8 research outputs found
Bis-Silicon-Bridged Stilbene: A Core for Small-Molecule Electron Acceptor for High-Performance Organic Solar Cells
Bis-Silicon-Bridged Stilbene: A Core for Small-Molecule
Electron Acceptor for High-Performance Organic Solar Cell
Nature of Ferroelectric Behavior in Main-Chain Dipolar Glass Nylons: Cooperative Segmental Motion Induced by High Poling Electric Field
Main-chain
dipolar glass polymers such as aromatic nylons are promising
for high energy density and low loss dielectric applications because
of the limited, noncooperative oscillation of highly dipolar amide
groups. However, quenched aromatic nylons have been reported to exhibit
significant ferroelectric switching upon high field poling. It is
desirable to suppress ferroelectric switching for electric energy
storage application, and this requires a fundamental understanding
of the nature of ferroelectric behavior in dipolar glass nylons. In
this work, a nearly 100% amorphous aromatic nylon, Selar, was used
to investigate the origin of ferroelectricity in glassy nylons. Using
Fourier transform infrared spectroscopy, it was found that hydrogen-bonding
strength played an important role in the ferroelectric switching of
amide dipoles in the loosely packed glassy matrix. When hydrogen bonding
was weak such as in the quenched film, significant ferroelectric switching
took place. In contrast, quenched and annealed films did not exhibit
any ferroelectric switching. High-voltage broadband dielectric spectroscopy
was used to study molecular and segmental motions in Selar. It was
observed that the primary contribution to ferroelectric switching
came from cooperative segmental motions (i.e., a combination of various
sub-<i>T</i><sub>g</sub> relaxations, where <i>T</i><sub>g</sub> is the glass transition temperature) in the main-chain
dipolar glass nylon. This understanding will help us design new aromatic
nylons with suppressed segmental motions for high energy density and
low loss dielectric applications
Achieving Relaxor Ferroelectric-like Behavior in Nylon Random Copolymers and Terpolymers
High dielectric constant
polymers, exhibiting relaxor ferroelectric
(RFE) behaviors (i.e., slim single and double hysteresis loops, SHLs
and DHLs), are attractive for high energy density and low loss dielectric
applications. Utilizing the principle of nanosized ferroelectric domains
(nanodomains), this study has designed and developed novel RFE-like
polyamides (PAs) based on 11-aminoundecanoic acid, 12-aminododecanoic
acid, and <i>N</i>-methyl-11-aminoundecanoic acid (NM11)
as an alternative to the high-cost and difficult-to-synthesize polyÂ(vinylidene
fluoride) (PVDF)-based RFE polymers. In the first attempt, quenched
and stretched (QS) PAÂ(11-<i>co</i>-12) copolymers exhibited
enhanced ferroelectricity as compared with either nylon-11 or nylon-12.
Although relatively narrow hysteresis loops could be achieved at 75
°C, the hydrogen-bonding interaction was not weak enough to induce
nanodomains in the nylon copolymers. To further reduce the hydrogen-bonding
interaction and achieve nanodomains, a PAÂ(11-<i>co</i>-12-<i>co</i>-NM11) 30/60/10 (molar ratio) terpolymer (terPA-NCH<sub>3</sub>) was synthesized. The NCH<sub>3</sub> groups were expected
to participate in the isomorphic crystals, blocking the formation
of hydrogen bonds and inducing chain twists in the mesophase. Indeed,
the RFE-like behavior with slim SHLs and high dielectric constant
(60–70) was successfully achieved for the QS terPA-NCH<sub>3</sub> at high temperatures (>75 °C). Pathways to achieve
RFE-like
behavior for nylon-based polymers are discussed and compared with
those for PVDF-based polymers. The knowledge obtained from this study
can inspire potential applications for nylon polymers in advanced
electrical and power applications
Understanding the Paraelectric Double Hysteresis Loop Behavior in Mesomorphic Even-Numbered Nylons at High Temperatures
Novel
ferroelectric properties, such as slim double and single
hysteresis loop (DHL and SHL) behaviors, are attractive for high energy
density and low loss dielectric applications. In this study, temperature-dependent
ferroelectric behavior was studied for mesomorphic even-numbered nylons
(i.e., nylon-12 and nylon-6) using electric displacement–electric
field (<i>D</i>–<i>E</i>) loop measurements.
