6 research outputs found
Triggered Structural Control of Dynamic Covalent Aromatic Polyamides: Effects of Thermal Reorganization Behavior in Solution and Solid States
Thermally
rearrangeable aromatic polyamides (TEMPO-PA) and random
copolyamides (TEMPO-PA-COOH) incorporating alkoxyamine moieties in
the main chain were synthesized, and the effects of thermal reorganization
behavior on their solution and solid-state structures were investigated.
The hydrodynamic radius in solution decreased as the solution temperature
increased because of the dissociation of the alkoxyamine unit. Additionally,
the dry density of the thin films decreased as the fabrication temperature
increased because of the suppression of polymer aggregation caused
by the thermally induced radical crossover reaction. In addition,
at the film surface of the random copolyamide containing hydrophobic
TEMPO and hydrophilic 3,5-diaminobenzoic acid (DABA) units, the hydrophilicity
decreased as the fabrication temperature increased. This is because
hydrophobic TEMPO and hydrophilic DABA units tend to be discretely
aggregated near the film surface to minimize the surface energy and
suppress the hydrogen bonding via a radical crossover reaction during
the thin-film fabrication process. The present study clearly shows
that both the solution structure and the solid-state molecular aggregation
structure of the dynamic covalent polymers can be easily controlled
by a thermal trigger, and it provides a new method for controlling
the higher-order structure of polymer solutions and solids
ESA-CF Synthesis of Linear and Cyclic Polymers Having Densely Appended Perylene Units and Topology Effects on Their Thin-Film Electron Mobility
A pair of topologically
contrastive, linear and cyclic polymers
having densely appended perylene diimide (PDI) units have been prepared
by means of an electrostatic self-assembly and covalent fixation (ESA-CF)
process, using an assembly composed of either linear or cyclic polyacrylate
anions of different segment lengths (DP<sub>n</sub> = 50, 93, and
128) accompanying countercations of a perylene diimide (PDI) derivative
having a cyclic ammonium salt group (<b>II</b><sub><b>L</b></sub><b>/III</b> and <b>II</b><sub><b>C</b></sub><b>/III</b>, respectively). The subsequent heating treatment
at 180 °C produced the covalently converted product, i.e., the
linear <b>IV</b><sub><b>L</b></sub> and the cyclic <b>IV</b><sub><b>C</b></sub>, respectively, in which the PDI
unit was introduced nearly quantitatively to the backbone acrylate
units. The obtained linear and cyclic polymers having pendant PDI
units were observed to form commonly spherical self-assemblies both
in bulk and in solution states, while the solution viscosity was noticeably
higher with the linear products than with the cyclic counterparts.
The electron-only device (EOD) measurement by using thin-film samples
of a series of cyclized products, <b>IV</b><sub><b>C</b></sub>, revealed consistently higher electron carrier mobilities
in comparison with the corresponding linear counterparts, <b>IV</b><sub><b>L</b></sub>
Enhancing the Effect of the Nanofiber Network Structure on Thermoresponsive Wettability Switching
This letter reports the enhancing effects of a nanofiber network structure on stimuli-responsive wettability switching. Thermoresponsive coatings composed of nanofibers were prepared by electrospinning from thermoresponsive polymer poly(<i>N</i>-isopropylacrylamide) (PNIPAAm). The nanofiber coatings showed a large amplitude of thermoresponsive change in the wettability from hydrophilic to hydrophobic states compared to a smooth cast film. In particular, the combination of the surface chemistry and unique topology of the electrospun nanofiber coatings enables a transition from the Wenzel state to the metastable Cassie–Baxter state with an increase in temperature and consequently an enhanced amplitude of change in the water contact angles: the apparent contact angle differences between 25 and 50 °C are Δθ*<sub>25–50 °C </sub>= 108 and 10° for the nanofiber coatings with a diameter of 830 nm and a smooth cast film, respectively. The fabrication of the 3D nanofiber network structure by electrospinning from stimuli-responsive materials is a promising option for highly responsive surfaces in wettability
New Semiconducting Polymers Based on Benzobisthiadiazole Analogues: Tuning of Charge Polarity in Thin Film Transistors via Heteroatom Substitution
As one of the most effective molecular
design strategies in organic
electronics, heteroatom substitution was employed for the first time
to study the acceptor variation effects on the optical, electrochemical,
molecular assembling, and charge-transport properties of novel semiconducting
polymers containing benzobisthiadiazole (BBT)-related heterocycles,
namely, polyÂ(dithiazolfluorene-<i>alt</i>-thiadiazoloÂbenzotriazole)
(PSN), polyÂ(dithiazolfluorene-<i>alt</i>-selenadiazoloÂbenzotriazole)
(PSeN), and polyÂ(dithiazolÂfluorene-<i>alt</i>-selenadiazoloÂbenzothiadiazole)
(PSeS). The effect of the heteroatom substitution was clearly shown
in the UV–vis–NIR absorption spectra in which the substitution
of the sulfur (S) and/or nitrogen (N) atoms in PSN with the selenium
(Se) and sulfur (S) atoms led to a red-shift in the absorption profile.
