Static and dynamic properties of block copolymer based grafted nanoparticles across the non-ergodicity transition

Abstract

We present a systematic investigation of static and dynamic properties of block copolymer micelles with crosslinked cores, representing model polymer-grafted nanoparticles, over a wide concentration range from dilute regime to an arrested (crystalline) state, by means of light and neutron scattering, complemented by linear viscoelasticity. We have followed the evolution of their scattering intensity and diffusion dynamics throughout the non-ergodicity transition and the observed results have been contrasted against appropriately coarse-grained Langevin Dynamics simulations. These stable model soft particles of the core-shell type are situated between ultrasoft stars and hard spheres, and the wellknown star pair interaction potential is not appropriate to describe them. Instead, we have found that an effective brush interaction potential provides very satisfactory agreement between experiments and simulations, offering insights into the interplay of softness and dynamics in spherical colloidal suspensions.

Universal Polymeric-to-Colloidal Transition in Melts of Hairy Nanoparticles

“…Despite the eventual terminal relaxation, we attribute this unusually slow time and low plateau modulus to a jammed colloidal material (i.e., with predominant solidlike character), , as discussed further below. It should be noted that soft colloidal glasses with an observable alpha relaxation have been discussed in the literature. − ,, These findings suggest that upon reducing the arm molar mass, the polymer-dominated response is augmented by a hierarchical relaxation mechanism where arm retraction is followed by a colloidal relaxation process. Colloidal cage-escape , dynamics continue until structural relaxation of the system takes place, as proposed for multiarm star polymers. , It is important to note that the lowest four frequency decades are not accessible by means of the tTS, as the temperatures required to reach these frequencies in conventional small-amplitude oscillatory shear measurements are prohibitively high and the samples would degrade.…”

“…It should be noted that soft colloidal glasses with an observable alpha relaxation have been discussed in the literature. [16][17][18]53,54 These findings suggest that upon reducing the arm molar mass, the polymerdominated response is augmented by a hierarchical relaxation mechanism where arm retraction is followed by a colloidal relaxation process. Colloidal cage-escape 55,56 dynamics continue until structural relaxation of the system takes place, as proposed for multiarm star polymers.…”

Internal Microstructure Dictates Interactions of Polymer-grafted Nanoparticles in Solution

“…In the case of spherical brushes, the theoretical prediction is α = −4/3. 52,64,65 Only for DP2690, the density profile was steeper and represented by α = −1.57. As depicted in Figure 2, for the brush system with the largest size R m (DP2300), the second-order peak was also resolved within the light scattering q's.…”

“…The model was originally developed by Likos and co-workers to describe interactions between colloidal particles with adsorbed stabilizing layers 70 and was recently assessed systematically for GNPs by some of us. 52 The modification described below was inspired by the analysis of interacting star polymers in solvents of varying quality. 50 Hence, the model comprises the steric repulsion of grafted chains and Van der Waals attraction due to the silica core−core dipole interactions.…”

“…It is exactly this challenge that we address in this work. Assuming fixed core and solvent characteristics, the interactions between GNPs can be tuned by variation of the grafting density, σ, and the chain degree of polymerization, N . − To facilitate control of these parameters, the material model system in this study is thus comprised of GNPs with the same silica (SiO 2 ) core and polystyrene (PS) grafts. The core radius is constant R c = 57 ± 4 nm, and the grafting densities range from 0.08 to 0.61 chains/nm 2 while N is in the range 130–2700.…”