3rd International TRR 61 Workshop Multilevel Molecular Assemblies: Structure,
Dynamics and Function
May 16th, 2011
Center for Nanotechnology (CeNTech)Heisenbergstrasse 11D - 48149 Münster
Short programme
8:55-9:00: WelcomeChair: Michael H. Koepf9:00-9:25 Yiliu Liu: Host-enhanced Noncovalent Interaction for Water-soluble Supramolecular
Polymerization9:25-9:50 Stefan Ostendorp: Advanced surface nano-structuring utilizing porous anodic alumina
membranes: breaking the limits9:50-10:15 Nina Winkler: Fabrication and investigation of regular arrays of magnetic nanowires
using a template synthesizing technique
10:15-10:30 Coffee break
Chair: Jens Smiatek10:30-10:55 Rakesh K. Harishchandra: Influence of ectoine and hydroxyectoine on the structural
organization of model lipid membrane systems10:55-11:20 Stefan F. Hopp: Kinetic Monte Carlo study of the anisotropic behavior of organic
molecules on patterned surfaces11:20-11:45 Chunlei Zhu: Visual Optical Discrimination and Detection of Microbial Pathogens Using
Conjugated Polyelectrolytes11:45-12:10 Christian Schulz: Ferrocene Multilayers by Thiol-ene Click Chemistry
12:10 – 13:30 Lunch at the CeNTech
Chair: Yiliu Liu13:30-13:55 Liying Wang: Synthesis and Self-Assembly of Amphiphilic DNA-Dendron Hybrids13:55-14:20 Maike Becker: Nitroxide Exchange Reactions for Site-Specific Functionalization and
Assembly of Zeolite L Crystals14:20-14:45 Kai Liu: Superamphiphiles Based on Directional Charge-Transfer Interactions: From
Supramolecular Engineering to Well-Defined Nanostructures
14:45-15:00 Coffee break
Chair: Jan Gauczinski15:00-15:25 Weina Li: Topochemical approach to efficiently produce main-chain poly(bile acid)s with
high molecular weights and adaptive responsive behavior15:25-15:50 Chuan Du: High-charge-mobility of organic field effect transistors
with single layer modified gate dielectric15:50-16:15: Steffen Kanzler: Knowledge Sharing and Knowledge Protection in Corss-cultural
Collaboration
16:30 – 18:30 Poster session at the CeNTech
19:00 – 23:00 Conference dinner at the Mensa da Vinci (Leonardo-Campus)
Abstracts for contributed talks
Host-enhanced Noncovalent Interaction for Water-soluble Supramolecular Polymerization
Yiliu Liu, Ying Yu, Kai Liu, Zhiqiang Wang, Xi Zhang*
Department of Chemistry, Tsinghua University, Beijing, China, 100084
Supramolecular polymers are defined as polymeric arrays of monomeric units that are brought together by reversible and highly directional secondary interactions.[1] In principle, different directional intermolecular interactions can be employed to fabricate supramolecular polymers, however the interactions must be strong enough in order to obtain supramolecular polymers with high degree of polymerization. Unfortunately, not many intermolecular interactions can meet such a criteria.[2]
How to make weak interaction string? To answer this question, host-enhanced interaction is one of the choices. For example, charge transfer interaction is not feasible for supramolecular polymerization because its binding constant is just in the range of 103. However, the binding constant can be enhanced to 106 by employing a host, such as cucurbit[8]uril (in short CB[8]) to enhance the charge transfer interaction. We have designed and synthesized a monomer, DADV, as shown in Fig. 1. To mix DADV with CB[8] in water, a supramolecular polymer is formed simultaneously.[3] Our recent study has shown that the similar method can be extended for π electronic system and confirmed that host-enhanced π−π interaction can used to fabricate supramolecular polymers. Therefore, it provides a general avenue for constructing supramolecular polymers with different architectures and functions.
Fig. 1: Supramolecular polymerization driven by host-enhanced charge transfer interaction.
[1] C. Fouquey, J. -M. Lehn, A.-M. Levelut, Adv. Mater., 2, 254. (1990)[2] L. Brunsveld, B. J. B. Folmer, E. W. Meijer, Chem. Rev., 101, 4071. (2001)[3] Y. L. Liu, Y. Yu, J. Gao, Z. Q. Wang, X. Zhang, Angew. Chem. Int. Ed., 49, 6576. (2010)
Advanced surface nano-structuring utilizing porous anodic alumina membranes: breaking the limits
S. Ostendorp1, Y. Lei1, G. Wilde1
1Institute of Materials Physics, WWU Münster, Wilhelm-Klemm-Str. 10,D-48149 Münster, Germany
Porous anodic alumina membranes (PAAMs) have been intensively investigated for more than two decades, especially for their applications as masks or templates for fabricating various nano-structures of regular hexagonal arrays of wires and tubes [1]. In addition, ultra-thin alumina membranes (UTAMs) are used as deposition masks for nano-particles [2]. The spacing of the hexagonal structure of PAAMs and UTAMs can be modified within certain size regimes that had been reported in the literature [3]. So far only distinct “allowed” combinations of parameter values were reported that lead to highly regular porous structures during the anodization process of the underlying aluminum foil. Here we present our latest results concerning the extension of these limits to larger interpore distances and pore sizes and concerning the ability to create structures with desired spacing. For this purpose, we combined two well known methods during the anodization process, which now allows adjusting the structural parameters beyond the previous known limitations.
Fig. 1: SEM micrograph of a PAAM anodized at 170V under mild anodization conditions
[1] Y. Lei, W. Cai, G. Wilde, Progress in Materials Science, 52 465 (2007)[2] M. Wu, L. Wen, Y. Lei, S. Ostendorp, K. Chen, G. Wilde, Small 6 695 (2010)[3] W. Lee, R. Ji, U. Gösele, K. Nielsch, Nature Materials, 5 741 (2006)
Fabrication and investigation of regular arrays of magnetic nanowires using a template synthesizing technique
N. Winkler1, 2, Y. Lei1, 2, G. Wilde1, 2
1Institute of Materials Physics, University of Münster, Wilhelm-Klemm-Str. 10,Münster, Germany 2CeNTech GmbH, Center for Nanotechnology, Heisenbergstr.11, Münster, Germany
Regular arrays of magnetic nanowires with a high aspect ratio have potential applications, amongst others, in high density magnetic recording media and concerning biological sensing of carbohydrates e.g. glucose [1, 2]. Modified Porous Alumina Membranes (PAMs) with pore diameters adjustable from 20 to 80 nm are well suited as templates due to their high pore regularity and their perpendicular pore alignment to a substrate [3]. The pores of the PAM are filled with nickel, iron and cobalt by electrodeposition. The template can be removed by chemical etching to obtain free-standing nanowires (see figure 1).The homogeneous morphology and the large-scale regularity of the nanowire arrays are observed by SEM. The TEM diffraction patterns indicate that the wires are polycrystalline. The magnetic properties of the nanowire arrays are investigated with vibrating sample magnetometry, which shows a preferential direction of magnetization along the wire axis due to the high aspect ratio of the nanowires. The dipole interaction which is related to an energy minimization of the overall stray field of the wire array is observed qualitatively with magnetic force microscopy.
