Langmuir (LANGMUIR)

Publications in this journal

• Article: The dynamics of nanoscale droplets on moving surfaces

  Konstantinos Ritos, Nishanth Dongari, Matthew K. Borg, Yonghao Zhang, Jason M. Reese
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  ABSTRACT: We use molecular dynamics (MD) simulations to investigate the dynamic wetting of nanoscale water droplets on moving surfaces. The density and hydrogen bonding profiles along the direction normal to the surface are reported, and the width of the water depletion layer is evaluated first for droplets on three different static surfaces: silicon, graphite, and a fictitious superhydrophobic surface. The advancing and receding contact angles, and contact angle hysteresis, are then measured as a function of capillary number on smooth moving silicon and graphite surfaces. Our results for the silicon surface show that molecular displacements at the contact line are influenced greatly by interactions with the solid surface and partly by viscous dissipation effects induced through the movement of the surface. For the graphite surface, however, both the advancing and receding contact angles values are close to the static contact angle value and are independent of the capillary number; i.e., viscous dissipation effects are negligible. This finding is in contrast with the wetting dynamics of macroscale water droplets, which show significant dependence on the capillary number.
  Langmuir 05/2013;
• Article: Computer Simulations of Evaporation of Pinned Sessile Droplets: Influence of Kinetic Effects

  Sergey Semenov, Victor M. Starov, Ramon G. Rubio, Manuel G. Velarde
  Langmuir 11/2012; 28(43):16724–16724.
• Article: The Simple Synthesis of Palladium Nanoparticles, the β- Phase Formation and the Control of Chain and Dipole Orientations in Palladium Doped Poly(vinylidene fluoride) Thin Films

  Dipankar Mandal, a Kap Jin Kim, † Jong Soon Lee‡
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  ABSTRACT: The palladium nanoparticles (Pd-NPs) are prepared by a simple one step procedure when poly(vinylidene fluoride) (PVDF) is used as a polymer stabilizer. The high quality Pd-NPs doped PVDF thin films are fabricated where heat-controlled spin-coating technique is adopted. The effect of Pd-NPs on the crystal modifications and lamellae orientation in PVDF film is investigated using the Fourier-Transform infrared-grazing incidence reflection absorption spectroscopy. The electroactive β-phase and edge-on crystalline lamellae are found to be formed preferentially in Pd-NPs doped PVDF films. As a result, Pd-NPs doped PVDF ultrathin films gave very good discernible contrast between the written and erased data bits, which suggests that they can be used as a scanning probe microscopy based ferroelectric memory device or a ferroelectric gate field effect transistor memory device in future.
  Langmuir 06/2012; accepted(---):-.
• Article: Electrically Conducting Nanopatterns Formed by Chemical e-Beam Lithography via Gold Nanoparticle Seeds

  Patrick A. Schaal, Astrid Besmehn, Eva Maynicke, Michael Noyong, Bernd Beschoten, Ulrich Simon
  Langmuir 01/2012; 28(5):2448–2454.
• Article: Silver-assisted colloidal synthesis of gold patchy particles with tunable patchiness

  Huixin Bao, Benjamin Butz, Zhou Zhou, Erdmann Spiecker, Martin Hartmann, Robin Klupp Taylor
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  ABSTRACT: Patchy particles possessing heterogeneous surface composition show great promise as self-organizing building blocks for new classes of hierarchical functional structures. A major hurdle is the scalable synthesis of stable patches on nanosized core particles with arbitrarily defined patch number and coverage. So far, few methods have been reported which could be expected to meet these challenges. Recently we described the heterogeneous nucleation and growth of silver patches on silica nanospheres via a template free colloidal route. The patches produced, although tunable in size and number and showing interesting plasmon resonant properties, were rather unstable and degraded rapidly during attempts to process them further. In the present work, therefore, we set out to explore if related approaches can be employed to produce patchy particles involving gold, which is known to be more stable. The differences between typical patch precursors Ag⁺ and [AuCl_x(OH)_4-x]^- and their respective interactions with amorphous silica make this a significant challenge. We show that preformed small silver patches in addition to the presence of a reducing agent are necessary for the formation of gold patches conformal to the silica nanosphere surface. Systematic study of the process parameters and their influence on the patchiness as well as in-depth analytical TEM investigation of the patch composition reveal that patches spread over the silica surface via a cycle of galvanic dissolution and redeposition of silver.The resulting gold patchy particles remain stable during subsequent storage or washing and display tunable plasmon resonances within the visible and near-IR spectrum.
  Langmuir 01/2012;
• Article: Effect of nanoroughness on highly hydrophobic and superhydrophobic coatings

