Viscoelastic Behavior Of Polymers Research Articles

Intensifying the performance of polymer suspensions to evaluate drag reduction using rotating disc apparatus

A rotating disc in a close chamber was fabricated to evaluate the drag reduction (DR) performance of different polymer suspensions which estimates it with evaluating tension of crude oil on the disk before and after adding suspensions. The main issue is the link between the rheological and functional behaviors of polymers in crude oil. Polyisobutylene (PIB), styrene butadiene rubber (SBR), and polystyrene (PS) were used as polymers, and their performances were compared with a commercial drag reducer agent. The viscoelastic behavior of polymers and their viscosity in crude oil were found to significantly alter the drag reduction efficiency. Although having been increasingly studied the more the elasticity of the agent, the greater the drag reduction efficiency, it was concluded that the drag force does not change monotonically with the increase in the concentration of polymers (or induction of higher turbulence), and one should use an optimum concentration of polymers to gain the maximum drag reduction. Furthermore, increasing the temperature was found an easy way to slightly promote the drag reduction efficiency. In addition, it will be possible to predict the optimal concentration and temperature with rheological studies before conducting operational tests. The results of rheological evaluations clearly show the entanglement and relaxation behavior depends on the polymer concentration. Also the operational tests show, although, due to its short-chain molecules and high viscosity, the drag reduction by means of PS contained DR was less than 10 %, the sample containing 15.0 ppm of PIB and SBR could cause up to ∼ 40 % drag reduction at 40 °C and Re = 300,000 (considered as the beginning of the turbulent flow in rotating disk apparatus (RDA)). This record is comparable to that of the commercial sample.

Fundamentals and Recent Progress in the Flow of Water-Soluble Polymers in Porous Media for Enhanced Oil Recovery

Due to increased energy demand, it is vital to enhance the recovery from existing oilfields. Polymer flooding is the most frequently used chemical enhanced oil recovery (cEOR) method in field applications that increases the oil sweep and displacement efficiencies. In recent years, there has been growing interest to assess the use of polymer flooding in an increasing number of field applications. This is due to the improved properties of polymers at high-salinity and high-temperature conditions and an increased understanding of the transport mechanisms of water-soluble polymers in porous media. In this review, we present an overview of the latest research into the application of polymers for cEOR, including mechanisms of oil recovery improvement and transport mechanisms in porous media. We focus on the recent advances that have been made to develop polymers that are suitable for high-salinity and high-temperature conditions and shed light on new insights into the flow of water-soluble polymers in porous media. We observed that the viscoelastic behavior of polymers in porous media (e.g., shear thickening and elastic turbulence) is the most recently debated polymer flow mechanism in cEOR applications. Moreover, advanced water-soluble polymers, including hydrophobically modified polymers and salt- and temperature-tolerant modified polyacrylamides, have shown promising results at high-salinity and high-temperature conditions.

Gear mesh stiffness of polymer-metal spur gear system using generalized Maxwell model

Polymer-metal gears become increasingly interesting to manufacturers and researchers for their advantages to combine the two material's efficiencies. Despite the variety of studies in the literature, there is a significant drop in the number of studies concerning the Gear Mesh Stiffness (GMS). The variation of the GMS by time has a major influence on the dynamic response of transmission. Therefore, this study proposes to take into consideration the viscoelastic behavior of polymer in order to model effectively the GMS of a gear system. The suggested rheological model is the Generalized Maxwell Model (GMM). It is first used to model the viscoelastic behavior of the plastic material of the pinion. Then, Pole Zero Formulation (PZF) is employed to identify parameters of the proposed model. A numerical simulation is then carried out to illustrate the results of this new approach adopted on a pure Nylon 6,6-steel pinions. The evolution of the GMS is illustrated to highlight the viscoelastic behavior's model presented in this paper. Finally, the influence of the change in the temperature is investigated.

Hybrid Application of Nanoparticles and Polymer in Enhanced Oil Recovery Processes.

