Time-resolved Dynamic Light Scattering Research Articles

Stability of uncapped gold nanoparticles produced via laser reduction in liquid

Nanoparticles are excellent catalysts due to their high surface area to volume ratio that results in an increased number of catalytically active sites per unit mass. This plethora of highly reactive sites is often in contrast with the catalyst stability. Capping agents are used to maintain stability against aggregation; they can however have adverse effects on the catalytic activity of the nanoparticles by obstructing reactant access to active sites. A unique set of synthesis methods that leverage lasers, such as Laser Reduction in Liquid (LRL), are capable of producing catalytic nanoparticles that remain stable despite their lack of capping agent. The mode of stabilization for uncapped laser nanoparticles must arise from electrostatic repulsion. There are three main hypotheses that seek to describe the source of this electrostatic repulsion: oxidized species at the particle surface, adsorbed anions at the particle surface, or trapped electrons within the particle. Two types of LRL particles were analyzed: particles produced using a laser pulse duration on the order of ns, and particles produced using a laser pulse duration on the order of fs. The primary difference between these two synthesis conditions arose from the presence (fs) or absence (ns) of an electron rich plasma during nanoparticle synthesis. The stability of LRL nanoparticles was investigated using zeta potential measurements. It was found that the ns particles were significantly less stable than their fs counterparts. Aggregation kinetics were investigated using time resolved dynamic light scattering (TR-DLS). Using the aggregation kinetics measurements, the surface potential of the fs nanoparticles were determined using DLVO theory. The surface potential allowed us to calculate the theoretical electron density of the fs particles as a function of laser focus. The particle electron densities are similar to the electron density of the plasma in which they were synthesized. These results support the trapped electron hypothesis as being a key mode of stabilization for LRL nanoparticles.

Influence of protein configuration on aggregation kinetics of nanoplastics in aquatic environment

Aggregation kinetics of nanoplastics in aquatic environment are influenced by their interactions with proteins having different structures and properties. This study employed time-resolved dynamic light scattering (TR-DLS) to investigate the effects of 5 proteins (bovine hemoglobin (BHb), bovine (BSA) and human serum albumin (HSA), collagen type I (Col I), and bovine casein (CS)) on aggregation kinetics of polystyrene nanoplastics (PSNPs) under natural water conditions, which were simulated using various ionic strength (1-1000 mM NaCl and 0.01-100 mM CaCl2), pH (3-9), and protein concentration (1-5 mg/L of total organic carbon). The results indicated that the interactions between proteins and PSNPs strongly depended on electrostatic properties, protein structures, and solution chemistries, which induced distinct aggregation behaviors in NaCl and CaCl2 solutions. Electrostatic repulsion and steric hindrance dominated their interactions in NaCl solution by stabilizing PSNPs with the order of spherical BSA and disordered CS > heart-shaped HSA > fibrillar Col I; whereas positively charged BHb destabilized PSNPs with aggregation rate of 1.71 nm/s at 300 mM NaCl. In contrast, at CaCl2 concentration below 20 mM, proteins destabilized PSNPs following the sequence of HSA > BHb > Col I > BSA depending on counterbalance among double layer compression, cation bridging, and steric hindrance; whereas CS stabilized PSNPs by precipitating Ca2+ that inhibited charge screening effect. Both protein concentration and solution pH affected protein corona formation, surface charge, and protein structure that altered stability of PSNPs. Characterizations using fluorescence spectroscopy, circular dichroism, and two-dimensional correlation analysis spectroscopy showed fluorescence quenching and ellipticity reduction of proteins, indicating strong adsorption affinity between PSNPs and proteins. The study provides insight to how protein configuration and water chemistry affect fate and transport of nanoplastics in aquatic environment.

