Simulation Study Of The Correlation Between Microstructure And Mechanical Properties Of Organogel Network By Using Finite Element Method And Study Of Electronic Structures Of Organic Molecules Through Quantum Chemical Calculation

In recent years,as the tremendous development of computational method and hardware,both of computer simulation and quantum chemical calculation play more and more important role in Physics,Biology,and Chemistry and so on.It is known that theory needs to be validated by the experiments.However,we often meet phenomena which are difficult to be resolved only by experimental methods.At this time,we need to take advantage of the theory and computer simulation to explore the nature of the experiments.Further more,as the more and more powerful computer ability computer simulation can do in advance to that of the experiments.They can predict the experimental results and guide the experiments.Bearing these in mind, combining with our latest experimental results we try to explore their nature through the methods of computer modeling and quantum chemical calculations.Recently,it is found that some low-mass molecules can gel organic solvent at very low concentration(≤2 wt %)to form organogel.These low-mass molecules are called low-mass-molecule gelators(LMOGs).LMOG self-assemble into fibers through hydrogen bonds,elactrostatic interaction,dipole-dipole interaction orπ-πinteraction.These fibers interconnect each other to form three-dimension networks. The organic solvent is trapped in the network through capillary force.Small-molecule organogel(SMOG)is thermal and chemical-reversible in contrast to irreversible covalent networks found in polymer or biopolymer gels.Due to its properties of thermal reversibility,3D network and viscoelasticity SMOG has great applications in drug delivery,catalysis,separation,and scaffolding for tissue engineering,templating nanostructure materials and so forth.Generally,SMOG must have enough elastic property in order to fulfil the applications.For instance,successful tissue engineering depends on the mechanical properties and network structure of the gel network in order to create and maintain a space for tissue development.Until now there are great and continuing efforts to examine the rheological and thermodynamic properties of organogels in order to identify new LMOGs; the formation mechanism and network structure of SMOG are also studied in detail. However,the relationship between the microstructure of organogels and macroscopic properties has not been examined.Based on the experiments,we construct two-dimensional(2D)radial-growth network.The finite element method is used to explore the correlation between microstructure and mechanical response of the network.A totally influences of structure and material parameters on the elastic modulus of the network are investigated.The network deformations under strain and stress distribution are also studied in detail.From our simulations we can make the following conclusions;1.The elastic modulus of the network decreases exponentially with the fiber length.By analyzing the difference between the computational and the experimental results we get two possible ways to engineer the network structure for desired elastic property;under the condition of the total number of spherulites being approximately constant,the network elastic modulus can be substantially enhanced by decreasing the mesh size or the average fiber length of fiber segments of the fiber networks; also if the mesh size of the network is approximately constant,the elastic modulus can also be significantly enhanced by decreasing the number of spherulites due to reduce the weak interaction in the system.2.When the aspect ratio of the fiber is smaller than 20,the radius of the fiber cross-section has great impact on the network elasticity; while the aspect ratio is larger than 20 it almost has no effect on the elastic property of the network.3.The elastic property of the network will increase with the junction density and fiber stiffness of fiber networks.4.The deformation in the planar spherulitic network is found to be stretching dominated and it belongs to affine deformation.The stress distribution mainly distributes along certain radii and around the central point.Organic materials with large two-photon absorption(TPA)cross sections are currently under considerable investigation for applications such as 3D microfabrication,two-photon up-conversion lasing,optical power limiting,two-photon fluorescence microscopy,and three-dimension optical data storage. However,the early development of TPA-based application was limited because the available materials had relatively small TPA cross-section.Organic compounds with large two-photon absorption cross-section have been extensively studied,it is also known that monodisperse semiconductor cluster belonging toⅡ-Ⅳgroup with a sharp exciton absorption band contribute to the enhancement of nonlinear optical response.Under this condition,in order to explore materials with large two-photon absorption cross-section we prepared two organic-inorganic composites of 1,2,4, 5-tetrakis(4-pyridylvinyl)benzene(TKPVB)/CdS and(E,E)-4-{2-[p'-(N,N-di-n-butylamino)stilben-pyl]vinyl} pyridine(DBASVP)/CdS.And study therir single-photon fluorescence properties.It is observed that the composite of TKPVB/CdS shows fluorescence quenching effect and DBASVP/CdS shows fluorescence enhancement effect.In order to explore the nature of these phenomena we studied the electronic structures of the two organic molecules using the Density Function Theory.Combining the computational results with experimental results we can understand well the phenomena from the points of the mechanisms of energy transfer and electron transfer.The conclusions are as follows;1.TKPVB and DBASVP are optimized by the method of b31yp/6-31g on the Gaussian03 Program.The electron distribution of the frontier orbits of the two molecules suggests that they can coordinate with metallic atoms.2.Comparing the energy levels of TKPVB and DBASVP with that of CdS both composites are favor to electron transfer,but it is suggested that the probabilities are very small due to the macro-molecules of AOT on the surface of CdS.3.The energy transfer is proportional to the overlap of acceptor's absorption spectrum and donor's emission spectrum.Observing the experimental results,we suggest that the composite of TKPVB/CdS is favor to energy transfer; DBASVP/CdS has little probability of energy transfer.In a conclusion,the composite of TKPVB/CdS has certain probability of energy transfer which leads to the fluorescence quenching.The composite of DBASVP/CdS has very low probabilities of electron transfer and energy transfer,which means that it should has no change.The enhancement of fluorescence in DBASVP/CdS is suggested that after combined with CdS nano-cluster DBASVP become more rigid and coplanar which enhance the emission of the fluorescence.