Adhesion-promoting polymer layer

Israelachvili and his colleagues have used the SEA to study the interactions between surface layers of surfactant and of other molecules representing functionalised polymer chains, adhesion promoters or additives. Typically a monolayer of the molecule concerned is deposited onto cleaved mica sheets. The values of surface energies obtained from the JKR equation (Eq. 18) throw some interesting light on the nature and roughness of surface layers in contact. 

The latter thicker adhesion layers are most likely polysiloxane condensation polymer layers. Photoresist adhesion to these layers may be electrostatic in nature, while the adhesion of the promoter layers to the gold substrate may be the result of chemisorption forces between the chelating moieties of the promoter layer and the gold surface atoms. 

THV can be readily bonded to itself and other plastics and elastomers. It does not require surface treatment, such as chemical etch or corona treatment, to attain good adhesion to other polymers, although in some cases tie-layers are necessary. For bonding THV to elastomers an adhesion promoter is compounded to the elastomer substrate.35... 

Applications of these layers as supports for sensor devices and biocompatible materials as well as for adhesion promotion have illustrated the ability of polymer surface chemistry. 

Surface functionalization of PP films in the O2 plasma was performed in the cw mode. PP films which were coated with plasma polymer layers of functional-group carrying monomers had been used without any additional plasma pretreatment. PTFE films were exposed first to H2 radio-frequency (RF) plasma (cw mode) for 1-1800 s at pressure p=6Pa and power P=300W, followed by the deposition of adhesion-promoting plasma polymer layers. 

Deposition of Adhesion-Promoting Plasma Polymer Layers... 

After peeling of Al-polymer systems with adhesion-promoting plasma copolymer layers, the peeled surfaces were inspected again with XPS to determine the locus of failure, i.e., whether the peel front propagated along the interface (interfacial failure) or within the material (cohesive failure). 

By means of OH- and COOH-containing plasma polymer layers the quahfica-tion of these layers as models of single-type functionalized adhesion promoters with variable concentrations of functional groups should be proved. The plasma-initiated copolymerization of acrylic acid with ethylene or 1,3-butadiene is shown in terms of measured COOH concentration as a function of the composition of the comonomer mixture in Fig. 18.3. Depending on the co-monomer reactivity, a more linear correlation (butadiene), or a parabolic behavior (ethylene), between precursor composition and COOH groups produced was observed. For each type and concentration of functional group, its concentration was determined by chemical derivatization followed by XPS analysis as described in Section 18.2.5. 

A few variants for producing well-adhering Al-PTFE systems were tested (a) deposition of plasma polymers bearing a single type of functional group as adhesion promoters on virgin PTFE (b) H2 plasma pretreatment of PTEE followed by deposition of an adhesion-promoting plasma polymer layer and (c) H2 plasma pretreatment of PTFE alone. 

The introduction of oxygen is most likely due to post-plasma reactions of plasma-produced C-radical sites at the PTFE surface by reaction with molecular oxygen when the samples were transferred from the plasma reactor to the XPS spectrometer with transient contact with air [73, 80]. This post-plasma reaction is unavoidable, but in this case it may help to promote the adhesion between the deposited plasma polymer layer and the pretreated PTFE. 

The introduction of an adhesion-promoting pulsed plasma polymer interlayer onto the H2-plasma pretreated (each for 10 s) PTFE substrate improved the peel strength further to a range of 350—400 N m limited by the adhesion of the adhesive (supporting) tape to the evaporated A1 layer. Because of this limitation of the peel test, the measured peel strength is no measure for the difference between OH and COOH groups at the PTFE interface in this case (Fig. 18.9). 

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