engleski

Liquid component influence on γ-radiation response of some low temperature cured PDMS gels

To obtain PDMS gels containing liquids with relatively low boiling points PDMS-DGE was diluted with a chosen liquid component – ethanol, t-butanol or benzene and then cured at 50 oC using either 1, 3-diamino-2-propanol (DAP) or tris(2-aminoethyl)amine (TAEA) [1]. Both amines can produce dense networks but in a different way. Hydroxyl group of DAP can form hydrogen bonds while TAEA is a triamine and is able to bond an additional PDMS chain. The highest mass fractions of benzene, ethanol and t-butanol that resulted in stable, firm and in case of TAEA brittle gels, varied between 25 and 28 %. The gels were characterized by thermal analysis, extraction, swelling and dielectric spectroscopy. Both values of Hansens solubility parameters that define compatibility of gel components [2] and electrical conductivities of pure liquid components increased in sequence PDMS-DGE<benzene<t- butanol<ethanol. Obtained gels were irradiated to selected doses in ambient conditions at a dose rate of 7.8 Gy/s in 60Co γ-irradiation facility of LRCD, RBI to assess their radiation stability. Like in the case of the corresponding gel networks that did not contain a liquid component, the apparent firmness of gels irradiated up to at least 50 kGy was preserved. An endothermic transition presumably caused by reversible gel network collapse was also detected by DSC in all studied gels. Compared to the corresponding unirradiated benzene containing gels the electrical conductivity of irradiated ones increased similarly and independently of the amine used for curing. In alcohol containing DAP gels, changes consistent with significant radiation crosslinking [3] were observed by all experimental techniques, particularly in the gel with ethanol. That included reduction of the electrical conductivity presumably because ethanol as a small molecule that can easily form additional hydrogen bonds to DAP residue increased polymer network density of the gel and reduced charge mobility. Like in the corresponding TAEA gel network, radiation slightly increased mass loss upon extraction of TAEA gels irrespective of the liquid component. Their electrical conductivity increase corresponded only to increase in solubility parameters of liquid components. The observed changes arise of difference in binding of PDMS chains in gel and the ability to form hydrogen bonds but the stability to gamma-radiation of the studied gels either remained the same or increased in the studied dose range.

PDMS ; chemical gels ; gamma-irradiation ; DSC ; vibrational spectroscopy ; dielectric spectroscopy

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