聚合物复合物层层组装膜

层层组装是一种基于物质交替沉积而制备复合膜的方法,可以实现膜的结构和组成的精确调控.聚合物复合物是基于各种分子间弱相互作用力而形成的超分子聚集体,其种类包括聚阳离子-聚阴离子复合物、聚电解质-有机小分子复合物、中性聚合物-聚合物复合物以及聚合物-无机杂化复合物等.在本文中,以作者的研究结果为基础,阐明聚合物复合物的层层组装是一种方便、快捷的功能复合膜的构筑方法,具有如下优点:(1)聚合物复合物大的尺度可以实现聚合物复合物层层组装膜的快速构筑;(2)聚合物复合物的结构在组装溶液中和成膜后都容易调控,方便聚合物复合物层层组装膜结构的精细调控.(3)聚合物复合物层层组装膜可以构筑非复合的聚合物层层组装所不能获得的膜结构及功能.     

聚合物层状组装膜

介绍了近几年来我们研究组在层状组装膜的构筑以及功能化研究方面取得的一些最新进展.包括结合表面溶胶-凝胶技术与静电层状组装技术,实现了二阶非线性基团在层状组装多层膜中的非对称排列,制备了具有二阶非线性效应的膜材料;采用室温压印技术,发展了一种简便、经济和具有普适性的层状组装聚合物膜图案化方法;以轻度交联的聚合物微凝胶为构筑基元,制备了具有高负载量的聚合物层状组装膜;发展了一种基于离子剥离技术的层状组装自支持膜制备方法;基于层状组装技术,制备了具有超疏水和抗反射功能的涂层.     

Robust multilayer thin films containing cationic thiol-functionalized gold nanorods for tunable plasmonic properties

Gold nanorods have great potential in a variety of applications because of their unique physical properties. In this article, we present the layer-by-layer (LbL) assembly of thin films containing positively charged gold nanorods that are covalently functionalized by cationic thiol molecules. The cationic gold nanorods are uniformly distributed in ultrathin nanocomposite LbL thin films. We studied the collective surface plasmon resonance coupling in the LbL films via UV-visible spectroscopy and evaluated their application in the surface-enhanced Raman scattering detection of rhodamine 6G probe molecules. Furthermore, we successfully manufactured freestanding nanoscale thin films containing multilayers of gold nanorods with a total thickness of less than 50 nm. The surface morphology and their optical and mechanical properties were systematically investigated, and the polycationic gold nanorods were found to play an important role in manipulating the properties of the nanocomposite thin films. Our findings reveal that such nanorods are excellent building blocks for constructing functional LbL films with tunable plasmonic behavior and robust mechanical properties.     

Layer-by-layer assembly of salt-containing polyelectrolyte complexes for the fabrication of dewetting-induced porous coatings

The layer-by-layer (LbL) assembly of salt-containing nonstoichiometric polyelectrolyte complexes (PECs) with oppositely charged uncomplexed polyelectrolyte for the fabrication of dewetting-induced porous polymeric films has been systematically investigated. Salt-containing poly(allylamine hydrochloride) (PAH) and poly(acrylic acid) (PAA) complexes (noted as PAH-PAA) with a molar excess of PAH were LbL assembled with polyanion poly(sodium 4-styrenesulfonate) (PSS) to produce PSS/PAH-PAA films. The structure of the PAH-PAA complexes is dependent on the concentration of NaCl added to their aqueous dispersions, which can be used to tailor the structure of the LbL-assembled PSS/PAH-PAA films. Porous PSS/PAH-PAA films are fabricated when salt-containing PAH-PAA complexes with a large amount of added NaCl are used for LbL assembly with PSS. In-situ and ex-situ atomic force microscopy measurements disclose that the dewetting process composed of pore nucleation and pore growth steps leads to the formation of pores in the LbL-assembled PSS/PAH-PAA films. The present study provides a facile way to fabricate porous polymeric films by dewetting LbL-assembled polymeric films comprising salt-containing PECs.     

