Small Colloids Research Articles

偏光と物質のコラボレーション:不斉性を有する低分子・高分子・コロイド・微小構造体の創成と制御

偏光と物質のコラボレーション:不斉性を有する低分子・高分子・コロイド・微小構造体の創成と制御

Depinning and heterogeneous dynamics of colloidal crystal layers under shear flow.

Using Brownian dynamics (BD) simulations and an analytical approach we investigate the shear-induced, nonequilibrium dynamics of dense colloidal suspensions confined to a narrow slit-pore. Focusing on situations where the colloids arrange in well-defined layers with solidlike in-plane structure, the confined films display complex, nonlinear behavior such as collective depinning and local transport via density excitations. These phenomena are reminiscent of colloidal monolayers driven over a periodic substrate potential. In order to deepen this connection, we present an effective model that maps the dynamics of the shear-driven colloidal layers to the motion of a single particle driven over an effective substrate potential. This model allows us to estimate the critical shear rate of the depinning transition based on the equilibrium configuration, revealing the impact of important parameters, such as the slit-pore width and the interaction strength. We then turn to heterogeneous systems where a layer of small colloids is sheared with respect to bottom layers of large particles. For these incommensurate systems we find that the particle transport is dominated by density excitations resembling the so-called "kink" solutions of the Frenkel-Kontorova (FK) model. In contrast to the FK model, however, the corresponding "antikinks" do not move.

Dynamics of dissolved major (Na, K, Ca, Mg, and Si) and trace (Al, Fe, Mn, Zn, Cu, and Cr) elements along the lower Orinoco River

AbstractThis study addresses the changes in dissolved major and trace element concentrations along the Orinoco River, including the mixing zone between the Orinoco and Apure Rivers. Water samples from the Apure and Orinoco Rivers were collected monthly in four sectors over a period of 15 months. Auxiliary parameters (pH, dissolved oxygen, conductivity, and temperature), total suspended sediments, dissolved organic carbon (DOC), and major (Na, K, Ca, Mg, and Si) and trace (Al, Fe, Mn, Zn, Cu, and Cr) element concentrations were measured in all sectors. The relative contribution of both rivers after the Apure–Orinoco confluence was determined using Ca as a tracer. Moreover, a mixing model was developed to determine whether dissolved species exhibit a conservative behavior during mixing. The results indicate that DOC is removed from waters during the Apure–Orinoco mixing, probably due to absorption of DOC on mineral phases supplied by the Apure River. Dissolved Na, Ca, and Mg behave conservatively during the mixing processes, and their concentrations are controlled by a dilution process. The anomaly in the temporal pattern of K in the Orinoco is caused by the input of biogenic K originating from the Apure River during the high‐water stage. The loss of dissolved Si during the low‐water stage can be explained by the uptake of Si by diatoms. Dissolved Mn, Zn, Al, and Fe showed a non‐conservative behavior during the Apure–Orinoco mixing. The removal of Mn and Zn from the dissolved phase can be explained by the formation of Mn‐oxyhydroxides and the scavenging of Zn onto Mn oxides. Dissolved Fe is controlled by redox processes, although the removals of Fe and Al due to the preferential adsorption of large organometallic complexes by mineral surfaces after the Apure–Orinoco confluence can affect the mobility of both elements during transport. The conservative behavior shown by Cu and Cr can be related to the tendency of both elements to be complexed with small organic colloids, which are not preferentially adsorbed by clays.

Spectroscopic and microscopic characteristics of natural aquatic nanoscale particles from riverine waters

