Całus Sylwia, Jabłońska Beata, Busch Mark, Rau Daniel, Huber Patrick, Kityk Andriy V
Faculty of Electrical Engineering, Czestochowa University of Technology, 42-200 Czestochowa, Poland.
Faculty of Environmental Engineering and Biotechnology, Czestochowa University of Technology, 42-200 Czestochowa, Poland.
Phys Rev E Stat Nonlin Soft Matter Phys. 2014 Jun;89(6):062501. doi: 10.1103/PhysRevE.89.062501. Epub 2014 Jun 9.
We explore the optical birefringence of the nematic binary mixtures 6CB_{1-x}7CB_{x} (0 ≤ x ≤ 1) embedded into parallel-aligned nanochannels of mesoporous alumina and silica membranes for channel radii of 3.4 ≤ R ≤ 21.0 nm. The results are compared with the bulk behavior and analyzed with a Landau-de Gennes model. Depending on the channel radius the nematic ordering in the cylindrical nanochannels evolves either discontinuously (subcritical regime, nematic ordering field σ<1/2) or continuously (overcritical regime, σ>1/2), but in both cases with a characteristic paranematic precursor behavior. The strength of the ordering field, imposed by the channel walls, and the magnitude of quenched disorder varies linearly with the mole fraction x and scales inversely proportionally with R for channel radii larger than 4 nm. The critical pore radius, R_{c}, separating a continuous from a discontinuous paranematic-to-nematic evolution varies linearly with x and differs negligibly between the silica and alumina membranes. We find no hints of preferred adsorption of one species at the channels walls. By contrast, a linear variation of the nematic-to-paranematic transition point T_{PN} and of the nematic ordering field σ versus x suggests that the binary mixtures of cyanobiphenyls 6CB and 7CB keep their homogeneous bulk stoichiometry also in nanoconfinement, at least for channel diameters larger than ∼7 nm.
我们研究了嵌入介孔氧化铝和二氧化硅膜的平行排列纳米通道（通道半径为3.4≤R≤21.0 nm）中的向列型二元混合物6CB₁₋ₓ7CBₓ（0≤x≤1）的光学双折射。将结果与本体行为进行比较，并用朗道-德热纳模型进行分析。根据通道半径，圆柱形纳米通道中的向列序要么不连续地演化（亚临界状态，向列序场σ<1/2），要么连续地演化（超临界状态，σ>1/2），但在这两种情况下都具有特征性的顺向列前驱体行为。由通道壁施加的序场强度和猝灭无序的大小随摩尔分数x线性变化，并且对于半径大于4 nm的通道，与R成反比。将连续的和顺向列到向列演化分开的临界孔径Rc随x线性变化，并且在二氧化硅和氧化铝膜之间的差异可忽略不计。我们没有发现一种物质在通道壁上优先吸附的迹象。相比之下，向列-顺向列转变点TPN和向列序场σ随x的线性变化表明，至少对于直径大于约7 nm的通道，氰基联苯6CB和7CB的二元混合物在纳米限域中也保持其均匀的本体化学计量。
