Shape Transformations and Self-Assembly of Hairy Particles under Confinement

Molecular dynamics simulations are used to investigate the behavior of polymer-tethered nanoparticles between two inert or attractive walls. The confinement in pores creates new possibilities for controlling the shape transformation of individual hairy particles and their self-organization. We introduce a minimalistic model of the system; only chain-wall interactions are assumed to be attractive, while the others are softly repulsive. We show how the shape of isolated particles can be controlled by changing the wall separation and the strength of the interaction with the surfaces. For attractive walls, we found two types of structures, “bridges” and “mounds”. The first structures are similar to flanged spools in which the chains are connected with both walls and form bridges between them. We observed various bridges, symmetrical and asymmetrical spools, hourglasses, and pillars. The bridge-like structures can be “nano-oscillators” in which the cores jump from one wall to the other. We also study the self-assembly of a dense fluid of hairy particles in slit-like pores and analyze how the system morphology depends on interactions with the surfaces and the wall separation. The hairy particles form layers parallel to the walls. Different ordered structures, resembling two-dimensional crystalline lattices, are reported. We demonstrate that hairy particles are a versatile soft component forming a variety of structures in the slits.

Adsorption of amphiphilic grafted polymers as polymer corrosion inhibitors: insights from mesoscopic simulations

The homogeneous covering of amphiphillic polymer molecules onto metallic surfaces is of great importance for corrosion inhibitor applications. Lyophillic side chains grafted onto a lyophobic backbone act as anchors that allow the molecule to absorb at the metallic surface preventing the exposure with the solvent. Coarse-grained simulations are used to study the sorption and conformation behaviour of amphiphillic grafted polymers for corrosion inhibition. The backbone insolubility is found to play a key role in the sorption and conformation behaviour in the dilute limit. For finite concentrations, moderate backbone solubility and moderate molecule concentrations achieve optimal surface coverage, while highly a lyophobic backbone leads to bulk-like structures as a consequence of aggregation.

Phase Behavior of Gradient Copolymer Melts with Different Gradient Strengths Revealed by Mesoscale Simulations

Design and preparation of functional nanomaterials with specific properties requires precise control over their microscopic structure. A prototypical example is the self-assembly of diblock copolymers, which generate highly ordered structures controlled by three parameters: the chemical incompatibility between blocks, block size ratio and chain length. Recent advances in polymer synthesis have allowed for the preparation of gradient copolymers with controlled sequence chemistry, thus providing additional parameters to tailor their assembly. These are polydisperse monomer sequence, block size distribution and gradient strength. Here, we employ dissipative particle dynamics to describe the self-assembly of gradient copolymer melts with strong, intermediate, and weak gradient strength and compare their phase behavior to that of corresponding diblock copolymers. Gradient melts behave similarly when copolymers with a strong gradient are considered. Decreasing the gradient strength leads to the widening of the gyroid phase window, at the expense of cylindrical domains, and a remarkable extension of the lamellar phase. Finally, we show that weak gradient strength enhances chain packing in gyroid structures much more than in lamellar and cylindrical morphologies. Importantly, this work also provides a link between gradient copolymers morphology and parameters such as chemical incompatibility, chain length and monomer sequence as support for the rational design of these nanomaterials.

Associative properties of poly(ethylene glycol)-poly(vinyl acetate) comb-like graft copolymers in water

The self-assembly of amphiphilic graft copolymers is generally reported for polymer melts or polymers deposited onto surfaces, while a small number of cases deal with binary mixtures with water. We report on the associative properties of poly(ethylene glycol)-graft-poly(vinyl acetate) (PEG-g-PVAc) comb-like copolymers in water, demonstrating the existence of a percolative behaviour when increasing the PEG-g-PVAc content. Rheology, light- and small-angle X-ray scattering experiments, together with dissipative particle dynamics simulations, reveal a progressive transition from spherical polymer single-chain nanoparticles (SCNPs) towards hierarchically complex structures as the weight fraction of the polymer in water increases. The ability of PEG-g-PVAc to attain different nano- and microstructures is of great importance in numerous applications such as in the fields of cosmetics, detergency and drug delivery.