This study demonstrates how simple structural modification of a prototypical organic ferroelectric molecule can be used to tune its key ferroelectric properties. In particular, it is found that shortening the alkyl chain length of trialkylbenzene-1,3,5-tricarboxamide (BTA) from C18H37 to C6H13 causes an increase in depolarization activation energy (approximate to 1.1-1.55 eV), coercive field (approximate to 25-40 V mu m(-1)), and remnant polarization (approximate to 20-70 mC m(-2)). As the polarization enhancement far exceeds the geometrically expected factor, these observations are attributed to an increase in the intercolumnar interaction. The combination of the mentioned characteristics results in a record polarization retention time of close to three months at room temperature for capacitor devices of the material having the shortest alkyl chain. The long retention and the remnant polarization that is as high as that of P(VDF:TrFE) distinguish the BTA-C6 material from other small molecular organic ferroelectrics and make it a perspective choice for applications that require cheap, flexible, and lightweight ferroelectrics.
Funding Agencies|NWO Nano program; Vetenskapsradet; Swedish Government Strategic Research Area in Materials Science on Functional Materials at the Linkping University (Faculty Grant SFO Mat LiU) [2009 00971]
A triazine based disc shaped molecule
with two hydrolyzable units,
imine and ester groups, was polymerized via acyclic diene metathesis
in the columnar hexagonal (Colhex) LC phase. Fabrication
of a cationic nanoporous polymer (pore diameter ∼1.3 nm) lined
with ammonium groups at the pore surface was achieved by hydrolysis
of the imine linkage. Size selective aldehyde uptake by the cationic
porous polymer was demonstrated. The anilinium groups in the pores
were converted to azide as well as phenyl groups by further chemical
treatment, leading to porous polymers with neutral functional groups
in the pores. The pores were enlarged by further hydrolysis of the
ester groups to create ∼2.6 nm pores lined with −COONa
surface groups. The same pores could be obtained in a single step
without first hydrolyzing the imine linkage. XRD studies demonstrated
that the Colhex order of the monomer was preserved after
polymerization as well as in both the nanoporous polymers. The porous
anionic polymer lined with −COOH groups was further converted
to the −COOLi, −COONa, −COOK, −COOCs,
and −COONH4 salts. The porous polymer lined with
−COONa groups selectively adsorbs a cationic dye, methylene
blue, over an anionic dye.
The remarkable ability of a charge-transfer (CT) complex prepared from a pyrene-based donor (Py-D) and a naphthalenediimide-based acceptor (NDI-A) led to the formation of a deep-violet in color, transparent hydrogel at room temperature (RT-gel). Simultaneously, the RT-gel was diluted beyond its critical gelator concentration (CGC) to obtain a transparent sol. Very interestingly, the resultant sol, on heating above 70 °C, transformed into a heat-set gel instantaneously with a hitherto unknown CGC value. Detailed studies revealed the smaller globular aggregates of the RT-gels fuse to form giant globules upon heating, which, in turn, resulted in heat-set gelation through further aggregation. The thermoresponsive property of Py-D alone and 1 : 1 Py-D : NDI-A CT complex was investigated in detail which revealed the hydrophobic collapse of the oxyethylene chains of the CT complex upon heating was mainly responsible for heat-set gelation. Thixotropy, injectability, as well as stimuli responsiveness of the RT-gels were also addressed. In contrast, heat-set gel did not show thixotropic behavior. The X-ray diffraction (XRD) patterns of the xerogel depicted lamellar packing of the CT stacks in the gel phase. Single crystal XRD studies further evidenced the 1 : 1 mixed CT stack formation in the lamellae and also ruled out orthogonal hydrogen bonding possibilities among the hydrazide unit in the CT gel although such interaction was observed in a single crystal of NDI-A alone. In addition, a Ag(+)-ion triggered metallogelation of NDI-A and nematic liquid-crystalline property of Py-D were also observed.
A Cu(2+)-selective metallo(hydro)gelation of a p-pyridyl ended oligo-phenylenevinylene system is reported over its respective meta- and ortho-regioisomers. The metallogel formed via the self-assembly of the nanoscale-metal-organic particles is injectable and also shows multi-stimuli responsiveness, including thixotropy.
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