Arijit Bose

Controlled Release from Bilayer-Decorated Magnetoliposomes via Electromagnetic Heating

Nanoscale assemblies that can be activated and controlled through external stimuli represent a next stage in multifunctional therapeutics. We report the formation, characterization, and release properties of bilayer-decorated magnetoliposomes (dMLs) that were prepared by embedding small hydrophobic SPIO nanoparticles at different lipid molecule to nanoparticle ratios within dipalmitoylphosphatidylcholine (DPPC) bilayers. The dML structure was examined by cryogenic transmission electron microscopy and differential scanning calorimetry, and release was examined by carboxyfluorescein leakage. Nanoparticle heating using alternating current electromagnetic fields (EMFs) operating at radio frequencies provided selective release of the encapsulated molecule at low nanoparticle concentrations and under physiologically acceptable EMF conditions. Without radio frequency heating, spontaneous leakage from the dMLs decreased with increasing nanoparticle loading, consistent with greater bilayer stability and a decrease in the effective dML surface area due to aggregation. With radio frequency heating, the initial rate and extent of leakage increased significantly as a function of nanoparticle loading and electromagnetic field strength. The mechanism of release is attributed to a combination of bilayer permeabilization and partial dML rupture.

Recent developments in materials synthesis in surfactant systems

The paper reviews the use of surfactant self-assembly to template the synthesis of polymers, ceramics with extended structures, and nanoparticles. The objective of the review is to highlight newer concepts linking self-assembly to materials nanostructure and to the realization of functional materials.

Effect of particle size and surface treatment on constitutive properties of polyester-cenosphere composites

Cenospheres (hollow, aluminum silicate spheres ranging from 10 to 400 μm in diameter) are used as filler in a homogeneous polyester composite. Particle size was varied to study its effect on mechanical properties of the composite. The effect of particulate surface modification using a silane coupling agent was also studied. Properties of the composites were characterized using standard testing methods. When compared to the largest particulate used, an increase in compression strength was achieved by particle size reduction and use of coupling agent. The Elastic modulus increased by using fine particles, while Poissons ratio remained constant and independent of silane treatment or particle size. Fracture toughness increased with particle size reduction and increased further with silane surface modification. Dynamic compressive strength increased with particle size reduction, while silane did not show improvement. The addition of cenospheres as well as silane treatment increased the glass transition temperature for polyester. A given mass fraction of particulate, of a mean diameter D, will have the surface area between the particulate and matrix scale as D−1 (specific surface area). The sensitivity of these properties to cenosphere size is a direct function of the interfacial surface contacts between the polyester and the cenospheres and the specific surface area.

PROCESSING AND CHARACTERIZATION OF A LIGHTWEIGHT CONCRETE USING CENOSPHERES

A study has been conducted in which a lightweight concrete was processed using ceramic microspheres, known as cenospheres, as a primary aggregate. The mechanical properties, including compressive strength, tensile strength, flexural strength and fracture toughness, were tested and cataloged. It was determined that the addition of high volumes of cenospheres significantly lowered the density of concrete but was also responsible for some strength loss. This strength loss was recovered by improving the interfacial strength between the cenospheres and the cement. The interfacial properties were quantified using interfacial fracture mechanics techniques. These techniques were also employed to find a suitable surface modifier with which to improve this interface. The admixture silica fume and the coupling agent Silane™ were found to be suitable candidates and both performed well in small-scale compression testing. Silica fume was eventually isolated as a prime candidate. The concrete produced with this admixture was tested and compared to a concrete with an equal volume fraction of cenospheres. The addition of silica fume improved the compressive strength of cenosphere concrete by 80%, tensile strength by 35%, flexural strength by 60% and fracture toughness by 41%.

Attachment of a hydrophobically modified biopolymer at the oil-water interface in the treatment of oil spills.

The stability of crude oil droplets formed by adding chemical dispersants can be considerably enhanced by the use of the biopolymer, hydrophobically modified chitosan. Turbidimetric analyses show that emulsions of crude oil in saline water prepared using a combination of the biopolymer and the well-studied chemical dispersant (Corexit 9500A) remain stable for extended periods in comparison to emulsions stabilized by the dispersant alone. We hypothesize that the hydrophobic residues from the polymer preferentially anchor in the oil droplets, thereby forming a layer of the polymer around the droplets. The enhanced stability of the droplets is due to the polymer layer providing an increase in electrostatic and steric repulsions and thereby a large barrier to droplet coalescence. Our results show that the addition of hydrophobically modified chitosan following the application of chemical dispersant to an oil spill can potentially reduce the use of chemical dispersants. Increasing the molecular weight of the biopolymer changes the rheological properties of the oil-in-water emulsion to that of a weak gel. The ability of the biopolymer to tether the oil droplets in a gel-like matrix has potential applications in the immobilization of surface oil spills for enhanced removal.

