Phase Analysis Light Scattering Research Articles

Temperature-Promoted Giant Unilamellar Vesicle (GUV) Aggregation: A Way of Multicellular Formation

The evolution of unicellular to multicellular life is considered to be an important step in the origin of life, and it is crucial to study the influence of environmental factors on this process through cell models in the laboratory. In this paper, we used giant unilamellar vesicles (GUVs) as a cell model to investigate the relationship between environmental temperature changes and the evolution of unicellular to multicellular life. The zeta potential of GUVs and the conformation of the headgroup of phospholipid molecules at different temperatures were examined using phase analysis light scattering (PALS) and attenuated total reflection-Fourier transform infrared spectroscopy (ATR-FTIR), respectively. In addition, the effect of increasing temperature on the aggregation of GUVs was further investigated in ionic solutions, and the possible mechanisms involved were explored. The results showed that increasing temperature reduced the repulsive forces between cells models and promoted their aggregation. This study could effectively contribute to our understanding of the evolution of primitive unicellular to multicellular life.

Synthesis of Cellulose Nanoparticles from Ionic Liquid Solutions for Biomedical Applications

A method for the synthesis of cellulose nanoparticles using the ionic liquid 1-ethyl-3-methylimidazolium acetate has been optimised. The use of a highly biocompatible biopolymer such as cellulose, together with the use of an ionic liquid, makes this method a promising way to obtain nanoparticles with good capability for drug carrying. The operating conditions of the synthesis have been optimised based on the average hydrodynamic diameter, the polydispersity index, determined by Dynamic Light Scattering (DLS) and the Z-potential, obtained by phase analysis light scattering (PALS), to obtain cellulose nanoparticles suitable for use in biomedicine. The obtained cellulose nanoparticles have been characterised by Fourier transform infrared spectroscopy (FTIR) with attenuated total reflectance (ATR), field emission scanning electron microscopy (FESEM) and thermogravimetric analysis (TGA/DTA). Finally, cell viability studies have been performed with a cancer cell line (HeLa) and with a healthy cell line (EA.hy926). These have shown that the cellulose nanoparticles obtained are not cytotoxic in the concentration range of the studied nanoparticles. The results obtained in this work constitute a starting point for future studies on the use of cellulose nanoparticles, synthesised from ionic liquids, for biomedical applications such as targeted drug release or controlled drug release.

Effect of temperature and inorganic salts concentration on syneresis rate of AM/DAC hydrogel

Compared with ordinary polyacrylamide, acrylamide copolymer of acryloyloxyethyl trimethylammonium chloride (AM/DAC) hydrogel is easier to reside in large pores and fractures in sandstone formation through electrostatic adsorption. However, the syneresis mechanism of AM/DAC hydrogel caused by high temperature and inorganic salts has not been clear. In this paper, the type of water in gelling solutions and hydrogels was analyzed by the DSC method, the results showed that the bound water in the hydrogel was transformed into free water and then the free water was separated from the hydrogel during the syneresis of AM/DAC hydrogel. Experimental investigations, including dynamic light scattering (DLS), differential scanning calorimetry (DSC), high-performance liquid chromatography (HPLC), phase-analysis light-scattering (PALS), and scanning electron microscope (SEM), have been conducted to elucidate the mechanism of temperature and inorganic salts on syneresis rate of AM/DAC hydrogel. The result showed that with the increase of temperature, the polymer in the AM/DAC hydrogel degraded and the molecular chain broken, which destroyed the grid of hydrogel and reduced the water holding capacity. At the same time, the formation of the hydrophobic group in the molecular chain led to the decrease of the hydrophilicity so that the AM/DAC hydrogel was easy to syneresis. In addition, the increase of temperature will promote the formation of crosslinking intermediate (di/trimethylol), improve the crosslinking rate between crosslinking intermediate and polymer, which makes the AM/DAC hydrogel easy to over crosslink. Inorganic salts diffused the electric double layer by compressing the polymer and competed with the hydrophilic groups on the polymer to absorb water, which will reduce the elongation and hydrophilicity of the polymer molecular chain. This will lead to the decrease of the hydrodynamic radius of polymer molecules in AM/DAC hydrogel, which is the main reason why inorganic salts promote hydrogel dehydration. Besides, inorganic salts had little effect on the formation rate and crosslinking rate of di/trimethylol. Therefore, reducing the molecular hydrodynamic radius of AM/DAC is the main reason why inorganic salts promote the syneresis of AM/DAC hydrogel. The research demonstrated the mechanism of high temperature and inorganic salts on syneresis rate of AM/DAC hydrogel. This study also provides technical guidelines for inhibiting hydrogel syneresis.

