Silicone fluids – structure and
properties
Structure
The two main silicone fluid structures are linear polydimethylsiloxanes
(PDMS) and cyclic volatile methylsiloxanes (VMS).
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.
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Did You Know ... silicones maintain their ability to flow
at lower temperatures and higher molecular weights than organic
materials!
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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.
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<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).
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Clear, colorless, and essentially odorless
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Low surface tension – the ability to coat surfaces and ingredients
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Very stable, resist degradation
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Very mobile, spread easily into thin films
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Generally inert, non-reactive
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Insoluble in water (water repellent)
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Good solubility in hydrocarbons
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Unique sensory feel and lubricity
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Non-stinging
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Do not become rancid (are not easily oxidized)
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Do not foster the growth of microorganisms
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Good release properties
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Good electrical insulating characteristics (dielectric)
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Act as liquid “springs”
Volatile silicone fluids: Typically cyclic volatile
methylsiloxane (VMS). (Very-low-viscosity linear silicones are also volatile,
but slightly more persistent.)
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The properties of non-volatile polydimethylsiloxanes but in a transient
form
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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
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Lower heat of evaporation – dry quickly leaving little residue and are
non-cooling on the skin
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May be mixed to achieve the desired rate of evaporation
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Non-staining
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Nonreactive; mild solvency – can be used with other solvents/cleaners;
better than organics for removing high-viscosity silicones; will not
attack/degrade most plastics
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Soluble with nonpolar organic solvents; excellent solvency with other
silicones – formulation flexibility; better than organics for carrying
silicones
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The ability to replace water, alcohol, and esters
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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!
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