In addition, the energy levels of these polymers, determined from
cyclic voltammetry (CV) measurements and density functional theory
(DFT) calculations, also varied due to the hetroatom substitution
effect. Accordingly, thin film transistors (TFTs) based on these polymers
showed different charge transport properties. For example, PSN displayed
p<i>-</i>type unipolar performances with a high hole mobility
up to 0.65 cm<sup>2</sup> V<sup>–1</sup> s<sup>–1</sup>. In contrast, PSeS showed n-type dominant charge transport properties
with an electron mobility up to 0.087 cm<sup>2</sup> V<sup>–1</sup> s<sup>–1</sup>. Intriguingly, PSeN exhibited ambipolar charge
transport properties with balanced ÎĽ<sub>h</sub> and ÎĽ<sub>e</sub> values. These different charge polarities in the TFTs were
correlated to the energy levels, π–π stacking distances,
and polymer crystallinities evaluated by their grazing-incidence wide-angle
X-ray scattering (GIWAXS) patterns and atomic force microscopy (AFM)
images. We believe that this simple and effective approach will guide
the way to developing high-performance ambipolar and/or n-channel
semiconducting polymers for TFTs
Ionic Liquid-Based Electrolytes Containing Surface-Functionalized Inorganic Nanofibers for Quasisolid Lithium Batteries
In the present study,
surface amino-functionalized silica nanofibers
(<i>f</i>-SiO<sub>2</sub>NFs, average diameter = 400 and
1000 nm) are used as one-dimensional (1-D) fillers of ionic liquid
(IL)-based quasisolid electrolytes. On adding <i>f</i>-SiO<sub>2</sub>NFs to an IL
(1-ethyl-3-methylimidazolium bisÂ(trifluoromethanesulfonyl)Âamide, EMITFSA)
containing lithium bisÂ(trifluoromethanesulfonyl)-amide (LiTFSA), the
well-dispersed 1-D nanofillers easily form a three-dimensional network
structure in the IL, function as physical cross-linkers, and increase
the viscosity of the composites, consequently providing a quasisolid
state at a 3.5 wt % fraction of the NFs. Rheological measurements
demonstrate that the prepared composites exhibit “gel-like”
characteristics at 40–150 °C. All prepared composites
show high ionic conductivities, on the order of 10<sup>–3</sup> S cm<sup>–1</sup>, around room temperature. To investigate
the additive effect of <i>f</i>-SiO<sub>2</sub>NFs in the
composites, the lithium transference numbers are also evaluated. It
is found that thinner NFs enhance the transference numbers of the
composites. In addition, quasisolid lithium-ion cells containing the
prepared composites demonstrate relatively high rate characteristics
and good cycling performance at high temperature (125 °C)
Electrospun Composite Nanofiber Yarns Containing Oriented Graphene Nanoribbons
The graphene nanoribbon (GNR)/carbon
composite nanofiber yarns were prepared by electrospinning from polyÂ(acrylonitrile)
(PAN) containing graphene oxide nanoribbons (GONRs), and successive
twisting and carbonization. The electrospinning process can exert
directional shear force coupling with the external electric field
to the flow of the spinning solution. During electrospinning, the
well-dispersed GONRs were highly oriented along the fiber axis in
an electrified thin liquid jet. The addition of GONRs at a low weight
fraction significantly improved the mechanical properties of the composite
nanofiber yarns. In addition, the carbonization of the matrix polymer
enhanced not only the mechanical but also the electrical properties
of the composites. The electrical conductivity of the carbonized composite
yarns containing 0.5 wt % GONR showed the maximum value of 165 S cm<sup>–1</sup>. It is larger than the maximum value of the reported
electrospun carbon composite yarns. Interestingly, it is higher than
the conductivities of both the PAN-based pristine CNF yarns (77 S
cm<sup>–1</sup>) and the monolayer GNRs (54 S cm<sup>–1</sup>). These results and Raman spectroscopy supported the hypothesis
that the oriented GONRs contained in the PAN nanofibers effectively
functioned as not only the 1-D nanofiller but also the nanoplatelet
promoter of stabilization and template agent for the carbonization