Multi-physics study of acoustofluidic delivery agents’ clustering behavior

Acoustofluidicly manipulated microbubbles (MBs) and echogenic liposomes (ELIPs) have been suggested as drug delivery systems for the ‘on demand’ release of drug in target tissue. This requires a clear understanding of their behaviour during ultrasonication and after ultrasonication stops. The main focus of this study is to investigate the behaviour of MBs and ELIPs clusters after ultrasonication stops and the underlaying cause of cluster diffusion considering electrostatic repulsion, steric repulsion and Brownian motion. It also examines the capability of existing models used to predict MBs’ attraction velocity due to secondary radiation force, on predicting ELIPs’ attraction velocity. Tunable resistive pulse sensing (TRPS) and phase analysis light scattering (PALS) techniques were used to measure zeta potentials of the agents and the size distributions were measured using TRPS. The zeta potentials were found to be −2.43 mV and −0.62 mV for Definity™ MBs, and −3.62 mV and −2.35 mV for ELIPs using TRPS and PALS, respectively. Both agents were shown to have significant cluster formation at pressures as low as 6 kPa. Clusters of both agents were shown to diffuse as sonication stops at a rate that approximately equals the sum of the diffusion coefficients of the agents forming them. The de-clustering behaviours are due to Brownian motion as no sign of electrostatic repulsion was observed and particles movements were observed to be faster for smaller diameters. These findings are important to design and optimise effective drug delivery systems using acoustofluidically manipulated MBs and ELIPs.

The Study of Physical and Chemical Characteristics of Organo-Clay Complexes of the Chronosequence of Albic Retisols Using Dynamic Light Scattering and Phase Analysis Light Scattering

Dynamic light scattering (DLS) and phase analysis light scattering (PALS) have been used to study the physical and chemical characteristics of organo-clay complexes of soddy-podzolic soils (Albic Retisols (Loamic, Cutanic, Differentic, Ochric)) of forest sites of the Central Forest Reserve. The study of the chronosequence of abandoned agricultural soils afforested for 100 years showed that the value of the average diameter of the organo-clay complexes slightly decreased compared to that at the site with minimum duration of afforestation (5–7 years), but remained still higher than in the forest soils. Multiple linear regression statistical models were developed to predict the average diameter of clay particles. The best model (r = 0.83), where all parameters were significant (P < 0.05), included the content of clay and carbon concentration in clay. The chronosequence of postagrogenic soddy-podzolic soils demonstrated the proximity of the colloidal system stability, but in a peptization state, as evidenced by the values of zeta potential and average diameter of the clay particles.

Deswelling studies of pH and temperature-sensitive ultra-low cross-linked microgels with cross-linked cores

