Dresden 2014 – wissenschaftliches Programm

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MI: Fachverband Mikrosonden

MI 10: Crystallography in Nanoscience (KR jointly with MI)

MI 10.2: Vortrag

Donnerstag, 3. April 2014, 11:15–11:30, CHE 184

Confined crystallization of n-hexadecane located inside of microcapsules or outside of submicron silica nanospheres: A comparison study — •Yunlan Su^{1, 2}, Xia Gao¹, Dujin Wang¹, and Patrick Huber² — ¹Key Laboratory of Engineering Plastics, Institute of Chemistry, Chinese Academy of Sciences, Beijing, China — ²Materials Physics and Technology, Hamburg University of Technology, Hamburg, Germany

Geometrical confinement of materials on the nm-scale is known to have an impact on many physical properties. For example, phase transitions can be entirely suppressed or significantly altered in comparison to their bulk counterparts and the molecular dynamics can be affected markedly, especially in the vicinity of glass transitions. In the work, we designed n-octadecanol/SiO2 nanosphere (d = 90 nm) composites and studied the crystallization behaviors of C18H37OH in nanosized space formed by SiO2 nanospheres by DSC and variable-temperature X-ray diffraction (VT-XRD). The transition temperatures for confined C18H37OH are lower than for bulk C18H37OH; In addition, under confinement, the low temperature ordered phase has changed, probably due to the suppression of mobility of molecular chain. While bulk C18H37OH exhibits a crystalline phase of γ form, geometrical confinement favors a mixture of γ and β phases. Geometrical confinement favors a phase closely related to the β form, in which the crystallites with an orthorhombic subcell and chain axes are parallel to the bilayer normal are formed. A reason for this might be the confinement effect, into which the crystallites have to fit, favoring the formation of the geometrically more simple and less bulky form.