Photonic crystals in biology

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Poster Session, Tuesday, June 15 Theme A1 - B702 Absorption Hypothesis: Attachment of Beetles to Nanoporous Substrates Elena Gorb 1 *, Solveig Kleinz 1 and Stanislav Gorb 1 1 Department of Functional Morphology and Biomechanics, Zoological Institute, University of Kiel, 24098 Kiel, Germany Abstract-Traction experiments with ladybird beetles showed that forces on nanoporous substrates were significantly lower t hat those on solid surface samples. The comparison of the evolution in contact angles of the two fluids, polar water and non-polar mineral oil, showed that porous substrates absorbed both polar and non-polar fluids, whereas solid surface samples did not. Thus, the reduction of insect attachment on nanoporous surfaces may be explained by (1) the absorption of the secretion fluid from insect adhesive pads by porous media and/or (2) the effect of surface roughness. It has been repeatedly reported that micro- and nanostructured waxy surfaces of plants strongly reduce insect attachment. To explain anti-adhesive properties of such substrates, four hypotheses have been previously proposed: (a) roughness hypothesis; (b) contamination hypothesis; (c) fluid absorption hypothesis; and (d) wax dissolving hypothesis [1]. Recently, only the two first hypotheses ([2 – 6] for (a) and [7 – 9] fo r (b)) were proven. To date, the wax d issolving hypothesis and the fluid absorption hypothesis have not been experimentally tested. In the present study, we used nanoporous substrates with the same pore diameter (220 – 235 nm), but different porosity (area of voids in a material surface, normalized over the total area), in order to test the fluid absorption hypothesis, claiming that the structured wax coverage of plants may absorb the fluid from the setal surface of insect adhesive pads and by this reduce the adhesion force. We performed traction force measurements with tethered seven-spotted ladybird beetles Coccinella septempunctata L. (Coleoptera, Coccinellidae), walking on five different substrates [10]: (1) smooth glass plate; (2) smooth solid Al 2 O 3 (sapphire) disc; (3 – 5) three types of nanoporous Al 2 O 3 discs (back side of anodisc membranes Whatman, Schleicher and Schuell, Whatman International Ltd., Maidstone, UK) having the porosity of 28, 42 and 51%. Forces were measured with a load cell force transducer (10g capacity, Biopac Systems Ltd., Santa Barbara, CA, USA). Both males (n=10) and females (n=10) were used in the experiments. We found that the forces ranged from 0.16 to 16.59 mN in males and from 0.32 to 8.99 mN in females. The highest force values were obtained on the smooth surfaces, where males generated considerably higher forces compared to females. On all three porous substrates, the forces were significantly reduced, and the only difference was obtained between nanoporous membranes having the highest and lowest porosity. Males produced essentially lower forces than females on porous samples [10]. The reduction of insect attachment on nanoporous substrates may be explained by (1) possible absorption of the secretory fluid from insect pads by porous media and (2) surface roughness, reducing real contact area between tenent setae of insect adhesive pads and substrate. To examine the ability of porous substrates to absorb fluids, we performed additional absorption experiments with solid and nanoporous surfaces samples using a high-speed optical contact angle measuring device OCAH 200 (DataPhysics Instruments GmbH, Filderstadt, Germany). The comparison of the evolution in contact angles of the two fluids, polar water and non-polar mineral oil (Mobil DTE Medium, viscosity 43.4 mm 2 •s at 40°C [11]), showed that porous substrates absorbed both polar and non-polar fluids (figure), whereas solid surface samples did not. Since the beetle secretion or at least a part of it consists of oily substances, we can conclude that adhesion reduction in our traction experiments at least partially can be explained by the ability of nanoporous substrates to adsorb non-polar lipid-like fluids. contact angle [ ° ] 70 60 50 40 30 20 10 0 0 10 20 30 40 50 60 30 25 20 15 10 5 absorption absorption 0 0 10 20 30 40 50 60 time [s] (a) (b) Figure 1. The evolution in contact angles of water (a) and oil (b) on the nanoporous surface sample with the porosity of 42%. This work was partially supported by the SPP 1420 priority program of the German Science Foundation (DFG) “Biomimetic Materials Research: Functionality by Hierarchical Structuring of Materials” (project GO 995/9-1). The first author thanks Naoe Hosoda (NIMS, Tsukuba, Japan) for fruitful discussions. *Corresponding author: egorb@zoologie.uni-kiel.de [1] E.V. Gorb and S.N. Gorb, Entomol. Exp. Appl. 105, 13 (2002). [21] S. Gorb, Attachment devices of insect cuticle (2001). [3] A. Peressadko and S. Gorb, Proc. 1st Int. Conf. Bionik, 257 (2004). [41] D. Voi gt et al., J. Insect Physiol. 54, 765 (2008). [51] E. Gorb and S. Gorb, Entomol. Exp. Appl. 130, 222 (2009). [6] J. M. Bullock and W. Federle, J. Exp. Biol. 212, 1876 (2009). [7] L. Gaume et al., Arthropod Structure & Development 33, 103 (2004). [8] E. Gorb et al., J. Exp. Biol. 208, 4651 (2005). [9] E. Gorb and S. Gorb, Ecology and biomechanics: A mechanical approach to the ecology of animals and plants, 147 (2006). [10] E. Gorb et al., Proc. 9th Biennial ASME Conf. on ESDA, 1 (2008). [11] M. Varenberg and S. Gorb, Adv. Mater. 21, 483 (2009). 6th Nanoscience and Nanotechnology Conference, zmir, 2010 208