Fig. 1: SEM top view image of an array of free-standing nickel nanowires
[1] B. D. Terris and T. Thomson, Microsyst. Technol., 13, 189, (2007).[2] K. J. Cash and H. A. Clark, Trends Mol. Med., 16, 584, (2010).[3] Y. Lei, W.Cai and G. Wilde, Prog. Mater. Sci., 52, 465, (2007).
Influence of ectoine and hydroxyectoine on the structural organization of model lipid membrane systems
Rakesh Kumar Harishchandra, Mridula Dwivedi, Stephanie Wulff, Hans-Joachim Galla
Institute for Biochemistry and NRW Graduate school of Chemistry, Westfälische Wilhelms-University, Wilhelm Klemm Strasse 2, 48149 Münster, Germany
e-mail address: [email protected]
Ectoine and hydroxyectoine belong to the family of compatible solutes and are among the most abundant osmolytes in nature [1]. These compatible solutes protect biomolecules from extreme conditions and maintain their native function. We have investigated the effect of these compatible solutes on the fluid-rigid domain structure of lipid mono- and bi-layer membrane systems. Mainly saturated dipalmitoyl-phosphatidylcholine (DPPC) membranes exhibiting a clear le/lc phase transition were used. Epi-fluorescence microscopy showed that ectoines added to the aqueous subphase expand and fluidize the lipid monolayers. These results can be explained by the fact that ectoines reduces the line tension, which is the interfacial energy at the domain edges leading to reduced domain sizes and increased number of rigid domains [2]. Further, the influence of these compatible solutes was studied on the lipid bilayer model systems such as large- and gaint- unilamellar vesicles (LUVs and GUVs), which mimic the biological membrane. Hence, increase in the fluidity in the presence of compatible solutes may be of advantage for cell membranes to withstand extreme conditions like temperature or osmotic pressure and might also accelerate cellular repair mechanisms.
Fig. 1: Epi-fluorescence microscopic images of DPPC monolayer on different aqueous subphases. Scale bar � 50µm.
[1] E. A. Galinski, Cell. Mol. Life. Sci. 49, 487, (1993).[2] R. K. Harishchandra, S. Wulff, G. Lentzen, T. Neuhaus, H. J. Galla, Biophys. Chem 2010, 150, 37, (2010).
mailto:[email protected]
Kinetic Monte Carlo study of the anisotropic behavior of organic molecules on patterned surfaces
S. F. Hopp1,2, A. Heuer1,2
1Institut für Physikalische Chemie, Westfälische Wilhelm-Universität Münster, Corrensstr. 28/30, 48149 Münster, Germany2Transregio SFB 61 (TRR 61), Westfälische Wilhelms-Universität Münster, Physikalisches Institut, Wilhelm-Klemm-Str. 10, 48149
Münster, Germany
The nucleation behavior of N,N-dioctyl-3,4,9,10-perylene tetracarboxylic diimide (PTCDI-C8) on Au-patterned silica surfaces is investigated by means of kinetic Monte Carlo simulations to get further insight into the related microscopic processes. In the experiment, one observes the molecules laterally attach to the Au pattern and thus form well-organized 2D terraces on the silica substrate between the template features [1]. The high internal order of these domains results from the strong intermolecular - interaction. The simulation of spherical Lennard Jones (LJ) particles as previously done [2] doesπ π not describe this anisotropic behavior sufficiently. For this reason, we proceed to model the molecules as ellipsoids and apply the Gay-Berne (GB) pair potential (an anisotropic generalization of a shifted LJ potential) to describe the interaction between the molecules. In practice, we employ the GB potential for biaxial particles as suggested by Berardi et al. [3, 4]. The substrate as well as the Au pattern is considered as continuum so that the respective interaction to the molecules can be depicted by the so-called EES potential which has been derived from the generalized Hamaker theory by Babadi et al. [5]. To analyze the structural order within the domains, we determine the orientation of the planar central part of a molecule with respect to its neighbor molecules, the substrate and the Au pattern.
[1] W. Wang, C. Du, D. Zhong, M. Hirtz, Y. Wang, N. Lu, L. Wu, D. Ebeling, L. Li, H. Fuchs, L. F. Chi, Adv. Mater., 42, 4721, (2009).
[2] W. C. Wang, D. Y. Zhong, J. Zhu, F. Kalischewski, R. F. Dou, K.Wedeking, Y. Wang, A. Heuer, H. Fuchs, L. F. Chi, Phys. Rev. Lett., 98, 225504, (2007).[3] R. Berardi, C. Fava, C. Zannoni, Chem. Phys. Lett., 297, 8, (1998).[4] R. Berardi, A. Constantini, L. Muccioli, S. Orlandi, C. Zannoni, J. Chem. Phys., 126, 044905, (2007).[5] M. Babadi, M. R. Ejtehadi, Europhys. Lett., 77, 23002, (2007).
Visual Optical Discrimination and Detection of Microbial Pathogens Using Conjugated Polyelectrolytes
Chunlei Zhu1, Qiong Yang1*, Libing Liu1, Shu Wang1*
1Beijing National Laboratory for Molecular Sciences, Key Laboratory of Organic Solids, Institute of Chemistry, Chinese Academy of Sciences, Beijing, P. R. China.
