oriented films. Microstructural changes following thermal annealing of films with cylindrical and lamellar morphology were monitored using two-dimensional small angle X-ray scattering, transmission electron microscopy and thermomechanical analysis. The microdomains in the unannealed films of cylindrical morphology were found to be assembled on a distorted hexagonal lattice, due to the roll-casting flow field. Thermal annealing significantly improved the alignment and packing of the cylinders, increased grain size, reduced the number of morphological defects and resulted in a 12% decrease in the area per junction. The microstructure of the unannealed films of lamellar morphology was observed to be composed of many small grains with low-angle helicoid surface twist boundaries. Annealing significantly reduced the number of grains and twist boundaries and resulted in a 7% decrease in the area per junction. Molecular models are presented for the relaxation of the chains during the annealing process in both cylindrical and lamellar morphologies based upon 2-D SAXS data and thermomechanical analysis.

Solvent swelling of roll-cast triblock copolymer films

Abstract Polystyrene-polybutadiene-polystyrene triblock copolymers were roll-cast from toluene solutions to form globally oriented films. As-processed films, containing process-related residual stresses, were exposed to solvent vapours. Three solvents were used in this study: toluene, which is a non-preferential solvent for polystyrene and polybutadiene; methyl-ethyl-ketone, which is a preferential solvent for the polystyrene blocks; and hexane, which is a preferential solvent for the polybutadiene block. Microstructural changes accompanying the solvent swelling of films with cylindrical and lamellar morphology were monitored using two-dimensional small angle X-ray scattering. Solvent swelling significantly improved the symmetry of the hexagonal packing of the cylindrical domains, which was initially distorted due to the roll-casting flow field. Solvent swelling was also found to improve the long range order in roll-cast film with lamellar morphology. Various phenomena were found to accompany the swelling and deswelling of films with both cylindrical and lamellar morphology with the three different solvents used. Especially intriguing results were observed for the case of swelling both morphologies in hexane. For films with a lamellar morphology, after 1 h of swelling and 2 h of subsequent deswelling the d-spacing decreased by 18%. For films with cylindrical morphology, a similar decrease of 9% was observed. Molecular models are presented to explain these microstructural changes, that are closely linked to the mobility of the glassy polystyrene blocks, the relaxation of process-related stress and the ability of the polybutadiene-polystyrene junctions at the interfaces to reposition and accommodate volume changes.

Bubble growth in viscous newtonian and non-newtonian liquids

Abstract A model for the dynamics of hydrodynamically controlled spherical bubble growth in quiescent viscous newtonian and non-newtonian liquids is presented. Two constitutive equations were used to describe the behavior of the liquid medium: (1) a simple power law relation and (2) a truncated power law. Application of the truncated power law resulted in four differen cases: (a) at all times the liquid acts as a newtonian liquid; (b) at all times the liquid behaves as a simple power law liquid; (c) at all times the liquid close to the growing bubble obeys a power law relation and the liquid far away from the bubble behaves as a newtonian liquid; (d) all the liquid initially behaves as a newtonian liquid and at some time transforms to a two-region liquid. Analytical expressions were derived for bubble growth as a function of dimensionless system parameters. The relevance of this work to the process of polymer devolatilization is discussed.

Use of a cooperative-motion domain model to analyze Brillouin light scattering measurements of the dynamic modulus in triblock copolymers

The use of the relaxation function is widespread in the study of polymer dynamics. Since the popular empirical KWW relaxation function consistently underestimates dielectric loss at high frequency, several models dealing explicitly with intermolecular cooperativity have been proposed as alternatives. In this article, the domain model proposed by Matsuoka, previously used only to analyze dielectric relaxation results, is used to analyze Brillouin light scattering results from polystyrene-polybutadiene-polystyrene triblock copolymers. A single relaxation time analysis and the KWW model are both compared to the domain model. Neither of these models fits the Brillouin data well. The single relaxation time analysis gives a physically unrealistic results; the KWW analysis fits the data at low frequency, but fails in the high-frequency region by underestimating the attenuation. The domain model fits the Brillouin data well over the entire temperature/frequency range. The results show that in order to understand the full range of dynamics in these materials and in polymeric materials in general, the KWW model is insufficient due to its underestimation of attenuation at high frequency. A model including cooperative motion is crucial to fully understand polymer dynamics.

The influence of melt processing on the spatial organization of polymer chains in a crystallizable diblock copolymer of nylon 6 and PDMS

Crystallized chains of nylon 6 lie parallel to the interfaces of the microphase-separated morphology of a nylon 6/PDMS diblock copolymer. Orienting the morphology in the melt using plane strain compression enabled the nylon chain direction to be determined through a combination of transmission electron microscopy, small-angle X-ray scattering and wide-angle X-ray scattering pole figure analysis. Processing at temperatures above the nylon 6 melting point serves to orient the microphase-separated morphology of the melt; the nylon 6 chain orientations are then largely dictated by thermodynamic considerations that apply to chains crystallizing within the confines of a microphase separated melt.