Computational Investigations Of Zwitterion Based Elastomers And Preparation Of TiO₂ Integrated Zwitterion Polyurethane Composites

Zwitterion contained polyurethane(ZPU)elastomers have largely sparked a lot of attention in the development of biomaterials owing to their simple synthesis,easy handling and good antifouling properties.The primary benefit of ZPU is that its physical and chemical properties can be readily controlled by manipulating and changing formulation contents of hard and soft segments present in PU.The additional distinguishing features of zwitterion-based materials include their specific morphology,the existence of both positive and negative region and the presence of substitute groups between the backbone and zwitterions,making them extremely versatile.In the past,various computational techniques like molecular dynamics(MD)simulation and density functional theory(DFT),and experimental studies have been effectively developed to analyze the zwitterion-based materials.Currently,the growth of PU surfaces with quaternary ammonium groups(zwitterions)is in fierce competition,however,ZPU could not be completely utilized as a strong engineering material to withstand harsh weathering conditions for outdoor applications.In this regard,the toughening mechanism of physically cross-linked zwitterionic moieties incorporated within flexible polymeric chains is analyzed by MD simulation,integrating of rutile TiO₂ nanoparticles into ZPU elastomers to increase the photo-stability and investigate the intersegmental hydrogen bonding interaction of ZPU via DFT method,which are arranged in the present dissertation in four chapters.The first chapter includes the detailed description of ZPU,along with its historical perspective,general preparation route,different zwitterionic system,different types of ZPU,MD simulation of ZPU,its photo-degradation and photo-stabilization with TiO₂ nanoparticles.In the second chapter,the thermo-mechanical behavior of a physically cross-linked system consisting of zwitterion monomers and completely springy elastomeric matrix was investigated using coarse-grained molecular dynamics simulations(CGMD).In the present study,the effective Lennard-Jones relationship has employed on this bead-spring network of zwitterion crosslinker(ZCL).The influence of the attractive interaction strength(?)of endlinking sites,ZCL chain length,its functionality effect on the thermomechanical properties are investigated.A specific network is created with dynamic ZCL functionality at constant molecular mass and multiple functional sites,and observed that the mechanical strength is increased with the increase of functional sites,as illustrated by the bond orientation curve.For ZCL's chain length,we observed that a short chain length has greater strength and a higher glass-transition temperature(Tg).Furthermore,the(?)of ZCL increases,the modulus response and orientation of chain are enhanced,as well as an increase of Tg.Finally,the standard tri-axial deformation has used to investigate the influence of different functional sites of ZCL on the recovery mechanism and fracturing activity.Through visual molecular dynamics(VMD)study,the findings of recovery and deformation process confirmed the linking of reactive sites even in physical system and found strong attractive interactions among the end groups linking.In addition,we expect that our research can provide some recommendations for the reasonable design and research of high-performance zwitterion contained elastomeric materials.The third chapter discusses the successful synthesis of zwitterion polyurethanes(ZPU)and preparation of various TiO₂/ZPU nanocomposites with the goal of improving the shelf life of ZPU,and forming an effective film for use in food packaging.According to the thermal and mechanical findings,the 4%TiO₂/ZPU specimen performs best,as proven by tensile tests and morphology analysis.The spectral analysis revealed that titanium(TiO₂)nanoparticles can improve absorption in UV region and reflectance in visible region,reducing photo-aging abilities and extending the service life of the material.Furthermore,after 5 hours of UV light irradiation,scanning electron microscopy(SEM)observations proved the photo-stability of the TiO₂/ZPU composite film.Moreover,TiO₂ nanoparticles improves ZPU's antioxidant performance from 51%to 71%.The antibacterial activities of TiO₂/ZPU shows that it inhibits bacterial growth of E.coli strains,indicating its fitness for food packaging applications.Besides,visual patterns in tomato fruit surfaces are used to monitor food preservation capacity.In general,we expect the TiO₂/ZPU composite films have all of the intended properties for use as a photo-stable food packaging material.Fourth chapter confers the intersegmental interactions(both hydrogen bonding and ionic interaction)among polyurethane(PU),zwitterion contained polyurethane(ZPU)as two hard segment(HS)models and poly(?-caprolactone)(PCL)based one soft segment(SS)model by employing standard density functional theory(DFT)technique at B3LYP level.The structures of hard segments(HS)and soft segments(SS)are optimized to the minimum energy before studying the interaction between these segments.The small energy gap(?E)values of PU(4.867 eV)and ZPU(5.403 eV)means that they are more reactive than PCL.The molecular electrostatic potential(MEP)analysis confirms that the cationic and anionic parts are corresponding to the complete electron density surfaces.The Mulliken Charges analysis shows that charge changes(?Q)values and hydrogen bonding energies in ZPU model are much higher than that of PU and PCL models.This fact is attributed due to the presence of bulky sulfonate groups that sterically hindered the surface,and thereby increasing all the mechanical properties as observed in our previous experimental work.