The physicochemical characterization of colloids in waters is vital for the understanding of their crucial role in transportation of pollutants and biogeochemical processes of trace elements in aquatic systems. However, there are still lack of knowledge about quantitative properties of natural aquatic nanoscale particles owing to their small size and matrix complexity. In the present work, the complementary spectroscopic and microscopic methods were applied to characterize the fluorescent properties of organic colloids, morphology of complex nanoparticles and colloidal speciation of Fe and Mn in rivers, namely Pu River (PR), Xi River (XR) and Haicheng River (HCR), located in northeast of China. Parallel factor analysis (PARAFAC) of excitation-emission matrix (EEM) spectra reveals ten fluorescent components occurring in colloidal organic matter fractionated by ultrafiltration process with cut off 1kDa or 100kDa membrane: five humic-like fluorophores (C1, C2, C3, C6 and C8) and five protein-like components (C4, C5, C7, C9 and C10). The majority of humic-like substances is present in small size colloids (1–100kDa) in these waters and the protein-like materials are, not truly dissolved or “free”, but associated with colloidal materials. Atomic force microscopy (AFM) measurement indicates that small near-spherical particles with height dimensions up to 6nm are main form in the three rivers and occasionally fibrillary material. The significant shift in the size distribution of natural colloids occurs across three rivers with average particle size of 1.43±1.01nm in the XR, 1.53±1.22nm in the PR and 2.22±1.31nm in the HCR. Analysis by Inductively Coupled Plasma-Optical Emission Spectrometer (ICP-OES) combined with ultrafiltration shows that over 73% of total dissolved Fe and <45% of total dissolved Mn are present in the colloidal phase despite diverse distribution of colloidal Fe and Mn in small size (1–100kDa) or large size (>100kDa) fractions across selected rivers.

Size distribution of FEBEX bentonite colloids upon fast disaggregation in low-ionic strength water

AbstractBentonite colloids generated from the backfill barrier in nuclear waste repositories may act as radionuclide carriers, if they are stable and mobile. Repository scenarios with highly saline groundwater inhibit colloid stability as particles tend to aggregate but, in the time frame of repositories, groundwater conditions may evolve, promoting particle disaggregation and stabilization. The disaggregation of FEBEX bentonite colloids by fast dilution to lower ionic strength was analysed in this study. Time-resolved dynamic light-scattering experiments were carried out to evaluate the kinetics of bentonite colloid aggregation and disaggregation processes in Na+ and Na+-Ca2+ mixed electrolytes of low ionic strength. Attachment and detachment efficiencies were determined.Aggregation is promoted by increasing ionic strength, being more efficient in the presence of divalent cations. Once bentonite colloids are aggregated, a decrease in ionic strength facilitates disaggregation, but the process is not fully reversible as the initial size of the stable bentonite colloids at low ionic strength is not fully recovered. Particle-size distribution and concentration in suspension were analysed on disaggregated samples by single particle-counting measurements. Small colloids were measured in the disaggregated samples but their population was smaller than in the initial stable sample, especially in the presence of Ca2+.

Francis P. Garvan-John M. Olin Medal: Annie Kersting

AWARDS Francis P. Garvan-John M. Olin Medal: Annie Kersting ShareShare onFacebookTwitterWechatLinked InRedditEmail C&EN, 2016, 94 (1), pp 38–43January 4, 2016Cite this:C&EN 94, 1, 38-43Figure1of1Sponsor: Francis P. Garvan-John M. Olin Medal Endowment Citation: For seminal contributions to understanding radionuclide behavior in the environment, mentoring students and postdocs, and developing successful education programs in nuclear forensics and environmental radiochemistry. Current position: director, Glenn T. Seaborg Institute, Lawrence Livermore National Laboratory Education: B.A., geology and geophysics, University of California, Berkeley; M.S., Ph.D., geology and geophysics, University of Michigan, Ann Arbor Kersting on her role model:“One of my favorite role models is Marie Curie. She was an amazing woman, and is an inspiration to many scientists, not just women scientists. She was a brilliantly creative scientist, who, through her accomplishments, broke down many barriers for women and made it possible for my generation to have opportunities in science. Her accomplishments were far reaching. She was the first woman to receive a Nobel Prize; she was the first scientist to win two Nobel Prizes; and she also was the first person to win two Nobel Prizes in two different fields, chemistry and physics. Through her accomplishments, she showed us that gender should not limit one’s ability to achieve. She was fearless in her pursuit of scientific discovery; her life has inspired many.” What her colleagues say:“Dr. Annie Kersting is internationally recognized for research on the fate and transport of plutonium and other actinides in the environment. Her research has transformed our fundamental chemical understanding of migration of plutonium and other contaminants in the biosphere. Specifically, she showed in her seminal paper (Nature 1999, DOI: 10.1038/16231) that plutonium is not immobilized as originally thought, but can be transported on small particulates or colloids.”—Darleane Hoffman, University of California, Berkeley

