surface free energy (sv) values via Youngfs (Eq. (1)) and Neumann[34] (Eq. (2)) equations, respectively.
WA =lv(1 + cos ) (1)
WA =2(lvsv)1/2 exp[..(lv .sv)2] (2)
where lv and sv are the surface tension of water (lv= 72.8 mJ/m2)and surface free energy of the film, respectively. is water contact angle and the value of . is equated to 0.0001247 } 0.000010(mJ/m2).2. To calculate surface free energy, the work of adhesion(WA) was first calculated according to Eq. (1) (Young equation).The surface free energy (sv) was then calculated by Eq. (2). There sults obtained are presented in Table 3.
Water contact angle and surface free energy values of 90.3.and 28.7 mJ/m2, respectively were measured on the degreased aluminium sample. This is an indicative of low hydrophilicity of degreased aluminum sample due to the presence of aluminum oxide layer on its surface. This means that this substrate shows poor wettability for the organic coating. It can be seen that the contact angle of water was significantly reduced after surface preparation process. Consequently, the work of adhesion and surface free energy were increased after this process. This can be attributed to the increase of surface roughness and also the aluminium oxide layer removal from the aluminium surface after chemical etching process. This finding reveals that the chemical etching of the
Table 3
Contact angle (CA), surface free energy (sv) and work of adhesion (WA) values
obtained from contact angle measurements for different samples.
WA (mJ) sv (mJ/m2) CA (.) Sample
72.4 28.7 90.3
}
2 Degreased Al
80.9 32.9 83.6
}
1 Surface prepared Al
83.0 34 81.9
}
0.5 Zr treated Al
surface free energy (sv) values via Youngfs (Eq. (1)) and Neumann[34] (Eq. (2)) equations, respectively.WA =lv(1 + cos ) (1)WA =2(lvsv)1/2 exp[..(lv .sv)2] (2)where lv and sv are the surface tension of water (lv= 72.8 mJ/m2)and surface free energy of the film, respectively. is water contact angle and the value of . is equated to 0.0001247 } 0.000010(mJ/m2).2. To calculate surface free energy, the work of adhesion(WA) was first calculated according to Eq. (1) (Young equation).The surface free energy (sv) was then calculated by Eq. (2). There sults obtained are presented in Table 3.Water contact angle and surface free energy values of 90.3.and 28.7 mJ/m2, respectively were measured on the degreased aluminium sample. This is an indicative of low hydrophilicity of degreased aluminum sample due to the presence of aluminum oxide layer on its surface. This means that this substrate shows poor wettability for the organic coating. It can be seen that the contact angle of water was significantly reduced after surface preparation process. Consequently, the work of adhesion and surface free energy were increased after this process. This can be attributed to the increase of surface roughness and also the aluminium oxide layer removal from the aluminium surface after chemical etching process. This finding reveals that the chemical etching of theTable 3Contact angle (CA), surface free energy (sv) and work of adhesion (WA) valuesobtained from contact angle measurements for different samples.
WA (mJ) sv (mJ/m2) CA (.) Sample
72.4 28.7 90.3
}
2 Degreased Al
80.9 32.9 83.6
}
1 Surface prepared Al
83.0 34 81.9
}
0.5 Zr treated Al
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