Study On Phase Behavior Of PS/SAN Blends At Static State And Under Shear Flow With SALS Method

Most of polymer blends are usually immiscible, this is because the combinatorial entropy of mixing of two polymers is dramatically decreased with the increase of the molecular weight of polymers, and the enthalpy of mixing, on the other hand, is often of a positive quantity. There are two methods that can improve the blend miscibility. One is to introduce a favorable specific intermolecular interaction, and the other is to introduce an intramolecular repulsive interaction into the blend system. The latter requests at least one component of the polymer blends is a random copolymer. Random copolymer is easy to make; and its miscibility with other components in polymer blends can be adjusted by changing the fraction of different segment in the copolymer. So, the study of multi-polymer system containing random copolymers is a fast developing area. On the other hand, polymer blends usually have to be processed before becoming the useful final products. During the processing the phase behavior of polymer blends is influenced by shear, therefore it is necessary to study the phase behavior of polymer blends undershear flow field in order to gain the materials with ideal properties. However until recently the research has been mainly concentrated on the homopolymer blend, and blends containing random copolymer were scarcely investigated.In this article a laser scattering system including a shear unit was established, and the miscibility of Polystyrene/Poly(styrene-co-acrylonitrile)(PS/SAN), was studied by using this facility, and the influence of copolymer composition, molecular weight, and the solvents used for the blends' film casting on the phase behavior was discussed; and the phase behavior of PS/SAN blends was discussed under shear flow field. The main experimental work and results were listed as follow:1. A laser scattering measurement system with a shear unit was established. The apparatus has advantages of steady laser frequency output, high pixel consolation CCD, quick signal collection, and high precision of temperature control et al. A software system used for the data collection, in-situ scattering pattern display and analysis was developed.2. The phase behaviors of PS/SAN blends were studied by using the Small Angle Light Scattering method (SALS) at static state. It has been found for the first time that PS/SAN (AN:20V%) blend (50/50Wt%) has UCST behavior, and the UCST temperature is around 171C. The miscibility of binary polymer blends of PS/SAN was predicted based on both Flory' s equation of state theory (EOS) and Wolf s theory on binary polymer blends of the A/AB style. The calculating and the experimental results were in accord with each other relatively well.3. When the thermodynamic driving force for the phase separation was removed suddenly, by a temperature jump forexample, the. self-diffusion between PS and SAN took place. In view of the results of the system' s scattering intensity deviation from Porod' s law and the course of blend' s boundary layer changing, it could be concluded that PS/SAN blend changed from a regular two-phase structure with a sharp interface to that with a broad interface during the course of self-diffusion. Analysis of Pick' s Model indicated that small phase domain could be dissolved quickly, while large phase domain could not. Phase development with the thermodynamic driving force removed gradually had similarity to the case mentioned above (temperature jump). But they had different kinetic characteristics: scattering intensity of the former decayed lineally with time, while the later exponentially.4. The UCST behavior of binary polymer blends of PS/SAN was influenced by many factors, such as copolymer composition, molecular weight, and the solvents used for the PS/SAN blend film casting. PS/SAN blends with higher AN' s Vume fraction in SAN, or with higher molecular showed worse miscibility than those with lower AN' s Vume fraction in SAN, or with lower molecular weight. The miscibility of PS/SAN blends varied with solvents used for the film cas...