Effect of contact geometry on the friction of acrylamide hydrogels with different surface structures

Polyacrylamide (PAAm) hydrogels with brush-covered or crosslinked surfaces were produced and their tribological behavior was studied over a wide range of sliding speeds for two different contact geometries: sphere-on-flat and flat-pin-on-flat. Irrespective of the contact geometry, the brushy hydrogel surfaces displayed up to an order of magnitude lower coefficients of friction μ (COF) compared to the crosslinked surfaces, even achieving superlubricity (μ < 0.01). In general, a hydrogel sphere showed a lower coefficient of friction than a flat hydrogel pin at a similar contact pressure over the entire range of sliding speeds. However, after normalizing the friction force by the contact area, the shear stress of hydrogels with either crosslinked or brushy surfaces was found to be similar for both contact geometries at low speeds, indicating that hydrogel friction is unaffected by the contact geometry at these speeds. At high sliding speeds, the shear stress was found to be lower for a sphere-on-flat configuration compared to a flat-pin-on-flat configuration. This can be attributed to the larger equivalent hydrodynamic thickness due to the convergent inlet zone ahead of the sphere-on-flat contact, which presumably enhances the water supply in the contact, promotes rehydration, and thus reduces the friction at high sliding speeds compared to that measured for the flat-pin-on-flat contact.

Evaluation of chemical contamination of surface water and groundwater in the landfill city of Ardabil

Todays in our country the problem of waste disposal and the effects of entry alluvial aquifer their leachate and pollution of aquifers by hydrodynamic thickness in the direction of groundwater flow is highly regarded analytical descriptive study was conducted. To this purpose, the concentration of heavy metals plumb and cadmium and some physicochemical and biological parameters of surface water and groundwater around the landfill city of Ardabil in two time periods in spring 2015 and summer seasons were measured. Sampling, preparation and analysis of samples in accordance with the standard method of station 10 to within 5.5 km of landfill were Ardabil. Measurement of heavy metals, plumb and cadmium by atomic absorption were performed. The Results were analyzed by SPSS software, for the comparison of each parameter with drinking water standards and Agriculture tests comparing the average (T-TEST) was used. The results showed that groundwater and surface water of heavy metals, non-contaminated area and their results are below international standards. The mean values ??of microbiological and physicochemical parameters other than normal turbidity level and at the level of 1% were significantly lower than international standards.