Strong Viscoelasticity Research Articles

High-performance cellulose/thermoplastic polyurethane composites enabled by interaction-modulated cellulose regeneration

Strong interfacial adhesion between cellulose and other polymers is critical to achieve the properties required for specific applications in composite materials. Here, we developed a method for the simultaneous homogeneous dissolution of cellulose and thermoplastic polyurethane (TPU) in 1,8-diazabicyclo (5.4.0) undec-7-ene levulinate/dimethyl sulfoxide ([DBUH]Lev/DMSO) solvent. This process is essential for preparing cellulose/TPU composite films and fibers through interaction-modulated cellulose regeneration. Both cellulose and TPU can be easily dissolved together in [DBUH]Lev/DMSO solvent under mild conditions. The resulting cellulose/TPU solutions exhibited strong temperature sensitivity, shear-thinning behavior and viscoelasticity, making them suitable for cast films and continuous spinning. More importantly, research findings, including density functional theory calculations and experimental characterization, confirmed the high compatibility and interaction modulability of cellulose and TPU in the composite films. The representative C90T10 sample (cellulose/TPU, 90/10) showed high transparency (90 % at 800 nm) and excellent mechanical properties (tensile strength: 176 MPa; elongation at break: 8.1 %). Additionally, the maximum tensile strength and elongation at the break of the composite fiber from C90T10 were 214 MPa and 48.1 %, respectively. This method may provide a feasible approach to design and produce homogeneous environmentally friendly composites of cellulose and other polymers at the molecular level.

Cyclic Electrogravimetry Reveals Details of Copper Electrodeposition in the Presence of Additives

Copper electroplating was studied based on cyclic voltammetry combined with a new type of acoustic microgravimetry. The instrument operates similarly to a quartz crystal microbalance with dissipation monitoring (EQCM-D), meaning that it reports shifts in resonance frequency, Δf, and half bandwidth, ΔΓ, on several overtones. Compared to the existing instruments, the time resolution was improved by a factor of 10 down to 10 ms using multifrequency lockin amplification. The frequency noise after accumulation was reduced below 10 mHz ≙ 0.12 ng/cm2 ≙ 0.14 pm (assuming ρ = 8.96 g/cm3) by modulating the electrode potential and averaging of Δf and ΔΓ. Mostly, Δf and ΔΓ are in line with the Sauerbrey prediction (Δf/n ≈const. and ΔΓ/n < -Δf/nwith n the overtone order). Small unsystematic deviations between overtones due to compressional wave effects are seen but no evidence for strong roughness or viscoelasticity. Further, the Faraday efficiency is almost unity, meaning that Δf is close to the expectations derived from the electrical current. The improved sensitivity enables to determine the time derivative of the frequency shift, which is equal to an apparent mass transfer rate that can be compared to the current directly. Again, small deviations are seen for bulk deposition and stripping. These go back to weak roughness effects most pronounced in the initial phase of bulk deposition and, also, to the presence of a Cu(I) intermediate during dissolution. When adding benzotriazole (BTA) or thiourea (TU) as plating additives, the gravimetric and the voltammetric response changes. For BTA, the deviations between mass transfer rate and current vanish indicative of decreased roughness. For TU additional features appear, related to a potential-dependent adsorption of TU and to increased underpotential deposition (UPD). In the presence of TU, the electrode-electrolyte interface displays viscoelasticity, evident by the bandwidth increases during deposition.[1] Caption: Currents, time derivatives of the frequency shift, and bandwidth shift obtained during copper electrodeposition without additives (A), in the presence of 10 µM benzotriazole (B), and in the presence of 10 µM thiourea (C). Reprinted with permission from Reference [1].

Effect of protease hydrolysis pretreatment on extruder response and the structural characteristics of high-moisture plant-protein extrudates

This study aimed to investigate the effect of protease hydrolysis pretreatment (PHP) on extruder response and the structural characteristics of high-moisture plant-protein extrudates. The results showed that specific mechanical energy of the extruder decreased from 147.06 kJ/kg to 116.14 kJ/kg, which reduced the energy consumption of the extruder and was beneficial for the application of hydrated wheat gluten with strong viscoelasticity during the extrusion process. Texturization degree that characterized the fibrous structure formation of high-moisture plant-protein extrudates reduced from 1.70 to 1.05. The hardness and chewiness decreased, while the springiness of the extrudates increased. Moderate PHP weakened the cross-linking strength and viscoelasticity of the extrudates, which can improve the problem of the excessively dense texture of high-moisture plant-protein extrudates. Meanwhile, PHP improved protein extractability and increased immobilized water and free water content in the extrudates.

