Evaluation of acid-base properties of ammonia plasma-treated polypropylene by means of XPS |
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Authors: | Noushine Shahidzadeh Mohamed M Chehimi Farzaneh Arefi-Khonsari Jacques Amouroux Michel Delamar |
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Institution: | (1) Laboratoire de Génie des Procédés Plasmas, Ecole Nationale Supérieure de Chimie de Paris, Université Pierre et Marie Curie, 11 rue Pierre et Marie Curie, 75005 Paris, France;(2) associé au CNRS (URA34), Institut de Topologie et de Dynamique des Systèmes de l'Université Denis Diderot. Paris 7, 1 rue Guy de la Brosse, 75005 Paris, France |
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Abstract: | Acid-base properties of ammonia plasma-treated polypropylene (APTPP) were characterized by X-ray photoelectron spectroscopy
(XPS) in conjunction with the molecular probe technique and using chloroform (TCM) as a reference Lewis acid. It is shown
that TCM is retained by the basic surfaces of APTPP but not by the untreated PP. The retention of TCM is shown to be entirely
due to the formation of TCM:APTPP acid-base complexes. This is supported by the C12p3/2 binding energy (BE) and the shape of the Cl2p peak from the adsorbed TCM. ΔHAB, the heat of TCM:APTPP acid-base interaction was found to be in the range of 3.1–4.3 kcal/mol using a published Cl2p3/2 BE−ΔHAB correlation. This ΔHAB compares remarkably well with the values of 4.3–4.9 kcal/mol determined for TCM:amine complexes, and shows indeed that TCM
is complexed by nitrogen containing basic groups grafted at the surface. However, the TCM/N ratio has an optimal value up
to 1 second of plasma treatment and then decreases sharply, showing that less specific interaction sites are accessible at
the surface for longer treatment times. This parallels previous findings about the metallization of APTPP by aluminium which
was found to be optimal for treatment times lower than 1 second in our experimental conditions. This work shows that XPS can
now indeed be used to quantitatively assess the acid-base properties of modified polymer surfaces. |
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Keywords: | Polypropylene ammonia plasma XPS acid-base interactions chloroform molecular probe adhesion |
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