2 research outputs found
Understanding Interfacial Alignment in Solution Coated Conjugated Polymer Thin Films
Domain
alignment in conjugated polymer thin films can significantly enhance
charge carrier mobility. However, the alignment mechanism during meniscus-guided
solution coating remains unclear. Furthermore, interfacial alignment
has been rarely studied despite its direct relevance and critical
importance to charge transport. In this study, we uncover a significantly
higher degree of alignment at the top interface of solution coated
thin films, using a donor–acceptor conjugated polymer, polyÂ(diketopyrrolopyrrole-<i>co</i>-thiophene-<i>co</i>-thienoÂ[3,2-<i>b</i>]Âthiophene-<i>co</i>-thiophene) (DPP2T-TT), as the model
system. At the molecular level, we observe in-plane π–π
stacking anisotropy of up to 4.8 near the top interface with the polymer
backbone aligned parallel to the coating direction. The bulk of the
film is only weakly aligned with the backbone oriented transverse
to coating. At the mesoscale, we observe a well-defined fibril-like
morphology at the top interface with the fibril long axis pointing
toward the coating direction. Significantly smaller fibrils with poor
orientational order are found on the bottom interface, weakly aligned
orthogonal to the fibrils on the top interface. The high degree of
alignment at the top interface leads to a charge transport anisotropy
of up to 5.4 compared to an anisotropy close to 1 on the bottom interface.
We attribute the formation of distinct interfacial morphology to the
skin-layer formation associated with high Peclet number, which promotes
crystallization on the top interface while suppressing it in the bulk.
We further infer that the interfacial fibril alignment is driven by
the extensional flow on the top interface arisen from increasing solvent
evaporation rate closer to the meniscus front
Direct Evidence of Conformational Changes Associated with Voltage Gating in a Voltage Sensor Protein by Time-Resolved X‑ray/Neutron Interferometry
The
voltage sensor domain (VSD) of voltage-gated cation (e.g.,
Na<sup>+</sup>, K<sup>+</sup>) channels central to neurological signal
transmission can function as a distinct module. When linked to an
otherwise voltage-insensitive, ion-selective membrane pore, the VSD
imparts voltage sensitivity to the channel. Proteins homologous with
the VSD have recently been found to function themselves as voltage-gated
proton channels or to impart voltage sensitivity to enzymes. Determining
the conformational changes associated with voltage gating in the VSD
itself in the absence of a pore domain thereby gains importance. We
report the direct measurement of changes in the scattering-length
density (SLD) profile of the VSD protein, vectorially oriented within
a reconstituted phospholipid bilayer membrane, as a function of the
transmembrane electric potential by time-resolved X-ray and neutron
interferometry. The changes in the experimental SLD profiles for both
polarizing and depolarizing potentials with respect to zero potential
were found to extend over the entire length of the isolated VSD’s
profile structure. The characteristics of the changes observed were
in qualitative agreement with molecular dynamics simulations of a
related membrane system, suggesting an initial interpretation of these
changes in terms of the VSD’s atomic-level 3-D structure