Experimental investigation of nanoparticles effects on cohesive model and bridging laws of mode I fracture in the adhesive joints

In this paper, an experimental study is conducted on bridging and cohesive mechanism of adhesive bonded joints including Nano-composite and Nano-adhesive for mode I fracture. Nano-composite adherents with glass fibers and alumina nanoparticle have been fabricated and underwent DCB test. The concentration of this study is on the comparison of three different types (ECM, CBT, and MCC methods) of traction-separation laws and the effect of adding nanoparticles on them. A modified trapezoidal model (P1) is presented. The obtained bridging laws and cohesive mechanism (traction-separation laws) for different nanoparticles wt% (in adhesive and adherent) can be used in the finite element method for numerical simulation. Values obtained for critical displacement by different methods have a good consistency with each other with a relatively similar value, except for the sample by 0.5% wt Nano-particle in adhesive. In addition, critical displacement increases with increasing nanoparticle content in the adhesive, and then decreases. In that, the greatest critical displacement was observed in adhesive samples with nanoparticle content of 0.5%. Although, critical stress obtained from CBT to MCC methods were consistent, they were different from ECM results. The critical stress decreased with further addition of nanoparticles to the adhesive, and then started increasing. In that, the lowest critical stress was observed in sample adhesives with nanoparticle content of 0.5%.     

Investigating peak stresses in fitting and repair patches of buried polyethylene gas pipes

Nowadays, polyethylene composes a large number of natural gas distribution pipelines installed under the ground. The focus of the present contribution is two fold. One of the objectives is to investigate the applicability of polyethylene fittings in joining polyethylene gas pipes which are electrofused onto the pipe ends and buried under the ground, by estimating stress distribution using finite element method. The second objective is to study the effectiveness of polyethylene repair patches which are used to mend the defected pipelines by performing a finite element analysis to calculate peak stress values. Buried polyethylene pipelines in the natural gas industry, can be imposed by sever loadings including the soil-structure interaction, traffic load, soil’s column weight, internal pressure, and thermal loads resulting from daily and/or seasonal temperature changes. Additionally, due to the application of pipe joints, and repair patches local stresses superimposed on the aforementioned loading effects. The pipe is assumed to be made of PE80 resin and its jointing socket, and the repair patch is PE100 material. The computational analysis of stresses and the computer simulations are performed using ANSYS commercial software. According to the results, the peak stress values take place in the middle of the fitting and at its internal surface. The maximum stress values in fitting and pipe are below the allowable stresses which shows the proper use of introduced fitting is applicable even in hot climate areas of Ahvaz, Iran. Although the buried pipe is imposed to the maximum values of stresses, the PE100 socket is more sensitive to a temperature drop. Furthermore, all four studied patch arrangements show significant reinforcing effects on the defected section of the buried PE gas pipe to transfer applied loads. Meanwhile, the defected buried medium density polyethylene gas pipe and its saddle fused patch can resist the imposed mechanical and thermal loads of 22°C temperature increase. Moreover, increasing the saddle fusion patch length to 12 inches reduces the maximum stress values in the pipe, significantly.     

Nonstoichiometric Titanium Oxides via Pulsed Laser Ablation in Water

Titanium oxide compounds TiO_, Ti₂O₃, and TiO₂ with a considerable extent of nonstoichiometry were fabricated by pulsed laser ablation in water and characterized by X-ray/electron diffraction, X-ray photoelectron spectroscopy and electron energy loss spectroscopy. The titanium oxides were found to occur as nanoparticle aggregates with a predominant 3+ charge and amorphous microtubes when fabricated under an average power density of ca. 1 × 10⁸ W/cm² and 10¹¹ W/cm², respectively followed by dwelling in water. The crystalline colloidal particles have a relatively high content of Ti²⁺ and hence a lower minimum band gap of 3.4 eV in comparison with 5.2 eV for the amorphous state. The protonation on both crystalline and amorphous phase caused defects, mainly titanium rather than oxygen vacancies and charge and/or volume-compensating defects. The hydrophilic nature and presumably varied extent of undercoordination at the free surface of the amorphous lamellae accounts for their rolling as tubes at water/air and water/glass interfaces. The nonstoichiometric titania thus fabricated have potential optoelectronic and catalytic applications in UV–visible range and shed light on the Ti charge and phase behavior of titania-water binary in natural shock occurrence.     