Nowadays, the addition of nanoparticles to polymer solutions would be of interest; however, the feasible property of nanoparticles and their impact on oil recovery has not been investigated in more detail. This study investigates the rheology and capillary forces (interfacial tension and contact angle) of nanoparticles in the polymer performances during oil recovery processes. Thereby, a sequential injection of water, polymer, and nanoparticles; Nanosilica (SiO2) and nano-aluminium oxide (Al2O3) was performed to measure the oil recovery factor. Retention decrease, capillary forces reduction, and polymer viscoelastic behavior increase have caused improved oil recovery due to the feasible mobility ratio of polymer–nanoparticle in fluid loss. The oil recovery factor for polymer flooding, polymer–Al2O3, and polymer–SiO2 is 58%, 63%, and 67%, respectively. Thereby, polymer–SiO2 flooding would provide better oil recovery than other scenarios that reduce the capillary force due to the structural disjoining pressure. According to the relative permeability curves, residual oil saturation (Sor) and water relative permeability (Krw) are 29% and 0.3%, respectively, for polymer solution; however, for the polymer–nanoparticle solution, Sor and Krw are 12% and 0.005%, respectively. Polymer treatment caused a dramatic decrease, rather than the water treatment effect on the contact angle. The minimum contact angle for water and polymer treatment are about 21 and 29, respectively. The contact angle decrease for polymer treatment in the presence of nanoparticles related to the surface hydrophilicity increase. Therefore, after 2000 mg L−1 of SiO2 concentration, there are no significant changes in contact angle.

An Elongational and Shear Evaluation of Polymer Viscoelasticity during Flow in Porous Media

This paper uses a combination of approaches to evaluate the viscoelastic phenomenon in high-molecular-weight polymers (24–28 M Daltons) used for enhanced oil recovery (EOR) applications. Rheological data were cross-analyzed with single- and two-phase polymer flooding experiments in outcrop cores and micromodels, respectively. First, the impact of semi-harsh conditions (salinity, hardness, and temperature) was evaluated. Second, the impact of polymer degradation (sand face flow), focusing on the viscoelastic properties, was investigated. Finally, polymer viscoelastic properties were characterized, proposing a threefold rheological approach of rotational, oscillatory, and elongational behavior. Data from the rheological approaches were cross-analyzed with core flooding experiments and performed at a room temperature of 22 °C and at a higher temperature of 55 °C. The change in polymer viscoelastic properties were analyzed by investigating the effluents from core flooding experiments. Oil recovery experiments in micromodel helped our understanding of whether salinity or hardness has a dominating impact on in situ viscoelastic polymer response. These approaches were used to study the impact of mechanical degradation on polymer viscoelasticity. The brines showed notable loss in polymer viscoelastic properties, specifically with the hard brine and at higher temperature. However, the same polymer solution diluted in deionized water exhibited stronger viscoelastic properties. Multiple flow-behaviors, such as Newtonian, shear thinning, and thickening dominated flow, were confirmed through pressure drop analysis against interstitial velocity as already reported by other peer researchers. Turbulence-dominated excessive pressure drop in porous media was calculated by comparing core flood pressure drop data against pressure data in extensional viscometer–rheometer on a chip (eVROC®). In addition, a significant reduction in elastic-dominated flow was confirmed through the mechanical degradation that happened during core flood experiments, using various approaches. Finally, reservoir harsh conditions (high temperature, hardness, and salinity) resulted in a significant reduction in polymer viscoelastic behavior for all approaches.

