Polyisobutylene Solutions Research Articles

Dynamics of a thin film of viscoelastic fluid flowing down an inclined or vertical plane

The stability characteristics of a thin film of viscoelastic (Walters’ B′ model) fluid flowing down an inclined or vertical plane are analyzed under the combined influence of gravity and surface tension. A nonlinear free surface evolution equation is obtained by using the momentum-integral method. Normal mode technique and multiple scales method are used to obtain the results of linear and nonlinear stability analysis of this problem. The linear stability analysis gives the critical condition and critical wave number kc which include the viscoelastic parameter Γ, angle of inclination of the plane θ, Reynolds number Re and Weber number We. The weakly nonlinear stability analysis that is based on the second Landau constant J2, reveals the condition for the existence of explosive unstable and supercritical stable zone along with the other two (unconditional stable and subcritical unstable) flow zones of this problem which is 3(1+3Γ)Re−3cotθ−4ReWek2 = 0. It is found that all the four distinct flow zones of this problem exist in Re-k-, θ-k- and Γ-k-plane after the critical value of Rec,θc and Γc, respectively. A novel result of this analysis is that the film flow is stable (unstable) for a negative (positive) value of Γ irrespective of the values of Re and θ, as for example, a solution of polyisobutylene in cetane, compared with the viscous (Γ=0) film flow case. Finally, we scrutinize the effect of Γ on the threshold amplitude and nonlinear wave speed by depicting some numerical examples in supercritical stable as well as subcritical unstable zone of this problem.

Correlation Dependence between Hydrophobicity of Modified Bitumen and Water Saturation of Asphalt Concrete

Improving the durability of asphalt concrete road surfaces by increasing their moisture resistance is an urgent task. Modified bituminous binders should be compacted into coatings with the lowest possible water saturation. The purpose of this study was to establish the effect of modifiers on the hydrophobicity of bituminous films in order to achieve minimum water saturation and to build a mathematical model of the wetting process with water. As modifiers, we used a product of amination of distillation residues of petrochemistry, waste sealing liquid (a solution of high molecular weight polyisobutylene in mineral oil), and a condensation product of polyamines and higher fatty acids. The water-repellent effect of modifiers was studied by measuring the contact angle of bituminous film with a water drop. The water saturation of asphalt concrete samples was determined by the amount of water absorbed by asphalt concrete at 20 °C. A close correlation was revealed between the hydrophobicity of modified bitumen and the water saturation of asphalt concrete. Generalized equations and a graphical representation of a function of several variables allowed for optimizing compositions by the content of modifiers to achieve the required performance properties of asphalt concrete coatings.

Non-Newtonian Flow Of Structured Systems. XXVII. Viscosity and Elasticity of Polyisobutylene Solution

Non-Newtonian Flow Of Structured Systems. XXVII. Viscosity and Elasticity of Polyisobutylene Solution

Неньютоновское течение структурированных систем. XXI. Реология растворов полиизобутилена

Неньютоновское течение структурированных систем. XXI. Реология растворов полиизобутилена

Gas-Phase Interaction of Anions with Polyisobutylenes: Collision-Induced Dissociation Study and Quantum Chemical Modeling.

The gas-phase interaction of anions including fluoride, chloride, bromide, iodide, ethyl sulfate, chlorate, and nitrate with polyisobutylene (PIB) derivatives was studied using collision-induced dissociation (CID). The gas-phase adducts of anions with PIBs ([PIB + anion](-)) were generated from the electrosprayed solution of PIBs in the presence of the corresponding anions. The so-formed adducts subjected to CID showed a loss of anion at different characteristic collision energies, thus allowing the study of the strength of interaction between the anions and nonpolar PIBs having different end-groups. The values of characteristic collision energies (the energy needed to obtain 50% fragmentation) obtained by CID experiments correlated linearly with the binding enthalpies between the anion and PIB, as determined by density functional theory calculations. In the case of halide ions, the critical energies for dissociation, that is, the binding enthalpies for [PIB + anion](-) adducts, increased in the order of I(-) < Br(-) < Cl(-) < F(-). Furthermore, it was found that the binding enthalpies for the adducts formed with halide ions decreased approximately with the square radius of the halide ion, suggesting that the strength of interaction is mainly determined by the "surface" charge density of the halide ion. In addition, the characteristic collision energy versus the number of isobutylene units revealed a linear dependence.