The effect of ionic strength, pH and natural organic matter on heteroaggregation of CeO2 nanoparticles with montmorillonite clay minerals

An accurate assessment of the fate and transport of engineered nanoparticles (ENPs) in aquatic environments hinges on developing an understanding of interaction between ENPs and natural colloids. In this study, we investigated the effects of pH and natural organic matter (NOM) on homoaggregation of CeO2 nanoparticles and their heteroaggregation with montmorillonite clay minerals. Time-resolved dynamic light scattering (TR-DLS) was employed to investigate the aggregation kinetics as function of electrolyte concentration in both homo- and heteroaggregation scenarios. The surface charge of CeO2 nanoparticles changed from positive to negative with pH increase while montmorillonite was negatively charged over the range of pH 4−11. At low pH, the critical coagulation concentration (CCC) of the montmorillonite-CeO2 mixtures shifted to a lower electrolyte concentration when compared to the homogenous system, indicating the negatively charged montmorillonite reduced the stability of positively charged CeO2 via heteroaggregation. In contrast, at high pH, the mixtures were stable because both montmorillonite and CeO2 nanoparticles were negatively charged. The presence of humic acid stabilized the systems against homo- and heteroaggregation. Our results suggest that the complex interactions between ENPs, natural colloids, and NOM should be considered to better understand the fate and transport of ENPs in realistic aquatic environments.

Comparing Zwitterionic and PEG Exteriors of Polyelectrolyte Complex Micelles.

A series of model polyelectrolyte complex micelles (PCMs) was prepared to investigate the consequences of neutral and zwitterionic chemistries and distinct charged cores on the size and stability of nanocarriers. Using aqueous reversible addition-fragmentation chain transfer (RAFT) polymerization, we synthesized a well-defined diblock polyelectrolyte system, poly(2-methacryloyloxyethyl phosphorylcholine methacrylate)-block-poly((vinylbenzyl) trimethylammonium) (PMPC-PVBTMA), at various neutral and charged block lengths to compare directly against PCM structure–property relationships centered on poly(ethylene glycol)-block-poly((vinylbenzyl) trimethylammonium) (PEG-PVBTMA) and poly(ethylene glycol)-block-poly(l-lysine) (PEG-PLK). After complexation with a common polyanion, poly(sodium acrylate), the resulting PCMs were characterized by dynamic light scattering (DLS) and small angle X-ray scattering (SAXS). We observed uniform assemblies of spherical micelles with a diameter ~1.5–2× larger when PMPC-PVBTMA was used compared to PEG-PLK and PEG-PVBTMA via SAXS and DLS. In addition, PEG-PLK PCMs proved most resistant to dissolution by both monovalent and divalent salt, followed by PEG-PVBTMA then PMPC-PVBTMA. All micelle systems were serum stable in 100% fetal bovine serum over the course of 8 h by time-resolved DLS, demonstrating minimal interactions with serum proteins and potential as in vivo drug delivery vehicles. This thorough study of the synthesis, assembly, and characterization of zwitterionic polymers in PCMs advances the design space for charge-driven micelle assemblies.

The characteristics of organic matter influence its interfacial interactions with MnO2 and catalytic oxidation processes

The influence of dissolved organic matter (DOM) properties on its interfacial interactions with MnO2 and on catalytic oxidation processes was studied by Time-Resolved Dynamic Light Scattering (TR-DLS) and Atomic Force Microscopy (AFM) under varied solution conditions. Four DOM fractions of different characteristics (e.g., SUVA, hydrophobic character, structural properties) were selected. Bared-MnO2 nanoparticles readily aggregated in NaCl and CaCl2 solutions. Classic DLVO Theory successfully described critical coagulation concentrations and aggregation behaviors. In NaCl solution, DOM adsorbed on MnO2 nanoparticles and provided electrosteric stabilization. The two DOM fractions of higher hydrophobic (HPO) character were more efficient in decreasing the aggregation rates. Enhanced MnO2 aggregation was observed at high Ca2+ concentrations due to charge screening and cation bridging between carboxyl groups in DOM structures. The addition of oxidant (H2O2) induced a high aggregation of bared-MnO2 nanoparticles, possibly due to the release of Mn2+ (i.e., complexation mechanisms) and generation of reactive species (O2−, HO2−, and H). Contrasted with their hydrophilic (HPI) counterparts, HPO isolates adsorbed on MnO2 significantly decreased the catalytic oxidation processes between H2O2/MnO2; suggesting a more efficient and stronger DOM coating. Interfacial forces measured by AFM, showed weaker interactions between HPI isolates and MnO2; suggesting unfavorable polar interactions. Conversely, the high adhesion forces between MnO2/HPO isolate would indicate stronger bonds and hydrophobic interactions. This study provided a nanoscale understanding of the impact of DOM characteristics on: a) performance of the MnO2 coated ceramic membranes in water treatment, and b) biogeochemical cycle of Mn-oxides in the environmental.

