EFFECT OF ADSORPTION ON THE VISCOSITY OF DILUTE POLYMER SOLUTION*

Careful measurements of the dilute solution viscosities of polyethylene glycol and polyvinylalcohol in water were carried out. The reduced viscosities of both polymer solutions plot upward curves atextremely dilute concentration levels similar to the phenomena observed for many polymer solutions in theearly 1950's. Upon observation of the changes of the flow times of pure water in and the wall surfacewettability of the viscometer after measuring solution viscosity, a view was formed that the observed viscosityabnormality at extremely dilute concentration regions is solely due to the effect of adsorption of polymerchains onto the wall surface of viscometer. A theory of adsorption effect based on the Langmuir isothermswas proposed and a mathematical analysis for data treatment was performed. The theory could adequatelydescribe the existing viscosity data. It seems necessary to correct the viscosity result of dilute polymersolutions measured by glass capillary viscometer by taking into account the effect of adsorption in all cases.     

STUDY ON THE CONCENTRATION DEPENDENCE OF ORIENTATION OF POLYSTYRENE ON SILVER BY THE SERS TECHNIQUE*

Polystyrene films were adsorbed onto a silver surface from dichloromethane solutions with concentrations of 0.1 to12 wt%, and then studied by the surface enhanced Raman technique. A critical concentration for coil interpenetration wasobserved.     

VISCOSITY BEHAVIOR OF PS／TOLUENE SOLUTION IN DILUTE AND EXTREMELY DILUTE CONCENTRATION REGION

The influences of both the volume of PS/toluene solution in the Ubbelohde viscometer and the precision of the time measuring on the viscosity behavior in dilute and extremely dilute concentration region are investigated. It was found that the influence of the former can neglect, but that of the latter is so prominent that the data fluctuate bitterly and linearity of the curve of the reduced viscosity vs. concentration (ηsp/c-c) becomes too bad to obey the Huggins equation down to the extremely dilute region, despite the error of the flow times Δt≤0.2s, which is permitted by the conventional method of viscosity measurement. Through strict mathematical analyses, it was found that the error (E) of the reduced viscosity is in proportion and inverse propor tion to Δt and concentration c, respectively. So the less the concentration, the more the error is. Consequently, a lowest concentration limit cL corresponding to given experimental error may exist and it will be meaningless for further operation below CL because of the great fluctuation of the data. Therefore, it needs to seriously reconsider the application of the conventional method of Ubbelohde viscosity measurement in the extremely dilute polymer solution under traditional conditions because of the great influence of the experimental error.     

VISCOSITY BEHAVIOR OF PS/TOLUENE SOLUTION IN DILUTE AND EXTREMELY DILUTE CONCENTRATION REGION

1.INTRODUCTIONAsearlyas1950sitwasfoundthatsolutionviscosityofasinglepolymerinextremelydiluteconcentrationregionusuallyrevealssomeabnormalities,i.e.,thereducedviscosityconcentration(hsp/c~c)curvesdeviatefromlinearrelationshippredictedasHugginsequationandshoweitheranupwardoradownwardturnasconcentrationisverylow[1].Evenifforthe[()-0.2()]identicalPMMA/toluenesolution,therearetwocontraryresults:onereportedthecurvebendsupward[2],whiletheotherfounditdownward[3].Inordertointerpretthisabnormalphe…     

高分子混合物溶液在极稀浓度区的粘度异常行为

上世纪50年代初人们就发现,高分子溶液的粘度在极稀浓度区往往表现出异常行为,即当浓度低于某一特定值后,比浓增比粘度-浓度图偏离预计的线性关系,出现上弯或下弯的曲线.     

离分子混合物溶液在极稀浓度区的粘度异常行为

上世纪50年代初人们就发现,高分子溶液的粘度在极稀浓度区往往表现出异常行为,即当浓度低于某一特定值后,比浓增比粘度浓度图偏离预计的线性关系,出现上弯或下弯的曲线.几十年来人们对此现象展开了大量研究,提出了一些互不协同的解释[1,2].最近,程时等[3,4]对该问题作了系统深入的研究,指出这种粘度异常是源于粘度测量中高分子溶液与毛细管内壁间的界面作用,并给出了消除界面作用干扰的理论改正公式.至此,单一高分子溶液粘度的异常问题得到了明确的解释.但是,关于高分子混合物在极稀浓度区的粘度行为的研究就比较稀少.80年代Ｄｏｎｄｏｓ…     

COMPUTER SIMULATION OF POLYMER SOLUTION THERMODYNAMICS

The statistical counting method for the computer simulation of the ther-modynamic quantities of polymer solution has been reviewed. The calculating results fora single athermal chain confirm the theory of the renormalization group. The results forthe athermal solution are consistent with the scaling law of the osmotic pressure with theexponent 2.25. The results for a single chain with the segmental interaction are in a goodagreement with the exact results obtained by the direct counting method. The results forthe polymer solution show us that the Flory-Huggins parameter is strongly dependent onboth the polymer concentration and the interaction energy between segments. Monte carlo simulation; Polymer solution; Thermodynamic quantities;Translational entropy; Conformational entropy; Scaling law     

