Size-Dependent Phase Behavior of the Hexadecane鈥?/i>Octadecane System Confined in Nanoporous Glass

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• 作者：Li Ping Wang ; Qi Feng Li ; Chao Wang ; Xiao Zheng Lan
• 刊名：Journal of Physical Chemistry C
• 出版年：2014
• 出版时间：August 7, 2014
• 年：2014
• 卷：118
• 期：31
• 页码：18177-18186
• 全文大小：625K
• ISSN：1932-7455

文摘

Solid鈥搇iquid phase behaviors of the hexadecane鈥搊ctadecane (n-C₁₆H₃₄鈥揅₁₈H₃₈, C₁₆鈥揅₁₈) system in the bulk, and confined in controlled porous glass (CPG) are investigated using differential scanning calorimetry and temperature-dependent powder X-ray diffraction. Bulk C₁₆鈥揅₁₈ mixtures show the special rotator phase R_I, and two intermediate phases with monoclinic (M_dcp) and orthorhombic (O_p) structures. Inside CPG (8.1 and 300 nm), the R_I and O_p phases could be found in wider compositions of the solid mixtures than the bulk, however the M_dcp form was not observed. Unexpectedly, under the confinement of CPG (8.1 nm) not only the rotator R_I appeared in the two pure components, C₁₆ and C₁₈, but a rotator phase R_II occurred in the pure C₁₈ and most of the mixtures upon heating. These new phase behaviors of the confined alkanes could be attributed to the size effect and the interface interactions. According to XRD analysis, in the small pores of CPG (8.1 nm) the alkane molecules effectively take the 2D arrangements. While in the large pores of CPG (300 nm), they take ordered packing to some extent both in the lamellar and lateral directions.