Yonghua Jiao

Facile and Efficient Approach to Speed up Layer-by-Layer Assembly: Dipping in Agitated Solutions

A facile and efficient approach has been developed to speed up the fabrication of LBL films through sequential dipping in vigorously agitated solutions. By this agitated-dipping (AD) LBL technique, the multilayer films of PAH and PSS were fabricated. The resulting films were explored by UV-vis spectroscopy, X-ray reflectivity, and AFM. Meanwhile, the comparison of the AD and conventional LBL films was made, which demonstrated that AD LBL can decrease dipping time by more than 15 times without reducing film quality remarkably. In addition, to verify the generality of AD LBL, we studied the AD LBL films of PDDA/PSS and PAH/PAA preliminarily as well. AD LBL promotes the efficiency of conventional LBL greatly while preserving its most advantages, such as simplicity, cheapness, precise control, universality in substrates, recycling use of sample solutions, and so on. It would be a promising alternative to build up LBL films rapidly.

Layer-by-Layer Assembly of Poly(lactic acid) Nanoparticles: A Facile Way to Fabricate Films for Model Drug Delivery

Layer-by-layer (LBL) films of poly(lactic acid) nanoparticles (PLA NPs) and poly(ethyleneimine) (PEI) were fabricated as a novel drug-delivery system. The PLA NPs, which encapsulated pyrene as a model drug, were prepared by nanoprecipitation methods. The assembly process of PLA NPs/PEI LBL films was monitored by UV-vis spectroscopy, and the load of pyrene in the multilayer films was verified by fluorescence spectroscopy. The morphology of the PLA NPs/PEI LBL films was observed by SEM. The release profile of pyrene from the LBL films in PBS solutions was further studied, and the result indicated that the PLA NPs/PEI films were capable of sustainably releasing pyrene as expected. The fabrication of PLA NPs/PEI LBL films provides a new facile method for drug delivery and paves the way for loading multiple types of drugs into a single LBL film.

Stirring-assisted assembly of nanowires at liquid-solid interfaces.

The assembly of Ag nanowires on quartz substrates from suspensions of water and ethylene glycol under stirring has been investigated. The introduction of stirring makes a remarkable difference to the assembly morphology. Firstly, the surface coverage of Ag nanowires is increased by a factor of 4 (in water) and 8 (in ethylene glycol) with stirring. Secondly, the Ag nanowires assembled in the stirred ethylene glycol dispersion were highly aligned. The influence of the surface of substrates, solvents and profile of the nanowires on the alignment has been explored, which indicates that stirring is an efficient way to generate nanowire arrays. This study has revealed the great potential of the stirring-assisted assembly technique in producing structurally controlled nanoarchitectures, opening up new opportunities for manufacturing ordered nanomaterials.

Transfer of inorganic thin films by soluble polymer layer for arbitrary surface coating

The transfer of inorganic films from the as-grown substrates to arbitrary surfaces has been demonstrated and investigated as a facile and versatile approach to alter surface properties. The transfer method employed soluble poly(lactic acid) delivery for ease of operation and flexibility in surface adhesion. Superhydrophobic Au and Ag thin films fabricated by electrochemical and chemical solution deposition, respectively, were chosen as the to-transfer inorganic films. A variety of materials, including silica, metal, ceramic, copper mesh, and lens tissue, were successfully coated with the two kinds of inorganic thin films by this transfer method. As a result of the transfer, the superhydrophobicity of Au and Ag films was imparted to these surfaces; SEM and comparison of contact angle before and after transfer indicated that the morphology and properties of the parent film were substantially preserved after transfer. This transfer method could eliminate the restriction of as-grown substrates on thin films, broadening thin film applications.

Fully branched hyperbranched polymers with a focal point: analogous to dendrimers

A fully branched hyperbranched polymer with a focal point has been prepared by superelectrophilic polycondensation of AB2 monomers with a core with six functional arms (B6′) in a slow addition manner. To reduce the chance of the homopolymerization of the monomers, the acenaphthenequinone group with higher reactivity was chosen as B′ for the core and the isatin group with lower reactivity as B in the monomer. The obtained polymers were characterized by 1H NMR, 13C NMR, TGA and GPC. The thermo-decomposition temperature of the polymer could reach 400 °C. The NMR spectra indicated the 100% branching degree of the hyperbranched polymers and the successful introduction of the core. The proportions of the terminal/dendritic groups in the hyperbranched polymers with low monomer/core feeding ratio were evaluated through NMR and GPC data respectively. Through comparison and analysis it was revealed that most of the hyperbranched polymers possessed quasi-spherical structures. The molecular weights of the hyperbranched polymers increased almost linearly with the feeding ratio of the monomer to the core and the polydispersities of the polymers were greatly influenced by the monomer concentration. At the optimal monomer concentration, the main parts of the GPC curves were symmetric and narrow. Although there were traces of faint shoulder, the molecular weight distributions of the polymers were still acceptable. The branching degree of 100%, controllable molecular weights, narrow distribution, plus the quasi-spherical and hierarchical architectures of cores, dendritic and terminal units made the fully branched polymer with a focal point analogous to dendrimers in all respects, offering a highly efficient option to fabricate dendrimer substitutes.

