Colloid Concentration Research Articles

The concentration and size distribution of iron‐rich colloids in pore waters are related to soil organic matter content and pore water calcium concentration

AbstractIron (Fe)‐rich colloids in the environment have a high surface reactivity and facilitate transport of oxyanions and trace metal cations in soil. This study was set up to help identify the soil properties that might affect the concentrations of colloidal Fe and its size distribution in pore waters of soils. The pore water was isolated by centrifugation from a collection of 97 topsoils with contrasting properties and land use. The total Fe concentration in the pore waters ranged between 0.2 and 26 μM (10th–90th percentile) and was largest at low soil solution calcium (Ca) and high dissolved organic carbon (DOC), indicating that enhanced colloidal stability determines total Fe in solution. The colloidal size distribution (<100 nm) of Fe in the pore waters of 11 soils was determined with flow field flow fractionation (FlFFF‐UV‐ICP‐MS), which yielded three different fractions that varied strikingly among soils. The smallest fraction (<5 nm) of Fe co‐eluted with high DOC and copper (Cu), suggesting mononuclear Fe‐organic carbon (OC) complexes. This fraction increased with an increasing DOC/Fe ratio in pore waters. The 5–50‐nm fraction of Fe prevailed in soils with >3.5% organic carbon (%OC), whereas the 50–100‐nm fraction was dominant in soils with low %OC content. This suggests that natural organic matter inhibits crystallization and growth of mineral Fe particles. The elemental ratios of mineral colloids (>5 nm) indicated the presence of clay minerals and Fe oxyhydroxides, which was confirmed by scanning electron microscopy (SEM) analysis. This study thus identified soil %OC and Ca in soil solution as the dominant factors predicting both the concentration and size of pore water Fe colloids, with the smallest and, potentially, most mobile Fe colloids occurring in OC‐rich soils.Highlights Pore water iron concentrations in topsoils are governed by colloid stability Flow field flow fractionation analysis allows characterization of iron colloids in the low nanometre range Iron colloid size and composition vary strikingly among soils Small iron colloids prevail in organic carbon‐rich soils due to colloid growth inhibition

Colloidal metal transport in soils developing on historic coal mine spoil

Chemical weathering of pyrite via oxidative dissolution is well-known for generating Fe(III)-bearing colloids at acid mine drainage (AMD) sites; however, the potential for physical weathering of pyrite-bearing materials and subsequent release and transport of colloidal pyrite and associated trace metals has not been studied. Here, we monitored the colloidal metal transport in soil developing on abandoned coal mine spoil with a history of AMD generation to systematically study the contribution of colloids to base and trace metal transport and determine the elemental and mineralogical composition of colloids. We collected soil pore water using lysimeters with a pore size of approximately 1.3 μm and centrifugation was used to separate the colloids from aqueous fractions. Metal concentrations of Na, Ca, Mg, K, Si, Al, Mn, Fe, Cu, and Zn were analyzed. Our results show only 14% of the total Al and Cu were present in colloidal fractions whereas 23%, 43%, and 54% of Fe, Mn, and Zn were transported in the colloidal phase, respectively. In contrast, all base metals were primarily present in the aqueous concentration with a small fraction (<10%) present in the colloidal phase. The colloidal fractions of the base metals were inferred to be associated with the concentration of clay colloids. The release of colloids exhibited possible sensitivity toward weather conditions such as alternating high temperatures and rainfall during summer (May–July) compared to fall (August–November). The morphology, elemental, and mineral composition of colloids were determined by a scanning electron microscopy equipped with energy dispersive spectroscopy (SEM-EDS) and X-ray diffraction (XRD). Colloids were dominated by phyllosilicates (biotite, muscovite, and kaolinite) with minor quartz and feldspars. Other minerals phases identified in colloidal fractions were hematite, goethite, arsenopyrite, and chalcopyrite. Colloids consisting of Fe, S, and O with structures resembling framboidal pyrite were identified, which is consistent with the non-silicates minerals identified by XRD. Our study suggests that the physical weathering of pyrite in the mine spoil can generate colloidal pyrite, which is mobilized and transported by soil pore water. Our results also indicate that these pyritic colloids are associated with toxic trace metals including Cu, Mn, and Zn. Colloid mobilization is also impacted by changes in temperature and precipitation, where clay mobilization afer rain events is favored. Further, sudden spikes in aqueous and/or colloidal concentrations may be the result of local heterogeneity within soils developing on mine spoil, indicating that further field-based work is necessary to better characterize pore-scale processes that control aqueous and colloid transport at similar sites to have a better understanding of potential contaminant transport from mine spoil systems.