Facile method for the fabrication of robust polyelectrolyte multilayers by post-photo-cross-linking of azido groups

In this letter, we have developed a facile method to enhance the stability of polyelectrolyte multilayers. We fabricate conventional polyelectrolyte multilayers of PAH/PAA through electrostatic layer-by-layer (LbL) assembly and then postinfiltrate photosensitive cross-linking agent 4,4'-diazostilbene-2,2'-disulfonic acid disodium salt into the LbL films. After cross-linking by UV irradiation, the stability of the photo-cross-linked multilayer is highly improved as evidenced by the lack of dissolution under ultrasonication in saturated SDS aqueous solutions for 10 min. Moreover, by taking advantage of the different stability of the LbL film before and after UV irradiation, a patterned surface can be achieved.     

pH-controlled exponential and linear growing modes of layer-by-layer assemblies of star polyelectrolytes

We report the unique layer-by-layer (LbL) assembly behavior of pH-sensitive star-shaped polyelectrolytes with both linear and exponential growth modes controlled by star architecture and assembly conditions. Cationic poly[2-(dimethylamino)ethyl methacrylate] and anionic poly(acrylic acid) stars were synthesized via "core-first" atom-transfer radical polymerization (ATRP) based on multifunctional initiators, in addition to their linear analogues. We demonstrated the LbL growth behavior as a function of deposition pH (ranging from 5 to 7), number of layers (up to 30 bilayers), and the method of assembly (dip- vs spin-assisted LbL). The spin-assisted LbL assembly makes it possible to render smoother and thinner LbL films with parameters controlled by the shear rate and pH conditions. In contrast, for dip-assisted LbL assembly, the pH-dependent exponential growth was observed for both linear and star polyelectrolytes. In the case of linear/linear pair, the exponential buildup was accompanied with a notable surface segregation which resulted in dramatic surface nonuniformity, "wormlike" heterogeneous morphology, and dramatic surface roughening. In contrast, star/linear and star/star LbL films showed very uniform and smooth surface morphology (roughness below 2.0 nm on the scale of 10 μm × 10 μm) with much larger thickness reaching up to 1.0 μm for 30 bilayers and rich optical interference effects. Star polyelectrolytes with partially screened charges and high mobility caused by compact branched architecture appear to facilitate fast diffusion and exponential buildup of LbL films. We suggest that the fast buildup prevents long-range lateral diffusion of polyelectrolyte star components, hinders large-scale microphase separation, and thus leads to unique thick, smooth, uniform, transparent, and colorful LbL films from star polyelectrolytes in contrast to mostly heterogeneous films from traditional linear counterparts.     

Electropolymerization of layer‐by‐layer precursor polymer films

The layer‐by‐layer (LbL) self‐assembly has been used to fabricate polymer thin films on any solid substrates. The multilayer polymer thin films are constructed by alternating adsorption of anionic and cationic polymers. Polyelectrolyte multilayer ultrathin films containing anionic poly[2‐(thiophen‐3‐yl)ethyl methacrylate‐co‐methacrylic acid]; P(TEM‐co‐MA) and cationic poly[4‐(9H‐carbazol‐9‐yl)‐N‐butyl‐4‐vinyl pyridium bromide]; P4VPCBZ, were fabricated. The growth of multilayer ultrathin films was followed by UV–Vis absorption spectrophotometer and surface plasmon resonance spectroscopy (SPR). The deposition of P(TEM‐co‐MA)/P4VPCBZ as multilayer self‐assembled ultrathin films regularly grow which showed linear growth of absorbance and thickness with increasing the number of layer pair. Cross‐linking of the layers was verified by cyclic voltammetry (CV), UV–Vis spectrophotometry and electrochemical surface plasmon resonance (EC‐SPR) spectroscopy with good electro‐copolymerizability. This was verified by spectroelectrochemistry. The SPR angular‐reflectivity measurement resulted in shifts to a higher reflectivity according to the change in the dielectric constant of the electropolymerized film. Copyright © 2011 John Wiley & Sons, Ltd.     

Drying and nondrying layer-by-layer assembly for the fabrication of sodium silicate/TiO2 nanoparticle composite films

Influences of drying and nondrying steps on structures of layer-by-layer (LbL) assembled sodium silicate/TiO(2) nanoparticles films (donated as silicate/TiO(2) films) have been systematically investigated. The nondrying LbL assembly produces highly porous silicate/TiO(2) films with large thickness. In contrast, the silicate/TiO(2) films fabricated with a drying step after each layer deposition are flat and thin without porous structures. In situ atomic force microscopy (AFM) measurements confirm that the sodium silicate and TiO(2) nanoparticles are deposited in their aggregated forms. A N(2) drying step can disintegrate the aggregated silicate and TiO(2) nanoparticles to produce thin silicate/TiO(2) films with compact structures. Without the drying steps, the aggregated silicate and TiO(2) nanoparticles are well retained, and their LbL assembly produces highly porous silicate/TiO(2) films of large thickness. The highly porous silicate/TiO(2) films are demonstrated to be useful as reusable film adsorbents for dye removal from wastewater because they can adsorb a large amount of cationic organic dyes and decompose them under UV irradiation. The present study is meaningful for exploring drying/nondrying steps for tailoring structure and functions of LbL assembled films.     

