Adsorption of Surfactants on Mineral Solids

Factors influendng 1he adsorption of ionic surfactants on solids are outlined. Emphasis is placed on the role of electrostatic forces and of lateral association within adsorbed layers. MechanLsms leading to charge gene.ration on solids are descdbed, and the dependence of adsorption on charge effects i\u27s mustrated by reference to published data on a number of different solid surfactan:t systems. It is shown how the electrostatic factor can be strongly modified · by the presence of inorganic salts. The importance of chain-chain interactions is illustrated by the influence of chains length and composition on adsorption, and also by the pH dependence of the adsorption of long chain, weak electrolytes. This leads to a discussion of the possible role of highly surface active long chain complexes. Lastly, the influence of polymers on the adsorption of surfactants is discussed

Impact of pulp rheology on selective recovery of value minerals from ores

Rheological behavior of mineral pulps plays a critical role in almost all mineral processing unit operations. Although the impact of rheology in unit operations such as grinding and slurry transport has received much attention in the past, this is not the case for flotation. The pathway by which the pulp rheology influences the flotation performance is not well understood. The aim of this paper is to explore how physical (shape, size and morphology) and surface chemical properties of minerals contribute to pulp rheology and pathways by which rheology can influence selective value mineral recovery and/or concentrate grade. Systematic studies involving spiking experiments (deliberate addition of fibrous minerals and other solids), measurement of pulp viscosity and yield stress, flotation tests, SEM, EDX and XRD were conducted on a Ni ore and a Cu ore. A phenomenological model was developed. The key components of the model are the formation of a macro-network comprising micro-aggregates of fibrous minerals which significantly increases pulp viscosity, and as a result impedes gas dispersion and bubble-particle attachment and influence froth phase properties. Additionally, the role of various reagent types in regulating pulp rheological behavior was explored

Cohesive force apparatus for interactions between particles in surfactant and polymer solutions

Abstract Measurement of forces between two individual particles in the millimeter and micrometer size range is difficult to accomplish and yet these are the particles that are normally encountered in many commercial systems. A cohesive force apparatus (CFA) first used by one of the authors [E.D. Shchukin, R.K. Yusupov, E.A. Amelina, P.A. Rebinder, Kolloidn. Zh. 31 (1969) 913] was modified here for studying cohesive force down to 1 nN between particles of various size, shape and chemical nature under different conditions. In this work, the interaction between fused glass surfaces in solutions containing surfactants, polymers and salts was investigated by measuring the detachment force using the cohesive force apparatus. The cohesive force between glass surfaces was found to gradually decrease with increase in pH due to a corresponding increase in their negative zeta potential. Addition of salt can increase the cohesive force significantly. Interestingly, the cohesive force was observed to increase significantly with the increase of DTAB concentration because of the hydrophobic interactions between monolayers of DTAB on glass. However, the force decreased with further increase in DTAB concentration due to electrostatic repulsion between surfaces and decrease of hydrophobic interactions when DTAB bi-layers are formed. In the case of the hydrophobically modified polymer, polyvinylcaprolactam (PVCAP), the cohesive force was shown to be directly proportional to the molecular weight of the polymer and the loading force. The cohesive interactions between PEO adsorbed glass also showed the force to increase as a function of the PEO concentration, reach a maximum, and then decrease gradually, the increase being due to the reduction in the zeta potential of the glass and the decrease due to steric effect between the fully covered layers. Interaction of anionic surfactant with the pre-adsorbed PEO layer can reduce the cohesive force between the surfaces

Incompatibility-Driven Self-Organization in Polycatenar Liquid Crystals Bearing Both Hydrocarbon and Fluorocarbon Chains

The synthesis and liquid crystal properties are reported for tri-and tetra-catenar mesogens in which both hydrocarbon and semiperfluorocarbon chains have been incorporated. In the tricatenar mesogens, the lamellar spacing in the smectic C phase of the all-hydrocarbon mesogen almost doubles when the isolated hydrocarbon chain is replaced by a semiperfluorinated chain on account of the localized segregation in different sublayers between the two chain types. In the tetracatenar materials, the replacement of at least one hydrocarbon chain by semiperfluorocarbon chains is sufficient to promote columnar phase formation, but when the molecule has two hydrocarbon chains at one end and two semiperfluorocarbon chains at the other, the requirement for localized phase segregation leads to the formation of a rectangular phase with very large lattice parameters. The juxtaposition of terminal chains of different nature within the same molecular structure thus leads to a reduction in mesophase symmetry and the emergence of more complex supramolecular organization

Free energy of alternating two-component polymer brushes on cylindrical templates

