The Influence of Nanoscale Roughness on the Electrostatic Double Layer: the Shift of the Isoelectric Point of Cluster-Assembled Nanostructured Zirconia Films

2018 ◽  
Author(s):  
Francesca Borghi ◽  
Bianca Scaparra ◽  
Costanza Paternoster ◽  
Paolo Milani ◽  
Alessandro Podestà
Keyword(s):  
Double Layer ◽  
Isoelectric Point ◽  
Electrostatic Force ◽  
Debye Length ◽  
Exponential Model ◽  
Morphological Properties ◽  
Corrugated Surfaces ◽  
Wide Range ◽  
Electrostatic Double Layer ◽  
Colloidal Probes

We investigated the influence of the nanoscale surface morphology on the electrostatic double layer at corrugated surfaces in aqueous electrolytes. To this purpose, we have produced cluster-assembled nanostructured zirconium dioxide (ns-ZrOx, x ≈ 2) films with controlled morphological properties by supersonic cluster beam deposition (SCBD), and measured the double layer interaction using atomic force microscopy with colloidal probes. SCBD allowed tuning the characteristic widths of the corrugated interface (the rms roughness, the correlation length) across a wide range of values, matching the width of the electrostatic double-layer (the Debye length), and the typical size of nano-colloids (proteins, enzymes, and catalytic nanoparticles). To accurately characterize the surface charge density in the high-roughness regime, we have developed a two-exponential model of the electrostatic force that explicitly includes roughness, and better accounts for the roughness-induced amplification of the interaction. We were then able to observe a marked reduction of the isoelectric point of ns-ZrOx surfaces on increasingly rough surfaces. This result is in good agreement with our previous observations on cluster-assembled nanostructured titania films, and demonstrates that the phenomenon is not limited to a specific material, but more generally depends on peculiar nanoscale morphological effects, related to the competition of the characteristic lengths of the system.<br>

The Influence of Nanoscale Roughness on the Electrostatic Double Layer: the Shift of the Isoelectric Point of Cluster-Assembled Nanostructured Zirconia Films

2018 ◽  
Author(s):  
Francesca Borghi ◽  
Bianca Scaparra ◽  
Costanza Paternoster ◽  
Paolo Milani ◽  
Alessandro Podestà
Keyword(s):  
Double Layer ◽  
Isoelectric Point ◽  
Electrostatic Force ◽  
Debye Length ◽  
Exponential Model ◽  
Morphological Properties ◽  
Corrugated Surfaces ◽  
Wide Range ◽  
Electrostatic Double Layer ◽  
Colloidal Probes

We investigated the influence of the nanoscale surface morphology on the electrostatic double layer at corrugated surfaces in aqueous electrolytes. To this purpose, we have produced cluster-assembled nanostructured zirconium dioxide (ns-ZrOx, x ≈ 2) films with controlled morphological properties by supersonic cluster beam deposition (SCBD), and measured the double layer interaction using atomic force microscopy with colloidal probes. SCBD allowed tuning the characteristic widths of the corrugated interface (the rms roughness, the correlation length) across a wide range of values, matching the width of the electrostatic double-layer (the Debye length), and the typical size of nano-colloids (proteins, enzymes, and catalytic nanoparticles). To accurately characterize the surface charge density in the high-roughness regime, we have developed a two-exponential model of the electrostatic force that explicitly includes roughness, and better accounts for the roughness-induced amplification of the interaction. We were then able to observe a marked reduction of the isoelectric point of ns-ZrOx surfaces on increasingly rough surfaces. This result is in good agreement with our previous observations on cluster-assembled nanostructured titania films, and demonstrates that the phenomenon is not limited to a specific material, but more generally depends on peculiar nanoscale morphological effects, related to the competition of the characteristic lengths of the system.<br>

Enzyme Immobilization Behavior on the Surface of Hydroxyapatite Capsules under Alkaline Condition

2018 ◽  
Vol 782 ◽  
pp. 21-26
Author(s):  
Takeshi Yabutsuka ◽  
Masaya Yamamoto ◽  
Shigeomi Takai ◽  
Takeshi Yao
Keyword(s):  
Enzyme Immobilization ◽  
Double Layer ◽  
Isoelectric Point ◽  
Electrical Double Layer ◽  
Alkaline Condition ◽  
Bicarbonate Buffer

We prepared hydroxyapatite (HA) capsules encapsulating maghemite particles. In order to evaluate enzyme immobilization behavior of the HA capsules under alkaline condition, we immobilized five kinds of enzymes with different isoelectric point in carbonate/bicarbonate buffer (CBB, pH 10.0). When the enzymes in CBB were moderately charged, immobilization efficiency on the HA capsules showed the highest value. It was suggested that immobilization efficiency was affected according to both pI of enzyme and pH of the surrounding solution and that enzyme immobilized on the HA capsules by not only electrical double layer interactions but also ion interaction and other interactions.

scholarly journals Dispersive evaluation and surface chemistry of advanced, multifunctional silica/lignin hybrid biomaterials