Estimating the creep behavior of glass-fiber-reinforced polyamide considering the effects of crystallinity and fiber volume fraction

BackgroundThe time-temperature superposition principle (TTSP) is often used to estimate the viscoelastic behavior of polymers. It can also be used to evaluate the influence of a given variable, or set of variables, on viscoelastic properties. In this research, the effects of time, temperature, fiber volume fraction and the relative crystallinity of polyamide (PA) and glass fiber-reinforced polyamide (GFRPA) were investigated using the time-temperature superposition principle to estimate viscoelastic behavior under each set of conditions.MethodsThe crystallinities of PA and GFRPA, which ranged from 33 to 45%, were controlled by adjusting the duration of crystallization as 250 °C. Creep tests were carried out with these materials, and creep compliance curves of each condition were obtained.ResultsUsing these creep compliance curves, the master curves for temperature, and the grand master curves for crystallinity and for fiber volume fraction were generated to show the relationships between fiber volume fraction, crystallinity, and viscoelastic parameters. Furthermore, the great-grand master curve for crystallinity and fiber volume fraction was generated to predict creep behavior in an arbitrarily condition. The predicted data were in good agreement with experimental results.ConclusionsA method for estimating creep deformation taking into account the effects of influencing variables was developed. The time-temperature superposition principle (TTSP) was applied to the effects of the fiber volume fraction and crystallinity. Grand master curves for crystallinity and fiber volume fraction were obtained by shifting the corresponding master curves. This study demonstrates that the creep behaviors of fiber-reinforced plastics can be estimated using these shift factors and a great-grand master curve. This method yielded estimates of creep deformation that fitted well with experimental results. Based on our findings, it should be possible to control creep deformation in plastics or fiber-reinforced resins by controlling the fiber volume fraction and the crystallinity of the matrix material.

Tribological Behavior of Polymer Seal Materials in Water-Based Hydraulic Fluids

In this work, two polymer materials have been tested in a lubricated reciprocating pin-on-plate contact geometry using water-based hydraulic fluids to simulate sliding conditions of seal materials used in offshore equipment. The effect of load, speed, water content of the lubricant, and soaking of the ultra-high molecular weight polyethylene (UHMWPE) and a polyketone (PK) sliding against a super-duplex stainless steel (SDSS) was studied. The results showed that for UHMWPE, an increase in normal force leads to a decrease in coefficient of friction for all velocities. While under the same sliding conditions, no relevant influence of load on friction coefficient was found for PK. On the other hand, an increase in sliding speed decreased the coefficient of friction for both materials. The effect of the water content of the hydraulic fluid on the tribological performance was also studied. In UHMWPE-SDSS system, increasing water content in the hydraulic fluid resulted in steady growth of the transfer film. One reason for this might be the decreasing lubricant viscosity, which moves the system toward the boundary lubrication regime. In addition, it was found that the incubation of both UHMWPE and PK in water-based lubricants showed a beneficial effect on friction and wear, which was explained by the change in polymer visco-elastic behavior.

Study about a new two-spring-two-piston constitutive model describing visco-elastic behavior of polymer

The constitutive equation of two-spring-two-piston visco-elastic mechanic model was deduced in this paper. The static creep and relaxation characteristics of PA66, PTFE, PMMA, POM and PEUR were studied on CETR UMT-2 tester and LKDM-2000 tester. The standard linear solid model and a new mechanic model, both were applicable in describing the fluctuation of creep and relaxation, were adopted to tracking the variations of experiment statistics separately for comparative study. According to testing results, comparing analysis showed that two-spring-two-piston mechanic model can described effectively visco-elastic behavior of polymer than standard linear solid model.

A Comprehensive Combination of Apparent and Shear Viscoelastic Data during Polymer Flooding for EOR Evaluations

