Single Particle Surface Research Articles

Links between single maltodextrin particles properties and powder functionality

Maltodextrins are extensively used in the food industry to shape the physicochemical properties of food products. This multiscale study investigates three different Dextrose Equivalent (DE) maltodextrins as model matrices to elucidate the relationship between techno-functional behaviors and single particle surface properties. It was evidenced that environmental variations and glass transition influence single particle properties, significantly impacting the powder bulk behavior. Utilizing Confocal Laser Scanning Microscopy (CLSM) and environmental Atomic Force Microscopy (AFM) at the single particle level, correlations between the wetting and nanomechanical properties of all maltodextrins were provided. It was revealed that wetting properties are directly DE dependent, as higher DE maltodextrins had shorter wetting times. Moreover, glass transition plays a critical role in determining surface elasticity and capillary adhesion, as it alters both physicochemical properties and particle morphology. Indeed, a decrease of the Young modulus with Relative Humidity (RH) and glass transition correlated with the increase of capillary forces. This was corroborated by Scanning Electron Microscopy (SEM) and Specific Surface Area (SSA) measurements at different RH. These findings confirmed that glass transition drives particle morphology, with global surface smoothing and swelling occurring in the rubbery state.

Revisit: derivation of induction heating power equation for a conductive metal sphere

AbstractCurrently, we are in the research of magnetic induction heating by using conductive metal particles. The technology (comes from a phenomenon known as the “skin effect”) generates heat produced by electrical eddy currents on metal particle’s surfaces. However, till now, the power equation to describe the energy consumption of the eddy current on a single particle surface still remains ambiguous. William R. Smythe derived this equation for metal ball. A minor error was clearly located in his derivation result. Today, similar ambiguous power equation is still adopted by researchers. In order to clarify this ambiguous situation and make our further deep study on particle-based induction heating process, in this paper, I revisit the derivation of the power equation with richful results.

Dynamic investigation of maltodextrins surface properties by environmental atomic force microscopy

For the first time on food powders, environmental Atomic Force Microscopy (AFM) was used to probe single particle surface properties in real time by variating relative humidity (RH) and temperature. Low, intermediate, and high dextrose equivalent (DE) maltodextrins values were used as a model matrix. Humidity ramps from 20 to 80% at constant temperatures of 20 and 50 °C and temperature ramps from 20 to 50 °C at a constant RH of 20 and 80% were performed. Surface topography, roughness, and Young modulus distribution evolutions at the particle surface were studied under these conditions. It was observed that glass transition and RH are driving particle surface properties. Glass transition was always accompanied by a significant global surface smoothing, whatever the DE value. Surface smoothing phenomenon were also accompanied by a large decrease of the surface roughness with the increase of RH. Apart from the impact on surface topography, glass transition also impacted particle physics. Particles in the glassy state were relatively hard with a high and heterogenous Young modulus distribution. An increase in the RH made the particle progressively softer, whereas crossing the glass transition temperature leads to a really soft surface and to the homogenization of the Young modulus distribution. These results showed that glass transition significantly impacts particle surface properties and is promising to optimize food powder formulation and their shelf-life extension.

Measurements of surface temperature distributions on coal dust particles

The rate of thermochemical conversion of solid fuel depends strongly on temperature. However, temperature can vary significantly across a single particle's surface and can locally change reactivity for combustion. To account for this phenomenon in numerical models, we carried out an experimental investigation of the temperature profiles for particles obtained from two chars prepared from hard coal and lignite. We used a custom-built, two-color pyrometer to measure surface temperature distributions for particles with an approximate diameter of 100 μm. We used CCD cameras as detectors what allowed for measure temperature with high resolution. The applied research method allowed for the analysis of thousands of individual particles in different conditions. We carried out experiments under O2/N2 and O2/CO2 atmospheres with the oxidizer concentration between 10 and 30% (vol%). We observed highly non-uniform temperature distributions on the surface of the reacting particles with differences greater than 100 K. The standard deviation of the surface temperatures increased with the mean temperature of the particles. The observed variations could be due to inherent particle heterogeneity for ash content, porosity, and shape. Non-uniform temperature profiles and reactivities may alter the Stefan flow at the outer surface of the particles, affecting the mass and heat transfer balance and changing the trajectory of the particles as they move through the combustion chamber. Therefore, the correction factors determined in this study may be applied to existing numerical models of solid fuel combustion.

Three-Dimensional Gold Nanosphere Hexamers Linked with Metal Bridges: Near-Field Focusing for Single Particle Surface Enhanced Raman Scattering.

