Colloidal Surface Research Articles

Polyacrylate crosspolymer-11 enhances soil clay dispersibility: An indication for inadvertent environmental impacts from personal care and cosmetic ingredients

Polymer ingredients are commonly found in personal care and cosmetic industry and their “leakages” into the environment have recently been warned as an emerging environmental risk. Daily use of personal care and cosmetic products can inadvertently release large amounts of polymer ingredients into water courses. However, their fate and interaction with other constituents, especially colloids (e.g., clays), have not been fully understood. This study primarily evaluates the colloidal dynamics of soil clays under the presence of polyacrylate crosspolymer-11 (PC11) (a common ingredient of cosmetic and personal care products) with the aim of identifying possible induced changes in the clay-accumulated environments, e.g., soil and sediment. The test-tube experiments were coupled with a particle charge detector to mutually evaluate the colloidal dynamics and surface charge properties of the soil clays. It was revealed that adsorption of PC11 onto the clays shifted clay surface to more negative, thereby intensifying repulsive force and favouring the dispersion state of the soil clays. This implies that various polymer ingredients can act in the same way in stabilizing clay dispersion or even altering the fate of the soil clays. As the growing consumption of personal care and cosmetic products will likely continue, it requires a tighter consideration of the possible impacts of polymer ingredient residues, not limited to dispersion-induced effects, in various clay-accumulated environments such as paddy fields, river mouths or mangroves.

Surface Chemistry Impact on the Light Absorption by Colloidal Quantum Dots.

At the size scale at which quantum confinement effects arise in inorganic semiconductors, the materials’ surface‐to‐volume ratio is intrinsically high. This consideration sets surface chemistry as a powerful tool to exert further control on the electronic structure of the inorganic semiconductors. Among the materials that experience the quantum confinement regime, those prepared via colloidal synthetic procedures (the colloidal quantum dots – and wires and wells, too –) are prone to undergo surface reactions in the solution phase and thus represent an ideal framework to study the ensemble impact of surface chemistry on the materials’ electronic structure. It is here discussed such an impact at the ground state by using the absorption spectrum of the colloidal quantum dots as a descriptor. The experiments show that the chemical species (the ligands) at the colloidal quantum dot surface induce changes to the optical band gap, the absorption coefficient at all wavelengths, and the ionization potential. These evidences point to a description of the colloidal quantum dot (the ligand/core adduct) as an indecomposable species, in which the orbitals localized on the ligands and the core mix in each other's electric field. This description goes beyond conventional models that conceive the ligands on the basis of pure electrostatic arguments (i. e., either as a dielectric shell or as electric dipoles) or as a mere potential energy barrier at the core boundaries.

Oligoarginine Peptide Conjugated to BSA Improves Cell Penetration of Gold Nanorods and Nanoprisms for Biomedical Applications.

Gold nanoparticles (AuNPs) have been shown to be outstanding tools for drug delivery and biomedical applications, mainly owing to their colloidal stability, surface chemistry, and photothermal properties. The biocompatibility and stability of nanoparticles can be improved by capping the nanoparticles with endogenous proteins, such as albumin. Notably, protein coating of nanoparticles can interfere with and decrease their cell penetration. Therefore, in the present study, we functionalized albumin with the r8 peptide (All-D, octaarginine) and used it for coating NIR-plasmonic anisotropic gold nanoparticles. Gold nanoprisms (AuNPrs) and gold nanorods (AuNRs) were coated with bovine serum albumin (BSA) previously functionalized using a cell penetrating peptide (CPP) with the r8 sequence (BSA-r8). The effect of the coated and r8-functionalized AuNPs on HeLa cell viability was assessed by the MTS assay, showing a low effect on cell viability after BSA coating. Moreover, the internalization of the nanostructures into HeLa cells was assessed by confocal microscopy and transmission electron microscopy (TEM). As a result, both nanoconstructs showed an improved internalization level after being capped with BSA-r8, in contrast to the BSA-functionalized control, suggesting the predominant role of CPP functionalization in cell internalization. Thus, our results validate both novel nanoconstructs as potential candidates to be coated by endogenous proteins and functionalized with a CPP to optimize cell internalization. In a further approach, coating AuNPs with CPP-functionalized BSA can broaden the possibilities for biomedical applications by combining their optical properties, biocompatibility, and cell-penetration abilities.