Theory and calculations of colloidal depletion interaction

Colloidal suspension is composed of particles with sizes between 1 nm and 1 m, suspended in liquid phase. The interaction between the particles consists of a hard core repulsive interaction and other kinds of repulsive and attractive interacions. Hard interaction forbids the particles from occupying the same places, resulting in a depletion effect. When big colloid particles are immersed in a colloid of small particles, each big particle has a depletion layer where the small particles cannot enter due to the hard interaction. The depletion layers of two big particles overlap when they are close enough so that extra free volume of the small particles increases and therefore the entropy of the small particles increase, thus an effective interaction between big particles is induced. This effective interaction is the so-called depletion interaction. In this review the concepts and an intuitive explanation of depletion interaction of colloidal suspensions are presented. The numerical calculation methods, including the acceptance ratio method, Wang-Landau-type method, and density functional theory method, are briefly reviewed. Several useful analytic approximations are presented. Stating from the depletion interaction between two flat plates, the Derjaguin approximation is introduced through the Asakura- Oosawa model. With this approximation, the approximate formulas of depletion interaction between two hard spheres, between a hard sphere and a hard wall, and between a hard sphere and curved hard walls in a small hard sphere colloid are derived. The depletion interaction between two hard spheres in a thin rod colloid and a thin disk colloid are also derived in the Derjaguin approximation.

Effect of different-sized colloids on the transport and deposition of titanium dioxide nanoparticles in quartz sand

Colloids (non-biological and biological) with different sizes are ubiquitous in natural environment. The investigations regarding the influence of different-sized colloids on the transport and deposition behaviors of engineered-nanoparticles in porous media yet are still largely lacking. This study investigated the effects of different-sized non-biological and biological colloids on the transport of titanium dioxide nanoparticles (nTiO2) in quartz sand under both electrostatically favorable and unfavorable conditions. Fluorescent carboxylate-modified polystyrene latex microspheres (CML) with sizes of 0.2–2 μm were utilized as model non-biological colloids, while Gram-negative Escherichia coli (∼1 μm) and Gram-positive Bacillus subtilis (∼2 μm) were employed as model biological colloids. Under the examined solution conditions, both breakthrough curves and retained profiles of nTiO2 with different-sized CML particles/bacteria were similar as those without colloids under favorable conditions, indicating that the copresence of model colloids in suspensions had negligible effects on the transport and deposition of nTiO2 under favorable conditions. In contrast, higher breakthrough curves and lower retained profiles of nTiO2 with CML particles/bacteria relative to those without copresent colloids were observed under unfavorable conditions. Clearly, the copresence of model colloids increased the transport and decreased the deposition of nTiO2 in quartz sand under unfavorable conditions (solution conditions examined in present study). Both competition of deposition sites on quartz sand surfaces and the enhanced stability/dispersion of nTiO2 induced by copresent colloids were found to be responsible for the increased nTiO2 transport with colloids under unfavorable conditions. Moreover, the smallest colloids had the highest coverage on sand surface and most significant dispersion effect on nTiO2, resulting in the greatest nTiO2 transport.

Membrane capacity and fouling mechanisms for ultrathin nanomembranes in dead-end filtration

Ultrathin membrane technologies hold promise for improvements in membrane-based separation, however much remains to be learned about the ability of these membranes to support practical filtration processes. Here we examine the performance of new nanoporous silicon nitride (NPN) membranes in dead-end filtration using different methods for generating transmembrane pressure while varying nanoparticle types, sizes and concentrations. We infer membrane fouling by the amount of filtrate generated after a minute of dead-end filtration and show that each of these parameters has a strong influence on the rate of NPN fouling. Inverted centrifugation, which pulls large particles and aggregates away from the membrane as solvent passes through, increases filtrate volumes compared to forward centrifugation. Fitting filtration results to classic fouling models indicate that particles larger than the pores appear to foul membranes via cake formation at all concentrations, while filtration with particles much smaller than pores are impacted by pore obstruction before cake build up. Using direct comparisons in centrifuge devices, we show that NPN membranes have a comparable capacity to process suspensions of small colloids by dead end filtration at similar solvent speeds to thicker polycarbonate track-etched membranes, even with permeabilities more than two orders of magnitude higher.