Microgels prepared without exogenous crosslinker have recently been explored for diverse applications in biotechnology. However, our fundamental understanding of structure-property relationships for this class of materials is still lacking, especially in the context of more complex structures such as core-shell particles. In this article, core-shell microgels were prepared by seed-mediated, surfactant-free emulsion polymerization using a N,N′-methylenebis (acrylamide) (BIS) cross-linked poly(N-isopropylacrylamide) (pNIPAm) microgel core upon which a crosslinker-free poly(N-isopropylacrylamide)-co-acrylic acid (ULC10AAc) shell was synthesized. Dynamic light scattering (DLS) and phase analysis light scattering (PALS) measurements show that the hydrodynamic radius and electrophoretic mobility of the core-shell microgels increase significantly with increasing pH due to the pH responsive ULC10AAc shell, while the temperature sensitivity of the microgels is also strongly pH dependent. The turbidity and the temperature-dependent scattering intensity plots of microgels at different pH also provide insight into the charged state of the microgels under the studied conditions. For example, we observe multiple temperature-induced transitions when the pH is either 4.5 or 6.5, illustrating that the core and shell domains, while remaining mechanically connected, are only partially coupled thermodynamically. These studies provide insight into the perturbation of ULC microgel behavior that might be brought about due to the presence of a higher density core region. Complex architectures such as these are relevant in biotechnology applications where the soft, deformable ULC shell is advantageous to control the polymer-biology interface, but a denser core region might be required to obtain a higher loading of encapsulated therapeutics, tracking dyes, or oligonucleotides. Thus, it is important to understand the synthetic conditions that allow a ULC shell to remain “ULC-like” despite the presence of a denser core.

Stability of Artificial Nano-Hydroxyapatite in the Presence of Natural Colloids: Influence of Steric Forces and Chargeability.

The stability of nano-hydroxyapatite (nHAP) affects its fate in the environment. Few studies have compared the influence of colloids with different properties on the stability of nHAP. Fulvic acid, montmorillonite, and goethite were chosen as representative colloids. An ultraviolet-visible spectrophotometer and NanoBrook 90Plus phase analysis light scattering (PALS) were used to determine absorbance, zeta potential, and hydrodynamic diameter. Results showed that addition of fulvic acids could make nHAP more stable through electrostatic and steric effects, whereas montmorillonite affected the stability mainly by electrostatic effects. Goethite could adsorb onto nHAP particles and form goethite-nHAP heteroaggregates at pH < pH (i.e., pH at point of zero charge), and its addition enhanced the electrostatic repulsion forces at pH > pH. Since fulvic acid has additional steric effects, its stability enhancement was greater than that of montmorillonite and goethite. Montmorillonite colloids were stronger than goethite colloids for enhancing the stability of nHAP, because montmorillonite had a higher absolute surface potential. The order in which organic and inorganic colloids were added affects the degree of stability of nHAP. Energy barriers calculated by extended Derjaguin-Landau-Verwey-Overbeek were in good agreement with the experimental results and implied that the nHAP particles were in the stage of reaction-limited aggregation at pH 7 ± 0.1 and pH 9 ± 0.1. Our findings are important for understanding the cotransport of nanoparticles and colloids.

Dispersion and electrokinetics of scattered objects in ethanol-water mixtures

Scattered objects ranging from 100 to 300 nm were detected in ethanol-water mixtures at increasing concentrations – 10–90% v/v ethanol using a particle size analyzer. To evaluate the structural transitions, two mechanisms of nanostructure formation from previous studies were considered: (1) molecular clustering and (2) nanobubble formation. Measurement of particle counts, polydispersities and sub-micron particle diameters were made available with the Dynamic Light Scattering (DLS) system and high resolution of detectors on the equipment (as small as 1 nm under dilute conditions). The electrokinetic property of colloidal dispersion through its zeta potential was simultaneously determined using the Phase Analysis Light Scattering (PALS) function of the instrument. Results suggest that the structural changes can be rooted, starting from an accumulation and amphiphilic encapsulation of gaseous phases forming nanobubble-like clusters at initial additions of ethanol, followed by bigger, and mostly aggregated ethanol-water and ethanol-ethanol clusters at higher concentrations. An inflection in the measured particle counts and zeta potentials at about 20% v/v ethanol as may be caused by the substantial amount of nanobubble clusters was observed similar to the reported anomalous trend in the measured thermophysical properties of ethanol-water mixtures.