Aggregation and deposition of colloidal particles: Effect of surface properties of collector beads

The effect of the surface properties of collector beads on the transport of colloidal particles in porous media has been experimentally investigated. Both batch and continuous column experiments were conducted to study the dynamics of deposition and aggregation of colloids (polystyrene latex sulfate, d=100nm) in contact with collector particles (soda lime glass beads, d=212–300 micron). Various rinsing methods were systematically used to wash the surface of soda lime glass beads. Time-resolved dynamic light scattering (TR-DLS) and ultraviolet-visible spectroscopy (UV–vis) were employed to evaluate the concentration of colloidal particles and their aggregation in columns packed with glass beads. Rinsing of glass beads was found to release the surface ions of collectors into the colloidal suspension and subsequently led to the aggregation of colloids. In batch experiments, leaching-induced increase of ion concentration in the suspension triggered the aggregation process, while, the collision frequency governed the aggregation dynamics later on. In column experiments, however, the initiation of aggregation by released ions was dependent on the length of the column. In a long column, a blocking-ripening mechanism was observed at the lower pH that indicated the concurrent aggregation and deposition of colloidal particles. In a short column, however, the concentration of eluted colloids did not decline over time that revealed incapability of leaching process to initiate aggregation. Furthermore, the solution chemistry was realized to be more effective in determining the fate of colloidal particles inside packed columns than the surface chemistry of collector beads. This study provides valuable insight into the effect of surface properties of collectors on aggregation and deposition of colloidal particles in a packed environment.

Role of Crystal Structure and Chalcogenide Redox Properties on the Oxidative Assembly of Cadmium Chalcogenide Nanocrystals.

Oxidative assembly of metal chalcogenide nanocrystals (NCs) enables the formation of 2-D (dense) and 3-D porous structures without the presence of intervening ligands between particles that can moderate transport properties. This route has been demonstrated to be successful for a range of single-component structures including CdQ, PbQ, and ZnQ (Q = S, Se, Te). En route to the controllable assembly of multicomponent nanostructures, the roles of Q redox properties (2Q2- → Q22- + 2e) responsible for particle cross-linking and the native structure (cubic zinc blende vs hexagonal wurtzite) in the kinetics of assembly in single-component CdQ NCs are evaluated using time-resolved dynamic light scattering (TR-DLS). For wurtzite CdQ, the rates follow the ease of oxidation, with telluride as the fastest, followed by selenide and sulfide. However, when comparing CdS wurtzite (w) and zinc blende (zb), the cubic NCs exhibit surprisingly slow kinetics. NMR studies reveal the zb structure to have lower ligand coverage (by a factor of 4) relative to that of w, and the formation of free disulfide (the product of ligand oxidation) is slow. This is attributed to differences in the surface energies of w and zb facets, with w having polar (0001) facets of high energy compared to the neutral facets of the zb structure. The zb-CdS NCs prepared by low-temperature synthesis methods are likely to suffer from surface defects that may moderate reactivity. EPR studies suggest that zb-CdS has paramagnetic sulfur vacancies not present in w-CdS. These data suggest that structure plays an unexpectedly large role in the kinetics of CdQ NC oxidative assembly, providing a useful lever to moderate activities in multicomponent assemblies.

Aggregation kinetics of stimulus-responsive polymer-coated gold nanoparticles driven by Hofmeister effects

Stability of engineered nanomaterials within natural aquatic systems is generally difficult to predict due to multiple roles that background electrolytes may play in these suspensions. Here we utilize core shell nanoparticles based on random copolymers of di(ethylene glycol) methyl ether methacrylate (x=MEO2MA) and oligo(ethylene glycol) methyl ether methacrylate (y=OEGMA) to investigate specific ion effects on colloidal stability. Aggregation kinetics (k11) of Au@(MEO2MAx-co-OEGMAy) NPs were measured for KCl, NaCl, SrCl2, and MgCl2 at various concentrations by means of time-resolved dynamic light scattering (TR-DLS). It was found that the smallest concentration of K+ and the greatest concentration of Mg2+ were required to increase the aggregation rate. Specifically, we demonstrate k11 scales not only as a result of ionic strength, but also in some cases in a direction opposite to that expected by the Schultz–Hardy rule. For these systems, aggregation kinetics can be better predicted by ion characterization within the well-established Hofmeister series.

