Photonic crystals in biology

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Poster Session, Tuesday, June 15 Theme A1 - B702 The Adsorption and Conformational Properties of Polyelectrolyte Complexes on the Oppositely Charged Surface Sedat Ondaral 1 *, Caroline Bergholtz Ankerfors 2,3 , Lars Wågberg 2 1 Department of Pulp and Paper Technology, Karadeniz Technical University, 61080 Trabzon, Turkey 2 Fibre and Polymer Technology, Royal Institute of Technology, SE-100 44 Stockholm, Sweden 3 Eka Chemicals AB, 445 80 Bohus, Sweden Abstract-We investigated how PEC’s adsorption properties and conformation behaviors change on silicon o xide surface depending on the molecular weight of polyelectrolytes. The findings of the present study are remarkably giving a new insight about the PEC’s properties related to their use and performance. By mixing oppositely charged polyelectrolytes in water, polyelectrolyte complexes can be formed, which is driven by the increase of entropy due to the release of small ions from the double layers around the individual polyelectrolytes. The main interaction force for complexation of two oppositely charged polyelectrolytes is Columbic forces. Additionally, hydrogen bonding, charge transfer, dipole-dipole and hydrophobic forces play role in the different complexation system. 1-2 Co mplexation can result in the three different form, soluble, colloidaly stable and coacervate complexes, depending on the factors such as mixing ratio, polyelectrolyte concentration, pH, electrolyte concentration, nature of ionic groups, temperature and preparation conditions. 3-5 Their uses have grown rapidly in the large scale industrial applications, such as coatings, binders, flocculants, as well as in biotechnical and biomedical applications, for few decades. 6-9 For these application, it is very important to determine how the properties of PEC change with such factors mentioned before as well as adsorption and conformational behaviors of PEC in both solution and on the surface. In the present study, we mainly focused on the adsorption properties and conformational behaviors of PECs prepared by combining poly(allylamine hydrochloride) (PAH) and poly(acrylic acid) (PAA) by using a confined impinging jet (CIJ) mixer. The adsorption properties of PECs were investigated with the aid of Stagnation Point Adsorption Reflectometry (SPAR) and Quartz Crystal Microbalance with Dissipation (QCM-D) using SiO2 surfaces. We found that the PEC-A, which prepared with higher molecular weight PAH/PAA, showed a higher adsorption to the SiO 2 surfaces compared to the PEC-B, which prepared with lower molecular weight PAH/PAA. The adsorption of the PEC-A also showed a larger change in the dissipation (D), fro m the QCM -D measurements, indicating that the adsorbed layer had a relatively lower viscosity and a lower shear modulus for the PEC-A. We also determined that “how PEC’s conformation changes on the oppositely charged surface” by means of Atomic Force Microscope (AFM). Complementary investigations of the adsorbed layer using AFM showed that the adsorbed layer was significantly different for PEC-A and PEC-B and that the change in properties with adsorption time was very different for the two types of PECs. PEC-A showed a coalescence type of behaviour whereas this was not detected for the PEC-B, as shown in Figure 1. The exact reason to this difference in behaviour is not known but size determinations of the complexes in solutions showed that they were very stable over time and therefore, the coalescence behaviour was concluded to be initiated by the interaction between the complexes and the surface. AFM results for the PEC-A showed the existence of two types of complexes with similar size but different mechanical properties, i.e. collapsing behaviour, when in contact with the surface. This could most probably be linked to the phase separation of the complexes during their preparation. Figure 1. AFM images (amplitude mode) of PEC-A and PEC-B on silicon oxide surface after different adsorption periods (image size 5x5 m). In summary, these results show that the higher adsorption amount and higher surface coverage of PECs can be achieved by increasing molecular weight of polyelectrolytes used for preparation of PEC. That is promising for the future application studies related to enhancing the PEC’s performance especially as a binder. This study was conducted in the laboratories of Fibre Technology Department (Royal Institute of Technology, Stockholm-Sweden). *Corresponding author: 2Tondaral@ktu.edu.tr [1] Thünemann, A. F.; Müller, M.; Dautzenberg, H.; Joanny J.-F.; Löwen H., Springer-Verlag Berlin Heidelberg, Germany, 2004, 166, 113. [2] Kovacevic, D.; Borkovic, S.; Pozar J., Colloids and Surfaces A: Physicochem. Eng. Aspects, 2007, 302, 107. [3] Philipp, B.; Dautzenberg, H.; Linow, K.