Oleic acid-modified layered double hydroxide for Pickering emulsion: (II) Emulsification behavior

Layered double hydroxides (LDHs) are plate-like particles, being potential Pickering emulsifiers. Surfactant modification can regulate their surface properties, and thus can influence their emulsifying behavior. However, there is a lack of full understanding on the correlation between the surface modification of LDHs and their emulsification behavior. In the current work, one LDH and five oleic acid (OA)-modified LDH (LDH@OA) samples were chosen as emulsifiers, and emulsifying tests for pentadecane (oil)-water mixtures were performed at different oil/water volume ratios (1/9−9/1) and solid dosages (Cs, 1.00−10.0 g/L). The type, droplet size, and stability of emulsions were determined. The interfacial adsorption energy (ΔGad) and the coverage of solid particles for droplet surfaces (Rcov) were estimated, and the oil-water interfacial tension and viscoelastic moduli were determined. Results showed that LDH and LDH@OA particles can emulsify the oil-water mixture, forming coalescence-stable Pickering emulsions. The emulsion type is only determined by the solid wettability, independent of the oil/water ratio and Cs. The OA modification can change the wettability of LDH from hydrophilic to hydrophobic, thereby can regulate the type of emulsions from oil-in-water (O/W) to water-in-oil (W/O). Enhancing solid hydrophobicity decreases droplet sizes and increases interfacial viscoelasticity, thus improving the stability of emulsions. The droplet size decreases with an increase in Cs, while it increases with an increase in the volume fraction of dispersed liquid, both independent of the type of emulsions. The solid particles can irreversibly adsorb at the oil-water interface (with |ΔGad|/kT > 107), forming interfacial particle-layers with Rcov ∼0.4 and strong viscoelasticity, which endow the Pickering emulsions with extremely strong stability against coalescence.

Viscoelasticity, stiffness gradient and their effects on adhesion of an epoxy shape memory polymer

The shape memory polymer based adhesives have demonstrated excellent programmable switchable adhesion, in which the material properties play an important role. Here, the viscoelasticity, stiffness gradient, and their effects on adhesion of an epoxy shape memory polymer (ESMP) were studied. The ESMP sample and polydimethylsiloxane control sample were fabricated firstly by mold casting and curing techniques. The sample was fixed on an electric heating plate with double-sided tape to conduct the adhesion measurements against a hemispherical glass indenter under different temperature and displacement conditions by using an adhesion tester and the temperature measurements on the double-sided tape and ESMP sample surfaces by using a digital thermodetector. Based on the measured force–displacement–time data, the hysteresis behavior and internal dissipation were evaluated; the peak force relaxation was studied; the reduced modulus was calculated and the stiffness gradient features were evaluated. The results show that the ESMP sample exhibits strong viscoelasticity and significantly enhanced adhesion that strongly depends on the compressive displacement in the glass-rubber transition zone near it is glass transition temperature ( Tg ), while weaker viscoelasticity and lower adhesion in the soft rubbery state. The reduced modulus of the ESMP sample obviously decreases with the increasing compressive displacement at a preset temperature below 70 °C. It is found that there exists a linear relation between the pull-off force, effective work of adhesion, reduced modulus, and contact area. This study helps deeply understand the material properties and adhesion mechanism of the ESMP, which can guide the design of switchable adhesives.

High internal phase emulsions stabilized by pea protein isolate modified by ultrasound and pH-shifting: Effect of chitosan self-assembled particles

