不同类型聚合物溶液对采油残余油的作用机理研究

通过实验测定了HPAM溶液和黄原胶溶液的流变性、在多孔介质中的流变性和残余阻力系数 ,计算了衰竭层效应 .用不同的浓度和注入速度进行了驱油实验 .提出聚合物分子缠结作用的增强不仅引起表观粘度增加或衰竭层厚度降低 ,而且使平行于油水界面的拉动残余油的力增加 ,从而使残余油饱和度降低 ,采收率提高 .随浓度增加 ,HPAM溶液的表观粘度和残余阻力系数增加 ,衰竭层厚度减小 ;黄原胶溶液的浓度高于缠结浓度时 ,衰竭层厚度和表观粘度变化不大 .注入速度增加时 ,两种聚合物溶液的衰竭层厚度均降低 ,HPAM溶液的残余阻力系数不变 ,粘弹性增加 ;而黄原胶溶液的残余阻力系数下降 .不同浓度和注入速度情况下两种聚合物溶液的驱油结果证实了文中提出的聚合物分子缠结作用和衰竭层效应对残余油的作用机理 .分子结构的不同是造成两种聚合物溶液在多孔介质中渗流规律和对残余油作用机理的差别的根本原因 .     

Rheological properties of poly(1-trimethylsilyl-1-propyne) solutions

The phase state and rheological properties of poly(1-trimethylsilyl-1-propyne) solutions in toluene and cyclohexane are studied. Samples of poly(1-trimethylsilyl-1-propyne) have the same backbone structure (cis-trans configuration ratio) but different molecular masses. Phase diagrams of these systems are derived via optical interferometry. It is found that they have an upper critical mixing temperature (UCMT) whose value exceeds the boiling points of the individual solvents. The two solvents exhibit limited solubility with respect to the studied polymer, and this parameter decreases with an increase in the molecular mass of the polymer. In the transition from dilute to concentrated solutions, the pattern of the rheological behavior changes from Newtonian to pseudoplastic. The concentration dependences of the zero-shear-rate viscosity of the solutions are typical for flexible-chain polymers. The viscous behavior of the poly(1-trimethylsilyl-1-propyne)-solvent system can be described through a single generalized viscosity-concentration relationship if dimensionless reduced values that take into account the contribution of the molecular mass, the nature of the solvent, and the pattern of intermolecular interactions in the solutions are used as the argument and the function.     

Predictions of Some Internal Microstructural Models for Polymer Melts and Solutions in Shear and Elongational Flows

Summary: In this work, the behavior of some internal microstructural models with different mobility tensors has been studied for polymer melts and solutions under steady and transient simple shear and elongational flows. The time evolution equations for conformation and stress tensors in the models reviewed have their root in the Generalized Poisson bracket formalism. Two different families of conformational models have been selected for this study. The first family is based on the Modified Finitely Extensible Nonlinear Elastic (FENE‐P) energy while the second uses a Volume Preserving Conformational Rheological (VPCR) model based on the Hookean Helmholtz free energy function. Several expressions for the mobility tensor based on the previously mentioned energy functions are used to obtain the models. The sensitivity of both families of models to the choice of the mobility tensors on the prediction of material functions in the transient and steady flows is discussed. Also, effects of shear rate on the material functions in start‐up and relaxation shear flows for both models are studied. The predictions of both models are compared with experimental data taken from the literature for some polymer melts. These results show that the family of VPCR models is able to predict the steady shear and elongational flow material functions in an extended range of deformation rates whereas the family of FENE‐P models can predict the behavior of only some specified polymer melts.

Experimental data and VPCR model predictions for steady and elongational viscosity for PS [data of H. Munstedt, 1980].     

Investigation of molecular chain orientation change of polymer crystals in phase transitions by friction anisotropy measurement

Direct observation of the molecular orientation change in polymer crystals provides us visible information for understanding their structural phase-transition mechanisms. In this letter, we successfully identified the main-chain orientation of poly(vinylidenefluoride-trifluoroethylene) (P(VDF-TrFE)) crystals over all directions using friction anisotropy measured by lateral-modulation friction force microscopy (LM-FFM). This technique made possible our investigation of molecular orientation changes caused by a ferroelectric phase transition and also a fabrication process for artificial nanometer-scale structures. These results give us visual information that is directly connected to the transition mechanisms.     

Anisotropy in nonlinear polymer rheology

A theory describing the behavior of liquids with anisotropic relaxation times in terms of the extended (locally nonequilibrium) thermodynamics of irreversible processes has been formulated. The theory forms the basis for a general approach to the investigation of anisotropy of the rheological properties of orientable polymer liquids. Uniaxial shear and elongation flows of a viscoelastic fluid in one preferred direction have been considered. The pattern of the obtained viscometric functions indicates the important role of macroscopic orientation effects in the rheology of polymeric media.     