Influence of colloids and colloids’ coagulation on selenite sorption

Colloids play a crucial role in the sorption and migration of contaminants in the environment，while up to today, limited information exists about the influence of bentonite colloids on the sorption of selenite due to the weak sorption capacity of bentonite colloids to anions. Since bentonite will be used as backfilling materials in granite hosted repositories, and colloids would be generated when bentonite contacts with groundwater, the investigation of the sorption of selenite onto bentonite colloids and the effects of colloids coagulation on the sorption of selenite onto the colloids are badly needed. In this work, the distribution of selenite in the bentonite/deionized (DI) water system and the influence of Beishan (potential granite-hosted geologic repository of China) groundwater on the distribution are investigated. The results show that in the bentonite/DI water system, about 40% of the selenite is adsorbed onto the colloids at pH~5. Selenite sorption onto colloids reaches maximum at pH~5 as a result of the synergy effects of charge of the edge sites and size of the colloids. However, high concentration of colloids cannot be generated or stable in Beishan groundwater. When the bentonite colloids coagulate, the sorption sites of the colloids for selenite decrease, which leads to selenite sorption decreasing. When the colloids bearing selenite coagulate, most of the selenite adsorbed onto the colloids would be released into the solution, and the sorption of selenite onto the colloids at pH~5 decreases from 70% to 10−20%. Selenite sorption onto coagulated colloids is mainly controlled by the surface complex of selenite and divalent cations in the system, which is different from that onto bentonite colloids (controlled by inner-complexation).

Experimental investigation on the effects of clay colloid-facilitated ammonium transport through saturated porous media under variable transport conditions

Ammonium contamination is one of the major environmental issues in subsurface contamination and groundwater which in turn poses risks to human health. Predicting and formulating desirable situations is necessary for the study of NH4+ ion adsorption and transport in the environment. The purpose of the present paper is to assess the influence of various factors, such as different colloidal concentration, different size of porous media and different flow rates on colloid-facilitated NH4+ ion transport. In order to understand the influence of colloid concentration on NH4+ ion transport in porous media, few soil column experiments were performed in laboratory scale. Different clay colloidal concentrations with NH4+ ion solution as contaminant were supplied to the soil column and the leached out solution was tested using UV–vis spectrophotometer to find the concentration of NH4+ ion; 500ppm clay colloidal concentration in fine sand medium at 5ml/min flow rate has been identified as most suitable condition for NH4+ ion subsurface adsorption with highest cumulative NH4+ ion adsorption of 1.9mg/g, whereas 200ppm clay colloidal solution had least cumulative NH4+ ion adsorbed values than other solutions. TherefoZhangre, 200ppm colloid solution was found to be most efficient for NH4+ ion transport. The efficiency of NH4+ ions transport in all the solutions in the study was doubled at a flow rate of 15ml/min than at 5ml/min. The outflow NH4+ ion concentration was lower for fine sand than medium sand in all the cases in the study. The results illustrated that variable factors in the study can either facilitate or retard ammonium ion adsorption.