Pathogen infections caused by Candida albicans (C. albicans) and Escherichia coli (E. coli) have led to extremely serious consequences. Cultures of blood samples, which are regarded as the diagnosis standard, often exhibit variable sensitivity and always take several days to detect certain pathogen. Here we demonstrate for the first time that a blend of two cationic conjugated polymers, between which fluorescence resonance energy transfer (FRET) can be induced, is used to detect and discriminate C. albicans and E. coli in a rapid, simple and visual way without demanding for any complicated instrumentation. Coupled with general polymerase chain reaction (PCR) technology, the method can detect pathogens specifically independent of electrophoresis analyses and real-time PCR, which avoids utilizing detrimental nucleic dyes and expensive fluorophore-labeled primers. The cationic conjugated polymer blend exhibits great potentials as ideal diagnostic agent for the identification of pathogens.
Fig. 1: Schematic representation of pathogen detection based on FRET between cationic conjugated polymers
[1] Zhu, C.; Yang, Q.; Liu, L.; Wang S. J. Mater. Chem. 2011, DOI: 10.1039/C0JM04424E.
[2] Zhu, C.; Yang, Q.; Liu, L.; Wang S. Chem. Comm. 2011, DOI: 10.1039/c0cc05158f.
Ferrocene Multilayers by Thiol-ene Click Chemistry
C. Schulz1, B. J. Ravoo1
1Organic Chemistry Institute, Westfälische Wilhelms-Universität Münster, Corrensstr. 40, D-48149 Münster, Germany
Surface modification of oxygen free silicon surfaces with organic molecules has been of great interest over the past years and many methods have been developed which allow the deposition of homogenous, densely packed monolayers on this surface.[1] Most commonly a hydrosilylation reaction between an alkyne or an alkene and the hydrogen terminated silicon surface is employed. In this work alkene terminated monolayers on silicon are further modified using the light induced reaction of thiols with alkenes[2] to fabricate ferrocene containing layers using a covalent layer by layer (LbL)[3] approach.
Si
1
Si
2
Si Si
16
HS
HS2
Fe
DMPA, hυ THF, DMPA, hυ
AScheme 1: Fabrication of ferrocene multilayers LbL deposition
As shown in scheme 1 the silicon surfaces are first functionalized with an alkene terminated monolayer A , which will readily react with thiols using light ( =365λ nm) and the photocatalyst 2,2-dimethoxy-2-phenylacetophenon (DMPA). In this case 1,4-butanedithiol is used, which will lead to a thiol terminated surface 1. Utilizing the same reaction conditions, decaallyl-ferrocene is grafted onto the surface, yielding in an alkene terminated surface 2 once again. The aforementioned steps can be repeated several times to deposit multiple layers of ferrocenes on the surface 16. The films build by this LbL technique were characterized using Ellipsometry, X-ray Photoelectron Spectroscopy (XPS) and cyclic voltammetry (CV).
[1] S. Ciampi, J. B. Harper, J. J. Gooding. Chem. Soc. Rev. 39, 2158, (2010).
[2] C. Wendeln, S. Rinnen, C. Schulz, H.F. Arlinghaus, B.J. Ravoo. Langmuir, 26, 15966, (2010).
[3] Y. Li, D. Wang, J.M. Buriak. Langmuir, 26(2), 1232, (2010).
Synthesis and Self-Assembly of Amphiphilic DNA-Dendron Hybrids
Liying Wang 1, Yu Feng 1, Yawei Sun 2, Zhibo Li 1, Qing-Hua Fan 1, Zhongqiang Yang 2, Yan-Mei He 1, Dongsheng Liu2
1 CAS Key Laboratory of Molecular Recognition and Function, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, China
2 Department of Chemistry, Tsinghua University, Beijing 100084, China
Precise molecular design becomes more and more important to achieve well-defined supramolecular assemblies. Besides designing completely new molecules, combining available components with different structures and functions, for example, biomacromolecules and organic polymers, to get new hybrid molecules is definitely efficient and consistently needed.1 We present herein a new kind of amphiphilic DNA-dendron hybrids consisted of a highly hydrophobic dendron and single stranded DNA.2 The hybrids were synthesized by solid phase synthetic strategy and assembled into long nanofibers in aqueous solution. The fibers were characterized by TEM, cryo-TEM and AFM. And the possible assembling mechanism was proposed according to the Nile Red encapsulation experiment.
Fig. 1: (A) the solid phase synthesis of G2Cl-18 hybrid and (B) the self-assembly of G2Cl-18 in aqueous solution.
[1] I.C. Reynhout, J.J.L.M. Cornelissen, R.J.M. Nolte, Acc. Chem. Res., 42, 681, (2009).[2] A.-M. Caminade, C.-O. Turrin, J.-P. Majoral, Chem. Eur. J., 14, 742, (2008).
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Nitroxide Exchange Reactions for Site-Specific Functionalization and Assembly of Zeolite L Crystals
M. Becker 1, L. De Cola2, A. Studer1
1Organic Chemistry Institute, University of Münster, Corrensstraße 40, 48149 Münster, Germany2Department of Physical Chemistry and Center for Nanotechnology, CeNTech, University of Münster, Mendelstraße 7, 48149 Münster,
Gemany
The synthesis, development and improvement of biocompatible systems are of great importance for future proceedings in the fields of medicine. Novel nano- or microscopic materials of inorganic particles can be conjugated to functionalized molecules and find direct application in medical imaging or therapy.
Zeolite L crystals in the range of 1-3 µm have been modified site-selectively at the coat or only at the basis area of the surface with alkoxyamines and nitroxides, respectively.[1] By using the concept of nitroxide exchange reactions[2] the assembly of two different zeolite L types into chains with strictly alternating red and green colour was achieved. The concept was proven to be reversible and dynamic.[3]
Fig. 1: Assembly of zeolite L microcrystals into linear chains.
As radical reactions tolerate various functional groups and can be performed under mild and biocompatible conditions at the crystal surface, the site-specific functionalization with fluorescent dyes, biologically interesting moieties (i.e. sugars, biotin) and the direct covalent immobilization of different proteins at the zeolite L surface is presented.[4]
Furthermore, investigations on reaction parameters like temperature, solvent or concentration effects for the thermal nitroxide exchange reaction were conducted.
[1] S. Huber, G. Calzaferri, Angew. Chem., 116, 6906, (2004).[2] H. Fischer, Chem. Rev., 101, 3581, (2001).[3] B. Schulte, M. Tsotsalas, M. Becker, A. Studer, L. De Cola, Angew. Chem., 122, 7033, (2010).[4] M. Becker, L. De Cola, A. Studer, Chem. Commun., 47, 3392, (2011).
