PE material will not have C=O and O-H functional groups. After treating with air plasma, you will see new peaks at around 1650 cm-1 and 3550 cm-1 respectively for new formed C=O and O-H functional groups.

Polyester bulk material will have C=O group in it. Surface of polyester material, which is exposed to open air, will have  C=O and O-H functional groups already. When this surface is treated with plasma in air, there is possibly difference in the intensity of these peaks compared to untreated, but there will not be any new peaks.

it could be a sensitivity issue. where in one case you have enough of the bonds you are looking for (good bond density and layer thick enough) while in the other case there are not enough of them (layer too thin, density of bonds too low for detection)

The problem could be related with different issues such as the thickness of the fabric, extent of the treatment inside the fibers, conformational ageing of the plasma formed oxygen species on the fabric surface, ATR low energy sensitivity, etc.

It is important remember that the ATR-FTIR analysis due to its high penetration depth (up to 1µm) could not "see" groups only formed in the plasma treated fabric surface.

A more sensitive analysis should be performed by X-Ray photoelectron spectroscopy (XPS) that have an average penetration depth of only 5 nm.

Which ATR-FTIR accessory do you apply ?

The Golden Gate accessory of Specac (Diamond, one reflection, pressure onto sample control ?)

Best regards,

Martin Müller

plasma treatment cleans your surface that's mean you remove organic residuals from the surface and may be also some functional groups.

Hello Purvi,

Attached a complete thesis file which will be surely of help to your work. Best wishes.

The sensitivity issue is enhanced with fabrics due to  their high porosity ( more than 60%)- this means that more of 60% of IR rays are "lost" in the fabric.-

Moreover the curvature of the fibres reflect the IR rays in all the directions

PE material will not have C=O and O-H functional groups. After treating with air plasma, you will see new peaks at around 1650 cm-1 and 3550 cm-1 respectively for new formed C=O and O-H functional groups.

Polyester bulk material will have C=O group in it. Surface of polyester material, which is exposed to open air, will have  C=O and O-H functional groups already. When this surface is treated with plasma in air, there is possibly difference in the intensity of these peaks compared to untreated, but there will not be any new peaks.

• If we give air plasma treatment to PET / polyester fabric and film both, plasma induced surface modification on both the surfaces should be same or different ?
• If in the case of fabric, due to porosity IR technique becomes less sensitive, results on film samples shall be considered or not?

Thanks to all of you in advance ....

 I think Ramasamy and Thierry will be right. It is an sensitivity issue due to Carbonyl and hydroxyl functions.

Be sure that your probe is really pressed onto the measuring crystal, porous sample often give bad signals due to the penetration depth of the evancescent wave (about 500 nm at 3500cm and Diamond Crystal).

two more ideas:

1) Enhance Signal to noise Ratio by adding more scans, so contour deviations of the carbonyl band will be seen clearer

2) Dry reference and treated sample and measure immediately (and flush your chamber with Nitrogen, do not breath on the sample during preparation). Even if the treated sample will be aged, the OH-Region (3400) will be not disturbed by water films adsorbed

There are two main reasons - overlapping differenc C=O bands ans sensitivity (as Ramasamy and Thierry said). Irradiation penetration depth under ATR-FTIR analysis of most polymer materials is reaches 2-3 micrometers, whereas modification by plasma allows to transform only few nm (PET is quite stable under variety of modification approaches). So, content of non-ester C=O functions is relatively low. Additionally, intensity of ester C=O stretching vibration band is very high and easily overlapped with plasma-initiated C=O band (i am not sure that multiple scanning will have a success). And I have no recommend to detect small concentration of OH groups by FTIR because in most cases it is impossible. 

But I have recomendation to measure contact angle before and after treatment. Changes within few degrees will be qualitative parameter that modification is carried out appropriately. Good luck!

I would suggest you to try XPS. Since certain groups cannot be detected by FTIR.

Yes I have measured contact angle before and after plasma treatment and shows significant improvement in hydrophilicity after plasma treatment. That is why wondering why there is no change in FTIR spectra !! Thank you Alexander.

Thank you Akshath ..

The problem with IR measurements is that the information depth of the IR is much higher compared to the modification depth of the plasma, thus resulting in a low detection sensitivity. As Akshath suggests, I would suggest XPS.

Also according to our experience XPS is the method of choice for detection of changes in the chemical composition of plasma-treated textile surfaces.

Wettability strongly depends on the outermost surface layer, with FT-IR you have a higher information depth in the range of µm. This might explain the observed "differences" after corresponding testing.

I suffer the same problem but with oxygen plasma treatment of parylene C. no differences in the FTIR spectra even after long exposure to plasma. I used XPS to identify the possible groups and LDI-MS.

Dear Madam,

As said by Alexander, Ramasamy and Thierry, the main reason why functional groups is not visible after plasma treatment is overlapping of ester C=O stretching bands with that of stretching of C=O of plasma generated of COOH and COO- groups. If you compare spectra of untreated and plasma treated (with oxidizing plasma of air, oxygen) polyester fabric you may observe slight increase in intensity between 1730 to 1750cm-1. This is due to C=O stretching of plasma generated COOH groups. According to literature there is slight difference in position of C=O stretching band of ester (at 1720 cm-1) and carboxyl groups (at 1750 cm-1). I observed this repeatedly in case of polyester fabric treated with air DBD while in case polyester fabric treated with ammonia no such increase in intensity is observed. If you take difference spectrum of plasma treated with untreated on you might observe shift in intensity towards the 1750cm-1 or separate peak at 1730-1750 cm-1 due to C=O stretching of plasma generated COOH groups. Also make sure that spectrum for plasma treated fabric is taken immediately ageing is very fast during first hour. Please let me know if there is any update in this topic.