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Properties and self-assembled packing morphology of long alkyl-chained substituted polyhedral oligomeric silsesquioxanes (POSS) cages

DOI: 10.1039/c3cp44356f DOI Help

Authors: Ellen L. Heeley (Open University) , Darren Hughes (University of Warwick) , Youssef El Aziz (Open University) , Ian Williamson (Open University) , Peter Taylor (Open University) , Alan R. Bassindale (Open University)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Physical Chemistry Chemical Physics , VOL 15 (15)

State: Published (Approved)
Published: February 2013
Diamond Proposal Number(s): 6719

Abstract: Polyhedral oligomeric silsesquioxane (POSS) cubic cage systems (octa-n-octadecyloctasilsesquioxane, (T8C18) and octakis(n-octadecyldimethylsiloxy)octasilsesquioxane, (Q8C18)) were synthesised with eight long n-alkyl chain (R = C18H37) substituent arms, as model nano-functionalized compounds. The crystalline packing morphology of the cages was studied using time-resolved Small- and Wide-angle X-ray scattering (SAXS/WAXS), thermal and optical techniques. From thermal analysis the melting and crystallization temperatures of the Q8 cage were significantly less than those for the T8 cage. X-ray scattering showed that both cage systems have long-range crystalline ordering where the alkyl chains align in a parallel axial disposition from the POSS core giving a ‘rod-like’ self-assembled packing morphology. The packing length-scale can be directly related to the overall dimensions of the POSS molecules. Compared to the T8 cages, the Q8 cages pack more efficiently allowing the interdigitation of the alkyl chain arms. Different packing modes and thermal behaviour observed for the T8 and Q8 cages is directly attributed to their structural chemistry. For the Q8 cage, the presence of the OSiMe2 spacer groups which tether the alkyl chain arms to the cage (absent in the T8 cages) allows greater flexibility of the arms letting them interdigitate with each other when packing which is not observed for the analogous T8 cages.

Journal Keywords: Long Alkyl-Chained Substituted Polyhedral Oligomeric

Subject Areas: Materials, Chemistry, Physics


Instruments: I22-Small angle scattering & Diffraction

Other Facilities: ESRF

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