Spin-coating deposition of thermoresponsive microgel thin films

Smart surfaces and surface coatings have been attracting increasing interest in the last decades. In particular, thin films assembled from microgels offer good control of morphology, elasticity and hydrophobicity thanks to the high tunability of microgel mechanical properties and chemical composition. Among smart microgels, Poly(N-isopropylacrylamide) (PNIPAM) based microgels are the most used systems for theoretical and experimental studies and for nanotechnological applications. When used as building blocks to fabricate 2D assemblies, they exhibit new properties offering many advantages for additional applications in different fields. Here we report a systematic investigation of aqueous suspensions of soft PNIPAM microgels through Dynamic Light Scattering (DLS), Small Angle X-ray Scattering (SAXS) and rheometry. Starting from these suspensions, optical and morphological properties of PNIPAM microgel thin films deposited by spin-coating on a glass substrate at different weight concentrations and deposition conditions are investigated through UV-Vis-NIR spectroscopy and Atomic Force Microscopy (AFM). Homogeneous and smooth thin films of soft PNIPAM microgels were obtained with high transparency in the whole wavelength range from the visible to the near-infrared region. Moreover, their optical properties were correlated to microgel arrangement at the solid surface that can be opportunely tuned by changing the spin-coating deposition parameters.