Citrate-Coated Silver Nanoparticles Interactions with Effluent Organic Matter: Influence of Capping Agent and Solution Conditions.

Fate and transport studies of silver nanoparticles (AgNPs) discharged from urban wastewaters containing effluent organic matter (EfOM) into natural waters represent a key knowledge gap. In this study, EfOM interfacial interactions with AgNPs, and their aggregation kinetics were investigated by atomic force microscopy (AFM) and time-resolved dynamic light scattering (TR-DLS), respectively. Two well-characterized EfOM isolates, i.e., wastewater humic (WW humic) and wastewater colloids (WW colloids, a complex mixture of polysaccharides-proteins-lipids), and a River humic isolate of different characteristics were selected. Citrate-coated AgNPs were selected as representative capped-AgNPs. Citrate-coated AgNPs showed a considerable stability in Na(+) solutions. However, Ca(2+) ions induced aggregation by cation bridging between carboxyl groups on citrate. Although the presence of River humic increased the stability of citrate-coated AgNPs in Na(+) solutions due to electrosteric effects, they aggregated in WW humic-containing solutions, indicating the importance of humics characteristics during interactions. Ca(2+) ions increased citrate-coated AgNPs aggregation rates in both humic solutions, suggesting cation bridging between carboxyl groups on their structures as a dominant interacting mechanism. Aggregation of citrate-coated AgNPs in WW colloids solutions was significantly faster than those in both humic solutions. Control experiments in urea solution indicated hydrogen bonding as the main interacting mechanism. During AFM experiments, citrate-coated AgNPs showed higher adhesion to WW humic than to River humic, evidencing a consistency between TR-DLS and AFM results. Ca(2+) ions increased citrate-coated AgNPs adhesion to both humic isolates. Interestingly, strong WW colloids interactions with citrate caused AFM probe contamination (nanoparticles adsorption) even at low Na(+) concentrations, indicating the impact of hydrogen bonding on adhesion. These results suggest the importance of solution conditions and capping agents on the stability of AgNPs in solution. However, the characteristics of organics would play a crucial role in the fate and transport of these nano contaminants in urban wastewaters and natural water systems.

Stimulus-Responsive Au@(MeO2MAx-co-OEGMAy) Nanoparticles Stabilized by Non-DLVO Interactions: Implications of Ionic Strength and Copolymer (x:y) Fraction on Aggregation Kinetics

Functionalized nanoparticles can assist in stabilizing fluid-fluid interfaces; however, developing and applying the appropriate surface modification presents a challenge because successful application of these nanomaterials for biotechnological, food processing, and environmental applications requires their long-term stability in elevated ionic strength media. This work studies stimulus responsive polymeric materials based on random copolymers of di(ethylene glycol) methyl ether methacrylate (x = MeO2MA) and oligo(ethylene glycol) methyl ether methacrylate (y= OEGMA) which, when grafted to gold nanoparticles, show significant, tunable, colloidal stability. The nanoparticles Au@(MeO2MAx-co-OEGMAy) display tunable, reversible aggregation that is highly dependent on the (x:y) ratio and ionic strength. Effects of these parameters on the initial rate constant of aggregation (k11) are studied by time-resolved dynamic light scattering (TR-DLS) experiments. At the same nanoparticle concentration, a strong sensitivity to salt concentration is observed. Over less than 300 mM increase in NaCl concentration, we observed a two-order of magnitude increase in aggregation rate constants, 4.2 × 10(-20) < k11 < 1.8 × 10(-18) m(3)s(-1). Additionally, for the same gold nanoparticles, a higher fraction of OEGMA requires a higher salt concentration to induce aggregation. A linear relationship between the critical NaCl coagulation concentration (CCC) and the copolymer composition is observed. Analysis of the experimental data with an extended Derjaguin-Landau-Verwey-Overbeek (xDLVO) theory that includes hydration and osmotic forces is used to explain the stability of these systems. We find the hydration pressure, 2.4 < P(h,0) < 7.2 MPa, scales linearly both with the osmotic pressure and the OEGMA monomer concentration (5 < y < 20%). Specific knowledge of P(h,0)(y, C(NaCl)) enables design of both aggregation kinetics and stability as a function of the copolymer ratio and external stimuli.