Optical properties of nanostructured gold-silver films formed by deposition of small colloid drops

The formation of gold-silver cluster structures on surfaces of glasses has been investigated. The properties of these structures are analyzed in dependence on the weight ratio of metal nanoparticles and the particle concentration in the colloid. It is shown that the optical properties of these structures may change significantly with a change in the morphological properties and chemical composition of the structures.

Organic characterisation of cave drip water by LC-OCD and fluorescence analysis

Cathedral Cave, Wellington, Australia, is a natural laboratory for studying water movement and geochemical processes in the unsaturated zone by using artificial irrigation to activate drip sites within the cave. Water sampled from two drip sites activated by irrigations carried out in summer 2014 was analysed for dissolved inorganic ions and fluorescent organic matter. The analysis allowed the development of a conceptual flow path model for each drip site. DOM analysis was further complemented by liquid chromatography with organic carbon detection (LC-OCD), applied for the first time to karst drip waters, allowing the characterisation of six organic matter fractions. The differences in organic matter fractions at each drip site are interpreted as a signature of the proposed flow paths. LC-OCD was also compared with parallel factor analysis (PARAFAC) of the fluorescence and good correlations were observed for high molecular weight organic matter. Strong positive correlations were also observed for high molecular weight matter and Cu and Ni. This is suggestive of colloidal transport of Cu and Ni by organic matter with high molecular weight, while small molecular weight colloids were not efficient transporters. LC-OCD uniquely provides information on non-fluorescent organic matter and can be used to further quantify drip water organic matter composition.

Classification of Zinc Sulfide Quantum Dots by Size: Insights into the Particle Surface–Solvent Interaction of Colloids

We present a detailed study on the classification of ZnS quantum dots (QDs) by size selective precipitation (SSP). SSP allows the postsynthetic narrowing of a given feed distribution and is usually realized by titration of a poor solvent into a suspension of dispersed particles. Thereby preferred flocculation of larger structures is induced. Our results confirm that SSP is a highly robust process, following a law of mass action. That means a certain solvent composition always leads to the same ratio between coarse and fines particles with respect to a specific particle size xi. This ratio is independent of the particle size distribution (PSD) of the feed, the washing history of the particles, and the solid concentration of the particles. Regarding the illustration of our findings, we established a combined approach that takes Hansen solubility parameters (HSP) of solvent mixtures as well as changing van der Waals interactions into account. Relating both to each other, a size-dependent region of enhanced solubility is clearly identified. Our concept allows a differentiation between volume-related effects like van der Waals interactions and surface-related effects like the interaction of a ligand with a solvent mixture. A comprehensive interpretation of classification results obtained with different good solvents and poor solvents enables to deduce a general strategy for the demanding determination of HSP for small colloids. Our work makes an important contribution to the design of an appropriate colloidal postprocessing which is applicable to larger quantities.

Effect of membrane polymeric materials on relationship between surface pore size and membrane fouling in membrane bioreactors

We investigated the effect of different membrane polymeric materials on the relationship between membrane pore size and development of membrane fouling in a membrane bioreactor (MBR). Membranes with different pore sizes were prepared using three different polymeric materials, cellulose acetate butyrate (CAB), polyvinyl butyral (PVB), and polyvinylidene fluoride (PVDF), and the development of membrane fouling in each membrane was evaluated by batch filtration tests using a mixed liquor suspension obtained from a laboratory-scale MBR. The results revealed that the optimal membrane pore size to mitigate membrane fouling differed depending on membrane polymeric material. For PVDF membranes, the degree of membrane fouling decreased as membrane pore size increased. In contrast, CAB membranes with smaller pores had less fouling propensity than those with larger ones. Such difference can be attributed to the difference in major membrane foulants in each membrane; in PVDF, they were small colloids or dissolved organics in which proteins are abundant, and in CAB, microbial flocs. The results obtained in this study strongly suggested that optimum operating conditions of MBRs differ depending on the characteristics of the used membrane.

Depletion, melting and reentrant solidification in mixtures of soft and hard colloids.

