Thin film rheology

Luengo G ef a/1997 Thin film rheology and tribology of oonfined polymer melts oontrasts with bulk properties Macromolecules 30 2482-94... 

Luengo, G., Schmitt, R, andHUl, R., Thin Film Rheology and Tribology of Confined Polymer Melts Contrasts with Bulk Properties," Macroniolecules,Vo. 30,1997, pp. 2482-2494. 

Liquid lubricant confined in molecularly thin films would experience dramatic changes in its physical properties, such as increased viscosity, slow relaxation, and solidihcation. Progress in studies of thin film rheology has greatly improved our understanding of boundary lubrication, which is the subject to be discussed in this section and in the next. 

Another remarkable feature of thin film rheology to be discussed here is the quantized" property of molecularly thin films. It has been reported [8,24] that measured normal forces between two mica surfaces across molecularly thin films exhibit oscillations between attraction and repulsion with an amplitude in exponential growth and a periodicity approximately equal to the dimension of the confined molecules. Thus, the normal force is quantized, depending on the thickness of the confined films. The quantized property in normal force results from an ordering structure of the confined liquid, known as the layering, that molecules are packed in thin films layer by layer, as revealed by computer simulations (see Fig. 12 in Section 3.4). The quantized property appears also in friction measurements. Friction forces between smooth mica surfaces separated by three layers of the liquid octamethylcyclotetrasiloxane (OMCTS), for example, were measured as a function of time [24]. Results show that friction increased to higher values in a quantized way when the number of layers falls from n = 3 to n = 2 and then to M = 1. 

Thin Film Rheology—from Author s Simulations... 

His research interests include EHL, mixed lubrication, nanotribology, thin film rheology, molecular dynamics simulations, etc., and he has more than 70 papers published in international journals. Professor Hu received the Edmond E. Bisson Award from STLE in 2003. He is now an Associate Editor of the Proceedings of IMechE, Part J, Journal of Engineering Tribology. 

Luengo Get aM 997 Thin film rheology and tribology of chocolate J. Food Sol. 62 767-72... 

Luengo, G., Schmitt, F.-J., Hill, R., and IsraelachvUi, J. N., Thin film rheology and tribology of confined polymer melts contrasts with bulk properties. Macromolecules, 30, 2482-2494 (1997). 

M. Schoen. Rheology and local structure of thin films confined between thermally corrugated walls. Physica A 240 328-339, 1997. 

M. Schoen, S. Hess, D. J. Diestler. Rheological properties of confined thin films. Phys Rev E 2 2587-2602, 1995. 

Jang, S., and Tichy, J. A., Rheological Models for Thin Film... 

In a later study [56], the effect of gas volume fraction (foam rheology was investigated. Two models were considered one in which the liquid was confined to the Plateau borders, with thin films of negligible thickness and the second, which involves a finite (strain-dependent) film thickness. For small deformations, no differences were observed in the stress/strain results for the two cases. This was attributed to the film thickness being very much smaller than the cell size. Thus, it was possible to neglect the effect of finite film thickness on stress/strain behaviour, for small strains. 

A number of peculiar properties are displayed, including rheology characterised by viscoelasticity. Viscosities are far higher than that of either bulk phase this is a result of the large amount of energy required to deform the network of thin films of the continuous phase. A yield stress is observed, below which HIPEs behave as elastic solids and will not flow. Resistance to flow occurs from the inability of compressed droplets to easily slip past each other. Above the... 

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