Self-Organization and Flow of Low-Functionality Telechelic Star Polymers with Varying Attraction

Abstract

We combine state-of-the art synthesis, simulations, and physical experiments to explore the tunable, responsive character of telechelic star polymers as models for soft patchy particles. We focus on the simplest possible system: a star comprising three asymmetric block copolymer arms with solvophilic inner and solvophobic outer blocks. Our dilute solution studies reveal the onset of a second slow mode in the intermediate scattering functions as the temperature decreases below the θ-point of the outer block, as well as the size reduction of single stars upon further decreasing temperature. Clusters comprising multiple stars are formed and their average dimensions, akin to the single star size, counterintuitively decrease upon cooling. A similar phenomenology is observed in simulations upon increasing attraction between the outer blocks and is rationalized as a result of the interplay between interstar associations and steric repulsion between the star cores. Since our simulations are able to describe the experimental findings reliably, we can use them with confidence to make predictions at conditions and flow regimes that are inaccessible experimentally. Specifically, we employ simulations to investigate flow properties of the system at high shear rates, revealing shear thinning behavior caused by the breakup of interstar associations under flow. On the other hand, the zero-shear viscosity obtained experimentally exhibits a rather weak activation energy, which increases upon rising star concentration. These findings demonstrate the unusual properties of telechelic star polymers even in the dilute regime. They also offer a powerful toolbox for designing soft patchy particles and exploring their unprecedented responsive properties further on.

Shape control of soft patchy nanoparticles under confinement

“…Taking as concrete example polybutadine-polysterene block copolymers, 27 we can provide an estimate for the size of the core particles, the molecular weight and the height of the con- finement. If we choose the Kuhn length of polysterene as the unit of length σ = σ PS = 1.8 nm, 27 the diameter of the central colloid is approximately 15 nm while (on average) the whole nanoparticle measures between 16 and 19 nm in the bulk; furthermore, the height of the confinement would range between 17 and 60 nm. Finally, the molecular weight (excluding the central colloid) can be estimated as…”

“…26 In this work we explore, by means of full-monomer numerical simulations, the properties of diblock copolymer brushes grafted to a spherical colloidalso referred to as diblock copolymer star (DCS) brush. Diblock copolymer brushes composed of polybutadine-polysterene have been recently synthesized using state-of-the-art techniques, 27,28 and the accompanying numerical simulations have shown that the simple modeling we put forward here is capable of capturing the salient characteristics under both dilute and semidilute conditions. First, we consider a DCS brush in the bulk and show that, as the solvophobic sections of the brush aggregate, we can identify patches as clusters of monomers belonging to different arms, as prescribed in the literature; 23 DCS brushes thus constitute examples of soft patchy particles.…”

Crowded solutions of single-chain nanoparticles under shear flow

“…29 There is a vast literature on the conformations and intramolecular dynamics of polymeric systems under shear flow at high dilution (experimental) or for isolated polymers (simulations). The effect of shear flow on such properties in semidilute and concentrated solutions have received less attention, though some very detailed studies have been reported, including e.g., experiments in solutions of DNA and common polymers, [41][42][43] and simulations of flexible linear chains, [44][45][46][47] end-functionalized semiflexible linear chains, 48 stars (simple, 49,50 telechelic 51 and block copolymer 52 ), and cluster-forming semiflexible rings. 53,54 There is a broad interest in the characterization of the structure and dynamics of complex macromolecules (stars, dendrimers, nanogels, etc.)…”

Dynamical Properties of Concentrated Suspensions of Block Copolymer Stars in Shear Flow

“…Examples of experimental realizations of such macromolecules are zwitterionic polybutadiene star polymers and polybutadiene/polyisoprene, poly(acrylic acid)/polystyrene, and poly(ethylene oxide)/poly(propylene oxide) BCSs. 6 − 10 …”

“… 21 On the other hand, for semidilute solutions of low-functionality telechelic star polymers ( f ≤ 3), which also form connected networks, an increasing viscosity is predicted as the concentration, functionality, or the attraction between B-monomers increases. 10 , 22 Furthermore, the steady-state response of these solutions under shear flow features both Newtonian and shear thinning behaviors, the latter being linked to the fission of inter- and intra-star patches.…”