A Constitutive Model Describing Molecular Configuration Evolution and Transient Rheological Behavior of Entangled Polymer Solutions

Entanglement network is an important structural feature in concentrated polymer solutions and polymer melts,which has a great influe nee on the transie nt rheological behavior and molecular con figurati on evolution.However,the existi ng constitutive models have limitations in describi ng the influe nee of dyn amic entan glement behavior on molecular chain motion,resulti ng in inaccurate descriptions of the transient rheological behavior.Thus,a molecular con figuration evoluti on model for polymer solutions considering the dyn amic entanglement effect is proposed by introducing an intermolecular force that changes with the orientation of the molecular chain in this work.The intermolecular force is introduced by consider!ng the friction coefficient as anisotropic,and the orientation effect is considered by introducing an excluded volume depende nt an isotropic diffusi on.The proposed model can better describe the stress relaxation,stress growth,and dielectric an isotropy of polymer soluti ons compared with the an isotropy FENE model and FENE model.In addition,the in fluence of different model parameters on the transient and steady shear response of polymer soluti on is investigated,and the results show that the in fluence of volume loss on the fricti on anisotropy factor k0 in creases as the solution concen tration in creases.

THEORETICAL EFFECTS OF MOLECULAR DIMENSION AND CONFIGURATION ON EFFECTIVE DIFFUSION COEFFICIENT OF MACROMOLECULES IN MICROPOROUS MEMBRANES

This paper presents a theoretical method for predicting the effective diffusion coefficient of macromolecules in the microporous membrfines in view of the effects of molecular dimension and configuration. On the basis of the hindered diffusion theory of spherical neutral macromolecules in a micropore of a long cylinder, the effects of molecular dimension and configuration are studied by defining two molecular dimensions:the mean projected radius to predict the concentration partition and the ' hydrodynamically equivalent sphere' radius to evaluate the hydrodynamic reverse drag force. The quantitative comparison shows that the effective diffusion coefficients for different macromolecules predicted by the present method are more consistent with the available published experimental data.

Analysis of Influential Factors of Konjac Glucomannan(KGM) Molecular Structure on Its Activity

Biological activity of konjac glucomannan is closely related to its structure,in particular to its high-level structure.Researches on the activity mechanism of konjac glucomannan are significant for revealing the mysteries of participation in life activity.In this paper,analysis of the effects of konjac glucomannan configuration and various factors on its structure and activity was conducted,mechanism of biological activity of konjac glucomannan was explored,and the hot research topic of konjac glucomannan was given.

Banana-shaped electron acceptors with an electron-rich core fragment and 3D packing capability

The emergence of Y6-type nonfullerene acceptors has greatly enhanced the power conversion efficiency(PCE)of organic solar cells(OSCs).However,which structural feature is responsible for the excellent photovoltaic performance is still under debate.In this study,two Y6-like acceptors BDOTP-1 and BDOTP-2 were designed.Different from previous Y6-type acceptors featuring an A–D–Aʹ–D–A structure,BDOTP-1,and BDOTP-2 have no electron-deficient Aʹfragment in the core unit.Instead,there is an electron-rich dibenzodioxine fragment in the core.Although this modification leads to a marked change in the molecular dipole moment,electrostatic potential,frontier orbitals,and energy levels,BDOTP acceptors retain similar three-dimensional packing capability as Y6-type acceptors due to the similar banana-shaped molecular configuration.BDOTP acceptors show good performance in OSCs.High PCEs of up to 18.51%(certified 17.9%)are achieved.This study suggests that the banana-shaped configuration instead of the A–D–Aʹ–D–A structure is likely to be the determining factor in realizing high photovoltaic performance.

Molecule configurations modulate packing array and charge transfer in cocrystal engineering

Organic cocrystal as an emerging assembly strategy has received increasing attention in constructing multiple functional materials,through continually screening suitable constituent monomers or changing their stoichiometry ratios.However,the role of molecule configuration in the cocrystal field is rarely explored despite the fascinating potential in regulating the packing mode.In this study,the N,N′-diphenyl-5,10-dihydrophenazine derivatives(DPPs) with the flexible scaffold and different methyl substitutions are selected as the donors bearing various molecular configurations.In a simple collaborative way,a series of cocrystals based on DPPs and OFN(octafluoronaphthalene) are fabricated,exhibiting two self-adaptive molecular stacking arrays.X-ray crystallographic analysis and theoretical calculation unveil their different π···π interactions and charge transfer characters,leading to the significant emission redshift up to 125 nm compared with individual DPPs.As a result,controllable molecule stacking structure,tunable emission,and charge transfer properties can be achieved.The study provides a new perspective to reveal the structure-property relationships at the molecular level by controlling the molecule configuration in cocrystal engineering,contributing to the development of cocrystal theoretical physics and organic functional materials.

Study of action mechanisms and properties of Cr^(3+) cross-linked polymer solution with high salinity

Performance characteristics of partially hydrolyzed polyacrylamide （HPAM） and cross- linked polymer （CLP, Cr^3＋ as the cross linker） solutions have been investigated. A Brookfield viscometer, rheometer, dynamic light scattering system, and core flow device have been used to measure the viscosity, viscoelasticity, polymer coil dimensions, molecular configuration, flow characteristics, and profile modification. The results show that, under conditions of high salinity and low HPAM and Cr^3＋ concentrations, cross-linking mainly occurred between different chains of the same HPAM molecule in the presence of Cr^3＋, and a cross-linked polymer （CLP） system with a local network structure was formed. Compared with an HPAM solution of the same concentration, the apparent viscosity of the CLP solution increased slightly or remained almost unchanged, but its viscoelasticity （namely storage modulus, loss modulus, and first normal stress difference） increased, and the resistance coefficient and residual resistance coefficient increased significantly. This indicates that the CLP solution exhibits a strong capability to divert the sequentially injected polymer flood from high-permeability zones to low- permeability zones in a reservoir. Under the same HPAM concentration conditions, the dimensions of polymer coils in the CLP solution increased slightly compared with the dimensions of polymer coils in HPAM solution, which were smaller than the rock pores, indicating that the cross-linked polymer solution was well adapted to reservoir rocks. Core flood experiments show that at the same cost of reagent, the oil recovery by CLP injection （HPAM-1, Cr^3＋ as the cross linker） is 3.1% to 5.2% higher than that by HPAM- 2 injection.

Performance evaluation of oil displacing agents for primary-minor layers of the Daqing Oilfield

A series of experiments were conducted to investigate the molecular coil dimension（D_h） and molecular configuration of partially hydrolyzed polyacrylamides（HPAM）,surfactant/HPAM system, and a living polymer.Compatibility between the polymer coils and the porous media was evaluated by instrumental analysis and laboratory simulation methods.Meanwhile,the performance of chemical flooding was investigated.Results indicated that the D_h decreased with an increase in water salinity and increased with an increase in polymer concentration.In aqueous solution,the polymer presented three-dimensional reticular configuration and exhibited a fractal structure characterized by self-similarity. The polymer in the surfactant/HPAM system was mainly in the form of＂surfactant-polymer＂complex compound and the living polymer had an irregular＂flaky-reticular＂configuration which resulted in relatively poor compatibility between the molecular coils and the porous media.The type of oil displacing agent and its slug size influenced the incremental oil recovery.For the same oil displacing agent,a larger slug size would lead to a better chemical flooding response.Given the final recovery efficiency and economic benefits,high-concentration polymer flooding was selected as the optimimal enhanced oil recovery（EOR） technique and the incremental recovery efficiency was forecast to be 20%.