Tuberculosis vaccine candidate: Characterization of H4-IC31 formulation and H4 antigen conformation

Tuberculosis (TB) is one of the leading causes of death worldwide, making the development of effective TB vaccines a global priority. A TB vaccine consisting of a recombinant fusion protein, H4, combined with a novel synthetic cationic adjuvant, IC31®, is currently being developed. The H4 fusion protein consists of two immunogenic mycobacterial antigens, Ag85 B and TB10.4, and the IC31® adjuvant is a mixture of KLK, a leucine-rich peptide (KLKL5KLK), and the oligodeoxynucleotide ODN1a, a TLR9 ligand. However, efficient and robust methods for assessing these formulated components are lacking. Here, we developed and optimized phase analysis light scattering (PALS), electrical sensing zone (ESZ), and Raman, FTIR, and CD spectroscopy methods to characterize the H4-IC31 vaccine formulation. PALS-measured conductivity and zeta potential values could differentiate between the similarly sized particles of IC31® adjuvant and the H4-IC31 vaccine candidate and could thereby serve as a control during vaccine formulation. In addition, zeta potential is indicative of the adjuvant to antigen ratio which is the key in the immunomodulatory response of the vaccine. ESZ was used as an orthogonal method to measure IC31® and H4-IC31 particle sizes. Raman, FTIR, and CD spectroscopy revealed structural changes in H4 protein and IC31® adjuvant, inducing an increase in both the β-sheet and random coil content as a result of adsorption. Furthermore, nanoDSF showed changes in the tertiary structure of H4 protein as a result of adjuvantation to IC31®. Our findings demonstrate the applicability of biophysical methods to characterize vaccine components in the final H4-IC31 drug product without the requirement for desorption.

Behavior of Spherical Poly(2-acrylamido-2-methylpropanesulfonate) Polyelectrolyte Brushes on Silica Nanoparticles up to Extreme Salinity with Weak Divalent Cation Binding at Ambient and High Temperature

The colloidal stability of nanoparticles (NPs) stabilized by grafted polyelectrolyte (PE) brushes in concentrated divalent ion solutions, at either ambient or high temperature, is of interest in a wide variety of applications including medicine, personal care products, oil and gas recovery, reservoir imaging, and environmental remediation. Previous attempts to determine the length of PE brushes at these conditions have been limited by lack of colloidal stability particularly when divalent ions form complexes with the charges on the brushes. We find that brushes of highly acidic strong PE poly(2-acrylamido-2-methylpropanesulfonate, AMPS) end-grafted to silica NPs provide colloidal stability at salinities up to 4.5 M CaCl2 or NaCl. Thus, the brush behavior could be studied with dynamic light scattering (DLS) and the electrophoretic mobility by phase analysis light scattering (PALS) from the salt-free condition to the extreme salinities of 4.5 M. In monovalent NaCl solutions, the highly extended poly(AMPS) b...

Instrument and method to determine the electrophoretic mobility of nanoparticles and proteins by combining electrical and flow field-flow fractionation.

A new FFF method is presented which combines asymmetrical flow-FFF (AF4) and electrical FFF (ElFFF) in one channel to electrical asymmetrical flow-FFF (EAF4) to overcome the restrictions of pure ElFFF. It allows for measuring electrophoretic mobility (μ) as a function of size. The method provides an absolute value and does not require calibration. Results of μ for two particle standards are in good agreement with values determined by phase analysis light scattering (PALS). There is no requirement for low ionic strength carriers with EAF4. This overcomes one of the main limitations of ElFFF, making it feasible to measure proteins under physiological conditions. EAF4 has the capability to determine μ for individual populations which are resolved into separate peaks. This is demonstrated for a mixture of three polystyrene latex particles with different sizes as well as for the monomer and dimer of BSA and an antibody. The experimental setup consists of an AF4 channel with added electrodes; one is placed beneath the frit at the bottom wall and the other covers the inside of the upper channel plate. This design minimizes contamination from the electrolysis reactions by keeping the particles distant from the electrodes. In addition the applied voltage range is low (1.5-5 V), which reduces the quantity of gaseous electrolysis products below a threshold that interferes with the laminar flow profile or detector signals. Besides measuring μ, the method can be useful to improve the separation between sample components compared to pure flow-FFF. For two proteins (BSA and a monoclonal antibody), enhanced resolution of the monomer and dimer is achieved by applying an electric field.

