Ling-Yueh Yang's research while affiliated with National Taiwan University and other places

The morphology and microstructure of crystalline blends of poly (ethylene glycol) (PEG) and poly (L-lactic acid) (PLLA) were examined using polarized optical microscopy (POM) and scanning electron microscopy (SEM). As PEG was in the melt state during PLLA crystallization, it was rejected from the PLLA bundles. The size of PEG inclusions determined by their extraction is around 1 μm. The PEG/PLLA blends exhibited not only spherulites with Maltese crosses but also distinct extinction rings. The formation of ring-banded spherulites and the periodic distance between the rings were related to the degree of supercooling of the polymer. The ring-banded structure was easily obtained at a high PEG content (70 wt%) and high PLLA crystallization temperature (120 °C). The end group of PEG significantly affected the morphology of PEG/PLLA blends. PLLA blended with PEG containing both end groups as CH3 exhibited the greatest melting temperature depression and lowest degree of supercooling of PLLA, implying the formation of ring-banded spherulites with the smallest PEG content (30 wt%) and lowest PLLA crystallization temperature (85 °C). PEG morphology was also observed using POM after the formation of PLLA crystals. Because PLLA crystals confined the formation of PEG crystals, the chain growth direction of PEG was in association with that of PLLA. Therefore, a brighter POM image was obtained on PEG crystallization.

In this study, porous poly(L‐lactic acid) (PLLA) films are prepared via a facile and low‐cost approach using poly(ethylene glycol) (PEG) and solution casting. In contrast to most studies, the PEG/PLLA samples are further processed under different crystallization conditions (i.e., different PLLA crystallization temperatures) before PEG removal. As the PEG is extracted via solvent at higher PLLA crystallization temperatures, the resultant PLLA samples have larger pores. Interconnected fibrillar‐shaped pores are found in all systems, and the fibrillar‐porous structure width is ~150 nm–1.2 μm, as observed via scanning electron microscopy. These pore sizes can be tuned by adjusting the blend composition and crystallization temperature. In addition, PEG/PLLA blends are subjected to hydrolytic degradation analysis according to their crystallization conditions. Higher PLLA crystallization temperature yields higher PLLA crystallinity and larger pores, as well as reduced surface interaction with water. Therefore, the PLLA degradation rate is decreased. The developed PLLA films have potential applications in drug delivery and tissue engineering.

Inverse opals are three-dimensionally ordered macroporous materials with properties important for sensor applications, such as high specific surface area and pore interconnectivity. The present paper investigates optical responses of polyaniline inverse opals to ethanol, hydrogen chloride, and ammonia, especially changes in the optical stop band originating from the structural periodicity. Examination by scanning electron microscopy shows that the chemically synthesized inverse opals were of good quality, and the stop band in reflectance spectra provides additional evidence of long-range order. When in ethanol vapor, the inverse opals had noticeable shifts in the stop band because of the swelling-induced dimension changes, as confirmed by atomic force microscopy. Moreover, hydrogen chloride and ammonia, both capable of varying the degree of protonation of polyaniline, significantly altered the refractive index and thus the stop band position; shifts of more than 100nm were observed.

Much attention has been directed toward the fabrication of nanostructured polyaniline and its applications. In this study, we examined the potential of polyaniline inverse opals as sensors. The inverse opals were chemically synthesized via templating polystyrene colloidal crystals and then subjected to four response tests: dry gas flow, ethanol vapor, hydrogen chloride, and ammonia. The three-dimensionally ordered macroporous polyaniline was of good quality as observed by scanning electron microscopy. The samples demonstrated high sensitivity and fast response to different conditions, which may be due to the porosity facilitating diffusion and large surface area interacting with substances. Moreover, the effect of the structural order on the responses is discussed.

This paper describes a simple method for fabricating nanostructured polyaniline (PANI) films from polystyrene (PS)–PANI core–shell particles and the environmental responses of the films. Monodisperse PS latex particles synthesized via surfactant-free emulsion polymerization were used as cores, onto whose surface aniline monomers adsorbed with the aid of sodium dodecyl sulfate and were polymerized by adding ammonium peroxydisulfate. The resulting suspensions of core–shell particles were then drop-cast onto substrates and dried. Films composed of fragments of thin PANI shells of tens of nanometers were obtained after the removal of PS by tetrahydrofuran extraction. Another kind of films was prepared by heating the core–shell particles above the glass transition temperature of PS for a short time before the extraction. The morphology was observed using scanning electron microscopy, and the UV–vis spectra were recorded by a spectrometer. Furthermore, we examined the resistance responses of the films to dry gas flow, ethanol vapor, hydrogen chloride, and ammonia. The high sensitivity and fast response should be due to the large surface area interacting with analytes and porosity that facilitates diffusion. In addition, the effect of the packing of PANI shells in the films on the responses was discussed.

