Barrier materials crosslinking

There are materials with low or no permeability to different environments or products. Barrier plastics are used with their technology not becoming more complex but more precise. Different factors influence performance such as being pinhole-fi ee chemical composition, crosslinking, modification, molecular orientation density, and thickness. The coextrusion and coinjection processes are used to reduce permeability while retaining other desirable properties. Total protection against vapor transmission by a single barrier material increases linearly... 

In the case of a polymeric amine such as polyethylenimine or polyepiamine, the solubility of the polymer in the organic phase would be very low. Reaction would take place at the interface to form an extremely thin, crosslinked network. This network would block the transport of further polymeric amine from the aqueous phase into the organic phase. Continued buildup of the membrane material on the organic side becomes impossible. Thereafter, the growth in thickness of the barrier layer is controlled by the much slower diffusion of acyl halide or isocyanate into the aqueous phase. As a result, composite membranes made by the NS-100/NS-101 type of approach will naturally tend to have very thin barrier layers-typically 200 to 250 angstroms thick. 

Other attempts to demonstrate the scope and usefulness of HRM constructs were devoted to field effect transistors and related devices. Using LB films of hairy rods as a carrier of ionophores, it is possible to manufacture highly sensitive and selective sensor membranes in combination with n-doped silicon/silicon oxide FETS [92,93]. As an example, a Na+ sensor was presented with a constant sensitivity of 53 mV/pNa for more than 61 days and a small baseline drift of only 1 mV/day. This was achieved by mixing a commercial Na+ ionophore with the LB material before film deposition. The best results were obtained with a crosslinked cover layer serving as a diffusion barrier for the ionophores but not for the ions to be detected. 

The permeability of gases depends also on their solubility in polymer matrix, which is adjusted by the strength of interactions between gas molecules and the functions existing in/on the macromolecular chains, by material crystallinity, by temperature and by free-volume extent. The barrier formed by the new inter-molecular bridges produced during radiation crosslinking is an additional specific element that slows down gas transport in the detriment of polymer stability and integrity. 

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