A single particle model to simulate the dynamics of entangled polymer melts

We present a computer simulation model of polymer melts representing each chain as one single particle. Besides the position coordinate of each particle, we introduce a parameter n(ij) for each pair of particles i and j within a specified distance from each other. These numbers, called entanglement numbers, describe the deviation of the system of ignored coordinates from its equilibrium state for the given configuration of the centers of mass of the polymers. The deviations of the entanglement numbers from their equilibrium values give rise to transient forces, which, together with the conservative forces derived from the potential of mean force, govern the displacements of the particles. We have applied our model to a melt of C(800)H(1602) chains at 450 K and have found good agreement with experiments and more detailed simulations. Properties addressed in this paper are radial distribution functions, dynamic structure factors, and linear as well as nonlinear rheological properties.     

The Microscopic Structure–Property Relationship of Metal–Organic Polyhedron Nanocomposites

Monodispersed hairy nanocomposites with typical 2 nm (isophthalic acid)₂₄Cu₂₄ metal–organic polyhedra (MOP) as a core protected by 24 polymer chains with controlled narrow molecular weight distribution has been probed by imaging and scattering studies for the heterogeneity of polymers in the nanocomposites and the confinement effect the MOPs imposing on anchored polymers. Typical confined‐extending surrounded by one entanglement area is proposed to describe the physical states of the polymer chains. This model dictates the counterintuitive thermal and rheological properties and prohibited solvent exchange properties of the nanocomposites, whilst those polymer chain states are tunable and deterministic based on their component inputs. From the relationship between the structure and behavior of the MOP nanocomposites, a MOP‐composited thermoplastic elastomer was obtained, providing practical solutions to improve mechanical/rheological performances and processabilities of inorganic MOPs.     

Rheology of polymers that are initially in the disentangled state

An attempt was made to measure the effects of molecular entanglements on the rheological properties of polymer melts. Two classes of polymers were studied; glassy atactic polystyrene polymers covering a 60-fold range in molecular weight, and semicrystalline high-density polyethylene from two sources covering about a twofold range in molecular weight. The entanglements initially present were removed or greatly reduced in number by freeze drying the polystyrene polymers from dilute solutions below and above C*, the critical overlap concentration, and by slowly crystallizing the polyethylene from very dilute solutions. Since only minor rheological changes were observed with polystyrene, it would appear that the initially isolated coils interpenetrate more rapidly than is indicated by the results of Liu and Morawetz, or that the rheological behavior is rather insensitive to whether the flow obstacles are intermolecular or intramolecular. The enhancement of the viscosity and elasticity observed with polyethylene polymers indicate the importance of the crystallization step on the local melt topology of the polymer chains.     

Influence of polyethylene oxide on the rheological properties of semidilute, wormlike micellar solutions of hexadecyltrimethylammonium chloride and sodium salicylate

The influence of polyethylene oxide (PEO) on the rheological properties of equimolar wormlike micellar solutions of hexadecyltrimethylammonium chloride (HTAC) and sodium salicylate (NaSal) is investigated, above the concentration where a micellar entanglement network is formed. PEO is known to have a temperature-dependent binding affinity for HTAC micelles. The influence of temperature, PEO concentration, and HTAC concentration is explored. Within the concentration and temperature range examined (25-100 mM HTAC and 25-50 degrees C), HTAC/NaSal solutions exhibit rheological characteristics of an entanglement network. Application of transient network theory provides information in the form of the plateau modulus, G(infinity)', the terminal viscoelastic relaxation time, tau(R), the reptation time, tau(rep), the micellar breaking time, tau(br), the mean micellar length, L , and the entanglement length, l(e). Consistent with literature data, increase of HTAC concentration results in an evolution from slow-breaking to fast-breaking behavior, accompanied by an increase in G(infinity)' and tau(rep), and decreases in tau(R), and tau(br), l(e) and L . Addition of PEO results in a substantial decrease in G(infinity)' (increase in l(e)), and corresponding increases in tau(R) and L . These observations are consistent with the idea that binding of HTAC micelles to PEO in aqueous solution decreases the number of surfactant molecules available to contribute to the entanglement network of wormlike micelles.     