-J.; Kötz, J.; Dawydoff, W., Adv. Polymer Sci. 1989, 14, 91. [4] Gärdlund, L.; Wågberg, L.; Norgren, M., J. Colloid Interface Sci. 2007, 312, 237. [5] Kabanov, V. in Multilayer Thin Films. G. Decher and J. B. Schlenoff, Wiley-VCH Verlag GmbH,Weinheim, Germany, 2003, 47-86. [6] Hubbe,M.A.; Moore, S.M.; Lee, S.Y., Ind. Eng. Chem. Res. 2005, 44, 3068. [7] Malay, Ö.; Y O., Journal of Thermal Analysis and Calorimetry, 2008, 94, 749. [8] Fredheim, G.; Christensen, B.E., Biomacromolecules 2003, 4, 232. [9] Wan, A.C.A.; Tai, B.C.U.; Schumacher, K.; Schumacher, A.; Chin, S.Y.; Ying, J.Y., Langmuir, 2008, 24, 2611. 6th Nanoscience and Nanotechnology Conference, zmir, 2010 232
Poster Session, Tuesday, June 15 Theme A1 - B702 Effect of Nanocrystallization on Magnetic Properties of Bulk Amorphous Fe 75-X Co X Nd 3 Zr 2 Y 3 B 17 alloys Mehmet Yıldırım * , M. Vedat Akdeniz and Amdulla O. Mekhrabov Novel Alloys Design and Development Laboratory (NOVALAB), Department of Metallurgical and Materials Engineering, Middle East Technical University, Ankara 06531, Turkey Abstract- It was shown that Fe 75-X Co X Nd 3 Zr 2 Y 3 B 17 alloys have soft magnetic properties in amorphous state, whereas they show single phase hard magnetic behavior after annealing due to containing nanocrystalline hard magnetic Nd 2 Fe 14 B phase and Fe 3 B and/or α-Fe soft magnetic phases. Fe-based bulk metallic glasses (BMG) have attracted considerable interest for engineering and technological applications because of their superior mechanical and magnetic properties [1-3]. Up to now, Fe-based BMG’s are classified into following three groups according to their magnetic behavior: 1. non-ferromagnetic alloys such as Fe– Mn–Mo–Cr–C–B [4], 2. soft magnetic alloys such as Fe-(Al, Ga)-metalloid [5] and (Fe, Co)–B–Si–Nb [6] and 3. hard magnetic alloys such as Fe–Co–Nd–Dy–B [7] and Nd (Pr)– (Fe, Co)–Al [8]. Among these, the B-rich Fe-Co-RE-B hard magnetic alloys containing rare earth elements such as Nd, Pr and Dy is a new class of Fe-based bulk glassy alloys that are potential materials for bulk permanent applications such as motors, speakers, sensors, magnetic recorders, telephone receivers and MRI systems. Lower rare earth content, lower melting temperature, higher glass forming ability and the appearance of glass transition and supercooled liquid region before crystallization are the advantages of this type of alloys over rare-earth (RE) rich Fe-RE-Co-B alloys. Figure 2. Hysteresis curves for amorphous and nanocrystalline Fe 75 Nd 3 Zr 2 Y 3 B 17 alloys. Fe 75 Nd 3 Zr 2 Y 3 B 17 alloy has fully amorphous structure in the as-cast state (Figure 1). However, after annealing formation of Nd 2 Fe 14 B and α-Fe phases exist. Amorphous alloy has soft magnetic behavior, while after annealing due to the exchange-coupled interaction between hard magnetic Nd 2 Fe 14 B phase and α-Fe soft magnetic phases their hysteresis loop seem to be single-hard magnetic behavior (Figure 2). This work is supported through The Scientific and Technological Research Council of Turkey, TUBITAK, for the support through National Scholarship Program for PhD Students and METU-ÖYP Program. * ymehmet@metu.edu.tr Figure 1. XRD patterns for amorphous and nanocrystalline Fe 75 Nd 3 Zr 2 Y 3 B 17 alloys. In this study, we have investigated the effect of nanocrystallization on magnetic properties of bulk amorphous Fe 75-X Co X Nd 3 Zr 2 Y 3 B 17 alloys with x = 0, 5, 10 and 15. Samples were produced by a commercially available centrifugal casting machine under high purity Ar atmosphere. Amorphous nature of the samples was verified by XRD analysis. Thermal stability of the alloys was investigated by thermal analysis measurements using a differential scanning calorimeter (DSC). The magnetic properties such as saturation magnetization (M S ), coercivity (H C ), remnantmagnetization (M R ) and maximum energy-product were measured using a vibrating sample magnetometer (VSM). [1] A. Inoue, T. Zhang, N. Nishiyama, Mater. Trans. JIM 34 (1993) 1234. [2] A. Inoue, T. Zhang, N. Nishiyama, Mater. Trans. JIM 32 (1991) 1005. [3] A. Peker, W.L. Johnson, Appl. Phys. Lett. 63 (1993) 2342. [4] V. Ponnambalam, S.J. Poon, G.J. Shiflet, V.M. Keppens, R. Taylor, G. Petculescu, Appl. Phys. Lett. 83 (2003) 1131. [5] A. Inoue, J.S. Gook, Mater. Trans. JIM 36 (1995) 1180. [6] B.L. Shen, A. Inoue, C.T. Chang, Appl. Phys. Lett. 85 (2004) 4911. [7] W. Zhang, A. Inoue, Appl. Phys. Lett. 80 (2002) 1610. [8] A. Inoue, Mater. Sci. Eng. A 226–228 (1997) 351. 19: 15-25. 6th Nanoscience and Nanotechnology Conference, zmir, 2010 233
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