Gelation and Re-entrance in Mixtures of Soft Colloids and Linear Polymers of Equal Size

Abstract

Liquid mixtures composed of colloidal particles and much smaller non-adsorbing linear homopolymers can undergo a gelation transition due to polymer-mediated depletion forces. We now show that the addition of linear polymers to suspensions of soft colloids having the same hydrodynamic size yields a liquid-togel-to-re-entrant liquid transition. In particular, the dynamic state diagram of 1,4-polybutadiene star−linear polymer mixtures was determined with the help of linear viscoelastic and small-angle Xray scattering experiments. While keeping the star polymers below their nominal overlap concentration, a gel was formed upon increasing the linear polymer content. Further addition of linear chains yielded a re-entrant liquid. This unexpected behavior was rationalized by the interplay of three possible phenomena: (i) depletion interactions, driven by the size disparity between the stars and the polymer length scale which is the mesh size of its entanglement network; (ii) colloidal deswelling due to the increased osmotic pressure exerted onto the stars; and (iii) a concomitant progressive suppression of the depletion efficiency on increasing the polymer concentration due to reduced mesh size, hence a smaller range of attraction. Our results unveil an exciting new way to tailor the flow of soft colloids and highlight a largely unexplored path to engineer soft colloidal mixtures.

Glassy phases of the Gaussian core model

“…1 The degree of softness is conveniently expressed by the ratio E el /k B T of their elastic deformation energy upon small overlaps or indentations, E el , over the thermal energy k B T, which can span several orders of magnitude. 1,2 Their suspensions exhibit structural and dynamical anomalies, [3][4][5][6] which accompany rich types of thermodynamic behavior, such as reentrant melting, [7][8][9][10][11] and clustering. 12,13 The deformability of these soft colloids manifests itself under flow as particle elongation, tumbling and shear-thinning.…”

Water-Driven Sol–Gel Transition in Native Cellulose/1-Ethyl-3-methylimidazolium Acetate Solutions

“…A viscoelastic fluid that does not show flow behavior within 100 s (0.01 rad/s) is considered to be a gel. 41 − 45 Further addition of water promotes an increase in the gel strength ( Figure 1 B). For larger polymer contents ( Figure 1 C), the amount of water needed to form a gel decreases.…”

“…As soon as an entangled polymer network is formed ( C p ∼ C e ), a water content as low as 6 wt % suffices to dynamically arrest the solution (Figure B). A viscoelastic fluid that does not show flow behavior within 100 s (0.01 rad/s) is considered to be a gel. − Further addition of water promotes an increase in the gel strength (Figure B). For larger polymer contents (Figure C), the amount of water needed to form a gel decreases.…”