2013 ◽  
Vol 11 (11) ◽  
pp. 1860-1873 ◽  
Author(s):  
Magdalena Nowacka ◽  
Łukasz Klapiszewski ◽  
Małgorzata Norman ◽  
Teofil Jesionowski
Keyword(s):  
Zeta Potential ◽  
Surface Charge ◽  
Electrochemical Sensors ◽  
Relevant Information ◽  
Structural Features ◽  
Kraft Lignin ◽  
Morphological Properties ◽  
Wide Range ◽  
Hybrid Biomaterials

AbstractAdvanced silica/lignin hybrid biomaterials were obtained using hydrated or fumed silicas (Aerosil®200) and Kraft lignin as precursors, which is a cheap and biodegradable natural polymer. To extend the possible range of applications, the silicas were first modified with N-2-(aminoethyl)-3-aminopropyltrimethoxsysilane, and then with Kraft lignin, which had been oxidized with sodium periodate. The SiO2/lignin hybrids and precursors were characterised by means of determination of their physicochemical and dispersive-morphological properties. The effectiveness of silica binding to lignin was verified by FT-IR spectroscopy. The zeta potential value provides relevant information regarding interactions between colloid particles. Measurement of the zeta potential values enabled an indirect assessment of stability for the studied hybrid systems. Determination of zeta potential and density of surface charge also permitted the quantitative analysis of changes in surface charge, and indirectly confirmed the effectiveness of the proposed method for synthesis of SiO2/lignin hybrid materials. A particularly attractive feature for practical use is their stability, especially electrokinetic stability. It is expected that silica/lignin hybrids will find a wide range of applications (polymer fillers, biosorbents, electrochemical sensors), as they combine the unique properties of silica with the specific structural features of lignin. This makes these hybrids biomaterials advanced and multifunctional.

scholarly journals Rainfall spatio-temporal correlation and intermittency structure from micro-γ to meso-β scale in the Netherlands

2021 ◽  
Author(s):  
Thomas C. van Leth ◽  
Hidde Leijnse ◽  
Aart Overeem ◽  
Remko Uijlenhoet
Keyword(s):  
The Netherlands ◽  
Spatial Scales ◽  
Rainfall Variability ◽  
Temporal Structure ◽  
Temporal Correlation ◽  
Exponential Model ◽  
Rain Gauges ◽  
Wide Range ◽  
Spatio Temporal ◽  
Two Parameter

AbstractWe investigate the spatio-temporal structure of rainfall at spatial scales from 7m to over 200 km in the Netherlands. We used data from two networks of laser disdrometers with complementary interstation distances in two Dutch cities (comprising five and six disdrometers, respectively) and a Dutch nationwide network of 31 automatic rain gauges. The smallest aggregation interval for which raindrop size distributions were collected by the disdrometers was 30 s, while the automatic rain gauges provided 10-min rainfall sums. This study aims to supplement other micro-γ investigations (usually performed in the context of spatial rainfall variability within a weather radar pixel) with new data, while characterizing the correlation structure across an extended range of scales. To quantify the spatio-temporal variability, we employ a two-parameter exponential model fitted to the spatial correlograms and characterize the parameters of the model as a function of the temporal aggregation interval. This widely used method allows for a meaningful comparison with seven other studies across contrasting climatic settings all around the world. We also separately analyzed the intermittency of the rainfall observations. We show that a single parameterization, consisting of a two-parameter exponential spatial model as a function of interstation distance combined with a power-law model for decorrelation distance as a function of aggregation interval, can coherently describe rainfall variability (both spatial correlation and intermittency) across a wide range of scales. Limiting the range of scales to those typically found in micro-γ variability studies (including four of the seven studies to which we compare our results) skews the parameterization and reduces its applicability to larger scales.

scholarly journals The influence of dielectric decrement on electrokinetics

2013 ◽  
Vol 724 ◽  
pp. 69-94 ◽  
Author(s):  
Hui Zhao ◽  
Shengjie Zhai
Keyword(s):  
Asymptotic Analysis ◽  
Double Layer ◽  
Debye Length ◽  
Charged Surface ◽  
Ion Specificity ◽  
Zeta Potentials ◽  
Condensed Layer ◽  
The Impact ◽  
Surface Conduction ◽  
Electro Osmotic Flow