We use computer simulations to investigate the stability of a two-component polymer brush de-mixing on a curved template into phases of different morphological properties. It has been previously shown via molecular dynamics simulations that immiscible chains having different length and anchored to a cylindrical template will phase separate into striped phases of different widths oriented perpendicularly to the cylindrical axis. We calculate free energy differences for a variety of stripe widths, and extract simple relationships between the sizes of the two polymers, N_1 and N_2, and the free energy dependence on the stripe width. We explain these relationships using simple physical arguments based upon previous theoretical work on the free energy of polymer brushes.Comment: 5 pages, 5 figures, accepted for publication in the Journal of Chemical Physic

Unique structural solution from a VH3-30 antibody targeting the hemagglutinin stem of influenza A viruses

Broadly neutralizing antibodies (bnAbs) targeting conserved influenza A virus (IAV) hemagglutinin (HA) epitopes can provide valuable information for accelerating universal vaccine designs. Here, we report structural details for heterosubtypic recognition of HA from circulating and emerging IAVs by the human antibody 3I14. Somatic hypermutations play a critical role in shaping the HCDR3, which alone and uniquely among VH3-30 derived antibodies, forms contacts with five sub-pockets within the HA-stem hydrophobic groove. 3I14 light-chain interactions are also key for binding HA and contribute a large buried surface area spanning two HA protomers. Comparison of 3I14 to bnAbs from several defined classes provide insights to the bias selection of VH3-30 antibodies and reveals that 3I14 represents a novel structural solution within the VH3-30 repertoire. The structures reported here improve our understanding of cross-group heterosubtypic binding activity, providing the basis for advancing immunogen designs aimed at eliciting a broadly protective response to IAV

Mutations in influenza A virus neuraminidase and hemagglutinin confer resistance against a broadly neutralizing hemagglutinin stem antibody

Influenza A virus (IAV), a major cause of human morbidity and mortality, continuously evolves in response to selective pressures. Stem-directed, broadly neutralizing antibodies (sBnAbs) targeting influenza hemagglutinin (HA) are a promising therapeutic strategy, but neutralization escape mutants can develop. We used an integrated approach combining viral passaging, deep sequencing, and protein structural analyses to define escape mutations and mechanisms of neutralization escape in vitro for the F10 sBnAb. IAV was propagated with escalating concentrations of F10 over serial passages in cultured cells to select for escape mutations. Viral sequence analysis revealed three mutations in HA and one in neuraminidase (NA). Introduction of these specific mutations into IAV through reverse genetics confirmed their roles in resistance to F10. Structural analyses revealed that the selected HA mutations (S123G, N460S, and N203V) are away from the F10 epitope but may indirectly impact influenza receptor binding, endosomal fusion, or budding. The NA mutation E329K, which was previously identified to be associated with antibody escape, affects the active site of NA, highlighting the importance of the balance between HA and NA function for viral survival. Thus, whole genome population sequencing enables the identification of viral resistance mutations responding to antibody-induced selective pressure.IMPORTANCE Influenza A virus is a public health threat for which currently available vaccines are not always effective. Broadly neutralizing antibodies that bind to the highly-conserved stem region of influenza hemagglutinin (HA) can neutralize many influenza strains. To understand how influenza virus can become resistant or escape such antibodies, we propagated influenza A virus in vitro with escalating concentrations of antibody and analyzed viral populations with whole genome sequencing. We identified HA mutations near and distal to the antibody binding epitope that conferred resistance to antibody neutralization. Additionally, we identified a neuraminidase (NA) mutation that allowed the virus to grow in the presence of high concentrations of the antibody. Virus carrying dual mutations in HA and NA also grew under high antibody concentrations. We show that NA mutations mediate the escape of neutralization by antibodies against HA, highlighting the importance of a balance between HA and NA for optimal virus function

Changes in the nanoparticle aggregation rate due to the additional effect of electrostatic and magnetic forces on mass transport coefficients

The need may arise to be able to simulate the migration of groundwater nanoparticles through the ground. Transportation velocities of nanoparticles are different from that of water and depend on many processes that occur during migration. Unstable nanoparticles, such as zero-valent iron nanoparticles, are especially slowed down by aggregation between them. The aggregation occurs when attracting forces outweigh repulsive forces between the particles. In the case of iron nanoparticles that are used for remediation, magnetic forces between particles contribute to attractive forces and nanoparticles aggregate rapidly. This paper describes the addition of attractive magnetic forces and repulsive electrostatic forces between particles (by 'particle', we mean both single nanoparticles and created aggregates) into a basic model of aggregation which is commonly used. This model is created on the basis of the flow of particles in the proximity of observed particles that gives the rate of aggregation of the observed particle. By using a limit distance that has been described in our previous work, the flow of particles around one particle is observed in larger spacing between the particles. Attractive magnetic forces between particles draw the particles into closer proximity and result in aggregation. This model fits more closely with rapid aggregation which occurs between magnetic nanoparticles.Ministry of Education of the Czech Republic of the Technical University in Liberec [7822]; Ministry of Education of the Czech Republic [FR-TI1/456]; Ministry of Industry and Trad