Real-time monitoring and control for high-efficiency autonomous laser fabrication of silicon nanoparticle colloids

Nanotechnology is a significant research tool for biological and medical research with major advancements achieved from nanoparticle (Np) applications in biosensing and biotherapeutics. For laser ablation synthesis in solution (LASiS) to be chosen by researchers for Np colloid production, the process must effectively compete with chemical synthesis in terms of produced colloid quality and productivity while taking advantage of LASiS benefits in terms of its ‘green-synthesis’ and single-step functionalisation abilities. In this work, a newly developed integrated LASiS Np manufacturing system is presented including a Np flow reactor design, an at-line Np size monitoring via 180° dynamic light scattering, and a UV-Vis spectroscopy system used to estimate colloid concentration and stability. The experimental outcomes are discussed in terms of Np productivity and quality via these at-line measurements from the UV-Vis and DLS systems. The developed instrument was validated via off-line SiNps DLS, UV-Vis and morphology tests via TEM. Ultra-high quality and nanoparticle fabrication rate efficiency was achieved and is reported here.

Advancements in Throughput, Lifetime, Purification, and Workflow for Integrated Nanoscale Deterministic Lateral Displacement

AbstractNanoscale deterministic lateral displacement (nanoDLD) has emerged as an effective method for separating nanoscopic colloids for applications in molecular biology, yet present limits in throughput, purification, on‐chip filtration, and workflow restricting its adoption as a practical separation technology. To overcome these impediments, array scaling and parallelization for integrated nanoDLD (i‐nanoDLD) enrichment devices are developed to achieve a density of ≈83 arrays mm−2 with 31 160 parallel arrays, producing an ≈30‐fold concentration of the target colloid and a record throughput of 17 mL h−1. Purification using a dual‐fluid input embodiment of i‐nanoDLD is demonstrated to successfully remove background contaminants from target colloid samples, including urine. Used serially, high‐throughput enrichment and purification chips achieve &gt;1700 gain in particle over protein concentration compared to input sample. Additionally, integration of upstream filter banks shows improved operation lifetime &gt; 7× for particles with diameters close to the gap size. Finally, the integrated design and associated flow rates allow a straightforward approach to chip‐to‐world interfacing as demonstrated using a prototype system for facile, turn‐key sample processing. Collectively, these developments advance nanoDLD into the range of sample volumes and process times needed for research and clinical samples.

Study of the functional properties of dough

The paper presents the studies of gluten - free types of unleavened dough, it shows the effect of hydrocolloids on the structure of the dough. The aim of the work is to study the functional and technological properties of the dough depending on the type and concentration of the flour and hydrocolloids. The tasks of the research are the following: to determine the concentration of colloids that makes dough plastic and strong dough; to identify the dependence of the concentration of flour on the type and properties of hydrocolloids; to study organoleptic quality indicators. The dynamic viscosity of the dough was determined by using a Brookfield viscometer. The methods of mathematical experiment planning were used to design the recipes of the unleavened dough. To define the reference dependency of viscosity on shear rate, the coefficients of nonlinear model equations have been estimated by using the methods of regression analysis in the program Statistica v6. For the experimental samples, the equation of the viscosity dependence is determined as a model of non-linear multiple regression. The graphs of the viscosity dependence on the shear rate compared to the reference rate are made. The methods of mathematical programming have been used to find the optimal ratio of flour and each type of structure-forming agents (soy protein isolate, xanthan gum, and potato starch) in the dough to maximize the approximation of the viscosity curve to the reference one. For this purpose, an objective function with limits on the shear rate is compiled. Using the MathCAD v15, the optimal values of the content of the components such as rice flour - 27.78%, soy protein isolate - 7.22%, potato starch - 32.22%. xanthan gum - 0.28 % are found. The results of the control measurement of the viscosity of the sample with the optimal composition indicate that the selected mathematical model corresponds to the elastoviscoplastic properties of this dough and the curve changes depending on the composition of the dry dough mixture. The description of the mathematical model and the regression analysis make it possible to select the ratio of the prescription components so that the resulting product has rheological characteristics close to the control sample.