Effects of structure of the ionic head of cationic surfactant on its inhibition of acid corrosion of mild steel

Two n-alkyl-quaternary ammonium compounds were studied as corrosion inhibitors for acid corrosion of mild steel using electrochemical and weight loss methods. The two compounds are hexadecylpyridinium bromide (HDPB) and hexadecyltrimethyl ammonium bromide (HDTB). The influence of the structure of the ionic head on the inhibition action of the two cationic surfactants was studied by analyzing the data at different concentrations and temperatures. The inhibition efficiency increases with the concentration. It increases with temperature in the case of HDPB but decreases in the case of HDTB. The apparent activation energy, E _a of corrosion in the presence of HDPB was found to be lower than in blank (0.5 m H₂SO₄). In the case of HDTB, E _a was larger than that of the blank. A larger extent of adsorption for HDPB on the metal surface was evident from the larger negative values of the free energy of adsorption. The results yielded the extent and mode of adsorption of the inhibitors on mild steel. The stronger adsorption of HDPB was attributed to the differences in the molecular structures of the inhibitors.     

Water-Driven Assembly of Laser Ablation-Induced Au Condensates as Mesomorphic Nano- and Micro-Tubes

Reddish Au condensates, predominant atom clusters and minor amount of multiply twinned particles and fcc nanoparticles with internal compressive stress, were produced by pulsed laser ablation on gold target in de-ionized water under a very high power density. Such condensates were self-assembled as lamellae and then nano- to micro-diameter tubes with multiple walls when aged at room temperature in water for up to 40 days. The nano- and micro-tubes have a lamellar- and relaxed fcc-type wall, respectively, both following partial epitaxial relationship with the co-existing multiply twinned nanoparticles. The entangled tubes, being mesomorphic with a large extent of bifurcation, flexibility, opaqueness, and surface-enhanced Raman scattering, may have potential encapsulated and catalytic/label applications in biomedical systems. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Mechanistic study of substrate-based galvanic replacement reactions

The sacrificial templates used in galvanic replacement reactions dictate the properties of the hollow metal nanostructures formed. Here, we demonstrate that substrate-based Au-Ag nanoshells with radically altered properties are obtained by merely coating silver templates with an ultrathin layer of gold prior to their insertion into the reaction vessel. The so-formed nanoshells exhibit much smoother surfaces, a higher degree of crystallinity and are far more robust. Dealloying the nanoshells results in the first demonstration of substrate-based nanocages. Such cages exhibit a well-defined pattern of geometric openings in directions corresponding to the {111}-facets of the starting template material. The ability to engineer the cage geometry through adjustments to the orientational relationship between the crystal structure of the starting template and that of underlying substrate is demonstrated. Together these discoveries provide the framework to advance our understanding of the mechanisms governing substrate- based galvanic replacement reactions.     

Efficient co‐cultivation of human fibroblast cells (HFCs) and adipose‐derived stem cells (ADSs) on gelatin/PLCL nanofiber

