Relationship Between Pore Sructure and ~H-NMR Relaxation Times in TiO_2/Poly(dimethylsiloxane) and CaCO_3/Poly(dimethylsiloxane) Composite Powders

摘要

Titanium(IV) oxide/polydimethylsiloxane (PDMS) and calcium carbonate/PDMS composite powders were obtained by adsorption of the polymer from a chloroform solution onto the inorganic particles followed by a thermal treatment.The composites were characterized by ~1H-NMR relaxation and porosimetry.The composites present shorter spin-lattice (T_1) and spin-spin (T_2) proton relaxation times than silica-reinformced PDMS,and the activation energies for the motions that cause spinlattice relaxation are 5.8,4.9,and 0.72 kJ mol~(-1) for TiO_2/PDMS,CaCO-3/PDMS,and neat PDMS,respectively,respectively,revealing the greater rigidity of the polymer chains within the composite.Spin-spin relaxation 9T_2) measurements of the composites showed a major component with a shorter T_2 and a minor component with a longer T_2.The intensity ratio of these two components is very close to the ratio between the amount of polymer that remains between the particles and that penctrating the particle pores as measured by Hg intrusion porosimetry.The shorter T_2 component was thus assigned to polymer interspersed among the particles,while the longer T_2 component was assigned to polymer within the particle pores.