AbstractWe treat the dielectric decrement induced by excess ion polarization as a source of ion specificity and explore its impact on electrokinetics. We employ a modified Poisson–Nernst–Planck (PNP) model accounting for the dielectric decrement. The dielectric decrement is determined by the excess-ion-polarization parameter $\alpha $ and when $\alpha = 0$ the standard PNP model is recovered. Our model shows that ions saturate at large zeta potentials $(\zeta )$. Because of ion saturation, a condensed counterion layer forms adjacent to the charged surface, introducing a new length scale, the thickness of the condensed layer $({l}_{c} )$. For the electro-osmotic mobility, the dielectric decrement weakens the electro-osmotic flow owing to the decrease of the dielectric permittivity. At large $\zeta $, when $\alpha \not = 0$, the electro-osmotic mobility is found to be proportional to $\zeta / 2$, in contrast to $\zeta $ as predicted by the standard PNP model. This is attributed to ion saturation at large $\zeta $. In terms of the electrophoretic mobility ${M}_{e} $, we carry out both an asymptotic analysis in the thin-double-layer limit and solve the full modified PNP model to compute ${M}_{e} $. Our analysis reveals that the impact of the dielectric decrement is intriguing. At small and moderate $\zeta ~({\lt }6kT/ e)$, the dielectric decrement decreases ${M}_{e} $ with increasing $\alpha $. At large $\zeta $, it is known that the surface conduction becomes significant and plays an important role in determining ${M}_{e} $. It is observed that the dielectric decrement effectively reduces the surface conduction. Hence in stark contrast, ${M}_{e} $ increases as $\alpha $ increases. Our predictions of the contrast dependence of the mobility on $\alpha $ at different zeta potentials qualitatively agree with experimental results on the dependence of the mobility among ions and provide a possible explanation for such ion specificity. Finally, the comparisons between the thin-double-layer asymptotic analysis and the full simulations of the modified PNP model suggest that at large $\zeta $ the validity of the thin-double-layer approximation is determined by ${l}_{c} $ rather than the traditional Debye length.

scholarly journals Electrokinetics in Micro-channeled Cantilevers: Extending the Toolbox for Reversible Colloidal Probes and AFM-Based Nanofluidics

2019 ◽  
Vol 9 (1) ◽  
Author(s):  
Andreas Mark ◽  
Nicolas Helfricht ◽  
Astrid Rauh ◽  
Jinqiao Xue ◽  
Patrick Knödler ◽  
...  
Keyword(s):  
Essential Element ◽  
The State ◽  
Micro Channel ◽  
Force Measurements ◽  
Ion Conductance ◽  
Nanoparticle Deposition ◽  
Micro Channels ◽  
Wide Range ◽  
Colloidal Probes

AbstractThe combination of atomic force microscopy (AFM) with nanofluidics, also referred to as FluidFM, has facilitated new applications in scanning ion conductance microscopy, direct force measurements, lithography, or controlled nanoparticle deposition. An essential element of this new type of AFMs is its cantilever, which bears an internal micro-channel with a defined aperture at the end. Here, we present a new approach for in-situ characterization of the internal micro-channels, which is non-destructive and based on electrochemical methods. It allows for probing the internal environment of a micro-channeled cantilever and the corresponding aperture, respectively. Acquiring the streaming current in the micro-channel allows to determine not only the state of the aperture over a wide range of ionic strengths but also the surface chemistry of the cantilever’s internal channel. The high practical applicability of this method is demonstrated by detecting the aspiration of polymeric, inorganic and hydrogel particles with diameters ranging from several µm down to 300 nm. By verifying in-situ the state of the aperture, i.e. open versus closed, electrophysiological or nano-deposition experiments will be significantly facilitated. Moreover, our approach is of high significance for direct force measurements by the FluidFM-technique and sub-micron colloidal probes.

Review of the genus Phormidesmis (Cyanobacteria) based on environmental, morphological, and molecular data with description of a new genus Leptodesmis

Phytotaxa ◽  
2019 ◽  
Vol 395 (1) ◽  
pp. 1-16 ◽  
Author(s):  
LENKA RAABOVÁ ◽  
LUBOMIR KOVACIK ◽  
JOSEF ELSTER ◽  
OTAKAR STRUNECKÝ
Keyword(s):  
Molecular Data ◽  
Morphological Properties ◽  
Phylogenetic Position ◽  
Rrna Gene ◽  
Filamentous Cyanobacteria ◽  
Wide Range ◽  
Significant Divergence ◽  
Taxonomic Methods ◽  
Morphological And Molecular Data ◽  
Definition Of

Very thin filamentous cyanobacteria are ubiquitous in a wide range of environments. For many years they were traditionally studied according to their morphological properties only. With the introduction of additional taxonomic methods (cytomorphological analyses, molecular sequencing, exact ecological studies, better data about phytogeographical distribution), traditional genera such as Leptolyngbya and Phormidium were found to be polyphyletic. Phormidesmis belonged to a newly formed genus that was supposed to explain the variability of such very thin simple filamentous cyanobacteria. However, even after definition of Phormidesmis based on distinct cytomorphological and phylogenetic traits, the variability within this genus remained unresolved. Here we analyzed 26 Phormidesmis strains to describe the variability within this genus, classified two new species (P. arctica and P. communis) and transferred Leptolyngbya nigrescens into P. nigrescens. A tabular review of Phormidesmis species is included. The diacritical features of all these species are: width up to 1–4 µm, barrel-shaped cells, which can be shorter or slightly longer than wide, with apparent constrictions at the cross-walls. Our study shows that Phormidesmis is a morphologically and genetically well-defined genus with a global distribution. A newly described genus Leptodesmis has significant morphological similarities both with Phormidesmis and Leptolyngbya, however with intermediate phylogenetic position with significant divergence in 16S rRNA gene. Leptodesmis is cryptic both to Phormidesmis and Leptolyngbya. In the initial part of the life cycle resembles Leptolyngbya, the appearance of older trichomes change to Phormidesmis like morphology.

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