PDMS, or poly(dimethylsiloxane), is an optically clear, inert, non-toxic, and non-flammable material that is elastic at low temperatures and viscoelastic at high temperatures. It is used in flexible electronics and gas/liquid separations due to its flexibility and low cost. Permeability measures the intrinsic permeation rate of a species through a material and is determined by the diffusion coefficient and solubility coefficient. PDMS permeability can be modified by changing the degree of substitution, silicone backbone chain length, structure, and alkyl chain length - with shorter alkyl chains and longer backbones increasing permeability. Further research aims to figure out reaction mechanisms to add more hydrocarbon chain length and decrease PDMS permeability

1. PDMS & its Permeability
Melissa Nguyen
An Introduction

2. PDMS
Characteristics ● Optically clear, inert, non-toxic,
non-flammable
● At low temperature, PDMS is
elastic solid, similar to rubber.
● At high temperature, PDMS is
viscoelastic, and it acts like
viscous liquid.
● After polymerization and
crosslink, solid PDMS has
hydrophobic surface.
PDMS = Poly(dimethylsiloxane)

3. PDMS
Applications
★ Used in some flexible
electronics (flexible batteries/
stretchable BFCs) due to its
low cost, easy fabrication,
flexibility
★ Used as a membrane for
gas/liquid separations

4. Permeability
Definition: Permeability, defined as volumetric flow rate which
penetrates a defined membrane area under a fixed pressure
difference and normalised on membrane thickness, measures the
intrinsic value of the permeation rate of a species in a specific
material.
Q. Song, Energy & Enviroment Science, 2012, 5, 8359-8369
P = D * S
P = Permeability; D = Diffusion coefficient;
S = Solubility Coefficient
G. Clarizia, C. Algieri, E. Drioli, Polymer 45 (2004)

5. Background
S. Xu et al., Nature Communication 4, 1543 (2013)
Schematic of Stretchable Battery

6. Water and Gas Permeability of the device
● PDMS is porous
● 0.1-0.2 g/ day - significant
Nature Communication, 5779, S1
Supplementary Figure: Water and Gas Permeability of the device

7. Organic Solvents Permeability
● Loss of gel electrolyte (dimethyl carbonate and ethylene carbonate)
● Organic solvents evaporate much faster.
Nature Communication, 5779, S1
DMC - most volatile organic compounds Ethylene carbonate

8. What determines
PDMS permeability
➢ Degree of substitution
➢ Silicone backbone chain length
➢ Structure
I. Reeth, A. Wilson, Cosmetic & Toiletry Magazine, 1994

9. PDMS permeability
➢ Alkyl chain length
○ Short = high permeability
○ Long = decrease permeability
➢ The impact of R group on
occlusivity depends on the
structure of the silicone
➢ Length of silicone backbone
chain influence the
permeability to a lesser extend
than the alkyl chain length and
substitution level parameters
I. Reeth, A. Wilson, Cosmetic & Toiletry Magazine, 1994

10. Conclusion & Further Research Direction
➢ A decrease in permeability means an increase in occlusivity.
➢ The permeability of PDMS can be modified by reacting hydrocarbons of
different chain length onto the siloxane backbone.
➔ Figure out the reaction mechanisms to add more hydrocarbon chain length
Challenge: Most research papers focus on how to improve permeability (meaning
increasing permeability).
I. Reeth, A. Wilson, Cosmetic & Toiletry Magazine, 1994

11. Comments & Questions?