ABSTRACT
It has been widely shown that water microdroplets have a plethora of unique properties that are highly distinct from those of bulk water, among which an especially intriguing one is the strong reducing power as a result of the electrons spontaneously generated at the air-water interface. In this study, we take advantage of the reducing power of water microdroplets to reduce ortho-diiodotetrafluorobenzene (o-C6F4I2) into a C6F4I2â¢- radical anion. Photoelectron spectroscopy and density functional theory computations reveal that the excess electron in C6F4I2â¢- occupies the I-C1-C2-I linkage, which elongates the C-I bonds but surprisingly shortens the C1-C2 bond, making the bond order higher than a double bond, similar to the benzyne molecule, so we named it "quasi-benzyne". The C6F4I2â¢- anion was further successfully utilized in a Diels-Alder reaction, a typical reaction for benzyne. This study provides a good example of strategically utilizing the spontaneous properties of water microdroplets and generating an especially exotic anion, and we anticipate that microdroplet chemistry can be an avenue rich in opportunities for new catalyst-free organic reactions.
ABSTRACT
A thorough understanding of the relevant factors governing the transport of nanoparticles in poly(ethylene glycol) diacrylate (PEGDA) is crucial for many applications utilizing this polymer. Here, single-particle tracking (SPT) was used to systematically investigate the role of the probe size (3-200 nm) on the diffusion behaviors of individual fluorescent nanoparticles in semidilute and unentangled PEGDA solutions. The quantitative assessment of the SPT data via the recorded single-particle trajectories and diffusion coefficients (D) not only showed that the observed probe dynamics in PEGDA were temporally and spatially heterogeneous, but more importantly that the measured D were observed to be significantly reduced (vs in solvent) and strongly size-dependent. We explained these results based on a modified multiscale model for particle diffusion, built upon well-established hydrodynamics and obstruction theories. We furthermore showed that the presence of steric interactions and probe confinement effects in highly crowded, unentangled PEGDA microstructures can lead to deviations in the single-particle displacements from the expected Gaussian behavior, as revealed by the van Hove displacement distributions and the associated non-Gaussian parameters. This study has demonstrated the power of SPT methods in offering an advanced characterization of the transport characteristics in complex polymer structures, overcoming challenges posed by traditional characterization techniques.
ABSTRACT
This paper reports single-molecule tracking (SMT) measurements of the diffusion behaviors of individual, anionic sulforhodamine B (SRB) dye molecules in a series of poly(ethylene oxide) (PEO) films, aimed at clarifying the influences of the molecular weight, network plasticization, and thermal annealing on such dynamics. Micrometer-thick PEO films were prepared by drop-casting from its aqueous (0.2%, 1 nM SRB) solution, followed by drying in air and thermal annealing at 90 °C for 36 h. The diffusion of individual SRB occurring within the amorphous domains was recorded at different relative humidities (5-95%) to characterize the microscale domains' local aspect-ratio, orientation, and molecular permeability at high spatial resolution. The results revealed the involvement of crystalline phases in confining SRB diffusion to submicron distances and guiding longer-range diffusion along one-dimensional-like amorphous morphologies. Upon annealing, amorphous domains were wider, more continuous, and more permeable to SRB probes. The enhanced transport in plasticized PEO, as reflected by the higher SRB mobility and diffusivity, was linked to the polymer's higher chain and segmental mobilities and reduced hydrogen-bonding interactions. This work has demonstrated the usefulness of SMT for an advanced characterization of solid polymer electrolytic films, highly beneficial for the development of safer lithium-ion batteries.