Abstract
We report on the counter intuitive reversible crystallisation of two-dimensional monolayer of Trisilanolisobutyl Polyhedral Oligomeric SilSesquioxane (TBPOSS) on water surface using synchrotron x-ray scattering measurements. Amphiphilic TBPOSS form rugged monolayers and Grazing Incidence X-ray Scattering (GIXS) measurements reveal that the in-plane inter-particle correlation peaks, characteristic of two-dimensional system, observed before transition is replaced by intense localized spots after transition. The measured x-ray scattering data of the non-equilibrium crystalline phase on the air-water interface could be explained with a model that assumes periodic stacking of the TBPOSS dimers. These crystalline stacking relaxes upon decompression and the TBPOSS layer retains its initial monolayer state. The existence of these crystals in compressed phase is confirmed by atomic force microscopy measurements by lifting the materials on a solid substrate.
Highlights
The values of the in-plane scattered angles (Q 5 2h) for the crystalline phase were estimated from the intensity profiles of the Grazing Incidence X-ray Scattering (GIXS) plot at qz 5 0 (Fig. 2(c)) and the corresponding dhkl values were determined by fitting the arcs assuming a triclinic crystal structure with P1 symmetry
Summary and Conclusion Characteristic phase transition has been observed for Trisilanolisobutyl Polyhedral Oligomeric SilSesquioxane (TBPOSS) monolayer on water surface
GIXS measurements have been performed on monolayer of TBPOSS before and after transition
Summary
We report on the counter intuitive reversible crystallisation of two-dimensional monolayer of Trisilanolisobutyl Polyhedral Oligomeric SilSesquioxane (TBPOSS) on water surface using synchrotron x-ray scattering measurements. Amphiphilic TBPOSS form rugged monolayers and Grazing Incidence X-ray Scattering (GIXS) measurements reveal that the in-plane inter-particle correlation peaks, characteristic of two-dimensional system, observed before transition is replaced by intense localized spots after transition. The measured x-ray scattering data of the non-equilibrium crystalline phase on the air-water interface could be explained with a model that assumes periodic stacking of the TBPOSS dimers. These crystalline stacking relaxes upon decompression and the TBPOSS layer retains its initial monolayer state The existence of these crystals in compressed phase is confirmed by atomic force microscopy measurements by lifting the materials on a solid substrate. Intense spots on the arcs tend to appear and disappear intermittently This is a clear signature that some preferred orientation of the crystalline planes occurs as a result of some movement of the crystallites over water surface within the coherent scattering volume despite the fact that during the process of data acquisition the barriers were locked after having reached the desired surface pressure. AFM measurements (Nanoscope IV, Digital Instruments) were carried out in tapping mode using etched Si cantilever on thin films of TBPOSS (pre and post phase transition) after transferring horizontally on hydrophilized Si substrate
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