Herein, we report the novel strategy for the synthesis of complex 3-dimensional (3D) nanostructures, mimicking the linker molecule-free 3D arrangement of six Au nanospheres at the vertices of octahedrons. We utilized 3D PtAu skeleton for the structural rigidity and deposited Au around the PtAu skeleton in a site-selective manner, allowing us to investigate their surface plasmonic coupling phenomenon and near-field enhancement as a function of sizes of nanospheres, which are directly related to the intrananogap distance and interior volume size. The resulting 3D Au hexamer structures with octahedral arrangement were realized through precise control of the Au growth pattern. The complex 3D Au hexamers were composed of six Au nanospheres connected by thin metal conductive bridges. The standard deviation of the metal conductive bridges and Au nanospheres was within ca. 10%, exhibiting a high degree of homogeneity and precise structural tunability. Interestingly, charge transfer among the six Au nanospheres occurred along the metal conductive bridges leading to surface plasmonic coupling between Au nanospheres. Accordingly, electric near fields were strongly and effectively focused at the vertices, intrananogap regions between Au nanospheres, and interior space, exhibiting well-resolved single-particle surface-enhanced Raman spectroscopy signals of absorbed analytes.

Microscopic visualization of heterogeneous nucleation process on smooth spherical particle: Method and results

Heterogeneous nucleation is a very fundamental step in vapor condensation. However, it is scarcely possible to directly visualize the nucleation process because it is very quick and complicated. In present work, a method is proposed to create a mixed surface, where the hydrophilic SiO2 particle is dispersed on the super-hydrophobic substrate for a direct visualization of the nucleation process. The time-resolved images are recorded by Environmental Scanning Electron Microscopy (ESEM) system. The results indicate that only one embryo drop forms at a random point of a single particle surface and subsequently grows up and finally wraps the single particle. For multiple particles, the embryo drop occurs on the junction of particles and continues to enlarge to finally wrap all the particles. The numerical analysis shows that the nucleation ability of SiO2 is qualitatively consistent with the theoretical prediction, and quantitatively, the experimental Scr is much smaller than the predicted results.

Green Synthesis of Dual Carbon Conductive Network-Encapsulated Hollow SiO x Spheres for Superior Lithium-Ion Batteries.

Designing hollow/porous structure is regarded as an effective approach to address the dramatic volumetric variation issue for Si-based anode materials in Li-ion batteries (LIBs). Pioneer studies mainly focused on acid/alkali etching to create hollow/porous structures, which are, however, highly corrosive and may lead to a complicated synthetic process. In this paper, a dual carbon conductive network-encapsulated hollow SiO x (DC-HSiO x) is fabricated through a green route, where polyacrylic acid is adopted as an eco-friendly soft template. Low electrical resistance and integrated electrode structure can be maintained during cycles because of the dual carbon conductive networks distributed both on the surface of single particles formed by amorphous carbon and among particles constructed by reduced graphene oxide. Importantly, the hollow space is reserved within SiO x spheres to accommodate the huge volumetric variation and shorten the transport pathway of Li+ ions. As a result, the DC-HSiO x composite delivers a large reversible capacity of 1113 mA h g-1 at 0.1 A g-1, an excellent cycling performance up to 300 cycles with a capacity retention of 92.5% at 0.5 A g-1, and a good rate capability. Furthermore, the DC-HSiO x//LiNi0.8Co0.1Mn0.1O2 full cell exhibits high energy density (419 W h kg-1) and superior cycling performance. These results render an opportunity for the unique DC-HSiO x composite as a potential anode material for use in high-performance LIBs.

Direct Surface Tension Measurements of Individual Sub-Micrometer Particles Using Atomic Force Microscopy.

Understanding the role of sea spray aerosol (SSA) on climate and the environment is of great interest due to their high number concentration throughout the Earth's atmosphere. Despite being of fundamental importance, direct surface tension measurements of SSA relevant sub-micrometer particles are rare, largely due to their extremely small volumes. Herein, atomic force microscopy (AFM) is used to directly measure the surface tension of individual sub-micrometer SSA particle mimics at ambient temperature and varying relative humidity (RH). Specifically, we probed both atmospherically relevant and fundamentally important model systems including electrolyte salts, dicarboxylic acids, and saccharides as single components and mixtures. Our results show that the single particle surface tension depends on RH or solute mole percentage and chemical composition. Moreover, for liquid droplets at and below 100 Pa s in viscosity, or at corresponding RH, we show good agreement between the AFM single particle and the bulk solution surface tension measurements at overlapping concentration ranges. Thus, direct surface tension measurements of individual particles using AFM is shown over a wide range of chemical systems as a function of RH, solute mole percentage, and viscosity than previously reported.