SERS Investigation on Oligopeptides Used as Biomimetic Coatings for Medical Devices.

The surface-enhanced Raman scattering (SERS) spectra of three amphiphilic oligopeptides derived from EAK16 (AEAEAKAK)2 were examined to study systematic amino acid substitution effects on the corresponding interaction with Ag colloidal nanoparticles. Such self-assembling molecular systems, known as “molecular Lego”, are of particular interest for their uses in tissue engineering and as biomimetic coatings for medical devices because they can form insoluble macroscopic membranes under physiological conditions. Spectra were collected for both native and gamma-irradiated samples. Quantum mechanical data on two of the examined oligopeptides were also obtained to clarify the assignment of the prominent significative bands observed in the spectra. In general, the peptide–nanoparticles interaction occurs through the COO− groups, with the amide bond and the aliphatic chain close to the colloid surface. After gamma irradiation, mimicking a free oxidative radical attack, the SERS spectra of the biomaterials show that COO− groups still provide the main peptide–nanoparticle interactions. However, the spatial arrangement of the peptides is different, exhibiting a systematic decrease in the distance between aliphatic chains and colloid nanoparticles.

Effect of paddy cultivation on the surface electrochemical properties of different‐sized particles of a Gleysol

AbstractBackgroundLimited information is available on the changes in surface electrochemical properties of different‐sized particles of an Anthrosol, compared with the corresponding parental upland soil.AimsOur overarching goal was to clarify the contribution of different‐sized particles to the soil surface charge. The specific objectives of this work were to examine the differences in the surface charge properties between the Anthrosol and its upland parental Gleysol and to reveal the properties of the different‐sized fractions separated from the Anthrosol, compared with those of the upland Gleysol.Materials and methodsThe properties (e.g., negative surface charge, zeta potential, and particle sedimentation) of different‐sized fractions of nanoparticle (NP), coarse colloid, silt, and sand fractions separated from an upland Gleysol and its derived Anthrosol were compared.ResultsNPs in both the Anthrosol and the Gleysol carried more negative charge than did the coarse colloids, with cation exchange capacities (CEC) being 186.5% and 58.8% greater, respectively. On the other hand, the presence of more positively charged Fe/Al (hydr)oxides compensated for the negative charge, resulted in a zeta potential of the NPs similar to that of the coarse colloids. More secondary minerals were observed in the coarse colloids of the Anthrosol than in the same fraction of the Gleysol, resulting in more negative charge on the surface of the Anthrosol coarse colloids. The coarse colloid fraction of the Anthrosol, therefore, had a greater CEC, despite representing a smaller mass fraction than in the Gleysol. Overall, the CEC of the Anthrosol was 21% lower than that of the parent Gleysol, which was consistent with the findings of the surface charge, using the cesium (Cs+)‐adsorption method. The sedimentation observations demonstrated that the suspension stability of the NPs was higher than that of the coarse colloids, and that they tended to disperse particularly under high pH conditions.ConclusionsAlthough the surface charge potential of the Anthrosol was lower than that of the upland Gleysol, the accumulation of organic matter and formation of secondary phyllosilicates resulted in maintenance of the nutrient‐ and pollutant‐binding capacity and agricultural productivity of the Anthrosol.

Formation of Sodium Dodecyl Sulfate Foams by Compression of Soft Porous Material

AbstractInteraction of foams with porous materials is frequently observed in industry and nature. An example is the interaction of foam of a cleaning product with a sponge, which has been investigated previously in Johnson et al., Colloids Surfaces A, 2019, 579, June, p. 123569 with commercial dishwashing solution using a compression device with a sponge saturated with a surfactant solution. The purpose of this study is to investigate the same process using sodium dodecyl sulfate (SDS), which has the same critical micelle concentration (CMC) as the commercial surfactant used. It is found that SDS concentration 10 times the CMC is the optimum concentration for foam formation. Any further increase in concentration above 10 CMC does not result in further increase of foam mass. Although the concentration of the surfactant solution was the most important parameter, temperature and pH of the surfactant also influenced the foam generation. Increasing the temperature resulted in decreasing the mass of foam generated and pH 7 was found as the optimal pH for foam generation.

Repulsive and attractive depletion forces mediated by nonadsorbing polyelectrolytes in the Donnan limit.