UV-Vis spectroscopic study of the stability of Silver nanoparticles in monovalent and divalent electrolyte solutions

Nanotechnology has been advanced since the last decades. Among all nanomaterials that have been developed, nanosilver is the most frequently used nanoparticles. Its release into natural water bodies is inevitable due to its broad applications. Nanosilver (nAg) was prepared via Tollens method using. The morphology, size distribution and average size of the obtained nAg was characterized using Transmission electron microscope (TEM) and Dynamic light scattering (DLS) technique. Stability of nanosilver was determined using UV-Vis spectroscopic method. Additionally, a time-resolved DLS technique was applied to confirm the UV-Vis spectroscopic results

Role of water temperature in the fate and transport of zinc oxide nanoparticles in aquatic environment

The influence of water temperature on the aggregation and dissolution kinetics of zinc oxide nanoparticles (ZnO NPs) (mean diameter ~40 nm) was investigated. Samples of 100 mg.L−1 ZnO NPs were incubated at 15, 25 and 35 °C, similar to the surface temperature of cold freshwater, temperate estuarine, and tropical/sub-tropical coastal marine ecosystems, respectively. The natural organic matter (NOM) content, pH, electrolyte type, and ionic strength (IS), were adjusted on the basis of the water chemistries of typical aqueous systems. Specifically, the time-dependent hydrodynamic diameters (HDDs) and sedimentation plots were obtained over the first 3 h and after 24 h using time-resolved dynamic light scattering (TR-DLS) and UV-visible spectroscopy, respectively. The settling distance was further modeled for the aggregates with various HDDs according to the Stokes' sedimentation equation. The dissolution kinetics was studied over the first 12 h and after 48 h in term of percentage of released zinc ions.The results showed that the HDD increased at elevated temperatures, termed as temperature-induced aggregation, while dissolution was reduced. The aggregation at higher temperatures further hindered the dissolution due to the decrease in the surface area of the NPs. We express this process as "aggregate-suppressed dissolution". The maximum aggregation was reached in the tropical coastal marine environment with the HDD >3 μm, and the released zinc ion of 9.2% was obtained in the cold freshwater. Based on the results, the aggregation rate of 1.57 nm.s−1 was estimated for the former, and the dissolution rate of 7.44 × 10−5 mol.L−1.h−1 was calculated for the latter, respectively. The predicted values successfully fitted to genuine water samples (<26% deviation). This study provides useful data for environmental risk assessment of exposure of ZnO NPs to water column and benthic organisms.

Gelation process of Tetra-PEG ion-gel investigated by time-resolved dynamic light scattering

The dynamics of Tetra-PEG prepolymer in ionic liquid (IL) and their gelation kinetics were investigated by means of time-resolved dynamic light scattering (TR-DLS). From the DLS measurements of prepolymer solutions at chain-overlapping concentration, c*, it was found that the prepolymers are dispersed homogeneously in the IL. The intensity correlation functions (ICFs) were well fitted with the sum of single and stretched exponential function throughout the gelation process, indicating that the dynamics of the gelation process always had both a fast and slow modes. In addition, we compared the gelation process with that of Tetra-PEG hydrogel. As a result, it was found for the hydrogel system, that relatively homogeneous network represented by a single exponential curve was obtained, while the network represented by stretched exponential function was formed for the ion gel system.

Aggregation Kinetics of Metal Chalcogenide Nanocrystals: Generation of Transparent CdSe(ZnS) Core(shell) Gels.

