Colloid Journal最新文献

The article is devoted to theoretical studying the dynamic response of ensembles of nanosized ferromagnetic particles immobilized in a nonmagnetic medium to an external field. The main attention of the work is paid to analyzing the effect of interparticle magnetic interactions on the complex magnetic susceptibility of a composite and the intensity of heat generation in it under the action of the alternating magnetic field. The analysis has shown that the dependence of the magnitude of the thermal effect on the parameter of the interparticle magnetodipole interaction is nonmonotonic and passes through a maximum. We hope that this result will help to understand the physical reason for the qualitative contradictions between the conclusions inferred in different studies devoted to the influence of the interparticle interactions on the components of the complex magnetic susceptibility of magnetic composites and the intensity of the heat generation under the action of alternating fields.

The key properties of aqueous Tween 80 micellar solutions as means for the delivery of biologically active substances inhibiting the reproduction of various pathogens have been studied in order to develop innovative methods for plant protection. It has been shown that these solutions exhibit no negative effects upon the contact with potato leaves. The wetting isotherms plotted for aqueous Tween 80 solutions have confirmed the hydrophilization of a potato leaf and a hydrophobic polymer film simulating its surface. The maximum adsorption of Tween 80 on the polymer surface has been determined by combining the methods of tensiometry and wetting, thereby making it possible to predict the structure of the adsorption layer of this surfactant on the surface of the potato leaf. A significant increase in the velocity of penetration into the leaf has been recorded for Tween 80 micellar solutions characterized by the maximum wetting ability.

It has been shown that associates of cationic glycerolipid (CGL), rac-N-{4-[(2-ethoxy-3-octadecyloxyprop-1-yl)oxycarbonyl]butyl}-N'-methylimidazolium iodide, which has a pronounced antitumor effect, can be used for the solubilization of two hydrophobic biologically active compounds (curcumin and capsaicin) and as templates in the sol–gel synthesis of silica mesoporous container particles (MCPs). The thermodynamic characteristics of solubilization are determined, and it is shown that this process contributes to a significant increase in the solubility of both hydrophobic drugs in water. The hydrolytic condensation of tetraethoxysilane in the presence of CGL associates containing curcumin or capsaicin leads to the formation of MCPs characterized by a narrow size distribution and a high content of encapsulated drugs. This combination of the stages of the synthesis and loading of MCPs is of undoubted interest in relation to the nanoencapsulation of cationic glycerolipids (including in combination with other drugs).

The paper presents the results of computer simulating the structure formation in nanodisperse magnetic fluids and the influence of this process on the kinetics of their magnetization reversal. The work considers a system of identical spherical single-domain ferromagnetic particles suspended in a Newtonian fluid with magnetic moments “frozen” into the particle bodies. The particles are involved in intense Brownian motion. The magnetic interactions of all particles with each other, as well as of the particles with an external magnetic field, are considered. The results have shown that the evolution of the internal structures upon a change in the external field can greatly, by several orders of magnitude, change the characteristic time of ferrofluid magnetization reversal. The results obtained may be useful for the development of both the general theory of these systems and many methods for their high-tech applications.

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.

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.

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.