Effect of solvent on the emulsion and morphology of polyfluorene films: all-atom molecular dynamics approach.

The morphology of conjugated polymer thin films deposited by the resonant infrared matrix-assisted pulsed laser evaporation (RIR-MAPLE) process is related to the emulsion characteristics. However, a fundamental understanding of how and why the emulsion characteristics control the film properties and device performance is yet unclear. We performed all-atom molecular dynamics simulations of emulsions containing a mixture of polyfluorene (PFO) polymer, various primary solvents, secondary solvent, and water. The emulsion properties were then examined as a function of variable primary solvent and correlated with the morphology of deposited PFO thin films. The examination of the explicit interactions between all components of the emulsion indicated that using a primary solvent with a lower solubility-in-water and a higher non-bonded interaction energy ratio, between the solvent, polymer, and water in the emulsion recipe, produced the best result with smoother and denser films. Additionally, our simulation results are consistent with the AFM experimental results, indicating that interactions driven by trichlorobenzene (TCB) primary solvent within the emulsion are responsible for high-quality, smooth, and continuous thin film surfaces. Overall, this study can support the choice of a suitable primary solvent and provides the computational framework for predictions of new recipes for polymeric emulsion systems.

Monomer Composition as a Mechanism to Control the Self-Assembly of Diblock Oligomeric Peptide-Polymer Amphiphiles.

Diblock oligomeric peptide-polymer amphiphiles (PPAs) are biohybrid materials that offer versatile functionality by integrating the sequence-dependent properties of peptides with the synthetic versatility of polymers. Despite their potential as biocompatible materials, the rational design of PPAs for assembly into multichain nanoparticles remains challenging due to the complex intra- and intermolecular interactions emanating from the polymer and peptide segments. To systematically explore the impact of monomer composition on nanoparticle assembly, PPAs were synthesized with a random coil peptide (XTEN2) and oligomeric alkyl acrylates with different side chains: ethyl, tert-butyl, n-butyl, and cyclohexyl. Experimental characterization using electron and atomic force microscopies demonstrated that the tail hydrophobicity impacted accessible morphologies. Moreover, the characterization of different assembly protocols (i.e., bath sonication and thermal annealing) revealed that certain tail compositions provide access to kinetically trapped assemblies. All-atom molecular dynamics simulations of micelle formation unveiled key interactions and differences in core hydration, dictating the PPA assembly behavior. These findings highlight the complexity of PPA assembly dynamics and serve as valuable benchmarks to guide the design of PPAs for a variety of applications, including catalysis, mineralization, targeted sequestration, antimicrobial activity, and cargo transportation.

Correlation of Emulsion Chemistry, Film Morphology, and Device Performance in Polyfluorene LEDs Deposited by RIR-MAPLE.

Thin films of polyfluorene (PFO) were deposited using emulsion-based resonant infrared, matrix-assisted pulsed laser evaporation (RIR-MAPLE). Here, it is shown that properly selected surfactant chemistry in the emulsion can increase crystalline ß phase (ß-PFO) content and consequently improve the color purity of light emission. To determine the impact of surfactant on the device performance of resulting films, blue light-emitting diodes (LEDs) with PFO as an active region were fabricated and compared. Molecular dynamics (MD) simulations were used to explain the physical and chemical changes in the emulsion properties as a function of the surfactant. The results indicate that the experimental film morphology and device performance are highly correlated to the emulsion droplet micelle structure and interaction energy among PFO, primary solvent, and water obtained from MD simulations. While the champion device performance was lower than other reported devices (luminous flux ∼0.0206 lm, brightness ∼725.58 cd/m2, luminous efficacy ∼0.0548 lm/W, and luminous efficiency ∼0.174 cd/A), deep blue emission with good color purity (CIE chromaticity diagram coordinate of (0.177,0.141)) was achieved for low operating voltages around 3 V. Furthermore, a much higher ß-phase content of 21% was achieved in annealed films (without the pinholes typically found in ß-PFO deposited by other techniques) by using sodium dodecyl sulfate (SDS) as the surfactant.