Hierarchical Ag mesostructures for single particle SERS substrate

Hierarchical Ag mesostructures with highly rough surface morphology have been synthesized at room temperature through a simple seed-mediated approach. Electron microscopy characterizations indicate that the obtained Ag mesostructures exhibit a textured surface morphology with the flower-like architecture. Moreover, the particle size can be tailored easily in the range of 250–500nm. For the growth process of the hierarchical Ag mesostructures, it is believed that the self-assembly mechanism is more reasonable rather than the epitaxial overgrowth of Ag seed. The oriented attachment of nanoparticles is revealed during the formation of Ag mesostructures. Single particle surface enhanced Raman spectra (sp-SERS) of crystal violet adsorbed on the hierarchical Ag mesostructures were measured. Results reveal that the hierarchical Ag mesostructures can be highly sensitive sp-SERS substrates with good reproducibility. The average enhancement factors for individual Ag mesostructures are estimated to be about 106.

Green Synthesis of Metal Nanoparticles via Natural Extracts: The Biogenic Nanoparticle Corona and Its Effects on Reactivity

The optical and catalytic properties of metal nanoparticles have attracted significant attention for applications in a wide variety of fields, thus prompting interest in developing sustainable synthetic strategies that leverage the redox properties of natural compounds or extracts. Here, we investigate the surface chemistry of nanoparticles synthesized using coffee as a biogenic reductant. Building on our previously developed synthetic protocols for the preparation of silver and palladium nanoparticle/carbon composite microspheres, a combination of thermogravimetric and spectroscopic methods was used to characterize the carbon microsphere and nanoparticle surfaces. Infrared reflectance spectroscopy and single particle surface enhanced Raman spectroscopy were used to characterize Pd and Ag metal surfaces, respectively, following synthesis. Strongly adsorbed organic layers were found to be present at metal nanoparticle surfaces after synthesis. The catalytic activity of Pd nanoparticles in hydrogenation reactions was leveraged to study the availability of surface sites, and coffee-synthesized nanomaterials were compared to commercial Pd-based hydrogenation catalysts. Our results demonstrate that biogenic adsorbates block catalytic surface sites and affect nanoparticle functionality. These findings highlight the need for careful analysis of surface chemistry as it relates to the specific applications of nanomaterials produced using greener or more sustainable methods.

Roughness analysis of single nanoparticles applied to atomic force microscopy images of hydrated casein micelles

The topography of fully hydrated casein micelles was measured by Atomic Force Microscopy and quantitatively investigated by a custom-made roughness analysis procedure. Casein micelles in ultra filtrated permeate (UFP) were chosen as a typical example of food nanoparticles in order to validate the approach. Casein micelles were first covalently immobilized on solid substrates by carbodiimide chemistry and subsequently a number of individual particles were scanned at high resolution. Parameters for characterizing single particle surface roughness were defined and implemented in MATLAB. An essential feature of the analysis is the discrimination between overall particle shape and short-scale surface roughness. Parameters determined were: Root-mean-square roughness, ratio of area to projected area, particle compression and particle size. The method is generally applicable to particles with radii from ∼15 nm–1 μm and will be useful for monitoring changes in hydrocolloid surface morphology in relation to environmental changes or industrial processing.

Plasmonic glasses: Optical properties of amorphous metal-dielectric composites

Plasmonic glasses composed of metallic inclusions in a host dielectric medium are investigated for their optical properties. Such structures characterized by short-range order can be easily fabricated using bottom-up, self-organization methods and may be utilized in a number of applications, thus, quantification of their properties is important. We show, using T-Matrix calculations of 1D, 2D, and 3D plasmonic glasses, that their plasmon resonance position oscillates as a function of the particle spacing yielding blue- and redshifts up to 0.3 eV in the visible range with respect to the single particle surface plasmon. Their properties are discussed in light of an analytical model of an average particle's polarizability that originates from a coupled dipole methodology.

Mechanistic understanding of surface plasmon assisted catalysis on a single particle: cyclic redox of 4-aminothiophenol

Surface plasmon assisted catalysis (SPAC) reactions of 4-aminothiophenol (4ATP) to and back from 4,4′-dimercaptoazobenzene (DMAB) have been investigated by single particle surface enhanced Raman spectroscopy, using a self-designed gas flow cell to control the reductive/oxidative environment over the reactions. Conversion of 4ATP into DMAB is induced by energy transfer (plasmonic heating) from surface plasmon resonance to 4ATP, where O2 (as an electron acceptor) is essential and H2O (as a base) can accelerate the reaction. In contrast, hot electron (from surface plasmon decay) induction drives the reverse reaction of DMAB to 4ATP, where H2O (or H2) acts as the hydrogen source. More interestingly, the cyclic redox between 4ATP and DMAB by SPAC approach has been demonstrated. This SPAC methodology presents a unique platform for studying chemical reactions that are not possible under standard synthetic conditions.