关于高分子极稀溶液粘度测定问题的探讨

对聚苯乙烯(PS)／甲苯稀及极稀溶液的粘度用常规的乌氏粘度法进行了测定．发现高分子在毛细管壁上无稳固吸附．在极稀浓度区，粘数(ηsp/c)值波动较大，在时间测量精度不变的条件下，粘数测量误差与浓度成反比，以致ηsp／c-c曲线的线性及重现性变差，并推导出了粘数测量误差与浓度及时间测量误差间的关系式．在此基础上，讨论了确定浓度测量下限的原则及计算公式，认为常规的乌氏粘度测定方法对极稀溶液的应用值得商榷．     

SHAPE OF POLYMER CHAINS ON A TETRAHEDRAL LATTICE*

The shape of unperturbed polymer chains was studied using the Monte Carlo technique on a tetrahedral lattice.The asphericity A, the ratios/and/ were calculated for different values of polymer chain length n,conformational energy ε (ε≥0) and temperature T. The asphericity A decreases with the increase of chain length and tends toreach its limiting value rapidly with the decrease of γ(γ=ε/k_BT). For large n, A is about 0.525±0.005, the ratios/ and/ are about 2.7 and 12.0, respectively, and are almost independent of γ, but for short chains, theydepend on γ.     

APPLICATION OF NONIONIC TEMPERATURE SENSITIVE HYDROGEL FOR CONCENTRATION OF PROTEIN AQUEOUS SOLUTION

Six different N-alkyl substituted acrylarnide nonionic hydrogels were prepared and their swelling characteristics were measured. Poly N-isopropyl acrylamide (PNIPA) and poly N-n-propyl-acrylamide (PNNPA) temperature sensitive hydrogels were chosen as the nonionic temperature sensitive hydrogels for concentration of very dilute aqueous protein solution. The separation properties of PNIPA and PNNPA hydr0gels with different network dimensions were studied and the modification of the hydrogels was surveyed in order to decrease their surface adsorption of protein molecules. The experimental results of the concentration of BSA (Bovin serum albumin) dilute aqueous solution by hydroxylpropyl methacrylate (HPMA) copolymerized PNIPA hydrogel were given. The value and the limitation of concentration of dilute aqueous protein solution by this method was evaluated.     

POLYMER SUPPORT EFFECTS OF METAL COMPLEXES FOR CATALYSIS*

In the course of investigating the catalytic behavior of metal complexes forring opening metathesis polymerization of cycloolefins, metathesis, hydroformylation andselective hydrogenation of olefins experimental results time and again indicate the pres-ence of effects of macromolecular supports -the utilization of macromolecular supportsincreases obviously the activity, selectivity, and stability of the catalysts and so as to in-crease the conversion of substrates, yields of reactions, properties of formed polymers andso on. Discussed these effects on the basis of the authors' experiments.     

A HYBRID POLYMER GEL AND ITS STATIC NONERGODICITY*

We used a thermally reversible hybrid gel made of billions of physically jam-packed swollen thermally sensitivepoly(N-isopropyl-acrylamide) chemical microgels. Laser light scattering study on a series of such hybrid gels formed atdifferent gelling rates and temperatures revealed that the position-dependence of the scattering speckle pattern(staticnonergodicity) came from large voids formed during the sol-gel transition. With a proper preparation, such a nonergodicitycould be completely removed, indicating that the static nonergodicity generally observed in a gel is not indinsic, but comesfrom the clustering "island" structure formed during the gelation process.     

A NOVEL METHOD FOR CHARACTERIZING THE WHOLE PROCESS OF POLYMER GELATION*

A novel method was established to investigate the gelation process of polymers. The change of refractive index ofa polymer system during gelation was determined in situ in a prismatic cell. It can give reliable information on the wholegelation process. The apparatus and the execution of this technique are illustrated and the error is also discussed.     

A NEW MODEL FOR CONCENTRATION DEPENDENCE OF POLYMER CHAIN DIMENSIONS

A new model for concentration dependence of polymer chain dimensions over the wholeconcentration range was proposed. The hydrodynamic volume of a solvated macromoleculewas found to be a universal function of the degree of coil overlapping (c/c~*). The radiusof gyration (R_g) and the expansion coefficient (α) of polymer in solution or in bulk. pre-dicted by this model are much better in agreement with the experimental data of small angleX-ray scattering and neutron scattering from literature, than with the values predicted byother models and theories.     