聚合物多相复合体系的结构和内耗行为特征

描述了聚合物共混物及纤维增强聚合物基复合体系的内耗研究现状，并着重分析了内耗行为与微观结构的相关性。目前迫切需要解决的问题包括对内耗微观机制的研究，建立起适当的模型，并赋予特征参数以明确的物理意义。     

A nonempirical anisotropic atom-atom model potential for chlorobenzene crystals

A nearly nonempirical, transferable model potential is developed for the chlorobenzene molecules (C6ClnH6-n, n = 1 to 6) with anisotropy in the atom-atom form of both electrostatic and repulsion interactions. The potential is largely derived from the charge densities of the molecules, using a distributed multipole electrostatic model and a transferable dispersion model derived from the molecular polarizabilities. A nonempirical transferable repulsion model is obtained by analyzing the overlap of the charge densities in dimers as a function of orientation and separation and then calibrating this anisotropic atom-atom model against a limited number of intermolecular perturbation theory calculations of the short-range energies. The resulting model potential is a significant improvement over empirical model potentials in reproducing the twelve chlorobenzene crystal structures. Further validation calculations of the lattice energies and rigid-body k = 0 phonon frequencies provide satisfactory agreement with experiment, with the discrepancies being primarily due to approximations in the theoretical methods rather than the model intermolecular potential. The potential is able to give a good account of the three polymorphs of p-dichlorobenzene in a detailed crystal structure prediction study. Thus, by introducing repulsion anisotropy into a transferable potential scheme, it is possible to produce a set of potentials for the chlorobenzenes that can account for their crystal properties in an unprecedentedly realistic fashion.     

Deciphering structural domains of alkanethiol self-assembled configurations by friction force microscopy

High resolution and high sensitivity friction force microscopy (FFM) is used to distinguish between different crystallographic domains of standing up molecular configurations of self-assembled alkanethiols partially covering Au(111) surfaces. We propose two suitable methods to decipher structural domains of the same configuration depending on the two-dimensional (2D) symmetry of the organic adlayer. For the hexagonal (radical3xradical3)R30 degrees where no differences among equivalent domains are expected in lattice-resolved scanning force imaging, different molecular domains however can be observed in lateral force images because of the friction asymmetry caused by domains presenting different relative orientations between the molecular tilt direction and the tip scanning direction. Since no lateral packing anisotropy is expected in this close-packed configuration, no friction anisotropy however is observed. Conversely, because of its rectangular space group symmetry, lattice resolved stick-slip imaging is enough to solve between the existing domains for the (2xradical3) rectangular configuration.     

RHEOLOGICAL STUDY ON HYALURONIC ACID AND ITS DERIVATIVE SOLUTIONS

ABSTRACT

Rheological measurements were performed on Hyaluronic acid (HA) and its derivative solutions to evaluate steady flow viscosity and dynamics response with the aim to correlate the materials properties to the concentration, molecular weight and chemical structure. At low molecular weight and concentration, the HA solutions behaved as viscous liquid, whereas a soft-gel response was evident at higher molecular weight and concentration due to chains entanglement. Increasing the molecular weight was more effective than increasing concentration in promoting entanglement of molecular chains of HA. Comparing the behavior of HA solutions with that of Hyaluronic acid derivatives, it is showed that it is possible to modulate the rheological properties of HA based solutions by chemical modification preserving the bio-compatibility of the materials. The results of the rheological analysis provide a valuable tool to properly design optimal substitutes for specific biomedical application.     

Anisotropic friction model of DNA electrophoresis in polymer solutions: Comparison with direct observations

The electrophoresis of DNA chains in uncrosslinked polymer solutions with a Brownian dynamics simulation with an anisotropic friction tensor was analyzed. According to the degree of anisotropy, three types of migration behavior are obtained: fluctuation without or with periodicity between U‐shaped and compact conformations, or migration with linear conformation. We found good agreement between our simulation results and the direct observations of DNA by fluorescence microscopy. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1316–1322, 2003     

Time-domain calculations of the polarized Raman spectra, the transient infrared absorption anisotropy, and the extent of delocalization of the OH stretching mode of liquid water

The polarized Raman spectrum and the time dependence of the transient infrared (TRIR) absorption anisotropy are calculated for the OH stretching mode of liquid water (neat liquid H2O) by using time-domain formulations, which include the effects of both the diagonal frequency modulations (of individual oscillators) induced by the interactions between the dipole derivatives and the intermolecular electric field, and the off-diagonal (intermolecular) vibrational coupling described by the transition dipole coupling (TDC) mechanism. The IR spectrum of neat liquid H2O and the TRIR anisotropy of a liquid mixture of H2O/HDO/D2O are also calculated. It is shown that the calculated features of these optical signals, including the temperature dependence of the polarized Raman and IR spectra, are in reasonable agreement with the experimental results, indicating that the frequency separation between the isotropic and anisotropic components of the polarized Raman spectrum and the rapid decay (approximately 0.1 ps) of the TRIR anisotropy of the OH stretching mode of neat liquid H2O are mainly controlled by the resonant intermolecular vibrational coupling described by the TDC mechanism. Comparing with the time evolution of vibrational excitations, it is suggested that the TRIR anisotropy decays in the time needed for the initially localized vibrational excitations to delocalize over a few oscillators. It is also shown that the enhancement of the dipole derivatives by the interactions with surrounding molecules is an important factor in generating the spectral profiles of the OH stretching Raman band. The time-domain behavior of the molecular motions that affect the spectroscopic features is discussed.     