In this study, we investigated whether the nanofibers produced by natural‐synthetic polymers can probably promote the proliferation of co‐cultured adipose‐derived stem cells/human fibroblast cells (ADSs/HFCs) and synthesis of collagen. Nanofiber was fabricated by blending gelatin and poly (L‐lactide co‐ɛ‐caprolactone) (PLCL) polymer nanofiber (Gel/PLCL). Cell morphology and the interaction between cells and Gel/PLCL nanofiber were evaluated by FESEM and fluorescent microscopy. MTS assay and quantitative real‐time polymerase chain reaction were applied to assess the proliferation of co‐cultured ADSs/HFCs and the collagen type I and III synthesis, respectively. The concentrations of two cytokines including fibroblast growth factor‐basic and transforming growth factor‐β1 were also measured in culture medium of co‐cultured ADSs/HDCs using enzyme‐linked immunosorbent assay assay. Actually, nanofibers exhibited proper structural properties in terms of stability in cell proliferation and toxicity analysis processes. Gel/PLCL nanofiber promoted the growth and the adhesion of HFCs. Our results showed in contact co‐culture of ADSs/HFCs on the Gel/PLCL nanofiber increased cellular adhesion and proliferation synergistically compared to non‐coated plate. Also, synthesis of collagen and cytokines secretion of co‐cultured ADSs/HFCs on Gel/PLCL scaffolds is significantly higher than non‐coated plates. To conclude, the results suggest that Gel/PLCL nanofiber can imitate physiological characteristics in vivo and enhance the efficacy of co‐cultured ADSs/HFCs in wound healing process.Inspec keywords: biomedical materials, enzymes, adhesion, fluorescence, polymer fibres, tissue engineering, wounds, nanofibres, cellular biophysics, molecular biophysics, gelatin, biochemistry, nanomedicine, field emission scanning electron microscopy, nanofabricationOther keywords: cell morphology, cell proliferation, efficient cocultivation, HFCs, ADSs, gelatin‐PLCL nanofiber, natural‐synthetic polymers, cocultured adipose‐derived stem cells‐human fibroblast cells, FESEM, fluorescent microscopy, MTS assay, quantitative real‐time polymerase chain reaction, collagen type I synthesis, collagen type III synthesis, cytokines, transforming growth factor‐β1, fibroblast growth factor‐basic growth factor‐β1, culture medium, enzyme‐linked immunosorbent assay assay, structural properties, toxicity analysis, cellular adhesion, physiological characteristics in vivo, wound healing     

Formation of (H+, Al+, Al2+) co-doped bayerite and gamma-Al2O3 plates from spinel-type related nanocondensates in water

The Al2O3 nanocondensates of spinel-type related structures, i.e., gamma- and theta-type with a significant internal compressive stress via pulsed laser ablation in water were subjected to prolonged dwelling in water to form columnar bayerite plates for further transformation as platy gamma-Al2O3. Transmission electron microscopic observations indicated the gamma-Al2O3 follows the crystallographic relationship (100)b//(011)gamma; [001]b//[111]gamma with relic bayerite (denoted as b). The gamma-Al2O3 also shows {111} twin/faults and rock salt-type domains due to dehydroxylation of bayerite which involves {1111} shuffling and disordering of the Al ions in the octahedral and tetrahedral sites. The combined evidences of X-ray photoelectron spectroscopy, vibrational spectroscopy and UV-visible absorbance indicated that the H+, Al+ and Al2+ co-doped bayerite and gamma-Al2O3 composite plates have a minimum band gap as low as approximately 5 eV for potential catalytic and electro-optical applications in water environment.     

Experimental investigation of different brines imbibition influences on co-and counter-current oil flows in carbonate reservoirs

Imbibition of water, as wetting phase in oil-wet fractured carbonate reservoirs, plays a key role in fluid flow be-tween matrix and fracture system. The type of injected seawater and its chemistry would profoundly influence the imbibition process. In this study, the impact of smart water (a brine that its ions have been adjusted to facil-itate oil recovery) and low salinity water on co-and counter-current imbibition processes for oil-wet carbonate cores has been experimentally investigated. The results show an increase of about 10％in oil recovery for co-and counter-currents for smart seawater imbibition compared to that of low salinity seawater. In addition, as a result of the influence of co-and counter-current on each other, by co-current removal from one core face, the counter-current in the other face would be intensified by as much as about 75％. A close examination of different lengths (5, 7 and 9 cm) of carbonate cores with the same permeability revealed that by decreasing porous medium length, the amount of counter-current producing oil would be decreased so that in the 5 cm core, counter current oil production will not happen. For similar core lengths by increasing permeability, the share of counter current flow would be decreased approximately 18％since the capillary pressure could not overcome non-wetting phase viscous forces. Considering the role of matrix length along with a modified brine (which is designed according to the matrix mixture) strengthen the relevant mechanisms to have more oil production so that the higher thick-ness of matrix causes the higher amount of co-current oil producing and consequently more total recovery.