Study Of The Confinement Effect On Mobility, Chemical Reaction And Glass Transition Behavior Of Molecules

The confinement of the molecules would modify their dynamics behaviours, and thus change their chemical and physical properties, including chemical reactivity, diffusion behaviours and glass transition dynamics, etc. Here we combined several techniques, including NMR, AC chip calorimeter and Surface Enhanced Raman Scattering (SERS) to study the chemical and physical properties of the confined molecules.We used two-dimensional diffusion-ordered NMR spectroscopy (DOSY) to measure the diffusion coefficient of the ligands in different confinement state. We proposed that the free and the bounded ligands were undergoing rapid exchanging. Then we investigated the gold nanoparticles (GNPs) system by 1H NMR and demonstrated our proposal. Besides, we found that the bounded octadecylamine self-assemblied into a certain kind of complex in the solution. The confinement of different ligands on GNPs was characterized by 1H dipolar filter solid-state NMR (SSNMR) under fast magic angle spinning. And the reactivities of these ligands were investigated by surface enhanced Raman scattering (SERS). We find that surface interaction relates not only to the terminal functional groups, but also to the entire chains. It is demonstrated that the surface confinement of ligand is one of the important factors which influence the reaction activities on nanoparticles.The combination of SSNMR with the SERS technique could be a unique tool which can reveal more underlying information of the ligand exchange reaction. The detailed knowledge of the ligand exchange reaction will help to fine-tune the physical and chemical properties on surfaces of nanoparticles.We characterized the interdiffusion of deuterated polystyrene (PS-D) and hydrogenated poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) by 1H dipolar filter solid-state NMR under fast magic angle spinning (MAS). It is observed that the interdiffusion process of PS-D/PPO is composed of two stages, the wetting stage and the diffusion stage. The characteristic time of the transition from the wetting to diffusion stage is independent of the temperature and PS-D molecular weight. On the other hand, the increment of dipolar filtered 1H NMR signal intensity at the wetting stage depends strongly on the temperature. The PS-D chains can be easily mixed with the PPO chains intimately when the temperature is above the glass transition temperature (Tg) of PPO. However, when the temperature is below the Tg of PPO, the PPO chains are frozen and it is more difficult for the PS-D chains approaching the PPO at a molecular level.There have been increasingly widespread interests in the investigation of the glass transition of polymer thin films. The glass transition of several kinds of polymer thin films was studied by a home-made differential alternating current (AC) chip calorimeter. We found that the molecular weight is an important factor that could influence the thickness dependence behaviour of the glass transition temperature of polymer thin film. When the molecular weight is large, the glass transition temperature detected by AC chip calorimeter is independent of the film thickness. However, the glass transition temperature detected by AC chip calorimeter is strongly depended on the film thickness when the molecular weight is very small. Our experimental results were in accord with the fragility index of the polymer.On the other hand, we characterized the chain mobility of polystyrene that adsorbed on the surface of nano SiO2 by solid-statre NMR. It is found that the surface curvature had a strong effect on the chain mobility of the adsorbed polystyrene. The polystyrene that adsorbed on nano SiO2 was more mobile than that in the bulk state. And the polymer chains became more and more mobile as the surface curvature increased.