Effect of pressure on the flow behavior of polybutene

Abstract

The rheology of submicron thick polymer melt is examined under high normal pressure conditions by a recently developed photobleached‐fluorescence imaging velocimetry technique. In particular, the validity and limitation of Reynold equation solution, which suggests a linear through‐thickness velocity profile, is investigated. Polybutene (PB) is sheared between two surfaces in a point contact. The results presented in this work suggest the existence of a critical pressure below which the through‐thickness velocity profile is close to linear. At higher pressures however, the profile assumes a sigmoidal shape resembling partial plug flow. The departure of the sigmoidal profile from the linear profile increases with pressure, which is indicative of a second‐order phase/glass transition. The nature of the transition is confirmed independently by examining the pressure‐dependent dynamics of PB squeeze films. The critical pressure for flow profile transition varies with molecular weight, which is consistent with the pressure‐induced glass transition of polymer melt. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014, 52, 708–715

Advances in nonequilibrium molecular dynamics simulations of lubricants and additives

“…In the field of tribology, shear localisation has only been directly observed experimentally in viscous model lubricants, such as polybutadiene and polyphenyl ethers (e.g., 5P4E) [196][197][198][199][200][201]. However, it has also been inferred from film thickness measurements in realistic mineral oils [202,203] and there is currently a growing consensus that this phenomenon may also be important for more realistic lubricants under extreme EHL conditions [185].…”

History, Origins and Prediction of Elastohydrodynamic Friction

“…From these distributions, velocity profiles across EHD films of ca 100 nm thickness were obtained. It was found shown that low MWt polybutenes give Couette shear at low pressure EHD contacts, but form a velocity profile suggestive of plug flow at higher pressures [107]. When a hydrophobic coating was applied to one surface, slip at this surface was observed [108].…”

“…Recently a very promising new experimental method for obtaining velocity profiles through EHD films has been described [107]. An EHD contact is established between two glass surfaces using a lubricant containing dissolved fluorescent dye.…”

Effect of Base Oil Structure on Elastohydrodynamic Friction

“…6 and 7 can be used to determine the mean temperature of the oil film in the contact for each friction measurement. For tungsten carbide, the product K s qc = 3.3 9 10 8 J 2 K -2 s -1 m -4 , b was 69 lm at a load of 22.7 N and 92 lm at 53.7 N. For most lubricants, K oil was estimated from data in [34] by selecting the nearest fluid type and correcting to the relevant mean contact pressures as suggested in this paper. Atmospheric pressure values for PFPEs were taken from [35] and ionic liquids from [36] and adjusted by assuming a similar conductivity-pressure dependence to other fluid types.…”