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Both the dispersion state of nanoparticles (NPs) within polymer nanocomposites (PNCs) and the dynamical state of the polymer altered by the presence of the NP/polymer interfaces have a strong impact on the macroscopic properties of PNCs. In particular, mechanical properties are strongly affected by percolation of hard phases, which may be NP networks, dynamically modified polymer regions, or combinations of both. In this article, the impact on dispersion and dynamics of surface modification of the NPs by short monomethoxysilanes with eight carbons in the alkyl part (C8) is studied. As a function of grafting density and particle content, polymer dynamics is followed by broadband dielectric spectroscopy and analyzed by an interfacial layer model, whereas the particle dispersion is investigated by small-angle X-ray scattering and analyzed by reverse Monte Carlo simulations. NP dispersions are found to be destabilized only at the highest grafting. The interfacial layer formalism allows the clear identification of the volume fraction of interfacial polymer, with its characteristic time. The strongest dynamical slow-down in the polymer is found for unmodified NPs, while grafting weakens this effect progressively. The combination of all three techniques enables a unique measurement of the true thickness of the interfacial layer, which is ca. 5 nm. Finally, the comparison between longer (C18) and shorter (C8) grafts provides unprecedented insight into the efficacy and tunability of surface modification. It is shown that C8-grafting allows for a more progressive tuning, which goes beyond a pure mass effect.
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Tunable Fluorophobic Effect Determines Nanoparticle Dispersion in Homopolymers and Block Polymers
Abstract The controlled placement of nanoparticles (NPs) within homopolymers and block polymers is of broad interest for functional nanomaterials. This manuscript focuses on small molecule‐stabilized NPs that bring a large fraction of functionality. For such NP mixtures with block polymers, the overwhelming focus to date has been the use of attractive interactions to localize hydrophilic NPs within the hydrophilic portion of block polymers. Related lipophilic approaches often place NPs at the block polymer interface. Here, a new modality for block polymer–NP control is developed that rather relies upon repulsion via the fluorophobic effect. Fluorinated species strongly associate via repulsion from nonfluorinated media. Here, fluorinated NPs are made with ligand mixtures for granular control over the strength of the fluorophobic effect. Small‐angle X‐ray scattering data reveal that all F‐NPs readily phase separate from polystyrene whereas increasing fluorophobic strength enables dispersions within a fluorinated homopolymer. Next, the F‐NP placement within diblock polymers is investigated as a function of the fluorophobic strength. Weakly fluorophobic F‐NPs are found predominantly near the diblock interface whereas strongly fluorophobic F‐NPs are found to disperse throughout the fluorinated block. The controlled placement of NPs is an emerging way to self‐assemble materials.
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- Award ID(s):
- 1752615
- PAR ID:
- 10457690
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Advanced Materials Interfaces
- Volume:
- 7
- Issue:
- 5
- ISSN:
- 2196-7350
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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