Comparative Study\nof Polymer Globules and Liquid Droplets\nin Poor Solvents: Effects of Cosolvents and Solvent Quality

We compare the structures of polymer globules, composed\nof flexible\npolymer chains, with liquid droplets made of nonbonded monomers of\nthe same polymer in poor solvents. This comparison is performed in\nthree different poor solvents, with and without the addition of cosolvents.\nMolecular dynamics simulations are used to analyze the properties\nof the polymer globules, while semigrand canonical Monte Carlo simulations\nare used to form metastable liquid droplets of nonbonded monomers\nthrough homogeneous nucleation in the same solvents. Our findings\nshow that both globules and droplets are nearly spherical, although\ndroplets display slightly more anisotropy. In the absence of cosolvents,\nthe surrounding solvent structures are similar for both globules and\ndroplets. However, in the presence of cosolvents, significant differences\narise in the liquid structure, with the disparities increasing as\nthe solvent quality worsens. Cosolvents tend to accumulate near the\nsurface of globules due to the restricted movement of bonded monomers,\nwhich partially immobilizes the cosolvents. This effect becomes more\npronounced as the solvent quality declines. Interfacial free energy\ncalculations reveal that cosolvents act like surfactants, promoting\nlarger interfacial areas for both globules and droplets. This effect\nis more significant for globules due to the greater accumulation of\ncosolvents at their surface. Therefore, modeling polymer globules\nas liquid droplets may underestimate the impact of cosolvents on the\nstability of the globule state. Additionally, the transition states\ninvolved in polymer collapse in the presence of cosolvents differ\nfrom those involved in the nucleation of liquid droplets in the same\nsolution.