Research On Synthesis, Molecular Dynamics Of Symmetric Gemini Imidazolium Surfactants

In this paper, the content, significance and development of synthesis and propertiesof Gemini surfactants in the relevance fields are summarized. A series of Geminiimidazolum surfactants with methylene spacer chains are synthesized by the reaction ofimidazolium, different bromoalkane and so on. The structure of the target product ischaracterized by1HNMR. The results show that all synthetic surfactants are objectiveconfigurations. The surface activities, structure-activity relationship and thermodynamicproperties of micellization of symmetric ionic-liquid Gemini imidazolum surfactants areinvestigated by means of surface tension and conductivity. The results show that theGemini imidazolum surfactant own high surface activities. As the carbon atoms ofhydrophobic group increase, the adsorption at the air-aqueous interface for Geminiimidazolum surfactant with fixed length of hydrophilic group is easier and the effciencyfor reducing the surface tension is increased; For the Gemini imidazolum surfactantwith shorter hydrophilic group, it has the higher surface activities and easier adsorptionat air-aqueous interface with the fixed hydrophobic group.At the low temperature, as the temperature increase, the counterion of micellizationincrease while the counterion decrease at higher temperature (45℃); The change ofGibbs free energy show that the micellization in aqueous solutions is a spontaneous andstable process; As the temperature increase, the free ernergy decrease but the stableproperties of micellization increase; At the same temperature, the free energy decreasewith increasing the length of hydrophobic group but increase with increasing the lengthof hydrophobic group.A molecular dynamics system suitable for many types of surfactant with differentstructure is constructed in this paper due to the drawback of exprimental investigatingon the micellization mechanism and structure-activity relationship from the molecularlevel. The surface activities, structure-activity relationship, thermodynamic anddynamics properties are investigated by means of pressurer tensor, free energyperturbation, radius of gyration and radial distribution function methods. The moleculardynamics results show that the theoretical value calculated from the moleculardynamics is close to the experimental value, and the system constructed can be used todiscriminate and predict the surface, thermodynamic and dynamics properties ofdifferent surfactants; For the surfactant with fixed structure, the surface activities andfavourability micellization are related to temperature, hydrophobic and hydrophilicgroup; As the temperature rises, the micellization of ionic liquid-type Geminiimidazolium surfactants becomes more difficult with the aggravation of molecularmovement; As the number carbon atom in the alkyl chains is increased, the tendencyand stability of micellization both increase; In addition, we found that ionic liquid-type Gemini imidazolium surfactants with different spacer lengths should follow the variousmechanism of micellization; If the length of spacer is less than6, as the carbon atoms ofspacer group increase, the formation ability of the micelles of surfactant is enhanced;But the formation ability of the micelles of surfactant decrease with the longer spacer(more than6).Under the same condition, the free energy of micellization of zwitterion Geminisurfactants are higher than the Gemini imidazolum surfactants, meaning that thestability of former are poor than the latter. Since the thermodynamic properties ofzwitterion Gemini surfactants are close to the traditional anion surfactant, it may showthe better compound properties than the ionic liquid Gemini imidazolum surfactants.The quantum chemical topology and molecular dynamics methods are applied tothe single molecular property, hydration in the aqueous solution and compound amongthe different surfactants. The results show that the hydrophobic tails of surfactant own anegative charge due to the influence of hydrophilic group; The total charge of polargroup can be greatly influenced by the numbers of carbon atoms of spacer group; As thelength of spacer group increase, the end part of hydrophobic group increase.Ionic liquid Gemini imidazolum surfactant can form the geometry cluster withwater molecules by constructing the hydrogen bonding formation; As the range ofmolecular from1to3, the hydrogen bonding formation between polar group ofsurfactant and water is1:1. As the number of water molecule is increased to4or5, thehydrogen bonding formations are2:1and2:2with the ring and cage hydration cluster;The analysis results for binding and free energy of hydration cluster show that thehydration cluster is a stable thermodynamic system; With the increased numbers ofwater molecular, the stability of cluster increase.The contour map with compounding ionic liquid Gemini imidazolum surfactantand traditional anionic surfactant shows that the the electrostatic repulsion force mayexist among the aggregation of hydrophobic groups due to the negative charge in theend of the alkyl chain; As the concentration of surfactant is low, the electrostaticrepulsion force can be ignored in the system; However, the influence of electrostaticrepulsion force should be important with increasing the concentration constantly andmay be unfavourable to form the micellization; Therefore, we can consider to changethe electrostatic repulsion force so that it can be suitable to the application of compoundamong different surfactants in the enhanced oil recovery by improving the length ofspacer group.