This study unveils an effective and simple approach to formulate solid-sate high internal phase emulsions (HIPEs) with strong viscoelasticity and high stability, using modified pea protein isolate (MPPI) as emulsifier and self-assembled chitosan (CS) particles as cofactor to stabilize the system. The results demonstrated that native pea protein isolate (PPI) has poor emulsification, whereas PPI modified by ultrasound and pH-shifting can successfully stabilize HIPEs. Incorporation of CS particles further increases the viscoelasticity and self-supporting properties of HIPEs. Micromorphological and microrheological analyses indicated that CS particles could enhance the interfacial adsorption of proteins and fill in the interdroplet network structure. Decreased droplet size, improved interfacial film strength, and improved viscoelasticity endow HIPEs with better properties, such as higher self-supporting capacity, improved plasticity, and superior stability, which are regulated by the CS particle level. These improvements provide the opportunity for HIPEs as 3D printing inks to print high-resolution, self-supporting products. In addition, the constructed HIPEs showed better tolerance to various processing environments such as centrifugation, storage, and heating and, remain stable at 0–400 mM NaCl and pH settings of 6.5–7.5. These findings promote the constructed HIPEs as potential solid fat substitutes for meat products.

Sonochemical Degradation of Gelatin Methacryloyl to Control Viscoelasticity for Inkjet Bioprinting.

Inkjet printing enables the mimicry of the microenvironment of natural complex tissues by patterning cells and hydrogels at a high resolution. However, the polymer content of an inkjet-printable bioink is limited as it leads to strong viscoelasticity in the inkjet nozzle. Here it is demonstrated that sonochemical treatment controls the viscoelasticity of a gelatin methacryloyl (GelMA) based bioink by shortening the length of polymer chains without causing chemical destruction of the methacryloyl groups. The rheological properties of treated GelMA inks are evaluated by a piezo-axial vibrator over a wide range of frequencies between 10 and 10000Hz. This approach enables to effectively increase the maximum printable polymer concentration from 3% to 10%. Then it is studied how the sonochemical treatment effectively controls the microstructure and mechanical properties of GelMA hydrogel constructs after crosslinking while maintaining its fluid properties within the printable range. The control of mechanical properties of GelMA hydrogels can lead fibroblasts more spreading on the hydrogels. A 3D cell-laden multilayered hydrogel constructs containing layers with different physical properties is fabrictated by using high-resolution inkjet printing. The sonochemical treatment delivers a new path to inkjet bioprinting to build microarchitectures with various physical properties by expanding the range of applicable bioinks.

Thickening effects of Ca2+ on apple high-methoxyl pectin: Dependences on Ca2+ concentration and the degree of esterification

To explore the application potential of high-methoxyl pectin (HMP), the effects of Ca2+ (0.00%–0.50%, w/w) on the behavior of three apple HMPs with degrees of esterification (DE) of 60.6% (AP1), 66.1% (AP1) and 72.4% (AP3) were investigated. The results in zeta potential, turbidity, and fluorescence characteristics revealed that Ca2+ promoted the aggregation of HMP molecules. In steady shear measurements, the incorporation of Ca2+ substantially increased the viscosity and thixotropy of HMP systems and changed their shear-thinning behavior in a case-specific manner. In dynamic shear measurements, the frequency sweep revealed strong viscoelasticity of AP1 at Ca2+ concentrations of 0.35% and 0.50% (w/w) and defined other HMP-Ca2+ systems as weak gels or concentrated solutions, while the temperature sweep uncovered that the enthalpy-dominated elasticity of AP1-Ca2+ system, while the facultative enthalpic and entropic nature of the network formation in AP2-Ca2+ system. For the AP3-Ca2+ system, the viscous modulus was entropic, but the elastic modulus was first entropic and then enthalpic upon cooling. Fundamentally, the incorporation of Ca2+ substantially affected the micelles formation and network construction as well as the interactions involved in these systems. All of these changes highly depended both on the DE value of pectin and the concentration of Ca2+. The results concluded herein are expected to encourage the application of HMP in acid- and sugar-restricted food products.

The most promising microneedle device: present and future of hyaluronic acid microneedle patch

Microneedle patch (MNP) is an alternative to the oral route and subcutaneous injection with unique advantages such as painless administration, good compliance, and fewer side effects. Herein, we report MNP as a prominent strategy for drug delivery to treat local or systemic disease. Hyaluronic acid (HA) has advantageous properties, such as human autologous source, strong water absorption, biocompatibility, and viscoelasticity. Therefore, the Hyaluronic acid microneedle patch (HA MNP) occupies a large part of the MNP market. HA MNP is beneficial for wound healing, targeted therapy of certain specific diseases, extraction of interstitial skin fluid (ISF), and preservation of drugs. In this review, we summarize the benefits of HA and cross-linked HA (x-HA) as an MNP matrix. Then, we introduce the types of HA MNP, delivered substances, and drug distribution. Finally, we focus on the biomedical application of HA MNP as an excellent drug carrier in some specific diseases and the extraction and analysis of biomarkers. We also discuss the future development prospect of HA MNP in transdermal drug delivery systems (TDDS).

