Synthesis, Morphology and Electrical Device Applications of Oligosaccharide-based Block Copolymers with Pendent Conjugated Moieties

Autor: Han-Sheng Sun, 孫翰笙
Rok vydání: 2016
Druh dokumentu: 學位論文 ; thesis
Popis: 105
Renewable polymers have attracted extensive research interest in the past decade, because they are environmentally sustainable, biodegradable and inexhaustible sources with the production of 1013 tons annually, which have been regarded as a promising candidate for substituting the petroleum-based materials. In this thesis, we report the synthesis, morphology, and organic memory application of the oligosaccharide-based diblock copolymers with pendent -conjugated moieties and their supramolecules with modified electron-accepting small molecules for the nonvolatile transistor memory devices were investigated as well. The following summarize the important discovery of this thesis: 1. Synthesis of Oligosaccharide-Based Block Copolymers with Pendent π-Conjugated Oligofluorene Moieties and Their Electrical Device Applications (Chapter 2): Oligosaccharide-based diblock copolymers consisting of a maltoheptaose (MH) block and a poly(4-oligofluorenylstyrene) block (PStFln, n = 1 or 2), referred to as MH-b-PStFln was prepared by the Cu(I)-catalyzed click reaction of ethynyl-modified MH and azido-terminated PStFln. The resulting diblock copolymers self-assembled to spherical microdomains with sub-10 nm sizes in both bulk and thin film state after annealing process. Thereafter, the MH-b-PStFln thin film (~50 nm) with the self-assembled nanoscale spherical aggregates was used as the charge storage layer for the pentacene-based field-effect transistor type memory devices. The MH-b-PStFln-based devices had the excellent hole mobility (0.25-0.52 cm2 V-1 s-1) and the high ON/OFF current (ION/IOFF) ratio of 107-108, of which the MH-b-PStFl1-based one had the higher mobility than that of the MH-b-PStFl2-based one because the pentacene crystals in the former device possessed the larger grain size and fewer boundaries. On the other hand, the MH-b-PStFl2-based device showed a larger memory window than the MH-b-PStFl1-based one because the stronger donating effect of the difluorenyl group in MH-b-PStFl2 increased the charge storage capability of its related device. All the memory devices showed a long-term retention time over 104 s with the high ION/IOFF ratio of 106-108. Among these devices, the MH-b-PStFl1-based device showed a good WRER endurance over 180 cycles. 2. Synthesis, Morphology, and Electrical Memory Application of Oligosaccharide-Based Block Copolymers with π-Conjugated Pyrene Moiety and Their Supramolecules (Chapter 3): Maltoheptaose-block-poly(1-pyrenylmethyl methacrylate) (MH-b-PPyMA) was prepared by the combination of the t-Bu-P4-catalyzed group transfer polymerization and the Cu(I)-catalyzed azide-alkyne cycloaddition reaction, and then formed supramolecules with (4-pyridyl)-acceptor-(4-pyridyl), MH(4Py-Acceptor-4Py)x-b-PPyMA. After thermal annealing process, the MH-b-PPyMA bulk sample underwent microphase separation to form the sub-10 nm periodic self-assembled nanostructure. The self-assembled morphologies transform from the hexagonally cylindrical packing to the body-centered cubic spherical arrangement and disorderly spherical nanodomain by increasing the PPyMA segment length. On the contrary, only spherical nanodomain was observed in the thermo-annealed thin film samples of both MH-b-PPyMA and MH(4Py-Acceptor-4Py)x-b-PPyMA. The electrical characteristics of the p-type pentacene-based OFET memory device using the thermo-annealed polymer thin film as the electret layer was studied. The MH(4Py-Acceptor-4Py)x-b-PPyMA-based organic field effect transistor (OFET) devices had the high hole mobility of 0.20-1.08 cm2 V-1 s-1 and the ON/OFF current (ION/IOFF) ratio of 107-108, in which the acceptor of benzo[c][1,2,5]thiadiazole (BT) based device possessed the higher hole mobility than that of isoindigo-based one due to the more ordered packing pentacene crystals. The memory window (ΔVTH) of the supramolecule-based device was increased with enhancing the 4Py-Acceptor-4Py blending composition, and that of MH(4Py-BT-4Py)1.5-b-PPyMA10-based device had the largest ΔVTH of ca. 34 V, a long-term retention time greater than 104 s and the high ION/IOFF memory ratio of 106-107 (reading at Vg = 0 V) for more than 100 programming/erasing cycles. The above studies demonstrate that the size of self-assembled morphologies and memory characteristics can be manipulated by incorporation of hydrophilic natural polymer blocks and the potential of the natural materials for nonvolatile flash memory applications.
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