Slaughterhouse Wastewater Treatment by Electrocoagulation Process

Slaughterhouse wastewater contains a high concentration of colloids, organic compounds, and suspended solids, which cannot be directly discharged to the environment. In this research, the electrocoagulation process was used to treat slaughterhouse wastewater. The pH of the solution was neutralized by adding Ca(OH)2. The influence of current density (933 mA/dm2 and 1400 mA/dm2) and electrode configuration (3 anodes 3 (three) cathodes and 4 (four) anodes 2 (two) cathodes) was investigated. The experimental results showed that the treated wastewater at a current density of 1400 mA/dm2 produced a lower contaminant concentration than the current density of 933 mA/dm2. The current density of 1400 mA/dm2 and electrode configuration of 4 anodes-2 cathodes reduced BOD by 56.4%, TDS by 20.25%, and TSS by 99.47%.

Review of Waterborne Organic Semiconductor Colloids for Photovoltaics.

Development of carbon neutral and sustainable energy sources should be considered as a top priority solution for the growing worldwide energy demand. Photovoltaics are a strong candidate, more specifically, organic photovoltaics (OPV), enabling the design of flexible, lightweight, semitransparent, and low-cost solar cells. However, the active layer of OPV is, for now, mainly deposited from chlorinated solvents, harmful for the environment and for human health. Active layers processed from health and environmentally friendly solvents have over recent years formed a key focus topic of research, with the creation of aqueous dispersions of conjugated polymer nanoparticles arising. These nanoparticles are formed from organic semiconductors (molecules and macromolecules) initially designed for organic solvents. The topic of nanoparticle OPV has gradually garnered more attention, up to a point where in 2018 it was identified as a "trendsetting strategy" by leaders in the international OPV research community. Hence, this review has been prepared to provide a timely roadmap of the formation and application of aqueous nanoparticle dispersions of active layer components for OPV. We provide a thorough synopsis of recent developments in both nanoprecipitation and miniemulsion for preparing photovoltaic inks, facilitating readers in acquiring a deep understanding of the crucial synthesis parameters affecting particle size, colloidal concentration, ink stability, and more. This review also showcases the experimental levers for identifying and optimizing the internal donor-acceptor morphology of the nanoparticles, featuring cutting-edge X-ray spectromicroscopy measurements reported over the past decade. The different strategies to improve the incorporation of these inks into OPV devices and to increase their efficiency (to the current record of 7.5%) are reported, in addition to critical design choices of surfactant type and the advantages of single-component vs binary nanoparticle populations. The review naturally culminates by presenting the upscaling strategies in practice for this environmentally friendly and safer production of solar cells.

Measurement of the colloidal particle concentration and size within a drop using the time-shift technique

Liquid drops containing particles of nano to micron size are omnipresent in the chemical, pharmaceutical and process industries. In order to optimize such processes, there is a need to characterize these drops in terms of size and colloidal particle concentration. This study is devoted to estimating the colloidal nanoparticle concentration within such drops by using the time-shift technique. The estimation is achieved using two different approaches. The first utilizes the signal strength generated by light scattering from the particles in the drop relative to reflective scattering from the undisturbed drop surface. The second approach monitors the attenuation of the portion of the time-shift signal generated by second-order refractive scattering, i.e. light which has passed twice through the drop. These methods have been simulated using previously developed light scattering codes based on Monte Carlo ray tracing. Corresponding experiments have been implemented to validate these two estimation methods. For this, colloidal drops were generated by mixing water with the polystyrene latex nanoparticles and varying the volume concentration. Good agreement between the experimental and simulation results has been achieved, indicating that the time-shift technique can be further developed to meet this measurement task.

Centrifugal ultrafiltration preconcentration for studying the colloidal phase of a uranium-containing soil suspension

