Use of Humidity Controlled Quartz Crystal Microbalance with Simultaneous Grazing Incidence Small Angle X-ray Scattering to Investigate the Self-assembly and Energetics of Lipid Thin Films

We present a novel method of analyzing lyotropic liquid crystal mesophases─self-organized amphiphile-water nanomaterials─using <i>in situ</i> grazing-incidence small-angle X-ray scattering (GI-SAXS) on a quartz crystal microbalance (QCM) in a controlled humidity environment. This combination simultaneously gives nanostructural dimensions and phase symmetry (through SAXS), compositional data (% water by weight, from QCM data), and water activity within the sample (from the equilibrium relative humidity above the film), as the sample film takes up and releases water during humidity sweeps. Analysis of the combined data provides immediate access to information typically built up from experiments on multiple individual samples prepared at different fixed compositions. Our approach greatly reduces the required sample quantities and preparation time while avoiding issues with sample-to-sample variations thanks to the collection of the multiple parameters simultaneously. It also extends the accessible range to the low water content region of the phase diagram, which is harder to access by fixed composition measurements and is highly relevant to coatings and powders exposed to ambient humidities. Here, we present data on dimyristoylphosphatidylcholine/water lamellar phases. Our calculated bilayer thickness and interbilayer repulsion values show good agreement with published data obtained from multiple individual samples, and we clearly demonstrate the ability to extend to lower water contents.