DILUTE SOLUTION BEHAVIOR OF CHITOSAN IN DIFFERENT ACID SOLVENTS

Dilute solution behavior of chitosan was studied in formic acid, acetic acid, lactic acid andhydrochloric acid aqueous solution under different pH values. The reduced viscosities, η_(sp)/C,ofchitosan solutions were dependent on the properties of acid and pH value of solvents. For a givenchitosan concentration, η~(sp)/C decreased with the increase of acid concentration, or decreasing pHof solvent, indicating shielding effect of excessive acid similar to adding salt into solution. Thestabilities of dilute chitosan solution in formic acid and lactic acid were better than that in acetic acid and hvdrochloric acid.     

STUDIES ON SELF-ASSOCIATIVE BEHAVIOR OF A NOVEL CATION AMPHIPHILIC POLYMER

A novel associating polymer P(AEBA) was synthesized by radical polymerization of the cationic amphiphilic monomer,4-(2-(acryloyloxy)ethoxy)benzyl tri-ethyl ammonium bromide(AEBA),in aqueous solutions.P(AEBA) displays a strong tendency for self-association in aqueous solutions and is sensitive to the external stimulation such as added salt.The associative properties and morphologies of P(AEBA) were studied by fluorescnece probe technique,viscometry and TEM.In dilute salt-free solutions P(AEBA) behaves as ...     

MECHANICAL RELAXATION TIME OF A TWO-COMPONENT EPOXY NETWORKLiClO_4 POLYMER ELECTROLYTE

The mechanical relaxation time of a two-component epoxy network-LiClO_4 system as a polymer electrolyte was investigated. The network is composed of diglycidyl ether of polyethylene glycol (DGEPEG) and triglycidyl ether of glycerol (TGEG), wherein LiCIO_4 was incorporated and acts as both the ionic carrier and the curing catalyst. As the relaxation time is informative to the segmental mobility, which is known to be essential for ionic conductivity, the average relaxation times of the specimens were determined through master curve construction. Experimental results showed that the salt concentration, molecular weight of PEG in DGEPEG and DGEPEG/TGEG ratio have profound effect on the relaxation time of the specimen. Among these factors , the former reinforces the network chains, leading to lengthen the relaxation time, whereas the latter two are in favour of the chain flexibility and show an opposite effect. The findings was rationalized in terms of the free volume concept.     

COMPATIBILITY STUDIES ON POLYMER/WAX AND POLYMER/RESIN-ASPHALTENE BY VISCOMETRY AND PHOTOMICROGRAPHY

The compatibility of mixtures of polymeric pour point depressants, i.e. poly(ethylene-co-vinylacetate) (EVA), poly (EVA-graft-octadecylacrylate) (EVA-g-POA ), poly (ethylene-co-octadecylacrylate) (EOA) and poly(ethylene oxide-co-propylene oxide) (EO-co-PO) withwax or resin-asphaltene from crude oil have been studied by means of dilute-solution vis-cometry. It was found that each mixture pair is incompatible, but the degrees of incompati-bility are quite different, which are in good agreement with the results from photomicrog-raphy.     

RHEOLOGICAL BEHAVIOR OF ERWINIA GUM IN AQUEOUS SOLUTION*

Erwinia (E) gum, an extracellular polysaccharide, is composed of fucose, galatose, glucose andglucuronic acid. Its viscosity behavior was investigated by a low-shear-rate multiball viscometer and arotational viscometer. Its weight-average molecular weight M_w and intrinsic viscosity [η] in 0.2 mol/L NaClaqueous solution were measured by light scattering method at 35℃and viscometry at 25℃and found to be1.06×10~6 g/mol and 1050 mL/g, respectively, and its aggregates in aqueous solution were proved by gelpermeation chromatography (GPC). These results indicated that E gum in water has exceedingly highviscosity and exhibits Binham fluid behavior, owing to its aggregation. The viscosity of E gum decreasedwith increasing temperature, and the turning point appeared at 38℃for dilute solution and 80℃forconcentrated solution suggesting that the aggregates of E gum in water started to disaggregate under thesetemperatures. In addition, the aggregates can be disrupted by adding either acid or base. The experimentalresults indicated that the E gum is a good thickening agent, and its fluid behavior is similar to xanthan.     

A RHEOLOGICAL MODEL FOR POLYMER MELTS WITH INTERNAL STRUCTURE IN FLOW FIELDS*

Conceptually, an imagined conformation ellipsoid is supposed to represent the shape of a polymerchain for polymer melts in flow fields and to be equivalent to the volume element in a mathematical sense incontinuum mechanics. A power law dependence of shear modulus of polymer melts on detC, referred to asenvelope volume, is proposed. Based on those assumptions and the non-linear relation of shear modulus, aphenomenological viscoelastic model is derived. The model is tested in simple shear flow, simpleelongational flow, oscillatory shear flow, and relaxation process after flow suddenly stopped. The resultsshow that the model works well to predict the change of internal structure and viscoelastic performance ofpolymer melts in flow fields.