We report for the first time the formation of spherical and branched structures when polymerizing maleic anhydride under very low power with pulsed plasma polymerization. A factorial experimental design evidenced duty cycle, frequency and their interactions as decisive factors for the formation and growth of these structures. A mechanism involving the decoupling of deposition (nucleation) and diffusion rates of active species was proposed to relate structure formation to processing parameters. While differences in surface chemistry were not detectable by surface spectroscopy (PM‐IRRAS, XPS), AFM force measurements on a carefully designed sample evidenced differences in adhesion and thus surface chemistry between the different film morphologies.
The understanding concerning structure formation during maleic anhydride plasma polymerization is focused based on growth kinetics study and chemical force titration through atomic force microscopy. Growth kinetics suggested that beads were formed initially and acted as intermediate for the random formation of needle-like and branched structures. The structures surface area followed a linear trend, except for the beads surface area that levels-off. Chemical force titration revealed that all the samples exhibited two pK a values, but the shifting of the values and the different trends indicated differences in the global chemistry of the films, associated to the presence of the structures.
Recently, it was shown that the microstructure of a maleic anhydride plasma polymer (MAPP) could be tailored ab initio by adjusting the plasma process parameters. In this work, we aim to investigate the ability of cellulose nanocrystals (CNCs) to induce topographical structuration. Thus, a new approach was designed based on the deposition of MAPP on CNCs model surfaces. The nanocellulosic surfaces were produced by spin-coating the CNC suspension on a silicon wafer substrate and on a hydrophobic silicon wafer substrate patterned with circular hydrophilic microsized domains (diameter of 86.9 ± 4.9 μm), resulting in different degrees of CNC aggregation. By depositing the MAPP over these surfaces, it was possible to observe that the surface fraction of nanostructures increased from 20% to 35%. This observation suggests that CNCs can act as nucleation points resulting in more structures, although a critical density of the CNCs is required.
Previous work revealed the possibility of controlling the nanostructuration of maleic anhydride plasma polymer (MAPP) by adjusting the plasma process parameters or adding cellulose nanocrystals (CNCs) previously on the substrate. This work aimed to evaluate the stability of MAPP coating to water drop evaporation. The evaporation process was followed by optical microscopy and the effects of substrate surface chemistry and presence of CNCs were investigated. The presence of CNCs affected not only the MAPP adhesion under wet condition, leading to an impressive morphological reconstruction of MAPP coating, but also the evaporation kinetics. Therefore, this work exhibits a simple way to obtain functional surface patterns by changing the coating wet adhesion and opens new opportunities for the utilization of CNCs.
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