We present a comprehensive workflow to obtain the best insights into the viscoelastic behavior of polymers. Viscoelasticity is depicted in most cases by the current commercially available polymers used for EOR applications. The phenomenon is debated to be one of the reasons for additional oil recovery during polymer flooding applications. It is somehow accepted that polymer increases volumetric sweep efficiency owing to improved mobility ratio. Recently researches have explained that flooding polymers in porous media with elastic characteristics could recover additional oil, due to the improved microscale oil displacement (pore-scale). This study focuses on the analysis of polymer viscoelasticity based on single-phase core, sand-pack and capillary tube (CT) experiments coupled with their detailed rheological characterization, in order to evaluate polymer behavior in porous media. A combination of hydrolyzed polyacrylamides (HPAM) polymers as well as a bio polymer is presented throughout this evaluation. The evaluation of the data is addressed on the basis of pressure drop across the pores, separating the shear associated pressure by the extensional thickening associated pressure. Apart from that, viscoelastic dependence of the converging-diverging geometry has been experimented. Based on the observed behavior through porous media, HPAM polymers are compared with bio polymers. Moreover, the behavior of solutions with induced mechanical degradation (pre-sheared) is compared with non-sheared solutions. Similarly, concentrations with different polymer solutions are evaluated. The results obtained in this work allow for additional understanding of polymer solutions behavior in flooding applications. Furthermore The results support the definition of optimized workflows to assess their behavior under flow through porous media. Finally this evaluation helps to describe the parameter that defines polymer viscoelastic properties.

Flow Characteristics of Viscoelastic Polymer Solution in Expansion Micro-Pores of Different Pore-Throat Ratio

Pore-throat ratio is a significant parameter expressing the characteristics of reservoir pores. It has an apparent influence on viscoelastic polymer solution flow in micro-pores. In this paper, Upper-Convected Maxwell (UCM) equation is applied in describing the viscoelastic polymer behavior. The expansion channel models of different pore-throat ratio are selected in process of simulation. And contours of stream function and velocity of different Weissenberg number (We) are calculated and drawn by Finite Volume Method. Results show that, vortex will occur at the re-entrant corner caused by the sudden expansion of channel, size and intensity of the corner recirculation vortex. The residual oil region is reduced and the mobile oil region is enlarged. Microscopic sweep efficiency is increased relatively. Vortex will be larger and stronger, and the velocity will be increased for We. Vortex will be lager as the bigger pore-throat ratio. Micro-sweep efficiency will be capitalized by viscoelastic polymer solution to the utmost.

Flow Characteristics of Viscoelastic Polymer Solution in Contraction Micro-Pores of Different Pore-Throat Ratio

Pore-throat ratio is a significant parameter expressing the characteristics of reservoir pores. It has an apparent influence on viscoelastic polymer solution flow in micro-pores. In this article, Upper-Convected Maxwell (UCM) equation is adapted to describe the viscoelastic polymer behavior. The contraction channel models of different pore-throat ratio are selected in process of simulation. And contours of stream function and velocity of different Weissenberg number (We) are calculated and drawn by Finite Volume Method. Results show that, vortex will occur at the re-entrant corner caused by the sudden contraction of channel, size and intensity of the corner recirculation vortex. The residual oil region is reduced and the mobile oil region is enlarged. Microscopic sweep efficiency is increased relatively. Vortex will be larger and stronger, and the velocity will be increased for We. Vortex will be lager with the bigger pore-throat ratio. Micro-sweep efficiency will be capitalized by viscoelastic polymer solution to the utmost.

CFD modeling of the melt spinning of poly (ethylene terepthalate) at low take-up velocities

In this study, a model was formulated to describe the melt spinning of Poly (ethylene terepthalate) (PET) at different quench air speeds and temperatures, mass throughputs and a low range of take-up velocities. The constitutive equations of the Newtonian model were used for modeling, which assumed the flow of polymer was viscous. To simulate the influence of the process parameters on the melt spinning process, a fiber model was used and coupled with computational fluid dynamics (CFD) calculations of the quench air flow. In the fiber model, energy, momentum and mass balance were solved for the polymer mass flow. The formulation was implemented in the Fluent Continuous Fiber Model. Numerical predictions of the model were compared with experimental data reported in the literature for PET. The take up speed, mass throughput and the temperature of melt spinning were the primary parameters of final fiber properties for both simulation and experimental results. In the simulation results, the effects of take-up speed and mass throughputs were clearly different at high take-up velocities and low mass throughputs because of viscoelastic behavior of polymers in the melt spinning. The Newtonian model was more reasonable for lower take-up speeds and higher mass throughputs. Key words: Melt spinning, poly (ethylene terepthalate), modeling, process parameters.

