Electroless nickel coatings for antibacterial applications

Author

Serra Fernandez, Víctor

Abstract

The final objective of this master's thesis has been the production of an effective electroless nickel biocidal coating by reinforcing the deposits with the addition of polystyrene microparticles containing Triclosan as an antibacterial and antiviral agent. To achieve this final objective, several steps and preliminary tests have been carried out.
This main objective can be structured into specific objectives that are summarized in the following points:

➢ Encapsulation of an antibacterial compound (Triclosan) within polystyrene microparticles during the emulsion polymerization process.
➢ Study the stability of polystyrene and polystyrene-triclosan microparticles within electroless nickel baths.
➢ Codposition of microparticles of pure polystyrene and polystyrene-triclosan within the electroless nickel-phosphorous deposits.
➢ Fully characterize each type of polymer and microparticle deposit.
➢ Develop a proof of concept test with bacteria to demonstrate the efficacy of antibacterial coatings.

To achieve these goals, the first step has been to become familiar with the electroless nickel deposition process from commercial nickel baths from ATOTECH®. The entire process must be carefully studied and understood. An exhaustive characterization of the nickel-phosphorus deposits must be carried out in order to subsequently produce more complex deposits and to understand the possible drawbacks that may arise. Characterization of the deposits will include scanning electron microscope (SEM) images of surface morphology and cross section, elemental analysis with energy dispersive X-ray spectroscopy (EDX), X-ray diffraction crystallographic determination and characterization of the microhardness of the deposits. Once the polystyrene has been successfully polymerized, the next objective will be to produce polystyrene microparticles containing encapsulated triclosan in their structure. The triclosan is dissolved in styrene prior to its incorporation into the emulsion polymerization reactor. Since triclosan is a highly hydrophobic molecule with a coefficient of partition (KOW) of 4.8, it is expected to remain within the monomer droplets during the polymerization reaction rather than mixing with water. The presence of Triclosan within the polystyrene microparticles will be determined by the same techniques as for characterizing the polystyrene with additional elemental analysis by EDX. Upon familiarization with the three different raw materials, electroless nickel composite deposits with embedded polystyrene microparticles will be produced. Since the suspension and dispersion of the polymer particles within the nickel bath is the main challenge, the stability of the baths will be studied using Zeta potentiometry. Different concentrations of a cationic surfactant and an anionic surfactant will be studied within electroless nickel baths in the presence of a constant concentration of polystyrene. The surface morphology and the cross section of the deposits obtained will be analyzed by SEM and the presence of polystyrene confirmed by Raman spectroscopy. In addition, the crystallographic structure and its hardness will be compared to electroless pure nickel-phosphorous deposits.When conditions are met for the incorporation of polymer particles into nickel deposits, electroless nickel deposits will be produced with embedded polystyrene-triclosan particles.
The biocidal properties of the final deposits will be studied in a bacterial growth inhibition test. A culture of bacteria will be inoculated on the surface of the tanks. Its growth to the plateau phase will be compared with control samples of 316 stainless steel and a nickel-phosphorus-polystyrene deposit without Triclosan.

Director

Colominas Guàrdia, Carles

Degree

IQS SE - Master’s Degree in Materials Science and Engineering

Date

2021-07-16