Superamphiphiles Based on Directional Charge-Transfer Interactions: From Supramolecular Engineering to Well-Defined Nanostructures
Kai Liu1, Chao Wang1, Zhibo Li2, and Xi Zhang1*1Department of Chemistry, Tsinghua University, Beijing, China, 100084,
2Institute of Chemistry, Chinese Academy of Sciences, Beijing, China, 100084
In this work, we have demonstrated the feasibility of obtaining well-defined nanostructures by using the supramolecular engineering of superamphiphiles[1]. Bolaamphiphiles that contain electron-rich naphthalene (BNAPH and IBNAPH) and electron-deficient naphthalene diimide (BNDI) groups have been designed as building blocks of the superamphiphiles. BNAPH and IBNAPH refer to the 1,5- and 2,6-substitutions, respectively, as shown in Fig. 1. When BNDI is complexed with BNAPH, an X-shape superamphiphile is formed on the basis of directional-charge-transfer interactions. In contrast, the complexation of BNDI and IBNAPH has led to formation of an H-shape superamphiphile. An interesting finding is that a small change of the building blocks can cause a large and predictable change of the nanostructures: the self-assembly of X-shape superamphiphiles favor the formation of one-dimensional nanostructures, and H-shape superamphiphiles prefer the formation of two-dimensional membranes. Therefore, this study represents a nice example of supramolecular engineering for well defined nanostructures.[2]
Fig. 1: Schematic representation of the X- and H- shape superamphiphiles and their assembly into one-dimensional and two-dimensional nanostructures, respectively.
[1] Xi Zhang, Chao Wang, Chem. Soc. Rev. 40, 94, (2011) [2] Kai Liu, Chao Wang, Zhibo Li, and Xi Zhang, Angew. Chem. Int. Ed. 50, ASAP (2011)
Topochemical approach to efficiently produce main-chain poly(bile acid)s with high molecular weights and adaptive responsive behavior
Weina Li, Xuesong Li, Yong Ju, Guangtao Li*
[email protected] of Chemistry, Tsinghua University, Beijing, China
Bile acids are naturally occurring compounds with prominent properties including unique facial amphiphilicity, biocompatibility and multifunctional groups. The polymers based on bile acids show remarkable biocompatibility and mechanical properties. We developed a new efficient � green� strategy for producing high-molecular-weight main-chain poly(bile acid)s based on a topochemical approach. Bile acids derivatives (1, 2 and 3) with terminal alkyne and azide groups at both sides could easily form single crystals in a head-to-tail motif. By topochemical approach, high molecular weight poly(bile acid)s were produced in quantitative yields, and no catalysts are necessary for the polymerization reaction. Solvent-free process is another distinct advantage for this preparation method. The obtained polymers showed remarkable swelling properties in most nonpolar organic solvents and the photonic films based on the these polymers were obtained, which could be directly transferred into readable optical signal without label upon exposure to different solvents.
Fig. (1) Schematic illustration of the preparation high molecular weight main-chain poly(bile acid)s; (2) Photographs of the polymer before (A) and after (B) swelling in THF. SEM images of colloidal silica template (C)
and inverse opal (D).
[1] J. W. Zhang and X. X. Zhu, Sci. China, Ser. B Chem., 52, 849, (2009).[1] J. E. Gautrot and X. X. Zhu, Angew. Chem. Int. Ed., 45, 6872, (2006).[2] J. W. Lauher, F. Fowler and N. S. Goroff, Acc. Chem. Res., 41, 1215, (2008).
High-charge-mobility of organic field effect transistors with single layer modified gate dielectric
Chuan Du, Liqiang Li, Wenchong Wang, Harald Fuchs, and Lifeng Chi
Physikalisches Institut and Center for Nanotechnology (CenTech), Universität Münster, 48149 Münster, Germany
Organic field-effect transistors (OFETs) have been the focus of intense research in the last two decades due to their potential application in low cost and flexible electronic circuits [1]. Several studies have been proposed to improve the properties of OFETs, especially the field effect mobility, by optimizing the deposition of organic semiconductor films and modifying surface properties of the gate insulators. The interface between gate dielectric and organic film plays an important role in field-effect behavior because the first two to three molecular layers next to the dielectric interface dominate the charge transport [2]. Self-assembled monolayer (SAM), such as octadecyltrichlorosilane (OTS), has been widely used to modify the gate electric surface (SiO2) [3].Here we demonstrate that the use of SiO2 gate dielectric modified with a single molecular layer of PTCDI-C8 can yield a high-mobility organic semiconductor of pentacene. An average hole mobility about 1.71 cm2/VS is achieved, that is ten times higher than the mobility of devices fabricated on bare SiO2 under the same fabrication conditions (0.15 cm2/VS) and it is also higher than that of the devices with OTS treated SiO2. Furthermore the single PTCDI-C8 layer modified devices show in general a lower threshold voltage and a higher on/off ratio. Finally the devices with single layer of PTCDI-C8 treated SiO2 do not exhibit ambipolar characteristic due to the single layer of PTCDI-C8. The differences in film morphology and grain size obtained from AFM-Images and the X-ray diffraction patterns could be used to explain the high mobility resulting from the modification of SiO2 with a single layer of PTCDI-C8.
Fig. 1: field effect characteristic of 30nm pentacene devices
[1] C.D. Dimitrakopoulos, P. R. L. Malenfant, Adv. Mater. 14, 99 (2002)[2] G. Horowitz, J. Mater. Res., 19, 1946 (2007)[3] M. Stein, J. Mapel, J. B. Benziger and S. R. Forrest, APL, 81, 268 (2002)
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Knowledge Sharing and Knowledge Protection in Corss-cultural Collaboration
Steffen Kanzler1, Jens Leker1
1Institute of Business Chemistry at the Department og Chemistry and Pharmacy, University of Münster, Leonardo Campus 1, 48149 Münster, Germany
In our poster we present qualitative and quantitative data regarding knowledge sharing activities in the TRR 61. The qualitative study investigates different perceptions of knowledge sharing in a cross-cultural research collaboration between German and Chinese scientists. Special emphasis is placed on the in-group and out-group orientation of partners, different communication styles and personal and organizational influence factors. Data was obtained by conducting six focus groups in Germany and China. All ideas expressed in these focus groups were categorized and thoroughly evaluated. Our analysis reveals that the in- and out-group orientation of collectivistic and individualistic cultures might not be as pronounced as theory would suggest. In fact, members of the more collectivistic Chinese culture even showed a higher out-group orientation than members of the more individualistic German culture in our study. The quantitative study reveals, that collaborating partners perceive a collaboration to be more successful, if they are able to balance learning and protecting critical knowledge. However finding the equilibrium is rather difficult. Too much protection might be self defeating, while being too open might cause a loss of knowledge power. Resulting theoretical and practical implications for managing cross-cultural collaboration projects are discussed.
