Abstract
The design of surface-modified functional nanoparticles (NPs) is used to control the properties of the NPs and the NP/environment interactions. The efficient control of the final behavior of the NPs demands a comprehensive understanding of the resulting system. This is particularly challenging for systems with an architecture of the type polymer core–polymer canopy. In such systems, one of the key parameters influencing the behavior of the NPs is the local dynamics of the polymer canopy. However, because the grafting points of the canopy are experiencing their own local dynamics, predicting the final behavior of such systems is difficult. To get a deeper understanding of NPs made of a soft and swollen polymer core and a swollen polymer canopy, we prepared a library of hairy NPs made of a polystyrene (PS) core and a canopy of grafted poly(methyl acrylate) (PMA) chains. The softness of the PS core and the thickness of the PMA canopy were controlled, and the behavior and dynamics of the soft and hairy PS–PMA NPs in suspension were measured by 1H NMR relaxation and dynamic light scattering. It was observed that the rigid PS core slowed down the subsegmental dynamics of the PMA chains, while thick PMA canopies accelerated the relaxation of the PS core. The dynamics of the NPs in suspension was the result of the interplay between the PS core and the PMA canopy.
Highlights
End-tethered polymer chains, or polymer brushes, are used extensively to modify the properties of nanoparticles (NPs) such as stability, solvent compatibility, dispersibility, and assembly
The length of the poly(methyl acrylate) (PMA) chains and the amount of the cross-linker in the PS cores were controlled by miniemulsion followed by surfaceinitiated atom transfer radical polymerization (SI-ATRP)
As observed by other techniques, grafting polymer chains slowed down the subsegmental relaxation dynamics of the grafted chain, but more interestingly, grafting polymer chains on soft and deformable NPs allowed us to address a new phenomenon, the relation between the local relaxation dynamics of the core and the local relaxation dynamics of the canopy
Summary
End-tethered polymer chains, or polymer brushes, are used extensively to modify the properties of nanoparticles (NPs) such as stability, solvent compatibility, dispersibility, and assembly. Tional changes of the polymer chains, and as the chain length increased, the relaxation rate of the tethered chains converged to the relaxation rate observed for untethered chains of a similar molecular weight.[10] Other studies have shown that the relaxation of grafted polymer chains was impeded in comparison to free polymer chains of the same molecular weight because of their immobilization on a substrate.[17] Such differences arise from different methods used to analyze the polymer dynamics, which can probe different types of relaxation processes and give access to different physical characteristics. The details of NMR experiments are described in the Supporting Information
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