In mixtures of colloids and nonadsorbing polyelectrolytes, a Donnan potential arises across the region between surfaces that are depleted of the polyelectrolyte and the rest of the system. This Donnan potential tends to shift the polyelectrolyte density profile toward the colloidal surface and leads to the local accumulation of polyelectrolytes. We derive a zero-field theory for the disjoining pressure between two parallel flat plates. The polyelectrolyte is allowed to enter the confined interplate region at the cost of a conformational free energy penalty. The resulting disjoining pressure shows a crossover to a repulsive regime when the interplate separation gets smaller than the size of the polyelectrolyte chain, followed by an attractive part. We find a quantitative match between the model and self-consistent field computations that take into account the full Poisson-Boltzmann electrostatics.

A Crowding Barrier to Protein Inhibition in Colloidal Aggregates.

Small molecule colloidal aggregates adsorb and partially denature proteins, inhibiting them artifactually. Oddly, this inhibition is typically time-dependent. Two mechanisms might explain this: low concentrations of the colloid and enzyme might mean low encounter rates, or colloid-based protein denaturation might impose a kinetic barrier. These two mechanisms should have different concentration dependencies. Perplexingly, when enzyme concentration was increased, incubation times actually lengthened, inconsistent with both models and with classical chemical kinetics of solution species. We therefore considered molecular crowding, where colloids with lower protein surface density demand a shorter incubation time than more crowded colloids. To test this, we grew and shrank colloid surface area. As the surface area shrank, the incubation time lengthened, while as it increased, the converse was true. These observations support a crowding effect on protein binding to colloidal aggregates. Implications for drug delivery and for detecting aggregation-based inhibition will be discussed.

Co-transport of U(VI) and bentonite colloids: Influence of colloidal gibbsite

Although various colloids co-exist in the environment, studies on the interaction between different kinds of inorganic colloids and their combined effects on radionuclide transport have scarcely been reported. In the present paper, the influence of colloidal gibbsite, a representative metal hydroxide in groundwater, on the transport of Na-bentonite colloids and their combined effects on U(VI) transport in saturated particulate granite columns were investigated. It was found that in the presence of the colloids, whether single Na-bentonite or the mixture of Na-bentonite and gibbsite, fewer pore volumes were needed for U(VI) breakthrough, indicating a colloid-facilitated U(VI) transport due to high binding affinity of uranyl for the colloids compared to granite. Meanwhile, the breakthrough curves of U(VI) were gradually flattened and the plateau of the curve for Na-bentonite was decreased as the concentration ratio of gibbsite to Na-bentonite increased from 1:10 to 1:6. Consequently, total recoveries of U(VI) and Na-bentonite decreased with more gibbsite in the mixed colloids. The inhibition effect of gibbsite colloids was ascribed to electrostatic interactions between positively charged surfaces of gibbsite colloids and negatively charged surfaces of bentonite colloids and granite granules. The electrostatic attraction between oppositely charged colloids led to an increase of mean size in the mixed suspension which declined colloid transport and the transport of colloid associated U(VI) as well. When the gibbsite-to-bentonite ratio was increased up to 1:5, the recoveries were obviously lower than those of single U(VI) and Na-bentonite transport. The results imply that positively charged materials may be further investigated as additives to decrease the loss of buffer material by groundwater erosion and the migration of radionuclide associated on bentonite colloids.

Controlling water adhesion on superhydrophobic surfaces with bi-functional polymers

With an aim to control the surface hydrophobicity and water adhesion, as observed on various natural surfaces, novel 3,4-propylenedioxythiophene (ProDOT) monomers having one and two 3-trimethylsilylpropyl (TMS) groups were synthesized and subjected to electropolymerization to form surface coatings. The monomer ProDOT is employed owing to its tendency to form fibrous structures by electropolymerization [T. Darmanin, F. Guittard, Mater. Chem. Phys. 146 (2014) 6–11], whereas the TMS groups generate very low surface energies comparable to short chain fluorocarbons [N. M. Kovalchuk, et al., Colloids Surfaces A 604 (2020) 125277.]. It is shown that even though these two types of monomer lead to fibrous structures, the dimensions of the fibers as well as the wetting properties are different. The monomer with only a single TMS group (ProDOTSiMe3) generates extremely long nanofibers with only low surface roughness. The resulting surfaces have extremely high apparent contact angles (θw) up to 141.7° and strong water adhesion, similar to rose petals or gecko feet. On the other hand, the analogue with two TMS groups (ProDOT(SiMe3)2) forms short nanofibers but with extremely high surface roughness. The resulting surfaces are superhydrophobic with θw > 160° and ultra-low water adhesion (hysteresis and sliding angles < 1°), similar to lotus leaves. These results point to interesting applications offering control over water adhesion whilst maintaining high hydrophobicity.

