正十六烷醇在硅纳米通道中的相变和分子动力学
Phase transitions and molecular dynamics of n-hexadecanol confined in silicon nanochannels
摘要：
我们提出了一个相行为和分子动力学的正十六烷醇在其体相态和限制在一个阵列的排列纳米通道的直径为8 nm的中孔硅的X-射线衍射和红外光谱相结合的研究。在限制下，液体、转子RII和结晶C相之间的转变温度降低约20 K。虽然散装正十六烷醇在低温下表现出正交β-和单斜γ-形式的多晶混合物，但几何限制有利于更简单的β-形式：仅形成微晶，其中链轴平行于层法线。然而，伽马形式，其中链轴相对于层法线倾斜，被完全抑制。β-微晶形成双层，其在孔中不是随机取向的。分子排列成其长轴垂直于长通道轴。在分子动力学方面，我们证明了禁闭并不影响CH_2自由振动的内分子动力学，并计算了C相中的分子间力常数。
英文摘要：
We present a combined x-ray diffraction and infrared spectroscopy study on the phase behavior and molecular dynamics of n-hexadecanol in its bulk state and confined in an array of aligned nanochannels of 8 nm diameter in mesoporous silicon. Under confinement the transition temperatures between the liquid, the rotator RII and the crystalline C phase are lowered by approximately 20K. While bulk n-hexadecanol exhibits at low temperatures a polycrystalline mixture of orthorhombic beta- and monoclinic gamma-forms, geometrical confinement favors the more simple beta-form: only crystallites are formed, where the chain axis are parallel to the layer normal. However, the gamma-form, in which the chain axis are tilted with respect to the layer normal, is entirely suppressed. The beta-crystallites form bi-layers, that are not randomly orientated in the pores. The molecules are arranged with their long axis perpendicular to the long channel axis. With regard to the molecular dynamics, we were able to show that confinement does not affect the inner-molecular dynamics of the CH_2 scissor vibration and to evaluate the inter-molecular force constants in the C phase.
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