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Fascinating Silicone™ The Versatile Silicone Toolbox – Silicone Fluids: Structure and Properties

Silicone fluids – structure and properties

Structure

The two main silicone fluid structures are linear polydimethylsiloxanes (PDMS) and cyclic volatile methylsiloxanes (VMS).

Linear polydimethysiloxaneCyclic volatile methylsiloxane

The chains of a polydimethylsiloxane fluid can contain from 2 to well over 1,000 silicon atoms. The longer the chain, the greater the degree of polymerization, the higher the molecular weight, and the higher the viscosity of the fluid. The higher the viscosity, the slower the flow.

Did You Know ... silicones maintain their ability to flow at lower temperatures and higher molecular weights than organic materials!

 

What tangled webs we weave!

Longer polymer chains have a greater capacity to entangle with one another. This enables them to “trap” low-molecular-weight PDMS within the tangle and prevent it from leaking out.

Short PDMS chainsMedium-length PDMS chainsLong PDMS chains
<10,000 cs
Minor Entanglement
60,000 cs
Moderate Entanglement
30,000,000 cs
High Entanglement – Ability to Trap Low-Molecular-Weight PDMS

Low-molecular-weight PDMS fluids and ultra-high-molecular-weight PDMS gums are truly compatible. So by blending the two, it is possible to create new silicones that display the best properties of both!

Properties

Non-volatile silicone fluids: “Classic” linear (straight chain) polydimethylsiloxane (PDMS).

  • Clear, colorless, and essentially odorless
  • Low surface tension – the ability to coat surfaces and ingredients
  • Very stable, resist degradation
  • Very mobile, spread easily into thin films
  • Generally inert, non-reactive
  • Insoluble in water (water repellent)
  • Good solubility in hydrocarbons
  • Unique sensory feel and lubricity
  • Non-stinging
  • Do not become rancid (are not easily oxidized)
  • Do not foster the growth of microorganisms
  • Good release properties
  • Good electrical insulating characteristics (dielectric)
  • Act as liquid “springs”

Volatile silicone fluids: Typically cyclic volatile methylsiloxane (VMS). (Very-low-viscosity linear silicones are also volatile, but slightly more persistent.)

  • The properties of non-volatile polydimethylsiloxanes but in a transient form
  • Surface tensions as low as 13 dynes/cm – faster spreading and wetting of hard-to-reach areas; the ability to reduce or eliminate negative sensory effects of other essential ingredients
  • Lower heat of evaporation – dry quickly leaving little residue and are non-cooling on the skin
  • May be mixed to achieve the desired rate of evaporation
  • Non-staining
  • Nonreactive; mild solvency – can be used with other solvents/cleaners; better than organics for removing high-viscosity silicones; will not attack/degrade most plastics
  • Soluble with nonpolar organic solvents; excellent solvency with other silicones – formulation flexibility; better than organics for carrying silicones
  • The ability to replace water, alcohol, and esters

Did you know ... silicones have a critical surface tension of wetting that is higher than their own surface tension; this means they are capable of wetting not only other things, but also themselves!

 
 

Did you know ... in the environment, polydimethylsiloxane fluid breaks down into water, carbon dioxide, and minerals already found in the earth’s
crust!

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Expand your understanding

Easy reading: Degradability vs. Biodegradability (PDF size 33 KB)

For environment, health, and safety professionals:

An Overview of PDMS in the Environment (PDF size 35 KB)

Volatile Methylsiloxanes and VOCs Regulation and Application (PDF size 114 KB)

Learn about silicone fluids from Dow Corning:  Explore products for your application.

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