Photonic crystals in biology

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Poster Session, Tuesday, June 15 Theme A1 - B702 Investigation of Potential Use of Carbon Nanotube Membranes in Desalination Pinar Baltaci 1 , Leyla Ozgur 1 , Deniz Rende 1,2 , Rahmi Ozisik 3 and Nihat Baysal 1* 1 Department of Chemical Engineering, Yeditepe University, Istanbul 34755, Turkey 2 Department of Chemical Engineering, Bogazici University, Istanbul 34342, Turkey 3 Department of Materials Science and Engineering, Rensselaer Polytechnic Institute, Troy, NY 12180, USA Abstract– The potential use of carbon nanotube membranes in water desalination was evaluated in the present study. Water transport by reverse osmosis through hexagonally packed carbon nanotube (CNT) membranes was studied with Molecular Dynamics simulations. Our results showed that due to the osmotic gradient, the distance between CNT membranes decreased until steady state conditions were reached. The flow rate of water during its transportation indicates high degree of desalination. Reduction of potable water sources is one of the primary environmental issues of the last two decades. This deficiency causes a decrease in the human lifetime expectancy, an increase in disease epidemics, and therefore, is a political issue [1]. In addition, desalination of soil and underground water is an important issue in regions that have very low precipitation. [2]. As a result, treatment of available water sources receives global attention and is a promising research area. Carbon nanotubes (CNTs), which are rolled up sheets of sp 2 -bonded graphite [3], are suggested as efficient membrane materials for desalination processes [4]. The current study focuses on the potential use of CNT membranes in the desalination processes to make desalination cheaper and fresh water more widely available [5]. Due to the importance of this subject in terms of environmental and health impact, the current study aims to study the separation of a NaCl solution from H 2 O by reverse osmosis. The system contains two (6,6) single walled carbon nanotube (SWNT) membranes separating NaCl solution and H 2 O (Figure 1). The simulation was carried out at 300 K and 1 atm for 60 ns via molecular dynamics (MD) simulations with a time step of 1 fs. Polymer Consistent Force Field (PCFF) was chosen as the governing force field and periodic boundary conditions were applied in all spatial directions. Initially, the distances between the two SWNT membranes was set to 2 nm across both compartments, and the concentration of salt compartment (Na + and Cl - ) was set to 5.4 M. All the systems were energy minimized prior to MD simulations. The periodically replicated simulation cell contains eight SWNTs each containing 144 sp 2 carbon atoms, 545 transferable intermolecular potential (TIP) water molecules and 25 pairs of Na + and Cl - ions. SWNTs were held together with van der Waals forces and solvent induced hydrophobic interactions. In this study, the flow of water molecules through openended SWNT membranes under an osmotic gradient was performed. The distance between membranes decreases continuously but not monotonically. Due to the high transportation rate of water molecules through the SWNTs, it can be concluded that SWNTs are promising desalination membrane materials. Computer resources supplied by Yeditepe University are gratefully acknowledged. Pinar Baltaci is an undergraduate student at Yeditepe University. *Corresponding author: nbaysal@yeditepe.edu.tr [1] Cygan, R.T., Liao, J-D., 2008. A molecular basis for advanced materials in water treatment, MRS Bulletin, V33-1: 42- 47. [2] Kotzer, E., 2005. Artificial kidneys for the soil – Solving the problem of salinization of the soil and underground water, Desalinization, V185: 71-77. [3] Robertson, J., 2004. Realistic applications of CNTs, Materials Today, V7-10: 46-52. [4] Kalra, A.S., Garde, S., Hummer, G., 2003. Osmotic water transport through carbon nanotube membranes, PNAS, V100-18: 10175-10180. [5] Wang, L., Zhao, J., Li, F.,Fang, H., Lu, J.P., 2009. First principles study of water chains encapsulated in singlewalled carbon nanotube, J. Phys. Chem. C, V113-14: 5368- 5375. NaCl Solution CNT Membrane H 2O CNT Membrane NaCl Solution Figure 1. The H 2 O compartment at the center is separated from the NaCl-solution compartment (left and right) by two water permeable membranes of hexagonally packed CNTs. 6th Nanoscience and Nanotechnology Conference, zmir, 2010 385
