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Register a new userMixing--Demixing Transition in Polymer-Grafted Spherical Nanoparticles
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Polymer-grafted nanoparticles (PGNPs) can provide property profiles than cannot be obtained individually by polymers or nanoparticles (NPs). Here, we have studied the mixing--demixing transition of symmetric copolymer melts of polymer-grafted spherical nanoparticles by means of coarse-grained molecular dynamics simulation and a theoretical mean-field model. We find that a larger size of NPs leads to higher stability for given number of grafted chains and chain length reaching a point where demixing is not possible. Most importantly, the increase in the number of grafted chains, $N_g$, can initially favour the phase separation of PGNPs, but further increase can lead to more difficult demixing. The reason is the increasing impact of an effective core that forms as the grafting density of the tethered polymer chains around the NPs increases. The range and exact values of $N_g$ where this change in behaviour takes place depends on the NP size and the chain length of the grafted polymer chains. Our study elucidates the phase behaviour of PGNPs and in particular the influence of the grafting density on the phase behaviour of the systems anticipating that it will open new doors in the understanding of these systems with implications in materials science and medicine.
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We present Monte Carlo simulations of colloidal particles pulled into grafted polymer layers by external fields. The insertion free energy of a single colloid into the polymer layer is qualitatively different for surfaces with an ordered and a disordered distribution of grafting points. Moreover, the tendency of colloidal particles to traverse the grafting layer is strongly size dependent. In dense colloidal suspensions, under the influence of sufficiently strong external force, a collective instability allows the colloids to penetrate and form internally ordered, columnar structures spanning the polymer layer. Depending on the conditions, these colloidal clusters may be isolated or laterally percolating. The morphology of the observed patterns can be controlled by the external fields, which opens up new routes for the design of thin structured films.
We simulate a strongly size-disperse hard-sphere fluid confined between two parallel, hard walls. We find that confinement induces crystallization into n-layered hexagonal lattices and a novel honeycomb-shaped structure, facilitated by fractionation. The onset of freezing prevents the formation of a stable glass phase and occurs at much smaller packing fraction than in bulk. Varying the wall separation triggers solid-to-solid transitions and a systematic change of the size-distribution of crystalline particles, which we rationalize using a semi-quantitative theory. We show that the crystallization can be exploited in a wedge geometry to demix particles of different sizes.
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 well-known 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.
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 well-known 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.
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