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1. Investigation of the flexural and thermomechanical properties of nanoclay/graphene reinforced carbon fiber epoxy composites

   https://doi.org/10.1557/jmr.2019.302  

   Tareq, Md Sarower; Zainuddin, S.; Woodside, E.; Syed, F. (November 2019, Journal of Materials Research)

   null (Ed.)

   Flexural and thermomechanical properties of the epoxy-based carbon fiber composites (CFCs) on addition of single and binary nanoparticles (nanoclay and graphene) have been investigated. It was found that nanoclay acts more effectively in increasing the stiffness of the CFCs, whereas graphene is more effective in achieving higher strength. Nanoclay-added samples exhibited highest flexural (64.5 GPa) and storage (25.3 GPa) modulus among all types. Graphene-added samples showed highest improvement (by 21%) in flexural strength and exhibited most stable thermomechanical properties with highest energy dissipation capability (3.1 GPa loss modulus) in flexural test and dynamic mechanical analysis (DMA), respectively. By contrast, addition of binary nanoparticles reduced the stiffness and significantly increased the strain to failure (42%) of the composites. Optical microscopy and scanning electron microscopy indicated that addition of nanoparticles significantly reduced delamination and matrix cracking of the CFCs because of strong interfacial bonding and toughened matrix, respectively. 

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2. Post-synthesis modification of slide-ring gels for thermal and mechanical reconfiguration

   https://doi.org/10.1039/D0SM02260H  

   Dikshit, Karan; Bruns, Carson J. (May 2021, Soft Matter)

   Ring-sliding behavior in polyrotaxanes imbues gels, elastomers, and glasses with remarkable stress-dissipation and actuation properties. Since these properties can be modulated and tuned by structural parameters, many efforts have been devoted to developing synthetic protocols that define the structures and properties of slide-ring materials. We introduce post-synthetic modifications of slide-ring gels derived from unmodified α-cyclodextrin and poly(ethylene glycol) polyrotaxanes that enable (i) actuation and control of the thermo-responsive lower critical solution temperature (LCST) behavior of ring-modified slide-ring hydrogels, and (ii) chemically bonding separate gels into hybrid or shape-reconfigured macro-structures with a slide-ring adhesive solution. The mechanical properties of the post-modified gels have been characterized by shear rheology and uniaxial tensile tests, while the corresponding xerogels were characterized by wide-angle X-ray scattering. These demonstrations show that post-synthetic modification offers a practical solution for re-configuring the properties and shapes of slide-ring gels. 

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3. Can AFM be used to measure absolute values of Young's modulus of nanocomposite materials down to the nanoscale?

   https://doi.org/10.1039/D0NR02314K  

   Liu, Yuke; Sokolov, Igor; Dokukin, Maxim E.; Xiong, Yongqiang; Peng, Ping'an (June 2020, Nanoscale)

   At present, a technique potentially capable of measuring values of Young's modulus at the nanoscale is atomic force microscopy (AFM) working in the indentation mode. However, the question if AFM indentation data can be translated into absolute values of the modulus is not well-studied as yet, in particular, for the most interesting case of stiff nanocomposite materials. Here we investigate this question. A special sample of nanocomposite material, shale rock, was used, which is relatively homogeneous at the multi-micron scale. Two AFM modes, force-volume and PeakForce QNM were used in this study. The nanoindentation technique was used as a control benchmark for the measurement of effective Young's modulus of the shale sample. The indentation rate was carefully controlled. To ensure the self-consistency of the mechanical model used to analyze AFM data, the model was modified to take into account the presence of the surface roughness. We found excellent agreement between the average values of effective Young's modulus calculated within AFM and the nanoindenter benchmark method. At the same time, the softest and hardest areas of the sample were seen only with AFM. 

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4. Low‐weight fractions of graphene and hydroxyapatite enhance mechanics in photocured methacrylate adhesives

   https://doi.org/10.1002/app.50442  

   Alabdali, Zinah N.; Irizarry, Emanuel; Reiter, Mary P.; Ashraf, Ali; Lynch‐Branzoi, Jennifer K.; Mann, Adrian B. (January 2021, Journal of Applied Polymer Science)

   Abstract In many applications, it is desirable for photocured adhesives to have high‐mechanical strength in the cured state, but relatively low viscosity when liquid. This was achieved by adding less than 0.5 wt% hydroxyapatite and graphene to methyl methacrylate with diurethane dimethacrylate (UDMA‐MMA). Nanoindentation shows hardness increasing by 30–40% and indentation modulus by >30% compared to UDMA‐MMA on its own. Rheometry shows only a small increase in uncured viscosity for the liquid state. The additives affect the optical properties, mobility of free radicals, photocuring, and degree of conversion, the effects of which are seen in Fourier transform infrared and micro‐Raman spectra. Thermographic images taken during curing show that the additives impact the photocuring process. In addition, changes in intermolecular bonding are seen in the vibrational spectra when the additives are present. The enhanced mechanical properties are attributed to the observed changes in photocuring and bonding. 

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5. Settling of barite particles in oil-based drilling fluids

   Kalaga, D. V. (May 2019, 10th International Conference on Multiphase Flow, ICMF 2019)

   Controlling the downhole pressure is an important parameter for successful and safe operation of the drilling operation. The drilling fluid density is an important design parameter for preventing the fluid formation and gas entering the wellbore. Several types of weighting agents, barite in the present work, are added to maintain the desired density of the drilling fluid. The uneven density distribution of the barite, which can lead to a density variation as high as 0.5 kg/L (4 lbs/gal) (Tehrani et al. 2011), is caused by the settlement of barite or other weighting materials in the well bore. This paper presents the rheological properties of the drilling fluid measured using a rheometer and estimated rates of barite particle settlement in an oil-based drilling fluid using gamma-ray densitometry for the first time. Experiments were performed in a static cell (with no shear) and in a Taylor Couette cell (with low shear stress). Further, an attempt has also been made to relate the rate of barite particle settling to the rheological properties of the drilling fluid. 

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