Effects of interaction between a polycation and a nonionic polymer on their cross-assembly into mixed micelles.

In this paper, to investigate the effects of interactions between poly(quaternary ammonium) salts (PQAs) and poly(ethylene glycol) on their mixed micellar surface structures and properties under spontaneous conditions, a series of PQAs were first designed and synthesized by atom transfer radical polymerization (ATRP) using 2-(dimethylamino) ethyl methacrylate (DMAEMA) quaternized by bromobutane, bromooctane, and bromododecane, respectively. Poly(poly(ethylene glycol) methyl ether methacrylate) (PPEG) with a similar degree of polymerization was also prepared using poly(ethylene glycol) methyl ether methacrylate by ATRP. Next, these PQAs were mixed with an equal weight of PPEG in water to cross-assemble into mixed micelles. The structures and features of these mixed micelles were characterized by fluorescence measurements, transmission electron microscopy (TEM), dynamic light scattering (DLS), phase analysis light scattering (PALS), proton nuclear magnetic resonance ((1)H NMR), and hydrogen-hydrogen correlation spectroscopy nuclear magnetic resonance (H-H COSY NMR). These results suggest that PQAs and PPEG mixtures can cross-assemble into mixed micelles with low CMC. The surface structures, particle sizes, size distributions, and zeta potentials of PQAs and PPEG mixtures can be tailored by varying the alkyl chain length in quaternary ammonium salts, and the alkyl chain length also influences the distribution and the alkyl chain orientation of quaternary ammonium salts on mixed micelle surfaces. In addition, cytotoxicity of these mixed micelles can be markedly reduced by PPEG compared with their corresponding PQAs, but their good antibacterial activities are still maintained to a certain degree, as evaluated by methyl tetrazolium assay (MTT) and minimum inhibitory concentration (MIC). Our present work provides a new avenue for the preparation of biocompatible and antibacterial materials for biomedical applications.

Surfactant mediated charging of polymer particles in a nonpolar liquid

We study the charging behavior of polystyrene and polymethyl methacrylate particles with different functional surface groups in water and in decane containing either ionic (AOT) or nonionic surfactant (Span 85). Electrophoretic mobilities in the nonpolar media are measured as a function of surfactant concentration and the applied electric field strength by phase analysis light scattering (PALS); acid–base characteristics of the particles and the surfactant are investigated via contact angle measurement and interfacial tensiometry, and the residual water content of the non-aqueous dispersions is assessed by Karl Fischer titration. The results suggest a competition of several mechanisms for particle charging in nonpolar media. At high concentrations of the nonionic surfactant, particle charging becomes insensitive to the functional surface groups responsible for charging in aqueous dispersions, but consistent with a charge transfer between the polymer surface and the surfactant due to acid–base interactions, which can be rationalized in terms of measurable acid–base parameters. By contrast, particle charging in nonpolar solutions of the ionic surfactant (with significantly larger amounts of residual water) suggests a strong influence of surface headgroup ionization, and of dissociated surfactants adsorbed to the particle surface.

