How to dip-coat and spin-coat nanoporous double-gyroid silica films with EO19-PO43-EO19 surfactant (Pluronic P84) and know it using a powder X-ray diffractometer

Previously, the synthesis of highly oriented pure double-gyroid nanoporous silica films has been demonstrated using evaporation-induced self-assembly (EISA) and dip-coating with a specialty triblock surfactant (PEO-PPO-alkyl) as the template. For these films, grazing-incidence small-angle X-ray scattering (GISAXS) was used to determine orientation and structure. However, GISAXS is not widely available, and we have observed significant batch-to-batch variability in the PEO-PPO-alkyl surfactants used. Here, we show for the first time: (1) synthesis of highly oriented pure double-gyroid nanoporous silica films using freely available EO(19)-PO(43)-EO(19) surfactant (Pluronic-P84) as the nanostructure-directing agent, (2) the use of spin-coating and dip-coating EISA to fabricate the double-gyroid films, and (3) the use of theta-theta X-ray diffractometers (commonly available and typically used for powder X-ray diffraction, PXRD) to identify the double-gyroid phase. Processing diagrams for P84 using dip-coating and spin-coating are shown in order to map the dependency of the nanostructure on solution composition, relative humidity, and solution aging time. In addition, an effect of the rate of evaporation during EISA is observed via dependence on the angular velocity in spin-coating. Also, through quantitative comparison of the GISAXS patterns with corresponding PXRD patterns, previously unexplained diffraction peaks in the PXRD patterns are shown to result from diffraction from crystallographic planes that are not parallel to the substrate (typically not observed in PXRD) due to the small angles involved and the nonzero acceptance angle of the PXRD Soller slits. These peaks provide a means to distinctly identify the double-gyroid phase using PXRD. The same trends relating aging-time-before-coating to the phase that forms via EISA are observed with EO(19)-PO(43)-EO(19) as was the case in previous studies using EO(17)-PO(14)-C(12). This shows the generality of use of aging time to synthesize nanoporous silica films with nonionic surfactants. Finally, a list of "tips and tricks" is provided to facilitate easy reproducible synthesis of double-gyroid nanoporous silica thin films in other laboratories.