QSPR Study of the Intrinsic Viscosity[η] of Polyisobutylene Solution

Quantitative structure-property relationship (QSPR) analysis to intrinsic viscosity (η) of polyisobutylene solution have been conducted. The study was done by using molecular modelling. The calculation was performed by the PBE method at 6-31G(d) basis set. The relationship analysis between intrinsic viscosity (η) and physicochemical properties of four solvents (benzene, toluene, cyclohexane, and CCl4) under study was done by MLR analysis to generate the equation that relates the structural features to the intrinsic viscosity (η) properties. The results show good models with two parameters linear equations. The best model using theoretical parameters was the Eq. 1a, that including LUMOs and T.Es parameters. While the best model using experimental parameters was Eq.1b, that involving Ԑs and S parameters, with excellent statistical fit as evident from its R 2 = 0.999, F= 1413.035 and SE=2.138.

Intrinsic nonlinearity from LAOStrain—experiments on various strain- and stress-controlled rheometers: a quantitative comparison

Strain-controlled large amplitude oscillatory shear (LAOStrain) experiments on a polyisoprene melt and a polyisobutylene solution were conducted on four different rheometers. The results are compared using nonlinear quantities such as the normalized intensity of the third harmonic (I 3/1) and the intrinsic nonlinearity in order to assess the reproducibility of the experiments. Two of the investigated instruments were strain-controlled rheometers, another two, were advanced stress-controlled rheometers. Since the stress-controlled rheometers are able to conduct strain-controlled tests when employing an active deformation control loop, the two different rheometer types could be compared. Experimental details like the gain of the deformation control loop, and the method of temperature control have been shown to play crucial roles in achieving reasonable reproducibility across the different instruments. Furthermore, deviations from the quadratic scaling of I 3/1 with the strain amplitude and the influence of instrument inertia on nonlinear quantities were observed for one of the stress-controlled instruments. The standard deviation of the intrinsic nonlinearity Q 0(ω 0) at a specific angular frequency as determined by measurements on the same instrument was found to be 8 % or lower. The relative deviations of Q 0 across different instruments were instead up to 12 % in the investigated frequency range with an exception for a specific instrument and one of the samples, where the deviation was considerably larger.

Mesoscale modeling of shear-thinning polymer solutions

We simulate the linear and nonlinear rheology of two different viscoelastic polymer solutions, a polyisobutylene solution in pristane and an aqueous solution of hydroxypropylcellulose, using a highly coarse-grained approach known as Responsive Particle Dynamics (RaPiD) model. In RaPiD, each polymer has originally been depicted as a spherical particle with the effects of the eliminated degrees of freedom accounted for by an appropriate free energy and transient pairwise forces. Motivated by the inability of this spherical particle representation to entirely capture the nonlinear rheology of both fluids, we extended the RaPiD model by introducing a deformable particle capable of elongation. A Finite-Extensible Non-Linear Elastic potential provides a free energy penalty for particle elongation. Upon disentangling, this deformability allows more time for particles to re-entangle with neighbouring particles. We show this process to be integral towards recovering the experimental nonlinear rheology, obtaining excellent agreement. We show that the nonlinear rheology is crucially dependent upon the maximum elongation and less so on the elasticity of the particles. In addition, the description of the linear rheology has been retained in the process.

Spreading of Boger fluid on horizontal surface

In this research we investigated the spreading of polyisobutylene solutions in polybutene on glass surfaces by measuring contact line speed as a function of dynamic contact angle. Polymer concentration was less than twice the coil overlap concentration (2c*). The contact line motion of polymer solutions was qualitatively similar to that of Newtonian liquid in that it followed the Tanner–Voinov–Hoffman relation. However the contact line speed was strongly affected by the migration of polymer molecules away from the wall due to the hydrodynamic interaction between the polymer and the wall at the contact line region. The hydrodynamic interaction is caused by the elasticity of polymer molecules in the shear flow. However, the elasticity of the polymer solution did not directly affect the bulk motion strongly since the Deborah number of the bulk motion was less than 0.1. The present result can be used in the derivation of the boundary condition for solving free surface flows of viscoelastic fluid on a solid surface.

