Colloid Journal最新文献

The great interest in SERS tags as bioanalysis platforms is due to their combination of strong optical signals, photostability, and narrow spectral lines. Despite significant progress in the synthesis of new types of SERS tags based on gold nanoparticles, obtaining microparticles possessing a Raman scattering intensity sufficient for detecting a single tag using a conventional Raman microscope is not a trivial task. In this work, hybrid colloidal nanocomposites based on silica microparticles and gold nanostars (AuNST) with the SiO₂/AuNSTs/SiO₂ composition have been synthesized and characterized. Two types of AuNSTs, one with a plasmon resonance at 700 nm and the other with two maxima at 650 and 900 nm, have been pre-synthesized and adsorbed on the surface of monodisperse colloidal silica particles 1.5 μm in diameter. Three types of thiolated aromatic molecules have been used as Raman reporters: 4-nitrothiophenol, naphthalenethiol, and 1,4-benzenedithiol. The possibility of measuring the SERS signal from a single microparticle with an intensity variation of no more than 20% has been demonstrated, as well as the possibility of multiplex determination of various microparticles in one Raman image. The stability, including photostability, of the measured SERS signal in time has been comprehensively assessed upon changes in the physicochemical parameters of a microenvironment.

Small-angle neutron scattering has been used to study the mechanisms of graphene oxide self-organization in aqueous dispersions during its interaction with detonation nanodiamonds having different surface potential signs. Being mixed with a hydrosol of positively charged diamonds, negatively charged graphene oxide yields a stable colloid due to the formation of planar heterostructures in the form of paired sheets tightly connected through diamonds (25 wt %) when the sheets are joined. Under similar conditions, diamonds with a negative potential are localized between graphene sheets to form, at an increased fraction (44 wt %), less dense assemblies with a gap between the sheets on the order of the diamond particle radius. The binding of graphene oxide to diamonds has been confirmed by transmission electron microscopy data.

Pristine Tin Oxide (SnO₂) and Zirconium-doped Tin Oxide (SnO₂:Zr) with varying composition Sn_1–xZr_xO₂ (x = 3, 5, 7 and 10%) are synthesized using sol-gel method. The structural, optical, and thermal properties of synthesized pristine SnO₂ and SnO₂:Zr nanoparticles were examined by using various characterization techniques including XRD, SEM, TEM, FTIR, UV-visible, and TGA/DSC. The EDAX analysis confirmed the presence of Zr atoms within SnO₂ phase. FTIR analysis revealed presence of various functional groups such as antisymmetric Sn–O–Sn stretching mode, symmetric Sn–O–Sn, Zr–O bonds, C–O stretching mode, and stretching vibration. TEM analysis indicated uniformity in polycrystalline grains within Zr-doped SnO₂ sample. UV-visible analysis demonstrated decrement in optical band gap which confirmed that Zr doping tuned the optoelectronic properties of SnO₂ nanoparticles. Results combined with TGA/DSC analysis establish that 7% doping is the optimum limit after which steric hindrance effects destabilize the structural and thermal properties of the material. Therefore, Zr doping plays crucial role in modifying structural, thermal and optoelectronic properties of SnO₂ thereby proposing their use in optoelectronic devices.

The determination of the amount and composition of artificial polymer microparticles in ponds requires the preparation of representative water samples. A new method has been proposed in this work for magnetic separation of polyethylene microparticles (PEMPs, 10–200 μm), with the method implying their aggregation with magnetic nanoparticles. Composite magnetic nanoparticles containing magnetite cores and silica shells functionalized with amino groups (Fe₃O₄@SiO₂–NH₂, d_hydr = 200 nm) have been synthesized and characterized. Due to electrostatic interactions, these nanoparticles can form aggregates with polyethylene particles and be separated from water under the action of a gradient magnetic field. The effects of added salts (NaCl, Na₂SO₄, NaH₂PO₄, and CaCl₂) and a surfactant, sodium dodecyl sulfate (SDS), on the separation conditions of PEMPs from water have been studied. It has been shown that the addition of the magnetic particles in concentration c = 0.01 g/L to aqueous suspensions containing NaCl and NaH₂PO₄ (c = 10 mM), and SDS (c = 3 mM) provides an efficiency of magnetic separation of PEMPs equal to, at least, 98% after preliminary exposure for 30 min and magnetic sedimentation for 15 min. As the concentration of NaCl and NaH₂PO₄ is increased to 100 mM or in the presence of Na₂SO₄, the efficiency of PEMP magnetic separation decreases. In the presence of CaCl₂ and SDS, the efficiency of the magnetic sedimentation is no less than 98% at the studied concentrations of the salts. At least 80% of PEMPs are separated by magnetic filtration from model solutions simulating river and sea water within 5 min.