  Mammen L, Deng X, Untch M, Vijayashankar V, Papadopoulos P, Berger R, Riccardi E, Leroy F, Vollmer D
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  ABSTRACT: The effect of nanoroughness on contact angles and pinning is investigated experimentally and numerically for low energy surfaces. Nanoroughness is introduced by chemical vapor deposition of tetraethoxysilane and was quantified by scanning force microscopy. Addition of a root mean square roughness of 2 nm on a flat surface can increase the contact angle after fluorination by a semifluorinated silane by up to 30°. On the other hand, nanoroughness can improve or impair the liquid repellency of superhydrophobic surfaces which were made from assembled raspberry particles. Molecular dynamics simulations are performed in order to gain a microscopic understanding on how the length and the surface coating density of semifluorinated silanes influence the hydrophobicity. Solid-liquid surface free energy computations reveal that the wetting behavior strongly depends on the density and alignment of the semifluorinated silane. At coating densities in the range of experimental values, some water molecules can penetrate between the semifluorinated chains, thus increasing the surface energy. Combining the experimental and numerical data exhibits that a roughness induced increase of the contact angle competes with increased pinning caused by penetration of liquid into nanopores or between neighboring semifluorinated molecules.
  Langmuir 01/2012;
• Article: Enhanced Optical Properties of Graphene Oxide – Au Nanocrystal Composites

  Y.H. Lee, L. Polavarapu, Nengyue Gao, Peiyan Yuan, Qing-Hua Xu
  Langmuir 01/2012;
• Article: Surface complexation of 2,5-dihydroxybenzoic acid at the nano-sized hematite-water interface: an ATR-FTIR study and modeling approach

  K. Hanna, F. Quilès
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  ABSTRACT: In this study, characteristic interactions of 2,5-dihydroxybenzoic acid (or gentisic acid, GA) with the surface of 15-nm-sized hematite (R-Fe2O3) were studied by combining batch macroscopic experiments, in situ attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopic investigations, and surface complexation modeling. A correlation between the pH, the amount of adsorbed GA, and the amount of Fe(III) released from the hematite surface was observed, whereas the dissolution of hematite nanoparticles became significant only at low pH and high ligand loading. From the ATR-FTIR results, two aqueous complex structures have been identified depending on pH. At the hematite-water interface, the occurrence of one deprotonated inner-sphere “bidentate” complex and one outer-sphere complex was suggested through all of the investigated pH range. At high surface coverage, variations of vibrational band intensities were observed, suggesting the occurrence of nonspecific molecular interactions. The macroscopic results (i.e., GA batch sorption and the ligand-promoted dissolution of hematite) obtained under a wide range of experimental onditions corroborated the ATR-FTIR microscopic findings. GA adsorption was described by a surface complexation model fitted to pH-adsorption curves with 1mMsorbate concentration in the pH range of 3-9. Two surface complexes (one outer-sphere species (tFeOH2)2 3 3 3H2L(1þ,1-) and one inner-sphere species (tFe)2H2L) were proposed using the three-plane model. The inner-sphere complexes were predominant at low pH values, and the relative concentrations of the outer-sphere species increased with the pH increase. The formation of inner-sphere complexes at acidic pH values can promote the dissolution of nanosized hematite. At high solute loading, GA oxidation into carboxybenzoquinone compounds by ferric species was suspected, suggesting the occurrence of a redox reaction analogous to that of hydroquinone compounds.
  Langmuir 02/2011; 27(6):2492-2500.
• Article: Nanoscale Water Condensation on Click-Functionalized Self-Assembled Monolayers

  M. James, S. Ciampi, T. A. Darwish, T. L. Hanley, S. O. Sylvester, J. J. Gooding
  Langmuir 01/2011; 27:10753.
• Article: Elemental Depth Profiling of Fluoridated Hydroxyapatite: Saving Your Dentition by the Skin of Your Teeth?

  Frank Müller, Christian Zeitz, Hubert Mantz, Karl-Heinz Ehses, Flavio Soldera, Jörg Schmauch, Matthias Hannig, Stefan Hüfner, Karin Jacobs
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  ABSTRACT: Structural and chemical changes that arise from fluoridation of hydroxyapatite (Ca5(PO4)3OH or “HAp”), as representing the synthetic counterpart of tooth enamel, are investigated by X-ray photoelectron spectroscopy (XPS). Elemental depth profiles with a depth resolution on the nanometer scale were determined to reveal the effect of fluoridation in neutral (pH = 6.2) and acidic agents (pH = 4.2). With respect to the chemical composition and the crystal structure, XPS depth profiling reveals different effects of the two treatments. In both cases, however, the fluoridation affects the surface only on the nanometer scale, which is in contrast to recent literature with respect to XPS analysis on dental fluoridation, where depth profiles of F extending to several micrometers were reported. In addition to the elemental depth profiles, as published in various other studies, we also present quantitative depth profiles of the compounds CaF2, Ca(OH)2, and fluorapatite (FAp) that were recently proposed by a three-layer model concerning the fluoridation of HAp in an acidic agent. The analysis of our experimental data exactly reproduces the structural order of this model, however, on a scale that differs by nearly 2 orders of magnitude from previous predictions. The results also reveal that the amount of Ca(OH)2 and FAp is small compared to that of CaF2. Therefore, it has to be asked whether such narrow Ca(OH)2 and FAp layers really can act as protective layers for the enamel.
  Langmuir 11/2010; 26(24):18750.