Optimization of Cyclopropylamine Plasma Polymerization toward Enhanced Layer Stability in Contact with Water Anton Manakhov, Lenka Zaj  ı  ckov a,* Marek Eli a s, Jan  Cechal, Josef Pol  c ak, Jaroslav Hnilica,  St ep anka Bittnerov a, David Ne cas The present investigation of cyclopropylamine (CPA) plasma polymerization in pulsed and continuous wave radio frequency (RF) discharges leads to the proposition of conditions at which amine-rich films exhibit a good stability in contact with water. The analyses reveal complex structure of CPA plasma polymers containing hydrocarbon chains, primary and secondary amines, nitriles and possibly imines. The decomposition of the monomer in plasma is progressing with the composite parameter W/F (RF power over monomer flow rate) but, in pulsed discharges, it is possible to deposit the films with N/C ratio above 0.24 using higher monomer flow rate. At the optimized monomer flow rate the 280 nm thick film exhibits only 20% thickness loss after 48 h immersion in water and still contains about 5 at% of the NH x environment. 1. Introduction The deposition of stable amine-rich thin films has attracted attention of numerous researchers due to its great potential applications, such as biomolecule immobilization, [1] micro- filtration membranes, [2] enzyme electrodes, [3] adhesion enhancement, [4] or biosensor development. [5] The simplest technique of amine grafting relies on plasma treatment in nitrogen or ammonia discharges. [6] However, these techniques lead to unstable functionalization of a thin near surface layer with rather short duration. It has been observed that the grafted groups almost disappeared after several days of ageing in air, and the composition of the surface became comparable with the untreated layer. [7] In contrary, the deposition of plasma polymers can enhance the stability of the surface and reduce the aging effect. [1] For many years, allylamine has been the monomer of choice thanks to the presence of vinyl groups that enable free radical polymerization of this amine compound. However, allylamine is a highly toxic flammable chemical compound with a lethal dose LD 50 equal to 35 mg kg 1 . [8] Moreover, the amine-rich plasma polymerized allylamine thin films showed a significant decrease in nitrogen concentration (N/C decreasing from 0.22 to 0.06) [9,10] and film thickness loss up to 90% after the immersion in water. [11] The stability can be improved by an increase of plasma power at the expense of amine concentration in the films. [12] The application of amine-rich thin films for cell adhesion enhancement or biosensing requires high stability of the layer in aqueous media and prevention of trapped toxic molecules. Therefore, substituents of the allylamine Dr. A. Manakhov, Prof. L. Zaj  ı ckov a, Dr. M. Eli a s,  S Bittnerov a, Dr. D. Ne cas Plasma Technologies, CEITEC – Central European Institute of Technology, Masaryk University, Kotl a  rsk a, 2, Brno 61137, Czech Republic E-mail: lenkaz@physics.muni.cz Dr. J.  Cechal, Dr. J. Pol  c ak CEITEC – Central European Institute of Technology, Brno University of Technology, Technick a 3058/10 616 00 Brno, Czech Republic Dr. J. Hnilica Faculty of Science, Department of Physical Electronics, Masaryk University, Kotl a  rsk a 2, Brno 61137, Czech Republic Full Paper Plasma Process. Polym. 2014, 11, 532–544 ß 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim 532 DOI: 10.1002/ppap.201300177 wileyonlinelibrary.com