Light scattering in binary and ternary (polymer) solutions with specific interactions

Concentration dependence of basic light-scattering quantities in three binary low-molecular and two ternary polymer solutions was studied. Depolarization ratio alone may serve as a sensitive measure of presence of specific interactions. Experimental data of anisotropic scattering in low-molecular mixtures were in harmony with the idea that the parameters determining molecular orientation should be considered as continuous probability variables; in the case of polymer solutions specific interactions do not influence the anisotropic scattering.The presence of specific interactions with the formation of a minimum on the course of isotropic scattering is characterized. Transition from one solution structure to another with a local maximum on the course of composition light scattering is indicated.     

The role of hydrogen-bonding interaction in poly(vinyl alcohol)/poly(acrylic acid) blending solutions and their films

<正>The aim of this work is to investigate the hydrogen-bonding interaction in poly(vinyl alcohol)(PVA)/poly(acrylic acid)(PAA) blending system and its influence on rheological properties in solution and the physical properties in solid state. Introducing PAA into PVA solutions resulted in a thickening behavior of blend solutions.The viscosity of the solutions increased with PAA content increasing,and a maximum viscosity could be obtained when the ratio of PVA/PAA was 70/30. The intermolecular hydrogen-bonding and miscibility between PVA and PAA in solid state were investigated by differential scanning calorimetry(DSC),Fourier transform infrared spectroscopy(FTIR) and mechanical measurements.The results displayed the great influence of introducing PAA on the properties of blending films.The tensile strength increased from 89.31 MPa to 119.8 MPa and Young's modulus improved by over 300%with increasing PAA concentration compared with those of pure PVA films.By systematically studying the rheological behaviors of solutions and the physical properties of films,the influence of hydrogen-bonding in solutions and solid states were discussed.     

Optical properties of stretched polymer dispersed liquid crystal films

The basic mechanisms determining the formation of optical anisotropy in stretched, thin polymer dispersed liquid crystal (PDLC) films with micron sized nematic droplets have been studied experimentally and the results analysed in terms of a proposed theoretical model. The experiments were performed on PDLC films with the bipolar nematic director configuration in the droplets, where the film transmittance, microscopic structure, and birefringence of the polymer matrix were studied. It is shown that the orientational ordering of bipolar nematic droplets, introducing the main contribution to the ability of stretched PDLC film to polarize the transmitted light, is strongly dependent upon initial droplet shape and the elastic properties of the polymer matrix. The 'anomalous' nematic director orientation is also observed in a portion of elongated droplets where the axes of bipolar configurations do not coincide with the major axes of the droplet cavities due to the presence of inclusions at the cavity walls. The effect of alternation of droplet size and shape upon stretching and the influence of optical anisotropy of the polymer matrix on film transmittance are analysed. On the basis of the results obtained, simple criteria for optimization of main PDLC polarizer performance are formulated.     

Local Transient Jamming in Stress Relaxation of Bulk Amorphous Polymers

Bulk amorphous polymers become stretched and parallel-aligned under loading stress,and their intermolecular cooperation slows down the subsequent stress relaxation process.By means of dynamic Monte Carlo simulations,we employed the linear viscoelastic Maxwell model for stress relaxation of single polymers and investigated their intermolecular cooperation in the stress relaxation process of stretched and parallel-aligned bulk amorphous polymers.We carried out thermal fluctuation analysis on the reproduced Debye relaxation and Arrhenius fluid behaviors of bulk polymers.We found a transient state with stretch-coil coexistence among polymers in the stress relaxation process.Further structure analysis revealed a scenario of local jamming at the transient state,resulting in an entropy barrier for stretch-coil transition of partial polymers.The microscopic mechanism of intermolecular cooperation appears as unique to polymer stress relaxation,which interprets the hydrodynamic interactions as one of essential factors raising a high viscosity in bulk amorphous polymers.Our simulations set up a platform of molecular modeling in the study of polymer stress relaxation,which brought new insights into polymer dynamics and the related mechanical/rheological properties.