Abstract
ABSTRACTThis paper presents a detailed analysis of the structure of the hexagonal phase of poly(ferrocenylsilane) (PFS)-based cylindrical micelles found at concentrations above ca. 5 wt. % in non-polar solvents such as decane. Small-angle X-ray scattering indicated that the hexagonal order is not long-range. In all samples, deviations in the lower order peak positions were observed with respect to those expected for a perfect hexagonal lattice, with the degree of deviation correlating with micelle length. Furthermore, analysis of the peak shapes and peak widths suggests that the phase possesses intermediate translational order similar. to the hexatic phase. The observed features can be reproduced by amending Hosemann’s paracrystal theory to include a distribution of lattice parameters to model well and poorly condensed regions. It is proposed that this distribution arises due to the bending and intertwining of individual micelles in a hexagonal lattice, resulting in a kinetically trapped phase that is initially neither perfectly hexagonal nor canonically hexatic but which anneals over time towards a perfect hexagonal lattice.
Highlights
In the natural world, hierarchical self-assembly and self-organisation are responsible for a stunning variety of different structures and architectures.[1]
In azimuthally averaged data from small angle X-ray scattering (SAXS) exp√erime√nts, t√his phase manifests as sharp Bragg reflections with scattering vectors in the ratio 1 : 3 : 4 : 7, indicating a 2-dimensional hexagonal lattice
This peak shift in the diffraction pattern can be quantified by calculating the apparent lattice parameter, a, from each peak assuming a 2D hexagonal lattice: 4π a =√
Summary
Hierarchical self-assembly and self-organisation are responsible for a stunning variety of different structures and architectures.[1]. Previous studies of cylindrical block copolymer micelles do report the existence of a hexagonal phase occurring at high concentrations, [24,25,26,27,28] in all cases where the order is discussed, this appears to be a regular, translationally well-ordered phase Another possible phase for systems of concentrated semi-flexible rods is the hexatic, which exhibits long-range sixfold orientational order but only short range translational order. Such phases have been observed for systems of DNA molecules, [29] cationic surfactants in protic ionic liquids, [30] and fd virus particles. A comparison of the results with those expected from other candidate phases shows that the phase exhibited by the block copolymer micelles is neither perfectly hexagonally crystalline nor canonically hexatic, it shares features with both
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