A New Figure of Merit to Assess the SERS Enhancement Factor of Colloidal Gold Nanoparticle Aggregates

Plasmonic nanoparticle aggregates are one of the most widely employed nanostructures as colloidal surface enhanced Raman spectroscopy (SERS) substrates mainly due to their ability to generate huge ...

Type I Photoinitiator-Functionalized Block Copolymer Nanoparticles Prepared by RAFT-Mediated Polymerization-Induced Self-Assembly.

Type I photoinitiators have been widely used in UV-vis curing technology for the fabrication of functional polymer materials such as coatings, inks, and adhesives. To overcome the drawbacks of using small molecular type I photoinitiators and expand the potential applications of UV-vis curing technology, attaching type I photoinitiators onto the surface of polymer colloids is an attractive strategy. Here we report a robust strategy for the efficient preparation of type I photoinitiator-functionalized block copolymer nanoparticles with various morphologies via aqueous reversible addition-fragmentation chain transfer (RAFT)-mediated polymerization-induced self-assembly (PISA), in which the photoinitiating ability of the type I photoinitiator end group provides a landscape for further functionalization. These block copolymer nanoparticles could also be used as heterogeneous photoinitiators to generate hydrogels with nanoparticles embedded inside. Significantly, the properties and functionalities of these hydrogels could be further controlled by using different block copolymer nanoparticles. This study provides a robust strategy toward the preparation of type I photoinitiator-functionalized block copolymer nanoparticles with the capacity to be modified with varying functionalities.

Response of Andisols to intensive agricultural land use: Implication on changes in P accumulation and colloidal surface charge

The response of Andisols to intensive agricultural practices were not fully explored although intensive cultivation has been practiced for a long period of time. The objective of the review is to bring together all findings, which have been documented with the focus on changes in soil organic matter, P content and retention, and colloidal surface charge. The Andisols contain an abundance of nano-clay consisting mainly of hollow allophane spherules forming globular aggregates of about 100 nm in diameter, indicating the large reactive surface area. A huge quantity of P has been accumulated in the uppermost two soil horizons, deriving from residue of continuous application of P fertilizer. Andisols have a strong ability to retain organic C through ligand exchange of metal hydroxyl functional groups with organic functional groups. The soil colloids bear a positive charge at soil pH less than 5. The colloidal negative charge is continuously increased with increasing soil pH over 5.0. Hence, the Andisols should be managed by maintaining soil pH above pH 5.0 by adding lime or compost to allow soil capability to retain cation and reduce P fixation. Nano-clay has positive impact on carbon stabilization and therefore C sequestration.

Soil colloids affect the aggregation and stability of biochar colloids

The stability of biochar colloids plays an important role in the transport and fate of contaminants and nutrients in soil. This study aimed to investigate the effects of main soil components, kaolin (Kao), goethite (Goe), and humic acid (HA) colloids on the aggregation kinetics of biochar colloids derived from dairy manure (DM), sewage sludge (SS), and wheat straw (WS). The WS biochar colloid had the highest critical coagulation concentration (CCC) (624 mM) than that of SS (200 mM) and DM (75 mM) due to its richest hydroxyl and carboxyl groups, showing the highest stability. Kao markedly improved the stability of DM and SS biochar colloids with 171% and 52.5% increase of CCC, respectively, by increasing the electrostatic repulsion of the system. However, the WS biochar colloid became more aggregated in the presence of Kao since the hydroxyl and carboxyl functional groups in WS biochar colloid could complex with Kao, generating electrostatic shielding. Goe could rapidly combine with biochar colloids via electrostatic attraction, resulting in the aggregation of SS and WS, while the aggregation rate of DM/Goe mixed colloids was inhibited. The HA increased the electrostatic repulsion of all biochar colloids through adsorbed on the surface of biochar colloids, resulting in the increased steric hindrance and stability of biochar colloids, with the CCC increased from 75 to 624 mM to 827–1012 mM. Our findings reveal that soil kaolin, goethite, and humic acid colloids have remarkable effects on the stability and aggregation of biochar colloid, which will advance understanding of the potential environmental fate and behaviors of biochar colloids.

