Dual Transient Networks of Polymer and Micellar Chains: Structure and Viscoelastic Synergy

Dual transient networks were prepared by mixing highly charged long wormlike micelles of surfactants with polysaccharide chains of hydroxypropyl guar above the entanglement concentration for each of the components. The wormlike micelles were composed of two oppositely charged surfactants potassium oleate and n-octyltrimethylammonium bromide with a large excess of anionic surfactant. The system is macroscopically homogeneous over a wide range of polymer and surfactant concentrations, which is attributed to a stabilizing effect of surfactants counterions that try to occupy as much volume as possible in order to gain in translational entropy. At the same time, by small-angle neutron scattering (SANS) combined with ultrasmall-angle neutron scattering (USANS), a microphase separation with the formation of polymer-rich and surfactant-rich domains was detected. Rheological studies in the linear viscoelastic regime revealed a synergistic 180-fold enhancement of viscosity and 65-fold increase of the longest relaxation time in comparison with the individual components. This effect was attributed to the local increase in concentration of both components trying to avoid contact with each other, which makes the micelles longer and increases the number of intermicellar and interpolymer entanglements. The enhanced rheological properties of this novel system based on industrially important polymer hold great potential for applications in personal care products, oil recovery and many other fields.

Improved Gelation Performance of an Acidic Low-Polymer Loading Zirconium Cross-Linked CMHPG Fracturing Fluid by Surface Functionalized 1T-Phase Molybdenum Disulfide Nanosheets

The low and ultra-low permeability reservoirs in China, such as the Changqing, Jidong, and Daqing peripheral oil fields, often apply CO2 as a flooding medium to enhance oil recovery. A serial of water-rock interactions will be occurred among the CO2, formation rock, and formation water under the HT/HP conditions. The pH value of the formation will be converted to acidity accordingly. As a side effect, the traditional guar-based fracturing fluids in an alkaline range, such as the borate cross-linked hydroxypropyl guar gum (HPG), cannot result in an effective hydrofracturing operation due to the incompatibility. Consequently, developing an acidic fracturing fluid system with a satisfactory performance is an imperative. Acidic fracturing fluids, such as the zirconium cross-linked carboxymethyl hydroxypropyl guar gum (CMHPG), can protect the formation during the hydrofracturing process from the damage arising from the swelling and migration of the clay particles. However, the shortcomings of the uncontrollable viscosity growth and the irreversible shear-thinning behavior limit the large-scale use of the acidic fracturing fluids. In this work, a novel organic zirconium cross-linker synthesized in the laboratory was applied to control and delay the cross-link reaction under the acidic condition. The ligands coordinated to the zirconium center were the L-lactate and ethylene glycol. The thickener used was the CMHPG at a low loading of 0.3% (approximately 25 pptg). Meanwhile, the surface functionalized metallic phase (1T-phase) molybdenum disulfide (MoS2) nanosheets were employed to improve the rheological performance of the zirconium cross-linked CMHPG fracturing fluid. The modification reagent utilized was the L-cysteine. The morphology, structure, and property of the fabricated functionalized 1T-MoS2 (Cys-1T-MoS2) nanosheets were systematically characterized using the transmission electron microscopy (TEM), scanning electron microscopy (SEM), Raman spectroscopy, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), and thermogravimetric analysis (TGA) measurements. The results of the characterization tests demonstrated a successful functionalization of the 1T-MoS2 nanosheets with L-cysteine. Then, the effects of this new nanosheet-enhanced zirconium cross-linked CMHPG fracturing fluid systems with different cross-linker and nanosheet loadings on gelation performance were systematically assessed employing the Sydansk bottle testing method combined with a rheometer under the controlled-stress or controlled-rate modes. The results indicated that the nanosheet-enhanced fracturing fluid had a desirable delayed property. Compared with the blank fracturing fluid (without nanosheets), the nanosheet-enhanced fracturing fluid had a much better shear-tolerant and shear-recovery performance.

