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Bio-inspired mechanics of bottom-up designed hierarchical materials: robust and releasable adhesian systems of gecko

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Yao H. , Gao H.

tom Vol. 55, nr 2

141-150

To explore the basic principles of hierarchical materials designed from nanoscale and up, we have been studying the mechanics of robust and releasable adhesion nanostructures of gecko [1]. On the question of robust adhesion, we have introduced a fractal-like hierarchical hair model to show that structural hierarchy allows the work of adhesion to be exponentially enhanced as the level of structural hierarchy is increased. We show that the nanometer length scale plays an essential role in the bottom-up design and, baring fracture of hairs themselves, a hierarchical hair system can be designed from nanoscale and up to achieve flaw tolerant adhesion at any length scales. For releasable adhesion, we show that elastic anisotropy leads to orientation-dependent adhesion strength. Finite element calculations revealed that a strongly anisotropic attachment pad in contact wit h a rigid substrate exhibits essentially two levels of adhesion strength depending on the direction of pulling.

Nanostructural Biochemical Modification Of Flax Fiber In The Processes Of Its Preparation For Spinning

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Koksharov S. , Aleeva S. , Lepilova O.

tom Vol. 15, no. 3

215--225

The elaborated principles of nanoengineering of linen textile materials implement the techniques of spatially localized effects of protein catalysts on polymeric cellulose companions with selective splitting of impurity compounds without damaging technologically necessary nano-sized formations of binders in the fiber structure. The ranges of optimal values of the residual content in flax fiber prepared for spinning are identified on the basis of the analysis of the successive stages of enzymatic and peroxide treatments contribution to the breakdown of polymers and the differentiation of the influence of impurities on the yarn technological properties. The recommended level of residual pectin, lignin and hemicellulose (wt. %) is: after enzymatic treatment P1 = 1,0±0,1; L1 = 3,9±0,3; Hc1 = 11,0±1,0; after peroxide bleaching P2 = 0,4±0,05; L2 = 2,3±0,3; Hc2 = 7,5±0,5. The required level of fiber structural modification at the stage of preparing roving for spinning can be achieved through use of protein catalysts whose globule size is 50...100 nm. The use of enzymes with these dimensional characteristics helps to ensure breaking of polymer adhesives on the surface of incrusts and in the areas of intercellular formations, which hinder fiber crushing, without damaging nano-sized binding fractions. The implementation of this method contributes to a significant improvement in the uniformity of structural and physical and mechanical properties of flax yarn. Increase in yarn fineness and strength properties of semi-finished products, as well as improvement of deformation properties and reduction of yarn breakages during the spinning processes are achieved.

Bio-inspired mechanics of bottom-up designed hierarchical materials: robust and releasable adhesion systems of gecko

100%

Yao H. , Gao H.