<< [[casting compounds]], [[plastic and polymers MOC]] https://www.silicones.eu/the-science-behind-silicones/ https://www.inmr.com/contemporary-reinforced-silicones-liquid-solid-resin-like-molding-materials/ ## Structure Cyclosiloxanes are rings of repeating Si-O units D4 = 4 units, D5 = 5 units, D6 = 6 units ## [[RTV Silicone Polymerization]] ## Orientation and crystallinity https://www.simtec-silicone.com/blogs/orientation-and-crystallinity-of-liquid-silicone-rubber/ ![[B539292E-42C3-4C2F-BBA3-07F1F6A70228.jpeg]] - Short chains are tangled and disordered, silicones become more ordered with longer chains - The structure formed depends on time and temperature - hard to control precisely ### crystallization process > - First, the chains fold together to create an ordered region called lamellae, which are fine layers of the chains form the structure. > - When a group of lamellae is big enough, another morphological structure is created: a spherulite. > - This structure can be seen by optical microscopy and it directly affects the mechanical properties of the material. > - another special crystalline arrangement is found at the same level as the spherulites. Shish-Kebab structures are formed by crystals in the shape of circular plates and whiskers. > - These appear when a shear deformation occurs during solidification ### Structure after vulcanization Some crystalline domains exist, but they are surrounded by amorphous material - Quick cooling reduces the extent of crystallization ### Injection molding > When the liquid silicone rubber enters the mold, two different mechanisms lead to orientation in the silicone rubber part: fountain flow effect and radial flow. The orientation of the injection flow doesn’t have much effect orientation in the cured product because a lot of crosslinking happens - However if there is preferential orientation, it is in the direction of the injection flow - Fillers in the silicone, such as fibers, can cause preferential orientation which affects mechanical properties in that orientation ### Thermal properties [[glass transition]] ![[2D3450B2-DAC9-4661-82D3-3280FF3770B5.webp]]