4 research outputs found
Tetra-Sensitive Graft Copolymer Gels as Active Material of Chemomechanical Valves
Stimuli-responsive
hydrogels combine sensor and actuator properties by converting an
environmental stimulus into mechanical work. Those materials are highly
interesting for applications as a chemomechanical valve in microsystem
technologies. However, studies about key characteristics of hydrogels
for this application are comparatively rare, and further research
is needed to emphasize their real potential. The first part of this
study depicts the synthesis of grafted hydrogels based on a poly(<i>N</i>-isopropylacrylamide) backbone and pH-sensitive poly(acrylic
acid) graft chains. The chosen approach of grafted hydrogels provides
the preparation of multiresponsive hydrogels, which retain temperature
sensitivity besides being pH-responsive. A pronounced salt and solvent
response is additionally achieved. Key characteristics for an application
as a chemomechanical valve of the graft hydrogels are revealed: (1)
independently addressable response to all stimuli, (2) significant
volume change, (3) sharp transition, (4) reversible swelling–shrinking
behavior, and (5) accelerated response time. To prove the concept
of multiresponsive hydrogels for flow control, a <i>net</i>-poly(<i>N</i>-acrylamide)-<i>g</i>-poly(acrylic
acid) hydrogel containing 0.6 mol % poly(acrylic acid)-vinyl is employed
as active material for chemomechanical valves. Remarkably, the chemomechanical
valve can be opened and closed in a fluidic platform with four different
stimuli
Fullerene-Functionalized Donor–Acceptor Block Copolymers through Etherification as Stabilizers for Bulk Heterojunction Solar Cells
A new synthetic method for the covalent linking of fullerenes
to
polymers is introduced. The Bingel-reaction was used to prepare bromine-functionalized
fullerene building blocks that could be covalently linked to hydroxyl
groups of model copolymers by the cesium carbonate promoted Williamson
ether synthesis. Subsequently, block copolymers with a second block
based on styrene and hydroxystyrene or hydroxyethyl methacrylate could
be synthesized with a poly(3-hexylthiophene)–TEMPO macroinitiator
through NMRP. Fullerene derivatives were linked to these polymers
in a controlled manner and donor–acceptor block copolymers
with high fullerene contents of near 50 wt % were achieved
Synthesis of High-Crystallinity DPP Polymers with Balanced Electron and Hole Mobility
We review the Stille coupling synthesis
of P(DPP2OD-T) (Poly[[2,5-di(2-octyldodecyl)pyrrolo[3,4-<i>c</i>]pyrrole-1,4(2<i>H</i>,5<i>H</i>)-dione-3,6-diyl]-<i>alt</i>-[2,2′:5′,2″-terthiophene-5,5″-diyl]])
and show that high-quality, high molecular weight polymer chains are
already obtained after as little as 15 min of reaction time. The results
of UV–vis spectroscopy, grazing incidence wide-angle X-ray
scattering (GIWAXS), and atomic force microscopy show that longer
reaction times are unnecessary and do not produce any improvement
in film quality. We achieve the best charge transport properties with
polymer batches obtained from short reaction times and demonstrate
that the catalyst washing step is responsible for the introduction
of charge-trapping sites for both holes and electrons. These trap
sites decrease the charge injection efficiency, strongly reducing
the measured currents. The careful tuning of the synthesis allows
us to reduce the reaction time by more than 100 times, achieving a
more environmentally friendly, less costly process that leads to high
and balanced hole and electron transport, the latter being the best
reported for an isotropic, spin-coated DPP polymer
Molecular Doping of a High Mobility Diketopyrrolopyrrole–Dithienylthieno[3,2‑<i>b</i>]thiophene Donor–Acceptor Copolymer with F6TCNNQ
Herein we present a molecular doping
of a high mobility diketopyrrolopyrrole–dithienylthieno[3,2-<i>b</i>]thiophene donor–acceptor copolymer poly[3,6-(dithiophene-2-yl)-2,5-di(6-dodecyloctadecyl)pyrrolo[3,4-<i>c</i>]pyrrole-1,4-dione-<i>alt</i>-thieno[3,2-<i>b</i>]thiophene], PDPP(6-DO)<sub>2</sub>TT, with the electron-deficient
compound hexafluorotetracyanonaphthoquinodimethane
(F6TCNNQ). Despite a slightly negative HOMO<sub>donor</sub>–LUMO<sub>acceptor</sub> offset of −0.12 eV which may suggest a reduced
driving force for the charge transfer (CT), a partial charge CT was
experimentally observed in PDPP(6-DO)<sub>2</sub>TT:F6TCNNQ by absorption,
vibrational, and electron paramagnetic resonance spectroscopies and
predicted by density functional theory calculations. Despite the modest
CT, PDPP(6-DO)<sub>2</sub>TT:F6TCNNQ films possess unexpectedly high
conductivities up to 2 S/cm (comparable with the conductivities of
the benchmark doped polymer system P3HT:F4TCNQ having a large positive
offset). The observation of the high conductivity in doped PDPP(6-DO)<sub>2</sub>TT films can be explained by a high hole mobility in PDPP(6-DO)<sub>2</sub>TT blends which compensates a lowered (relatively to P3HT:F4TCNQ)
concentration of free charge carriers. We also show that F6TCNNQ-doped
P3HT, the system which has not been reported so far to the best of
our knowledge, exhibits a conductivity up to 7 S/cm, which exceeds
the conductivity of the benchmark P3HT:F4TCNQ system