In Situ X-ray Scattering Studies of Protein Solution Droplets Drying on Micro- and Nanopatterned Superhydrophobic PMMA Surfaces

Superhydrophobic poly(methyl methacrylate) surfaces with contact angles of similar to 170 degrees and high optical and X-ray transparencies have been fabricated through the use of optical lithography and plasma etching The surfaces contain either a microscale pattern of micropillars or a random nanofibrillar pattern Nanoscale aspen ties on top of the micropillars closely resemble Nelumbo nucifera lotus leafs The evolution of the contact angle of water and lysozyme solution droplets during evaporation was studied on the micro- and nanopatterned surfaces, showing in particular contact-line pinning for the protein solution droplet on the nanopatterned surface The microstructural evolution of lysozyme solution droplets was studied on both types of surfaces in situ under nearly contact-free conditions by synchrotron radiation microbeam wide-angle and small-angle X-ray scattering revealing the increasing protein concentration and the onset of precipitation The solid residuals show hollow sphere morphologies Rastermicrodiffraction of the detached residuals suggests about a 1/3 volume fraction of >= 17 nm lysozyme nanocrystalline domains and about a 2/3 short-range-order volume fraction. About 5-fold larger nanocrystalline domains wet e observed at the attachment points of the sphere to the substrates, which is attributed to particle growth in a shear now Such surfaces represent nearly contact-free sample supports for studies of inorganic and organic solution droplets, which find applications in biochips