|Title:||Fabrication and adhesion analysis of bio-inspired hierarchical nano- and micro-structured fibrillar surfaces|
|Subject:||Hong Kong Polytechnic University -- Dissertations|
|Department:||Department of Mechanical Engineering|
|Pages:||xviii, 118 p. : ill. ; 30 cm.|
|Abstract:||During the last decade, the "gecko effect" has raised increasing interest. The nano- and micro-structured fibrillar surfaces show the strong adhesion forces to smooth and rough, dry and wet, inclined and vertical surfaces. Both theoretical modeling and experimental analysis have been focused on this area, which involves researches in the disciplines of physics, chemistry, biology, applied mechanics, materials science, etc. Besides, versatile fabrication methods have been developed in fabricating the nano- and micro-structured fibrillar structures and different adhesion test methods have been conducted to achieve the adhesive behavior of the fibrillar surfaces. In this dissertation, a new method based on cast moulding methods was proposed using the dentin of black carp tooth, which contains tubular structures, as templates. Cutting methods using Diamond Saw was used to prepare the dentin templates with thickness of 300-500 μm. Both the morphologies and mechanical properties of the tooth dentin templates were studied. The pores have diameters of 1-2 μm and interpillar distances of 1-10 μm. The nanoporous structures on the wall of the micro pores were also studied and the diameters of the nanopores are around 200 nm.|
Fabrication methods of the nano- and micro-structured fibrillar surfaces were carried out using cast moulding methods with PDMS, which had outstanding bio-compatibility, high resistance to acid, ease to fabrication and high elastomeric properties. SEM imaging was conducted to investigate the morphologies of the nano- and micro-structured fibrillar surfaces and several special structures of the fibrillar surfaces have been found. The diameters of the fibers are 1-2 μm and the aspect ratios are between 1/15 and 1/30. The inter distances of two neighbor micro fibers are 1-10 μm. Moreover, the secondary nanofibers have diameters of ~200 nm and inter distances of 1-5 μm. These dimensions are consistent with the nano- and micro-porous structures of the dentin templates and this is why dentin templates were only etched after molding due to twining of the secondary nanofibers. Furthermore, the packed bundles of approximately 20-50 micro fibers were found due to the extreme large length of the certain fabricated micro fibers. Last but not least, the microtubular structures which have diameters of 600 nm - 1 μm were found and the formation of the micro tubes was due to the fillers in the micro pores of the dentin templates. Finally, the adhesion tests using MTS Tytron 250 and DMA Q800 were conducted to research on the adhesive behavior of the fibrillar surfaces. Mainly two kinds of contact surfaces, a spherical glass ball (15 mm diameter) and an iron ball (3 mm diameter), were used. SEM was used to investigate the morphologies of the fibrillar surfaces after the adhesion tests. The adhesion strengths of adhesion tests show a little drop than the previously studied adhesion tests in other references. This drop is mainly due to the packed and disordered structures of the fibers, the tilted angles in certain fibrillar surfaces and the contact between the backing layers and the contact surfaces. However, the effects of the hierarchical structures are probably contributing to the adhesion strength since the secondary nanofibers may contact with the contact surfaces after the bending of the micro fibers. Besides, the effects of the microtubular structures remain to be investigated in further steps.
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