Plasma surface modifications

Purpose

This is a service within the test bed “Surface analysis and Surface design” at RISE

Advantages

Plasma surface modifications have several important advantages compared with traditional wet chemical methods. Only the uttermost part of the surface is treated/coated without affecting the bulk properties of the treated material and extremely small amounts of chemicals are required. This leads to reduced need for chemicals, reduced impact on environment, improved work environment and lowered production costs.

What is plasma?

Plasma is referred to the fourth state of matter, ionized gas. It consists of electrons, ions, free radicals, various neutral molecules and photons. Low temperature plasmas can be created in several ways, but the most common way is the creation of a glow discharge by electric breakdown of gases. A low temperature plasma process, also referred to as cold plasma or glow discharge plasma, is in general a vacuum process which utilizes interactions of reactive species created in a low temperature plasma with solid surfaces. The interactions have unique features for surface modification of solids. The plasma processes are sometimes classified into Plasma Treatment (or plasma activation) and Plasma Polymerization (or plasma film deposition), depending on what type of gas or vapor is used and whether the interactions end up with deposition of a thin film or not.

Depending on choice of process gas or monomer (precursor), plasma surface modifications have found several different functions and applications. Some examples:

• Cleaning of surfaces. Plasma cleaning means that organic contaminants are removed through a chemical reaction or physical ablation of hydrocarbons on treated surfaces. Chemically reactive process gases (e.g. oxygen or air) react with monolayers of hydrocarbons and form carbon dioxide and water vapor which are removed from the reactor via the vacuum exhaust. All solid surfaces can be cleaned in this way.

• Improved wetting and adhesion. using for instance oxygen, air or vinyl-, acrylic- or allyl-based monomers containing either carboxylic (COOH), amino (-NH₂) or hydroxyl (-OH) functionality. Proper choice of these functional groups allows them to react with both substrate and coating with formation of covalent bonds, which is important for adhesion since it is expected that covalent bonding produces more powerful and highly durable adhesion, for instance between the substrate and paints, lacquers and/or adhesives. Another example is plasma activation of the current collector in a battery cell for improved adhesion to the catode and anode, and modification of the separator for improved wettability of the electrolyte.

• Improved water- and oil repellent properties. Hydrophobic and oleophobic surfaces are obtained by plasma polymerization of organosilicon-, hydrocarbon-, fluorocarbon-based precursors. This results in silicone-, polyolefin- and Teflon-like coatings which can be deposited on any solid surface. If these coatings are combined with a suitable micro/nano surface structure, even superhydrophobic and superoleophobic surfaces can be obtained.

• Improved gas diffusion barrier coatings. Oxygen (O₂TR) and water vapor transmission rates (WVTR) through various polymeric packaging materials, films as well as containers, can be significantly reduced by plasma deposition of ultra-thin, glass-like SiO_x coatings (from a mixture of hexamethyldisiloxane (HMDSO) (or similar organosilicons) and oxygen). Similar barrier improvements can also be achieved by deposition of hydrocarbon-rich coatings from acetylene or methane/helium mixtures.

• Improved corrosion protection. Corrosion-resistant coatings can be obtained on metal substrates by plasma deposition of hydrophobic coatings (e.g. HMDSO) with a high degree of crosslinking.

• Improved biocompatibility. Poly(ethylene oxide) (PEO), also known as poly(ethylene glycol) (PEG), is one of the most common surface coating in the biomedical materials field used to render a material resistant against protein fouling. PEG-like films have been developed through the use of plasma polymerization of monomers containing ethylene oxide units, typically glycol diethers, which are also commonly known as the ‘glyme’ family of monomers

Method

At RISE we work closely with our customers in research projects or in direct assignments. We usually use plasma surface modifications to:

• clean surfaces
• functionalize surfaces, i.e. to introduce specific chemically functional groups for various applications
• Increase the adhesion and be able to paint, lacquer and/or glue materials which otherwise would have been impossible, and to enable the use of more types of waterborne adhesives and lacquers for a given substrate
• Prepare water- and oil-repellent surfaces, e.g. for preventing ice accretion or dirt pickup
• Apply gas diffusion barrier coatings on various packaging materials
• Activation of the current collectors in a battery cell for improved adhesion to the catode and anode
• Functionalization of the separator in a battery cell for improved wetting of the electrolyte

Deliveries

What we can do for you

We at RISE can help you to evaluate different types of plasma surface modifications for your own applications. Our plasma lab contains several different types of plasma reactors, both for treatment/coating in vacuum and at ambient pressure. Our laboratory resources are at your disposal and we perform treatments/coatings, testing, verification, research and development. In addition, we also have access to a large instrument park with several advanced surface analytical instruments to characterize the modified surfaces and confirm the surface modification has given the desired result. The customer will receive a written report upon completed work.