Self-assembly of polymer-grafted nanoparticles in solvent-free conditions

Abstract

Grafting of polymer chains onto the surface of spherical nanoparticles leads to a hybrid type of fluid that exhibits properties of both particle suspensions and melts of star polymers–these properties being controlled by the relative dimensions of the grafted polymer chains to the nanoparticle diameter, D, and the number of the number of chains grafted on the nanoparticle surface, f. While polymer-grafted nanoparticles (GNP) of this kind typically have a spherical average shape after grafting even a moderate number of chains, their instantaneous molecular shape can fluctuate significantly due to the deformation of the grafted chains. Both simulations and measurements have previously revealed that these “conformationally polarizable” particles can exhibit self-assembly into large scale polymeric structures in both solution and in polymer melts, and we simulate polymer-grafted nanoparticles with D and temperature (T) variations without a dispersing solvent to better understand the nature of this self-assembly process. We observe a reversible self-assembly into linear and branched dynamic GNP structures, where the extent of the assembly and geometry depend on D and T, and we constructed a map capturing the GNP structural behavior with D and T variations. Since the shape of the GNPs appeared to be correlated with the occurrence of the GNP self-assembly, we quantified the average shape and a measure of shape fluctuations to better understand how molecular shape influences their propensity to self-assemble into different structural forms. Based on this framework, we describe the clustering process of the GNPs as an equilibrium polymerization phenomenon and we calculate the order parameter governing the dynamic clustering behavior of GNPs, the average mass of the clusters, size distribution, and the apparent fractal dimension of the clusters.

Particle localization and hyperuniformity of polymer‐grafted nanoparticle materials

“…In the limit of purely repulsive nanoparticle‐nanoparticle interactions, structural behavior diagrams have been constructed in previous studies , which are essential to define the thermodynamic and structural state of the material. Fig.…”

“…A G‐1 material exhibits the same structural features as a star‐liquid, but below a temperature threshold () exhibits a reversible self‐assembly of dynamic polymeric nanoparticle structures. We have described this crossover from liquid to gel transition in a previous study as an “equilibrium polymerization process”; we note the temperature at which half the nanoparticles in the system belong to a cluster as .…”

“…The symbols correspond to liquid‐like structure (circles) and when nanoparticles form dynamic clusters (squares). The dashed lines represent approximately two characteristic temperatures : at half the GNPs in the system belong to GNP clusters and below T a structural features of clustering appear at the nanoparticle radial distribution function. (b) Snapshots a nanoparticle with it grafted chains and the distribution of the grafted points, as well as, a snapshot of 8000 GNPs at temperature .…”

A comparative study of thermodynamic, conformational, and structural properties of bottlebrush with star and ring polymer melts

“…This is also the same number of arms at which a configurational transition from highly anisotropic linear chains to highly symmetric particle-like star polymers occurs. 31,116 The colloidal/spherical-like structural correlations are evident for stars having f = 16, as illustrated in Fig. 13b.…”

Exactly solvable model for self-assembly of hard core–soft shell particles at interfaces

“…The minimization of the surface-tension contribution to the free energy leads to effective attraction between the particles when their distance is larger than their diameter σ a . Attraction might result from the van der Waals interactions between the monomers too [13]. On the other hand, when the shells of the two particles overlap, they repel each other.…”