Abstracts for contributed posters
Computer simulations of charged particles in polymer electrolytes
Volker Lesch1, Diddo Diddens1, Andreas Heuer1
1Institute of physical chemistry, Corrensstraße 28/ 30, 48149 Münster, Germany
Background Maitra and Heuer investigated a PEO/LiBF4-electrolyte by means of MD simulations [1]. They found three different kinds of motion for the Li+-ions. Diddens research was focused on the cation dynamics in a similar electrolyte, namely PEO/LiTFSI [2]. The aim of this work was to investigate the anion dynamics and associated transport mechanisms in the latter.Results Anions don't enhance the cation dynamics directly but their motion is strongly affected by the polymer dynamics.
Fig.1 shows the mean square displacements of polymers and anions. On short time scales both curves have the same slope whereas at longer times the anions show a crossover. The polymer chains build cages around the anions and a change in the slope can be identified as � cage-break� . Furthermore, an indirect influence of the anions on the cation jumps was observed.Conclusion A correlation between the anion and polymer dynamics was found as well as an indirect anion influence on the cation jumps.
[1] A. Maitra, A. Heuer, Phys. Rev. Let., 2007, 98(22):227802.
[2] D.Diddens, A. Heuer, O. Borodin, Macromol., 2010, 43, 2028-2036.
Polymeric Superamphiphile for Controlled Self-assembly and Disassembly
Peng Han, Yapei Wang, Huaping Xu , Zhiqiang Wang, Xi Zhang*
Department of Chemistry, Tsinghua University, Beijing, China, 100084
Double-hydrophilic block copolymers with ionic and nonionic water-soluble segments and oppositely charged polyions or surfactants can form polymeric superamphiphile based on the macromolecular complex driven by electrostatic interaction. Self-assembly of such polymeric superamphiphile have the advantages such as simple preparation processes and no organic solvent. For example, we have employed poly(ethylene glycol)-b-poly(acrylic acid) (PEG-b-PAA) and azobenzene-containing surfactant (AzoC10) to fabricate photo-responsive superamphiphiles, which can self-assemble in water to form vesicles. Interestingly, the photoisomerization of azobenzene moieties can influence the amphiphilicity of the surfactant reversibly, which results in the self-assembly and disassembly of vesicles.[1]
In this presentation, we will discuss how to fabricate an oxidation-responsive polymeric superamphiphile (Fig. 1), which contains PEG-b-PAA and selenium-containing surfactant (SeQTA). [2] The polymeric superamphiphiles are able to self-assemble to form micelles in solution, and the micelles can be disassembled with the addition of 0.1% H2O2 because SeQTA is very sensitive to oxidation. It is anticipated that aggregates formed by polymeric superamphiphile may be explored as a container for controllable loading and releasing of drugs.
Fig. 1: Oxidation-responsive polymeric superamphiphile
[1] Y. P. Wang, P. Han, H. P. Xu, Z. Q. Wang, X. Zhang, A. V. Kabanov, Langmuir, 26, 709, (2010).[2] P. Han, N. Ma, H. F. Ren, H. P. Xu, Z. B. Li, Z. Q. Wang, X. Zhang, Langmuir, 26, 14414, (2010).
Reversible Dispersion of Single-Walled Carbon Nanotubes Based on a CO2-Responsive Dispersant
Yan Ding1, Senlin Chen1, Thien Huynh Ngo2, Huaping Xu1, Zhiqiang Wang1, Mario Smet2, Xi Zhang*1
1Department of Chemistry, Tsinghua University, Beijing, China, 1000842Department of Chemistry, University of Leuven, Belgium
Single-walled carbon nanotubes (SWNTs) are promising materials due to their unique structural, mechanical, and electronic properties.[1] However, their application has been greatly limited by difficulty in regulating their solubility in common solvents. To solve this problem, different kinds of stimuli-responsive dispersants that can change surface property of SWNTs in response to external stimuli have been developed, such as light[2] and redox[3] responsive dispersants.Herein, we have designed and synthesized a CO2-responsive dispersant, N,N-dimethyl-N� -(pyren-1-ylmethyl) acetimidamidinium (PyAH+, Fig. 1), which bears both a pyrene group and an amidinium moiety. Through strong π-π interaction between the pyrene group and SWNTs, PyAH+ can be modified onto SWNT surfaces to facilitate the dispersion of SWNTs in water. Furthermore, taking advantage of reversible interconversions between amidinium cation and amidine (PyA),[4,5] which can be simply triggered by bubbling CO2 or Ar, gas controlled dispersion and aggregation of SWNTs has been achieved.
Fig. 1 Gas Controlled Dispersion and Aggregation of SWNTs with a CO2-Responsive Dispersant
[1] R.H. Baughman, A.A. Zakhidov, W.A. de Heer, Science, 297, 787, (2002).[2] S. Chen, Y. Jiang, Z. Wang, X. Zhang, L. Dai, M. Smet, Langmuir, 24, 9233, (2008).[3] K. Nobusawa, A. Ikeda, J. Kikuchi, S. Kawano, N. Fujita, S. Shinkai, Angew. Chem. Int. Ed., 47, 4577, (2008).[4] Y. Liu, P.G. Jessop, M. Cunningham, C.A. Eckert, C.L. Liotta, Science, 313, 958, (2006).[5] T. Yu, R. Cristiano, R.G. Weiss, Chem. Soc. Rev., 39, 1435, (2010).
A pH responsive dendron-DNA-protein hybrid supramolecular system
Ping Chen 1 , Yawei Sun1, Huajie Liu1, Lijin Xu2, Qinghua Fan3 and Dongsheng Liu1
1Key Laboratory of Organic Optoelectronics & Molecular Engineering of the Ministry of Education, Department of Chemistry, Tsinghua University, China.
2Department of chemistry, Renmin University of China, 3Beijing National Laboratory for Molecular Sciences, Centre for Chemical Biology, Institute of Chemistry, Chinese Academy of Sciences
A pH responsive dendron-DNA-protein hybrid molecular system has been designed and prepared via chemical synthesis and assembly process. The size of this molecular system could be switched by the conformation change of the i-motif DNA. Its structure and switching mechanism has been characterized by mass spectroscopy, electrophoresis, circular dichroism (CD) spectroscopy and UV/Vis spectroscopy.
