Structure
MemorySil is a highly engineered polymeric network composed of a polydimethylsiloxane (PDMS) backbone modified with specific chemical crosslinks and plasticizing additives to intentionally introduce high hysteresis and time-dependent mechanical damping. Unlike standard elastic silicones that instantly rebound, viscoelastic silicones use specific intermolecular configurations to delay structural recovery after deformation. Shape recovery can take a few seconds or a few hours depending on the formulation.
The primary structural framework consists of repeating organosilicon units, specifically polyborosiloxanes.
Density of crosslinks
Low covalent crosslink density
Chains are sparsely joined using functional crosslinkers, such as methylhydrogen siloxane copolymers via platinum-catalyzed hydrosilylation. The long, unlinked segments between crosslink points preserve fluid-like movement (the viscous component).
The elastic network
The sparse covalent bonds provide the ultimate structural memory. They store potential energy during compression and dictate the slow return to original shape once stress is removed.
Mechanism of damping
The “memory” effect comes from the relationship between the storage modulus (G′, elasticity) and the loss modulus (G″, viscosity).
Energy dissipation
When force is applied, the long, unjoined siloxane chains slide past one another. Mechanical energy is dissipated as heat through molecular friction rather than stored like a perfect spring.
Hydrogen-bonding additives
Viscoelastic silicones frequently incorporate non-reactive silicone oils or polar additives that form transient hydrogen bonds along the PDMS matrix. These temporary bonds break during compression and slowly reform during relaxation, retarding elastic recovery.
Maxwell-Wiechert model
The time-dependent behavior is classically modeled by the Maxwell-Wiechert framework, a parallel network of spring-dashpot elements. The relaxation modulus over time, G(t), is:
G(t) = Ge + Σi=1..m Gi · exp(−t / τi)
where Ge is the equilibrium elastic modulus, Gi are the stiffness coefficients of individual polymer segments, and τi are the discrete relaxation time constants designed into the silicone network to control how slowly it recovers.
Composition
MemorySil® is a proprietary, patented viscoelastic silicone elastomer formulated from a mixture of base silicone polymers, crosslinking agents, catalysts, and non-reactive plasticizing additives.
1. The matrix (base polymers)
Liquid silicone components establish the physical volume and rubbery texture.
- Vinyl-terminated polydimethylsiloxane (PDMS): the foundational backbone polymer. Linear chains with reactive vinyl (−CH=CH₂) end groups that link together during curing.
- Dimethyl siloxane copolymers: short-to-medium chain siloxanes that adjust the starting viscosity of the uncured mixture.
2. Crosslinkers and network regulators
- Methylhydrogen siloxane copolymer: the bridging molecule, with reactive silicon-hydrogen (Si-H) bonds that stitch vinyl-terminated PDMS chains into a 3D network.
- Siloxane resin modifiers: used in precise proportions to balance hard elastic components against soft flowing components.
Durometer: why MemorySil has no single value
MemorySil changes hardness when you touch it, while a standard 10A elastomer stays at one constant hardness.
| Standard 10A elastomer | MemorySil | |
|---|---|---|
| Feel | Like a soft gummy bear or gel shoe insert | Like a liquid and a solid combined |
| Durometer | Fixed at 10A regardless of press time or count | Starts soft; temporarily drops to near zero under pressure and slowly oozes out of the way |
| Recovery | Springs back instantly | Stays squished for a few seconds, then slowly crawls back to its original shape |
A standard 10A elastomer is like a soft metal spring that always pushes back. MemorySil is like wet clay that turns back into rubber a few seconds after you stop touching it.