Abstract
This study reports a general scenario for the out-of-equilibrium features of collapsing polymeric architectures. We use molecular dynamics simulations to characterize the coarsening kinetics, in bad solvent, for several macromolecular systems with an increasing degree of structural complexity. In particular, we focus on: flexible and semiflexible polymer chains, star polymers with 3 and 12 arms, and microgels with both ordered and disordered networks. Starting from a powerful analogy with critical phenomena, we construct a density field representation that removes fast fluctuations and provides a consistent characterization of the domain growth. Our results indicate that the coarsening kinetics presents a scaling behaviour that is independent of the solvent quality parameter, in analogy to the time–temperature superposition principle. Interestingly, the domain growth in time follows a power-law behaviour that is approximately independent of the architecture for all the flexible systems; while it is steeper for the semiflexible chains. Nevertheless, the fractal nature of the dense regions emerging during the collapse exhibits the same scaling behaviour for all the macromolecules. This suggests that the faster growing length scale in the semiflexible chains originates just from a faster mass diffusion along the chain contour, induced by the local stiffness. The decay of the dynamic correlations displays scaling behavior with the growing length scale of the system, which is a characteristic signature in coarsening phenomena.
Highlights
Understanding the collapse of fully polymeric, topologically complex objects in a bad solvent is of broad importance, because of its relevance in the early stages of the protein folding [1,2], and its connections with arresting processes or aging phenomena [3,4]
In order to quantify the growing length scale we introduce a density field representation of the macromolecules that removes artifacts arising from the local, fast density fluctuations in the coarsening structure [22]
We have investigated the coarsening kinetics emerging during the collapse of several macromolecular architectures in bad solvent: microgels with realistic and with ideal regular networks, star polymers of 3 and 12 arms, and linear chains
Summary
Understanding the collapse of fully polymeric, topologically complex objects in a bad solvent is of broad importance, because of its relevance in the early stages of the protein folding [1,2], and its connections with arresting processes or aging phenomena [3,4]. In the context of macromolecular collapse in bad solvent, the coarsening process initiates with the formation of small clusters of monomers along the polymeric strands Afterwards, these clusters become stable and start to grow by withdrawing monomers from the bridges connecting them or by coalescence with other clusters. In a previous work by some of us [23] a scaling exponent of ∼0.7 has been found at intermediate times for the growth of the domains during the deswelling of microgels in bad solvent This accelaration (higher exponent) with respect to the system of Ref. Domain growth in microgels shows a power law, though an overshoot is found in the late stage of the collapse for the case of diamond-like networks This unusual behavior is related to the fast late merging of the regularly distributed nucleating centers.
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