Oil Emulsification Using Surface-Tunable Carbon Black Particles

Emulsification of oil from a subsurface spill and keeping it stable in the water is an important component of the natural remediation process. Motivated by the need to find alternate dispersants for emulsifying oil following a spill, we examine particle-stabilized oil-in-water emulsions. Emulsions that remain stable for months are prepared either by adding acid or salt to carboxyl-terminated carbon black (CB) suspension in water to make the particles partially hydrophobic, adding the oil to this suspension and mixing. When naphthalene, a model potentially toxic polycyclic aromatic hydrocarbon, is added to octane and an emulsion formed, it gets adsorbed significantly by the CB particles, and its transport into the continuous water is markedly reduced. In contrast to an undesirable seawater-in-crude oil emulsion produced using a commercially used dispersant, Corexit 9500A, we demonstrate the formation of a stable crude oil-in-seawater emulsion using the CB particles (with no added acid or salt), important for natural degradation. The large specific surface area of these surface functionalized CB particles, their adsorption capability and their ability to form stable emulsions are an important combination of attributes that potentially make these particles a viable alternative or supplement to conventional dispersants for emulsifying crude oil following a spill.

Release of surfactant cargo from interfacially-active halloysite clay nanotubes for oil spill remediation.

Naturally occurring halloysite clay nanotubes are effective in stabilizing oil-in-water emulsions and can serve as interfacially-active vehicles for delivering oil spill treating agents. Halloysite nanotubes adsorb at the oil-water interface and stabilize oil-in-water emulsions that are stable for months. Cryo-scanning electron microscopy (Cryo-SEM) imaging of the oil-in-water emulsions shows that these nanotubes assemble in a side-on orientation at the oil-water interface and form networks on the interface through end-to-end linkages. For application in the treatment of marine oil spills, halloysite nanotubes were successfully loaded with surfactants and utilized as an interfacially-active vehicle for the delivery of surfactant cargo. The adsorption of surfactant molecules at the interface serves to lower the interfacial tension while the adsorption of particles provides a steric barrier to drop coalescence. Pendant drop tensiometry was used to characterize the dynamic reduction in interfacial tension resulting from the release of dioctyl sulfosuccinate sodium salt (DOSS) from halloysite nanotubes. At appropriate surfactant compositions and loadings in halloysite nanotubes, the crude oil-saline water interfacial tension is effectively lowered to levels appropriate for the dispersion of oil. This work indicates a novel concept of integrating particle stabilization of emulsions together with the release of chemical surfactants from the particles for the development of an alternative, cheaper, and environmentally-benign technology for oil spill remediation.

Synthesis of submicrometer crystals of aluminum oxide by aqueous intravesicular precipitation

Abstract Single compartment unilamellar vesicles were used as microreactors for controlled precipitation of crystals in the nanometer size range within their internal cavity. The model explored was the aqueous phase reaction of aluminum and hydroxyl ions. The method relies on the fact that the vesicle wall is selectively permeable to the anions only. An aluminum salt solution was first encapsulated within the intravesicular space. The extravesicular aluminum ions were replaced with sodium ions by ion exchange. A sodium hydroxide solution was then added to the extravesicular phase. When hydroxyl ions permeated through the vesicle wall and reacted with the encapsulated aluminum ions, the product was found to be spherical crystals of alumina. The specific polymorph appeared to depend on the aluminum salt anion. Under similar conditions, in the absence of vesicles, a gelatinous precipitate of aluminum hydroxide comprising of plate-like particles was formed.

Processing and mechanical characterization of lightweight polyurethane composites

A simple procedure was established to fabricate polyurethane-cenosphere particulate composite materials. Composites having four different volume fractions of cenospheres (hollow ceramic microspheres) ranging from 10 to 40% in increments of 10% were prepared and their mechanical properties were evaluated. A predictive model to estimate the fracture toughness of the composite was developed. The dynamic constitutive behavior of the composite in compression was investigated using the split Hopkinson pressure bar (SHPB) technique in conjunction with high-speed photography. The results of the material characterization indicated that addition of cenospheres decreased the density of the composite. The quasi-static stiffness, both in tension and compression, and the quasi-static fracture toughness of the composite increased with addition of cenospheres. The high strain rate constitutive behavior of 100% polyurethane showed monotonic stiffening whereas the composite at higher cenosphere volume fractions (40%) exhibited a stiffening-softening-stiffening behavior. Scanning Electron Microscopy (SEM) studies were also carried out to determine the failure mechanisms of the composite.

Uptake and loss of water in a cenosphere–concrete composite material

Abstract Cenospheres are hollow, aluminum silicate spheres, between 10 and 300 μm in diameter. Their low specific gravity (0.67) makes them ideal replacements for fine sand for producing low-density concrete. In an effort to understand the potential for practical use of the cenospheres as a fine aggregate in concrete, the moisture uptake and loss by cenospheres and water uptake and loss in cenosphere–concrete composites have been studied in this paper. The equilibrium moisture content of cenospheres is about 18 times higher than that of sand, reflecting the porous nature of cenospheres. The temporal evolution of water penetration into the cenosphere–concrete is modeled using Washburn kinetics. The effective pore size using this model is of the order of several nanometers. These results imply a lack of connectivity within the pores, leading to a low permeability. SEM images of the concrete reveal pore sizes of the order of 2–5 μm. The drying flux for cenospheres shows a classical behavior—a constant rate followed by a linear falling rate period. Thus, experiments done at these conditions can be used to predict drying times for wet cenospheres exposed to other environments. The flux of water vapor away from both the cenosphere–concrete as well as the normal concrete shows a nonlinear change with moisture content throughout the drying cycle, implying that the pore structure within the concrete strongly influences the drying behavior.