Silicone Oil

Properties keywords:  Newtonian, viscous, liquid, viscoelastic, colourless

Analogue keywords: silicate melt, viscous fluid

Common names: Polydimethylsiloxane (PDMS), Dimethicone

General Information: Silicone oil (PDMS) is a colourless, transparent, viscous liquid that can be obtained in a range of viscosities.  PDMS can be combined with a thickener, usually fumed silica, to produce silicone grease (a thick white paste), or with fillers, typically boron, to produce silicone putty (see Silly Putty page).

Properties

PDMS is commonly used in the cosmetic, pharmaceutical and engineering industries, and as lubricants, anti-foaming agents and insulation.

Viscosities of silicone oils at room temperature range from approximately 1 x 104 to 3 x 104 Pas (Weijermars et al., 1986; Corti et al., 2005) and decrease exponentially with decreasing temperature (Arrhenian dependence, Hailemarian and Mulugeta, 1998; Cagnard et al., 2006).  This viscosity range may be expanded through mixing with other materials (Galland et al., 2015), and different silicone oils can be blended together to change the viscosity (see Shin-Etsu Silicone technical sheet for method).

Silicone oils are Newtonian fluids at typical laboratory temperatures and strain-rates (Galland et al., 2015) and at low molecular weight up to strain-rates of 1000 s-1 (http://www.dowcorning.com/content/discover/discoverchem/weight-vs-viscosity.aspx).  However at high molecular weight and high strain-rates, PDMS becomes shear thinning i.e. viscosity decreases with strain-rate (Figure 1).

Figure 1. Newtonian rheology of silicone oil, from Mall-Gleissle et al. (2002) and shear thinning behaviour at high viscosity and strain-rate, from www.dowcorning.com.

Surface tension of silicon oil is low, approximately 0.02 N/m (Shin-Etsu Silicone technical sheet), which results in high wettability and spreading characteristics (Khan et al., 2009) and densities on the order of 0.8 x 103 to 1 x 103 kg m-3 (de Bremond d’Ars et al., 2001; Watanabe et al., 2002; Kervyn et al., 2010; Spina et al., 2016).

The material is viscoelastic i.e. it has a component of time-dependent strain, for example, experiments by Kokuti et al. (2011) on a silicone fluid show a viscosity variation from 400 Pas to 50 Pas with increasing frequency.  Silicone oil is also incompressible.

Silicone oils are transparent and therefore very useful for experiments that require imaging of processes.  Furthermore, there is a good contrast in x-ray attenuation between PDMS and less absorbent materials such as quartz (Colleta et al., 1991), making it ideal for CT analysis (e.g. Kervyn et al., 2010).

Applications

Due to their synthetic nature, silicone oils can be customised to meet the exact viscosity, density, surface tension requirements of an experiment, therefore quantitative scaling of experiments may be easier than if using organic materials.

Having such well-constrained flow properties, silicone oils are frequently used as a silicate melt analogue in studies of the two or three-phase rheological behaviour of magmas (e.g. Mall-Gleissle et al., 2002; Mueller et al., 2010; Cimarelli et al., 2011).  The addition of solid particles and/or gas bubbles to silicone oil is aided by the fact that it is chemically inert.

Silicone oils are often used as a ductile deformable layer in 3D models of volcano spreading or deformation (e.g. Donnadieu and Merle, 2001; Corti et al., 2005; Kervyn et al., 2010) and as the magmatic component in models of dyke propagation and nucleation in the crust (e.g. Takada, 1990; Watanabe et al., 2002).

Silicone oils of lower viscosity (~ 0.1 Pa s) may be used to give experimental insight into the flow processes within conduits, and such research is ongoing as part of the Nemoh project.

Limitations and tips for use

Silicone oil is a widely used analogue material due to its versatility and consistency i.e. physical properties do not vary significantly between different batches.  It also displays minimal degradation over a wide temperature range (-40 to 280 °C).

