Browsing by Author "Lan, Shih-Ting"

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Conformational Preferences and the Phase Stability of Fullerene Hexa-adducts
(2016-07-20)
Wu, San-Lien
;
Hong, Chen-Yang
;
Wu, Kuan-Yi
;
Lan, Shih-Ting
;
Hsieh, Chou-Ting
Molecular conformation and the assembly structure determine the spatial arrangements of the constituent units and the functions of a molecule. Although, fullerene hexa-adducts (FHAs) have been known as functional materials with great versatility, their conformational preferences and phase stability remain a complicate issue. By choosing bithiophene (T-2) and dodecyl bithiophene (C12T2) as the peripheral units of FHA, and using microscopic, scattering and diffraction characterizations, our study reveals how the intramolecular interaction and environmental stimulus affects the conformational preferences and phase stability of FHAs.
Estimating Percent Crystallinity of Polyethylene as a Function of Temperature by Raman Spectroscopy Multivariate Curve Resolution by Alternating Least Squares
(2017-03-07)
Samuel, Ashok Zachariah
;
Lai, Bo-Han
;
Lan, Shih-Ting
;
Ando, Masahiro
;
Wang, Chien-Lung
We have recently demonstrated a methodology to estimate the percent crystallinity (PC) of polymers directly with Raman spectroscopy and multivariate curve resolution (MCR) by alternating least-squares (ALS). In the MCR-ALS methodology, the Raman spectrum of a semicrystalline polymer is separated into two constituent components (crystalline and molten/amorphous) and their corresponding concentrations. The methodology necessitates that the Raman spectrum at any temperature be a linear combination of two MCR spectral components (one molten and one crystalline). This is true in the case of simple systems such as crystalline pendant alkyl domains in polymers (Samuel et al. Anal. Chem. 2016, 88, 4644). However, in the case of main chain polymer crystals (e.g., polyethylene), the situation can be complicated owing to several molecular changes in the lattice in addition to conformational reorganizations during melting. Under this circumstance, a simple two-state model may not be adequate and we describe the modifications required to treat such systems, keeping the basic principles of the proposed methodology unchanged. A comparative study with wide-angle X-ray scattering (WAXS) and Raman spectroscopy is also performed to substantiate our findings. In addition to estimating percent crystallinity (PC), our methodology is capable of revealing additional information, such as interchain interactions in crystal lattice, that in principle will help distinguishing polymorphic transformations, subtle changes in lamellar lattice dimensions, and other phase changes in polymers.
Influences of Out-Of-Plane Lattice Alignment on the OFET Performance of TIPS-PEN Crystal Arrays
(2016-11)
Wu, Kuan-Yi
;
Hsieh, Chou-Ting
;
Wang, Liang-Hsun
;
Hsu, Chih-Hao
;
Chang, Shu-Ting
In organic field-effect transistors (OFETs), the quality of charge transport pathway, controlled by crystal structures of organic semiconductors (OSCs), strongly affects the performance of the device. To achieve higher charge mobility, solution-processed single-crystal (SPSC) techniques have been used to decrease crystal defects by aligning the crystals of OSCs in the in-plane direction. Nonetheless, through SPSC techniques, whether the crystalline lattices are well aligned in the out-of-plane direction and how the out-of-plane lattice misorientaion affects OFET performances remain unclear. Here, a characterization protocol based on polarized optical microscope, X-ray diffraction, and electron diffraction is established to identify the lattice structure, the in-plane and out-of-plane lattice alignment in the crystal array of 6,13-bis(triisopropylsilylethynyl)pentacene (TIPS-PEN). Regardless of the solvents used in the PDMS-assisted crystallization, the characterization protocol confirms that all the crystal arrays share the same lattice structure (form I phase), and have similar in-plane lattice alignment. However, TIPS-PEN molecules have sufficient time to unify their out-of-plane orientation and prevent the formation of low angle grain boundary (LAGB) during crystal growth if high boiling temperature solvents are used. The improved out-of-plane lattice alignment increases the hole mobility and decreases the performance fluctuations of devices. The results confirm that the out-of-plane lattice alignment significantly impacts the performance of the devices and the reproducibility of the solution-processed TIPS-PEN OFETs.