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The photothermal effect, which is a phenomenon of converting light energy into thermal energy using photothermal conversion materials, has recently attracted significant attention in biological applications because of the minimal invasiveness to healthy tissues, high specificity, and easy operation. Polymer-based photothermal materials have emerged as a promising category of photothermal agents in biological applications because they show superiorities in tailorable molecular structures, high photothermal conversion efficiencies, and excellent biocompatibility. In this Review, we summarize the recent progresses achieved in polymer-based photothermal materials for biological applications. To have a better understanding of the working mechanism and the design of polymer-based photothermal materials, this Review starts with the fundamental description of photothermal conversion mechanism of polymer-based photothermal materials. According to their structures and compositions, the polymer-based photothermal materials can be classified into three types: conjugated polymers, polymer-modified carbon nanomaterials, and polymer-modified metals and metal compounds. Then we present the recent advances of the polymer-based photothermal materials in a diversity of biological areas such as photothermal therapy and photothermal sterilization. In the last section, we summarize the critical existing issues in polymer-based photothermal materials for biological applications and propose some perspectives that are related to the design and synthesis of polymer-based photothermal materials for biological applications.

Sulfur has received considerable attention as a cathode material for lithium-sulfur (Li-S) batteries due to its high theoretical energy density (2567 W h kg(-1)), high earth abundance, and environmental benignity. However, the insulating nature of sulfur and the shuttle effect of soluble lithium polysulfides result in serious technical issues, such as low utilization rate of sulfur, reduced columbic efficiency, and poor cycling stability, which compromise the high theoretical performance of Li-S batteries. In the past years, various attempts have been made to achieve high specific capacity and reliable cycling stability of Li-S batteries. Incorporation of sulfur into functional host materials has been demonstrated to be effective to improve the electrochemical performance of sulfur-based cathodes via enhancing the electron and Li ion conductivities, immobilizing sulfur/lithium polysulfides in cathodes, and accommodating the volume changes in sulfur-based cathodes. Therefore, the rational design of sulfur-containing composites needs to be emphasized as key strategies to develop high-performance cathodes for Li-S batteries. In this perspective, after reviewing the achievements obtained in the design of sulfur-containing composites as cathodes for Li-S batteries, we propose the new issues that should be overcome to facilitate the practical application of Li-S batteries.

The phase transition behaviors and corresponding structures of 6-{[(4'-([(undecyl)carbonyl]oxy)biphenyl-4yl)carbonyl]oxyl-l-hexyne (A4EE11) were investigated using differential scanning calorimetry (DSC), polarizing optical microscopy (POM) and wide angle X-ray diffraction (WAXD). In comparison with the published homologues, 5- [(4'-heptoxy-biphenyl-4-yl)carbonyl]oxyl-1-pentyne (A3EO7) which shows a monotropic smectic A (SmA) phase and a metastable monotropic smectic C (SmC) phase; 5-\{ [(4'-heptoxybiphenyl-4-yl)oxy]carbonyl)- I-pentyne (A3E'O7) that exhibits three enantiotropic stable liquid crystalline (LC) phases, SmA phase, SmC phase and smectic X (SmX) phase; 5-\{[(4'-heptoxy-biphenyl-4-yl)carbonyl]oxy}-1-undecyne (A9EO7) which has a monotropic SmA phase and a metastable crystal phase, A4EE11 integrates the enantiotropy, monotropy and metastability of the LC phases of those three compounds. Upon cooling from isotropic state to room temperature, in the temperature range of 62.0 to 58.5 degrees C, A4EE11 shows an enantiotropic smectic A (SmA) phase with a layer spacing d=32.69 angstrom. Further lowering the temperature, it enters into a metastable monotropic smectic B (SmB) phase with a longer layer spacing d=34.22 angstrom which has a tendency towards crystallization. The metastability of the liquid crystalline phase may associate to the linkage order of the ester bridge between the mesogenic core and the flexible spacer. (C) 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Electric-field-induced molecular alignments of side-chain liquid-crystalline polyacetylenes [-{HC=C[(CH2)(m)OCO-biph-OC7H15]}-, where biph is 4,4'-biphenylyl and m is 3 (PA3EO7) or 9 (PA9EO7)] were studied with X-ray diffraction and polarized optical microscopy. An orientation as high as 0.84 was obtained for PA9EO7. Furthermore, the molecular orientation of]PA9EO7 was achieved within a temperature range between the isotropic-to-smectic A transition temperature and 115 degreesC, and this suggested that the orientational packing was affected by the thermal fluctuation of the isotropic liquid and the mobility of the mesogenic moieties. The maximum achievable orientation for PA9EO7 was much greater than that for PA3EO7. This was the first time that the electric-field-induced molecular orientation of a side-chain liquid-crystalline polymer with a stiff backbone was studied. (C) 2004 Wiley Periodicals, Inc.