The effect of end groups (2NH2) of poly(ethylene glycol) (PEG) on the miscibility and crystallization behaviors of binary crystalline blends of PEG/poly(L-lactic acid) (PLLA) were investigated. The results of conductivity meter and dielectric analyzer (DEA) implied the existence of ions, which could be explained by the amine groups of PEG gaining the protons from the carboxylic acid groups of PLLA. The miscibility of PEG(2NH2)/PLLA blends was the best because of the ionic interaction as compared with PEG(2OH, 1OH-1CH3, and 2CH3)/PLLA blends. Since the ionic interaction formed only at the chain ends of PEG(2NH2) and PLLA, unlike hydrogen bonds forming at various sites along the chains in the other PEG/PLLA blend systems, the folding of PLLA blended with PEG(2NH2) was affected in a different manner. Thus the fold surface free energy played an important role on the crystallization rate of PLLA for the PEG(2NH2)/PLLA blend system. PLLA had the least fold surface free energy and the fast crystallization rate in the PEG(2NH2)/PLLA blend system, among all the PEG/PLLA systems studied. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

A simple method for chemically synthesizing PANI inverse opals by templating colloidal crystals is presented. The use of dodecylbenzene sulfonic acid resulted in structures with reduced shrinkage, allowing the position of the optical stop band to be tuned. The conductivity of the inverse opals was increased, and that of PANI was estimated to be 8 S · cm ⁻¹ . The inverse opals were of good structural integrity and fidelity, and the overall thickness could be controlled by that of the templates. Optical reflection spectra provided additional evidence of the high crystalline quality of the samples. These inverse opals might be attractive materials for sensor applications and studies of novel optical properties. magnified image

The polyaniline (PANI)-coated polystyrene (PS) latexes were synthesized, and the electrically conductive films were prepared thereafter. The weight ratio of PANI was 5%. Thermal analysis of the latices was performed using DSC and TGA. In this study, the electrically conductive films were prepared above the PS glass transition temperature (Tg). During the film formation, the effects of the annealing temperature and atmosphere (air or N2) on the film resistance were investigated. In addition, the film morphology was observed utilizing scanning electron microscopy. The film resistance decreased in the initial heating stage due to the increasing temperature and the compaction of film. Then the film resistance increased with further annealing due to the aging of PANI. Typically, the film resistance was about 6000 Ω/sq, and the conductivity was 0.3 S/cm. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 5406–5413, 2006

The miscibility and crystallization behavior of binary crystalline blends of poly(butylene terephthalate) [PBT] and polyarylate based on Bisphenol A and a 27/73 mole ratio of isophthalic and terephthalic acids [PAr(I27-T73)] have been investigated by differential scanning calorimetry (DSC). This blend system exhibits a single composition-dependent glass transition temperature over the entire composition range. The equilibrium melting point depression of PBT was observed, and Flory interaction parameter χ12=−0.96 was obtained. These indicate that the blends are thermodynamically miscible in the melt. The crystallization rate of PBT decreased as the amount of PAr(I27-T73) increased, and a contrary trend was found when PAr(I27-T73) crystallized with the increase of the amount of PBT. The addition of high-Tg PAr(I27-T73) would suppress the segmental mobility of PBT, while low-Tg PBT would have promotional effect on PAr(I27-T73). The crystallization rate and melting point of PBT were significantly influenced when the PAr(I27-T73) crystallites are previously formed. It is because not only does the amorphous phase composition shift to a richer PBT content after the crystallization of PAr(I27-T73), but also the PAr(I27-T73) crystal phase would constrain the crystallization of PBT. Thus, effects of the glass transition temperature, interaction between components, and previously formed crystallites of one component on the crystallization behavior of the other component were discussed and compared with blends of PBT and PAr(I-100) based on Bisphenol A and isophthalic acid.