The objective of this work was to explore centrifugal ultrafiltration (UF) to separate and / or preconcentrate natural colloidal particles for their characterization. A soil suspension obtained by batch leaching was used as a laboratory reference sample. It was preconcentrated with concentration factors (CF) varying from 10 to 450. The dimensional analysis of the colloidal phase was carried out by Asymmetric Flow Field-Flow Fractionation (AF4)-multidetection. The colloidal masses were estimated by mass balance of the initial suspension, its concentrates and filtrates. The size-dependent distribution (expressed in gyration radius) and total colloidal mass (especially recovery), as well as chemical composition and concentration (including species partitioning between dissolved and colloidal phases) were determined to assess the effects of UF preconcentration on colloidal particles. The gyration radius of the colloidal particles recovered in these concentrated suspensions ranged from about 20 nm to over 150 nm. Neither de-agglomeration nor agglomeration was observed. However, only (64 ± 4) % (CF = 10) of the colloidal particles initially in the soil suspension were found in the recovered concentrated suspensions, and this percentage decreased as CF increased. The filter membrane trapped all other particles, mainly the larger ones. Whatever the CF, the centrifugal UF did not appear to change the dissolved-colloidal partitioning of certain species (Al, organic carbon); whereas it led to an enrichment of the colloidal phase for others (Fe, U). The enrichment rate was specific to each species (15% for Fe; 100% for U). By fitting the observed trends (i.e. conservation, depletion or enrichment of the colloidal phase in the concentrate) as a function of CF, the colloidal concentrations (total and species) were assessed without bias. This methodology offers a new perspective for determining physicochemical speciation in natural waters, with a methodology applicable for environmental survey or site remediation studies.

Two-Stage Seebeck Effect in Charged Colloidal Suspensions.

We discuss the peculiarities of the Seebeck effect in stabilized electrolytes containing the colloidal particles. Its unusual feature is the two stage character, with the linear increase of differential thermopower as the function of colloidal particles concentration during the first stage (“initial state”) and dramatic drop of it at small during the second one (“steady state”). We show that the properties of the initial state are governed by the thermo-diffusion flows of the mobile ions of the stabilizing electrolyte medium itself and how the colloidal particles participate in the formation of the electric field in the bulk of the suspension. In its turn, we attribute the specifics of the steady state thermoelectric effect the massive colloidal particles undergoing slow thermal diffusion and the break down of their electro-neutrality in the vicinity of electrodes.

Colloidal Stability and Concentration Effects on Nanoparticle Heat Delivery for Magnetic Fluid Hyperthermia.

The heat produced by magnetic nanoparticles, when they are submitted to a time-varying magnetic field, has been used in many auspicious biotechnological applications. In the search for better performance in terms of the specific power absorption (SPA) index, researchers have studied the influence of the chemical composition, size and dispersion, shape, and exchange stiffness in morphochemical structures. Monodisperse assemblies of magnetic nanoparticles have been produced using elaborate synthetic procedures, where the product is generally dispersed in organic solvents. However, the colloidal stability of these rough dispersions has not received much attention in these studies, hampering experimental determination of the SPA. To investigate the influence of colloidal stability on the heating response of ferrofluids, we produced bimagnetic core@shell NPs chemically composed of a ZnMn mixed ferrite core covered by a maghemite shell. Aqueous ferrofluids were prepared with these samples using the electric double layer (EDL) as a strategy to maintain colloidal stability. By starting from a proper sample, ultrastable concentrated ferrofluids were achieved by both tuning the ion/counterion ratio and controlling the water content. As the colloidal stability mainly depends on the ion configuration on the surface of the magnetic nanoparticles, different levels of nanoparticle clustering are achieved by changing the ionic force and pH of the medium. Thus, the samples were submitted to two procedures of EDL destabilization, which involved dilution with an alkaline solution and a neutral pH viscous medium. The SPA results of all prepared ferrofluid samples show a reduction of up to half the efficiency of the standard sample when the ferrofluids are in a neutral pH or concentrated regime. Such results are explained in terms of magnetic dipolar interactions. Our results point to the importance of ferrofluid colloidal stability in a more reliable experimental determination of the NP heat generation performance.