A new strategy to improve the performance of MoS2-based 2D photodetector by synergism of colloidal CuInS2 quantum dots and surface plasma resonance of noble metal nanoparticles

Owing to their extraordinary optoelectronic properties, 2D transition metal dichalcogenides (TMDs) are proved to be promising materials for photodetectors. However, they suffered from poor absorptivity due to their atomically thin profile. Herein, CuInS2 quantum dots (QDs) and plasmonic Au nanoparticles (AuNPs) were adopted to achieve a MoS2-CuInS2-AuNPs 2D–0D hybrid by simultaneous deposition of CuInS2 QDs and AuNPs on the MoS2 nanosheet. In this configuration, MoS2 is used as a high mobility carrier transport channel, while CuInS2 QDs act as an efficient light absorber, and the AuNPs serve as a light sensitizer to enhance the local electric field around MoS2 and CuInS2 QDs via surface plasmon resonance (SPR). With such synergism of CuInS2 QDs and Au NPs, the highest responsivity of 16.65AW−1 and D* as high as 2.27×1012Jones are achieved for the MoS2-CuInS2-AuNPs hybrid devices under 635 nm laser, which is two orders of magnitude higher than the pristine MoS2 devices and outperformed most of the other MoS2-based photodetectors. Finally, the synergistic effect of the CuInS2 QDs and Au nanoparticles is illustrated by Finite-Difference Time-domain(FDTD) simulation. The underlying synergism strategy for such a 2D–0D configuration may also be applied to other photo-electric devices.

A simple and sensitive colorimetric sensor for cadmium (II) detection based on self-assembled trimethyl tetradecyl ammonium bromide and murexide on colloidal silica

A sensitive and selective colorimetric sensor based on self-assembled trimethyl tetradecyl ammonium bromide (TTAB) and murexide on colloidal silica surface was developed for the detection of cadmium ion (Cd2+). Cd2+ was formed complex with murexide on the colorimetric probe (TTAB/Murexide/Silica sol) which the solution was changed immediately from light purple to orange color and was detected by spectrophotometry at 485 nm. Under the optimum conditions, the linearity was in the range of 0.01–0.12 mM with the determination coefficient of 0.9933, the limit of detection was 0.21 µM. Good precision was obtained with %RSD less than 1.28 and 4.17 for the intra-day and inter-day, respectively. The proposed colorimetric method, TTAB/Murexide/Silica sol, was successfully applied for determination of Cd2+ in rice samples and the obtained results were comparable to those from AAS method. In addition, smartphone combined with Image J program was also employed for the determination of Cd2+. The superiority of this colorimetric sensor is simple, rapid and low cost.

Anti-biofilm activity of LC-MS based Solanum nigrum essential oils against multi drug resistant biofilm forming P. mirabilis.

Urinary tract infections are second most important diseases worldwide due to the increased amount of antibiotic resistant microbes. Among the Gram negative bacteria, P. mirabilis is the dominant biofilm producer in urinary tract infections next to E. coli. Biofilm is a process that produced self-matrix of more virulence pathogens on colloidal surfaces. Based on the above fact, this study was concentrated to inhibit the P. mirabilis biofilm formation by various in-vitro experiments. In the current study, the anti-biofilm effect of essential oils was recovered from the medicinal plant of Solanum nigrum, and confirmed the available essential oils by liquid chromatography-mass spectroscopy analysis. The excellent anti-microbial activity and minimum biofilm inhibition concentration of the essential oils against P. mirabilis was indicated at 200 µg/mL. The absence of viability and altered exopolysaccharide structure of treated cells were showed by biofilm metabolic assay and phenol–sulphuric acid method. The fluorescence differentiation of P. mirabilis treated cells was showed with more damages by confocal laser scanning electron microscope. Further, more morphological changes of essential oils treated cells were differentiated from normal cells by scanning electron microscope. Altogether, the results were reported that the S. nigrum essential oils have anti-biofilm ability.