We present extensive experimental and theoretical investigations on the structure, phase behavior, dynamics and rheology of model soft-hard colloidal mixtures realized with large, multiarm star polymers as the soft component and smaller, compact stars as the hard one. The number and length of the arms in star polymers control their softness, whereas the size ratio, the overall density and the composition are additional parameters varied for the mixtures. A coarse-grained theoretical strategy is employed to predict the structure of the systems as well as their ergodicity properties on the basis of mode coupling theory, for comparison with rheological measurements on the samples. We discovered that dynamically arrested star-polymer solutions recover their ergodicity upon addition of colloidal additives. At the same time the system displays demixing instability, and the binodal of the latter meets the glass line in a way that leads, upon addition of a sufficient amount of colloidal particles, to an arrested phase separation and reentrant solidification. We present evidence for a subsequent solid-to-solid transition well within the region of arrested phase separation, attributed to a hard-sphere-mixture type of glass, due to osmotic shrinkage of the stars at high colloidal particle concentrations. We systematically investigated the interplay of star functionality and size ratio with glass melting and demixing, and rationalized our findings by the depletion of the big stars due to the smaller colloids. This new depletion potential in which, contrary to the classic colloid-polymer case, the hard component depletes the soft one, has unique and novel characteristics and allows the calculation of phase diagrams for such mixtures. This work covers a broad range of soft-hard colloidal mixture compositions in which the soft component exceeds the hard one in size and provides general guidelines for controlling the properties of such complex mixtures.

Colloidal binary mixtures at fluid-fluid interfaces under steady shear: structural, dynamical and mechanical response.

We experimentally study the link between structure, dynamics and mechanical response of two-dimensional (2D) binary mixtures of colloidal microparticles spread at water/oil interfaces. The particles are driven into steady shear by a microdisk forced to rotate at a controlled angular velocity. The flow causes particles to layer into alternating concentric rings of small and big colloids. The formation of such layers is linked to the local, position-dependent shear rate, which triggers two distinct dynamical regimes: particles either move continuously ("Flowing") close to the microdisk, or exhibit intermittent "Hopping" between local energy minima farther away. The shear-rate-dependent surface viscosity of the monolayers can be extracted from a local interfacial stress balance, giving "macroscopic" flow curves whose behavior corresponds to the distinct microscopic regimes of particle motion. Hopping regions reveal a higher resistance to flow compared to the flowing regions, where spatial organization into layers reduces dissipation.

Surface Modification: Simple Multipurpose Surface Functionalization by Phase Transited Protein Adhesion (Adv. Mater. Interfaces 2/2015)

By exploiting the lysozyme from egg white that is distinct from classical polydopamines, P. Yang and co-workers report in article 1400401 a universal method for multipurpose functionalization on arbitrary material surfaces. Small molecules, macromolecules and colloids are immobilized onto versatile substrates of metals, oxides, and synthetic polymers by manipulating the phase-transited protein as a priming layer.

Fate and Immunotoxic Effects of Silver Nanoparticles on Rainbow Trout in Natural Waters

This study investigates the fate and the effects of silver nanoparticles (AgNPs) in rainbow trout (Oncorhynchus mykiss). Juveniles were exposed to 50 μg/L of AgNPs 20 nm and 1 μg/L of dissolved silver Ag+ (as AgNO3) in three types of water differing in conductivity, pH and organic matter: green water (Saint-Lawrence River), brown water (Ottawa River), and UV-treated and dechlorinated tap water. After a 96 h exposure, chemical analyses were performed on both water samples and fish tissues (liver and gills) and a suite of immune and hepatic biomarkers were also performed on fish.Results demonstrated that brown water with high organic carbon values (7 mg/L), promoted the formation of small AgNP aggregates that were bioaccumulated in fish gills and liver. In fish exposed to AgNPs, immunostimulation and hepatic oxidative stress were observed in pronephros and liver respectively. Dissolved Ag+ in brown water was associated to small colloids, promoted silver bioavailability and induced leucocytes immunostimulation. The higher alkalinity and conductivity of green water promoted morphological AgNPs transformations. Although, AgNPs neither induced immune nor hepatic damages, AgNO3 induced leucocyte stimulation and a hepatic pro-inflammatory response. Ag from AgNPs and AgNO3 was bioaccumulated in gills, and liver without hepatic injury (oxidative stress). AgNO3 induced immunosuppression and oxidative stress in pronephros. This study shows that water parameters influence the fate, bioavailability and the toxicity AgNPs and dissolved Ag+ in fish. Brown water showed more harmful effects with AgNPs than tap and green waters.

