摘要:

Experimental results are reported for the constant‐force squeezing of three highly viscous polymers. Profiles for the plate separation versus time were measured with the use of a modified materials testing system. Two polybutenes were tested at 25 °C, and a low‐density polyethylene melt (IUPAC sample X) was studied at 150 °C. Measured half‐times show that the polybutenes behave as inelastic fluids with viscosities that decrease slightly with shear rate. In slow squeezes the experimental results agree with the predictions of Newtonian fluid theory corresponding to the available viscosity measurements. The behavior of LDPE X is described by the CEF model in both slow and fast squeezes. Although shear rates are as high as1000 s−1,the elastic effects for LDPE X are small compared to viscous effects.

ISSN:0148-6055    

DOI:10.1122/1.549993

出版商:The Society of Rheology    

年代:1988

数据来源: AIP

摘要:

Both Hinch and Leal and Stewart and Sørensen solved the diffusion equation for the configurational distribution function of rigid dumbbells at high shear rates by several different numerical methods and obtained asymptotic expressions for the viscometric functions. In this note we have considered only a contracted distribution function which, however, can be calculated analytically. This contracted distribution function not only contains interesting information about the behavior of rigid dumbbells at high shear rates but can also be used to find an exact asymptotic expression for the first normal‐stress coefficient. By introducing modified time constants, the results of the present paper, which have been derived for rigid dumb‐bells with Oseen‐Burgers hydrodynamic interaction, can easily be generalized to rigid multibead rods and Rotne‐Prager‐Yamakawa hydrodynamic interaction.

ISSN:0148-6055    

DOI:10.1122/1.550004

出版商:The Society of Rheology    

年代:1988

数据来源: AIP

摘要:

Stress relaxation behavior of concentrated solutions of high molecular weight polystyrene following a step shear strain is studied using both mechanical and optical birefringence techniques. Using the stress‐optic law, which we find to be valid for our solutions, we obtain time‐dependent shear stress and first normal stress difference values from birefringence measurement that are free of transducer compliance effects. Similar to the previously reported experimental observations of Fukuda, Osaki and Kurata, we obtain unusually low values for nonlinear shear moduli, much lower than the predictions of Doi‐Edwards model, for the sample with more than about 60 entanglements per molecule. Moreover, the shear stress and first normal stress difference data measured on this sample do not conform to the Lodge‐Meissner relationship, especially at long times, suggesting the formation of regions in which the imposed strain is not homogeneously distributed.

ISSN:0148-6055    

DOI:10.1122/1.549965

出版商:The Society of Rheology    

年代:1988

数据来源: AIP

摘要:

Sealants and caulks are used in construction situations where they are subjected to sizable deformations relative to the stress required for flow while curing and after curing. This study was designed to examine the elastic and viscous nature of specially prepared materials having built‐in variations in time‐dependent structure development. Few measurements have been made to characterize the elastic nature of the structure developed by such materials and to relate these to performance properties. When strains which exceed the elastic limit are developed, these systems can form brittle fractures. Above the elastic limit, the viscous properties of the material become dominant which should reduce the tendency to fracture. Tests were performed with the Rheometrics Mechanical Spectrometer and the Carri‐Med Controlled Stress Rheometer. The viscoelastic components(G′,G″,η*)and steady shear transient tests were obtained with the Mechanical Spectrometer. Since the Stress Rheometer induces a stress and measures a strain, a greater sensitivity is produced making the instrument ideal for yield stress determinations. Low shear rate creep tests were also made using the Controlled Stress Rheometer. Results show that these sealants behave as soft elastic materials which recover their structure rapidly when the yield value is exceeded.

ISSN:0148-6055    

DOI:10.1122/1.550003

出版商:The Society of Rheology    

年代:1988

数据来源: AIP

摘要:

Rib and web growth leading to fiber generation and dissipation—to spatter in waterborne latex coatings and to misting in water‐reducible coatings—in roll applications are discussed. The extent of growth and dissipation phenomena are related to the coating's dynamic uniaxial extensional viscosity (DUEV). Complexities in the analysis include limitations in DUEV determinations via the fiber‐suction technique, variations in maximum shear and extension rates in roll application, and the relative contribution of the shear viscosifying component to the magnitude of DUEV data. The extensional behavior of polymer solutions varying in segmental and conformational rigidity are examined as a means of delineating the complexities.

ISSN:0148-6055    

DOI:10.1122/1.549966

出版商:The Society of Rheology    

年代:1988

数据来源: AIP

摘要:

The importance of dynamic uniaxial extensional viscosities (DUEVs) relative to shear viscosity and viscoelastic parameters in the onset of ribbing, web growth, and fiber formation in roll application is illustrated with water‐soluble polymer blends. The blends consist of variable component ratios of high‐molecular‐weight, water‐soluble polymers of different segmental rigidities. The blends provide non‐Newtonian aqueous solutions varying in dynamic uniaxial extensional viscosities, but with identical shear viscosities at a given shear rate over a104 s−1range. As the DUEV of these “same‐shear viscosity,” non‐Newtonian fluids is increased an earlier onset of ribbing is observed. After onset, a decrease in the number of ribs is observed with increasing DUEV of the fluid; the decrease is associated with growth in web size. Increasing the radius of the roll effects an earlier onset of ribbing, but the number of ribs formed at higher peripheral velocities and smaller nip spacings decreases relative to smaller radii rolls.

ISSN:0148-6055    

DOI:10.1122/1.549967

出版商:The Society of Rheology    

年代:1988

数据来源: AIP