Fig. : the pH responsive dendron-DNA hybrid supramolecular systemThe system comprises three functional domains: the amphiphilic dendrons, i-motif based proton-driven DNA nanomachines and the streptavidin as a core. The size of this molecular system could be switched by the conformation change of its i-motif DNA.
Modelling the dynamics of micro-swimmers
E. Baresel1, R. Friedrich1
1Institute for Theoretical Physics, WWU Münster, Wilhelm-Klemm-Str. 9, 48149 Münster, Germany
The motion of self-propelled flagellated bacteria consists of two different modalities: � running� if all flagella rotate counter-clockwise or � tumbling� if at least one flagellum rotates clockwise [1].As a model for these bacterial motors we consider the dynamics of an ensemble of swimming objects which are composed of two rigidly connected point vortices. The single objects are able to show translation or rotation depending on the circulations of the single point vortices. We discuss the collective behaviour for several of these objects and the resulting velocity fields by means of numerical calculations.
Fig. 1: Flow fields of simulated micro-swimmers
[1] H. C. Berg, Phys. Today, 53, 24, (2000)
Simulation of Structure Forming on Surfaces
F. Lied1, T. Mues1, A. Heuer1
1Institute of Physical Chemistry, Westfälische Wilhelms-Universität Münster, Corrensstraße 28, Münster, Germany
Due to the liquid behavior of selected organic molecules, buldge formation was observed when depositing the molecules on patterned surfaces (Au-lines on SiO2) using electron force microscopy (EFM) [1].To gain a better understanding of the physical quantities, which are responsible for this effect, a 3D discrete Monte Carlo simulation was conducted. It was found that this rather simple simulation was capable of reproducing the experimental observations if the right sets of prerequisites were chosen.The shape of the growing buldge depends on the interaction energies between the single particles (εpp), the particles and the gold (εpg) and the particles and the SiO2 substrate (εps).The essential constraint for the buldge formation is the εpp/ εpg ratio.If εpp/ εpg < 1, no buldge formation will occur. For values of εpp/ εpg > 1 a transition in morphology from an equal distribution of the particles on the Au-surface for small εpp over differently shaped buldges to random nucleation along the Au-lines for large εpp.
Fig. 1: Buldge formation on Au-line on a 50x100x24 cubic primitve lattice
[1] W. Wang, C. Du, H. Bi, Y. Sun, Y. Wang, C. Mauser, E. Da Como, H. Fuchs, L. Chi, Adv. Mater. 22 (2010), 2764-2769
Phase behavior of chain molecules on surfaces: Monte Carlo simulation
Pritam Kumar Jana 1 and Andreas Heuer1
1Institute of Physical Chemistry, University of Muenster, Corrensstr. 28/30, Muenster, Germany
Self assembled monolayers of organic molecules on solid substrate build well defined surfaces, which can be structured efficiently on a nanometer scale. Self assembled monolayers are formed by organic molecules which spontaneously chemisorb on solid substrate [1,2], e.g. alkanethiolates attaching to gold surfaces with their sulfur head groups.We have studied an idealized model of chain molecules adsorbed on a flat substrate by means of extensive Monte Carlo Simulations. Our study focuses on phase transitions within a monolayer rather than on self aggregation. We model the molecules as rigid chains of Lennard-Jones spheres with one head group. As chain molecules are considered as rigid rod, all intra molecular degrees of freedom have been neglected. The Monte Carlo dynamics involves translational as well as rotational moves in the complete 3D space. Simulations were carried out in a simulation box of variable size and shape with periodic boundary condition in all directions. In the course of the simulation the concentration of chain molecules is increased with a fixed flux. Our goal is to determine the phase diagram in dependence of the different energetic and structural parameters (e.g. chain length) of the model.
[1] A. Ulman, Chem.Rev., 96, 1533, 1996.[2] G. E. Poirier, Chem. Rev., 97, 117, 1997.
Preparation and spectroscopic studies of perylene dyes on SiO2
D. K. Bhowmick, N. Aghdassi, F. Kleimeier, S. Linden, A. Devaux,L. De Cola, H. ZachariasPhysikalisches Institut and Center for Nanotechnology (CeNTech), Westfälische Wilhelms-Universität, 48149 Münster, Germany
Organic-inorganic hybrid systems have gained increasing interest due to their versatile applications e.g. organic solar cells, biosensors, light emitting devices or molecular electronics [1]. Polyaromatic hydrocarbons (PAHs) are the focus of our attention due to a high fluorescence quantum yield, a high sensitivity to the local environment and the possibility to tune their photophysical and electrochemical properties. SiO2 substrates are functionalized with two different perylene derivatives, N-benzyl perylene-3,4:9,10-tetracarboxylic-3,4-anhydride-9,10-imide (PMI) and Benzo (ghi) perylene-1,2-dicarboxylic anhydride, respectively. In both cases aminopropyltriethoxysilane (APTES) molecules are used as linker molecules which bind the dyes covalently to the surface via imide bonds. The covalent attachment of the dyes to the surface is verified by X-ray photoemission spectroscopy and FT-IR spectroscopy. UV absorption and steady-state fluorescence is measured for both systems.
OSi
O SiOO
SiO O
N N N
N OO
O O
SiO2
OSi
OSi
OO
SiO
O
N N NOO
SiO2
Fig. 1: SiO2 functionalized with PMI and Benzo (ghi) perylene-1, 2- dicarboxylic anhydride, respectively
[1] Martin Stutzmann, Applied Phys. Lett. 94, 113301 (2009)
Field Ion Microscopy meets Atomic Force Microscopy
J. Falter1, D.-A. Braun1, G. Langewisch1, H. Hölscher3, A. Schirmeisen2, and H. Fuchs1
1Center for Nanotechnology and Institute of Physics, University of Münster, Germany2Institute of Applied Physics (IAP), Justus-Liebig-University Giessen, Germany
3Karlsruhe Institute of Technology (KIT), Karlsruhe, Germany
Non-contact atomic force microscopy (ncAFM) is a well-established tool to image surfaces with atomic resolution. Yet, the mechanism which leads to these high resolution images is not completely understood. Theoretical simulations are addressed to this question but also demand the knowledge of the position of each atom. So far, the comparison of experimental AFM data with the results from simulations, suffer from the lack of knowledge of the real tip structure.A method which is able to resolve the probing tip apex with atomic precision is the Field Ion Microscope (FIM) [1].
