Studies On Synthesis And Properties Of Monolayer Films Of Multialkyl Cationic Gemini Surfactant

Gemini surfactants are made up of two identical amphiphilic moieties covalently connected at the level of the headgroups by a spacer group, The introduce of spacer group made it possible to efficient control the distance of headgroups. And this make it exhibit excellent surface activity and interesting rheological properties, Owing to this, it have attracted considerable attention in colloid and interface chemistry domain. Langmuir-Blodgett film which made from monolayer films is highly ordered in molecular scale and form laminar structure with anisotropy, Could fabricate multilayer in a molecular scale and with controllable. And this made it have a broad application foreground in high-technological fields, such as semiconductor, nonlinearoptics, bionics and so on. Gemini surfactants exhibited unique properties on gas/liquid surface. And this makes it possible to apply this novel structure amphiphilic moieties to LB film domain for the purpose of new functional material exploit. A series of different alkyl length and spacer length multialkyl cationic Gemini surfactant was designed and synthesized in this article, And pressure-area isotherms of it's monolayer film was measured under different condition. Methyldidodecylamine and α,ω-dibromoalkane was mixed with the molar ratio of 3:1 in ethanol and reflux for 48h, recrystallized for several times,then a series of Multialkyl cationic Gemini Surfactants was synthesized. The structures were confirmed by IR, ~1H NMR, elemental analysis. The pressure-area isotherms was measured of this compounds under different condition, it shows: i. The change of molecular structure have a great effect on the property of it's monolayer. As the length of alkyl-chain increased, π-A isotherm has a more condensed tendency,the transition from liquid phase to solid phase is less clear and the collapse pressure of film increased which indicates strength of film increased; As spacer length increased, π-A isotherm has a more expanded tendency, and the extrapolated molecular area increased at the same time. ii. The substance of subphase also causes great effect on its film. When use 0.01mol?L-1 NaBr as subphase , the π-A isotherm of film was more condensed; we also compared the collapse pressure on salt solution and on pure water as subphase, find the difference increased as the number of carbon atom of spacer decreased; and the extrapolated molecular area consistent with each other. All of these changes are caused by the fact that large amount of bromide ion exist in subphase should penetrate into the diffusion layers formed by counter ion of ionic surfactant because of the concentration degree, and compressed the diffusion layers of insoluble film. And in the process of research for temperature effect on π-A isotherm, it's proved that temperature has a little effect on the insoluble films of synthesized dimeric surfactants. But it has a great effect to the monomer of the surfactants. All of this proved the novel structure surfactant has a good ability to form films, and we can adjust the molecular structure and external condition to get the best method for the deposition process of LB films. And it's an ideal material to form LB films.