Droplet Evaporation Method Research Articles

On the origin of surfaces-dependent growth of benzoic acid crystal inferred through the droplet evaporation method

Crystal growth behavior of benzoic acid crystals on different surfaces was examined. The performed experiments documented the existence of very strong influence introduced by polar surfaces as glass, gelatin, and polyvinyl alcohol (PVA) on the growth of benzoic acid crystals. These surfaces impose strong orientation effect resulting in a dramatic reduction of number of faces seen with x-ray powder diffractions (XPRD). However, scrapping the crystal off the surface leads to a morphology that is similar to the one observed for bulk crystallization. The surfaces of low wettability (paraffin) seem to be useful for preparation of amorphous powders, even for well-crystallizable compounds. The performed quantum chemistry computations characterized energetic contributions to stabilization of morphology related faces. It has been demonstrated, that the dominant face (002) of benzoic acid crystal, growing on polar surfaces, is characterized by the highest densities of intermolecular interaction energies determining the highest cohesive properties among all studied faces. Additionally, the inter-layer interactions, which stand for adhesive properties, are also the strongest in the case of this face. Thus, quantum chemistry computations providing detailed description of energetic contributions can be successfully used for clarification of adhesive and cohesive nature of benzoic acids crystal faces.

A Further Indication of the Self-Ordering Capacity of Water Via the Droplet Evaporation Method

The droplet evaporation method (DEM) is increasingly used for assessing various characteristics of water. In our research we tried to use DEM to detect a possible self-ordering capability of (spring) water that would be similar to the already found and described autothixotropic phenomenon, namely increasing order of non-distilled water subject to aging. The output of DEM is a droplet remnant pattern (DRP). For analysis of DRP images we used a specially developed computer program that does the frequency distribution analysis of certain parameters of the images. The results of experiments demonstrated statistically significant differences in both aging of water as well as in the glass exposed surface/volume ratio of the aged water. The most important result supporting the self-ordering character of water was found in an increasing dependence between two analyzed parameters: distance and frequency, at the peak frequency. As the result concerns mostly aging and shows increasing order it further corroborates other findings concerning increasing order by aging. Such further confirmation of self-ordering capacity of water is not important only for physical chemistry, but also for biology.

Qualitative discrimination between organic and biodynamic Sangiovese red wines for authenticity

In this study the ability of the droplet evaporation method (DEM) to discriminate between organic and biodynamic Sangiovese red wines was studied for the first time. The relationship between the sizing-parameters and shape-descriptors of the crystal structures and the chemical parameters of wines was evaluated, and the most significant correlations were found between the intensity of red color of wines with circularity (r = 0.90) and solidity (r = 0.94). Moreover the shape-descriptors allowed a discrimination between the organic and biodynamic Sangiovese red wines based on two kinds of structures: (i) needle-like and (ii) flower-like forms.

Droplet evaporation method as a new potential approach for highlighting the effectiveness of ultra high dilutions

This study sought to verify whether the droplet evaporation method (DEM) can be applied to assess the effectiveness of ultra-high dilutions (UHDs). We studied the shape characteristics of the polycrystalline structures formed during droplet evaporation of wheat seed leakages. The experimental protocol tested both unstressed seeds and seeds stressed with arsenic trioxide 5mM, treated with either ultra-high dilutions of the same stressor substance, or with water as a control. The experimental groups were analyzed by DEM and in vitro growth tests. DEM patterns were evaluated for their local connected fractal dimension (measure of complexity) and fluctuating asymmetry (measure of symmetry exactness). Treatment with arsenic at UHD of both stressed and non-stressed seeds increased the local connected fractal dimension levels and bilateral symmetry exactness values in the polycrystalline structures, as compared to the water treatment. The results of in vitro growth tests revealed a stimulating effect of arsenic at UHD vs. control, and a correlation between the changes in growth rate and the crystallographic values of the polycrystalline structures was observed. The results indicate that polycrystalline structures are sensitive to UHDs, and so for the first time provide grounds for the use of DEM as a new tool for testing UHD effectiveness. DEM could find application as a treatment pre-selection tool, or to monitor sample conditions during treatment. Moreover, when applied to biological liquids (such as saliva, blood, blood serum, etc.), DEM might provide information about UHD effectiveness on human and animal health.

Might evaporation-induced droplet patterns serve in agro-homeopathic research and support experimental trials?