The crystal structure and liquid crystalline properties of a biphenyl-containing acetylene, [5-[(4'-heptoxy-4- biphenylyl) carbonyloxy]-1-pentyne (A3EO7) were investigated by electron crystallography, X-ray diffraction, polarizing optical microscopy, differential scanning calorimetry, transmission electron microscopy, and atomic force microscopy. A3EO7 crystals obtained from a toluene solution adopts a monoclinic P112/m space group with unit cell parameters of a = 6.25 Angstrom, b = 7.82 Angstrom, c = 46.70 Angstrom and gamma = 96.7degrees, as determined using electron diffraction. Upon cooling from the isotropic phase, A3EO7 exhibits a smectic A phase in the temperature range 72.4 - 53.6degreesC. Further lowering of the temperature results in the formation of a smectic C phase which exhibits a strong tendency towards crystallization.

The liquid crystalline properties of a mesogenic poly(1-alkyne) and the corresponding monomer were studied using transmission electron microscopy, X-ray diffraction, polarizing optical microscopy and differential scanning calorimetry. The monomer exhibits a monotropic smectic A phase and a metastable crystalline phase. The rigid polymer backbones do not prevent the mesogenic moieties from packing into smectic A and B phases in the temperature ranges 127.6 - 74.1degreesC and 74.1degreesC - room temperature, respectively, on cooling from the isotropic melt.

Mesomorphic properties of a side chain liquid crystalline polyacetylene, poly(11-{[(4'-heptyloxy-4-biphenylyl)carbonyl]oxy}-1-undecyne) (PA9EO7), are investigated using polarized optical microscope, X-ray diffraction, and transmission electron microscope. Polymer PA9EO7 forms enantiotropic smectic A and smectic B phases. It also exhibits an additional high order smectic phase, a sandwich structure consisting of different molecular packing of biphenyl mesogenic moieties from that of alkyl spacers and terminals, when it is prepared from its toluene solution. Shearing the polymer film at its smectic A phase generates banded texture with the alignment of the backbones parallel to the direction of shear force. While at its high order smectic phase, the mesogen pendants of the polymer are arranged parallel to the direction of shear. The different mesomorphic behaviors arise from different molecular alignments influenced by the fluidity. (C) 2003 Elsevier Ltd. All rights reserved.

Liquid crystalline properties of a mesomorphic polyacetylene {-[HC=C(CH2 )(9)OOC-Biph-OC7H15](n)- (PA9EO7), Biph=4-4'-biphenylyl} are investigated by X-ray diffraction, polarizing optical microscope, and transmission electron microscope. Polyacetylene PA9EO7 from solution adopts a sandwich structure, which is a high order smectic phase. The biphenylyl pendants pack in a hexagonal fashion and the distance between two appendages is 4.51 Angstrom. The heptyloxy tails on one polymer backbone overlap with those on the neighboring chain. The nonyl spacer and the heptyloxy tail exhibit a hexagonal packing arrangement with intermolecular distance of 3.24 Angstrom.