Investigation of the physicochemical properties of magnetic nanoparticles: size, magnetic properties, concentration

This work presents the results of studies of a series of samples of aqueous dispersions of magnetic nanoparticles. The particle sizes were measured for these samples by the dynamic scattering method. Using the method of ultramicroscopy, the number concentration of particles in the samples and the concentration of particles remaining in the volume of the samples after exposure to a magnetic field at various time intervals were measured.

Aqueous dispersions of epoxy oligomers: Stability and rheological properties

In this study, the stability of the aqueous dispersions of epoxy oligomers was investigated. The following epoxy oligomers with various numbers of epoxy groups were used for the characterization: NPEL 127, NPEL 128, NPEL 134, NPPN 631, EPOXY 520 and DEG-1. A non-ionic surfactant Emulsogen LCN-287 based on alkyl polyethylene glycol ether was used as an emulsifier. The dispersions of epoxy resins were fabricated by changing the content of a non-ionic surfactant (emulsifier) in a range from 2 to 6 wt.%. It was demonstrated that the stability of aqueous emulsions depends not only on the type of resin, but also on the content of the oil phase and the concentration of the emulsifier. The rheological properties of the aqueous dispersions of epoxy oligomers were investigated as well.

DIRECTED REGULATION OF THE STRUCTURAL AND RHEOLOGICAL PROPERTIES OF HEAT-INSULATING ACRYLIC AQUEOUS DISPERSIONS USING THE COMBINED USE OF HYDROPHILIC AND HYDROPHOBIC SILICATE FILLERS

The formation technology and performance characteristics of coatings based on aqueous dispersions are largely determined by the properties of the initial film-forming materials, which should ensure uniform thin-layer distribution on the substrate surface and the formation of coatings with the required technological complex of properties. Among them, due to their functional properties and relatively low cost, the most widespread are water-dispersion polymer coatings based on acrylic film-formers. In this paper, mathematical models of the structural and rheological dependences of heat-insulating acrylic aqueous dispersions are considered depending on the combined content of hydrophilic-hydrophobic fillers. To describe these dependencies, it is advisable to use equations of the second degree. According to the mathematical theory of experiment, the second-order orthogonal central compositional design makes it possible to predict the behavior of the response function. Carrying out an experiment in accordance with this plan makes it possible to establish the analytical dependence of the response function on the corresponding factors in the form of a polynomial equation of the second degree. The main response functions were: conditionally static yield stress, viscosity at the minimum rate of onset of fracture (initial effective viscosity), viscosity of the “destroyed” structure according to the Newtonian nature of the flow, activation energy of viscous flow at minimum, average and maximum shear rates. On the basis of the established dependences, the optimal ratios of hydrophobized aerosil and aluminosilicate microspheres were selected, the combined use of which makes it possible to reduce shear stresses to create a homogeneous aqueous acrylic dispersion, to predict the activation energy at various technological stages of preparation and application of heat-insulating coatings. The established results made it possible to create a hydrophilic-hydrophobic aqueous acrylic dispersion, which, without the use of surfactants, makes it possible to simplify the production technology of heat-insulating water-dispersion coatings, namely, to exclude the stage of pretreatment of fillers, to reduce the rotation speed of the frame mixer, and also to increase the kinetic stability of the finished dispersion.

Electrospun Amphiphilic Nanofibers as Templates for In Situ Preparation of Chloramphenicol-Loaded Liposomes

The hydration of phospholipids, electrospun into polymeric nanofibers and used as templates for liposome formation, offers pharmaceutical advantages as it avoids the storage of liposomes as aqueous dispersions. The objective of the present study was to electrospin and characterize amphiphilic nanofibers as templates for the preparation of antibiotic-loaded liposomes and compare this method with the conventional film-hydration method followed by extrusion. The comparison was based on particle size, encapsulation efficiency and drug-release behavior. Chloramphenicol (CAM) was used at different concentrations as a model antibacterial drug. Phosphatidylcoline (PC) with polyvinylpyrrolidone (PVP), using ethanol as a solvent, was found to be successful in fabricating the amphiphilic composite drug-loaded nanofibers as well as liposomes with both methods. The characterization of the nanofiber templates revealed that fiber diameter did not affect the liposome size. According to the optical microscopy results, the immediate hydration of phospholipids deposited on the amphiphilic nanofibers occurred within a few seconds, resulting in the formation of liposomes in water dispersions. The liposomes appeared to aggregate more readily in the concentrated than in the diluted solutions. The drug encapsulation efficiency for the fiber-hydrated liposomes varied between 14.9 and 28.1% and, for film-hydrated liposomes, between 22.0 and 77.1%, depending on the CAM concentrations and additional extrusion steps. The nanofiber hydration method was faster, as less steps were required for the in-situ liposome preparation than in the film-hydration method. The liposomes obtained using nanofiber hydration were smaller and more homogeneous than the conventional liposomes, but less drug was encapsulated.

Effect of density, phonon scattering and nanoporosity on the thermal conductivity of anisotropic cellulose nanocrystal foams

Anisotropic cellulose nanocrystal (CNC) foams with densities between 25 and 130 kg m−3 (CNC25 –CNC130) were prepared by directional ice-templating of aqueous dispersions. Estimates of the solid and gas conduction contributions to the thermal conductivity of the foams using a parallel resistor model showed that the relatively small increase of the radial thermal conductivity with increasing foam density can be attributed to interfacial phonon scattering. The foam wall nanoporosity and, to a lesser extent, the orientation of the CNC particles and alignment of the columnar macropores, also influence the insulation performance of the foams. The insight on the importance of phonon scattering for the thermal insulation properties of nanocellulose foams provides useful guidelines for tailoring nanofibrillar foams for super-insulating applications.