Agro-homeopathy provides numerous solutions for a sustainable agricultural production, like for instance cost-saving and residue-free treatments for yield improvement and management of diseases and pests. However, one of the main difficulties in this approach is the right treatment choice (i.e. the curative principle and its dilution level) that often requires numerous time & cost consuming experimental trials. In the present experiment we applied the droplet evaporation method, previously developed by our research team for wheat quality analysis, to test the influence of highly diluted homeopathic treatments (HD) of Arsenicum album on both healthy and previously arsenic trioxide stressed wheat seeds (isopathic model). The pattern evaluation of the resulting polycrystalline structures consisted in (i) the calculation of their local connected fractal dimension, known to reflect the pattern complexity, and (ii) in the fluctuating asymmetry measurement, known to be inversely correlated with the symmetry exactness of the structures, and thus also the vitality of the sample. In polycrystalline structures formed under the same conditions these two measurements have been found to reflect the sample health. Additionally, in order to support the crystallographic data with traditional analysis methods for seed viability, we performed the seed germination test and measured the shoot lengths: our results show that the complexity and symmetry of polycrystalline structures correlates with the viability of non-stressed and stressed wheat seeds following Arsenicum album HD with respect to control. These first results indicate that the droplet evaporation method might constitute a support for experimental trials and/or a pre-screening method for treatment test, since it shows to be sensitive to the sample vitality.

Vortical superlattices in a gold nanorods’ self-assembled monolayer

This paper describes the novel vortical self-assembly of CTAB-capped gold nanorods. Representative left-hand, radial, and right-hand vortices are shown. Micelles formed by CTAB molecules enhance the organized self-assembly process. The drag force of solvent flow and dynamic vortex flow in the thin solvent layer are thought to be responsible for the final vortical superlattices. FDTD simulation suggests these structures have potential applications in nanofocusing and polarized light response.

Near-infrared broadband absorber with film-coupled multilayer nanorods

Turning the surfaces of noble metals (metasurfaces) into black (highly absorptive) surfaces can be potentially applied in thermophotovoltaics, sensing, tailoring thermal emissivity, etc. Here we demonstrate an extremely broadband absorber for the 900-1600nm wavelength range with robust high absorption efficiency. The inexpensive droplet evaporation method is implemented to create patterns of nanoparticles dispersed on a gold film spaced by a thin dielectric layer. The diversity of the complicated random stacking of the chemically synthesized gold nanorods is the major factor for the broad absorption band. Such a metamaterial absorber may pave the way for cost-effective manufacture of large-area black metasurfaces.

Controllable Two-Stage Droplet Evaporation Method and Its Nanoparticle Self-Assembly Mechanism

Bottom-up self-assembly is able to constitute a variety of structures and has been thought to be a promising way for advanced nanofabrication. Droplet evaporation, as the simplest method, has been used in various self-assemblies. However, the assembled area is not large enough and the order is still not well controlled. Here we show a facile and controllable two-stage droplet evaporation method by adjusting the humidity and temperature of the evaporating droplet. Taking the highly monodispersed gold nanorods (GNRs) as an example, large-area, self-assembly monolayer arrays are reproducibly achieved. To understand the self-assembly mechanism, we adopted simplified models to analyze the interactions between the nanorods. The results show that a metastable state of secondary-energy-minimum exists, especially in the latter stage of the assembly process, leading to the ordered arrays. A large electrostatic barrier between the assembled arrays prevents the formation of the multilayer structures and thereby leads to the preferential monolayers. Moreover, we predict possibilities of different types of assemblies of the nanorods, and a schematic phase diagram is finally given. The results here may offer a way toward high-quality self-assembled nanoparticles superlattices for use in enhanced spectroscopy, sensors, or nanodevices.

Fundamental Studies of Electrochemically Controlled Surface Oxidation and Hydrophobicity of Natural Enargite

The surface oxidation and hydrophobicity of natural enargite (Cu(3)AsS(4)) and the formation of oxidation species at the mineral surface have been examined by a novel experimental approach that combines electrochemical techniques and atomic force microscopy (AFM). This approach allows for in-situ, synchronized electrochemical control and examination of the oxidative surface morphology of enargite. Combined with ex-situ cryo X-ray photoelectron spectroscopy surface analysis, the surface speciation of enargite surface oxidation has been obtained, comparing the newly fractured natural enargite surface with those that have been electrochemically oxidized at pHs 4 and 10. At pH 4, surface layer formations consisting of metal-deficient sulfide and elemental sulfur were identified, associated with a limited increase in root-mean-square (rms) roughness (1.228 to 3.143 nm) and apparent heterogeneous distribution of surface products as demonstrated by AFM imaging. A mechanism of initial rapid dissolution of Cu followed by diffusion-limited surface layer deposition was identified. At pH 10, a similar mechanism was identified although the differences between the initial and diffusion-limited phases were less definitive. Surface species were identified as copper sulfate and copper hydroxide. A significant increase in surface roughness was found as rms roughness increased from 0.795 to 9.723 nm. Dynamic (receding) contact angle measurements were obtained by a droplet evaporation method. No significant difference in the contact angle on a surface oxidized at pH 10 and the freshly polished surface was found. A significant difference was found between the polished surface and that oxidized at pH 4, with an increase in contact angle of about 13° (46° to 59°) after oxidation. Competing effects of hydrophilic (copper oxides and hydroxides) and hydrophobic (elemental sulfur) species on the mineral surface under oxidizing conditions at pH 4 and the change in surface roughness at pH 10 may contribute to the observed effects of electrochemically controlled oxidation on enargite hydrophobicity.

