Electrospray-scanning Mobility Particle Sizer Research Articles

Size distribution measurement of mixed abrasive slurry for chemical mechanical planarization using an electrospray scanning mobility particle sizer

As the popularity of mixed abrasive slurry (MAS) use in chemical mechanical planarization (CMP) increases, analysis of number concentration and mixing ratios become increasingly important. In this study, the applicability of an electrospray-scanning mobility particle sizer (ES-SMPS) to particle-size analysis of MAS for measuring number concentration and mixing ratio is investigated. Additives to improve the CMP process cause non-volatile residue (NVR) peaks, making it difficult to obtain clear particle-size distributions. Because NVR peaks are affected by the size of the generated droplets, an aerosol generator that produces droplets of different sizes. Compared to atomizers that generate large droplets, an electrospray that generates small droplets minimizes disturbance of NVR peaks, allowing for clear particle-size distributions. Using ES-SMPS, the number concentration and mixing ratio of an MAS were analyzed with no interference from NVR peaks. CMP evaluation of an MAS of a certain number concentration confirmed that using an MAS with a constant number concentration improves the removal rate. Number concentration–based MAS analysis is therefore possible using existing weight concentration–based MAS research and ES-SMPS measurements. Measurement of abrasive number concentrations using ES-SMPS can also provide more realistic information on the number of participating abrasives.

Experimental and theoretical retentions of sub-10 nm colloidal nanoparticles by large-pore ultrafiltration membranes in isopropanol and water

Effective removal of small colloidal nanoparticles (NPs, e.g., <20 nm), including rigid particles, macromolecules, organics, viruses, antibiotics, hormones, etc., by dead-end filtration, is very important in drinking water, chemical, biopharmaceutical, and semiconductor factories. Most existing operations focused on sieving mechanism-based filtration with small-pore membranes (e.g., <20 nm) to capture these tiny NPs, which unfortunately leads to high energy consumption. This study proposed an emerging method that is to use large pore membranes (i.e., ∼100 nm) to capture NPs down to 2.8 nm. The ultimate goal is to address the grand challenge presented in the United Nations Sustainable Development Goal 12 on energy saving. To capture (or adhere) small NPs by large-pore membranes, the surface electrostatic interactions between NP and membrane should be considered in addition to the sieving mechanism. To examine the feasibility of the proposed method, the retention efficiency of ∼100 nm rated polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), and polycarbonate track-etched (PCTE, as a model filter) membranes against 2.8 nm ZnS quantum dot (QD), 5 and 10 nm Au and 100 nm PSL in water and isopropanol (IPA, a representative organic solvent) were studied experimentally and theoretically. In the experiments, the electrospray-scanning mobility particle sizer (ES-SMPS) was used to measure the size distribution of these nanosized colloids before and after the membrane to determine the retention efficiency. In the theory, we combined the hydrodynamic particle transport, extended Derjaguin-Landau-Verwey-Overbeek (xDLVO), and Maxwell models to calculate the NP retention. Results showed that the data agreed with the theoretical model very well, and the NP retentions in IPA were higher than that in water due to a significant change of acid-base interaction from repulsion to attraction. The retention of the 10 nm Au NPs and the 2.8 nm NPs could be attained by ∼80 and 35%, respecively, in IPA by the PTFE. This study was the first to show the combined theoretical model can accurately predict the retention of sub-10 nm NPs by different membranes in an organic solvent and water. The model predicts the retention of 5 nm Au NPs can be increased to higher than 99% by increasing the zeta potential of the PTFE about 5 times, thus a sustainable UF cutting significant carbon footprint is foreseeable in near future.

Temperature and Particle-size Effects on the Formation of Silica Gels from Silica Sols

