Asymmetric Modification And Self-assembly Behavior Of Graphene Oxide

Two-dimensional?2D?materials are composed of a single layer or a few atomic or molecular layers.They are connected by strong covalent or ionic bonds in the layers,and they are combined by weak Van der Waals forces between layers and layers.At present,the two-dimensional materials that are currently being studied are graphene?conductor?,molybdenum disulfide?semiconductor?,and boron nitride?insulator?etc.The 2D material has the characteristics of large surface area,soft and easy to fold,and it has a wide range of applications,such as drug carrier and catalysis.However,when it is applied to organisms,its large surface area limits its function due to the high risk of capture by immune system.The assembly of 2D materials is a common method for intelligently regulating the specific surface area of materials.The assembly methods mainly include:?1?in-situ assembly,?2?one-dimensional template-assisted assembly,?3?shear force and solvent-assisted assembly,?4?assembly by two-dimensional material surface modification etc.Among them,asymmetric modification induced self-assembly of 2D material results from the free energy in different solvents.Thus,it can spontaneously assemble.In this paper,foucs on graphene oxide?GO?,PS chains were monofacially modified on GO through electrostatic attractions.The dynamic assembling of GO with different sizes were studied,and its feasibility as a smart probe was verified.1.When a 2D material is applied to an organism,its large specific surface area will greatly increase the probability of immune clearance,decreasing the function of drug delivering or tumor diagnosis.Imaging technology is an important method to assist tumors diagnosis.But at present imaging methods can only proved some information about tumor location,size and boundaries etc.Direct diagnosis is not achievable.In this chapter,positively charged PS microspheres were prepared by the same method as the former chapter.Based on electrostatic attraction,GO were monofacially grafted with hydrophobic PS chains and metal cations absorbed on the other sides.The fabricated Janus PS-GO-Fe³⁺sheets self-assembled in THF,where metal ions were enveloped inside the assembly.The assembly possessed intelligent off/on magnetic resonance imaging?MRI?contrasting performance.By mimicking the tumor microenvironment,the nanoprobes can be smartly turned on by disassembling and exposing the mental ions.Such nanoprobes may provide new sight for intelligent tumor diagnosis through imaging techniques.2.The small-sized 2D material GO was poorly dispersed in the water,and it was easy to agglomerate and difficult to peel.It is difficult and challenging to assemble GO into ordered structure-without the presence of external force or energy.In this chapter,PS microspheres with positive charges were prepared by surfactant-free polymerization in alcoholic dispersion;a small-sized GO nanosheets were adhered to the surface of PS microspheres by electrostatic attraction;after etching in DMF,PS-GO sheets were obtained,which were similar to maggots with GO as the head and PS as the tail.The analysis of scanning electron microscope?SEM?,transmission electron microscope?TEM?,contact angle,gel permeation chromatography?GPC?,zeta potential,and thermal weight loss analysis?TGA?were used to prove the successful preparation of PS-GO nanosheets,The self-assembly behavior of PS-GO nanosheets in THF was studied,and the assemblies including nanowires and nanofilms were obtained before the final formation of bamboo-like assemblies.The dynamic formation of the above assemblies was monitored and discussed.It is proved that the PS chain segment played a key role in triggering the morphological change of assembly.This work may provide deep understanding and guidance for small-sized 2D materials.