Ordered gold nanoparticle arrays as surface-enhanced Raman spectroscopy substrates for label-free detection of nitroexplosives

Nitroexplosives, such as 2,4,6-trinitrotoluene (TNT) which is a leading example of nitroaromatic explosives, are causing wide concern. Motivated by the urgent demand for trace analysis of explosives, novel surface-enhanced Raman spectroscopy substrates based upon highly ordered Au nanoparticles have been fabricated by a simple droplet evaporation method. It is noteworthy that an ethylhexadecyldimethyl ammonium bromide bilayer surrounding each individual nanoparticle not only is responsible for these periodic gap structures, but also tends to promote the adsorption of TNT on the composite NPs, thus resulting in a considerable increase of Raman signal. These desirable features endow the resulting SERS substrates with excellent enhancement ability and allow for a label-free detection of common plastic explosive materials even with a concentration as low as 10 −9 M.

Optimizing the yield and selectivity of high purity nanoparticle clusters

Here we investigate the parameters that govern the yield and selectivity of small clusters composed of nanoparticles using a Monte Carlo simulation that accounts for spatial and dimensional distributions in droplet and nanoparticle density and size. Clustering nanoparticles presents a powerful paradigm with which to access properties not otherwise available using individual molecules, individual nanoparticles or bulk materials. However, the governing parameters that precisely tune the yield and selectivity of clusters fabricated via an electrospray droplet evaporation method followed by purification with differential mobility analysis (DMA) remain poorly understood. We find that the product of the electrospray droplet mean diameter to the third power and nanoparticle concentration governs the yield of individual clusters, while the ratio of the nanoparticle standard deviation to the mean diameter governs the selectivity. The resulting, easily accessible correlations may be used to minimize undesirable clustering, such as protein aggregation in the biopharmaceutical industry, and maximize the yield of a particular type of cluster for nanotechnology and energy applications.

Functionalisation of glassy carbon electrodes with deposited tetrabutylammonium microcrystalline salts of lacunary and metal-substituted α-Keggin-polyoxosilicotungstates

Novel glassy carbon modified electrodes were functionalised with tetra-n-butylammonium (TBA) hybrid salts of several α-Keggin-type polyoxosilicotungstate anions. The salts were immobilized via a one-step deposition of micrometer thick coatings by the droplet evaporation method. The polyanion salts included the lacunary anion compound [(C4H9)4N]4H4[SiW11O39], and the metal-substituted derivatives [(C4H9)4N]4H[SiW11FeIII(H2O)O39] and [(C4H9)4N]4H2[SiW11CoII(H2O)O39]·H2O. The chemically modified electrodes were medium term stable and their preparation was quite reproducible and easy to perform. The morphology of the deposits was evaluated by optical microscopy and by scanning electron microscopy. The electrochemical features of the immobilized polyanion salts were to some extent different from those of the corresponding soluble species, namely in what concerns peak potential values and the effect of the substituting transition metal on the tungsten processes. Additionally, for all immobilized polyanion salts, the effect of the scan rate and of pH on the voltammetric features of the first W reduction process allowed to conclude that this process was diffusion controlled and accompanied by uptake of protons. The iron monosubstituted TBA modified electrode retained the mediation properties towards the reduction of nitrite found for the corresponding soluble polyoxoanion.

Ramified fractal-patterns formed by droplet evaporation of a solution containing single-walled carbon nanotubes

Single-walled carbon nanotubes (SWNTs) in aqueous and ethanol solutions can be self-assembled into ramified fractal-patterns, ring-patterns or fingering-patterns on silicon wafers over a large area under controlled evaporation conditions by the droplet evaporation method. The formation of these regular patterns can be attributed to the Marangoni effect and diffusion-limited aggregation (DLA) in the liquid film during droplet evaporation at different conditions. This simple method to assemble SWNTs will provide potential applications for advanced devices and sensors.

Formation of an Ordered Array of Nanocrystalline Si Dots by Using a Solution Droplet Evaporation Method

AbstractThis paper reports on a new bottom-up technique of forming silicon nanostructures based on natural aggregation of nanocrystalline (nc) -Si dots in the solution. We first study how the nc-Si dots deposited on the Si substrate get mobile in the solution by simply dipping the substrate with the nc-Si dots on into various solutions. We then demonstrate a solution droplet evaporation method that utilizes aggregation of the dots when we evaporate a solution droplet applied onto the nc-Si dots randomly deposited on the Si substrate. It is shown that the nc-Si dots are assembled well in a droplet of the hydrofluoric acid solution, resulting in various regular patterns on the substrate.