Investigation of organic thermoelectric materials using potential-step chronocoulometry: Effect of polymerization methods on thermoelectric properties of poly(3-hexylthiophene)

To establish the correlation between the thermoelectric properties of conducting polymers and their doping levels, we have utilized the potential-step chronocoulometry for the quantitative estimation of the doping levels. In this paper, three types of poly(3-hexylthiophene)s synthesized by different polymerization methods were investigated. The electrical conductivities and the Seebeck coefficients of poly(3-hexylthiophene)s with various doping levels were measured and plotted against the doping level. It was found that the electrical conductivity linearly increased with increasing the doping level in the range of 1–10%, and then saturated. On the other hand, the relationship between the Seebeck coefficient and the doping level showed a good linearity in all the polymers.     

On a contact 3-structure

A contact 3-structure consists of three contact metric structures which satisfy the relation (2.1). On a product manifold of the real line and a manifold with a contact 3-structure, we can construct three almost Hermitian structures satisfying the quaternionic identities. From this view point we discuss a contact 3-structure. Owing to Hitchin's well known Lemma concerning to hyperk?hler structure (Lemma H), we show that a contact 3-structure is necessarily a Sasakian 3-structure. Received: 26 August 1999; in final form: 2 May 2000 / Published online: 4 May 2001     

Preparation of divinylbenzene copolymer particles with encapsulated hexadecane for heat storage application

From the viewpoint of heat storage application, encapsulation of n-hexadecane (HD) was carried out by microsuspension copolymerizations of divinylbenzene (DVB) and acrylic monomers (butyl acrylate, BA; ethyl acrylate, EA) utilizing the self-assembling of phase-separated polymer (SaPSeP) method proposed by the authors. The heat of solidification (H _s) of encapsulated HD in the micron-sized, cross-linked particles was determined by the differential scanning calorimeter (DSC). H _s of the encapsulated HD in poly(DVB) particles was much lower than that of pure HD, but it was increased with BA or EA content copolymerized up to that of pure HD. Such an influence of encapsulation on the H _s was discussed. Part CCIIIC of the series “Studies on suspension and emulsion”.     

Fabrication of metal nanoparticle monolayers on amphiphilic poly(amido amine) dendrimer Langmuir films

A newly designed 1.5th generation poly(amido amine) dendrimer with an azacrown core, hexylene spacers, and octyl terminals was spread on gold nanoparticle (Au-NP) suspension. The surface pressure-area isothermal curves indicated that the molecular area of dendrimer on Au-NP suspension was significantly smaller than that on water, indicating the formation of dendrimer/Au-NP composites. The dendrimer Langmuir films on the Au-NP suspension were transferred to copper grids at various surface pressures and observed by transmission electron microscopy. The transferred films consisted of a fractal-like network of nanoparticles at low surface pressure and of a defect-rich monolayer of nanoparticles at high surface pressure. From these results, it was suggested that the dendrimers bind Au-NPs, and dendrimer/Au-NP composites formed networks or monolayers at the interface. From the intensity decrease of the Au plasmon band of Au-NP suspension after the formation of composite, it was estimated that some (approximately 14) dendrimer molecules bind to one Au-NP. Furthermore, neutron reflectivity at the air/suspension interface and X-ray reflectivity of the film transferred on a silicon substrate revealed that the dendrimer molecules are localized on the upper-half surface of Au-NP. Metal affinity of azacrown, flexibility of hexylene spacer, and amphiphilicity of dendrimer with octyl terminals played important roles for the formation of dendrimer/Au-NP hybrid films. The present investigation proposed a new method to fabricate the self-assembled functional polymer/nanoparticle hybrid film.     

Preparation of ionic liquid-encapsulated polymer particles

Encapsulation of ionic liquid, 1-hexyl-3-methylimidazolium bis(trifluoromethane sulfonyl)amide ([Hmim][TFSA]), was carried out by microsuspension polymerization of ethylene glycol dimethacrylate (EGDM) utilizing the self-assembling of phase-separated polymer method, which had been proposed by us for the preparation of hollow polymer particles. After the optimization of the polymerization conditions, ionic liquid-encapsulated polymer particles, which have smooth surface morphology and a single hollow structure, were successfully prepared. Encapsulation efficiency of [Hmim][TFSA] was significantly improved from about 20–70 % by changing the shell polymer from polyEGDM homopolymer to poly(EGDM-butyl methacrylate) (50/50, w/w) copolymer, which was likely to have relatively low affinity for [Hmim][TFSA]. Additionally, ionic liquid-encapsulated polymer particles displaying ionic conductivity were successfully prepared using triethylene glycol dimethacrylate as divinyl monomer instead of EGDM.     