Silica nanoparticles (silica sols) based gels have increasingly been used as alternative grouting material for sealing the small fractures in the tunnel walls. Gelling of silica nanoparticles at room temperature has been investigated thoroughly but gelling at different temperatures scarcely investigated. At the same time temperature is one of major factor which can affect the long-term stability of grouted silica. In this work we have investigated the gelling of three different types of silica sols (Levasil CS40-213, Levasil CS40-222, and Levasil CS30-236) having different particle sizes, in 0.28 M NaCl at 10, 20 and 30 °C. Aggregation process, starting from the addition of salt to the gelling point, was monitored by measuring the time dependent particle size distribution. Electrospray scanning mobility particle sizer (ES-SMPS) was used to measure the aggregating. These measurements were complemented by rheological measurements in order to get a relationship between changes in aggregate structure and in the viscosity of silica suspension. Data from the temperature dependent gel time measurements were used to calculate the activation energy. At room temperature, silica sols with smallest average particle size showed the shortest gel times whereas the sols with the largest particle size showed the longest gel time. However, at increasing temperature shorter gel times were seen for all the sols. Temperature dependent rheological measurements showed similar trends in viscosity changes as seen for gel times i.e., increased temperature leads to quicker increase in the viscosity and a sharp increase in viscosity near the gelling point. Our calculations of fractal dimensions showed that in the gel network there are still many free particles which continuously incorporated into the gel network. Apparent activation energies calculated for CS40-213, CS40-222, CS30-236 were 13.40, 23.36 and 41.45 kJ/mol, respectively. These values are lower than values reported for silica in the literature. Moreover, temperature dependent zeta potential measurements show that zeta potential get less negative as temperature increase. The above mentioned measurements are at odd what has been reported in literature but we have provided plausible explanation of these results.

Application of an Electrospray Scanning Mobility Particle Sizer to Mixed Abrasive Slurry for Chemical Mechanical Planarization

Application of an Electrospray Scanning Mobility Particle Sizer to Mixed Abrasive Slurry for Chemical Mechanical Planarization

Application of electrospray-scanning mobility particle sizer for the measurement of sub-10 nm chemical mechanical planarization slurry abrasive size distribution.

A scanning mobility particle sizer (SMPS) was used for measuring the size of a sub-10 nm chemical mechanical planarization slurry abrasive. An atomizer and an electrospray were used for aerosolization of slurry abrasives. It was difficult to measure the exact particle size distribution using the atomizer due to the agglomeration peak generated by the relatively large droplet size. However, the electrospray-SMPS (ES-SMPS) measurement result well matched with that of the transmission electron microscopy analysis without the agglomeration peak as ES is known to generate a relatively small droplet during aerosolization. The particle size distribution of the two sub-10 nm ceria slurries was measured using the ES-SMPS. To avoid the dispersion stability issue due to the pH change, pH adjustment was required when the sample was diluted.

Effect of colloidal nanoparticle concentration on sizing analysis with an electrospray scanning mobility particle sizer

Precise measurement of the size and size distribution of colloidal nanoparticles are an important component of evaluating nanoparticle safety. However, size measurements become increasingly difficult to perform as particle size decreases. The sizes and size distributions of nanoparticles can be determined using a variety of techniques. In this study, we used an electrospray scanning mobility particle sizer (ES-SMPS) to investigate the effect of nanoparticle concentration on the size and size distribution measurements of 20 nm and 50 nm silica nanoparticles. To calculate the size of the water droplets in the electrospray, the droplet size distribution in sucrose solutions was determined at various sucrose concentrations. The average water droplet diameter was ~ 697.5 nm, regardless of sucrose concentration. Based on these results, we estimated the appropriate nanoparticle concentration ranges for the ES-SMPS size determination of 20-nm and 50-nm silica nanoparticles. Reliable measurements of the 20- and 50-nm silica nanoparticles could be performed at concentrations of < 0.01 wt% and < 0.1 wt%, respectively.

Characterization of colloidal nanoparticles in mixtures with polydisperse and multimodal size distributions using a particle tracking analysis and electrospray-scanning mobility particle sizer

Characterization of polydisperse liquid-borne particles was investigated using a particle tracking analysis (PTA) and electrospray-scanning mobility particle sizer (ES-SMPS). The results showed PTA measurements based on light scattering accurately predicted mode sizes of monodisperse colloidal particles, but the geometric standard deviation of 40 nm polystyrene latex (PSL) particles was underestimated because of a screening effect that makes the smaller particles less visible. ES-SMPS could precisely predict the size distributions with sizes and standard deviations of monodisperse particles when compared to scanning electron microscopy data. From the results for the mixture of 40 nm Au and PSL and mixtures of 40 nm Au and 100, 150 and 240 nm PSL, it was shown that ES-SMPS is a very promising method to characterize colloidal particles with a wide or multimodal size distributions. Therefore, the results of this study provide detailed insights into various applications that require accurate characterizations of polydisperse colloidal particles.