Atmospheric markers of African and Arabian dust in an urban eastern Mediterranean environment, Beirut, Lebanon

Long range transport of dust originating from Arabian and African Deserts causes the transformations in the morphology and chemical composition of aerosols. Changes result from physical and chemical reactions occurring in the bulk or at the surface of single particles. Being an urban Mediterranean city, Beirut is subject to dust outbreaks from two desert sources between fall and summer seasons and hence, presents a typical case study of urban mixing with dust aerosols. In this study, particles collected during dust-rich episodes help to elucidate the different sources of long range transported aerosols. Elemental composition when coupled with specific morphological structures of single particles serves as markers to differentiate between these sources.

Laser wavelength- and power-dependent plasmon-driven chemical reactions monitored using single particle surface enhanced Raman spectroscopy

Plasmon-driven chemical reaction of p-nitrothiophenol (pNTP) dimerizing into p,p'-dimercaptoazobenzene (DMAB) has been monitored using single particle surface enhanced Raman spectroscopy, which provides laser wavelength- and power-dependent conversion rates of the reaction.

Online Laser Desorption-Multiphoton Postionization Mass Spectrometry of Individual Aerosol Particles: Molecular Source Indicators for Particles Emitted from Different Traffic-Related and Wood Combustion Sources

Direct inlet aerosol mass spectrometry plays an increasingly important role in applied and fundamental aerosol and nanoparticle research. Laser desorption/ionization (LDI) based techniques for single particle time-of-flight mass spectrometry (LDI-SP-TOFMS) are a promising approach in the chemical analysis of single aerosol particles, especially for the detection of inorganic species and distinction of particle classes. However, until now the detection of molecular organic compounds on a single particle basis has been difficult due to the high laser power densities which are required for the LDI process as well as due to the inherent matrix effects associated with this ionization technique. By the application of a two-step approach, where an IR desorption laser pulse is applied to perform a gentle desorption of organic material from the single particle surface and a second UV-laser performs the soft ionization of the desorbed species, this drawback of laser based single particles mass spectrometry can be overcome. The postionization of the desorbed molecules has been accomplished in this work by resonance enhanced multiphoton ionization (REMPI) using a KrF excimer laser (248 nm). REMPI allows an almost fragmentation free trace analysis of polycyclic aromatic hydrocarbons (PAHs) and their derivatives from individual single particles (laser desorption-REMPI postionization-single particle-time-of-flight mass spectrometry or LD-REMPI-SP-TOFMS). Crucial system parameters of the home-built aerosol mass spectrometer such as the power densities and the relative timing of both lasers were optimized with respect to the detectability of particle source specific organic signatures using well characterized standard particles. In a second step, the LD-REMPI-SP-TOFMS system was applied to analyze different real world aerosols (spruce wood combustion, gasoline car exhaust, beech wood combustion, and diesel car exhaust). It was possible to distinguish the particles from different sources by their molecular signature. Finally, exemplary ambient aerosol measurements have been carried out, which demonstrate the potential of the method for investigating urban aerosol and making contributions to source attribution studies.

Heightened Electromagnetic Fields between Metal Nanoparticles: Surface Enhanced Raman Scattering from Metal−Cytochrome c-Metal Sandwiches

This manuscript reports the demonstration of strong interparticle electromagnetic coupling in nanoparticle:molecule:nanoparticle sandwiches. These assemblies were prepared by adsorption of cytochrome c (Cc)-coated colloidal Au nanoparticles onto aggregated colloidal Ag. Surface enhanced Raman scattering (SERS) spectra for the Cc:Au conjugates (Ag:Cc:Au) were compared to those obtained by direct adsorption of Cc (Ag:Cc) at several visible excitation wavelengths. The use of identically prepared samples with the same effective [Cc] and the same laser power allows the effects of sample geometry and interparticle coupling to be probed. As expected, at all excitation wavelengths, Ag:Cc:Au gave less intense spectra than Ag:Cc, because (i) only a small percentage of the Cc molecules were close to the more SERS-active metal (Ag), and (ii) the heme, from which all observed vibrations arise, was oriented toward the Au, not the Ag. Nonetheless, the ratio of Ag:Cc:Au to Ag:Cc SERS intensity varied significantly with excitation wavelength, a phenomenon that can be accounted for only by a wavelength-dependent electromagnetic field. This, in turn, results from wavelength-dependent electromagnetic coupling between closely spaced colloidal Ag and colloidal Au. In addition to wavelength-dependent SERS intensity ratios, three separate lines of evidence support the existence of strong electromagnetic coupling: (i) the presence of a wavelength-shifted single particle surface plasmon band for Cc:Au conjugates upon exposure to agggregated Ag, (ii) demonstration of excitation wavelength-dependent photodriven conformational changes in Ag:Cc:Au, and (iii) dramatic increases in SERS intensities from protein−colloid conjugates prepared with Ag in place of Au.