Creation Of Novel Supramolecular Gels Supramolecular Film And Performance Studies

As the fouth generation materials, smart materials have emerged as one of main issues of advanced materials. Stimulus-responsive physical gels, especially the physical gels based on low-molecular-mass gelators (LMMGs), are the most promising smart materials due to their excellent designability and reversible stimulus-responsibility. Supramolecular gels are formed and maintained by weak interactions including hydrogen bonding,Ï€-Ï€ stacking, van der Waals interactions etc. The non-covalent nature of these weak interactions endow them excellent reversible stimulus-responsility to chemicals, electric field, shear and magnetic field, etc. Therefore, this kind of gels has versatile potential uses in molecular devices, sensors, biomedicines.The stimulus responsibilities of physical gels can be achieved by two methods:(a) incorporating responsive segments (electroactive or photoresponsive moieties) into the respective gelators;(b) doping functional micro/nano particles (such as magnetic particles). Except chemicals stimulus (pH, anions), increasing attentions have been paid on stimulus-responsibility of physical gels to shear force, electric field, magnetic field and ultrasound. On the other hand, the importance of responsive sensitivity, chemical and physical stability, machanical strength and processibility of stimuli responsive physical gels were recognized recent years. However, researches about these characters are in their infancy period. Our group has focused on smart supramolecular gels based on cholesterol derivatives for more than one decade and we have designed and synthesized a series of gelators containing fluorescent or electric segments and studied their stimuli responsibility. According to the researches form literatures and as the contination of our work, a series of LMMGs for the gelation of ionic liquids and ionic gelators with iodides were prepared. The supramolecular gels attained displayed fansnating properties, such as multi-stimulus responsibility, high machnical strength and super gelation ability. On the other hand, oligomers with ferrocene in the main chain and cholesterol as a pendant group was synthesized, and their self-assembly behaviors were studied. Many techniques, including rheological methods, electrochemical methods, SEM, TEM, AFM, XRD, FTIR and1H NMR etc., have been employed to investigate their properties and the mechanism. This thesis is mainly composed of the following four parts:(1) Cholesterol-based low-molecular mass gelators towards smart ionogelsIonic liquids are "designable solvents" and "solvents of future". One of the promising methods to boost their uses is to solidify them in a physical way but with little interruption of their properties. It is therefore of interest to create gels of ionic liquids by using low-molecular mass compounds as gelators (LMMGs). Herein, we report a number of ionic liquid gels (ionogels) of which specially designed and synthesized cholesteryl derivatives were employed as gelators. The obtained ionogels are thermo-reversible. In particular, the one with1-butyl-3-methyl-imiodiolium tetrafluoroborate (IL2) as solvent and a cholesteryl derivative containing a D-phenylalanine residue (1D) as a gelator is very stable both in neutral and acidic mediums as demonstrated by a yield stress of76Pa for a self-standing cylinder of the ionogel. Furthermore, the ionogel can be easily converted into a hydrogel via simple replacing of the solvent with water in situ. More interestingly, the conversion is reversible, a phenomenon never reported before. At the same time, the critical gelation concentration (CGC) of1D for IL2is only0.06%, w/w, which is almost the lowest value, reported for ionogels till now, and falls into the category of "super-gelator". Magnetization of the ionogel has been realized by introduction of micro-/nano-Fe3O4particles. As expected, the magnetic gel as obtained is responsible to external magnetic field. Specifically, it changes into fluid with the presence of a magnetic field exceeding certain strength, and retains to gel upon removing the magnetic field and with a treatment of sonication and heating-cooling cycle. SEM and TEM observations revealed the continuous fibrous networks of the ionogels. To the best of our knowledge, this is the first report on ionogels possessing stimulus-responsive properties, good mechanical strength, and super-gelation talent.(2) A smart redox responsive supramolecular gel based on iodide/iodineThree cholesterol-based ionic gelators with iodide as anions and imidazolium as caions were rationally designed and synthesized. It is demonstrated that this kind of gelators prefer to gel nonpolaric solvents, and the attained gel showed excellent redox responsibility to H2O2/NH2NH2or I2/NH2NH2at room temperature. Moreover, the gelation ability of gelators was also dependent on counter ions. SEM and AFM studies showed that the primary structure of the gel is fibrous. FTIR and1H NMR measurements revealed that one of the NH was incorporated into formation of hydrogen bonding, which is one of the main dirving forces for the formation of gels. This kind of ionic gelators would be promising compentnets of electrolytes for chemical batteries.(3) Oligomer with ferrocene in the main chain and cholesterol as a pendant groupWith ever-increasing need for thin, flexible and functional materials in electrochemical systems, various techniques have been explored for creating materials used in fuel-cells, batteries, electro-chromic devices, solar cells, and sensors. In the present study, a novel ferrocene (Fc) and cholesterol (Chol)-containing oligomer, oligo(FcDC-co-CholDEA), was specially designed and prepared by putting Fc in the main chain and Chol as a side group. MALDI-TOF MS and freezing point depression measurements revealed that in average each oligomer contains three Fc units and three Chol units. UV-irradiation and cyclic voltammetric measurements revealed that the oligomer displays superior photo-chemical and electro-chemical stability, which is not common in polyesters and polyamides of which the main chains contain Fc units. In particular, the Fc-containing oligomer possesses an unusual oxidation center, of which the oxidation potential could be as high as1.81V. The oligomer is also superior in self-assembly as demonstrated by forming L-B film of layered structures. Furthermore, supramolecular films with high mechanical strength in wet state can be prepared by employing a simple solution casting method. This finding demonstrates that self-assembly is a simple but effective way to create films of potential uses in real-life applications provided proper building blocks are designed and employed.(4) Preparation and self-assembly behaviors of ferrocenyl oligomer based on click chemistryAs a contination of the previous work, we conducted a more selective and reactive method, click reaction, on ferrocenyl derivatives and cholesteryl derivatives in the hope of improving the degree of polymerization. It was found that the maximum polymerization degree of oligomer is5and the wavelength of fluorescence emission shift from423nm to433nm as the concentration increasing. Moreover, the intensity of emission would be enhanced in the presence of water, which are a meaningful phenomenon, aggregation induced enhancement emission. TEM measurements had shown that the oligomer would aggregate to nanospheres in presence of water. It is believed that the aggregation was originated form van der Walls interaction between cholesterols. Furthermore, a high machanical strenghth supramolecular film would be prepared by evaporvation of solvents.