If I pour PDMS (like Sylgard 184) oligomer onto a piece of cured PDMS slab and let it cure at room temperature, will the oligomer diffuse into the cured PDMS network? Intuitively, it is affected by the free volume in the cured network and the surface energy of both cured and uncured PDMS.
Hi Le,
If your PDMS is fully cured then i don't think PDMS oligomer can diffuse through it at normal conditions. It will only possible at high temperature and vacuum that PDMS oligomer start diffusing through cured PDMS.
I hope this answer helps you.
PDMS always contains cyclic residues and freequently also linear oils used for compounding. There is virtually no PDMS rubber without low olecular residues. Even after a thorough extraction you will see hydrophobization if you put silica flour onto a piece of silicone rubber. Therefore it is very complicated to study the diffusion of siliocne oligomers into silicone rubber.
Isotope labeling with radiating nuclei is a fairly expensive technique, additionally you would need spatial resolution. I would suggest rather deuterium NMR with isotope labelled oligomers.
The cured PDMS has -O-Si R2-O bond which can rotate at very low energy. This makes the system unique for many point of view. The void volume is also expected to be high. Added PDMS can penetrate into cured matrix as the requirement for solubility (enter) in matrix is met as both are alike and both have many labile bond. However, due to labile nature having extra mobility the added PDMS may partially come out again.
There has going a lot of water down the rivers in USA and Germany were PDMS's has his birthplaces in the fourties and fities since last century. Since most, chemical and technical writings are from this time it's same time dificult to get with.
PDMS crosslinked are one kind of polymers the most permeabilty born with, so they said me, the big one chemist by the technical producers of silicones ( the very lamentable breast implantants too)
As such all kind of solventes-and siloxane cyclics actually are used as such-swells the silicone rubbers und -resins, often to twice is weight or volumen.
Swelling is (mostly) reversible without mayor losses on former values.
Be kind with this old class of polymers-they still can a lot do , in academies and factorys. Beware strongly on the cross contamination, they will go to every place in the lab.
good luck !
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