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.

Effect of Fluorophobic Character upon Switching Nanoparticles in Polymer Films from Aggregated to Dispersed States Using Immersion Annealing

“…The NP/polymer distribution states were checked by SAXS both as spin-coated (Figure 4a) and after immersion annealing (Figure 4b). These as spin-cast trends are similar but different from those previously reported 31 and were possibly associated with the changes to the NP synthesis and purification procedures (size, dispersity, ligand shell density), the PFOA synthesis (molecular weight, viscosity), or the spin coating conditions (rpm, gas flow rates). Overall, the ability of the NPs to switch between dispersed and aggregated states was observed to progress through two distinct fluorophobic-based mechanisms; the lowto-moderately fluorophobic F-NP distribution trends were consistent with enthalpy of mixing considerations, whereas highly fluorophobic F-NP distribution trends were consistent with PFOA behaving as a compatibilizer/surfactant.…”

“…To compare the effects of NP intermolecular interactions, comparisons should ideally be carried out with identical NP sizes for criteria (1) and (2). Here, a ligand displacement strategy was chosen to decouple NP size effects from subsequent deliberate changes to the ligand chemistry. , Furthermore, NP stability is important to consider where thiols were chosen as a sufficiently strong binding group while also being able to displace weakly bound amine ligands from the initial synthesis step. The existence of mixed thiol ligand could avoid the gold core size change and form a mixed monolayer, which could thereby ensure NP stability throughout the immersion annealing process (from 0.5 to 24 h).…”

“…30 Similarly, the distribution of xF-NPs into a fluorophobic homopolymer was recently shown to depend significantly upon the fluorophobic strength of the NPs where highly fluorophobic NPs were more dispersed. 31 Fluorophobic intermolecular interactions are thus uniquely strong and are promising candidates to enable switchable NP distribution states by altering the molecular environment within polymer films.…”

“…For this reason, the term “fluorophobic” is often preferred to the equivalent term “fluorophilic”. − A remarkable example demonstrated that two immiscible homopolymers with short fluorinated end groups self-assembled into a lamellar arrangement based on the fluorophobic repulsion of the end groups, leading to pseudo-diblock polymer type behavior . Similarly, the distribution of x F-NPs into a fluorophobic homopolymer was recently shown to depend significantly upon the fluorophobic strength of the NPs where highly fluorophobic NPs were more dispersed . Fluorophobic intermolecular interactions are thus uniquely strong and are promising candidates to enable switchable NP distribution states by altering the molecular environment within polymer films.…”

Bottom‐Up Assembly of Micro/Nanostructures

“…Marsh et al report about a new methodology to control block copolymer/nanoparticle interactions taking advantage of the so-called fluorophobic effect: fluorinated species strongly associate via repulsion from non-fluorinated media. [19] Placement of fluorinated nanoparticles within a block copolymer matrix with a fluorinated block was investigated as a function of the fluorophobic strength. This demonstrates the possibility to control nanoparticle position in the polymeric template, and paves the way to future controlled assembly of nanocomposites with multiple type of nanoparticles selectively segregated within specific block of the polymer matrix.…”