Intramolecular nucleation

Hu WB, Mathot VBF, Frenkel D (2003a) Lattice model study of the thermodynamic interplay of polymer crystallization and liquid-liquid demixing. J Chem Phys 118 10343-10348 Hu WB, Frenkel D, Mathot VBF (2003b) Sectorization of a lamellar polymer crystal studied by dynamic Monte Carlo simulations. Macromolecules 36 549-552 Hu WB, Frenkel D, Mathot VBF (2003c) Intramolecular nucleation model for polymer crystallization. Macromolecules 36 8178-8183... 

Abstract. We review how the nucleation mechanism of polymer crystallization could be assigned to intramolecular processes and what are the preliminary benefits for understanding some fundamental crystallization behaviors. The speculative concept of molecular nucleation and the theoretical model of intramolecular nucleation have been elucidated in a broad context of classical nucleation theory. The focus is on explaining the phenomenon of molecular segregation caused by polymer crystal growth. 

Fig. 3.9. Depicted free-energy curve of a single macromolecule participating the crystal growth through multiple events of intramolecular nucleation [45]...

According to this intramolecular-nucleation model, when the melt of long-chain macromolecules is quenched to low temperatures for fast crystallization, each macromolecule may perform multiple local intramolecular nucleation events and hence will be included in several lamellae or several positions of the same lamellae, with only little changes of their unperturbed coil-size scaling. At each position, intramolecular nucleation yields folded-chain clusters. This picture is quite consistent with Hoffman s proposition of a variable-cluster model for the conformation of macromolecules in the semi-crystalline state [50[. 

From the classical Lauritzen-Hoffman model to the molecular-nucleation concept, and then the intramolecular-nucleation model, polymer crystal nude-... 

Fig. 4.15 Schematic pictures of (a) intermolecular nucleation and (b) intramolecular nucleation...

It should be noted fliat intermolecular nucleatitm could coexist with intramolecular nucleation. Intermolecular nucleation is often observed with short chains, rigid chains, polymerizing chains, or when chains are stretched. Recently, upon stretching network polymers, the transition from intramolecular nucleation to intermolecular nucleation was observed in Monte Carlo simulations (Nie et al. 2013). By analyzing the probability of adjacent chain-folding of those newly formed crystallites with a size between 50 to 200 parallel packed bonds at each step of stretching, an obvious reduction was observed in its evolution curve under each temperature as shown in Fig. 4.20a. The corresponding critical strain was considered to be the transition point under which intramolecular nucleation is the favorite and above which intermolecular nucleation becomes the dominant. 

Compared the critical strain with the onset strain of crystallization during stretching under each temperature as shown in Fig. 4.20b, it is fotmd that at low temperatures (the dimension-reduced T < 4.0) intramolecular nucleation dominates the initiation of polymer crystallization with a smaller strain than the critical value, and when temperature becomes higher, intermolecular nucleation begins to dominate the initiation of crystalhzation. 

The intramolecular nucleation was then developed by supposing that all the secondary nucleation is mainly controlled by intramolecular nucleation (Hu et al. 2003b Hu 2007) and the basic crystal lamella is resulted due to the preference of chain-folding in this unique style of secondary nucleation. 

The free energy barrier for critical intramolecular nucleation under a certain temperature is independent of chain length, but not for the opposite direction, i.e., melting. Therefore, a critical molecular length exists for the equilibrium... 

Under a low temperature, the critical chain length for secondary nucleation may be much smaller than the chain length, and several events of intramolecular nucleation could happen along the same chains. If they occur in the same lamellar crystal, loops are formed and if in different lamellar crystals, tie molecules are formed. The intramolecular nucleation model allows a statistical treatment on the semicrystalline texture. 

Let us first consider the intramolecular nucleation. The specific free energy on the lateral surfaces of PE crystals was estimated to be ll.Serg/cm, and its specific free... 

In practice, intermolecular nucleation could coexist with intramolecular nucleation. Intermolecular nucleation is often observed with short chains, rigid chains, or when chains are stretched. Recently, upon stretching network polymers, the transition from intramolecular nucleation to intermolecular nucleation was observed in dynamic Monte Carlo simulations [59]. By analyzing the probability of adjacent chain folding... 

Hu W, Frenkel D, Mathot VB. Intramolecular nucleation model for polymer crystallization. Macromolecules 2003 36 8178-8183. 

---