Journal of Physical Chemistry B, Vol.110, No.20, 10151-10164, 2006
A Monte Carlo simulation of the aggregation, phase-separation, and gelation of model globular molecules
Monte Carlo computer simulation on a square 3- D lattice is used to model state behavior of globular copolymers. Two types of globular molecules were defined. One consisted of a single type of subunit ( a homopolymer) while the second contained a core of strongly attractive subunits and an outer layer of less strongly attractive subunits ( a heteropolymer). Systems of globules were simulated at varied volume fraction ( V-F) and reduced temperature ( T-R), and state diagrams were constructed. These state diagrams contained state boundaries defined by the V-F/ T-R combinations at which the system formed a percolating network and at which the various component subunits in the globule unfolded. Simulated systems could exist in a number of states ( between 4 and 7), depending on the V-F, T-R, whether the molecule was a homo-or heteroglobule and whether the globules were allowed to interact with each other or not. All systems exhibited a gelation/ crossover line that resembled a lower critical solution temperature. All systems also exhibited a critical gelation concentration, above which a continuous network was formed. The critical gelation concentration varied between about 2- 4% V-F depending on the type of system. This is comparable to experimental critical gelation concentrations of in the region of 4% ( w/ w) for a range of associating polymers and biopolymers such as globular proteins and polysaccharides. Other states were formed which included one where elongated, fibril- like aggregated strands were formed, and a micelle- like aggregated state. The results are discussed in terms of the known state behavior of associating polymers and biopolymers ( proteins and polysaccharides).