Influence of colloidal particles with bimodal size distributions on retention and pressure drop in ultrafiltration membranes

In membrane processes, fouling from ongoing deposition of particles is the major issue for membrane failure and thus many researches on fouling characteristics have been conducted. Most of the researches have been performed with monodisperse particle systems to clarify effects of particle size on the deposition and fouling mechanisms. However, particle systems in nature have a wide size distribution with polydispersity. In this study, we used an electrospray-scanning mobility particle sizer method, which is suitable for characterizing the concentration of each component in mixtures. A series of filtration tests for 0.03 µm rated Polyethersulfone membrane against mixtures of different sized polystyrene latex particles was performed. The results showed a significantly enhanced retention efficiency of 60 nm particles in mixtures with larger particles. This was attributed from the larger particles clogging large pores, so 60 nm particles could not penetrate. For the cases of mixtures of 60 + 150 nm and 100 + 150 nm, we found much more pressure drop increases compared to the summation of the pressure drop increase for each monodisperse case. In these mixture cases, smaller particles supposed to have a depth filtration mechanism formed the cake layers due to initially blocked larger pores.

Development and Evaluation of Polyether Ether Ketone (PEEK) Capillary for Electrospray.

With the rapid development of nanotechnology, there is urgent need of characterizing techniques; especially determining the particle size distribution directly from solution. Dynamic light scattering is often used but presence of a small number of aggregates can greatly influence the size distribution. Electrospray scanning mobility particle sizer (ES–SMPS) is rapidly emerging as an alternative method in colloidal science. However, a major limitation is the use of silica-coated capillaries, which are negatively charged at pH > 3, and therefore making its use difficult for positively charged nanoparticles. In this work, we have developed the polyether ether ketone (PEEK) capillary for ES–SMPS, which removes this limitation because it carries no charge. We have shown that the new capillary not only produced equally good particle size distributions for negatively charged particles (SiO2, Au, and latex) as obtained with silica capillaries, but also precise particle size distributions for positively charged particles (TiO2). Moreover, the PEEK capillaries are much cheaper than the silica capillaries. Thus, the results shown in this paper strengthen the development of the ES–SMPS method as a versatile method for determining the particle size distributions of colloidal sols directly from solution.

Ionomer and protein size analysis by analytical ultracentrifugation and electrospray scanning mobility particle sizer.

By combining analytical ultracentrifugation (AUC) in liquid phase and scanning mobility particle sizer (SMPS) in the gas phase, additional information on the particle size and morphology has been obtained for rigid particles. In this paper, we transfer this concept to soft particles, allowing us to analyze the size and molar mass of the short side chain perfluorosulfonic acid ionomer Aquivion® in a dilute aqueous suspension. The determination of the primary size and exact molar mass of this class of polymers is challenging since they are optically transparent and due to the formation of different aggregate structures depending on the concentration and solvent properties. First, validation of AUC and SMPS measurements was carried out using the well-defined biopolymers bovine serum albumin (BSA) and lysozyme (LYZ) to confirm the reliability of the results of the two unique and independent classifying methods. Then, the ionomer Aquivion® was studied using both techniques. From the mean molar mass of 185 ± 14kDa obtained by AUC, a mean hydrodynamic diameter of 7.6 ± 0.5nm was calculated. The particle size obtained from SMPS (7.1nm) agrees very well with the results from AUC showing that the molecule was transferred into the gas phase without significantly changing its structure. In conclusion, the Aquivion® is molecularly dispersed in the used aqueous buffer solution without any aggregate formation in the investigated concentration range (< 2gl-1).

Evaluation of concentration measurement techniques of colloidal nanoparticles for microfiltration and ultrafiltration applications: Inductively coupled plasma-mass spectrometry, nanoparticle tracking analysis and electrospray-scanning mobility particle sizer

Abstract Three different liquid-borne particle concentration measurement methods, including the inductively coupled plasma-mass spectrometry (ICP-MS), nanoparticle tracking analysis (NTA) and electrospray-scanning mobility particle sizer (ES-SMPS), for determining the efficiency of liquid filtration were investigated and compared for their applicability and feasibility. These methods were first calibrated using commercial Au monospheres with various sizes from 5 to 50 nm and several sizes of NIST traceable polystyrene latex (PSL) from 20 to 125 nm. Calibration results showed that the prepared concentrations of liquid-borne particles according to that provided by the manufacturers were proportional to the concentrations measured by all these methods. The calibration results were then used to determine the filtration efficiencies of Au and PSL nanoparticles through the 0.1 μm pore diameter polycarbonate track-etched (PCTE or Nuclepore filter) membrane filters, which were performed as the dead-end type filtration. It was found that the filtration efficiencies obtained by different measurement methods under the same condition were comparable with each other. The results of this study provide a very useful guidance in selecting the proper method for liquid-borne particle filtrations under different circumstances.