An Efficient Implementation of Polymer Viscoelastic Behavior Through a Pseudo Viscoelastic Model

Modeling of viscoelastic relaxation of polymer materials is important to understand the thermo-mechanical behavior of organic microelectronic systems. However, incorporation of viscoelastic behavior into numerical models makes the models compute-intensive. This paper presents a different technique to incorporate the polymer viscoelastic behavior into the numerical models such that the computation time is not adversely affected without compromising the accuracy of the results obtained. In the proposed “pseudo viscoelastic” modeling technique, the modulus of the viscoelastic material is computed as a function of time and temperature loading history outside of the finite-element simulation, and is then input into the simulation as a thermo-elastic material incorporating the viscoelastic relaxation of the material. This paper compares the warpage results obtained through the proposed technique against a complete viscoelastic simulation model and experimental data, and it is seen that the maximum warpage predicted using the proposed technique agree within 10% compared with the results obtained from a “full” viscoelastic model. Also, it is shown through some of our simulations that the proposed technique could result in a computational time saving of more than 50% and hard disk space saving of 65%.

Influence of local chain dynamics on diffusion of gases in polymers as determined by pulsed field gradient NMR

AbstractDiffusion of gases in polymers below the glass transition temperature, Tg, is strongly modulated by local chain dynamics. For this reason, an analysis of pulsed field gradient (PFG) nuclear magnetic resonance (NMR) diffusion measurements considering the viscoelastic behavior of polymers is proposed. Carbon‐13 PFG NMR measurements of [13C]O2 diffusion in polymer films at 298 K are performed. Data obtained in polymers with Tg above (polycarbonate) and below (polyethylene) the temperature set for diffusion measurements are analyzed with a stretched exponential. The results show that the distribution of diffusion coefficients in amorphous phases below Tg is wider than that above it. Moreover, from a PFG NMR perspective, full randomization of the dynamic processes in polymers below Tg requires long diffusion times, which suggests fluctuations of local chain density on a macroscopic scale may occur. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 231–235, 2010

A study of rheological and molecular weight properties of recycled polysaccharides used as thickeners in textile printing

Polysaccharide thickeners (alginate, carboxymethylated guar gum and carboxymethylated cellulose) used for the preparation of printing pastes, were recycled from printing paste residues and from wastewater concentrates, which were separated by ultrafiltration technique from wastewater after screen printing of cotton with reactive dyes. Concentrated aqueous polysaccharide solutions were studied via rheological measurements under steady and oscillatory shear conditions. Molecular weight averages and molecular weight distribution of thickeners were determined by size exclusion chromatography. A satisfactory fitting of viscosity data is obtained with the Cross equation and mechanical spectra are described with satisfactory approximation with the Friedrich–Braun model. The obtained parameters enable a quantitative interpretation of the changes in rheological properties. Moderate changes produced by thickener recycling on the shear-thinning and viscoelastic behaviour of polymers are a direct result of changes in molecular weight averages (MWA) and molecular weight distribution (MWD).

Temperature field and wear prediction for UHMWPE acetabular cup with assumed rectangular surface texture

Surface texture design of a tribo-pair affects its tribological behaviors and temperature distribution, subsequently its performance behaviors and servicing life. Numerical simulation and experiment to study the influence of rectangular texture, on UHMWPE acetabular cup reciprocally slid with steel ball was performed. Results demonstrated the occurrence of periodical and regular fluctuation of the surface temperatures in the cup and ball in accordance with the swing of the ball arm. Higher temperature and amplitude of fluctuation were observed in the ball for cup/steel-ball pairs. Predicted temperature for steel ball sliding in UHMWPE cup with rectangular texture is close and comparable with experimental data under steady state. Prediction reveals that: (i) increase in load and frequency increases the wear depths; (ii) wear of rectangular texture for the condition of short sliding time seems agreeable with experimental data; (iii) thermal effect changes the service performance of UHMWPE after a significant long period of operation that may be explained by the viscoelastic behavior of polymer; and (iv) thermal effect is likely to accelerate the degradation of polymer.