Slow flow of Boger fluids through model fibrous porous media

The flow of viscoelastic fluids through square arrays of parallel cylinders was investigated experimentally by measuring the pressure drop and flow rate and by mapping the velocity field using particle image velocimetry. The arrays had solid volume fractions of 2½%, 5%, and 10% and the fluids were Boger fluids—specifically, two solutions of polyisobutylene in polybutene. With Reynolds numbers less than 0.1, viscosity and elasticity were the only relevant fluid properties. Measurements were made first with a glycerol/water mixture to establish an inelastic baseline. For the three arrays and two viscoelastic fluids, elastic effects started consistently at a Deborah number (De) of 0.5. For De up to 4, the flow resistance due to elasticity was up to several times that due to viscosity, which is comparable to previous findings with much higher volume fractions. But, unlike prior flows, the present ones were steady. Particle image velocimetry measurements revealed unit-cell velocity profiles, which became progressively asymmetrical as De increased. Also, flow structures related to elasticity were found in the wake regions; they were spaced periodically in the spanwise direction and offset from column to column to create a honeycomb-like pattern. Stress analyses indicate that the flow resistance due to elasticity was likely caused more by the normal stresses of N1 than by extensional stresses.

Free volume effect on behavior of polymer liquids in shear flows

Summary — Rheological properties of polymers such as non-Newtonian viscosity and non-zero normal stress differences during the shear flow of polymeric liquids were interpreted from the point of view of the free volume theory. It was shown that the shear viscosity variations result from the changes of the total free volume, while the normal stress differences stem from the anisotropy of the free volume distribution in a polymer liquid subjected to the shearing flow. Theoretical predictions were compared with literature data for PE-LD melt (known as IUPAC melt A) and polyisobutylene (PIB) solution in 2,6,10,14-tetramethylpentadecane (NIST standard reference material). Good agreement between theory and the experiment was found.

Force-free swimming of a model helical flagellum in viscoelastic fluids

We precisely measure the force-free swimming speed of a rotating helix in viscous and viscoelastic fluids. The fluids are highly viscous to replicate the low Reynolds number environment of microorganisms. The helix, a macroscopic scale model for the bacterial flagellar filament, is rigid and rotated at a constant rate while simultaneously translated along its axis. By adjusting the translation speed to make the net hydrodynamic force vanish, we measure the force-free swimming speed as a function of helix rotation rate, helix geometry, and fluid properties. We compare our measurements of the force-free swimming speed of a helix in a high-molecular weight silicone oil with predictions for the swimming speed in a Newtonian fluid, calculated using slender-body theories and a boundary-element method. The excellent agreement between theory and experiment in the Newtonian case verifies the high accuracy of our experiments. For the viscoelastic fluid, we use a polymer solution of polyisobutylene dissolved in polybutene. This solution is a Boger fluid, a viscoselastic fluid with a shear-rate-independent viscosity. The elasticity is dominated by a single relaxation time. When the relaxation time is short compared to the rotation period, the viscoelastic swimming speed is close to the viscous swimming speed. As the relaxation time increases, the viscoelastic swimming speed increases relative to the viscous speed, reaching a peak when the relaxation time is comparable to the rotation period. As the relaxation time is further increased, the viscoelastic swimming speed decreases and eventually falls below the viscous swimming speed.