Fig. 1: FIM image of a very sharp tungsten tip with an apex radius smaller 3nm (left). Such a sharp tip attached to a Qplus AFM Sensor (middle) yields to atomic resolution of the Au(110) surface reconstruction (right)
We present experiments carried out with FIM-characterized tungsten tips in low temperature ncAFM. The homemade sensors are based on a quartz tuning fork in the Qplus design [2] and etched electrochemically with the double lamellae technique [3]. From the FIM-experiments the apex radius of these tips can be calculated by the so called � ring couting method� [1]. Even an atom by atom reconstruction of the foremost atomic layers can be extracted from the FIM image. Combining both microscopy techniques offer the full information of the two interaction partners acting in AFM with atomic precision.
[1] E.W. Müller and T.T. Tsong, Field Ion Microscopy, American Elsevier 1969[2] F.J.Giessibl, Appl. Phys. Lett. 76, 1470 (2000)[3] M. Kulawik et al, Rev. Sci. Instrum. 74, 1027 (2002)
Markov analysis of the dynamics of biomolecules
Daniel Janssen-Mueller1, Jens Smiatek1, Andreas Heuer1
1Institute of Physical Chemistry, University of Muenster, Corrensstr. 28/30, Muenster, Germany
Molecular dynamic simulations are important instruments in the study of the dynamics of polymers, liquids and biomolecules. One characteristic quantity in biomolecular MD-simulations is the free energy. The set of geometric variables that span the free energy landscape may cause hysteresis effects of the motion of the system in the energy landscape. The cause of these effects is that relevant inner motions of the systems cannot be pictured by the set of the spanning variables. The topic of our studies is to detect incomplete sets of these variables. For this purpose, we studied the history-dependence of the system i.e. the Markovian characteristics and investigated the influence of one variable on two other variables during the movement of the system.
Fig. 1: Weighted Pearson-Correlations of the two most important Variables of a DNA i-motif high-temperature unfolding Simulation [1].
[1] J. Smiatek, D. Liu, A. Heuer, ArXiv e-prints 2011, arXiv:1103.5932v1.
Conservative and Dissipative Tip-Molecule Forces: Force Spectroscopy Investigations of an Organic Adsorbate
G. Langewisch1, D.-A. Braun1, H. Fuchs1, and A. Schirmeisen 1,2
1Institute of Physics, University of Münster, Wilhelm-Klemm-Str. 10, Münster, Germany2Institute of Applied Physics, University of Gießen, Heinrich-Buff-Ring 16, Gießen, Germany
Non-contact atomic force microscopy (ncAFM) [1] is an ideal tool to study structural properties of organic layers on solid substrates, which are for instance of high relevance for nanoelectronic applications. In addition to high resolution topography scans, conservative as well as dissipative tip-sample forces can be measured by ncAFM [2]. However, the image contrast mechanisms and processes leading to energy dissipation on organic layers are still under discussion. In order to study these processes, we investigated monolayers of 3,4,9,10-perylenetetra-carboxylic-dianhydride (PTCDA) adsorbed on Ag(111) by ncAFM. We performed force field experiments with submolecular resolution, which provided detailed information about forces and energy dissipation as a function of tip-sample distance and lateral position. From the force field measurements, we extracted force and dissipation spectroscopy curves that can be assigned to different areas within the molecules. Based on the results, we are able to identify systematic differences in the tip-sample interactions between end groups and the center of the molecules. The observed trends are in qualitative agreement with ab-initio simulations of the PTCDA/Ag system performed in cooperation with R. Perez (University of Madrid).
Fig. 1: Sitespecific force and dissipation spectroscopy with submolecular resolution
[1] R. Garcia, and R. Perez, Surf. Sci. Rep. , 47, 197 (2002).[2] J.P. Cleveland, B. Anczykowski, A.E. Schmid, and V.B. Elings, Appl. Phys. Lett., 72, 2613 (1998).
Microstructures and electronic properties of one-dimensional ZnO nanostructures
Peter Heß, Martin Peterlechner, Yong Lei, Gerhard Wilde
Institute for Materials Physics, WWU Münster, Wilhelm-Klemm Str. 10, 48149 MünsterCenter for Nanotechnology, Heisenbergstraße 11, 48149 Münster
One-dimensional (1-D) ZnO nanostructures were systematically investigated concerning their micro-structures and their photoluminescence properties. The main focus of this work is on the assembly of nanowires of different shapes and sizes to investigate their properties. The 1-D and 2-D ZnO structures were prepared using a Chemical Vapour Deposition (CVD) system with ZnO/C mixtures as sources, Au-coated silicon or sapphire as substrates, and an argon and oxygen gas flow as a distributor and oxidation source. Depending on the conditions during the CVD process, different kinds of ZnO nanostructures were obtained (e.g. Fig. 1, Fig. 2). The morphology of the ZnO nanostructures was checked by SEM whereas the photoluminescence properties were investigated using a spectrometer. Additionally, the crystalline structures, the growth direction, and the lattice spacing of ZnO nanostructures were characterized using TEM.
Fig. 1: Aligned ZnO nanowires Fig. 2: ZnO nanosails
Controlled pattern formation at moving contact lines of surfactant covered thin liquid films
Michael H. Köpf, Svetlana V. Gurevich, Rudolf Friedrich
Institute for Theoretical Physics, University of Münster, Wilhelm-Klemm-Str. 9, D-48149 Münster, Germany
Surfactant monolayers can be transfered from a liquid subphase onto a solid substrate by use of well-established methods like Langmuir-Blodgett transfer, that is, controlled withdrawal of the solid from the surfactant covered liquid bath.
Under certain experimental conditions, an instability of the transfer process has been discovered, that leads to the formation of highly regular periodic stripe patterns of merely a few hundred nanometers period length [1].
This phenomenon results from phase decomposition in the monolayer triggered by an interaction with the substrate at the contact line. It can be understood in terms of a model describing a receding contact line of a surfactant covered liquid film in the vicinity of a monolayer phase transition [2,3]. The model comprises two coupled nonlinear partial differential equations that have been derived within the framework of the lubrication approximation.
On the basis of this model, we discuss possibilities to control the properties of the transfered patterns. As has been predicted recently, chemically prepatterned substrates can be utilized to yield structures of higher complexity [4], such as well-aligned arrays of circular monolayer domains. Such structures can be applied in exciton experiments and might even provide self-assembled templates for surface plasmon experiments.
