Solid, liquid and gas are the three states of matter we are all familiar with. We can move between the states by adding or removing energy (e.g. heating/cooling). If we continue to add enough energy (for a plasma, we add electrical energy), gas molecules will become ionised (lose one or more electrons) and so carry a net positive charge. If enough molecules are ionised to effect the overall electrical characteristics of the gas the result is called a plasma. Plasmas are therefore, quite rightly, often referred to as the fourth state of matter.
A plasma contains positive ions, electrons, neutral gas atoms or molecules, UV light and also excited gas atoms and molecules, which can carry a large amount of internal energy (plasmas glow because light is emitted as these excited neutral particles relax to a lower energy state). All of these species can and do interact with any surface placed in contact with the plasma. By choosing the gas mixture, power and other conditions we can quite precisely tune, or specify, the effects of the plasma upon the surface.
Plasma treatment modifies the surface of an object. It doesn’t affect the object in any other way and doesn’t change the bulk of the material at all. We can ‘tune’ the plasma to change the adhesion characteristics of the surface. We can make the surface easier to bond, print, glue etc. We can also introduce a range of other surface properties such as liquid repellency or low friction.
The plasma creates reactive molecules, electrons, ions and UV light. These interact in various ways with a surface. Organic contamination, in the form of long chain hydrocarbons, can be broken down by the plasma and removed from the surface, leaving an ultra-clean surface. On polymers, the plasma also breaks surface bonds, and then terminates these bonds with oxygen containing polar molecules, greatly improving the adhesion characteristics of the material by improving its wettability.
The 4 major effects of plasma are;
- Surface cleaning: removal of hydrocarbons which impede adhesion
- Micro-sandblasting: which increases the surface area and therefore wettability
- Cross-linking or branching of surface molecules: which impedes the migration of waxy additives from the bulk material to the surface
- Modification of surface chemical structure: to increase the surface energy and render a surface wettable and also to impart other specific functionality such as liquid repellency
Nearly all materials can benefit from plasma treatment. Metals, glass and ceramics can all be rendered ultra-clean. Polymers and rubbers can all be made easier to glue, print, paint and bond and the final mechanical bond strength is usually greatly enhanced. We can also treat powders, textiles, fabrics, and composite materials.
- engineering polymers
- optics & lenses
- medical devices
Yes. Our type of plasma is often referred to as ‘cold plasma’ and should not be compared to e.g plasma cutting torches, which are a very different form of plasma. There is very little heat transfer to an object during processing.
This really depends on the part but in general can be anywhere from 20 seconds to just a few minutes for activation to improve bonding. Removal of organic contamination can take a little longer depending on the degree of contamination.
This depends on the material and subsequent handling and storage. It can be from minutes for glass, and metals to many months for e.g. polypropylene. It is always better to print, paint, glue etc. as soon as possible following plasma treatment but the ‘relaxation’ of the surface is asymptotic and even after days the surface is often much more active compared with an un-treated surface.
The reason for material dependency is that most commercial polymers contain additives such as anti-oxidants, mould release agents and anti-block agents, which are oily or wax-like. These are incorporated to improve manufacturability and are designed to migrate to the surface.
Plasma modified surfaces form a covalent bond with many adhesives. The resulting bonding enhancement can range from a 2-fold to a 10-fold improvement in lap-shear strength and peel-strength. Some materials can even be bonded in the absence of adhesive, such as PDMS to glass, of particular importance in the production of microfluidic devices.
We supply plasma treatment equipment ranging in size from small bench-top machines no larger than a domestic microwave oven to thousands of litres in volume for large industrial applications.
Absolutely. The plasma is a gas phase process and the plasma will usually get everywhere that a gas can get. There is a restriction for treating the inner diameter of long thin tubes where typically the plasma effects are less when the tube length > x10 diameter.