Synthesis And The Gelation Mechanism Of Amide Derivatives Containing Urea Group

Low-molecular-weight organogels(LMWGs)are a type of smart soft material with nanoscaled three-dimensional networks formed through weak noncovalent interactions,such as hydrogen bonding,?-? stacking,and hydrophobic interactions.They have attracted increasing interest because of their potential applications in template materials,sensors,and gene delivery devices.It is not difficult for researchers to design a gelator that gels certain solvents based on previous experiments.However,understanding the process of gelation and determining experimental evidence for a number of speculations has remained a challenge,and up to now,there is still no universal model to describe organogels.In addition,the change of the external environment in the process of sol-gel has a profound influence on the gelation process and gel behavior.Tuning the morphology and structure of gel aggregates through external stimulus,and thus changing the growth process of the gel,have become the focus of attention in recent years.Therefore,in this thesis,we mainly focus on the sol-gel transition mechanism and the effect of external environment condition on the morphology and structure for the organogels based on hydrazide derivatives containing urea group.The main conclusions are as follows.1.The effects of substituting position on the gel properties of BMUC and BPUC were studied.The meta-substituted BMUC could form gels in ethanol,while BPUC could't due to its poor solubility in the tested solvents.2.Results of morphology and structure evolution during gelation of BMUC by SEM and optical microscope revealed that BMUC molecules self-assembled to form a large number of separated clew-like spheres and then the spheres were connected along different directions to form short rod-like aggregates which showed extension growth,leading to form fibers finally.The evolution of the gel morphology was accompanied by changes in the molecular arrangement,the unknown arrangement in the spheres has evolved into a more tightly packed hexagonal in the fibers.Intermolecular hydrogen bonding between-C=O and-N-H was found to be the driving force for the formation of fibers and spheres,and its strength in the fibers was greater than that in the clew-like spheres.The kinetics of the gelation of BMUC in ethanol showed a two-stage kinetic pathway with different fractal values of 1.27 and 0.84.3.Ultrasound can speed up the growth speed of the BMUC gel in ethanol although its growth pathway of gelation and hydrogen bonding intensity remained unchanged.The ultrasound induced organogels of BMUC in ethanol showed improved thermal stability and mechanical properties compared to those of the T-gels.Further,the hydrophobicity of the xerogels of the S-gel of BMUC in ethanol decreased with the increase of ultrasonic time.4.BMUC in methanol showed either crystallization or gelation depending on temperature and ultrasound.BMUC molecules in the crystals showed a layered structure,in contrast,they are arranged an unknown structure in the spheres and a hexagonal column structure in fibers,respectively.Both intramolecular and intermolecular hydrogen bonds of-N-H groups were confirmed in BMUC crystals,while intermolecular hydrogen bonds in the spheres and fibers in gels.The xerogels of BMUC gels prepared at low concentration(15 mg/mL)showed three-dimensional networks fiber,while spiral fibers were observed in that at 20 mg/mL.