Upon raising the temperature from room temperature to 100 °C,
the <i>D</i>–<i>E</i> loops became increasingly
narrower, finally leading to slim DHLs with significantly enhanced
apparent dielectric constants (i.e., ∼30 and ∼60) and
small remanent polarizations (i.e., 3.5 and 8.2 mC/m<sup>2</sup>)
for quenched and stretched nylon-12 and nylon-6, respectively. Combining
wide-angle X-ray diffraction and infrared studies, changes in the
mesophases and orientation of hydrogen-bonded amide groups after electric
poling were used to unravel the structure–ferroelectric property
relationship for the even-numbered nylons. At 100 °C, the quenched
and stretched nylon-12 and nylon-6 films exhibited a paraelectric
mesophase with twisted chain conformation and disordered hydrogen
bonds. Upon high field poling (>100 MV/m), transient nanodomains
could
be generated with additional twists in the main chain. The observed
DHL behavior was attributed to the electric-field-induced reversible
transitions between the paraelectric (less twisted chains) and ferroelectric
(more twisted chains) states in the mesomorphic crystals of even-numbered
nylons. The knowledge gained from this study can inspire potential
applications of <i>n</i>-nylons for electric energy storage,
e.g., high temperature and high energy density multilayer polymer
film capacitors
High Dielectric Constant Sulfonyl-Containing Dipolar Glass Polymers with Enhanced Orientational Polarization
Dipolar glass (DG)
polymers, which utilize sub-<i>T</i><sub>g</sub> orientational
polarization (<i>T</i><sub>g</sub> is the glass transition
temperature) to enhance dielectric constants,
are promising candidates for use in advanced electronic and power
applications because conduction of space charges (electrons and impurity
ions) is suppressed in the glassy state, and thus, the dielectric
loss is low. In this study, we studied the effects of dipole density
and dipole arrangement in sulfonyl-containing side-chain DG polymers
on their dielectric performance in terms of dielectric constant, energy
density, and dielectric loss. Monosulfonyl (i.e., CH<sub>3</sub>SO<sub>2</sub>-) and disulfonyl [i.e., CH<sub>3</sub>SO<sub>2</sub>(CH<sub>2</sub>)<sub>3</sub>SO<sub>2</sub>-] groups were quantitatively grafted
to polyepichlorohydrin (monosubstitution) and polyÂ(3,3-bisÂ(chloromethyl)Âoxatane)
(bis-substitution), respectively, in order to vary the dipole density
and dipole arrangement in the side chains. As a result of orientation
polarization from highly polar sulfonyl (4.5 D) groups, these DG polymers
exhibited high apparent dielectric constants (7–11.5) in the
glassy state with reasonably low dissipation factors (tan δ
∼ 0.003–0.02). It was found that disulfonylated DG polymers
exhibited a higher dielectric constant than monosulfonylated DG polymers
because of their higher dipole densities. Meanwhile, bis-substituted
DG polymers showed a higher dielectric constant than monosubstituted
DG polymers. Upon high-field electric poling, reversible transitions
between the low-field DG state and the high-field ferroelectric state
induced double hysteresis loops, and disulfonylated DG polymers had
more significant ferroelectric switching than monosulfonylated DG
polymers due to stronger dipolar interactions among the disulfonyl
groups. On the basis of the experimental results, monosulfonylated
DG polymers, whether mono- or bis-substituted, should be more appropriate
for electric energy storage applications
1,3-Bis(thieno[3,4‑<i>b</i>]thiophen-6-yl)‑4<i>H</i>‑thieno[3,4‑<i>c</i>]pyrrole-4,6(5<i>H</i>)‑dione-Based Small-Molecule Donor for Efficient Solution-Processed Solar Cells
A small molecule <b>TBTT-1</b> with 5-(2-ethylhexyl)-1,3-bisÂ(2-(2-ethylÂhexyl)ÂthienoÂ[3,4-<i>b</i>]Âthiophen-6-yl)-4<i>H</i>-thienoÂ[3,4-<i>c</i>]Âpyrrole-4,6Â(5<i>H</i>)-dione (<b>TBTT</b>) as the central moiety was designed and synthesized for solution-processed
bulk-heterojunction solar cells. <b>TBTT-1</b> exhibits a broad
absorption with a low optical band gap of approximately 1.53 eV in
the thin film. An optimized power conversion efficiency (PCE) of 7.47%
with a high short-circuit current of 14.95 mA cm<sup>–2</sup> was achieved with diphenyl ether (DPE) as additive, which is the
highest PCE for TPD-based small-molecule solar cells. According to
the detailed morphology investigations, we found that DPE processing
helped to enhance π–π stacking and reduce the scales
of phase separation, which led to improved exciton splitting and charge
transport in BHJ thin film, and thus enhanced device performance
Achieving High Dielectric Constant and Low Loss Property in a Dipolar Glass Polymer Containing Strongly Dipolar and Small-Sized Sulfone Groups
In this report, a dipolar glass polymer,
polyÂ(2-(methylÂsulfonyl)Âethyl methacrylate) (PMSEMA), was
synthesized by free radical polymerization of the corresponding methacrylate
monomer. Due to the large dipole moment (4.25 D) and small size of
the side-chain sulfone groups, PMSEMA exhibited a strong γ transition
at a temperature as low as −110 °C at 1 Hz, about 220
°C below its glass transition temperature around 109 °C.
Because of this strong γ dipole relaxation, the glassy PMSEMA
sample exhibited a high dielectric constant of 11.4 and a low dissipation
factor (tan δ) of 0.02 at 25 °C and 1 Hz. From an electric
displacement-electric field (D-E) loop study, PMSEMA demonstrated
a high discharge energy density of 4.54 J/cm<sup>3</sup> at 283 MV/m,
nearly 3 times that of an analogue polymer, polyÂ(methyl methacrylate)
(PMMA). However, the hysteresis loss was only 1/3–1/2 of that
for PMMA. This study suggests that dipolar glass polymers with large
dipole moments and small-sized dipolar side groups are promising candidates
for high energy density and low loss dielectric applications
Diaceno[<i>a</i>,<i>e</i>]pentalenes from Homoannulations of <i>o</i>‑Alkynylaryliodides Utilizing a Unique Pd(OAc)<sub>2</sub>/<i>n</i>‑Bu<sub>4</sub>NOAc Catalytic Combination
A heterogeneous
catalytic system, PdÂ(OAc)<sub>2</sub>/<i>n</i>-Bu<sub>4</sub>NOAc, for the efficient synthesis of diacenoÂ[<i>a</i>,<i>e</i>]Âpentalenes via a tandem Pd catalytic
cycle is reported. The catalytic partner <i>n</i>-Bu<sub>4</sub>NOAc played indispensable and versatile roles, acting as both
the media for recovering active Pd(0) species and their stabilizer.
A series of new diacenoÂ[<i>a</i>,<i>e</i>]Âpentalenes
were obtained in moderate to high yields, among which the octacyclic
dianthracenopentalene was found to be highly emissive