When is the best time in determining the surface chemistry of a material after plasma treatment?
Just right after the treatment or 1 day after, etc.? Does ageing affect the surface chemistry of a material like a polymer?
The best time to characterize the nature (surface chemistry and topography) of a surface is immediately before you will use it in a processing step. For example, suppose you have plasma treated a surface. Suppose that you will store that surface for three days in a dry nitrogen container before you use it in the next step (coating it with a protein or polymer or ...). You should characterize a comparable surface at the same time you are coating a second one.
Alternatively, you _could_ make an entire publication about the changes in the nature of a surface after various treatments. In this case, how often you characterize the surface is almost entirely up to you.
Yes ... almost any surface will change when pulled from one environment (plasma treatment) to another (air exposure or storage or ...).
I fully agree with Jeffrey.
In general I would suggest not to plasma-treat surfaces ages before performing surface analysis and further processing. Alteration during storage not only depends on storing environment, but also on chemical nature of surface treated material. For example for polymers factors influencing chain mobility significantly influence alteration behaviour. E.g. plasma-induced effects on polymers with high degree of crystallinity or higher glass transition temperature are less sensitive towards alteration. So is the hydrophobic recovery of a plasma oxidised PDMS (TG: -120 °C) significantly faster than that of a correspondingly treated PTFE (TG: 120 °C). To stabilise e.g. oxidised PDMS you need very low storage temperatures (significantly below TG) or storage in water (water storage may also influence your surface).
Our experience showed that surface analysis and further processing should be performed immediately after treatment (within 1 h).
Its up to you. Just make sure that plasma treated films are stored properly.
It depends on the aim of your experiments. Normally, the best time is just before you start your next process.
It is all about timing. When will you use your sample? You can have a perfectly clean piece of silicon for example on day 0 with a contact angle of zero degrees for water, then seal in up in a dust proof container then come back in 3 months and the contact angle will be 45-60 degrees.
totally agree with Jeffrey and Helga... nicely explained... I personally do the plasma treatment and within an hour further process it... in my case, adhesive bonding...
I agree with the previous answers. In case of polymers, surface analysis should be done immediately after plasma surface modification. For better understanding of the surface reactions, aging study may be carried out.
I have seen changes in FTIR spectrum and contact angle measurements of plasma processed PE film, with time.
Plasma treatment of polymers generally graft chemical functionalities to polymer surface. This means that often the functionalities increase the polarity of the polymer. In other words the polymer increases adhesion to other materials and becomes more wettable (more hydrophilic). Often however the hydrophilicity changes with time and the material shows an increase of water contact angle (i.e. mecomes more hydrophobic). This phenomenon is called HYDROPHOBIC RECOVERY. There are some tricks to reduce the hydrophobi recovery, e.g. my making a pre-treatment which increases the cross-linking of the polymer.
From what said above it is clear that the surface composition can change with time (rotation of the functional groups). The answer to the question is:
1- if the treated material is stable after plasma treatment (no hydrophobic recovery) the composition will remain constant (no ageing)
2- if wettability is changing with time just wait until the variation eneds. The composition at this point is the one you look for.
Right away is the best. You may study the surface changes due to aging by characterizing the surfaces immediately as well as a function of time after treatment. Surface does change, surface energy changes, and therefore, doing the treatment right before use is strongly recommended.
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