Effect of emulsification methods on the physicochemical properties of emulsion stabilized by calcium carbonate and sodium alginate.

Our lab’s studies have found that heavy calcium carbonate (CaCO3) with sodium alginate (SA) can synergistically stabilize Pickering emulsion. However, there were significant differences in the flow characteristics of the emulsions obtained by different preparation methods during storage. Herein, in this current work, Pickering emulsions were prepared by two-step emulsifying method (SA was added into the primary emulsion stabilized by CaCO3 for secondary shearing, M1) and one-step emulsifying method (oil phase was added to homogeneous dispersed CaCO3-SA solution for one-step shearing, M2), respectively. The particle size, microstructure, rheology and microrheological properties of these two kinds of emulsions and the interaction of CaCO3 with SA were analyzed. The results showed that the droplet size of M1 emulsion was 21.78–49.62 μm, and that of M2 emulsion was 6.50–11.87 μm. M1 emulsion had stronger viscoelasticity, and could transform into a gel state during storage. However, M2 emulsion remained in flow condition all the time which was related to the interaction between SA and CaCO3 in the aqueous phase.

The electrical response and self-sensing of the fully flexible PVC gel actuator based on flexible electrodes

There has recently been a substantial increase in interest in research on PVC gel actuators because of its numerous advantages over traditional actuators, such as low mass density, large actuation strain, great compliance, and simple manufacturing. However, the current PVC gel actuator is mainly based on the research of rigid electrodes, and there are few researches based on flexible electrodes. In this paper, a fully flexible actuator based on PVC gel film and carbon grease electrode has been prepared. The mechanical properties of the prepared PVC gels with different plasticizer ratios were tested. Three commonly used hyperelastic models (Neo-Hookean, Mooney-Rivlin and Yeoh models) were used to characterize the mechanical properties of PVC gels, and only the Yeoh model was found to be better for the characterization of the mechanical properties of PVC gels. In addition, we used the Prony series to successfully characterize the viscoelasticity of PVC gels. Then, the fully flexible PVC gel actuator (FFPGA) with long-time static and dynamic response characteristics was studied. It was found that the FFPGA has strong viscoelasticity when working. Finally, we proposed to simplify the FFPGA into a capacitor and designed a high-pass filter in the driving circuit. The self-sensing function of the FFPGA was achieved by superimposing a high-frequency low-voltage sensing signal on the low-frequency high-voltage driving signal as the input signal.

Effects of M/G Ratios of Sodium Alginate on Physicochemical Stability and Calcium Release Behavior of Pickering Emulsion Stabilized by Calcium Carbonate.

The gel properties of sodium alginate (SA) have been revealed to be strongly correlated with its ratio of D-mannuronate to L-guluronate (M/G ratio). Herein, we focused on SA with different M/G ratios to conduct an in-depth study on the effect of the M/G ratio difference on physicochemical stability and calcium release behavior of the Pickering emulsion stabilized by calcium carbonate (CaCO3). The oil phase was added to the aqueous phase, prepared by SA with different M/G ratios (2.23, 0.89, and 0.56) and CaCO3, for one-step shearing to obtain the E1, E2, and E3 emulsions, respectively. The results of the particle size, microstructure, long-term stability, rheological, and microrheological properties of the emulsions showed that the E3 emulsion, prepared by SA with a smaller M/G ratio, had a smaller particle size and has remained in a flow condition during the long-term storage, while the E1 and E2 emulsions had a gelation behavior and a stronger viscoelasticity. Moreover, the emulsion, as a liquid calcium supplement, is not only convenient for oral intake while meeting the calcium needs of the body, but also controls the release of Ca2+. The calcium release of the emulsions in a simulated gastric environment demonstrated that the calcium release ratio increased with the decrease of SA concentration, with the increase of M/G ratio, and with the decrease of oil phase volume.

