Study On The Preparations And Properties Of Rosin-based Small Molecular Weight Organic Gels

Through weak intermolecular interactions,low molecular weight molecules with specific structures can form various mesoscopic aggregates,which leads to the formaion of small molecular weight gels by gelating water or organic solvents.Compared with that of macromolecule-based gels,low molecular weight gels received wide attentions and applications due to their unique rheological behavior and stimuli-responsive properties.Although a large number of small molecule gelling agents have been reported,exploration on the relationship between molecular structure and the properties of low molecular weight gels is still a hot topic of this field due to the complexity of molecular self-assembly.Rosin is an important forestry resource in our country,and its main component is rosin acid with significant hydrophobicity.The carboxyl group of abietic acid can be used as an active site to connect with other hydrophilic groups.In this thesis,a rosin derivative dehydroabietic acid is taken as the raw material to synthesize new structured rosin-based low molecular weight molecules.Their self-assembly and the properties in forming gel emulsions are investigated.The main contents and results are as follows.1.Using disproportionated rosin as a raw material,dehydroabietic acid with a high purity was obtained through several purification steps.The structure of dehydroabietic acid was fully analyzed using 1-D and 2-D NMR techniques.Using dehydroabietic acid as the raw material,four rosin-based molecules R-Lys（n）-R（n=0,2,6,12）were designed and synthesized.The structure and purity of the products were confirmed by ¹H NMR and mass spectrometry.2.The gelation ability of R-Lys（n）-R（n=0,2,6,12）on common organic solvents was investigated.It is found that the alkyl tail length connected to the ester group significantly affected the gelation behavior of the molecules.R-Lys（0）-R cannot gel any solvent investigated;R-Lys（2）-R can gel cyclohexane and tetraethyl orthosilicate;R-Lys（6）-R and R-Lys（12）-R showed better performance and can gelate a variety of saturated hydrocarbon solvents.3.The gelation properties R-Lys（6）-R were investigated in detail using differential scanning calorimeter,atomic force microscope,circular dichroism,nuclear magnetic resonance,rheometer and other instruments.The results showed that R-Lys（6）-R formed ultra-long fiber aggregates with left-handed chirality in n-decane（the cross-sectional diameter was about 15 nm）.While in cyclohexane,R-Lys（6）-R formed cluster-like structures composed of fine fibers.Hydrophobic interactions and intermolecular hydrogen bonding are the main driving forces in the aggregate formation.4.The effects of R-Lys（6）-R in the preparation of emulsion gels were explored.R-Lys（6）-R itself shows poor emulsification abiltiy and can only gel the oil phase in an mixture of oil and water.In the presence of nonionic surfactant C₁₂EO₃,R-Lys（6）-R of certain concentraions can promote the formation of W/O emulsion gels.The presence of the emulsifier C₁₂EO₃greatly reduces the interfacial energy between the continuous phase and the dispersed phase,and the fibers formed by R-Lys（6）-R show amphiphilicity to certain extent.Both C₁₂EO₃ molecules and and R-Lys（6）-R molecules are adsorbed at the oil/water interface to form stable films.Therefore,the formation of emulsion gels is caused by the synergistic effects of the aggregates formed by R-Lys（6）-R and C₁₂EO₃.In these new emulsion gels,the volume fraction of the oil phase can be freely adjusted between 40%and 90%,which provides possibilities in preparing emulsion gels with rich formulations.