TTS in LAOS: validation of time-temperature superposition under large amplitude oscillatory shear

The validation of time-temperature superposition of non-linear parameters obtained from large amplitude oscillatory shear is investigated for a model viscoelastic fluid. Oscillatory time sweeps were performed on a 11 wt.% solution of high molecular weight polyisobutylene in pristane as a function of temperature and frequency and for a broad range of strain amplitudes varying from the linear to the highly non-linear regime. Lissajous curves show that this reference material displays strong non-linear behaviour when the strain amplitude is exceeding a critical value. Elastic and viscous Chebyshev coefficients and alternative non-linear parameters were obtained based on the framework of Ewoldt et al. (J Rheol 52(6):1427–1458, 2008) as a function of temperature, frequency and strain amplitude. For each strain amplitude, temperature shift factors a T (T) were calculated for the first order elastic and viscous Chebyshev coefficients simultaneously, so that master curves at a certain reference temperature T ref were obtained. It is shown that the expected independency of these shift factors on strain amplitude holds even in the non-linear regime. The shift factors a T (T) can be used to also superpose the higher order elastic and viscous Chebyshev coefficients and the alternative moduli and viscosities onto master curves. It was shown that the Rutgers-Delaware rule also holds for a viscoelastic solution at large strain amplitudes.

Multi-sample micro-slit rheometry

We have developed a multi-sample micro-slit rheometer (MMR) which is capable of measurements over a broad range of temperatures, viscosities and shear rates. The instrument is mechanically simple as the flow is generated by external gas pressure and the shear rate is measured through optical tracking of the flow front. In the current implementation, the required volume of each sample is approximately 20μL and we measure four samples simultaneously. We demonstrate the performance of the MMR by measurement of the flow curves (viscosity versus shear rate) of three representative polymers: A polydimethylsiloxane melt, a polyisobutylene solution, and a polystyrene melt. We adapt standard data correction methods to account for shear-thinning and entry/flow-front effects. We report a high level of accuracy and precision. This instrument will be particularly useful in cases of multiple samples, limited material quantity, and when optical access is useful.

Analysis of the Phase Separation Induced by a Free-Radical Polymerization in Solutions of Polyisobutylene in Isobornyl Methacrylate

We analyze a polymerization-induced phase separation taking place in solutions of a polymer dissolved in a vinyl monomer undergoing an isothermal free-radical polymerization. The selected system was a solution of polyisobutylene (PIB) in isobornyl methacrylate (IBoMA). Cloud-point curves for PIBs of different molar masses were fitted with the Flory-Huggins equation stated for a 3-component system. Phase separation was analyzed for two different PIBs at off-critical compositions. Comparing experimental values of the volume fraction of dispersed phase with those predicted by the coexistence curves it was found that the system evolved close to equilibrium during an initial stage. But phase separation stopped at intermediate monomer conversions as assessed by scanning electron micrographs of partially converted materials. The evolution of the size distribution of dispersed domains was obtained from the fitting of light scattering (LS) spectra. Average sizes predicted by LS and measured in scanning electron micrographs were in rough agreement.

Instability of entangled polymers in cone and plate rheometry

Flow instability in three entangled polymer systems including a 10 wt% 1,4-polybutadiene (PBD) solution, an 11.4 wt% polyisobutylene (PIB) solution, and a long chain branched polyethylene melt (LD 146) was investigated in both stress-controlled and rate-controlled experiments in the cone–plate geometry. It was found that flow instability occurred for experiments in both rate- and stress-controlled modes. The effects of cone angle or rim gap and shearing time on flow instability were studied. The smaller cone angle and shorter shearing time delay (in terms of stress or shear rate) the occurrence of severe instability and mass loss of the PBD solution but not for the PIB. Our data are consistent with the dramatic shear rate jump for the flow curve constructed from the stress-controlled experiments being associated with mass loss after the severe instabilities. We also find that the Cox–Merz representation gives a powerful tool for investigation of flow instability. Finally, another interesting result in this work is that it seems that the stress overshoot can be related to the onset of flow instability in the present system.

Development and evaluation of a micro–macro algorithm for the simulation of polymer flow