Characteristics of colloids and their affinity for heavy metals in road runoff with different traffic in Beijing, China

The characteristics of colloids in urban road runoff with different traffic in Beijing, China, such as concentration, particle size, chemical property, and affinity for heavy metals were determined. The concentration of colloids was high, and an evident first flush effect was found in the runoff of road with heavy traffic. A large portion of colloids were distributed in the range of 1-10 μm. Traffic activity, rainfall intensity, and time of sample collection would not change the size distribution of colloids in the road runoff. The chemical property of colloids in the road runoff would be influenced by the soil erosion nearby green space, causing the content of organic colloids was high. The correlation coefficient between the concentration of colloids in colloidal fractions and the concentration of heavy metals (Cu, Zn, Cd, Pb, Fe, and Mn) in the road runoff with different traffic decreased with the same sequence from 0.02-0.2 μm, 0.2-0.45 μm, 0.45-1 μm, to 1-10 μm, suggesting that the heavy metals had stronger affinity for the colloids with small size. The concentration of Cu, Pb, and Zn exhibited significant correlations with the concentration of organic colloids in the road runoff. More aggregated spherical particles were found in the TEM image of the road runoff with heavy traffic. Zeta potentials and RMV data showed that the colloids with smaller size and the colloids in the road runoff with lighter traffic were much more stable.

Soil cadmium mobilisation by dissolved organic matter from soil amendments

Dissolved organic matter (DOM) release from Cd contaminated soils been linked to mobilisation of the metal as Cd-DOM complexes and this may be exacerbated by organic matter-rich soil amendments. The quantity and quality of the DOM can determine the proportion of dissolved Cd that partitions to mobile complexes and their stability and, thus, the potential for Cd transport from contaminated soils. The aim of this work was to examine differences in Cd mobilisation from soils to which different types of soil amendments/conditioners have been applied and the importance of DOM characteristics in determining the extent to which this can happen. Three soils were spiked with Cd to 2 mg kg−1, allowed to equilibrate and then treated with compost and peat. These soils and an untreated subsample of each soil were then adjusted to three different pHs: 5.6, 6.4 and 7.4, using lime. The amount of Cd mobilised from each soil was tested using a column leaching experiment. Ultrafiltration and speciation modelling were used to determine amounts of Cd as DOM-complexed, “truly” dissolved (<5 kDa) and colloidal species, while DOM quality was assessed using UV–Vis and fluorescence spectroscopy. Most colloidal Cd was mobilised from the compost treated soils (50%–60%), followed by the peat treated soils (20–44%). The relationships between colloidal Cd, DOC concentration and soil pH, together with the spectroscopic and modelling results showed that structural properties of DOM are an important factor in mobilising Cd from contaminated soils.

Colloidal aggregation in anisotropic liquid crystal solvent.

The mutual attraction between colloidal particles in an anisotropic fluid, such as the nematic liquid crystal phase, leads to the formation of hierarchical aggregate morphologies distinct from those that tend to form in isotropic fluids. Previously it was difficult to study this aggregation process for a large number of colloids due to the difficulty of achieving a well dispersed initial colloid distribution under good imaging conditions. In this paper, we report the use of a recently developed self-assembling colloidal system to investigate this process. Hollow, micron-scale colloids are formed in situ in the nematic phase and subsequently aggregate to produce fractal structures and colloidal gels, the structures of which are determined by colloid concentration and temperature quench depth through the isotropic to nematic phase transition point. This self-assembling colloidal system provides a unique method to study particle aggregation in liquid crystal over large length scales. We use fluorescence microscopy over a range of length scales to measure aggregate structure as a function of temperature quench depth, observe ageing mechanisms and explore the driving mechanisms in this unique system. Our analyses suggest that aggregate dynamics depend on a combination of Frank elasticity relaxation, spontaneous defect line annihilation and internal aggregate fracturing.

Integral equation theory for mixtures of spherical and patchy colloids. 2. Numerical results.

Thermodynamic properties and structure of binary mixtures of patchy and spherical colloids are studied using a recently developed theory [Y. V. Kalyuzhnyi, et al., Soft Matter, 2020, 16, 3456]. The theory is based on a solution of the multidensity Ornstein-Zernike equation and provides completely analytical expressions for the structure factors of these systems and for all their major thermodynamical quantities. The considered mixtures are made up of particles of different size and with a different number of patches. A set of molecular simulation data has been generated to enable a systematic comparison and to access thus accuracy of the theoretical predictions. In general, the predictions of the theory appear to be in good agreement with computer simulation data. For the models with a lower number of patches (np = 1, 2) the theoretical results show very good accuracy. Less accurate are the predictions for the four-patch versions of the model. While theoretical results for the radial distribution functions are, generally, relatively accurate for all the models, results for thermodynamics deteriorate with increasing concentration of the spherical colloids. Possible ways to improve the theory are briefly outlined.

