Influence of Crosslinking Extent on Free Volumes of Silicone Rubber and Water Diffusion after Corona Discharge

Abstract

Silicone rubber is widely used as an insulating material. In this article, silicone rubber samples were prepared by varying the content of crosslinker (2,5-bis(tert-butyl-peroxy)-2,5-dimethylhexane, DBPMH), and the free volume holes in the samples were investigated by means of positron annihilation lifetime spectroscopy (PALS) measurement. The surface chemical structure, surface micromorphology and water diffusion of the samples after corona discharge treatment were studied by FTIR, SEM and EIS measurements, respectively. As the crosslinker weight ratio increased from 0.2 wt.% to 1.5 wt.%, the mean free volume hole size first decreased and then remained unchanged. However, the concentration of free volume holes did not vary as the crosslinker weight ratio increased. SEM morphologies show that surface cracks were produced on samples having high crosslinking levels after corona treatment. The water diffusion coefficient of samples after corona treatment increased from 3.13 × 10−10 cm2 s−1 to 17.68 × 10−10 cm2 s−1 in the initial immersion period, as the crosslinker weight ratio increased from 0.2 wt.% to 3.0 wt.%. The results indicated that deterioration of samples with high crosslinking levels were more serious and water repellency more easily lost. The corona resistance ability of low crosslinking level silicone rubber stems from internal low molecular weight molecules.

Influence of Lead Nanoparticles on Structural, Morphological, and Mechanical Characteristics of (SiR-PU/Micro-Pb) Composites and Radiation Shielding Applications

“…Absorption peaks at 1258.4 cm −1 , 790.75 cm −1 , and 1010.90 cm −1 were attributable to methyl groups and Si-O bonds, respectively. The results suggested that methyl groups on the side-chain were degraded during the corona process and the polymer main-chain became decomposed [22].…”

Water Induced Reversible Switching of Optical Transparency of an Elastomer-Hydrogel based Two-phase Composite

“…Diffusion of water through the hydrophobic network of crosslinked PDMS has been a subject of intense study [26][27][28] , in the context of pervaporation 29,30 and desalinations 11 . Free volume in the three-dimensional network of crosslinked silicone 19,31 facilitates this transport. The size of free volumes depends on the extent of crosslinking.…”

“…The size of free volumes depends on the extent of crosslinking. Limited extent of crosslinking of the network is expected to render it more liquid like between the crosslinking points, thereby increasing the free volume 19 , which is expected to enhance the transport of the guest molecules through it. It is known that platinum catalyst, that is used to crosslink silicone elastomer, gets poisoned by Sulphur and Nitrogen.…”

“…For example, how exactly the size and number density of the hydrophilic inclusions within the silicone would affect the rate of water transport and water retention within it, has not yet been worked out in sufficient detail. Viscoelasticity of the network or localized viscoelastic regions embedded within an otherwise elastic material are also important parameters 19 , which too are expected to affect the water transport through it and the resultant effective characteristics of the material. In other word, the coupled effect of material and geometric properties of the two phases opens up both many possibilities and also many scientific questions.…”