Raman investigation of stable and metastable states of 4-octyl-4'-cyanobiphenyl confined in porous silica matrices.
Raman investigation of stable and metastable states of 4-octyl-4'-cyanobiphenyl confined in porous silica matrices.
复制标题
限制在多孔二氧化硅基质中的 4-辛基-4-氰基联苯的稳定和亚稳定状态的拉曼研究。
DOI：
10.1103/physreve.67.061706
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发表时间：
2003
期刊：
影响因子：
--
通讯作者：
E. Anglaret
中科院分区：
文献类型：
--
作者：
C. Fehr;P. Dieudonné;J. Sauvajol;E. Anglaret
用拉曼光谱研究了4-辛基-4（'）-氰基联苯（8 CB）固相的多晶型。对于块体8 CB，CN伸缩的拉曼光谱的特征在于由一个单峰，其在近晶-A-晶体转变处突然移位。在限制中，CN峰在高温和低温下分裂。在各向同性和液晶相，签名的液晶体（LC）共存的另一个峰被分配到LC分子与基质界面相互作用。我们发现界面液体的体积分数和矩阵的纹理之间的相关性。在低温下，我们分配的CN峰的分裂不同的亚稳固相的共存。对于强约束，CN伸缩频率的温度依赖性扩展到液体，这表明存在冻结的smecticlike固相。我们根据中子衍射测量结果讨论了这些亚稳固相的结构。我们还报告了由于多孔基质的淬火无序的效果和热淬火的效果之间的特殊的类比。
We study the polymorphism of solid phases of 4-octyl-4(')-cyanobiphenyl (8CB) by Raman spectroscopy. For bulk 8CB, the Raman spectrum of the CN stretch is featured by a single peak, which shifts abruptly at the smectic-A-crystal transition. In confinement, the CN peak splits both at high and low temperatures. In the isotropic and liquid crystal phases, the signature of the liquid crystal bulk (LC) coexists with another peak that is assigned to LC molecules interacting with the matrice interface. We find correlations between the volumic fractions of interfacial liquid and the texture of the matrices. At low temperatures, we assign the splitting of the CN peak to the coexistence of different metastable solid phases. For strong confinements, the temperature dependence of the CN stretching frequency extends to that of the liquid, which suggests the existence of frozen-in smecticlike solid phases. We discuss the structure of these metastable solid phases in the light of neutron diffraction measurements. We also report on the peculiar analogy between the effect of quenched disorder due to the porous matrices and the effect of thermal quenching.