Research Papers: Lubricants

Modeling Polysiloxane Volume and Viscosity Variations With Molecular Structure and Thermodynamic State

[+] Author and Article Information
Thomas J. Zolper

Department of Mechanical Engineering,
Northwestern University,
Evanston, IL 60208
e-mail: ThomasZolper2010@u.northwestern.edu

Manfred Jungk

Dow Corning GmbH,
Rheingaustr. 34,
Weisbaden 65201, Germany

Tobin J. Marks

Department of Chemistry,
Northwestern University,
Evanston, IL 60208

Yip-Wah Chung

Department of Mechanical Engineering,
Department of Materials Science
and Engineering,
Northwestern University,
Evanston, IL 60208

Qian Wang

Department of Mechanical Engineering,
Northwestern University,
Evanston, IL 60208

1Corresponding author.

Contributed by the Tribology Division of ASME for publication in the JOURNAL OF TRIBOLOGY. Manuscript received January 25, 2013; final manuscript received August 1, 2013; published online October 7, 2013. Assoc. Editor: Xiaolan Ai.

J. Tribol 136(1), 011801 (Oct 07, 2013) (12 pages) Paper No: TRIB-13-1029; doi: 10.1115/1.4025301 History: Received January 25, 2013; Revised August 01, 2013

Siloxane-based polymers (polysiloxanes) exhibit a range of volume, viscosity, and pressure-viscosity behaviors that are strongly influenced by the macromolecular structure. In this report, a combination of extant rheological models is applied to develop a molecular-rheological modeling formalism that predicts polysiloxane rheological properties, such as specific volume, which means density, viscosity, and pressure-viscosity index variations with macromolecular structure, pressure, and temperature. Polysiloxane molecular features are described in terms of alkyl branch length L, pendant type J, density of branch functional monomers Q, and degree of polymerization DP. Both new and published data are used for model parameter determination and validation. Several siloxane-based polymers with alkyl, aryl, alkyl-aryl, cycloalkyl, and halogenated branches were synthesized to examine the modeled relationship between their molecular structures and rheological behaviors.

Copyright © 2014 by ASME
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Fig. 1

General molecular structure of siloxanes depicting branch content (Q), alkyl length (L), pendant group (J), and degree of polymerization (DP)

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Fig. 2

Siloxane molecular-rheological model

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Fig. 3

Measured (symbols) and calculated (lines) van der Waals volume and specific volume versus branch content for PDMS (D-D) and n-dodecyl branched PAMS as functions of molecular structure at atmospheric pressure and 298 K for atomic lengths of Zn = 100

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Fig. 5

Measured (symbols) and calculated (lines) viscosity versus molecular length of PDMS (triangles) and dodecyl branched PAMS copolymers (squares) at 298 K

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Fig. 6

Measured (symbols) and calculated (lines) reduced volume versus pressure of PDMS (D-D) based on data of (blue) ASME [23], (green) Winer [24], and (black) Bridgman [93] at 298, 372, and 491 K

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Fig. 7

Measured (symbols) and calculated (lines) reduced viscosity versus pressure of PDMS (D-D) based on data of (blue) ASME [23] and (green) Winer [24] at 298, 372, and 491 K

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Fig. 4

Ratio of radii of gyration versus macromolecule length for n-octyl branched polysiloxane copolymers at 298 K




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