Effective fields in magnetic colloids and features of their magnetization kinetics.

We present results of magnetization and magnetic susceptibility dependence investigations performed for undecane-based ferrofluids with dominant of Brownian relaxation for particles. A robust and effective method of fine particle size characterization is presented. It is based on the core-shell model and the analysis of the dependence of saturation magnetization on particle concentration. A novel advantage method has been used as a straightforward way to determine the concentration dependence of the effective field related to particle interaction that was calculated from the experimentally obtained concentration dependence of low field susceptibility. The computed relationship is compared with the concentration dependences of effective fields derived from several well-known theoretical models. We present some peculiarities of the real part of dynamic magnetic susceptibility on temperature. Investigated features are defined both by the magnetic state of fine particles and by crystallization of carrier at the liquid to a solid phase transition. For the first time, the dependence of the magnetization relaxation time on the colloidal particle concentration and the magnitude of bias DC magnetic field was investigated experimentally. Results are in good agreement with theoretical predictions for moderate concentration and significantly differs for concentration greater 7 vol%. It is concluded that this effect can be related either to the enhanced particle interaction or to the transition of some particles from superparamagnetic to a ferromagnetic state. These predictions are verified through the calculation in terms of Cole-Cole diagrams methods.

Optothermal pulling, trapping, and assembly of colloids using nanowire plasmons.

Optical excitation of colloids can be harnessed to realize soft matter systems that are out of equilibrium. In this paper, we present our experimental studies on the dynamics of silica colloids in the vicinity of a silver nanowire propagating surface plasmon polaritons (SPPs). Due to the optothermal interaction, the colloids are directionally pulled towards the excitation point of the nanowire. Having reached this point, they are spatio-temporally trapped around the excitation location. By increasing the concentration of colloids in the system, we observe multi-particle assembly around the nanowire. This process is thermophoretically driven and assisted by the SPPs. Furthermore, we find such an assembly to be sensitive to the excitation polarization at the input of the nanowire. Numerically-simulated temperature distribution around an illuminated nanowire corroborates sensitivity to the excitation polarization. Our study will find relevance in exploration of SPP-assisted optothermal pulling, trapping and assembly of colloids, and can serve as a test-bed of plasmon-driven active matter.

Improved synthesis of Ti3C2Tx MXenes resulting in exceptional electrical conductivity, high synthesis yield, and enhanced capacitance.

For the first time, an "Evaporated-Nitrogen" Minimally Intensive Layer Delamination (EN-MILD) synthesis approach is reported to synthesize exceptionally high quality MXene sheets. In the EN-MILD method, the concentrations of acids and Li-ions are continuously increased during the etching process. By implementing the EN-MILD approach, the electrical conductivity increases up to 2.4 × 104 S cm-1, which is the highest reported value to date for Ti3C2Tx MXenes (a traditional MILD approach results in a conductivity of 5.8 × 103 S cm-1). This significant improvement in electrical conductivity arises from the high quality of the synthesized MXene sheets as well as a larger flake size. The EN-MILD synthesis approach also offers high yield of delaminated single MXene layers (up to ∼60% after the first round of washing/centrifugation) and high colloidal concentrations (up to 31 mg ml-1). The working electrode prepared from free-standing MXene paper shows an exceptional capacitance of ≈490 F g-1 at 1 A g-1 in a supercapacitor, which is among the highest values reported for MXene-based supercapacitor electrodes. The exceptional electrical conductivity, high yield of delaminated MXene single layers, and high colloidal concentration of the EN-MILD approach significantly expand the applications of MXenes.