Microfibrous surface

The second category was concerned with adhesion to porous or microfibrous surfaces on metals. Aluminium may be anodised to form an oxide surface comprising pores of diameter of tens of nanometers. Electroforming and chemical oxidation can be used to produce microfibrous or needle-like coatings on metals, including copper, steel and titanium. The substrate topography was demonstrated to play an vital part in adhesion to these surfaces [45-48]. 

Microporous and microfibrous surfaces on metals are increasingly used in biomedical applications. A recent review by Wen et al. [60] identified advantages over metals with smooth surfaces which included early better adhesion of biomolecules and cells and firmer fixation of bone or connective tissue. 

The common feature of microfibrous surfaces is their topography, rather than their chemical nature. It is well known that certain oxidation conditions produce a whisker or blade-like oxide growth on a metal surface, rather than a film of uniform thickness. Similarly, certain conditions of electrodeposition give dendritic crystals of the deposited metal, not a smooth coating. These are ways of preparing microfibrous surfaces. Details of some typical methods are given in Ref. [1]. 

In contrast to polyethylene and EVAs, Epoxide adhesives are thermosets and are much stiffer and less ductile. The adhesion fracture energy (Gc, see Fracture mechanics), between both unmodified and rubber-toughened epoxies (see Toughened adhesives) and several metals has generally been found to be much higher when microfibrous surfaces were involved (Table 2) ... 

It is clear from an investigation of the locus of failure and analysis of the fracture surfaces by X-ray photoelectron spectroscopy that the microfibrous surfaces lead to considerable plastic deformation of the polymer. They appear to increase the adhesion by enhanced energy dissipation during fracture (see Rheological theory. Peel tests). 

Additionally, chemical etching from either acid or alkaline solutions. Conversion coating and Anodizing are all capable of generating highly modified surface structures compared to the untreated case. These processes alter the surface by introducing surface micro-roughness, where features may be present on the nanometre scale and above (see Microfibrous surfaces). 

Qnite apart from any increase in AG resnlting from chemical changes in a surface, AG will be increased as a result of roughening the snrface per se. An atom near an asperity peak or fine fractal feature will clearly have a much greater atomic surface energy than a chemically similar atom in a plane crystal snrface (see figures in Microfibrous surfaces). 

Pre-treatment of copper D E PACKHAM Conventional and microfibrous surfaces... 

Microfibrous surfaces D E PACKHAM Examples of preparation of Fe, Cu, Zn. Use as substrates in adhesion-energy dissipation... 

Versace D-L, Ramier J, Babinot J, Lemechko P, Soppera O, Lalevee J, Albanese P, Renard E, Langlois V. Photoinduced modification of the natural hiopolymer poly(3-hydroxy-hutyrate-co-3-hydroxyvalerate) microfibrous surface with anthraquinone-derived dextran for biological applications. J Mater Chem B 2013 1 4834-4844. 

VER 13a] Versace D.-L., Ramier J., Babinot J. et al., Photoinduced modification of the natural biopolymer poly(3-hydroxybutyrate-co-3-hydroxyvalerate) microfibrous surface with anthraquinone-deriveddextran for biological applications . Journal of Materials Chemistry B, vol. 1, pp. 4834-4844, 2013. 

A series of papers by Packham and co-workers [20-26] also emphasizes the improvements in joint strength that may be observed when a microfibrous surface topography is created. In their studies on the adhesion of polyethylene (used as a hot-melt adhesive) to metallic substrates they found that high peel strengths were obtained when a very rough, microfibrous, oxide surface was produced on the substrate. Fig. 3.3a is a scanning electronic micrograph of the... 

For very rough, microporous and microfibrous surfaces, the effective increase in area becomes enormous Go can be raised to a very high value indeed. Many engineering surfaces... 

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