Pseudo-melting phase transition

Many aliphatic poly(amides), more commonly known as nylons, exhibit an unusual phase transition below their melting point. First noted by Brill [122], the phenomenon has been studied extensively [128-131]. It is observed for instance in nylon (6,6) at a temperature of about 210°C, when the stable low-temperature triclinic oc phase of the crystalline polymer changes to a pseudo-hexagonal phase. 

The gel-to-fluid chain-melting transition in pseudo-two-dimensional lipid bilayer membranes induces formation of lipid domains of gel-like lipids in the fluid phase and and fluid-like lipids in the gel phase. The average domain size and in particular the average length of the one-dimensional interfaces between lipid domains and bulk have a dramatic temperature dependence with anomalies at the transition temperature. These anomalies are related to similar anomalies in response functions. The interfacial area may be modulated by intrinsic impurities which are interfacially active molecules such as cholesterol [1,2]. The properties of the interfacial area provide a means for understanding aspects of the functioning of certain biological membrane processes like the passive permeability of small ions and the activity of some membrane enzymes. 

Porous Particles. Some fillers such as zeolites are sufficiently porous to accommodate monomers, which can then be polymerized. This threads the chains through the cavities, with unusually intimate interactions between the reinforcing phase and the host elastomeric matrix (311-313). Unusually good reinforcement is generally obtained. Also, because of the constraints imposed by the cavity walls, these confined polymers frequently show no glass transition temperatures or melting points (27,314). PDMS chains have also been threaded through cy-clodextrins, to form pseudo-rotaxanes (315). 

Fig. 5.2(a)] result in a pseudo-transition which is represented by the first specific-heat peak in Fig. 5.1. The second less-pronounced peak in Fig. 5.1 around T 0.6 — 0.7 signals the melting into globular structures, whereas at still higher temperatures T 1.5 the well-known collapse peak indicates the dissolution into the random-coil phase. The distribution of the maximum values of the specific heat with respect to the maximum temperatures is shown in Fig. 5.3. Not surprisingly, the peaks belonging to the... 

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