Amphiphilic star block copolymers as gene carrier Part I: Synthesis via ATRP using calix[4]resorcinarene-based initiators and characterization

In this work, a cationic star polymer [poly(2-dimethylamino)ethyl methacrylate (PDMAEMA)] was prepared via atom transfer radical polymerization (ATRP), using brominated calix[4]resorcinarene as an initiator. Hydrophobic moieties, methyl methacrylate (MMA) and butyl acrylate (BA), were further incorporated via “one-pot” method. Well-defined eight-armed star block copolymers bearing hydrophilic blocks inside and hydrophobic blocks outside were synthesized. The molecular weight, particle size, electrophoretic mobility and apparent charge density were determined by gel permeation chromatography (GPC), dynamic light scattering (DLS), phase analysis light scattering (PALS) and colloidal titration, respectively. The zeta potentials and apparent charge densities of the products exhibited the characteristics of polyelectrolyte. The incorporation of hydrophobic moieties generated electrostatic screening effect. The as-synthesized amphiphilic star copolymer is promising as a thermo-sensitive gene carrier for gene therapy.

A Variable Pressure Method for Characterizing Nanoparticle Surface Charge Using Pore Sensors

A novel method using resistive pulse sensors for electrokinetic surface charge measurements of nanoparticles is presented. This method involves recording the particle blockade rate while the pressure applied across a pore sensor is varied. This applied pressure acts in a direction which opposes transport due to the combination of electro-osmosis, electrophoresis, and inherent pressure. The blockade rate reaches a minimum when the velocity of nanoparticles in the vicinity of the pore approaches zero, and the forces on typical nanoparticles are in equilibrium. The pressure applied at this minimum rate can be used to calculate the zeta potential of the nanoparticles. The efficacy of this variable pressure method was demonstrated for a range of carboxylated 200 nm polystyrene nanoparticles with different surface charge densities. Results were of the same order as phase analysis light scattering (PALS) measurements. Unlike PALS results, the sequence of increasing zeta potential for different particle types agreed with conductometric titration.

Measuring surface zeta potential using phase analysis light scattering in a simple dip cell arrangement

A technique for the measurement of surface zeta potential of a test surface, mounted on a dip cell is presented. The mobility of tracer particles in the vicinity of the charged test surface is measured using phase analysis light scattering (PALS) and a simple model used to describe the electroosmotic flow near the surface fitted. The technique is a considerable simplification over previous measurements of surface zeta potential, requiring only a single small test surface (5mm×4mm) with no sealing with advantages for the measurement of expensive and/or fragile surfaces. The technique is shown to be characterised by a relative standard deviation in reproducibility of 10% for well behaved systems, yielding accurate and reproducible surface potential values in excellent agreement with literature values from streaming potential, electroosmotic (capillary) flow and particle dispersions for various surface types, temperatures and ionic strengths.

Electrokinetics of Limestone and Dolomite Rock Particles

Summary High-salinity water such as seawater, or formation brines, is frequently injected in carbonate reservoirs. Ion interactions between injection water, reservoir fluids, and rock surface are quite complex. It has recently come to be believed that the chemistry of injection water can significantly enhance oil recovery. Several reaction mechanisms were suggested, including rock dissolution, change of surface charge, and/or sulfate precipitation. This study attempts to characterize the electrokinetics of limestone and dolomite suspensions at 25 and 50°C. In addition, reaction mechanisms at the water/rock interface were established. Synthetic formation brine, seawater, and aquifer water were chosen from Middle East reservoirs. Carbonate particles were soaked in high- and low-salinity water. A phase-analysis-light-scattering (PALS) technique was used to determine the zeta potential (surface charge) of carbonate particles over a wide range of pH, ionic strength, and temperature. Zeta potential of limestone particles was significantly affected by calcium ion. Low-salinity water created more negative charges on limestone and dolomite particles by expanding the thickness of the diffuse double layer. Individual divalent cations decreased the zeta potential of limestone particles in sodium chloride solutions, while sulfate ions showed a negligible effect. Limestone particles in high-salinity water had decreased zeta potential. The solubility of calcium ions increased as temperature was increased and thus created additional negative charges. The absence of sulfate in aquifer water strongly influenced the dolomite surface charge. In summary, surface-charge adjustment from positive to negative can alter the wettability of carbonate rock from preferentially oil-wet to water-wet. As a result, residual-oil saturation should be decreased.

