Phase Transitions in Polymers: The Role of Metastable States by Stephen Z.D. Cheng

By Stephen Z.D. Cheng

A classical metastable nation possesses a neighborhood unfastened power minimal at endless sizes, yet no longer an international one. this idea is section measurement self sufficient. we now have studied a couple of experimental effects and proposed a brand new idea that there exists quite a lot of metastable states in polymers on diversified size scales the place their metastability is significantly made up our minds via the part dimension and dimensionality. Metastable states also are saw in part variations which are kinetically impeded at the pathway to thermodynamic equilibrium. This used to be illustrated in structural and morphological investigations of crystallization and mesophase transitions, liquid-liquid section separation, vitrification and gel formation, in addition to mixtures of those transformation tactics. The section behaviours in polymers are hence ruled through interlinks of metastable states on various size scales. this idea effectively explains many experimental observations and gives a brand new solution to attach diversified facets of polymer physics. * Written by way of a number one pupil and specialist* provides new and leading edge fabric encouraging innovation and destiny learn* Connects scorching subject matters and best study in a single concise quantity

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Recently, phase transition kinetics involving the discotic columnar mesophases of 2,3,6,7,10,11-hexa(40 -octyloxybenzoyloxy)triphenylene were reported. Multiple phase transformations provided opportunities to investigate the transition kinetics between different ordered states. , 2001). The monoclinic phase was found to be metastable with respect to the orthorhombic phase. When the crystallization kinetics of the rectangular columnar phase to both highly ordered phases were measured, the monoclinic phase grows faster than the orthorhombic phase in a large region of relatively low temperatures.

For transitions from a mesophase to a crystalline solid, the transition kinetics are less difficult to monitor. For example, the transition kinetics from cholesteryl pelargonate and caproate liquid crystals to crystalline solids can be analyzed using the Avrami treatment of Eq. 20) (Adamski and Czyzewski, 1978; Adamski and Klimczyk, 1978). However, some of these transitions exhibit much smaller values of the Avrami exponent, n. Note that this exponent is intended to represent the growth dimensionality of the ordered phase.

The solution of the differential Eq. 25) is given by Nakatani and Han (1998): Sðq; tÞ ¼ S1 þ ½S0 ðqÞ À S1 ðqފexpf2RðqÞtg ð2:26Þ The S1(q) here is the virtual structure factor, and it can be written as: S1 ðqÞ ¼ kT ðDinter =M þ 2kq2 Þ ð2:27Þ and the characteristic length becomes RðqÞ ¼ ÀðDinter q2 þ 2kMq4 Þ ð2:28Þ 47 Thermodynamics and Kinetics of Phase Transitions Therefore, within the spinodal decomposition region, any concentration fluctuation grows exponentially at a scattering vector q with a characteristic length R(q).

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