Thermodynamics of polymer -diluent systems at high pressure
Diblock copolymers have enormous potential use as templating materials for the fabrication of highly ordered materials on a nanometer scale. This derives from the complexity of phase behavior in microphase-separated block copolymer systems. In the ordered state block copolymers commonly self-organize into ordered lamellae, cylinders or spheres. Recently, high-pressure diluents have been used as a processing aid when using block copolymers as a templating material. In this study several aspects of polymer-diluent phase behavior have been investigated using high-pressure carbon dioxide as a diluent.
It is well established that dilation of a copolymer changes the characteristic interdomain spacing of a phase-separated system. The interdomain spacing decreases with dilation by non-selective diluents and increases with selective diluents. The characteristic spacing of poly(styrene-block-dimethyl siloxane) has been measured using small angle neutron scattering (SANS) in high-pressure CO2. A new power-law scaling for the change in interdomain spacing induced by dilation, which accounts for selectivity of the diluent, is presented.
The effect of high-pressure carbon dioxide on the order-to-disorder transition (ODT) of poly(styrene-block-2-vinyl pyridine) has been investigated using static birefringence. The results of these experiments indicate that in addition to the suppression of the ODT, dilation of a copolymer by carbon dioxide can induce the appearance of a second morphology. Further the appearance of this second morphology is strongly dependant on the sample history.
Methods for measuring the swelling of homopolymers in carbon dioxide have also been investigated. High-pressure spectroscopic ellipsometry and laser interferometry have been developed as methods to measure the swelling of homopolymer films. It is shown that spectroscopic ellipsometry and laser interferometry are both capable of measuring the swelling of homopolymer films at high pressure.
0542: Chemical engineering