Chitosan nanoparticles for tamoxifen delivery and cytotoxicity to MCF-7 and Vero cells

In this study, tamoxifen citrate-loaded chitosan nanoparticles (tamoxcL-ChtNPs) and tamoxifen citrate-free chitosan nanoparticles (tamoxcF-ChtNPs) were prepared by an ionic gelation (IG) method. The physicochemical properties of the nanoparticles were analyzed for particle size, zeta (ζ) potential, and other characteristics using photon correlation spectroscopy (PCS), zeta phase analysis light scattering (PALS), scanning electron microscopy (SEM), Fourier transform infrared (FTIR), and differential scanning calorimetry (DSC). The variation in particle size was assessed by changing the concentration of chitosan, pentasodium tripolyphosphate (TPP), and the pH of the solution. The optimized tamoxcL-ChtNPs showed mean diameter of 187 nm, polydispersity of 0.125, and ζ-potential of +19.1 mV. The encapsulation efficiency (EE) of tamoxifen citrate (tamoxc) increased at higher concentrations, and release of tamoxc from the chitosan matrix displayed controlled biphasic behavior. Those tamoxcL-ChtNPs tested for chemosensitivity showed dose- and time-dependent antiproliferative activity of tamoxc. Further, tamoxcL-ChtNPs were found to be hemocompatible with human red blood cells (RBCs) and safe by in vitro cytotoxicity tests, suggesting that they offer promise as drug delivery systems in therapy.

Determination of the electrokinetic potential of Rhizobium leguminosarum bv trifolii Rt24.2 using Laser Doppler Velocimetry — A methodological study

Electrokinetic potential ( ζ, zeta potential) is one of the parameters which characterize the physicochemical properties of the bacterial cell envelope. The term is often used in the context of adhesiveness of bacteria and biofilm formation. This work presents the methodological aspects of zeta potential determination in strain Rt24.2 of Rhizobium leguminosarum using Laser Doppler Velocimetry combined with Phase Analysis Light Scattering and changed electric field techniques. The influence of media (0.9% NaCl, 0.2% NaCl, TY, GYM, 79CA, 20E and M1), temperature of measurement, number of measurement repetitions, phase of culture, concentration of bacteria, and storage at low temperature on the value of electrokinetic potential was investigated and a comparison was drawn between live and dead bacteria. All of those factors modified the zeta potential, showing that these parameters should be precisely specified in studies of bacterial electrokinetic potential, which is not always done. The obtained results also indicated that the zeta potential of Rhizobium leguminosarum should be determined directly in samples without storage at a defined bacterial density. The measurement should be done only once in a sample inserted into the cell of a measuring device to eliminate changes occurring in the sample (increase of electrolytic conductivity) under the electric field used.

Tuning size and electrostatics in non-polar colloidal asphaltene suspensions by polymeric adsorption

The destabilization of asphaltenes adversely affects many aspects of the petroleum energy industry. Although polymeric dispersants have been shown to stabilize asphaltene colloids in non-polar media, the mechanism by which they prevent aggregation is not well-understood. We use a variety of techniques to investigate systems of colloidal asphaltenes stabilized in heptane by an effective dispersant. Phase analysis light scattering (PALS) measurements reveal an increase in the electrophoretic mobility as a function of dispersant concentration, suggesting electrostatic repulsion as the primary stabilizing force. Dynamic light scattering (DLS) measurements indicate that the increase in mobility corresponds to a decrease in particle size. A simple scaling argument suggests that the dispersant adsorbs to the surface of the asphaltene colloids. UV-visible spectroscopy and static light scattering (SLS) measurements corroborate this proposal. Interestingly, the colloidal asphaltene properties change below the critical micelle concentration (cmc) of the dispersants used. The nature of the asphaltenes themselves plays an important role in allowing for this tunability of their properties. Contrary to currently accepted views of non-polar colloidal suspensions, our results indicate that isolated dispersant molecules, not inverse micelles, can lead to charge-stabilization of asphaltene colloids.