An original methodology is discussed for studying the aggregation kinetics of colloidal solutions. The methodology is based on the joint application of dynamic and static light scattering methods. The proposed methodology is theoretically justified by the concept of fractal dimension and scaling. Its experimental implementation is carried out using the example of colloidal gold solution aggregation initiated by a change in the ionic strength of the solution. The fractal dimension of Au clusters is determined from the angular and kinetic dependences of static light scattering. The hydrodynamic radii of the clusters are determined by the dynamic light scattering method. Based on the experimental results and a constructed model dependence of light scattering intensity on the sizes of clusters, a kinetic dependence is plotted for the concentration of Au clusters and the rate of their aggregation is estimated. The proposed method can be used to study the aggregation kinetics of fractal clusters in various colloidal systems.

Effect of a poly(vinyl alcohol) (PVA) stabilizer concentration on the parameters of nanoparticles prepared by nanoprecipitation of biodegradable poly(D,L-lactide-co-glycolide) (PLGA) copolymers has been studied. It has been revealed that, at a constant concentration of the organic phase (5 mg/mL), the hydrodynamic diameter of PLGA particles does not depend on stabilizer concentration in an aqueous phase (2.5–15 mg/mL) and is ~130–140 nm, while the polydispersity index and the absolute value of the electrokinetic potential of the particles decrease with an increase in the PVA concentration. It has been shown that the PVA concentration has almost no effect on the content of a hydrophobic model drug, docetaxel, loaded into the PLGA particles, as well as on its in vitro cytotoxic activity against mice colorectal carcinoma cells and human embryo lung fibroblasts of the CT26 and WI-38 lines, respectively. At the same time, the ability of drug-loaded PLGA particles to lyophilization and subsequent redispersion in water depend on the stabilizer concentration: the higher the PVA concentration in the system the easier the redispersion of the particles to their initial sizes.

It has been shown that the wettability of a material synthesized in the interfacial layer of a liquid/liquid heterogeneous system can be controlled by local vibrations. The influence of the nature of an organic acid, a metal, and a solvent on the contact angle of a material adhered to various substrates has been studied. It has been found that, under local vibrations, a material is synthesized with a more ordered structure, a higher roughness, a lower water content, and, as a consequence, a larger contact angle. Hydrophobic coatings with contact angles of 100–163° have been obtained on the studied substrates, with the coatings retaining their water-repellent properties under atmospheric conditions for a long time.

Kinetic dependences have been determined for the surface tension, dilatational dynamic surface elasticity, and ellipsometric angles of solutions of styrene copolymers with 4-vinylbenzyl chloride modified with N,N-dimethyldodecylamine. The micromorphology of the adsorbed and spread layers of these polyelectrolytes has also been studied. All kinetic dependences of the dynamic surface elasticity have turned out to be monotonic in contrast to those observed for previously studied solutions of polyelectrolytes free of polystyrene fragments. The peculiarities of the surface properties of the studied solutions may be related to the formation of microaggregates in the surface layers, because these microaggregates suppress the formation of loops and tails of polymer chains at the interfaces, and, consequently, decrease the surface elasticity after the local maximum. Atomic force microscopy data also indicate the formation of aggregates with sizes in the Z direction of 1–4 nm in the surface layers. The obtained results confirm the conclusions previously made about the formation of aggregates in the surface layers of solutions of polyelectrolytes containing fragments of sodium poly(styrene sulfonate). A 2D phase transition to a denser surface phase and the formation of aggregates with a size of 40 nm in the Z direction have been observed at surface pressures of 25–30 mN/m for the layers of the studied styrene-free polyelectrolyte spread over an aqueous substrate.

Currently, composites based on glass fibers and epoxy resins are successfully used to produce various structural elements. Such structures often serve under extreme conditions of both the Far North and the tropics, with such conditions having a destructive effect on the materials causing degradation of their properties. In this case, water resistance is an important characteristic of the materials. One of the ways to protect such materials is the use of organosilicate coatings (OSCs) obtained on the basis of organosilicon varnishes and highly dispersed hydrosilicates. This article presents the results of laboratory studies and field tests carried out in areas with very cold, as well as tropical savannah and subequatorial climates, of composite and metallic materials protected with OSCs. The objects of the studies are OSCs based on a binder, KO-921 varnish modified with the aim to improve weather resistance, primarily, moisture resistance, with poly(dimethylsiloxane) and epoxy resin. Water absorption, contact angle, and hardness of OSCs have been studied as depending on the composition of the polymer binders, and the optimal concentrations of the precursors have been determined. The results of field tests have shown that the developed OSCs retain their water-repellent properties during long-term exposure in different climatic conditions, thereby confirming their applicability to protecting various materials under the conditions of both tropics and the Far North.

Superhydrophilic copper surfaces with hierarchical textures have exhibited a high efficiency in fighting against nosocomial infections. However, one of the key drawbacks of these surfaces is their high susceptibility to mechanical contamination with fibrous materials in the course of sanitation procedures. This study has proposed a method for a laser modification enhancing the resistance of superhydrophilic copper surfaces to fiber contamination during their sanitary treatment. The modified surfaces retain their superhydrophilicity and exhibit superhydrophobic properties after the application of a hydrophobic agent. Moreover, the proposed modification method improves the resistance of a hierarchical texture to abrasive wear while remaining preserved high bactericidal properties. The results obtained have suggested that these modified textured copper materials can be used as bactericidal contact surfaces to combat nosocomial infections in medical facilities.