Removal of the Colloidal Suspension from Dam Water Using Mineral Coagulants Prepared by Co-Precipitation

In this work, we were interested in eliminating the organic and mineral compounds that pose problems in obtaining drinking water using the method of coagulation. These substances are stable in the medium due to their colloidal sizes and surface loads, which require appropriate treatment. For this purpose, we explored the removal of colloidal suspension using a coagulant formed by co-precipitation of AlCl3.6H2O in an alkaline medium. This practice leads to the formation of polymeric species mixtures such as Al45O45(OH)45Cl and Al2O3.H2O after washing. The removal efficiency of mineral and organic matter is evaluated by measuring the turbidity and permanganate index by varying the concentration of the coagulant from 0.04 to 0.4 g.1−1. It has been shown that the effectiveness of the treatment had been increased in parallel with the concentration. The preliminary hydrolysis of aluminium leads to a fixation of the pH throughout the concentration range. This character had solved the problem of direct use of aluminium salts (conventional method) resulting in a modification of the pH and subsequently, variable efficiency. The refined coagulant (after washing) reaches the removal of 97% turbidity and almost all oxidisable matter using only a mass of 0.08 g.1−1. However, using the crude coagulant (without washing) containing a significant amount of NaCl requires 0.4 g.1−1 to reach only 87% removal of turbidity as well as 35% of oxidisable matter, with an increase of conductivity compared with that of the refined coagulant.

Photoinitiated Transformation of Nanocrystal Superlattice Polymorphs Assembled at a Fluid Interface

AbstractDirecting the assembly of nanoscale building blocks into programmable superstructures is of broad scientific and technological interest. Advances in nanocrystal self‐assembly at fluid interfaces are combined with digital light processing to demonstrate that how the extent and spatial region of superlattice structure transformation can be controlled. It is shown that the addition of a photoacid generator to the fluid subphase provides new experimental degrees of freedom to modulate the dynamic equilibrium of ligands bound to the colloidal nanocrystal surface. Within the photoexposed regions, the nanocrystal ligand coverage is reduced which impacts the interactions between proximate nanocrystals and drives the transformation from a sixfold to a fourfold symmetric superlattice. Structural analysis is presented from transmission electron microscopy and chemical analysis is presented from infrared spectroscopy to establish the relationship between superlattice structure and ligand coverage. Beyond new insights understanding of and control over deprotection of colloidal nanocrystals at fluid interfaces, the processing method described in this work presents new opportunities to create nanocrystal assemblies with spatially programmable structures.

Aluminum Hydroxide Impurities Occlusions and Contamination Sources

This paper is reporting the data concerning impurities occlusion in the dried, milled and classified aluminum hydroxide, the sources of contamination and the ways to control the purity of classified aluminum hydroxide as raw material for special aluminas. Mainly, all the micronic size particles, floating in the super-saturated Bayer liquors, are potential sources of occluded impurities in the aluminum hydroxide particles. There are several mechanisms for embedding the impurities in crystalline substances. Of these, most probable ones in the Bayer alumina process are: a) occlusion of the spent liquor drops containing impurities inside the polycrystalline aluminum hydroxide congregates; b) hetero-nucleation of aluminum hydroxide on the surface of particles or colloids containing one or more impurities (the foreign particles are seized inside a crystals or inside of a crystalline multi-particulate association); c) incorporation of available ions or molecule reactive fragments in the poor crystalline structures of aluminum hydroxide after nucleation, during different growth stages of all already aggregated particles, under certain super-saturations. d) building up bridges between the scanty aggregated particles or filling the inside hollows of these aggregates with new quickly crystallized material, including the particulate impurities, mainly, during large fluctuations of the super-saturation. Using scanning electron microscopy (SEM) coupled with energy dispersive X-ray spectroscopy EDS (Apollo SSD detector, EDAX), the contributions of each of these mechanisms can be investigated simply and assumed from the collected data. It was shown that well crystallized phases originating directly from bauxite (like the aluminum substituted goethite and substituted hematite, rutile or quartz), as well as the well as the crystallized new born phases during specific Bayer reactions (like cancrinite, are not promoting directly the impurities occlusion. Poor crystalline phases (like sodalite and katoite or other secondary phases and their micronic size fragments are really sustaining impurities occlusion through all the acknowledged mechanisms.