Water absorption mechanism and some anomalous effects on the mechanical and viscoelastic behavior of an epoxy system

AbstractDuring the past decades there has been a great accumulation of important data on the diffusion of water molecules in polymeric solids and its effect on the mechanical and viscoelastic behavior of polymers. It has become apparent that in many cases diffusion in polymers as well as its effect exhibits features that cannot be expected from classical theories and that such departures are related to the molecular structure characteristics of polymers. In the present investigation, the mechanical and viscoelastic behavior of an epoxy resin system is studied as a function of absorbed water, temperature, and time of immersion. Water sorption was achieved by immersing the material in distilled water at constant temperature of 60°C and 80°C for 2, 5, 8, 13, 32, 74, 128, 266, 512, 1024, and 1536 h. Subsequently the specimens were tested in static and dynamic three‐point bending tests to study their mechanical and viscoelastic behavior. The variation of Tg, tan δ, bending modulus, and strength was measured as a function of exposure time and respective percentage of water uptake for both temperatures. Some anomalies in their behavior due to water absorption were observed, and a model for the description of the experimentally observed mechanical behavior due to hygrothermal aging is proposed. The results show that the model predictions are in good agreement with experimental findings. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 1328–1339, 2006

Mold deformation in nanoimprint lithography

In nanoimprint lithography (NIL), one of the key points to be addressed is the printing uniformity on large area. During the process, the silicon mold undergoes significant mechanical stress of different kinds (tension, compression, flexion, and torsion). These stresses are function of the mold design and appear under the concurrent influence of both the applied pressure on the backside of the mold and an opposite force due to the polymer viscoelastic behavior. This translates into non-negligible deformations within patterned or unpatterned zones. This is a major issue because it causes nonuniformity of the printing, mold pattern break and degradation of the polymer surface. In this article, we demonstrate that during the imprint process mold deformations really occur at the local scale of the patterns but also at a larger scale.

Brownian dynamics simulations of the effects of hydrodynamic interactions on the polymer viscoelastic behavior

Brownian dynamics simulation is used to investigate the viscoelastic response of the Gaussian chain to a step shear deformation in both the linear and non-linear regions under the influence of hydrodynamic interactions. Both the preaveraged Oseen tensor and the Rotne–Prager tensor are used in the study. In the former case, the simulation results are shown to be in agreement with the expected results calculated using the eigenvalues of the normal modes of motion obtained numerically. It is shown that an initial state with zero second normal-stress difference is generated by the step shear deformation. The subsequent rise of the second normal-stress difference as revealed by the simulation is shown mainly arising from the coupling of the recoil of the stretched bond in the direction of deformation and the anisotropy in the hydrodynamic interaction created by the step deformation.

An integrated process modeling methodology and module for sequential multilayered substrate fabrication using a coupled cure-thermal-stress analysis approach

An integrated process modeling methodology using a coupled cure-thermal-stress analysis approach has been developed to determine the evolution of warpage and stresses during the sequential fabrication of high-density electronic packaging structures. The process modeling methodology has been demonstrated, for example, with a bi-layer structure consisting of a 3 mil (76.2 /spl mu/m) thick Vialux 81 photo-definable dry film (PDDF) polymer on a silicon substrate. Extensive material characterization of the thermo-mechanical properties of the thin film polymer is presented, including the development of a viscoelastic material model. The predicted warpage values have been validated with shadow Moire experiments, while the predicted stress values have been validated with experimental data using the Flexus Thin Film Stress Measurement Apparatus. Good agreement is seen between the predicted and the experimental warpage and stress values during the entire cure cycle. Finally, the importance of incorporating viscoelastic polymer behavior and processing history is emphasized in the context of developing the multi-layered high-density wiring integrated substrate fabrication process.