Study on gelation, temperature resistance and micromorphology of modified nano-ZrO2 crosslinked hydroxypropyl guar gum

In order to improve the temperature and shear resistance of fracturing fluid, a kind of nano-zirconium-boron crosslinker, which is different from the traditional zicral-boron crosslinker, is prepared using 4wt% borax, 50 v/v% glycerol, 8 v/v% triethanolamine and 40 v/v % acetylacetone as raw materials, and its chemical structure is characterized of by infrared spectroscopy and its performance, such as viscoelasticity, temperature and shear resistance and gel breaking property, have also been evaluated. The results show that firstly the elastic modulus of the fracturing system is much larger than the viscous modulus at frequency of 0.1–10 Hz, indicating that the fluid is a typical structural fluid. Secondly the fracture fluid crosslinked by nano-zirconium-boron crosslinker is sheared at 180 °C, 170 s−1 for 2 h, and the viscosity is maintained above 60 mPa.s. Finally viscoelasticity, gel breaking property and damage evaluation also meet the requirements of national standard code for Chinese. Analysis of the temperature resistance mechanism of the HPG fracturing fluid crosslinked by nano-zirconium-boron crosslinker shows that its connecting lines are thicker and stronger to make the fracturing fluid have better temperature and shear resistance.

Rheological and thermal stability of interpenetrating polymer network hydrogel based on polyacrylamide/hydroxypropyl guar reinforced with graphene oxide for application in oil recovery

The purpose of the present work is to enhance the thermal stability and rheological properties of semi-interpenetrating polymer network (IPN) hydrogel based on partially hydrolyzed polyacrylamide/hydroxypropyl guar (HPAM/HPG) nanocomposite reinforced with graphene oxide (GO), at temperatures (200 and 240 °F) for use in oil recovery applications. FTIR spectra of the IPN nanocomposite hydrogels revealed interactions of GO with HPAM/HPG chains. An increase in the viscosity is also observed from the rheological study. Moreover, IPN and its nanocomposite hydrogels exhibited non-Newtonian behavior. The decline of viscosity of IPN nanocomposite hydrogels was observed with an increase in the temperature from 200 to 240 °F but was still higher than IPN hydrogel without GO. Dispersion of GO through the HPAM/HPG hydrogel matrix was evaluated by SEM morphology and electrical conductivity. The IPN nanocomposite hydrogels showed high viscosity stability, thermal stability, and flow activation energy as compared to IPN hydrogel without GO. Therefore, the addition of 0.1 wt.% of GO to the HPAM/HPG matrix is suitable to create a cross-linked polymer solution with improved properties which may be beneficial for use in oil recovery applications.

Robust Conductive Hydrogels with Ultrafast Self-Recovery and Nearly Zero Response Hysteresis for Epidermal Sensors

Robust conductive hydrogels are in great demand for the practical applications of smart soft robots, epidermal electronics, and human–machine interactions. We successfully prepared nanoparticles enhanced polyacrylamide/hydroxypropyl guar gum/acryloyl-grafted chitosan quaternary ammonium salt/calcium ions/SiO2 nanoparticles (PHC/Ca2+/SiO2 NPs) conductive hydrogels. Owing to the stable chemical and physical hybrid crosslinking networks and reversible non-covalent interactions, the PHC/Ca2+/SiO2 NPs conductive hydrogel showed good conductivity (~3.39 S/m), excellent toughness (6.71 MJ/m3), high stretchability (2256%), fast self-recovery (80% within 10 s, and 100% within 30 s), and good fatigue resistance. The maximum gauge factor as high as 66.99 was obtained, with a wide detectable strain range (from 0.25% to 500% strain), the fast response (25.00 ms) and recovery time (86.12 ms), excellent negligible response hysteresis, and good response stability. The applications of monitoring the human’s body movements were demonstrated, such as wrist bending and pulse tracking.

Remotely Self-Healable, Shapeable and pH-Sensitive Dual Cross-Linked Polysaccharide Hydrogels with Fast Response to Magnetic Field

The development of actuators with remote control is important for the construction of devices for soft robotics. The present paper describes a responsive hydrogel of nontoxic, biocompatible, and biodegradable polymer carboxymethyl hydroxypropyl guar with dynamic covalent cross-links and embedded cobalt ferrite nanoparticles. The nanoparticles significantly enhance the mechanical properties of the gel, acting as additional multifunctional non-covalent linkages between the polymer chains. High magnetization of the cobalt ferrite nanoparticles provides to the gel a strong responsiveness to the magnetic field, even at rather small content of nanoparticles. It is demonstrated that labile cross-links in the polymer matrix impart to the hydrogel the ability of self-healing and reshaping as well as a fast response to the magnetic field. In addition, the gel shows pronounced pH sensitivity due to pH-cleavable cross-links. The possibility to use the multiresponsive gel as a magnetic-field-triggered actuator is demonstrated.