Investigation On Adsorption Properties Of Biological Molecules On Mica Surface Using The Surface Forces Apparatus

Recently, with the wide application of the micro-nano mechanical and electrical equipments, biofilms (especially biological macromolecular membrane) are gradually understood and applied to life science, micro-nano medical treatment, biological chip, micro-nano lubrication, etc. Depending upon its superb physical, chemical and mechanical properties, biofilms attract researchers' wide attention. This thesis focuses on the geometry morphology and adsorption properties of biological adsorption film on mica surface by using Surface Forces Apparatus (SFA) and main works are as follows:1. The adsorption properties of methanol on mica surface were investigated. Under the assistance of a modified SFA system, the methanol gas was directly adsorbed on mica surface. Meanwhile, the adsorbed methanol films owned layered characteristics and the outer layer presented the similar fluidity of bulk methanol while the inner layer behaved as a solid-like structure, which could even bear more than 5.6 atm normalized loads. Therefore this aspect provides the experimental evidence to support the application of methanol membrane in the boundary lubrication.2. The adsorption behaviors and mechanical properties of ssDNA (single-strand DNA) on mica surface as well as the surface forces and adsorption properties of the adsorbed ssDNA layers were investigated under different experimental conditions, which mainly includes the effects of some factors, such as the concentration of ssDNA, the concentration of the bridging ions and its species and so forth, on the thickness and geometrical morphology of DNA adsorption layers and its adhesion forces. The physical mechanism of the formation of ssDNA layers was also analyzed, which proves the existence of the cationic bridge effects.3. The desorption phenomenon of ssDNA layer was studied. By adding the monovalent cations into the buffer solution, the ssDNA layers, which was originally adsorbed on the mica surface, began to fall off from the surface till the end of the desorption. Besides, the internal causes of ssDNA desorption phenomenon were deeply discussed.On the basis of cationic bridging effects, this thesis initially adopted the SFA technique to investigate the adsorption and desorption properties of the ssDNA layers on mica surface, the morphology and mechanical properties of the adsorption layers and main factors affecting its formation, etc. At the same time, the relevant work in this thesis can provide reliable experimental methods and preliminary experimental results to systematically investigate the features of DNA on the solid-liquid interface, and even the development of the adsorption research about the organic macromolecular membrane on the interface. Besides, this work will provide the theoretical foundations and experimental instructions for the application of biofilms in micro-nano mechanical and electrical equipments. Moreover, it will have great significance in the application and development of the biofilms in nano devices, medical equipments and other fields.