Highly Transparent, Conductive, and Bendable Ag Nanowire Electrodes with Enhanced Mechanical Stability Based on Polyelectrolyte Adhesive Layer

In this paper, a highly transparent, conductive, and bendable Ag nanowire (AgNW)-based electrode with excellent mechanical stability was prepared through the introduction of an adhesive polyelectrolyte multilayer between AgNW networks and a polyethylene terephthalate (PET) substrate. The introduction of the adhesive layer was performed based on a peel-assembly-transfer procedure, and the adhesive polyelectrolyte greatly improved the mechanical stability of the AgNW transparent conductive films (TCFs) without obviously attenuating the morphology and optoelectrical properties of the AgNW networks. The as-prepared AgNW TCFs simultaneously possess high optical transparency, good conductivity, excellent flexibility, and remarkable mechanical stability. It is believed that the proposed strategy would pave a new way for preparing flexible transparent electrodes with a long-term stability, which is significant in the development and practical applications of flexible transparent electronic devices operated in severe environments.

Layer-by-Layer Strippable Ag Multilayer Films Fabricated by Modular Assembly

We have developed a new method to fabricate multilayer films, which uses prepared thin films as modular blocks and transfer as operation mode to build up multilayer structures. In order to distinguish it from the in situ fabrication manner, this method is called modular assembly in this study. On the basis of such concept, we have fabricated a multilayer film using the silver mirror film as the modular block and poly(lactic acid) as the transfer tool. Due to the special double-layer structure of the silver mirror film, the resulting multilayer film had a well-defined stratified architecture with alternate porous/compact layers. As a consequence of the distinct structure, the interaction between the adjacent layers was so weak that the multilayer film could be layer-by-layer stripped. In addition, the top layer in the film could provide an effective protection on the morphology and surface property of the underlying layers. This suggests that if the surface of the film was deteriorated, the top layer could be peeled off and the freshly exposed surface would still maintain the original function. The successful preparation of the layer-by-layer strippable silver multilayer demonstrates that modular assembly is a feasible and effective method to build up multilayer films capable of creating novel and attractive micro/nanostructures, having great potential in the fabrication of nanodevices and coatings.

Transfer of ordered nanoparticle array and its application in high-modulus membrane fabrication

This work has developed a method to transfer a nanoparticle array from the parent substrate to the target surface. A close-packed and ordered Au nanoparticle (Au NP) array has been successfully transferred using poly(lactic acid) (PLA) as the mediator. For the transfer, the last step, i.e. removing the PLA mediator, plays a crucial role. The commonly-used dissolution of PLA in organic solvents cannot maintain array integrity. In this study, we have introduced wedging to peel off the PLA mediator. Relative to dissolution, wedging is a mild procedure and able to meet the requirement of transferring the vulnerable nanoparticle array. The Au NP arrays before and after transfer were thoroughly characterized by optical microscopy, TEM and SAXS. All the experimental results proved that the structure of the array was well preserved after transfer, at both the macroscopic and microscopic scales. Further, the transfer method was combined with layer-by-layer (LbL) self-assembly to fabricate a freestanding nanoparticle-array-sandwiched membrane. In the polymer/nanoparticle nanocomposite membrane, the nanoparticles were arranged in a close, ordered and single-layer way, which is hardly achieved by in situ LbL self-assembly. The distinct architecture endows the membrane with excellent mechanical properties. Buckling instability testing exhibited that the modulus of the transfer membrane is four times higher than that of the LbL analogues. This exploration indicates an efficient way to manipulate two-dimensional nanoparticle structures, enabling them to fulfill their true potential.

Mechanical stabilization of metallic microstructures by insertion of an adhesive polymer underlayer for further optical and electrical applications

In this work a novel strategy to significantly improve the mechanical stability of metallic microstructures on substrates by inserting an adhesive polymer layer has been developed. The insertion was performed by a peel-assembly-transfer process. The microstructures were first peeled off from the prepared substrate and then transferred to the target substrate, between which the polymer layer was layer-by-layer (LBL) assembled on the interface sides of the microstructures and the substrates. The inserted polymer layer enhanced the adhesion between the metallic microstructures and the substrate without any visible damage to the morphology or significant deterioration with respect to functions. Besides, this strategy can be applied to a broad range of microstructures, such as isolated arrays, continuous films, and nanowire networks. The proposed peel-assembly-transfer strategy will pave the way to effectively improve the mechanical stability of metallic microstructures for practical applications.