Thickness-Dependent Swelling Behavior of Vapor-Deposited Smart Polymer Thin Films

In this contribution, the temperature-dependent swelling behavior of vapor-deposited smart polymer thin films is shown to depend on cross-linking and deposited film thickness. Smart polymers find application in sensor and actuator setups and are mostly fabricated on delicate substrates with complex nanostructures that need to be conformally coated. As initiated chemical vapor deposition (iCVD) meets these specific requirements, the present work concentrates on temperature-dependent swelling behavior of iCVD poly­(<i>N</i>-isopropylacrylamide) thin films. The transition between swollen and shrunken state and the corresponding lower critical solution temperature (LCST) was investigated by spectroscopic ellipsometry in water. The films’ density in the dry state evaluated from X-ray reflectivity could be successfully correlated to the position of the LCST in water and was found to vary between 1.1 and 1.3 g/cm³ in the thickness range 30–330 nm. This work emphasizes the importance of insights in both the deposition process and mechanisms during swelling of smart polymeric structures

Thickness-Dependent Swelling Behavior of Vapor-Deposited Hydrogel Thin Films

Hydrogel thin films containing temperature sensitive chemical functionalities (such as N-isopropylacrylamide, NIPAAm) are particularly interesting for sensor and actuator setups. Complex 3D structures can be conformally coated by the solvent free technique initiated Chemical Vapor Deposition, with precise control over chemical composition and film thickness. In this study, NIPAAm-based thin films with film thicknesses ranging from tens to several hundreds of nanometers and with different amounts of cross-linking were deposited. Above the lower critical solution temperature (LCST), these films repel out water and hence shrink. The amount of cross-linking and the deposited film thickness were successfully identified to both affect shape and position of the LCST transition of these systems: a promising basis for tuning response properties

Growth Regimes of Poly(perfluorodecyl acrylate) Thin Films by Initiated Chemical Vapor Deposition

Control over thin film growth (e.g., crystallographic orientation and morphology) is of high technological interest as it affects several physicochemical material properties, such as chemical affinity, mechanical stability, and surface morphology. The effect of process parameters on the molecular organization of perfluorinated polymers deposited via initiated chemical vapor deposition (iCVD) has been previously reported. We showed that the tendency of poly­(1<i>H</i>,1<i>H</i>,2<i>H</i>,2<i>H</i>-perfluorodecyl acrylate) (pPFDA) to organize in an ordered lamellar structure is a function of the filament and substrate temperatures adopted during the iCVD process. In this contribution, a more thorough investigation of the effect of such parameters is presented, using synchrotron radiation grazing incidence and specular X-ray diffraction (GIXD and XRD) and atomic force microscopy (AFM). The parameters influencing the amorphization, mosaicity, and preferential orientation are addressed. Different growth regimes were witnessed, characterized by a different surface structuring and by the presence of particular crystallographic textures. The combination of morphological and crystallographic analyses allowed the identification of pPFDA growth possibilities between island or columnar growth