NUCLEAR-MAGNETIC-RESONANCE APPROACH TO THE CHARACTERIZATION OF SILOXANE-SILICA NETWORK-LIKE STRUCTURES

This work deals with mesh size properties of network-like structures associated with random siloxane-silica mixtures. The transverse magnetic relaxation function of protons is shown to obey a superposition property controlled by the silica concentration C//S//i, in the range 0 less than equivalent to C//S//i less than equivalent to 0. 50 (w/w). Correspondingly, its invariant mathematical structure is governed by the average residual energy H D-BAR DELTA //e of dipole-dipole interactions only. The parameter DELTA //e is given the role of a timescale shift factor; it is related to the average mesh size of a given network. Nuclear magnetic resonance measurements show that silica aggregates do not induce any strong deviation from the primary entanglement system established in a pure siloxane melt.