Osmotic Interactions, Rheology, and Arrested Phase Separation of Star–Linear Polymer Mixtures

Abstract

Starting from a glassy suspension of star polymers in molecular solvent, we add linear homopolymer with a fixed size ratio and ever increasing concentration, hence diluting the glass and eventually approaching the regime of stars in polymer matrix. We show that we can quantitatively decompose the rheology of the mixtures into colloidal star and linear polymer contributions by accounting for the osmotic shrinkage of the stars due to the added polymers. We also estimate the effective star overlap concentration in the mixtures and show how the rheological properties change at the crossover concentration, where the number of star-particle contacts decreases and the star repulsions weaken and eventually become attractive upon increasing the linear polymer concentration. The attraction is accompanied by a phase separation, pointing to the presence of unstable regions in the star/linear polymer phase diagram, where gelation results from an arrested phase separation. The crossover concentration is also probed by nonlinear rheological measurements. These findings are of generic nature for soft colloidal mixtures and suggest guidelines for tailoring their rheology and phase/state behavior.

Depletion gels from dense soft colloids: Rheology and thermoreversible melting

“…Note that the key difference between the two states (repulsive glass and reentrant solid) is the presence or not of caging [Truzzolillo et al (2011)]. Furthermore, attractive glasses (exhibiting both caging and attractions) are characterized by a larger storage modulus when compared to the corresponding repulsive glasses (with the same number density of particles) [Pham et al (2008); Koumakis and Petekidis (2011)].…”

“…In particular, softness of the interactions and the particles has been shown to dramatically alter nonergodic-to-ergodic transitions leading to multiple glassy states [Stiakakis et al (2002); Stiakakis et al (2005); Bartsch (2002, 2003); Datta et al (2011);Truzzolillo et al (2011Truzzolillo et al ( , 2013a; Wiemann et al (2012)]. In our work, we employed multiarm star polymers as model soft colloids encompassing the two main macroscopic response features of entropically interacting soft particles, namely, squeezing and interpenetration [Bonnecaze and Cloitre (2010); Vlassopoulos and Fytas (2010)].…”

“…Earlier studies confirmed that depletion is at work in these soft colloid-homopolymer mixtures, and indeed repulsive star glasses melt upon addition of smaller polymer chains, though the range of size ratios over which this effect is observed appears broader as compared to the hard sphere case. At the same time, it was shown that the osmotic pressure due to the linear polymers is imparted on the stars through both depletion (like in hard spheres) and compression effects [Stiakakis et al (2002); Stiakakis et al (2005); Truzzolillo et al (2011)].…”

Glassy States in Asymmetric Mixtures of Soft and Hard Colloids

“…Stars with functionalities f S * 50 form glassy states at large volume fractions [7,10]. Mixtures of star polymers and smaller, linear polymers have shown great richness in metastable states, controlled by the osmotic pressure of the latter, and leading to star shrinkage and depletion [11,12]. Star polymers with f S 32 were also mixed with larger hard spheres and the phase behavior of the mixtures was examined experimentally and theoretically [13].…”

Dynamics of solvent-free grafted nanoparticles

“…However, there are many experimental and theoretical studies of star polymers in both small molecule solvents and linear polymer melts. 53,[55][56][57] The softness of star polymers in solution affects their dynamical behavior as seen in measurements of relative viscosity versus the effective volume fraction in solution as seen, for example, in Fig. (6) of Ref.…”