Papers by Keyword: Colloidal

Abstract: Synthesis of colloidal silver nanoparticles has been successfully conducted through the chemical reduction technique. The synthesis used AgNO₃, NaOH, and alginate as the precursor, accelerator reagent, and reducing agent and stabilizer, respectively. The effects of heating temperature, reaction time, accelerator concentration, and precursor concentration were investigated according to the localized surface plasmon resonance (LSPR) phenomenon using a UV-Vis spectrophotometer. The nanoparticle size distribution was observed via a Particle Size Analyzer (PSA). The stability of silver nanoparticles was studied for 8 weeks based on the LSPR phenomenon. Then, their antibacterial performance toward S. Aureus ATCC 25923 and E. Coli ATCC 25922 was examined. The results showed the absorbance intensities representing the number of silver nanoparticles formed were influenced by temperature, reaction time, NaOH concentration, and AgNO₃ concentration. At 50°C heating, the optimum synthesis of silver nanoparticles was achieved at 50 min with a NaOH concentration of 0.013M. The higher AgNO₃ concentration resulted in a greater concentration of silver nanoparticles produced. From the PSA characterization, the average particle sizes for the samples were 1.82 nm and 1.30 nm for AgNO₃ concentrations (% w/w; AgNO₃/Alginate) of 1.6% and 2.4%, respectively. Based on the LSPR phenomenon, colloidal silver nanoparticles were stable in storage for 8 weeks at room temperature. The increase in the concentration of silver nanoparticles within colloidal could enhance antibacterial performance against S. Aureus and E. Coli. Accordingly, silver nanoparticles synthesized with alginate as a stabilizer have the potential as an antibacterial compound for medical applications.

Abstract: Colloidal CdSe Nanocrystals (NCs) or quantum dots (QDs) have been developed using a yielding solution technique utilizing chemical reactions in chloroform and oleic acid in different organic solvents. This assembly is an improvement of the systematic thermal decomposition of high temperature organic solvent compounds. CdSe NCs of specific sizes can be produced easily by adjusting the solvent. This technique is reproducible and clear, so industrial development can be easily scaled up. Characterization at room temperature of the UV-Vis absorption and Photoluminescence (PL) spectra. Results reveal that the CdSe prepared with the creation of defects was nanocrystalline. The energy difference (Eg) measured in PL was 2.3 and 2.69 eV respectively for CdSe NCs in chloroform and oleic acid. The structures of the CdSe quantum dots were determined by scanning electron microscopy (SEM). The phase-transfer of chloroform and oleic acid stabilized CdSe nanocrystals solutions was studied for their potentials in white light generation applications.

Abstract: The main objective of this study was to prepare bead milled-silica nanoparticles (SiO₂) as reinforcing materials for transparent hard coating films. SiO₂ dispersed in Dowanol PM without any stabilizer was used as a main component in the nanocomposite hard coating films to improve hardness of Poly methyl methacrylate (PMMA) sheets. However, the major challenge in hard coating formulation is the dispersion of nanoscale SiO₂ particles. Bead milling machine (MiniCer, NETZSCH, Germany) equipped with different sizes of zirconia (ZrO₂) beads (0.1, 0.5, and 1.0 mm) was used for dispersing 40wt% SiO₂ in Dowanol PM to achieve target sizes of 200, 500, and 800 nm. The dispersed nanoparticles were characterized by UV-visible spectroscopy for their optical transmission, transmission electron microscopy (TEM) for particle morphologies, and dynamic light scattering technique (DLS) for the particles sizes. The milled-SiO₂ nanoparticles were stable in Dowanol PM as suspensions with their particles sizes closed to the target sizes. The 200-nm suspension showed the longest storage time without any aggregate formation. Whereas, the dispersed nanoparticles suspensions with the particles size >500 nm formed agglomerates during storage. The SiO₂/MTMS nanocomposite coating film was then prepared coated milled-SiO₂ suspension in Dowanol PM on PMMA sheets. The film with 200 nm SiO₂ showed the highest transparency (92% at 550 nm) which was like the uncoated PMMA sheets. At thickness of 3-microns, SiO₂/MTMS nanocomposite films could improve pencil hardness of PMMA sheets from <H to 3H.

Abstract: Most microorganisms grow on surfaces as biofilms rather than as individual planktonic cells, and cells within biofilms show high levels of resistance against antimicrobial drugs. Thereby biofilm formation complicates treatment and contributes to high morbidity and mortality rates associated with infections. This study explores the physical, optical, and nano-structural properties of silver and copper nanoparticles dispersed in aqueous suspensions (nanoparticulate colloidal water) and examines their in vitro activity against microbial biofilms. Silver and copper nanoparticulate colloidal water of various concentrations were prepared and studied. Their surface energies, surface charge and surface plasmonic resonance properties were determined using contact angle measurement, zeta potential measurement and optical spectrometry, respectively. A model of biofilm formation on the wells of microtiter plates was used to determine the activity of the nanoparticulate suspensions against fungal and bacterial biofilms. Scanning electron microscopy (SEM) was used to observe the nanoparticle interactions with microbial cells within the biofilms. Results show that silver nanoparticle-containing liquids have higher surface energy than their copper counterparts; and that the surface energy increases as the concentration of silver nanoparticles increases. Altogether, the effectiveness of silver nanoparticle colloidal suspensions in controlling biofilm formation is observed and reported. For a given size of silver nanoparticles studied, it is found that the effective concentrations against microbial biofilms are far lower than their cytotoxic concentrations, indicating an overall safety and a good therapeutic index thus substantial application potential.

Abstract: Electrophoretic deposition of ligand-free platinum nanoparticles has been studied to elucidate how wettability, indicated by contact angle measurements, is linked to vital parameters of the electrophoretic deposition process. These parameters, namely the colloid concentration, electric field strength and deposition time, have been systematically varied in order to determine their influence on the contact angle. Additionally, scanning electron microscopy has been used to confirm the homogeneity of the achieved coatings.

Abstract: In this work the stability of TiN and TiC nanopowders in isopropyl alcohol as well as the fabrication of dense and well adhered thin coatings based on TiN and TiC by electrophoretic deposition (EPD) have been evaluated in terms of zeta potential and mass deposited when hydrazine is added. The surface of TiN and TiC nanoparticles has been modified to improve the dispersion in isopropyl alcohol adding a cationic polymer (polyethylenimine) as dispersant with two different molecular weights. The influence of acidic/basic character of the solvent also has been evaluated in order to reach the most efficient EPD process. It was found that the adsorption of polyethylenimine with higher molecular weight can preserve the homogeneity of TiC coatings. The surface of TiN nanoparticles can be tuned in order to achieve a similar polyethylenimine adsorption which also improves the deposition in basic media.

Abstract: Conventional electrophoretic deposition is being combined with pulse electric fields to deposit yttria stabilized zirconia from ethanol based suspensions onto bondcoated turbine alloys for thermal barrier coatings. The addition of the pulse electric fields to the electrophoretic process has demonstrated the capability to decrease the coating roughness, minimize hydrolysis, and decrease coating edge effects commonly encountered in electrokinetic and electrochemical deposition processes. Subsequent to the electrophoretic deposition process the green body coatings were subjected to a combined binder burnout and sintering process for further coating densification. The coatings have been qualified in terms of surface roughness as well as microstructure and experiments have been performed to show that the pulse EPD process can deposit TBC materials onto turbine components.