Transparent CdSe(ZnS) sol-gel materials have potential uses in optoelectronic applications such as light emitting diodes (LEDs) due to their strong luminescence properties and the potential for charge transport through the prewired nanocrystal (NC) network of the gel. However, typical syntheses of metal chalcogenide gels yield materials with poor transparency. In this work, the mechanism and kinetics of aggregation of two sizes of CdSe(ZnS) core(shell) NCs, initiated by removal of surface thiolate ligands using tetranitromethane (TNM) as an oxidant, were studied by means of time-resolved dynamic light scattering (TRDLS); the characteristics of the resultant gels were probed by optical absorption, transmission electron microscopy (TEM) and small angle X-ray scattering (SAXS). At low concentrations of NCs (ca. 4 × 10(-7) M), the smaller, green-emitting NCs aggregate faster than the larger, orange-emitting NCs, for a specific oxidant concentration. The kinetics of aggregation have a significant impact on the macroscopic properties (i.e. transparency) of the resultant gels, with the transparency of the gels decreasing with the increase of oxidant concentration due the formation of larger clusters at the gel point and a shift away from a reaction limited cluster aggregation (RLCA) mechanism. This is further confirmed by the analyses of the gel structures by SAXS and TEM. Likewise, the larger orange-emitting particles also produce larger aggregates at the gel point, leading to lower transparency. The ability to control the transparency of chalcogenide gels will enable their properties to be tuned in order to address application-specific needs in optoelectronics.

Aggregation Kinetics and Transport of Single-Walled Carbon Nanotubes at Low Surfactant Concentrations

Little is known about how low levels of surfactants can affect the colloidal stability of single-walled carbon nanotubes (SWNTs) and how surfactant-wrapping of SWNTs can impact ecological exposures in aqueous systems. In this study, SWNTs were suspended in water with sodium dodecylsulfate (SDS) as a surface-active dispersing agent. The effect of SDS concentration on SWNT suspension stability was investigated with time-resolved dynamic light scattering (TRDLS) initial aggregation studies utilizing both monovalent (Na(+)) and divalent (Ca(2+)) cations. The critical coagulation concentration (CCC) values increased with SDS concentration for the Na(+) treatments, but the Ca(2+) treatments were less sensitive to SDS concentration changes. Longer term stability studies with SDS concentrations orders of magnitude below the SDS critical micelle concentration demonstrated that SWNTs remained suspended for over six weeks in a surface water. Transport studies in a freshwater sediment similarly showed a SDS concentration-dependent mobility of SDS-wrapped SWNTs in that SWNTs showed a relatively greater retention at lower SDS concentrations (0.001%-0.05% w/v) than at a higher SDS concentration (0.1%). It is hypothesized that the stability and mobility of SWNT suspensions is directly related to the surface coverage of SDS on the SWNT surface that simultaneously increases electrosteric repulsion and decreases surface chemical heterogeneity. Overall, these studies demonstrate that low levels of surfactant are effective in stabilizing and mobilizing SWNTs in environmental media.

Attachment Efficiency of Nanoparticle Aggregation in Aqueous Dispersions: Modeling and Experimental Validation

To describe the aggregation kinetics of nanoparticles (NPs) in aqueous dispersions, a new equation for predicting the attachment efficiency is presented. The rationale is that at nanoscale, random kinetic motion may supersede the role of interaction energy in governing the aggregation kinetics of NPs, and aggregation could occur exclusively among the fraction of NPs with the minimum kinetic energy that exceeds the interaction energy barrier (E(b)). To justify this rationale, we examined the evolution of particle size distribution (PSD) and frequency distribution during aggregation, and further derived the new equation of attachment efficiency on the basis of the Maxwell-Boltzmann distribution and Derjaguin-Landau-Verwey-Overbeek (DLVO) theory. The new equation was evaluated through aggregation experiments with CeO(2) NPs using time-resolved-dynamic light scattering (TR-DLS). Our results show that the prediction of the attachment efficiencies agreed remarkably well with experimental data and also correctly described the effects of ionic strength, natural organic matter (NOM), and temperature on attachment efficiency. Furthermore, the new equation was used to describe the attachment efficiencies of different types of engineered NPs selected from the literature and most of the fits showed good agreement with the inverse stability ratios (1/W) and experimentally derived results, although some minor discrepancies were present. Overall, the new equation provides an alternative theoretical approach in addition to 1/W for predicting attachment efficiency.

