Sharif Digital Repository

This paper addresses the fabrication of bronze-nano-graphite coatings containing 30. nm sized graphite particles. Addition of Poly Vinyl Pyrrolidone (PVP) and dispersing the suspension by ultrasound was utilized to stabilize the electroplating solution. Pulsed current electrodeposition was used and the deposits were characterized in terms of graphite content, particle dispersion in coating and morphology. The wear behavior of the coating was compared to bronze-micro-graphite coatings prepared with the same experimental conditions. The present coating showed improved wear resistance in comparison to bronze-micro-graphite coatings at the same graphite content  

A sensitive colorimetric method for the detection of ascorbic acid was proposed in this research based on the reduction of silver ions by ascorbic acid in the presence of citrate-stabilized silver seeds, additional trisodium citrate and a polymer such as polyvinylpyrrolidone. The color of the stable sol is controlled by varying the concentration of trisodium citrate (TSC), polyvinylpyrrolidone, silver nitrate and silver seeds. The reduction of Ag + to triangle silver nanoparticles (Ag-NPs) by ascorbic acid in the presence of trisodium citrate (TSC) and silver seeds produced two very intense surface plasmon resonance peaks of Ag-NPs. The plasmon absorbance of Ag-NPs allows the quantitative... 

Chitosan films have a great potential to be used for wound dressing and food-packaging applications if their physicochemical properties including water vapor permeability, optical transparency, and hydrophilicity are tailored to practical demands. To address these points, in this study, chitosan (CS) was combined with polyvinylpyrrolidone (PVP) and graphene oxide (GO) nanosheets (with a thickness of ∼1 nm and lateral dimensions of few micrometers). Flexible and transparent films with a high antibacterial capacity were prepared by solvent casting methods. By controlling the evaporation rate of the utilized solvent (1 vol % acidic acid in deionized water), self-organization of GO in the... 

Foams for biomedical applications were made from polyvinyl alcohol, polyvinyl alcohol / polyvinyl pyrrolidone blend and their nanocomposites with nanoclay by clean processes. Air was entrapped into the aqueous polymer solutions during vigorous mixing and then the solutions were freeze-dried. The foams structure was stabilized by crosslinking via gamma irradiation without using any harmful chemicals. The hydrophilic biocompatible foams possessed interconnected open cell structure with remarkable capacity to absorb and retain water. The foams in wet state were soft and flexible. Desirable pore structure and higher water absorption was obtained at a solution concentration of 5 wt% for both... 

Nanofibrous structures that mimic the native extracellular matrix and promote cell adhesion have attracted considerable interest for biomedical applications. In this study, GO-modified nanofibrous biopolymers (GO) were prepared by electrospinning blended solutions of chitosan (80 vol%), polyvinyl pyrrolidone (15 vol%), polyethylene oxide (5 vol%) containing GO nanosheets (0–2 wt%). It is shown that GO nanosheets significantly change the conductivity and viscosity of highly concentrated chitosan solutions, so that ultrafine and uniform fibers with an average diameter of 60 nm are spinnable. The GO-reinforced nanofibers with controlled pore structure exhibit enhanced elastic modulus and... 

Ultrafiltration (UF) membranes were prepared from poly(vinyl chloride) (PVC) as main polymer, poly(vinyl pyrrolidone) (PVP) as additive, and 1-methyl-2-pyrrolidone (NMP) as solvent using Design Expert software for designing the experiments. The membranes were characterized by SEM, contact angle measurement, and atomic force microscopy. The performance of UF membranes was evaluated by pure water flux (PWF) and blue indigo dye particle rejection. In addition, the molecular weight cutoff of UF membranes was determined by poly(ethylene glycol) (PEG) rejection. The UF membranes were used as substrates for fabrication of polyamide thin film composite (TFC) reverse osmosis (RO) membranes. The... 

In the present study, the morphology of asymmetric poly(vinylidene fluoride) blend membranes which were prepared by the phase inversion method is rationalized by comparing two non-dimensional number represent thermodynamic and kinetic properties of the prepared membrane. These two parameters change phase diagram and demixing rate between solvent and nonsolvent. TiO2 nanoparticles and polyvinylpyrrolidone were used as additives. Hansen solubility parameters of the components are calculated by Van Krevelen method. Furthermore, kinetic and thermodynamic properties of the prepared solutions are determined by drawing phase diagrams and controlling mass transfer rate during precipitation of... 

Titanium(IV) tetraisopropoxide was employed as a metal oxide sol-gel precursor to prepare ceramic composite nanofibers by the electrospinning system. To facilitate this process and obtain the desired nanofibers with higher aspect ratios and surface area, poly(vinylpyrrolidone) was added to the sol of titania. Four ceramic nanofibers sheets based on titania were prepared while each sheet contained different transition metals such as Fe-Mn, Fe-Ni, Fe-Co, and Fe-Mn-Co-Ni. The scanning electron microscope images showed good homogeneity for all the prepared ceramic composites with a diameter range of 100-250 nm. The sorption efficiency was investigated by a micro-solid-phase extraction setup in... 

Abstract: In recent years, temporary skin grafts (TSG) based on natural biopolymers modified with carbon nanostructures have received considerable attention for wound healing. Developments are required to improve physico-mechanical properties of these materials to match to natural skins. Additionally, in-deep pre-clinical examinations are necessary to ensure biological performance and toxicity effect in vivo. In the present work, we show superior acute-wound healing effect of graphene oxide nanosheets embedded in ultrafine biopolymer fibers (60 nm) on adult male rats. Nano-fibrous chitosan-based skin grafts crosslinked by Genepin with physico-mechanical properties close to natural skins were...