Intermethod comparison of the particle size distributions of colloidal silica nanoparticles

There can be a large variation in the measured diameter of nanoparticles depending on which method is used. In this work, we have strived to accurately determine the mean particle diameter of 30–40 nm colloidal silica particles by using six different techniques. A quantitative agreement between the particle size distributions was obtained by scanning electron microscopy (SEM), and electrospray-scanning mobility particle sizer (ES-SMPS). However, transmission electron microscopy gave a distribution shifted to smaller sizes. After confirming that the magnification calibration was consistent, this was attributed to sample preparation artifacts. The hydrodynamic diameter, dh, was determined by dynamic light scattering (DLS) both in batch mode, and hyphenated with sedimentation field flow fractionation. Surprisingly the dh were smaller than the SEM, and ES-SMPS diameters. A plausible explanation for the smaller sizes found with DLS is that a permeable gel layer forms on the particle surface. Results from nanoparticle tracking analysis were strongly biased towards larger diameters, most likely because the silica particles provide low refractive index contrast. Calculations confirmed that the sensitivity is, depending on the shape of the laser beam, strongly size dependent for particles with diameters close to the visualization limit.

Near Room Temperature Synthesis of Monodisperse TiO2 Nanoparticles: Growth Mechanism

Hydrolysis of TiCl4 was used to form monodisperse nanoparticles of TiO2 with clean surfaces. The solid fraction and solution composition during synthesis were simulated using equilibrium data, and formation and growth was followed with two complementary techniques, an electrospray-scanning mobility particle sizer (ES-SMPS) and dynamic light scattering (DLS). In ES-SMPS the number density of particles is measured. Droplets formed in the spraying step mainly contain electrolyte, giving rise to residue particles that are detected together with the nanoparticles of interest. Discrimination between the two kinds of particles can be made by changing the flow conditions and applicability of the method for in situ measurements of particle size during growth is demonstrated. In DLS the hydrodynamic mobility is measured, and further insight into the initial growth mechanism was revealed by observation of slow, sustained oscillations in the scattered intensity, indicating a dissolution–precipitation mechanism at the...

Combined Electrospray-Scanning Mobility Particle Sizer (ES-SMPS) and Time-Resolved Synchrotron Radiation-Small-Angle X-ray Scattering (SR-SAXS) Investigation of Colloidal Silica Aggregation. Part II. Influence of Aggregation Initiator on Gel Stability

The effect of ion specificity on the slow aggregation of silica nanoparticles with various initial morphology was investigated with an electrospray-scanning mobility particle sizer (ES-SMPS) and time-resolved synchrotron radiation-small-angle X-ray scattering (SR-SAXS). This combination provides a unique tool to monitor and resolve the early aggregate development in detail. Aggregation was induced by varying the K(2)CO(3) or KCl concentration to obtain a fixed gelation time of ∼40 min, and the results were compared with those obtained in a previous paper (Johnsson et al. J. Phys. Chem. B 2011, 115, 765-775) for NaCl. All dispersions produced gels that contained free primary particles well past the point of gelation (PoG). The initial aggregate formation and obtained gel morphologies were independent of the aggregation initiator. Nevertheless, ion-specific effects were observed for the rate of the stability increase of the 3-dimensional (3D) gel structure. The formation of a stable structure was fastest in the presence of the strongly hydrated counterions, and a clear anion effect was observed. The obtained gel stabilities were interpreted by relating the rate of formation of covalent siloxane bonds to the polarization of the water molecules surrounding structure-maker ions.