Dynamic behaviors and mechanisms of fluid-fluid interaction in low salinity waterflooding of carbonate reservoirs

Low salinity waterflooding of carbonate reservoirs has attracted wide attention and many mechanisms have been proposed. However, the dynamic behaviors and mechanisms of the fluid-fluid interaction in low salinity waterflooding have not yet been thoroughly classified. Regarding this, core flooding, contact angle & zeta potential, interfacial tension & interfacial dilatational rheology, total organic carbon, and cryogenic-scanning electron microscopy (cryo-SEM) experiments were combined in this study to investigate the role of the fluid-fluid interaction in low salinity waterflooding and reveal its in-depth mechanism. Core flooding & contact angle & zeta potential experiments results showed that the rock-fluid and fluid-fluid interactions act synergistically to enhance oil recovery. Thereof, as ionic strength decreases, the contribution of the fluid-fluid interaction for additional recovery first increases to the maximum 67.04 % in 20-times diluted formation waterflooding and then decreases to 29.99 % in 40-times diluted formation waterflooding. Moreover, Mg2+ and SO42− as the potential determining ions both showed positive effects on the fluid-fluid interaction in low salinity waterflooding. As Mg2+ concentration increases, the contribution of the fluid-fluid interaction for additional recovery increases to 82.63 % and then decreases. As SO42− concentration increases, the contribution of the fluid-fluid interaction continuously increases and reaches 84.56 %. Interfacial tension and interfacial dilatational rheology results illustrated that the interfacial viscoelasticity enhancement is the important mechanism of the fluid-fluid interaction in low salinity waterflooding which could suppress the snap-off and stabilize the crude oil. Moreover, the total organic carbon and cryo-SEM results showed the oil-in-water emulsions with strong interfacial viscoelasticity are stably dispersed in low saline water, which could block the pores and throats and increase the sweep efficiency. In conclusion, the enhancement of interfacial viscoelasticity and the formation and existence of oil-in-water emulsion are the two important mechanisms of the fluid-fluid interaction in low salinity waterflooding. Herein, these two mechanisms both first enhance and then weaken as ionic strength decreases; enhance and then weaken as Mg2+ concentration increases, continuously enhance as SO42− concentration increases.

Basic Amino Acid-Modified Lignin-Based Biomass Adjuvants: Synthesis, Emulsifying Activity, Ultraviolet Protection, and Controlled Release of Avermectin.

Avermectin (AVM) is a highly effective and safe biopesticide but is very sensitive to ultraviolet (UV) light and exhibits poor water solubility. Developing green and multifunctional adjuvants is important for the protection and controlled release of AVM. In this work, a number of water-soluble enzymatic hydrolysis lignins (W-EHLs) were prepared via grafting basic amino acids and used as emulsifiers with co-surfactants to prepare high-internal phase emulsions (HIPEs). The results showed that W-EHLs with co-surfactants could be prepared with HIPEs that contained 90 vol % green oil phases such as turpentine, and the stability of the HIPEs first increased and then decreased when the rate of grafting of basic amino acids on lignin increased from 0.26 to 1.46 mmol/g. The more polar oil droplets were less deformable due to their higher viscosity, thereby affording a stability advantage to HIPEs. Subsequently, the relations between the stability and interfacial viscoelasticity of the emulsion were effectively correlated by interfacial rheology, droplet size, and physical stability tests. The results showed that HIPEs with smaller droplets had poor fluidity and strong interfacial viscoelasticity due to their higher droplet packing density, which resulted in good macroscopic stability. Like the AVM carrier, the retention rate of AVM in HIPEs was 80.1% after UV radiation for 72 h, which represented the highest UV protection efficiency in AVM delivery systems. The release curves showed that the rate of release of AVM from HIPEs was adjusted by controlling the pH value of the medium. In addition, the release of HIPEs is completely in accord with both diffusion and the matrix erosion mechanism. The strategy could be extended to other sensitive pesticides and used to promote the development of sustainable agriculture.