A high yield, one-pot dialysis-based process for self-assembly of near infrared absorbing gold nanoparticles

HypothesisA facile, dialysis-based synthesis of stable near infrared (nIR) absorbing plasmonic gold nanoparticles (λmax=650–1000nm) will increase the yield of nIR particles and reduce the amount of gold colloid contaminant in the product mixture. ExperimentsChloroauric acid and sodium thiosulfate were reacted using a dialysis membrane as a reaction vessel. Product yield and composition was determined and compared to traditional synthesis methods. The product particle distribution, yield, and partitioning of gold between dispersed product and membrane-adsorbed gold were determined. FindingsThe synthesis results in polydisperse particle suspensions comprised of 70% spheroid-like particles, 27% triangular plates, and 3% rod-like structures with a 3% batch-to-batch variation and a prominent nIR absorption band with λmax=650–1000nm. The amount of small gold colloid (λmax=530nm; d<10nm) in the isolated product was reduced by 96% compared to traditional methods. Additionally, 91.1% of the gold starting material is retained in the solution-based nanoparticle mixture while 8.2% is found on the dialysis membrane. The synthesis results in a quality ratio (QR=AbsnIR/Abs530) of 1.7–2.4 (twice that of previous techniques) and 14.3 times greater OD∗ml yield of the nIR-absorbing nanoparticle fraction.

Effect of natural organic matter on the adsorption and fractionation of thorium and protactinium on nanoparticles in seawater

Laboratory experiments were carried out to examine the role of natural organic matter (NOM) in regulating the adsorption and fractionation of 234Th and 233Pa in seawater on inorganic nanoparticles (20nm), including SiO2, CaCO3, Fe2O3, Al2O3 and TiO2. Model macromolecules and natural colloidal organic matter (COM) tested in the present study included dextran with different molecular weights, acid polysaccharides (APS), humic acids (HAs), protein (bovine serum albumin, BSA), and COM isolated from river water and seawater. APS and HAs had comparable affinity and higher partition coefficients (Kd) for 234Th, with logKd values close to 7, while proteins showed weaker binding strength with 234Th and had a logKd value of 5.75. Compared to 234Th, 233Pa showed lower affinity for different organic matters, with logKd values ranging from 4.41 on APS to 5.46 on 6-kDa-dextran. In general, macromolecules and COM preferentially complexed with 234Th over 233Pa, which resulted in a fractionation between 234Th and 233Pa on different NOMs with a fractionation factor (FTh/Pa) following the order of APS>HA≥Dextran>BSA. Results from binary-sorbent experiments (nanoparticles plus NOM) indicated that NOMs evidently affected the adsorption of 234Th and 233Pa on different inorganic nanoparticles likely through the formation of organic coatings. While SiO2 preferentially adsorbed 233Pa over 234Th, the presence of APS could compete the effective sorption sites and thus reduced the adsorption of 233Pa on SiO2 nanoparticles. Based on a two end-member mixing model (Li, 2005), coating extent seemed to depend on the relative abundance and chemical composition of organic matter and inorganic nanoparticles. In addition to organic composition, NOM concentrations also affected the partitioning of 234Th and 233Pa between seawater and particles, showing a strong ‘colloidal concentration effect’. Nevertheless, there was little change in logKd values of 234Th and 233Pa on dextran with a molecular weight between 6–500kDa or 2–10nm in size, indicating negligible NOM size effect from small colloids on the adsorption of Th and Pa in seawater.

Ubiquitous Presence of Fe(II) in Aquatic Colloids and Its Association with Organic Carbon

Despite being thermodynamically less stable, small ferrous colloids (60 nm to 3 μm in diameter) remain an important component of the biogeochemical cycle at the Earth’s surface, yet their composition and structure and the reasons for their persistence are still poorly understood. Here we use X-ray-based Fe L-edge and carbon K-edge spectromicroscopy to address the speciation and organic–mineral associations of ferrous, ferric, and Fe-poor particles collected from sampling sites in both marine and freshwater environments. We show that Fe(II)-rich phases are prevalent throughout different aquatic regimes yet exhibit a high degree of chemical heterogeneity. Furthermore, we show that Fe-rich particles show strong associations with organic carbon. The observed association of Fe(II) particles with carboxamide functional groups suggests a possible microbial role in the preservation of Fe(II). These finding have significant implications for the behavior of Fe(II) colloids in oxygenated waters, and their role in different aquatic biogeochemical processes.