Parisi Daniele, Truzzolillo Domenico, Slim Ali H, Dieudonné-George Phillippe, Narayanan Suresh, Conrad Jacinta C, Deepak Vishnu D, Gauthier Mario, Vlassopoulos Dimitris
Department of Chemical Engineering, Product Technology, University of Groningen, Nijenborgh 4, Groningen 9747 AG, The Netherlands.
FORTH, Institute of Electronic Structure and Laser, Heraklion 70013, Crete, Greece.
Macromolecules. 2023 Feb 22;56(5):1818-1827. doi: 10.1021/acs.macromol.2c02491. eCollection 2023 Mar 14.
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-to-gel-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 X-ray 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.
由胶体颗粒和小得多的非吸附性线性均聚物组成的液体混合物，可因聚合物介导的排空力而发生凝胶化转变。我们现在表明，向具有相同流体动力学尺寸的软胶体悬浮液中添加线性聚合物会产生从液体到凝胶再到再入液体的转变。具体而言，借助线性粘弹性和小角X射线散射实验确定了1,4 - 聚丁二烯星型 - 线性聚合物混合物的动态状态图。在使星型聚合物低于其标称重叠浓度的情况下，增加线性聚合物含量会形成凝胶。进一步添加线性链会产生再入液体。这种意外行为可通过三种可能现象的相互作用来解释：(i) 排空相互作用，由星型聚合物与聚合物长度尺度（即其缠结网络的网眼尺寸）之间的尺寸差异驱动；(ii) 由于施加在星型聚合物上的渗透压增加导致的胶体去溶胀；(iii) 随着聚合物浓度增加，由于网眼尺寸减小，排空效率随之逐渐受到抑制，因此吸引力范围变小。我们的结果揭示了一种调节软胶体流动的令人兴奋的新方法，并突出了一条很大程度上未被探索的设计软胶体混合物的途径。
