Imaging of nonlinear optical response in biopolyesters via second harmonic generation microscopy and its dependence on the crystalline structures
Imaging of nonlinear optical response in biopolyesters via second harmonic generation microscopy and its dependence on the crystalline structures
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DOI：
10.1016/j.polymer.2006.11.037
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发表时间：
2007-01
期刊：
影响因子：
4.6
通讯作者：
Jun Xu;Jin Bao;Baohua Guo;Hui Ma;Tianliang Yun;Liang Gao;Guo-Qiang Chen;T. Iwata
中科院分区：
文献类型：
--
作者：
Jun Xu;Jin Bao;Baohua Guo;Hui Ma;Tianliang Yun;Liang Gao;Guo-Qiang Chen;T. Iwata
用二次谐波显微镜(SHGM)研究了不同聚羟基烷酸酯(PHAs)的非线性光学响应。结果表明，聚合物的二次谐波效率与聚合物的化学结构和晶体结构有关。在所研究的PHA中，微生物聚酯、聚(R-3-羟基丁酸酯)(PHB)和聚(R-3-羟基戊酸酯)(PHV)具有最强的SHG活性，这可以归因于氢键增强了结晶片核中的羰基的超极化率，以及SHG部分的非中心对称排列。β-型和γ-型聚(β-丙内酯)具有不同的倍频效率，这是由于相同链构象的链段在晶格中的堆积方式不同所致。此外，带状球晶的倍频响应随片层取向的不同而不同。通过对厚膜不同深度的光学切片，将其应用于PHB/聚(ɛ-己内酯)共混物中PHB球晶的三维成像。对于PHB/聚(L-丙交酯)(PLLA)共混物，SHGM分析表明，在偏光显微镜下观察不到的情况下，预制的PLLA扭转片层之间的熔体约束形成的PHB扭转片层具有与后者相同的扭转周期。由于其优点，SHGM有望在非均相结构的非线性光学材料的表征中得到更多的应用。
Nonlinear optical response in various polyhydroxyalkanoates (PHAs) was investigated via second harmonic generation microscopy (SHGM). It was revealed that the second harmonic generation (SHG) efficiency depended on both the polymer chemical structure and the crystalline structure. Among the PHAs studied, the microbial polyesters, poly(R-3-hydroxybutyrate) (PHB) and poly(R-3-hydroxyvalerate) (PHV) showed strongest SHG activity, which could be attributed to hydrogen bonding that enhanced hyperpolarizability of the carbonyl groups in the crystalline lamellar core, and the noncentrosymmetric arrangement of the SHG moieties. The β- and γ-type poly(β-propiolactone) demonstrated different SHG efficiency due to the different packing scheme of the chain stems in the crystal lattice despite the same chain conformation. In addition, SHG response in the banded spherulite varied with the lamellar orientation. Furthermore, SHGM was applied for 3-D imaging of PHB spherulite in PHB/poly(ɛ-caprolactone) blends via optical sectioning of the thick film at different depths. For PHB/poly(l-lactide) (PLLA) blends, SHGM revealed that the PHB twisting lamellae formed from the melt confined between the preformed PLLA twisting lamellae had the same twisting period as the latter, which could not be observed under polarized optical microscope. Due to the advantages, SHGM is expected to find more applications in characterization of nonlinear optical (NLO) materials with heterogeneous structures.