Coil to globule transition

The coil-to-globule transition was studied for designed HP copolymer chains both by means of lattice Monte Carlo simulations using bond fluctuation algorithms and multiple histogram reweighting [100,101] and by a numer- 

With a further increase in temperature, at the end of the molten globule regime, there is a sudden jump in the interaction energy. At this temperature, the coil-to-globule transition is found. The transition temperature increases 

Finally, at very high temperature the chains are swollen and behave as a random coil. In such a chain the majority of the interactions are between polymer units and solvent molecules. This state does not depend on the primary structure of the chains and, therefore, the interaction energy levels off to a constant value that depends only on chemical composition. 

The effect of copolymer sequence on coil-to-globule transition was also studied using Langevin molecular dynamics [103]. The method for estimation of the quality of reconstruction of core-shell globular structure after chain collapse was proposed. It was found that protein-like sequences exhibit better reconstruction of initial globular structure after the cooling procedure, as compared to purely random sequences. 

For a while, it was a big mystery why nanoscale polymer domains at the early stages of polymerization would remain relatively hot in FRRPP systems. Intuition formalized by arguments in Section 1.2 tells us that with this small size scale, heat dissipation will be relatively fast. One plausible answer to this mystery is the so-called coil-globule transition for isolated polymer macromolecules. 

Since the polymer molecules at this point exist as in a poor solvent environment, they assume the form of highly collapsed polymer globules (Doi, 1996). For dilute systems, the internal volume fraction of the globule is independent of the bulk concentration of polymer in the system and is a function of polymer-polymer, polymer-solvent, and solvent-solvent interactions. 

For typical nonpolar organic liquids, interaction forces are dispersive or London-type forces (Olabisi et al., 1979). The physics of the globular state is not well understood, although it has been studied extensively both experimentally (Nishio et al., 1982, Nierlich et al., 1978) and theoretically (Sanchez, 1979, Kholodenko and Freed, 1984, Raos and Allegra, 1996). 

A schematic diagram showing the collapse of a polymer coil into a dense globule with decreasing quality of solvent is shown in Fig. 2.1.12. Rq and Roe refer to the radii of gyration of the coil/globule and the coil/globule at -conditions, respectively. 

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Volume approximation (when the surface contribution to the free energy of a globule is neglected) works the better the farther the system is from the point of the coil-to-globule transition. In the framework of this approximation, it coincides with the -point, whereas under the theoretical consideration where the surface layer is taken into account, a gap appears separating these two points. The less is the length of polymer chain l, the more pronounced is this gap. Hence, the condition, imposed on the thermodynamic and stoichiometric parameters of the system by the equation of the -point,... 

Coil-to-Globule Transition of Linear PNIPAM Homopolymer Chains. . .. 117... 

Before discussing the folding of amphiphilic copolymer chains, let us first briefly examine the past studies of the coil-to-globule transition of homopolymer chains in dilute solutions. More than three decades ago, Stockmayer [17]... 

Fig. 8 Schematic of different chain conformations and the coil-to-globule transition of NIPAM-co-VP copolymers prepared at two temperatures, respectively, lower and higher than the lower critical solution temperature of PNIPAM homopolymer [56]...

Fig. 10 Schematic of formation of a single chain core-shell nanostructure through the coil-to-globule transition of the PNIPAM-g-PEO copolymer chain backbone [67]...

Figure 24 shows that both (i g) and (jq,) decrease as the temperature increases. Each data point was obtained only after the solution had reached thermodynamically equilibrium and the measured value was stable. Note that in each curve there exists a small kink at 29.4 °C and that (Rg)/(Rh) remains constant at 1.15 in the range 29-30.6 °C, representing an additional transition prior to the collapse of the PNIPAM chain segments. The decreases of both (Rg) and (R ) after the kink become faster. As shown before, the coil-to-globule transition of PNIPAM homopolymer chains do not present such a kink [32-34,37-40]. The sharp decrease of (Rg)/(Rh) from 1.5 to 0.6 in the inset confirms the coil-to-globule transition of individual copolymer chains. However, a careful examination of Fig. 24 raises a number of questions. 

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