Study On The Adsorption Behavior Of Gemini Surfactants Containing Amide And Ester Groups At The Solid-liquid Interfac

Gemini surfactants have high surface activity and have be widely used in many fields.Introducing amide groups or ester groups into the structure of a Gemini surfactant can enhance its biodegradability and environmental friendliness.Having special functional groups,Gemini surfactants can interact with macrocyclic compounds to produce some special functions.Therefore,it is of great significance to study the properties of Gemini surfactant having function groups such as amide groups and ester groups.In this paper,we synthesized the Gemini surfactants containing esters or pyridine rings,and characterized their structures by means of ¹H NMR and Fourier infrared spectroscopy.For the Gemini cationic surfactants containing esters,increasing the connecting groups from 3 to 6 methylene increases the cmc value and decreases the adsorption at the water-air interface and the contact angle on the quartz surface,and increases the adhesion tension,and decreases the adhesion work.The adsorption of the ester-based Gemini surfactants on the quartz surface conforms to the kinetic model of two-step adsorption,which includes a fast adsorption process and a slow one.The adsorption was studied for the Gemini surfactants containing amide groups or esters on the quartz surface,and we compared them with the Gemini surfactants without these function groups.These Gemini surfactants adsorb on the quartz surface through the physical adsorption,and their adsorption films are rigid film on the quartz surface.Moreover,when the linking group increased from 3 to 6 methylene,the adsorption of the three kinds of the Gemini surfactants decreases on the quartz surface.For the three types of Gemini surfactants,when the linking groups contain the same amount of CH₂,the adsorption of the Gemini surfactants containing amide groups are the lowest in three kinds of the Gemini surfactants on the quartz surface.The introduction of ester groups did not change the adsorption of the Gemini surfactants on the quartz surface.Through kinetic fitting of the adsorption of three surfactants on quartz surface,we found that the two-step adsorption model was suitable for their kinetic adsorption process on the quartz surface.The flotation experiments of quartz and collophanite were carried out using these kinds of the Gemini surfactants as the collectors.These kinds of the Gemini surfactants have strong flotation properties for quartz,but low flotation ability for collophanite.Among three kinds of surfactants,the surfactants containing amide groups have the lest flotation properties to float quartz and collophanite.The surface properties of the Gemini surfactants（C8,C10,C12）containing pyridine rings were studied.When the hydrophobic chain increases,the critical micellar concentration（cmc）,the minimum surface tension(γ_cmc)and the minimum molecular cross-section area(A_min)appear to decrease,and the saturated adsorption(Γ_max)and the surface pressure(π_cmc)tend to increase.The wettability of the Gemini surfactant containing pyridine ring was determined on the quartz surface.When the hydrophobic chain increases,the maximum contact angle of the Gemini surfactants with pyridine ring increases successively on the quartz surface,and the wettability of the quartz surface is decreased.QCM-D was used to study the adsorption of the Gemini surfactants containing pyridine ring on quartz surface.When the hydrophobic chain increases,the adsorbed mass of the Geminin surfactants on quartz surface increases,and the adsorption film is rigid.Through kinetic fitting,it was found that the two-step adsorption model had the highest fitting degree.The results of XPS and Fourier infrared spectroscopy show that the Gemini surfactants containing pyridine ring adsorb onto the quartz surface through the physical adsorption,and they have better properties to float quartz than collophanite.With an increase in the surfactant concentration,the adsorption of the Gemini surfactant increases on the surface of quartz or collophanite.The surfactant（C12）can interact with CB[6]with a ratio of1:1.After the interaction with CB[6],the surfactant shows higher the values of cmc andγ_cmc.The adsorption/desorption equilibrium of the surfactant on the quartz surface can be controlled by use of CB[6].