With the advances in science and engineering in the second part of the 20th century, emerging plasma-based technologies continuously find increasing applications in the domain of polymer chemistry, among others. Plasma technologies are predominantly used in two different ways: for the treatment of polymer substrates by a reactive or inert gas aiming at a specific surface functionalization or for the synthesis of a plasma polymer with a unique set of properties from an organic or mixed organic-inorganic precursor. Plasma polymer films (PPFs), often deposited by plasma-enhanced chemical vapor deposition (PECVD), currently attract a great deal of attention. Such films are widely used in various fields for the coating of solid substrates, including membranes, semiconductors, metals, textiles, and polymers, because of a combination of interesting properties such as excellent adhesion, highly cross-linked structures, and the possibility of tuning properties by simply varying the precursor and/or the synthesis parameters. Among the many appealing features of plasma-synthesized and -treated polymers, a highly reactive surface, rich in free radicals arising from deposition/treatment specifics, offers a particular advantage. When handled carefully, these reactive free radicals open doors to the controllable surface functionalization of materials without affecting their bulk properties. The goal of this review is to illustrate the increasing application of plasma-based technologies for tuning the surface properties of polymers, principally through free-radical chemistry.

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In recent years, shape-memory polymers (SMPs) have gained a key position in the realm of actuating applications from daily life products to biomedical and aeronautic devices. Most of these SMPs rely mainly on shape changes upon direct heat exposure or after stimulus conversion (e.g., magnetic field and light) to heat, but this concept remains significantly limited when both remote control and fine actuation are demanded. In the present study, we propose to design plasmonic silver nanoparticles (AgNPs) grafted onto cellulose nanocrystals (CNCs) as an efficient plasmonic system for fast and remote actuation. Such CNC- g-AgNPs "nanorod-like" structures thereby allowed for a long-distance and strong coupling plasmonic effect between the AgNPs along the CNC axis, thus ensuring a fast photothermal shape-recovery effect upon IR light illumination. To demonstrate the fast and remote actuation promoted by these structures, we incorporated them at low loading (1 wt %) into poly(ε-caprolactone) (PCL)-based networks with shape-memory properties. These polymer matrix networks were practically designed from biocompatible PCL oligomers end-functionalized with maleimide and furan moieties in the melt on the basis of thermoreversible Diels-Alder reactions. The as-produced materials could find application in the realm of soft robotics for remote object transportation or as smart biomaterials such as self-tightening knots with antibacterial properties related to the presence of the AgNPs.

Plasma-polymerized films (PPF) synthesized by plasma-enhanced chemical vapor deposition (PECVD) find increasing applications in biomedicine and differ in many ways from conventional polymers. One of the most specific properties of the PPF is the high reactivity of its free-radical-rich surface, arising from the deposition mechanism. Although generally considered as a disadvantage leading to the aging of the PPF, reactivity of the plasma-treated polymers and PPF surfaces can be beneficially employed, for example, for grafting of a specific chemical functionality or short polymer chains. The quantitative evaluation of the surface radical density of the PPF is thus considered as the necessary preparatory step toward any subsequent grafting reaction. In the present study, the surface radical density of an isopropanol-based PPF was quantitatively determined by a combination of NO chemical derivatization and X-ray photoelectron spectroscopy (XPS). Once the derivatization conditions were optimized, the radical density, derived from at % N determined by XPS, was evaluated as a function of the deposition power. It was found out that the surface density of free radicals presents a maximum for the deposition power of 200 W (~2.3 × 10(14) spin/cm(2)) and it stabilizes (~2.1 × 10(14) spin/cm(2)) with further power increase. XPS findings were supported by in situ FTIR measurements that provided additional information about the degree of plasma fragmentation denoting fragmentation saturation for a deposition power of 200 W. By fitting the N1s peak it was possible to identify primary, secondary and ternary radicals and to study their respective evolutions with different deposition conditions. Angle-resolved XPS analysis allowed the in-depth distribution of radicals to be addressed, revealing that on the top surface, primary, and secondary radicals are dominating, whereas more tertiary radicals are present in the subsurface region. Finally, some preliminary chemical grafting experiments have allowed the relevance of derivatization results to be cross-checked.