An atmospheric pressure non-equilibrium plasma (APNEP) developed
in the UK by EA Technology Ltd is currently being investigated in
collaboration with the University of Surrey. Of the many applications of
surface modification that can be induced using plasmas, adhesion
enhancement is one of the most commercially important. In this paper, we
illustrate the use of an atmospheric plasma to enhance the adhesion
characteristics of low-density polyethylene (LDPE) and poly(ethylene
terephthalate) (PET). The polymers were treated in the remote afterglow
region of an atmospheric pressure plasma to avoid the thermal effects that
can cause degradation for thermally sensitive materials when placed in
direct contact with the plasma. Reactive (oxygen containing) and inert
(oxygen free) atmospheric plasmas rapidly impart adhesion enhancement by a
factor of two to ten as measured by 180° peel tests. However,
extended exposure to the atmospheric plasma does not impart additional
adhesion enhancement as the surface is ablated revealing the underlying
polymer with poor adhesive characteristics. In contrast, vacuum plasma
treated LDPE and PET show increased adhesion with extended plasma
treatment. An adhesion enhancement in excess of two to three orders of
magnitude was found to be achievable for vacuum plasma treatment times
greater than 10 min.
An atmospheric pressure non-equilibrium plasma (APNEP) has been
developed in the UK by EA Technology Ltd and is currently being
investigated in collaboration with the University of Surrey. The main
focus is the use of atmospheric pressure plasmas to modify the surfaces of
commercially important polymers including polyolefins, poly(ethylene
terephthalate) and poly(methyl methacrylate). These surface modifications
include surface cleaning and degreasing, oxidation, reduction, grafting,
cross-linking (carbonization), etching and deposition. When trying to
achieve targeted surface engineering, it is vital to gain an understanding
of the mechanisms that cause these effects, for example, surface
functionalization, adhesion promotion or multi-layer deposition. Hence
comparisons between vacuum plasma treated surfaces have also been sought
with a view to using the extensive vacuum plasma literature to gain
further insight. In this paper, we will introduce the APNEP and compare
the key characteristics of the plasma with those of traditional vacuum
plasma systems before highlighting some of the surface modifications that
can be achieved by using atmospheric plasma. Data from the analysis of
treated polymers (by spectroscopy, microscopy and surface energy studies)
and from direct measurements of the plasma and afterglow will be
presented. Finally, our current understanding of the processes involved
will be given, particularly those that are important in downstream surface
treatments which take place remote from the plasma source.
Small-angle neutron scattering (SANS) has been used to investigate the conformation of linear and cyclic poly(dimethylsiloxane)s (PDMS) in chemically identical, undiluted blends. SANS measurements have been carried out on (1) linear hydrogenous (H) mixed with linear deuterated (D) PDMS and (2) cyclic H mixed with cyclic D PDMS. The conformational behavior of the cyclic and linear polymers is studied over a wide range of molar mass and composition. Isotopic blends of linear PDMS are shown to adopt conformations that agree well with theoretical predictions for Gaussian random-coil polymers and confirm previous SANS studies. As expected for chains obeying Gaussian statistics, the mean radii of gyration, R g, scale with the weight-average molar mass as Rg ∝ Mw 0.5 . A detailed study of H/D cyclic PDMS mixtures is presented, and we demonstrate that, since Rg ∝ Mw 0.4 , highly flexible cyclic polymers in the melt adopt an even more compact conformation than that of unperturbed rings. This behavior confirms previous predictions based on computer simulations and theoretical studies. The results are in excellent agreement with computer simulations and theoretical predictions reported in the literature.
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