Poster Session, Tuesday, June 15 Theme A1 - B702 Green Reactive Extrusion Technology of Functional Copolymer–Polyolefin–Modified Organic Silicate Nanofilms Eren Altungöz, * Ernur Söylemez, Zakir M. O. Rzayev and Erdoğan Alper Department of Chemical Engineering, Hacettepe University, Ankara 06800, Turkey Abstract—This work is an approach to develop a green technological process for the preparation of polyolefin biaxially oriented nanofilms without utilization of toxic and volatile monomers as grafting agents. Novel polymer nanosystems were prepared by an one step twin-screw extrusion in situ processing using poly(α-olefin-alt-maleic anhydride)s as reactive compatibilizers, functionalized organoclays as reactive nano-fillers and plasma surface treated powder polyolefins as matrix polymers. Polymer/layered organoclay nanosystems and nanocomposites with large quantity of interfacial area offer significant potential to develop the high performance engineering materials for a wide range of numerous applications. In the last decade, the attention of many academic and industrial researchers was focused on development of green technology of production and processing of thermoplastic polymer silicate layered nanomaterials using various type of reactive extrusion systems. This reactive polymer melt intercalation/exfoliation method is one of the mostly used processes because of its versatibility, and compatibility with current polymer processing techniques, controllability of the chemical and physical interfacial interactions, and its environmentally green character [1-7]. Most known technological methods are based on two step extrusion processes: (1) grafting of toxic and volatile functional monomers onto thermoplastic polymer chains and (2) melt compounding polymer/graft copolymercompatibilizer/organoclay mixtures. In this report, we discuss the results of (a) designing and utilizing the green technological line including Rondol twinscrew extruder (21 mm) supported by plasma surface treatment unit (Lab. Plasmatron), unit for morphology control of melt blending process by polarized microscopy, (b) granulation-milling system and biaxially oriented filmforming unit (blowing method) for the preparation of nanofilms (Scheme 1), (c) investigation of extruder parameters–nanofilm properties relations and evaluation of optimum technological parameters for the formation of nanostructures with higher interfacial interaction area and degree of exfoliation of polymer chains between silicate galleries, (d) investigation of nanofilm composition–physical and chemical structure–surface morphology relationships. Scheme 1: Schematic representation of melt intercalation green technology for preparation of polymer thin nanofilms. Functional alternating copolymers of α-olefins (C 6-18 ) with maleic anhydride (MA) were synthesized by complex-radical copolymerization method. Polyolefins (PO) such as isotactic polypropylene (i-PP) and ethylene-propylene (EP) copolymer were supported from PETKIM Inc. (Izmir, Turkey). Reactive and non-reactive organoclays (Aldrich) were used without any purification. Modification of organoclays was carried out by in situ intercalation of functional copolymer chains between silicate galleries through amidization and complex-formation reactions. Hybrid nanofilms with different compositions were prepared by Rondol twin-screw extrusion system supported plasmatron and biaxially oriented film-forming unit according to technology line presented in Scheme 1. The results of FTIR and XRD analysis of chemical and physical structures of functional copolymer/organoclay composites indicated that the pre-intercalation of functional copolymer between silicate layers proceeds via complex-formation and amidolysis reactions of anhydride units with ammonium cation and primary amine groups of organoclays, respectively. DMA and DSC analysis of prepared hybrid films show that long alkyl groups of functional copolymer-compatibilizer also play a role internal plastification in the processing and formation of nanofilms. Obtained mechanical properties, thermal behaviors, MFI, XRD patterns and SEM images of nanofilms showed that these important characteristics strongly depend on the technological and operational parameters designed technology system, composition of reactive polymer blends and chemical structure of surfactants of organoclays and length of branched alkyl linkages of functional copolymers. In summary, this work presents design and utilization of a novel technological line, including reactive extrusion system, plasmatron, biaxially oriented film-forming unit and melt blending morphology control unit and granulation-milling system, for the melt intercalation/exfoliation in situ processing and preparing PO/functional copolymer pre-intercalated organoclay hybrid nanofilms with higher exfoliation degree of polymer chains and physico-mechanical properties as compared with conversional POs and known PO/organoclay/ compatibilizer films. *Corresponding author: altungoz@uniturk.net [1] M. Alexandre, P. Dubois, Mater. Sci. Eng. R. 28, 1 (2000). [2] S.S. Ray, M. Okamoto, Prog. Polym. Sci. 28 1538 (2003). [3] L.A. Goettler, K.Y. Lee, H. Thakkar, Polym. Reviews, 47, 291 (2007). [5] Z.M.O. Rzayev, A. Yilmazbayhan, E. Alper, Adv. Polym. Technol. 26, 41 (2007). [6]. L.S. Schadleret et al., MRS Bulletin 32, 340 (2007). [7]. Rzayev ZMO. Polyolefin nanocomposites by reactive extrusion. In: Advances in Polyolefin Nanocomposites, Chapter 4, Taylor & Francis Groups: New York, 2010. 6th Nanoscience and Nanotechnology Conference, zmir, 2010 386
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