Tata N. Rao

Silica-silver core-shell particles for antibacterial textile application.

The silica-silver core-shell particles were synthesized by simple one pot chemical method and were employed on the cotton fabric as an antibacterial agent. Extremely small (1-2 nm) silver nanoparticles were attached on silica core particles of average 270 nm size. The optimum density of the nano silver particles was found which was sufficient to show good antibacterial activity as well as the suppression in their surface plasmon resonance responsible for the colour of the core-shell particle for antibacterial textile application. The change in the density and size of the particles in the shell were monitored and confirmed by direct evidence of their transmission electron micrographs and by studying surface plasmon resonance characteristics. The colony counting method of antibacterial activity testing showed excellent results and even the least silver containing core-shell particles showed 100% activity against bacterial concentration of 10(4) colony counting units (cfu). The bonding between core-shell particles and cotton fabric was examined by X-ray photoelectron spectroscopy. The antibacterial activity test confirmed the firm attachment of core-shell particles to the cotton fabric as a result 10 times washed sample was as good antibacterial as that of unwashed sample. The bacterial growth was inhibited on and beneath the coated fabric, at the same time no zone of inhibition which occurs due to the migration of silver ions into the medium was observed indicating immobilization of silver nanoparticles on silica and core-shell particles on fabric by strong bonding.

Donut-shaped Li4Ti5O12 structures as a high performance anode material for lithium ion batteries.

Lithium titanate (LTO) spinel 3D porous sub-micrometer donuts synthesized by combined sol-gel and electrospraying reveal a wall thickness of 200-250 nm with grain sizes in the range of 60-100 nm. Electrochemical testing of sub-micrometer donuts in half-cell mode exhibited a reversible specific capacity of 141 mAh/g even after 200 cycles of charging and discharging at 1C rate. The LTO structures with nanograins effectively reduce the Li ion diffusion path length, providing easy charge and discharge with good cyclability.

Preparation of bi-functional silica particles for antibacterial and self cleaning surfaces

Synthesis of bi-functional silica particles by a simple wet chemical method is described where the mixture of ultra fine nanoparticles (1-3 nm) of titania and silver were attached on the silica particle surface in a controlled way to form a core-shell structure. The silica surface showed efficient bi-functional activity of photo-catalytically self cleaning and antibacterial activity due to nanotitania and nanosilver mutually benefiting each others function. The optimum silver concentration was found where extremely small silver nanoparticles are formed and the total composite particle remains white in color. This is an important property in view of certain applications such as antibacterial textiles where the original fabric color has to be retained even after applying the nanosilver on it. The particles were characterized at each step of the synthesis by X-ray photoelectron spectroscopy, UV-visible spectroscopy, X-ray diffraction, scanning electron microscopy, transmission electron microscopy and electron energy loss spectroscopy. Bi-functional silica particles showed accelerated photocatalytic degradation of methylene blue as well as enhanced antibacterial property when tested as such particles and textiles coated with these bi-functional silica particles even at lower silver concentration.

Fabrication and surface functionalization of electrospun polystyrene submicron fibers with controllable surface roughness

Polystyrene (PS) submicron fibers of 14 wt% concentration were fabricated by electrospinning using dimethylformamide (DMF)–tetrahydrofuran (THF) solvent system. The surface morphology of PS fibers was modified from smooth to rough by changing the mixing ratio of DMF and THF in the spinning solution. The electrospun PS fibers with smooth and rough surfaces were then amidomethylated by treating with N-hydroxymethyl-2-chloroacetamide. PS fibers with higher roughness incorporated more amidomethyl functional groups on their surface, as confirmed by XPS analysis. This observation was further supported by BET adsorption isotherm results which showed a significant increase in specific surface area of rough PS electrospun fibers. Interestingly, amidomethylation has altered rough electrospun PS submicron fibers from extremely hydrophobic to hydrophilic. These chemically modified electrospun PS fibers with controllable surface roughness and wettability may be utilized as a carrier for proteins, mainly enzymes and antibodies, by covalent linkage through amino groups attached to their surface.

Nanomanufacturing for Aerospace Applications

In this chapter synthesis of nanomaterials by various nanomanufacturing (top-down and bottom-up) processes, synthesis and properties of aerogel, and advanced electrodeposited coatings and their properties, are reviewed. Further, the potential applications of nanomaterials, aerogels, and electrodeposited coatings in the aerospace industry are concisely surveyed.