Liposome Formation from Bile Salt–Lipid Micelles in the Digestion and Drug Delivery Model FaSSIFmod Estimated by Combined Time-Resolved Neutron and Dynamic Light Scattering

The flow of bile secretion into the human digestive system was simulated by the dilution of a bile salt-lipid micellar solution. The structural development upon the dilution of the fed state bile model FeSSIF(mod6.5) to the fasted state bile model FaSSIF(mod) was investigated by small-angle neutron scattering (SANS) and dynamic light scattering (DLS) in crossed beam experiments to observe small and large structures in a size range of 1 nm to 50 μm in parallel. Because of the physiologically low lipid and surfactant concentrations of 2.625 mM egg-phosphatidylcholine and 10.5 mM taurocholate the sensitivity of the neutron-structural investigations was improved by partial solvent deuteration with 71% D(2)O, with control experiments in H(2)O. Static experiments of initial and end state systems after 6 days of development revealed the presence of mixed bile salt-lipid micelles of 5.1 nm size in the initial state model FeSSIF(mod6.5), and large liposomes in FaSSIF(mod), which represent the late status after dilution of bile secretion in the intestine in the fasted state. The liposomes depicted a size of 34.39 nm with a membrane thickness of 4.75 nm, which indicates medium to large size unilamellar vesicles. Crossed beam experiments with time-resolved neutron and light scattering experiments after fast mixing with a stopped-flow device revealed a stepwise structural dynamics upon dilution by a factor of 3.5. The liposome formation was almost complete five minutes after bile dilution. The liposomes 30 min after dilution resembled the liposomes found after 6 days and depicted a size of 44.56 nm. In the time regime between 3 and 100 s a kinetic intermediate was observed. In a further experiment the liposome formation was abolished when the dilution was conducted with a surfactant solution containing sodium dodecyl sulfate.

Aggregation kinetics of CeO2 nanoparticles in KCl and CaCl2 solutions: measurements and modeling

To characterize the environmental transport and health risks of CeO2 nanoparticles (NPs), it is important to understand their aggregation behavior. This study investigates the aggregation kinetics of CeO2 NPs in KCl and CaCl2 solutions using time-resolved dynamic light scattering (TR-DLS). The initial hydrodynamic radius of CeO2 NPs measured by DLS was approximately 95 nm. Attachment efficiencies were derived both from aggregation data and predictions based on the Derjaguin–Landau–Verwey–Overbeek (DLVO) theory. The deviations of the DLVO predictions were corrected by employing the extended DLVO (EDLVO) theory. The critical coagulation concentration (CCC) of CeO2 NPs at pH = 5.6 is approximately 34 mM for KCl and 9.5 mM for CaCl2. Furthermore, based on the EDLVO theory and the von Smoluchowski’s population balance equation, a model accounting for diffusion-limited aggregation (DLA) kinetics was established. For the reaction-limited aggregation (RLA) kinetics, a model that takes fractal geometry into account was established. The models fitted the experimental data well and proved to be useful for predicting the aggregation kinetics of CeO2 NPs.

Influence of dissolved oxygen on aggregation kinetics of citrate-coated silver nanoparticles

Aggregation, an important environmental behavior of silver nanoparticles (AgNPs) influences their bioavailability and cytotoxicity. The work studied the influence of dissolved oxygen (DO) or the redox potential on the stability of AgNPs in aqueous environments. This study employed time-resolved dynamic light scattering (TR-DLS) to investigate the aggregation kinetics of citrate-coated AgNPs. Our results demonstrated that when DO was present, the aggregation rates became much faster (e.g., 3–8 times) than those without DO. The hydrodynamic sizes of AgNPs had a linear growth within the initial 4–6 h and after the linear growth, the hydrodynamic sizes became random for AgNPs in the presence of DO, whereas in the absence of DO the hydrodynamic sizes grew smoothly and steadily. Furthermore, the effects of primary particles sizes (20, 40, and 80 nm) and initial concentrations (300 and 600 μg/L) of AgNPs on aggregation kinetics were also investigated.

Charging and stability of anionic latex particles in the presence of linear poly(ethylene imine)

Charging properties and colloidal stability of negatively charged polystyrene latex particles were investigated in the presence of linear poly(ethylene imine) (LPEI) of different molecular masses by electrophoresis and dynamic light scattering (DLS). Electrophoretic mobility measurements illustrate that LPEI strongly adsorbs on these particles leading to charge neutralization at isoelectric point (IEP) and charge reversal. Time-resolved DLS experiments indicate that the aggregation of the latex particles is rapid near the IEP and slows down away from this point. Surprisingly, the colloidal stability does not depend on the molecular mass, which indicates that the adsorbed LPEI layer is rather homogeneous.