Transport And Diffusion Of The Small Molecules Within Supramolecular Gel

Supramolecular organogels formed by the self-assembly of gelator through intermolecular hydrogen bonding,Ï€-Ï€stacking and other non-covalent bond interations have been receiving considerable attention.As a stable host matrix,some guest molecules such as organic dyes and drugs can be entrapped in organogels by simply adding them to the sol prior to its gelation.Therefore,a better understanding of the mass transfer behavior of guest molecules in organogel is required not only for the development of fundamental research on host/guest interaction,but also for potential applications such as drug delivery and gel electrolytes.In this dissertation,when supramolecular organogels of a bis-(4-stearoylaminophenyl) methane(BSAPM) in some solvents or electrolyte solution in propylene carbonate were used as host,the diffusional release or the electrooxidation reaction of guests was investigated by different methods.A novel organogel based on the gelation of aqueous microemulsion was prepared by using low molecular weight gelator N-stearine-N'-stearyl-L-phenylalanine(Bis18-L-Phe).Sodium salicylate was entrapped within the gelled microemulsion and used as model drug.The in vitro sodium salicylate release behavior in gelled microemulsion was investigated by using UV-Vis spectroscopy. In addition,we reported herein self-assembly of supramolecular organogel when confined within the multiwalled carbon nanotubes,the thermodynamic properties and the possible mechanism of self-assembly were studied.This paper are consisted of several sections as the following:1) BSAPM as a gelator was used for preparation of 1,1,2-trichloroethane(TCE) supramolecular organogels.The existence of salicylic acid and Rhodamine B as the guest molecules slightly led to the decrease of gel-sol phase transition temperatures(T_GS) of the organogels.The diffusion and release of the guest molecules in the organogels were investigated by using UV-Vis spectroscopy.The results indicated that release ratios of the guest molecules decreased with the increase of the gelator concentration.Wherein,the release ratios of Rhodamine B were less than that of salicylic acid,which could be attributed to the larger molecular size of Rhodamine B.In addition,the diffusion coefficients of Rhodamine B were also less than that of salicylic acid.This trend was more clearly with the increase of BSAPM concentration.The investigation indicated that the diffusion and release behavior of the guest molecules in the self-assembled organogel followed the Higuchi equation and diffusion-controlled mechanism of Fickian model.2) Supramolecular organogel was formed by self-assembly of BSAPM in propylene carbonate containing LiClO₄.The electrochemical behavior and diffusion of ferrocene (Fc) and ferricenium(Fc⁺) entrapped within the organogel was investigated by cyclic voltammetry.The Fc molecules still show redox activity within the organogels in comparison with corresponding solutions of propylene carbonate containing LiClO₄.The shape of the cyclic voltammograms of the Fc electrooxidation in organogel was similar to that in corresponding solutions.The results indicated that redox reactions of Fc/Fc⁺ were a quasi-reversible process of diffusion-controlled single electron transfer in organogels.The diffusion coefficients of Fc and Fc⁺ in organogels decreased with an increase of the concentration of gelator BSAPM,but increased with an increase of temperature.The temperature dependence of the diffusion coefficient in organogels followed classical Arrhenius equation.The activation energy in organogels was found of no difference from that in corresponding solutions.3) Low molecular weight organogelator,N-stearine-N'-stearyl-L-phenylalanine (Bis18-L-Phe) is able to gelatinize the microemulsion consist of isopropyl myristate (IPM),Tween 80,propylene glycol(PG) and water in a very low concentration.The resulting gelled microemulsions showed good thermo-reversibility.The phase transition temperature(T_GS) of gelled microemulsion increased with an increase of Bis18-L-Phe and the ratio of SC to IPM.The mechanism of formation of the gelled microemulsions was studied by POM and FTIR.POM image showed elongated and strandlike aggregates dispersed throughout the continuous phase to form a coherent network.FTIR spectroscopy indicated that intermolecular hydrogen bonding may be responsible for the gel formation.4) Water-soluble sodium salicylate was used as a model drug and its release from the gelled microemulsions was studied.The results showed that the release of drug exhibited a sustained release behavior and the release rate reduced with increasing the proportion of Bis18-L-Phe.Moreover,the release rate of drug increased as the content of drug increased and decreased with an increase in the proportion of IPM.The release behavior of drug followed first-order release kinetics.These results indicated that the gelled microemulsion was potentially useful in drug delivery systems5) A bisurea gelators 1-methyl-2,4-bis(N'-octadecylureido)benzene(MBUB-18) was affused into the the multiwalled carbon nanotubes(MWCNTs) by heating and ultrasonication to investigate the gelation of chlorobenzene confined within the MWCNTs.Based on an analysis of the DSC and XRD data for the gels confined within the MWCNTs and formed in the bulk space,we argued that the self-assembled of supramolecular organogel in an unusual manner when confined within MWCNTs in comparison with that in bulk space.The results not only provide a good addition to the development of new types of CNT-based composites,but they also are helpful for the understanding of the mechanism of natural self-assembling processes and the related phenomena within nano-scale environments.