Substrate and drying effect in shape and ordering of micelles inside CTAB–silica mesostructured films

Abstract

Deviation from a perfect 2D-hexagonal (p6m) structure, for CTAB-silica mesostructured films prepared by adding different amounts of excess ethanol to a solution of CTAB and TEOS just before spin coating on OH-and H-terminated Si substrates, is observed from combined X-ray reflectivity and grazing incidence small angle X-ray scattering measurements. Such a deviation can be well understood in terms of the shape and ordering of the micelles, with or without the silica coating layer's contribution, inside the film. For example, cylindrical shaped micelles, which are initially circular on a hydrophilic OH-terminated Si substrate in order to form a perfect 2D-hexagonal structure, become elliptical (extended along the in-plane) on a hydrophobic H-terminated Si substrate to form a slightly compressed 2D-hexagonal structure due to a different attachment of the film to the substrate. With time, due to the drying of the silica materials and its restricted movement along the in-plane direction, the films on both the substrates are compressed along the out-of-plane direction only, to form observed centered rectangular (c2mm) structures. Also, due to the asymmetric shrinkage, stress is developed, which deteriorates the ordering in the film. The final shape of the micelles, including the silica coating layer's contribution, shows maximum and minimum deviations from the circular shape inside the thick film on a OH-Si substrate and the thin film on a H-Si substrate, respectively. The deviation in the shape of the micelles itself, which is of actual importance, seems to be maximum and minimum inside the thick film on a H-Si substrate and the thin film on a OH-Si substrate, respectively, and is essentially determined by the substrate nature and initial silica wall thickness.

Wettability of bare and fluorinated silanes: A combined approach based on surface free energy evaluations and dipole moment calculations

“…In the case of the laboratory experiments, the different siloxane molecules are deposited onto the glass slides by spin-coating. This procedure is adopted since it provides a stable and reproducible coating [34,43], easily adoptable in the common practice [44,45]. Actually, it is a procedure comparable to the coating methods adopted in industrial applications [5].…”

Solvent dependent ordering of poly(3-dodecylthiophene) in thin films

“…[38][39][40][41][42] In short, Si substrates (of size about 15 Â 15 mm 2 ) were first sonicated in acetone and ethanol solutions to remove organic contaminants and subsequently etched with hydrogen fluoride [HF, Merck, 10%] solution for 60 s at room temperature (25 1C) to terminate the Si surface with H after removing the native oxide layer. Chloroform (CF, CHCl 3 ) and toluene (TL, C 7 H 8 ) were obtained from Merck and chlorobenzene (CB, C 6 H 5 Cl) was obtained from Sigma-Aldrich.…”

“…9,40,42,43 VXRD consists of a diffractometer (D8 Discover, Bruker AXS) with a Cu source (sealed tube) followed by a Göbel mirror to select and enhance Cu Ka radiation (l = 1.54 Å). 9,40,42,43 VXRD consists of a diffractometer (D8 Discover, Bruker AXS) with a Cu source (sealed tube) followed by a Göbel mirror to select and enhance Cu Ka radiation (l = 1.54 Å).…”

“…10. 34,[38][39][40][41][42] It is clear that such surface free energy or the potential energy landscape of the substrate surface, which is generally known to control the substrate-polymer interactions, 13,14 is necessarily modified differently depending upon the solvent environment. Such differences is generally related to diffusion, adsorption and pinning effects.…”

Tuning the Properties of Periodic Mesoporous Organosilica Films for Low‐k Application by Gemini Surfactants

“…Figure shows the scattering pattern observed for the Gemini‐templated PMO. The deduced pore organization is a distorted p6 m which has been shown to correspond better to a c2 mm space group . The distortion is the result of a uniaxial shrinkage normal to the stiff Si substrate.…”