Fractal structures have attracted considerable scientific interest,and fractal geometry is an effective tool to study the complicated structure and dynamic processes,such as dilation symmetry of disorder structure,percolation,gelation,and metal-insulator transition.Here,we summarized our findings of fractal growth of giant amphiphiles in Langmuir-Blodgett(LB)film.Giant amphiphiles composed of polyhedral oligomeric silsesquioxanes(POSS)derivatives and poly(ethylene oxide)(PEO),with structural diversities of POSS head modification,POSS head number,PEO chain length,are precisely synthesized.The effect of molecular structures and operation parameters on the fractal growth patterns are discussed,in addition,other fractal growth patterns in LB films and in Langmuir films are included,aiming to understand the basic molecular principle of fractal growth in LB system.
Wei-Jie WangXian XuYu ShaoJian-Wen LiaoHan-Xin JianBing XueShu-Guang Yang
In recent years, covalent organic frameworks(COFs) are evolving as a novel kind of porous materials for catalysis and molecular separation, gas adsorption, etc. Various functional building blocks have been explored to tune the pore channels, including the pore size and structures. In this article, a new terphenyl(TP) based COF(TP-COF) was developed via a “two-in-one” strategy by using a symmetric A2B2monomer, i.e., 4,4''-diamino-2',5'-diformyl-1,1':4',1''-terphenyl(DADFTP). The pore size of TP-COF was only 0.99 nm by shortening the arm length of the DADFTP monomer. Freestanding, continuous and ultrathin COF films could be facilely prepared at the air-liquid interface through the modified Langmuir-Blodgett(LB) method. TP-COF films exhibited high rejection of over 90% for dyes removal.
MENG WeijiaLI YangZHAO ZiqiangSONG XiaoyuLU FanliCHEN Long
Large roughness and structure disorder in ferroelectric ultrathin Langmuir-Blodgett(LB)film results in severe space scatter in electrical,ferroelectric and piezoelectric characteristics,thus limiting the nanoscale research and reliability of nano-devices.However,no effective method aiming at large-area uniform organic ferroelectric LB film has ever been reported to date.Herein,we present a facile hot-pressing strategy to prepare relatively large-area poly(vinylidene fluoride)(PVDF)LB film with ultra-smooth surface root mean square(RMS)roughness is 0.3 nm in a 30μm×30μm area comparable to that of metal substrate,which maximized the potential of LB technique to control thickness distribution.More importantly,compared with traditionally annealed LB film,the hot-pressed LB film manifests significantly improved structure uniformity,less fluctuation in ferroelectric characteristics and higher dielectric and piezoelectric responses,owing to the uniform dipole orientation and higher crystalline quality.Besides,different surface charge relaxation behaviors are investigated and the underlying mechanisms are explained in the light of the interplay of surface charge and polarization charge in the case of nanoscale non-uniform switching.We believe that our work not only presents a novel strategy to endow PVDF LB film with unprecedented reliability and improved performance as a competitive candidate for future ferroelectric tunnel junctions(FTJs)and nano electro mechanical systems(NEMS),but also reveals an attracting coupling effect between the surface potential distribution and nanoscale non-uniform switching behavior,which is crucial for the understanding of local transport characterization modulated by band structure,bit signal stability for data-storage application and the related surface charge research,such as charge gradient microscopy(CGM)based on the collection of surface charge on the biased ferroelectric domains.