Experimental Study of CO 2 Responsive Enhanced Foam System

The channeling of CO2 seriously affects the development effect of CO2 flooding technology. In response to this problem, the construction of the CO2 responsive enhanced foam system and the evaluation of its channeling performance have been carried out. The foaming agent is optimized by the stirring method, the CO2 responsive enhanced foam system is constructed based on the optimization of foam agent, and the rheological performance test and the enhanced oil recovery experiment are carried out to study the stability mechanism and channeling plugging performance of the responsive enhanced foam system. The developed responsive enhanced foam system formula is 0.1 wt% AOS foaming agent + 4 wt% small molecule amine. The viscosity of this system is close to that of water before exposure to CO2, and the viscosity can increase by more than 18 times corresponding to CO2. The CO2 responsive enhanced foam system has obvious shear thinning characteristics, and its rheological equation conforms to the power law fluid rheological model. The enhanced foam system has stronger viscoelasticity than conventional foams. The foam comprehensive value of the enhanced foam system can reach more than 11 times that of the conventional foam system, which can effectively inhibit the CO2 channeling of heterogeneous low permeability reservoirs and improve the development effect of CO2 flooding in low permeability reservoirs.

Effect of pH on the mechanical, interfacial, and emulsification properties of chitosan microgels

Food microgels have attracted much attention recently especially in the use of emulsion stabilization due to their colloidal nature, such as nano-to micro-size, large amount of dangling chains and deformability. However, the stabilization mechanism for pH-sensitive microgels is still not well understood. In this paper, the polysaccharide chitosan (CS) was used to prepare pH-responsive chitosan microgels (CSMs) by physically cross-linking with sodium tripolyphosphate (TPP) and the subsequent ultrasound treatment. The particle size and morphology of CSMs, the mechanical properties of CSM at different pH, and the adsorption and interfacial rheology of CSMs at oil-water interface were characterized by nanoparticle size analyzer, confocal laser scanning microscope, atomic force microscopy, and pendant drop tensiometer, respectively. The results showed that the optimum condition for CSM formation occurred at CS/TPP mass ratio of 1:1 under mechanical stirring at 1000 rpm, and sonication for 9 min. The size of the CSM particles strongly depended on pH with larger size under weak acid conditions and smaller size under neutral condition. CSMs obviously have better interfacial activity than pure CS polymers under the same conditions, and their interfacial properties strongly depended on pH and concentration. It was found that although the swollen CSM particles diffuse more slowly than the smaller ones, they formed interface with stronger viscoelasticity, and displayed strain hardening during extension process in the dilatational measurement under relatively large amplitude. Combined with the mechanical strength results, these may be due to the greater deformability of the swollen CSMs at weak acid condition. However, over swelling may not facilitate the decrease of surface tension due to the steric and electrostatic repulsion of the dangling chains. The interfacial behaviors of the CSMs were successfully linked to their emulsification ability and confirmed by the emulsion structure and stability tests. It was found that the interfacial viscoelasticity played a vital role in the emulsification ability of the CS microgels.

Physic-based and control-oriented modeling based robust control for soft dielectric elastomer actuator

Dielectric elastomer actuators (DEA) have attracted increasing attention in the field of soft robotics for use in generating soft and compliant motions. However, owing to their strong viscoelasticity, nonlinearity, and uncertainty, it is often difficult to gain high-precision tracking control. Here, a physic-based and control-oriented modeling based robust control is proposed to alleviate this difficulty in tracking. First, a conical DEA is designed, along with a physics-based and control-oriented model used to describe its dynamic behaviors. After this, a two-step identification method is proposed to obtain the model’s parameters. Using the model, a robust control approach is then developed to achieve satisfactory control performance—even when tracking multi-frequency and wide-range reference trajectory under uncertain conditions. Its stability is then analyzed and proofed. Finally, we conduct experiments to demonstrate and test the effectiveness of the actuator.

Effect of molecular weight and pH on the self-assembly microstructural and emulsification of amphiphilic sodium alginate colloid particles

Biopolymer-based Pickering emulsions have attracted increasing interest in research areas including food, pharmaceutics and drug delivery. However, understanding of self-assembly behavior from the dedicate structure of stabilizers has not been well explored yet. In this work, we proposed to investigate how molecular weight affect the self-assembly behavior and to explore the potential of biopolymer colloidal particle-stabilized Pickering emulsion for controlling release of hydrophobic drugs. Amphiphilic sodium alginate derivatives (Ugi-Alg) with three molecular weights (685 kDa, 307 kDa and 48 kDa) were successfully incorporated with a hydrophobic group. Based on the characterizations of morphology and rheology behavior, the high-molecular-weight derivatives (H-Ugi-Alg) can form a compact micelle structure in aqueous solution. Emulsions stabilized by H-Ugi-Alg exhibited a higher stability and stronger viscoelasticity than those using Ugi-Alg with a lower molecular weight. In addition to the entangled polymer chains caused by higher molecular weight and hydrophobic association, the partially protonated carboxyl groups reduced electrostatic repulsion at pH = 4.2 also facilitate the formation of compact micelle structure. Approximately 78.6% of the encapsulated curcumin released from the emulsion stabilized by H-Ugi-Alg, which exhibits a similar release efficiency compared with the nanoparticle-stabilized Pickering emulsions.

