Study On Highly Efficient Adsorption And Orientation Of Polymer In Metal-organic Frameworks

The photonic and optoelectronic devices fabricated with optical anisotropic materials have unique functions and properties,and become one of the most important research topics in the future.Optical anisotropy mainly refers to birefringence and dichroism,that is,the refraction and absorption properties of materials are different for optical beams at different states of polarization.Polymeric optical materials have drawn many interests,because of their advantages such as low cost,easy fabrication,good performance and adjustable refractive index.The birefringence of polymer optical material is related to the orientation degree of polymer molecular chain.The higher the degree of orientation is,the greater the birefringence is.There are many ways to improve the orientation of polymer optical materials.Among them,highly oriented polymer materials can be fabricated with the help of metal-organic frameworks(MOFs).When the oriented channels of MOFs are utilized as the reaction vessels for polymerization,the resulting polymers will also have high orientation as the channels have.In this work,based on the density functional theory,the Monte Carlo method and the molecular dynamics(MD),the all-atom models of methyl methacrylate(MMA),methyl methacrylate(TFMA),PMMA,PTFMA and MOFs are established.The adsorption of MMA and TFMA in MOFs is simulated and MD simulations of PMMA and PTFMA hosted in MOFs are performed.By analyzing the simulation results,the three main factors affecting the adsorption characteristics are obtained: A)the electrostatic interactions between the pore walls of MOFs and polymer monomers.The electrostatic interactions between the polarized pore walls of MOFs and the polarized monomers promote the adsorption and orientation of the monomers in the channels;B)the electrostatic interactions between monomers.The electrostatic interactions between polarized monomers make the molecular space more compact,and promote the adsorption of monomers in MOFs,and also promote the molecular orientation;C)the relative size of the pore in MOFs and monomer,that is,the relative size between the organic ligand and monomer.Employing of ligands with different length,pore size and the adsorption amount of monomers will be different,and it will affect the degree of orientation of the polymer chains,and the conversion rate of polymerization will also be influenced.These three factors have important influence on the selection of polymer monomer or MOFs,and provide a theoretical prediction method for the control of polymer chain orientation.