Preparation of amphiphilic diblock copolymers with pendant hydrophilic phosphorylcholine and hydrophobic dendron groups and their self‐association behavior in water

Generation 3.5 poly(amido amine) dendron (G3.5) with 16 n‐butyl terminal groups containing an acrylamide monomer (AaUG3.5) was prepared by condensation between an amino focal group in G3.5 and 11‐acrylamidoundecanoic acid. AaUG3.5 was polymerized using poly(2‐methacryloyloxyethyl phosphorylcholine) (pMPC)‐based macro‐chain transfer agent via reversible addition‐fragmentation chain transfer (RAFT) radical polymerization to obtain amphiphilic diblock copolymers with different compositions. The diblock copolymers (P_mD_n) were composed of a hydrophilic pMPC block and hydrophobic pendant dendron‐bearing block, where P and D represent pMPC and pAaUG3.5, respectively, and m and n represent the degree of polymerization for each block, respectively. P₂₉₆D₁ and P₉₈D₃ formed vesicles and large compound micelles and vesicles, respectively, which was confirmed by light scattering measurements and transmission electron microscopic (TEM) observations. The large compound micelles formed from P₉₈D₃ could not incorporate hydrophilic guest polymer molecules, because the aggregates did not have a hydrophilic hollow core. In contrast, the vesicles formed from P₂₆₉D₁ could incorporate hydrophilic guest polymer molecules into the hollow core. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 4923–4931     

Variation of the morphology of a carboxylated polymer film by alkali treatment

The variation of the morphology of a carboxylated polymer film cast from tetrahydrofuran solution, in which styrene/methacrylic acid copolymer particles produced by emulsion copolymerization were dissolved, before and after alkali treatment at temperatures higher than the glass-transition temperature was observed with a scanning electron microscope. The treated film had a porous structure. This result provides important evidence for the formation mechanism of the multihollow structure in submicron-sized, carboxylated polymer emulsion particles by the stepwise alkali/acid method and the alkali/cooling method which the authors proposed.     

Photovoltaic performance of dye-sensitized solar cells based on donor-acceptor pi-conjugated benzofuro[2,3-c]oxazolo[4,5-a]carbazole-type fluorescent dyes with a carboxyl group at different positions of the chromophore skeleton

Donor-acceptor pi-conjugated benzofuro[2,3-c]oxazolo[4,5-a]carbazole-type fluorescent dyes 3a, 3b, 8a, and 8b with a carboxyl group at different positions of the chromophore skeleton have been designed and synthesized. The absorption and fluorescence spectra and cyclic voltammograms of the fluorescent dyes agree very well, showing that the position of the carboxyl group has a negligible influence on the photophysical and electrochemical properties of these dyes. When these dyes are used in dye-sensitized solar cells, however, their photovolatic performances are considerably different. The short-circuit photocurrents and energy conversion efficiencies under a simulated solar light increase in the order: 3a (2.12 mA cm(-2), 1.00%) approximately 3b (2.10 mA cm(-2), 1.06%) > 8b (1.50 mA cm(-2), 0.67%) > 8a (0.84 mA cm(-2), 0.34%). Based on semi-empirical molecular orbital calculations (AM1 and INDO/S) together with spectral analyses and their photovolatic performance, the relationships between the observed photovolatic properties and the chemical structures of the benzofuro[2,3-c]oxazolo[4,5-a]carbazole-type fluorescent dyes are discussed. It is found that strong interaction between a TiO(2) surface and the electron accepting moiety of the dye leads to a high photovoltaic performance.     

A Comparative Study of Cellular Uptake and Subcellular Localization of Doxorubicin Loaded in Self‐Assemblies of Amphiphilic Copolymers with Pendant Dendron by MDA‐MB‐231 Human Breast Cancer Cells

Previously synthesized amphiphilic diblock copolymers with pendant dendron moieties have been investigated for their potential use as drug carriers to improve the delivery of an anticancer drug to human breast cancer cells. Diblock copolymer (P₇₁D₃)‐based micelles effectively encapsulate the doxorubicin (DOX) with a high drug‐loading capacity (≈95%, 104 DOX molecules per micelle), which is approximately double the amount of drug loaded into the diblock copolymer (P₂₉₆D₁) vesicles. DOX released from the resultant P₇₁D₃/DOX micelles is approximately 1.3‐fold more abundant, at a tumoral acidic pH of 5.5 compared with a pH of 7.4. The P₇₁D₃/DOX micelles also enhance drug potency in breast cancer MDA‐MB‐231 cells due to their higher intracellular uptake, by approximately twofold, compared with the vesicular nanocarrier, and free DOX. Micellar nanocarriers are taken up by lysosomes via energy‐dependent processes, followed by the release of DOX into the cytoplasm and subsequent translocation into the nucleus, where it exert its cytotoxic effect.

     

Fabrication and properties of fullerodendron thin films

Thin films of fullerodendron (C(60)(Gn-COOMe) (n = 0.5, 1.5, 2.5)), which was synthesized from fullerene and anthracenyl poly(amido amine) dendron with methyl ester terminals and different generations (G), were fabricated by the Langmuir-Blodgett (LB) and adsorption techniques. It was characterized by X-ray reflectometry that the LB films possessed well-ordered structure, although the adsorption method led to random orientation of molecules. As to C(60)(G0.5-COOMe) and C(60)(G1.5-COOMe), the LB films took a four-layer structure consisting of a double layer of molecules, and fullerene moieties exist in the interior of the LB films. On the other hand, C(60)(G2.5-COOMe) led to a two-layer structure in which the fullerene moieties were at the air side and the dendron moieties were at the substrate side. With increasing generation of dendron, the monolayer formation ability at the air/water interface as amphiphilic molecule strengthens and the amphiphilic property becomes superior to the fullerene-fullerene attractive interaction that prevents the monolayer formation. Furthermore, in the case of C(60)(G0.5-COOMe) and C(60)(G1.5-COOMe), the reduction peak in cyclic voltammetry of the LB film remained even after UV light irradiation. On the contrary, the peak of the C(60)(G2.5-COOMe) LB film disappeared, indicating that molecular arrangement in the films affects electrochemical properties.