Coil-globule collapse transition

In Fig. 12.1(a), the specific-heat curve for a system of two identical semiflexible polymers (2 x i3) is compared with the energetic fluctuations of a single chain (1 ycA ). The single chain exhibits a very weak coil globule collapse transition (shoulder near T 0.88), whereas the crystallization near T 0.24 is a pronounced, separate process. The thermodynamic phase behavior of single semiflexible polymers in solvent has already been discussed in Chapter 7. The first result for the semiflexible multiple-cham system obtained from... 

Zhulina EB, Borisov OV, Pryamitsyn VA, Birshtein TM. Coil-globule type transition in polymers. 1. Collapse of layers of grafted polymer chains. Macromolecules 1991 24 140-149. 

P.-G. de Gennes later also considered the multisegment attraction regime. He suggested the so-called p-cluster model [11] in order to explain certain anomalies in behavior observed in many polymer species such as polyethyle-neoxide (PEO) see also [12]. The scenario of coil-globule transition with dominating multisegment interaction first considered by I.M. Lifshitz has been recently studied in [13]. The authors used a computer simulation of chains in a cubic spatial lattice to show that collapse of the polymer can be due to crystallization within the random coil. 

The above analysis implies that the coil-globule transition is essentially a gas-liquid transition within a single chain. Unlike usual molecular gases, the translational entropy is absent due to the chain connectivity, and instead, the conformational entropy shows up. The collapsed state is a spherical droplet, that is, globule, to minimize the surface area, the size of which is self-adjusted to satisfy the mechanical balance between the inside and the outside of the globule. 

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