Coordinative supramolecular assembly of electrochromic thin films

The article is concerned with the layer-by-layer (LbL) assembly of electrochromic films using coordinative interactions between compounds. At first the concepts of coordinative supramolecular assembly are explained and examples are presented. Subsequently electrochromic LbL assemblies prepared upon electrostatic and/or coordinative interactions are briefly discussed. In the focus of the article are films of terpyridine(tpy)-functionalized polyiminoarylene metal ion complexes, which are prepared upon coordinative LbL assembly of the tpy-substituted polyiminoarylenes and metal ions. The films exhibit reversible electrochromic behavior with high contrast and fast response times. It is demonstrated that the electrochromic behavior of the films can be modified by a variation of polymer structure, metal ions, and counterions.     

Ordered Polyelectrolyte Multilayers: Unidirectional FRET Cascade in Nanocompartmentalized Polyelectrolyte Multilayers

Multifunctional polyelectrolyte (or layer‐by‐layer, LbL) multilayers consisting of a set of nanocompartments separated by impermeable ultrathin barriers, whereby the thickness of the compartments is tuned in the range 1–10 nm, are synthesized. Each compartment contains a different dye, introduced by co‐adsorption during multilayer deposition. Different LbL barriers are tested for impermeability towards dye diffusion while simultaneously allowing energy transfer to occur between the compartmentalized dyes. Cross‐linked LbL multilayers based on poly(acrylic acid) and poly(allyl amine) are shown to provide the desired impermeability for thicknesses as small as about 2.5 nm. A proof‐of‐concept system is then realized involving a cascade of two FRET processes, whereby the light energy is collected in a first nanocompartment containing pyranine, sent to a second nanocompartment loaded with fluorescein, before finally being transferred to a third, Nile blue‐filled compartment located at the external surface of the film. This demonstrates the possibility to fabricate complex light‐harvesting antenna systems by LbL assembly while controlling the architecture of the antenna down to a few nanometers.     

Self assembly and optical properties of dendrimer nanocomposite multilayers

Ultrathin multilayers are important for electrical and optical devices, as well as for immunoassays, artificial organs, and for controlling surface properties. The construction of ultrathin multilayer films by electrostatic layer-by-layer deposition proved to be a popular and successful method to create films with a range of electrical, optical, and biological properties. Dendrimer nanocomposites (DNCs) form highly uniform hybrid (inorganic-organic) nanoparticles with controlled composition and architecture. In this work, the fabrication, characterization, and optical properties of ultrathin dendrimer/poly(styrene sulfonate) (PSS) and silver-DNC/PSS nanocomposite multilayers using layer-by-layer (LbL) electrostatic assembly techniques are described. UV-vis spectra of the multilayers were found to be a combination of electronic transitions of the surface plasmon peaks, and the regular frequency modulations attributable to the multilayered film structure. The modulations appeared as the consequence of the highly regular and non-intermixed multilayer growth as a function of the resulting structure. A simple model to explain the experimental data is presented. Use of DNCs in multilayers results in abrupt, flat, and uniform interfaces.     

Pd-Pt and Fe-Ni nanoparticles formed by covalent molecular assembly in supercritical carbon dioxide

We report the formation of Pd-Pt nanoparticles within a dendrimer-laden ultrathin film matrix immobilized on a solid support and constructed by covalent layer-by-layer (LbL) assembly using supercritical carbon dioxide (SCCO2) as the processing medium. Particle size distribution and composition were controlled by precursor composition. The precursor compositions are optimized for Pd-Pt nanoparticles and later extended to the formation of Fe-Ni nanoparticles. As an example of the application of nanoparticles in tribology, Fe-Ni nanoparticle-laden films were observed to exhibit better tribological properties than those containing the monometallic species, thereby suggesting that combination of nanoparticles can be used to derive greater benefits.     

Assembly of ultrathin polymer multilayer films by click chemistry

Layer-by-layer (LbL) assembly is a versatile and robust technique for fabricating tailored thin films of diverse composition. Herein we report a new method of covalent coupling, click chemistry, to facilitate the LbL assembly of thin films. Linear film growth was observed using both UV-vis and FTIR spectroscopy, and film thicknesses were determined by ellipsometry and atomic force microscopy. The assembled films are shown to be stable in a wide pH range. This technique offers the potential to enable the synthesis of new types of stable and responsive LbL films from a variety of polymers.     

