Journal of Materials Science

, Volume 27, Issue 13, pp 3424–3434

Water absorption, swelling, rupture and salt release in salt-silicone rubber compounds

  • R. Schirrer
  • P. Thepin
  • G. Torres
Papers

DOI: 10.1007/BF01151816

Cite this article as:
Schirrer, R., Thepin, P. & Torres, G. J Mater Sci (1992) 27: 3424. doi:10.1007/BF01151816

Abstract

Water vapour diffuses rapidly in silicone polydimethylsiloxane (PDMS) rubber. In a PDMS-salt compound surrounded by water, the water which has entered the rubber is absorbed by the salt particles, creating an osmotic pressure in the rubber. This pressure leads to internal cracks in the rubber, which eventually percolate and result in a salt exchange between the rubber-salt compound and the surrounding pure water. The absorption and rupture phenomena were derived, measured, and quantitatively analysed. Equations describing the onset and propagation of the microcracks in the silicone were derived as a function of rubber fracture toughness, tensile modulus and osmotic pressure of the salt. A single figure summarizes three possible situations: (1) the salt plus water pockets in the compound reach an equilibrium without cracking, (2) the salt pockets are fully dissolved, and cracking occurs, (3) the salt pockets generate microcracks before full dissolution of the salt. Finally, the salt release has been quantitatively related to the PDMS tensile modulus, fracture surface energy, and salt grain size.

Nomenclature

å

crack speed

A

mean distance between two salt grain centres

B

mean distance between two salt grain borders

D

mean cavity diameter in rubber (D=2r)

D0

mean diameter of salt grains or mean initial cavity diameter (D0=2r0)

E

tensile modulus

G

shear modulus

G1

fracture toughness

G1c

critical value ofG1 at rupture instability

h0

sample height (fracture experiment)

k

reduced fracture coefficient for holes in rubber

K1

fracture toughness (MPa m1/2)

K1c

critical fracture toughness at rupture instability

M

sample mass

M0

initial value ofM

n

moles of particles formed upon solution of 1 mol solute (n=2 for NaI)

P

pressure in a cavity in the rubber

Pc

critical value ofP at rupture instability

Q

salt volume in a rubber-salt compound

Q0

initial value ofQ

R

0.082 055 dm3 105 Pa K−1 mol−1

r

radius of a spherical cavity in the rubber

r0

initial value ofr

S

sample surface

S0

initial value ofS

S2

volume fraction of solute in solution

T

temperature

t

time (s)

V

volume of the swollen rubber-salt sample

V0

initial volume of the rubber-salt sample

vc

mean microcrack front speed

W

energy per unit volume in a rubber sample under stress

α

experimental best fit coefficient

β

experimental best fit coefficient

Δh

displacement

ϑ

salt volume fraction in the compound

Ψ

water flow in PDMS per unit time and unit area at the PDMS-salt interface

λ

extension ratio of a spherical cavity in the rubber

λc

critical value of λ at rupture instability

v2

molar volume

π

osmotic pressure

τc

critical duration for swelling a salt pocket up to rupture

Copyright information

© Chapman & Hall 1992

Authors and Affiliations

  • R. Schirrer
    • 1
  • P. Thepin
    • 1
  • G. Torres
    • 2
  1. 1.ICS(CRM-EAHP)StrasbourgFrance
  2. 2.Rhône PoulencSaint-FonsFrance

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