A micro–macro algorithm for the calculation of polymer flow is developed and numerically evaluated. The system being solved consists of the momentum and mass conservation equations from continuum mechanics coupled with a microscopic-based rheological model for polymer stress. Standard finite element techniques are used to solve the conservation equations for velocity and pressure, while stochastic simulation techniques are used to compute polymer stress from the simulated polymer dynamics in the rheological model. The rheological model considered combines aspects of reptation, network and continuum models. Two types of spatial approximation are considered for the configuration fields defining the dynamics in the model: piecewise constant and piecewise linear. The micro–macro algorithm is evaluated by simulating the abrupt planar die entry flow of a polyisobutylene solution described in the literature. The computed velocity and stress fields are found to be essentially independent of mesh size and ensemble size, while there is some dependence of the results on the order of spatial approximation to the configuration fields close to the die entry. Comparison with experimental data shows that the piecewise linear approximation leads to better predictions of the centerline first normal stress difference. Finally, the computational time associated with the piecewise constant spatial approximation is found to be about 2.5 times lower than that associated with the piecewise linear approximation. This is the result of the more efficient time integration scheme that is possible with the former type of approximation due to the pointwise incompressibility guaranteed by the choice of velocity–pressure finite element.

Kinetics of the Free-Radical Polymerization of Isobornyl Methacrylate in the Presence of Polyisobutylenes of Different Molar Masses

The effect of a linear polymer dissolved in a reactive monomer on the kinetics of free-radical polymerization is studied. The selected system was a solution of polyisobutylene (PIB) in isobornyl methacrylate (IBoMA). Ternary phase diagrams of PIB, IBoMA and poly(isobornyl methacrylate) (PIBoMA) were built at 80C. They were shifted to lower conversions when increasing the molar mass of PIB. Different PIBs exhibiting CPC at advanced conversions were selected for the kinetic study performed employing differential scanning calorimetry (DSC) at 80C. A simple kinetic model for free-radical polymerizations describing the relevant termination rate constant in terms of the free-volume theory, provided a consistent fitting of the polymerization rates in the conversion range where the solution remained homogeneous. Increasing the molar mass of PIB led to an increase in polymerization rate due to the decrease in free volume and the corresponding decrease of the termination rate. Increasing the amount of a particular PIB in the initial formulation led to a less marked gel effect, explained by the smaller relative variation of free volume with conversion. The dimensionless free volume of PIB obtained from the kinetic model was found to increase with the volume concentration of chain ends, as expected. Under conditions where phase separation took place at very low conversions, the overall polymerization rate exhibited the presence of two maxima (gel effects), representing the polymerization in two different phases. The first maximum was associated to the polymerization taking place in the phase lean in PIB and the second maximum was associated to the polymerization of the monomer that was initially fractionated with PIB.

Calculation of the Die Entry Flow of a Concentrated Polymer Solution Using Micro-Macro Simulations

A micro-macro simulation algorithm for the calculation of polymeric flow is developed and implemented. The algorithm couples standard finite element techniques to compute velocity and pressure fields with stochastic simulation techniques to compute polymer stress from simulated polymer dynamics. The polymer stress is computed using a microscopic-based rheological model that combines aspects of network and reptation theory with aspects of continuum mechanics. The model dynamics include two Gaussian stochastic processes, each of which is destroyed and regenerated according to a survival time randomly generated from the material’s relaxation spectrum. The Eulerian form of the evolution equations for the polymer configurations is spatially discretized using the discontinuous Galerkin method. The algorithm is tested on benchmark contraction domains for a polyisobutylene solution. In particular, the flow in the abrupt die entry domain is simulated and the simulation results are compared to experimental data. The results exhibit the correct qualitative behavior of the polymer and agree well with the experimental data.

Absorption of Carbon Dioxide into Non‐Newtonian Liquid. III. Effect of Chemical Reaction

Carbon dioxide was absorbed into water‐in‐oil (w/o) emulsion composed of aqueous diethanolamine (DEA) droplets as a dispersed phase and benzene solutions of polybutene (PB) and polyisobutylene (PIB) as a continuous phase in a flat‐stirred vessel to investigate the effect of non‐Newtonian rheological behavior on the rate of chemical absorption of CO2, where the reaction between CO2 and DEA in the aqueous phase was assumed to be a pseudo‐first‐order reaction. The liquid‐side‐mass‐transfer coefficient, k L, which was obtained from the dimensionless empirical equation containing the properties of pseudoplasticity of the non‐Newtonian liquid, was used to estimate the enhancement factor due to chemical reaction. It was expressed that PIB with elastic property accelerated the rate of chemical absorption of CO2 by the comparison of k L in the non‐Newtonian liquid with that in the Newtonian liquid.