The Effect Of Electrostatic Interaction Between Ions And Monolayer On The Structure And Stability Of LB Films

LB film is a kind of artificial membrane. It is not only a powerful tool to study of membranes, but also a high-quality material. Combining with metal ions, LB film will have some special features, such as conductivity, magnetism and quantum properties, Which make LB film can be applied in much more fields. Metal ions interact with monolayer by electrostatic or coordination interactions. At present, most researches have focused on the coordination between metal ions and Langmuir film. However, few studies have been found on the electrostatic interaction between metal ions and monolayers, and only some experimental results were explained presumably. No universal laws were given. Because amphiphilic molecules have a polar head, the electrostatic interaction plays an important role on ions and film. Therefore, studies on the electrostatic interaction between metal ions and monolayers on the formation, strength, structure, phase behavior and morphology of monolayer are necessary. The laws about the influence of various properties of ions(ionic radius, valence state, ion concentration, etc.)on Langmuir and LB film can provide scientific basia for making LB film as new material, and theoretical foundations for life processes on biomembrane.This study begins with the structure feacrures of phospholipid molecule and presents a simplified model. This model points out that the force between two amphiphilic molecules have two nature force at different distances in valid range. Then based on classical electrostatics-theory to analyze the interaction between ions and monolayer, and then analyze the effection from ions to monolayer by considering the force in pressing film process. It concludes that various properties of ions have effection on isotherm. Specifically speaking, the higer the ionic valence state,the smaller the radius, the greater the ion concentration, so the the collapse pressure will be increased, the molecule limited areas reduce, the turning point will become obviouse, the cruve will expand. Under the circumstance of exsiting ions, the electrostatics effection between ion and amphiphilic molecules have two aspect effection on LB film. Firstly, it has effection on the density in LB film arraying; Secondly, it effects the combing power beween monolayer and substrate. With the example of mica, the analyse shows that the higer the ionic valence state,the smaller the radius, the greater the ion concentration,the molecule of LB films are arried more intensive and the combing power between monolayer and substrate will be stronger, the stability of films will be better. Finally, by related experiments to test inferences from theoretical analysis. The experimental choses ways of comparing, controlled variable and indrect explaining and so on, we find that data is consistent with the theoretical.