[1] M. Gleiche, L. F. Chi, H. Fuchs, Nature, 403, 173 (2000)[2] M. H. Köpf, S. V. Gurevich, R. Friedrich, EPL, 86, 66003 (2009)[2] M. H. Köpf, S. V. Gurevich, R. Friedrich, L. F. Chi, Langmuir, 26, 10444 (2010)[2] M. H. Köpf, S. V. Gurevich, R. Friedrich, Phys. Rev. E, 83, 016212 (2011)
Spiking Neural Networks � Pattern Formation and Plasticity
Cornelia Petrovic1, Rudolf Friedrich1
1Institute for Theoretical Physics, University of Münster, Wilhelm-Klemm-Straße 9, D-48149 Münster, Germany
We study spiking neuronal networks which consist of pulse-coupled phase oscillators. The underlying model was introduced by Hermann Haken as the lighthouse model [1]. It is a single neuron model that falls between spiking neuron models and firing rate descriptions and thus combines the "best of both worlds". In the limit of slow synaptic interactions it can be reduced to the classic Wilson-Cowan and Amari type firing rate models [2,3,4]. For fast synaptic dynamics, it shows some of the complex properties of spiking neural networks. On the one hand, we will present some work on pattern formation in these spiking networks. On the other hand, we will discuss the influence of spike timing dependent plasticity (STDP) [5].
Fig. 1: Dendritic currents (x,t): multi-bump pattern formation.ψ
[1] H. Haken, Brain Dynamics, Springer, New York, Berlin (2002)[2] H.R. Wilson, J.D. Cowan, Biophys. J., 12 , 1 (1972).[3] S. Amari, IEEE Trans. Systems Man Cybernet., 2, 643 (1972). [4] C.C. Chow and S. Coombes, SIAM J.Appl. Dyn. Syst., 5 (4), 552 (2006).[5] G. Bi, M. Poo, Annu. Rev. Neurosci., 24, 139 (2001)
Effect of Topography on the Differentiation of Embryonic Stem Cells to Neuronal Lineage in the Nano-micro Range
Fei Pan1, Guangming Wu2, Hans Schöler2, Lifeng Chi1
1Physikalisches Institut, University Münster, Germany 2Department of cell and developmental biology, Max Planck Institute for Molecular Biomedicine, Münster, Germany
Embryonic stem cells (ESC) are pluripotent cells, which have the ability to differentiate into three germ layers. Differentiation of ESC towards neuronal lineage leads great potential for disease modeling and drug screening. As extracellular matrix (ECM) in vivo comprises topography in the nanoscale, topography could also influence stem cell differentiation in the nano-micro range in vitro. In this work, we use lithography to fabricate nano/micro structure with finely controlled dimensions and different pitches (ridge/groove width: 700, 2000, 10000nm, height: 350nm). HM1 mouse ESC were seeded on structured PDMS substrates, and cultured for 10 days. Nuclei of ESC were aligned and elongated in the direction of nano/micro structure, while distributing randomly in flat PDMS control. This contact guidance significantly increased when the cells were cultured on the substrates with smaller pitch. Gene expression profiling by RT-PCR and immunostaining showed significant up-regulation of neuronal markers in structured PDMS. We also tested HB9 ESC on structured surface in induction medium, and found that the efficiency of motor neuron generation could be enhanced by combining topographical and chemical cues. Even though the elongations of cytoskeleton and nucleus were correlated with such changes in gene and protein expression,the mechanism of topography induced differentiation remains unclear. This study demonstrate the significance oftopography, especially the pitch width of structured surfaces in directing differentiation of embryonic stem cells towards neuronal lineage, suggesting potential application of topography in clinical regenerative medicine.
SURFACE MOLECULAR IMPRINTING IN LAYER-BY-LAYER FILMS ON SILICA PARTICLES
Jan Gauczinski1, Zhihua Liu2, Xi Zhang2, Monika Schönhoff1
1 Institute of Physical Chemistry, University of Muenster, Corrensstr. 28/30, 48149 Münster, Germany; 2 Key Laboratory of Organic Optoelectronics & Molecular Engineering, Department of Chemistry, Tsinghua University, Beijing 100084, P. R. China.
Molecularly imprinted polymers (MIPs), mimicking complex molecular recognition systems in nature, are a promising method to obtain systems for specific separation or reactive sites for nanoreactors. The challenge is to find structures with high stability, high affinity and low diffusion time of guest molecules. Deeply buried binding sites in bulk hinder template removal and guest diffusion. The combination of layer-by-layer (LbL) self-assembly of oppositely charged polymers[1] with the concept of molecular imprinting[2] in polymers promises to be a solution to achieve fast loading/unloading. Based on the experience with Surface Molecular Imprinted LbL films (SMILbL)[3,4] our goal was to obtain a selective material on the surface of dispersed silica particles to maximise the active area and study the material with advanced techniques. The multilayer is designed to include the template during the LbL build-up and to form a cross-linked network upon UV-irradiation for enhanced stability. A theophylline moiety is grafted to poly(acrylic acid) as the template molecule, while a UV-sensitive diazo polycation (DAR) cross-links the polymers after irradiation. The successful build-up is strongly depending on the deposition conditions, such as pH-value, salt concentration and solvent composition. Therefore, zeta-potential and size measurements are suited to observe the build-up and UV-vis spectroscopy is used to determine complete cross-linking. The release of the template leads to the imprinted binding sites, that show different rebinding selectivity to theophylline and caffeine. Both of these processes can be observed by NMR spectroscopy in the particle dispersion, by locating the probe molecule in the liquid phase or adsorbed to the solid phase.
[1] G. Decher, Science 277, 1232 (1997).[2] G. Wulff, Angew. Chem. Int. Ed. Engl. 34, 1812 (1995).[3] a) F. Shi, Z. Liu, G. L. Wu, M. Zhang, H. Chen, Z. Wang, X. Zhang, I. Willner, Adv. Func. Mater. 17, 1821 (2007); b) J.
Gauczinski, Z. Liu, X. Zhang, M. Schönhoff, Langmuir 26, 10122 (2010)[4] J. Niu, Z. Liu, L. Fu, F. Shi, H. Ma, Y. Ozaki, X. Zhang, Langmuir 24, 11988 (2008).
Chuan Du, Liqiang Li, Wenchong Wang, Harald Fuchs, and Lifeng Chi
