NMR Studies On Adsorption Mechanism Of Water Molecules In Amorphous Materials

The water molecules adsorbed in the material often have a great influence on the performance of material.Studying the adsorption mechanism of water molecules in materials is often of great significance for understanding the origin of the changes in the material properties before and after adsorbing water molecules.In this thesis,a variety of advanced solid-state nuclear magnetic resonance techniques are used to conduct an in-depth study on the water molecules in the amorphous structures of several functional materials.The contents and results of this thesis are as follows:1.The locations of water molecules adsorbed in porous COF material Tp Pa-1 and the interaction between water and COF pores were studied.The nascent Tp Pa-1 sample and the Tp Pa-1 sample after high pressure were prepared.Two-dimensional ¹H double quantum-single quantum?DQ-SQ?correlation experiments and two-dimensional ¹H-¹³ C heteronuclear correlation?HETCOR?experiments and other nuclear magnetic techniques were used to study the interaction between water molecules and the interactions between the water molecules and the chemical groups on the surface of the material.By analyzing and comparing the nascent sample and the compressed one,the effects of pressure on the sample's water absorption mechanism were studied.The results show that the water molecules adsorbed in the nascent sample and the compressed one have different locations in the material: the water molecules adsorbed in the nascent sample are mainly located in the pores and only loosely interact with the chemical groups of the material.In contrast,a part of the water molecules in the compressed sample enters into the interlayers of the Tp Pa-1 material and interacts with the amino and carbonyl groups of the material.The redistribution of water molecules in the compressed sample provides a molecular level explanation for the change in the adsorption capacity of water molecules under pressure in this type of material.2.The form and distribution of water molecules in the amorphous phase of nylon 6 were studied.In order to prepare the nylon materials having high content amorphous components,Li+ ions were used to weaken the hydrogen bonding interactions within and between the polymer chains of nylon 6.The high content of amorphous components facilitates the enrichment of water molecules in the material.Then the form and distribution of water molecules in the amorphous phase of the samples were studied using a variety of advanced solid-state nuclear magnetic resonance techniques: the ¹H MAS NMR was performed to study the presence of water molecules in the samples;The ¹H SQ-DQ experiment and the ¹H-¹H NOESY experiment were used to study the interactions between the water molecules and the interactions between the water molecules and the polymer chains;the ¹H-¹³ C HETCOR experiment were used to study the spatial correlation between the water molecules and the polymer chains;the ¹H-⁷Li HETCOR experiment was used to study the spatial correlation between water molecules and the Li ions.The results show that a large number of water molecules are present in the sample.The water molecules in the sample mainly exist in the amorphous phase of the material.The water molecules interact weakly with the polymer chains,but have a strong interaction with the Li ions.