Segregative phase separation spinodal decomposition

In a previous paper (1), phase segregation by spinodal decomposition in mixtures of polyethylene terephthalate and polyhydroxybenzoic acid copolymer (PET-PHB) and polycarbonate (PC) has been investigated. It was shown that thermally induced phase segregation takes place above the Tg of PC and exhibits a lower critical solution temperature (LCST). However, the phase separated domains do not grow until the temperature exceeds 255°C. Some disclinations developed within the liquid crystal rich regions. Even in the pure PET-PHB component, four dark brushes with negative sense of disclinations form around 240°C, indicating the presence of nematic liquid crystals. Paci and coworkers (2) claimed that a smectic-nematic transition exists near 270°C in this liquid crystalline copolyester. 

It is energetically favourable for the SS and HS not to mix. Thus during cooling from above a critical order-disorder temperature, spontaneous segregation of SS and HS into separate soft (SS-rich) and hard (HS-rich) phases occurs by the process of spinodal decomposition. To achieve elastomeric performance, the SS must be the majority constituent by mass, and the phase structure then takes the form of discrete hard domains dispersed within a soft matrix. Such a phase structure impacts on mechanical properties, and a further structural parameter of importance, therefore, is the degree of phase separation. 

In the melt phase, thermodynamics would indicate that chains with different chain lengths should have different energies. As a consequence there is the possibility that chains with a similar energy will tend to segregate themselves in space. Phase separation is well known in polymer blends (Chapter 8) and can be described by the process of spinodal decomposition. In the case of a broad molecular mass distribution polymer system, the individual chains will... 

Currently, AFM, neutron reflection (NR) spectroscopy and SIMS are used to examine phase separation in symmetrically segregating thin polymer blend films (ca. 1000 A). Phase separation in the film leads to undulations of the liquid-air interface, provided that the film is sufficiently thin to suppress any surface-directed spinodal decomposition waves. Flattened droplets are formed at a very... 

As discussed in Section 2.23.1.2, one of the advantages of AFM over electron miaoscopy is that it enables 3D imaging of untreated samples in a physically relevant environment. Given the surface nature of the technique, initial AFM studies of phase separation processes in polymer mixtures have been primarily focused on thin or ultrathin films. " " The confinement in a film and component segregation to the interfaces have been shown to have a profound effect in both spinodal decomposition, and nucleation and growth processes of the phase separation. The spectrum of AFM applications has been extended to bulk phase separation of polymer mixtures using conventional and oblique microtoming of polymer blend films. 

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