Computer Simulation Of Temperature-sensitive PNIPAM Hydrogels

Environmentally sensitive hydrogels are wildly used in sensors, release switch and other fileds, for the hydrogels colud perceive the change and stimulate of external environment (such as temperature, pH, light, electricity, pressure, etc.) and then generate a corresponding change in physical structure and chemical properties. However, the development of environmentally sensitive hydrogels encounter to many challenges, such as the accuracy of sensors communicate information, the reliability of controlled-release switch, the burst release phenomenon of drug delivery, etc. Which limit the applications of environmentally sensitive hydrogels. It's necessary to identify the key factors which control the reponse of environmentally sensitive hydrogels, in order to controlled and applicate them more effectively. With continuous improvement of the theoretical system of molecular simulation technology, the simulation can obtain unique results which are difficult to draw from the conventional experiment. Molecular simulation technology favored by more and more researchers, wildly used in the research of reaction mechanism, the properties forecast of materials and other fields.Molecular modelings of the environment-sensitive hydrogel poly (N-isopropylacrylamide) (PNIPAM) were established and optimized used computer simulation technology. The intramolecular and inter-interaction force, changes of molecular configuration before and after the volume phase transition were studied by quantum chemistry and molecular dynamics and other research methods. The occurrence mechanism of environmental sensitivity was discussed. The main research contents and results are as follows:In this thesis, the temperature-sensitive hydrogel poly (N-isopropyl acrylamide) was selected as a sample. The Gaussian software and density functional theory was used to analysis the structure of the PNIPAM monomer based on the computer simulation technology. The results showed that the NIPAM molecules containing both carbonyl and amine displayed the characters of the electron donor and acceptor. There were amounts of negative charge near oxygen atom of the carbonyl, while the hydrogen atoms of the amino have a strong positive character, both all facilitated the formation of hydrogen bonds. There were a large number of hydrogen bonds between intramolecular and intermolecules in PNIPAM dimmer and NIPAM-co-AA monomer analysed by quantum chemistry. These hydron bonds would play an important role in the gel sensitive phase transition of the temperature-sensitive hydrogel. studies on the micro hydrogel monomer solution have shown that a large number of hydrogen bonds could form between the hydrogel and water molecule in water environment. A large number of water molecules were combined, which formed a relatively closed water shell and kept the water molecules within the gel from lost. P (NIPAM-co-AA) hydrogels were easier to form intramolecular hydrogen, bond more water molecules, and more interaction energy with water molecules than that of PNIPAM hydrogels. Addition of the acrylic acid (AA) could affect the temperature sensitive properties of hydrogel, or even made the temperature sensitive disappear. The conformational states of the PNIPAM chains at different temperatures were simulated successfully. The PNIPAM chains crimped serious bove the the lower critical phase transition temperature, the macro performance was the contraction of the gel volume, which consistented with the experiments'results. There were a large number of non-bond interactions in PNIPAM chains. The strenthes of the non-bonding interactions increased with increasing temperature, and became more obvious bove the the lower critical phase transition temperature.