Rheometer

About: Rheometer is a research topic. Over the lifetime, 5759 publications have been published within this topic receiving 125849 citations.

Thermal conductivity and rheological studies for Cu–Zn hybrid nanofluids with various basefluids

Abstract: The trend toward renewable lubricant technology is now irreversible; an eco-friendly cutting fluid will go along with machining to achieve relative sustainability. Eco-friendly nanofluids are developed in this work and compared with traditional cutting fluids used for heat transfer. In this work, in-situ novel hybrid nanoparticles of Cu–Zn (50:50) alloy were synthesized. The stability of the hybrid nanofluids was carried out using photo capturing method and DLS method. The flash point was measured using Pensky–Martens open cup apparatus as per ASTM D6450. The thermal conductivity and rheological studies were carried out using KD-2 Pro and Rheometer. The results illustrate that the hybrid nanofluids exhibited stability for 72 h and then the agglomeration of particles starts and by 168 h almost all the particles tend to settle down. Nanofluids with vegetable oil as basefluid showed better increment in flash point, thermal conductivity and showed marginal less stability. Vegetable oil behaved as Newtonian fluid and the change in viscosity with application of shear was less noticed compared with other two fluids. On the basis of integrated study of thermal conductivity and viscosity, in the point of cost and higher relative thermal conductivity to relative viscosity for effective heat transfer vegetable oil based nanofluid showed better results.

In situ rheology of Staphylococcus epidermidis bacterial biofilms

Abstract: We developed a method to grow Staphylococcus epidermidis bacterial biofilms and characterize their rheological properties in situ in a continuously fed bioreactor incorporated into a parallel plate rheometer. The temperature and shear rates of growth modeled bloodstream conditions, a common site of S. epidermidis infection. We measured the linear elastic (G′) and viscous moduli (G′′) of the material using small-amplitude oscillatory rheology and the yield stress using non-linear creep rheology. We found that the elastic and viscous moduli of the S. epidermidis biofilm were 11 ± 3 Pa and 1.9 ± 0.5 Pa at a frequency of 1 Hz (6.283 rad per s) and that the yield stress was approximately 20 Pa. We modeled the linear creep response of the biofilm using a Jeffreys model and found that S. epidermidis has a characteristic relaxation time of approximately 750 seconds and a linear creep viscosity of 3000 Pa s. The effects on the linear viscoelastic moduli of environmental stressors, such as NaCl concentration and extremes of temperature, were also studied. We found a non-monotonic relationship between moduli and NaCl concentrations, with the stiffest material properties found at human physiological concentrations (135 mM). Temperature dependent rheology showed hysteresis in the moduli when heated and cooled between 5 °C and 60 °C. Through these experiments, we demonstrated that biofilms are rheologically complex materials that can be characterized by a combination of low modulus (∼10 Pa), long relaxation time (∼103 seconds), and a finite yield stress (20 Pa). This suggests that biofilms should be viewed as soft viscoelastic solids whose properties are determined in part by local environmental conditions. The in situ growth method introduced here can be adapted to a wide range of biofilm systems and applied over a broad spectrum of rheological and environmental conditions because the technique minimizes the risk of irreversible, non-linear deformation of the microbial specimen before analysis.

Surface Tearing and Wall Slip Phenomena in Extrusion of Highly Filled HDPE/Wood Flour Composites

Abstract: The extrudate surface tearing of highly filled high-density polyethylene (HDPE)/wood flour composites has been investigated in relation to the rheological properties and the wall slip phenomenon in capillary dies. Rotational and capillary rheometers were employed to measure the rheological properties. Mooney analysis was used for determination of wall slip velocity. The results showed considerable increase of storage modulus, dynamic and shear viscosity with increasing wood flour loading. It was also found that all wood filled composites did not obey the Cox–Merz rule. The wall slip velocity depends on wood filler content and shear rate. Generally, with increasing shear rate the slip velocity sharply increases leading to plug-like flow. It was observed that the surface of the extrudates becomes smoother with increase in shear rate and wood flour content. POLYM. ENG. SCI., 46:1204 –1214, 2006. © 2006 Society of Plastics Engineers

The rheological behaviour of concentrated dispersions of graphene oxide

Abstract: The rheological behaviour of concentrated aqueous dispersions of graphene oxide (GO) was studied as a model system and then compared to those of GO in poly(methyl methacrylate) (PMMA). Dynamic and steady shear tests were conducted using a parallel plate rheometer. The aqueous system behaved as a reversibly flocculated dispersion with linear viscoelastic regions (LVR) extending up to strains of 10 %. Dynamic frequency sweeps conducted within the LVR showed a classic strong-gel spectrum for high concentrations. Under steady shear, the dispersions shear-thinned up to a Peclet number (Pe) <1, followed by a power law at higher Pe. The dispersions were thixotropic and recovered their structure after 60 min rest. The change in rheological properties of the PMMA upon the addition of the GO was less pronounced possibly due to the absence of hydrogen bonding; a relatively small increase in viscosity was found, which is encouraging for the melt processing of graphene composites.