Poster Session, Tuesday, June 15 Theme A1 - B702 Phosphorus Containing Novel Polyimide/Silica Nanocomposite Materials via Sol-Gel Technique Canan Kızılkaya *, Sevim Karataş , Nilhan Kayaman Apohan , Atilla Güngör Marmara University, Department of Chemistry 34722 Istanbul/Turkey Abstract- In this work, the high temperature capability and fire-resistance of phosphorus-containing polyimide/ silica (PI/SiO 2 ) nano hybrid films were synthesized by sol-gel reaction and thermal imidization.The silica content in the hybrid films was varied from 0 to 20 wt %. The thermal, mechanical, optic, electrical and surface properties of the hybrid films have been investigated and compared to pure PI. Organic-inorganic nanocomposite materials prepared by the sol-gel technique are an important class of newgeneration materials, which combine the desirable properties of an inorganic component (heat resistance, retention of mechanical properties at high temperatures and low thermal expansion) and those of organic polymer (toughness, ductility and processability) [1,2]. Polyimides (PI) are promising materials used for a wide range of applications because of their high glass transition temperature, good heat resistance, low dielectric constant, and excellent mechanical properties. The sol–gel process is a unique and versatile approach among the various methods used to produce polyimide/SiO 2 hybrid materials .The nature of the interfaces between SiO 2 particles and polyimides matrix, the content and size of SiO 2 particles, greatly affect the properties of the hybrid materials. Strong interfaces in which covalent bond should be formed between SiO 2 particles and polyimides matrix, are needed for obtaining excellent properties [2,3] . Polymers containing the phenylphosphine oxide (PPO)group have been studied extensively for a number of applications in recent years. These polymers are the most important ones both due to good their thermal and chemical stability, excellent mechanical properties, very good fire retardancy. Polyimides containing phosphine oxide moieties display good flame resistance and excellent adhesion properties. It has been proven that the phenylphosphine oxide moiety provides a strong interacting site for imparting miscibility with several systems [2-5]. In this work, a series of novel phosphine oxide containing polyimide / silica nanocomposite materials were prepared via sol-gel technique and imidization. The silica content in the hybrid coating materials was varied from 0 to 20 wt%. The FTIR and 29 Si-NMR spectra showed that the fully condensed inorganic network had formed during the imidization. Tensile modulus and hardness of the polyimide/silica coating materials increased gradually with increasing inorganic content due to the enhanced interfacial interaction between PI matrix and silica particles. The thermal analysis of the coating materials showed that the degradation of PI was largely reduced with incorporation of silica and also the flame retardancy of the nanocomposite increased. The morphology studies indicated that, the silica particles in the polyimide matrix are dispersed homogeneously and the particle size is in the range of 30-55 nm. Furthermore, it was observed that optical transparencies of the hybrid coating materials decreased due to the introduction of higher silica content into the polyimide matrix and the increasing contact angles demonstrated the formation of hydrophobic nanocomposite surface. (a) Figure 1: SEM micrographs of (a) PI/SiO2-15 (b) Si mapping of PI/SiO2-15. *Corresponding author: ckizilkaya@gmail.com [1] S Karatas, N.K. Apohan, H. Demirer, A. Gungor Polym. Adv. Technol., 18,490–496 (2007) [2] C.Kızılkaya ,S. Karataş , N. K. Apohan , A. Güngör, Journal of Applied Polymer Science, 115, 3256-3264 (2010). [3] M. Çakır, S Karataş, Y.Menceloğlu, N.K.Apohan, A. Güngör, Macromol. Chem. and Phys., 209 , 919 , (2008). [4] C.J Cornelius, E. Marand, Polymer , 43, 2385( 2002) [5] Y.Delaviz, A. Güngör, J.E. McGrath, H.W Gibson, Polymer, 34, 210 (1993). (b) 6th Nanoscience and Nanotechnology Conference, zmir, 2010 209
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