Synthesis, characterization and particle size distribution of TiO 2 colloidal nanoparticles

Nanoparticles of controlled size, well defined shape, pure phase and of clean surfaces are ideal model systems to investigate surface/interfacial reactions. In this study we have explored the possibility of synthesizing TiO 2 nanoparticles in the size range of 7–20 nm under well controlled experimental conditions. A simple method based on the hydrolysis of TiCl 4 was used to obtain particles having surfaces free from organics. Stable dispersions of TiO 2 nanoparticles of various sizes were obtained by optimizing the reaction/dialysis time and temperature. The synthesized TiO 2 particles were found to be predominantly of anatase phase and narrow particle size distributions were obtained. The TiO 2 particles were characterized with respect to their phase, size and shape by X-ray diffraction (XRD) and transmission electron microscopy (TEM), respectively. Particle size distribution in a colloidal dispersion was obtained by the electrospray scanning mobility particle sizer (ES-SMPS) method and compared with an average particle size determined from dynamic light scattering (DLS). The average particle sizes obtained by the DLS and ES-SMPS methods were in good agreement, while a primary particle size of ∼4 nm was found in X-ray diffraction irrespective of the particle size in solution. Early stages of the nucleation process were monitored by the ES-SMPS method. These results show that small particles of 4–5 nm are initially formed and it is highly likely that large particles are formed due to aggregation of primary particles.

Combined Electrospray-SMPS and SR-SAXS Investigation of Colloidal Silica Aggregation. Part I. Influence of Starting Material on Gel Morphology

The slow aggregation of monodisperse, polydisperse, and preaggregated silica nanoparticles was studied with an electrospray-scanning mobility particle sizer (ES-SMPS) and time-resolved synchrotron radiation-small-angle X-ray scattering (SR-SAXS). Aggregation was induced by varying the NaCl concentration to obtain a fixed gelation time of ∼40 min. The combination of these techniques provides a unique tool to monitor and resolve the aggregate development in detail. The monodisperse spherical particles were converted to dimers, trimers, and eventually larger clusters as the aggregation proceeded, while the polydisperse spherical particles formed large clusters at an early stage. The initial particle shape and polydispersity had profound effects on the morphology of the aggregates; spherical primary particles produced compact spherical clusters, whereas the preaggregated dispersions formed open, elongated aggregates. All dispersions produced gels that contained free primary particles well past the point of gelation. The stability of the aggregates and the gel morphology were interpreted by relating to the structure of porous gel layers around the particles.

Formation of paratacamite nanomaterials via the conversion of aged and oxidized copper nanoparticles in hydrochloric acidic media

Nanoparticles and nanostructured aggregates of paratacamite are prepared in acidic solutions through the conversion of copper-based nanoparticles. Aged and oxidized copper nanoparticles with an average primary particle size of ∼15 nm, when combined with hydrochloric acid solutions in the range of 0.025 to 0.1 M, show interesting behavior yielding both a change in nanoparticle primary size, as measured by an electrospray scanning mobility particle sizer, and in chemical composition to produce a copper chloride hydroxide mineral identified as paratacamite (γ-Cu2(OH)3Cl) by powder X-ray diffraction of the dehydrated solid sample. Taken together, these data suggest that paratacamite nanoparticles in solution can aggregate to yield microporous paratacamite materials. Microporous paratacamite was characterized by several techniques including X-ray diffraction, transmission electron microscopy, energy dispersive X-ray analysis, electron energy loss spectroscopy, X-ray photoelectron spectroscopy and surface area measurements. Oxidation of these copper-based nanoparticles with molecular oxygen and the role of the oxidized layer in the formation of paratacamite have been investigated. Comparison to microscale copper particles showed there is unique oxidation behavior of nanoscale copper particles that results in unique reaction chemistry of oxidized nanoscale copper particles with hydrochloric acid solutions to form paratacamite. This study provides a new route for the formation of paratacamite nanomaterials that can be used in a wide range of chemically interesting applications including hydrogen storage materials and as a heterogeneous catalyst for the synthesis of green solvents such as dimethyl and diethyl carbonates. Additionally, this study suggests a potentially new pathway for the degradation of art objects and ancient artifacts as well as other cultural heritage materials containing small copper particles that has not been previously considered.

Superparamagnetic iron oxide nanoparticles functionalized with peptides by electrostatic interactions

Superparamagnetic iron oxide nanoparticles coated with dextran were functionalized with negatively charged functionalities in order to connect specific peptide labels by electrostatic interactions. Peptide binding on the nanoparticles was indicated by HR-TEM, an electrospray scanning mobility particle sizer, and fluorescence measurements.