Hei community! Im new here and I've cross posted this from the chemistry Reddit to get more eyes on this, to see if any if you here can help. Thanks in advance for reading this.
Due to a heavy interest in/use of fabrication materials for the last 9 years (5 of which were spent working as a costume/prop maker and SFX artist in the film industry) and a sudden overwhelming interest in material science/engineering for polymers, I am currently studying chemistry from the ground up. Due to not having the time or being able to afford formal studies I am stuck with self study using books. In light of that information I would like to ask you guys/gals a question about this please because I am not at this level of understanding yet:
I received a call yesterday from a representative of a Silicone manufacturer to discuss an email I had sent regarding medical grade Silicone gels.
She warned me about an issue that various scientists/researchers (and the company she worked for I guess) had been struggling with and that the majority of Silicone manufacturers/engineers do not mention (she couldn't say whether this issue was solved for obvious reasons but just that it took several years)
The conversation was very technical so I might miss something out (we were on the phone for an hour and five minutes!)
Essentially she said to me that due to the layering system I am intending to use with different shore <0 hardness, RTV2 addition cure, medical grade Silicone gels that I would run into the same problem these people had using the same method (layering and curing different gels on top of each other inside a mold).
She mentioned the different molecular weights between the gels caused each layer to swell or shrink. So the top layer would shrink/wrinkle out of it's moulded shape because the layer below it had swelled, also out of it's shape.
She never stated how much swelling and shrinkage occurred but she sounded like it was a very serious issue to overcome. I remember mentioning that this sounded similar to osmosis but in a different system with no membrane, she wouldn't confirm or deny that.
From my limited knowledge of chemistry I've acquired so far, what this lady is describing sounds like osmosis but not. It sounds like, over time (days, weeks, months?) post cure the different Mwt* of the silicone gel layers in the casting are trying to achieve equilibrium between them, with the higher Mwt gel losing atoms to the lower Mwt gel causing the shape of the silicone cast to warp/deform. From what I can gather on Google, this happens when silicone is submerged in solvents. Apparently due to the two systems trying to equalise chemical, the solvent ions can transfer inbetween the cross-links of the silicone because there's so much space in-between the chains, causing the silicone to swell. But there's no mention of this happening between two silicone gels bonded/casted to each other. And at a cost of £12 /kg with an MOQ of 50-200 units...I'd like to find out why before I buy anything...Which I guess she was also trying to warn me about subtlety!
Does this sound close at all? Would anyone like to share an opinion on this and how to stop it happening? My first initial thought to ask her was, "WHY not just paint a thin barrier of something in-between the layers to stop this transfer happening?" It can't be that simple though? Plus there's the added problem of finding a similar material to the gels that will bond with them, is flexible/stretchy/soft but that isn't silicone itself.
Thank you for reading! Any help on this would be greatly appreciated as it's for a good cause! (I am trying to develop a more realistic mammary prosthesis prototype to help mastectomy survivors and the transgendered.)
*If Mwt=molecular weight=molar mass...Aren't weight and mass mutually exclusive?