Due to being insoluble in water, silicone oil can be difficult to clean.  Vegetable oil and washing up liquid should be used to clean up any leftover material.

There are no major safety issues in using silicones. They are non-toxic and non-flammable. Care needs to be taken, however, with spillages. 

Users may prefer to wear protective clothing to protect own clothes.

References

Cimarelli C, Costa A, Mueller S, and Mader HM (2011) Rheology of magmas with bimodal crystal size distributions. Geochemistry Geophysics Geosystems 12: 7, 1-14

Colletta B, Letouzey J, and Pinedo R (1991) Computerized X-ray tomography analysis of sandbox models: Examples of thin-skinned thrust systems.  Geology 19: 1063-1067

Corti G, Moratti G, Sani F (2005) Relations between surface faulting and granite intrusions in analogue models of strike-slip deformation. Journal of Structural Geology 27 (9): 1547–1562

de Bremond d’Ars J, Arndt NT, Hallot E (2001) Analog experimental insights into the formation of magmatic sulfide deposits. Earth and Planetary Science Letters 186(3–4): 371– 381

Donnadieu F, Merle O (2001) Geometrical constraints of the 1980 Mount St. Helens intrusion from analogue models. Geophysical Research Letters 28(4): 639–642

Dow Corning (2015) Fascinating Silicone: Silicone Rheology.http://www.dowcorning.com/content/discover/discoverchem/si-rheology.aspx

Galland O, Holohan E, van Wyk de Vries B, and Burchardt S (2015) Laboratory modelling of volcano plumbing systems: a review.  Advances in Volcanology.  Springer Berlin Heidelberg. 1-68

Hailemariam H, Mulugeta G (1998) Temperature-dependent rheology of bouncing putties used as rock analogs. Tectonophysics 294(1–2): 131– 141

Kervyn M, Boone MN, van Wyk de Vries B, Lebas E, Cnudde V, Fontjin K, and Jacobs P (2010) 3D imaging of volcano gravitational deformation by computerized X-ray micro-tomography. Geosphere 6: 5, 482-498

Khan MI, and Nasef MM (2009) Spreading behavior of silicone oil and glycerol drops on coated papers. Leonardo Journal of Sciences 14: 18-30

Kokuti Z, Kokavecz J, Czirjak A, Holczer I, Danyi A, Gabor Z, Szabo G et al. (2011) Nonlinear viscoelaxticity and thixotropy of a silicone fluid. Annals of Faculty Engineering Hunedora IX: 2, 177-180

Mall-Gleissle SE, Gleissle W, McKinley GH, and Buggisch H (2002) The normal stress behavior of suspensions with viscoelastic matrix fluids. Rheologica Acta 41: 61-76

Mueller S, Llewellin EW, and Mader HM, The rheology of suspensions of solid particles.  Proceedings of the Royal Society A 466: 2116, 1201-1228

Scheider F, Draheim J, Kamberger R, and Wallrabe U (2009) Process and material properties of polydimethylsiloxane (PDMS) for Optical MEMS. Sensors and Actuators A: Physical 151: 95-99

Shin-Etsu Silicone (2015) KF-96 technical sheet.

http://www.shinetsusilicone-global.com/catalog/pdf/kf96_e.pdf

Spina L, Cimarelli C, Scheu B, Di Genova D, and Dingwell DB (2016) On the slow decompressive response of volatile- and crystal-bearing magmas: An analogue experimental investigation. Earth and Planetary Science Letters 433: 44-53

Takada A (1990) Experimental study on propagation of liquid-filled crack in gelatin: shape and velocity in hydrostatic stress condition. Journal of Geophysical Research 95 (B6): 8471–8481

Watanabe T, Masuyama T, Nagaoka N, Tahara T (2002) Analog experiments on magma-filled cracks: competition between external stresses and internal pressure. Earth Planets Space 54:1247–1261

Weijermars R (1986) Flow behaviour and physical chemistry of bouncing putties and related polymers in view of tectonic laboratory applications. Tectonophysics 124(3–4): 325–358