In-Situ SAXS Study on the Alignment of Ordered Systems of Comb-Shaped Supramolecules:  A Shear-Induced Cylinder-to-Cylinder Transition

Abstract

Citation for published version (APA): Polushkin, E., Bondzic, S., de Wit, J., van Ekenstein, GA., Dolbnya, N. V., Bras, W., ... Ikkala, I. (2005). Insitu SAXS study on the alignment of ordered systems of comb-shaped supramolecules: A shear-induced cylinder-to-cylinder transition. Macromolecules, 38(5), 1804-1813. https://doi.org/10.1021/ma048314k Copyright Other than for strictly personal use, it is not permitted to download or to forward/distribute the text or part of it without the consent of the author(s) and/or copyright holder(s), unless the work is under an open content license (like Creative Commons).Take-down policy If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim. ABSTRACT: A tooth rheometer, designed to investigate in-situ the influence of large-amplitude oscillatory shear on the macroscopic orientation of complex fluids, is used to study the alignment of two supramolecular systems composed of a polyisoprene-block-poly(2-vinylpyridine) block copolymer with octyl gallate (OG) hydrogen bonded to the vinylpyridine block. The molecular ratio x between OG and pyridine groups in these two PI-b-P2VP(OG) x systems is 0.50 and 0.75, respectively. In both cases, a hexagonally ordered cylindrical self-assembly was revealed by small-angle X-ray scattering in a broad temperature range. The spacing of the hexagonal structure decreases significantly on heating and reversibly increases on cooling. In in-situ SAXS experiments, performed with the tooth rheometer, a gradual macroscopic alignment of the nanoscale structure is observed on heating for both supramolecular systems. The most striking feature is a shear-induced transition from one hexagonal structure to another, more aligned, hexagonal structure observed for PI-b-P2VP(OG) 0.75 in the temperature range 120-140°C. The transition is accompanied by an abrupt reduction of the domain spacing and additionally by a decrease of the phase angle measured by the rheometer. In the PI-b-P2VP(OG) 0.5 system a comparable reduction in the spacing is observed at 90-95°C. In this case, it coincides with the most intensive macroscopic alignment of the sample, proceeding in a continuous rather than discontinuous fashion. This behavior is discussed in terms of the breaking of the hydrogen bonds between OG and P2VP being facilitated by shear.

SAXS study of the lamellar–cylindrical transition in the PI-b-P2VP(OG) supramolecules' system

“…However, at temperatures from 170 to 190 C, the phase angle shows a second decay, indicating new structural changes in the sample, i.e., the DHS-CYL transition. Similar to a slightly different PI-b-P2VP(OG)0.75 system [46], the DHS-CYL transformation observed for the PI-b-P2VP(OG) 1.0 sample can be referred to as a cylinder-to-cylinder transition, characterized by an abrupt change in the diameter of the P2VP(OG) 1.0 cylinders, caused by practically complete breaking of the hydrogen bonding. Because of such diameter collapse, the packing of P2VP(OG)1.0 cylinders becomes more dense, resulting in a phase angle decrease.…”

“…In fact, the decrease shown in Fig. 6 is much larger than it was found for the system with a lower amount of OG [46]. This is presumably due to the fact that in the case of PI-b-P2VP(OG) 1.0 the transition occurs at even higher temperatures, where both the local disordering and the disorientation of cylindrical domains on shear become quite possible.…”

“…Apart from the influence of temperature, the level of hydrogen bonding in PI-b-P2VP(OG) x systems, and therefore their morphology, is known to be affected by shear [46]. To elucidate the influence of shear on the LAM-to-CYL transition in this particular PI-b-P2VP(OG) 1.0 system, additional in situ SAXS experiments were conducted.…”

“…On the other hand, our previous experimental data suggest that shear may facilitate the temperature-induced breaking of H-bonds [46]. This results in a much faster transformation of the ellipsoidal cylinders into regular circular ones upon shear, since being less bonded with OG the P2VP blocks can readily adopt a more coil-like conformation.…”

In situ investigation of the liquid/solid interface of a block copolymer solution under shear stress using microbeam grazing-incidence small-angle x-ray scattering

“…Except for some recent grazing incidence SANS measurements under shear, 2,3 only transmission experiments were conducted on in situ combination of rheology and small-angle measurements. [4][5][6][7][8][9] Because the interface of the colloidal solution inside a shear geometry is sometimes of special interest, we conducted an in situ combination of rheology with microbeam gracing incidence SAXS ͑ -GISAXS͒. 10 For our investigations, we used a 13 wt.…”