Polymer mixtures, crystallization kinetics

Mandelkern, L. Crystallization kinetics in high polymers. II. Polymer-diluent mixtures. J. Appl. Phys. 26, 443—451 (1955). 

Nam, I.Y., Okamoto, M., Okamoto, H. et al. (2006) Morphology and crystallization kinetics in a mixture of low-molecular weight aliphatic amide and polylactide. Polymer. 47,1340-1347. 

The method has been used to show that phase separation in poly(phenylene oxide)-toluene occurs by crystallization (see Chapter 12) of the polymer rather than by liquid-liquid phase separation, and to follow the kinetics of the process Kleintjens et al. have used PICS to obtain spinodals for branched polymer solutions. Koningsveld and Kleintjens have used it widely to study phase separation in polymer mixtures. 

For nonreacting polymer mixtures, several efforts have been made to elucidate the effects of viscoelasticity on phase separation of polymer mixtures from a theoretical viewpoint [40, 41]. These particular effects on phase separation were shown to be important as a long-range interaction in the phase separation kinetics of polymer mixtures [42]. On the other hand, for reacting polymer systems, very recently, Ohta and coworkers took into account the elastic effects of the polymer on the phase separation kinetics of a mixture composed of liquid crystals dissolved in monomer undergoing polymerization [43]. 

Palberg T, Stipp A, Bartsch E (2009) Unusual crystallization Kinetics in a hard sphere colloid-polymer mixture. Phys Rev Lett 102 038302-1-038302-4... 

The chapter is divided into five sections. Section 10.2 deals with the thermodynamics of polymer blends the general principles and the main theories on the phase behavior of polymer mixtures are briefly presented. Section 10.3 deals with the properties of miscible blends with crystallizable components. The phase morphology, crystal growth rate, overall crystallization kinetics, and melting behavior of miscible blends are analyzed. The crystallization phenomena in blends with miscibility gap are also described. Then, examples of miscible systems comprising one or two crystallizable components are reported with particular attention to the thermodynamic and kinetic aspects of the crystallization process. 

In this section, we focus on the interplay between phase separations and phase ordering kinetics in mixtures of a flexible polymer and a liquid crystal (nematogen). When the system is thermally quenched from a stable isotropic phase into an unstable part of the biphasic region, the fluctuations of concentration and orientation take place and isotropic or nematic droplets appear with time [109, llOj. The instability of these systems is driven by the competition between phase separation and nematic ordering. Figure 2.22 shows the phase diagram of the polymer/liquid crystal mixture with Up = fir = 2 and a = 1.4. The solid curve refers to the binodal and the dotted line shows the first-order NIT. The dash-dotted line shows the spinodal. The arrows indicate temperature quenches from a stable isotropic phase... 

Crystallization of Blends The first polymer blend was made from two polymeric mbbers in 1846, but polymer blend technology and a scientific understanding of the underlying principles controlling the compatibility (or lack of) in polymer mixtures (alloys as they have been named recently) has taken place only in the latter part of the current century. Many blends are non-crystalline but our interest in this document is focused on the kinetics of phase transformations of binary and ternary systems that receives more attention annually. Some of these systems can be very complicated, often comprised of multiple phases that m involve homopolymers, copolymers, mesophases and the like. Polymorphism and even isomorphism may occur... 

A large number of studies concerned with the crystaUization kinetics of polymer-polymer mixtures have been reported. One reason for this abundance of information is a basic scientific interest coupled with the many ranuficafions that are inherent to such systems. There is also a pragmatic interest since physical and mechanical properties, as well as environmental features, can be altered and controlled by the appropriate mixing of polymeric components. Itis useful to foUow the same methodology used in discussing the equilibrium aspects of crystalline polymer-polymer mixtures (see Chapter 4, Volume 1) when analyzing their crystallization kinetics. 

Based on the experimental results that have been described, it is natural to inquire whether the basic theoretical framework that has been developed for the crystallization kinetics of one-component systems can be adapted to polymer mixtures. This question is addressed in the next section. 

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