Experimental Study of Defect Localization in a Cross-Ply Fiber Reinforced Composite with Diffuse Ultrasonic Waves

Diffuse wave inspection benefits from multiple scattering and is suitable for the nondestructive testing of complex structures with high sensitivity. This paper aims to localize the defect in a cross-ply carbon fiber reinforced polymer composite with the diffuse wave field experimentally based on the Locadiff technique. Firstly, the wave diffusivity and dissipation parameters are determined from the diffuse waveforms. Great dissipation is found for this composite plate due to its strong viscoelasticity, which makes the amplitude attenuate fast in a short propagation distance. The signal-to-noise ratios degrade significantly at off-axis directions so that only measurements along the X and Y axes are chosen. Secondly, the decorrelation coefficients are determined using the stretching technique. The decorrelation coefficients decrease initially due to the interaction between the wave fields and the defect and subsequently increase due to the low signal-to-noise ratio at the later time. Based on these data, a sensitivity time domain is chosen to center at t = 50 μs. Together with the defect sensitivity kernel calculated under constant diffusion property assumption, the defect is localized at [270 mm, 265 mm] compared to [300 mm, 280 mm] in the final reference state. This method is promising for early damage detection in fiber reinforced composite structures.

ИССЛЕДОВАНИЕ ФИЛЬТРАЦИОННЫХ И РЕОЛОГИЧЕСКИХ СВОЙСТВ ПОЛИМЕРНОГО ГЕЛЯ ДЛЯ ПОВЫШЕНИЯ НЕФТЕОТДАЧИ ПЛАСТОВ

Актуальность. Полимерное заводнение широко применяется на практике при разработке нефтяных месторождений. Высококонцентрированные растворы полимера с высокой массовой концентрацией обладают повышенной вязкоэластичностью, но с увеличением массовой концентрации полимерного раствора возникает проблема о совместимости между размером агрегата молекул полимера и размером пор в пласте. Cr3+ полимерный гель, основанный на внутримолекулярном сшивании молекул, имеет меньший размер агрегата и хорошую совместимость с пластом, поэтому очень актуальными являются исследования эффекта гелеобразования. Цель: исследование фильтрационных и реологических свойств водного геля на основе полиакриламида в присутствии ацетата хрома для повышения нефтеотдачи платов. Методы: физическое моделирование процесса нефтевытеснения и процесса фильтрации жидкости при пластовых условиях на фильтрационной установке, определение вязкости полимерного геля на вискозиметре Брукфилда DV-II, измерение размера полимерного молекулярного клубка Dh на установке Brookhaven BI-200SM, широкоугольная динамическая/статическая система рассеяния света (Brookhaven Instruments Cop., США), определение вязкоэластичности с помощью реометра Harke10. Результаты. Регулированием массовой концентрации полимерного раствора, степени минерализации воды и соотношения содержания полимера к хрому (w(П/Cr3+)) можно получить Cr3+ полимерную гелевую систему, основанную на внутримолекулярном сшивании молекул с меньшим размером молекулярной агрегации и большим фильтрационным сопротивлением. После реакции внутримолекулярного сшивания полимерного раствора, с одной стороны, вязкоэластичность системы значительно улучшается и коэффициент вытеснении нефти из пластов увеличивается. С другой стороны, реакция внутримолекулярного сшивания молекул снижает гибкость агрегатов полимерной молекулы, повышает их жесткость, ухудшает их деформируемость в процессе прохождения через поры и увеличивает задержки молекул полимера в слое с высокой проницаемостью пласта. Cr3+ полимерная гелевая система не только обладает хорошей приемистостью, но может также постепенно достигать более высокого давления нагнетания, за счет этого увеличивается коэффициент охвата пласта. В итоге коэффициент извлечения нефти с применением системы полимерного геля становится выше, чем коэффициент извлечения нефти из пласта с использованием системы полимерного раствора.