Defoaming and Toughening Effects of Highly Dispersed Graphene Oxide Modified by Amphoteric Polycarboxylate Superplasticizer on Oil Well Cement.

The aggregation of graphene oxide (GO) during the hydration process limits its wide application. Polymer superplasticizers have been used to improve the dispersion state of GO due to their adsorption and site-blocking effects, though the formation of a large amount of foam during the mixing process weakens the mechanical properties of cement. A highly dispersed amphoteric polycarboxylate superplasticizer-stabilized graphene oxide (APC/GO) toughening agent was prepared by electrostatic self-assembly. Results demonstrate that the APC/GO composite dispersed well in a cement pore solution due to the steric effect offered by the APC. Additionally, the well-dispersed GO acted as an antifoaming agent in the cement since GO nanosheets can be absorbed at the air-liquid interface of APC foam via electrostatic interactions and eliminate the air-entraining effect. The well-dispersed APC/GO sheets promoted cement hydration and further refined its pore structure owing to the nucleation effect. The flexural and compressive strength of the cement containing the APC/GO composite were enhanced by 21.51% and 18.58%, respectively, after a 7-day hydration process compared with a blank sample. The improved hydration degree, highly polymerized C-S-H gel, and refined pore structure provided enhanced mechanical properties.

Effects of Hybrid Graphene Oxide-Nanosilica on Calcium Silicate Hydrate in the Simulation Environment and Cement.

This research aims to investigate the synergistic reinforcing mechanisms of chemically combined graphene oxide and nanosilica (GO-NS) in the structure of calcium silicate hydrate (C-S-H) gels compared with physically combined GO/NS. The results confirmed that the NS chemically deposited on the GO surface formed a coating to keep GO from aggregation, while the connection between GO and NS in GO/NS was too weak to prevent GO from clumping, making GO-NS better dispersed than GO/NS in pore solution. When applied to cement composites, the incorporation of GO-NS enhanced the compressive strength by 27.3% after 1-day hydration compared to that of the plain sample. This is because that GO-NS generated multiple nucleation sites at early hydration, reduced the orientation index of calcium hydroxide (CH), and increased the polymerization degree of C-S-H gels. GO-NS acted as the platforms for the growing process of C-S-H, enhancing its interface bonding strength with C-S-H and increasing the connection degree of the silica chain. Furthermore, the well-dispersed GO-NS was prone to insert in C-S-H and induced deeper cross-linking, thereby refining the microstructure of C-S-H. All these effects on hydration products resulted in the mechanical improvement of cement.

Dispersion Mechanism of Styrene-Butadiene Rubber Powder Modified by Itaconic Acid and Its Toughening Effect on Oil Well Cement.

Styrene-butadiene rubber (SBR) has been extensively applied to enhance the toughness of hardened cement. The instability of existing liquid latex leads to difficulties in storage and transportation, and even performance regression. Thus, the well-dispersed carboxylated butylbenzene (SISBR) latex powders were fabricated through the seed emulsion polymerization of liquid polybutadiene (LPB), styrene (St), itaconic acid (IA), and sodium p-styrenesulfonate (SSS) to overcome the difficulties. The dispersion performance of latex powders with various IA amounts was quantitatively evaluated using particle size distribution, zeta potential, and ultraviolet-visible spectrophotometry. Results showed that the carboxylic ionic (COO-) from IA enhanced the dispersing abilities of SISBR latex powders, which ensured the uniform distribution in water. Based on this, the influence of latex powder on cement was assessed mainly by fluidity, isothermal heat flow calorimetry, X-ray diffraction (XRD), and triaxial mechanical testing. Results showed the fluidity and dispersion performance of cement were improved with more IA in latex, while the hydration of cement was retarded due to excessive adsorption of carboxyl (-COOH) groups in IA. Triaxial mechanical testing showed that cement with SISBR-3 (latex containing 3% IA) exhibited the minimal elastic modulus of 3.16 GPa, which was lower than that of plain cement (8.34 GPa).

Objective evaluation of wearable thermoelectric generator: From platform building to performance verification.

Wearable thermoelectric generators can harvest heat from the human body to power an intelligent electronic device, which plays an important role in wearable electronics. However, due to the complexity of human skin, there is still no unified standard for performance testing of wearable thermoelectric generators under wearable conditions. Herein, a test platform suitable for a wearable thermoelectric generator was designed and built by simulating the structure of the arm. Based on the biological body temperature regulation function, water flow and water temperature substitute blood flow and blood temperature, the silicone gel with some thickness simulates the skin layer of the human arm, thus achieving the goal of adjusting the thermal resistance of human skin. Meanwhile, the weight is used as the contact pressure to further ensure the reliability and accuracy of the test data. In addition, the environment regulatory system is set up to simulate the outdoor day. Actually, the maximum deviation of the performance of the thermoelectric generator worn on the test platform and human arm is ∼5.2%, indicating the accuracy of objective evaluation.