Abstract
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(1H,1H,2H,2H-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.
Highlights
Fluorine-containing polymers are a subclass of low-surfaceenergy materials which have gained particular attention in materials science due to their intrinsic hydrophobicity as well as peculiar morphology and surface structure.[9−12] Perfluorinated chains inpolymers often result in strongly apolar surfaces with reduced wettability for both water and/or organic molecules, reduced adhesion, and excellent antisticking properties due to the low surface energy and strong chemical inertness.[13]
We studied the effect of initiated chemical vapor deposition (iCVD) process parameters on the degree of crystallinity and crystallographic orientation of pPFDA.[10]
The iCVD technique has been used for the synthesis of pPFDA thin films following the procedure previously reported.[21,30]
Summary
Low-surface-energy compounds are a class of materials showing peculiar physicochemical properties, such as hydrophobicity and oleophobicity, which make them appealing for a wide variety of applications, from bioinspired and biocompatible materials[1−3] to anticorrosion[4,5] and antifouling coatings,[6] self-cleaning surfaces,[7] and permeation membranes.[8]Fluorine-containing polymers are a subclass of low-surfaceenergy materials which have gained particular attention in materials science due to their intrinsic hydrophobicity as well as peculiar morphology and surface structure.[9−12] Perfluorinated chains in (co)polymers often result in strongly apolar surfaces with reduced wettability for both water and/or organic molecules, reduced adhesion, and excellent antisticking properties due to the low surface energy and strong chemical inertness.[13]. The thermal decomposition of the radical initiator (generally a peroxide) occurs in the gas phase and is driven by a filament heated to 200−350 °C, suspended over a temperature-controlled substrate. Temperatures in this range have been demonstrated to affect only the labile peroxide bond of the initiator molecules while leaving the monomer structure intact.[19] The initiator radicals attack the unsaturated bonds of the monomers adsorbed on the substrate (due to their generally low vapor pressure). The advantages of iCVD compared to other vaporbased deposition techniques (e.g., PE-CVD or physical vapor deposition) are the ability to finely control the possible reaction pathways and, most importantly, to fully retain the characteristic functional groups of the monomer
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