2, Charles University, Prague, , Czechia
Polymer nanoparticles (NPs) can offer numerous advantages in the field of photonics, water purification, nanomedicine and many others. Performance of polymer NPs strongly depends on their size, shape, architecture, physical and chemical properties; these should be tailor-made to meet the requirements of specific applications. In certain cases, such as drug delivery and imaging technology, polymer NPs need to be functionalized with chemical groups to achieve coupling of drugs or contrast agents to the NP surface. Carboxyl groups are known to be of particular importance in biomedicine since they may participate in covalent coupling with the terminal primary amines of peptides or proteins via a dehydration reaction.
In this work, we utilized a gas aggregation cluster source (GAS) for the synthesis of COOH-functionalized NPs by plasma polymerization of acrylic acid. Vapors of acrylic acid mixed with argon were supplied into the GAS and an rf discharge was ignited both in a continuous wave and in a pulsed mode to trigger the formation of the plasma polymer NPs. Depending on the effective power delivered to the discharge, spherical NPs were obtained with the size ranging from 15 nm to 100 nm, higher power resulting in higher fluxes of smaller NPs. In the CW mode, 10% retention of the COOH groups was detected by XPS which was constant regardless the discharge power applied. By contrast, the pulsed mode allowed tuning of the carboxyl concentration from 1 to 16% by decreasing the power at constant duty cycle. Duty cycle itself was found to be a powerful parameter to control the size, the flux and the chemical composition of the NPs at constant effective power. The plasma polymerization mechanism was found to be contributed by the radical recombination as well as by reactions of intact acrylic acid molecules with unquenched radicals.
This work was supported by the grant GACR 17-12994S from the Grant Agency of the Czech Republic.