Layer-by-layer electrostatic assembly with a control over orientation of molecules: anisotropy of electrical conductivity and dielectric properties

While forming layer-by-layer (LbL) electrostatic assembly of a magnetic organic molecule, namely, nickel phthalocyanine (NiPc), we apply a magnetic field. The field orients the magnetic moment of the molecules on a monolayer along the direction of magnetic field. Such an orientation of the molecules is then electrostatically immobilized with a monolayer of a polycation. By repeating the dipping cycle, we form LbL films with planar NiPc molecules facing a particular direction. With NiPc's moment perpendicular to the molecular plane, two types of LbL films were formed: (a) NiPc's molecular plane parallel to the substrate (moment is perpendicular) and (b) molecules perpendicular to the substrate and facing one particular direction, the direction of magnetic field. Such films, with the molecules lying either (a) parallel or (b) perpendicular to the substrate, provide unique systems to study anisotropy of optical, dielectric, and electrical characteristics in these planar organic molecules. The latter film responds to the polarization of incident beam in electronic absorption spectroscopy. Here we show methods to obtain an orientation of molecules in LbL films and study anisotropy of dielectric constant and conductivity of the molecules in ultrathin films.     

智能响应与自修复的层层组装聚合物膜

具有刺激响应性和自修复功能的复合膜是重要的仿生功能膜材料.层层组装是一种基于物质交替沉积而制备复合膜的方法,可以实现膜的结构和组成的精确调控.通过结构与组成的精确调控,基于层层组装制备的微米厚度的聚电解质厚膜可以对外界刺激产生快速有效的响应,因而在制备智能仿生膜材料方面具有重要的价值.本文以作者的研究结果为基础,阐明了基于层层组装的聚电解质膜可以成功用于制备湿度和温度响应的双结构自支持膜和高效的促动器及行走机器,以及自修复超疏水和划痕修复聚电解质膜.     

表面印迹交替层状组装薄膜

在简要概述非常规交替层状组装这一进展后,重点总结了如何利用非常规交替层状组装以实现表面印迹膜的制备.模板分子与聚电解质在溶液中组装形成超分子复合物,然后以此超分子复合物为构筑基元,与感光性高分子,如重氮树脂,通过常规交替层状组装形成聚合物多层膜.利用聚合物多层膜之间的光化学反应形成稳定的多层膜,然后去除模板分子得到分子...     

Polymeric multilayer capsules for drug delivery

The advent of Layer-by-Layer (LbL) assembly to fabricate polymeric as well as hybrid multilayer thin films has opened exciting avenues for the design of multifunctional drug carriers with extreme control over their physico-chemical properties. These polymeric multilayer capsules (PMLC) are typically fabricated by sequential adsorption of polymers onto a spherical substrate with dimensions varying from 10 nm to several microns and larger. In this critical review, we give an overview of the recent advances in the field of PMLC with respect to drug delivery and point out how sophisticated capsule engineering can lead to well-defined drug carriers with unique properties (139 references).     

Fabrication of novel multilayered thin films based on inclusion complex formation between amylose derivatives and guest polymers

Novel types of layer-by-layer (LbL) assembly films were successfully fabricated onto a solid substrate through the inclusion complex formation between partially 2,3- O-methylated amyloses (MAs) and polytetrahydrofuran (PTHF). The formation of the LbL assembly films was confirmed by quartz crystal microbalance (QCM) analysis, atomic force microscopy (AFM) observation, and X-ray diffraction (XRD) measurement. The film formation was significantly affected by the methylation degree of amylose. When MAs with 8 and 20% methylation were used as hosts, the formation of LbL assembly films with PTHF was clearly observed. On the other hand, MAs with more than 33% methylation barely formed LbL assembly films with PTHF.     

Layer-by-layer assembly: from conventional to unconventional methods

Layer-by-layer (LbL) assembly is a powerful means for fabricating multilayer thin films with controlled architecture and composition. This feature article discusses different types of methods for LbL assembly. On the one hand, some of the conventional LbL methods are introduced, which are driven by electrostatic interactions, hydrogen bonds, step-by-step reactions, sol-gel processes, molecular recognition, charge-transfer, stepwise stereocomplex assembly, and electrochemistry. On the other hand, some of the unconventional methods for fabricating of the building blocks which can not be assembled by conventional methods are also summarized. These unconventional methods usually involve the formation of supramolecular structures via one type of self-assembly. These structures can subsequently be used as building blocks in another type of self-assembly. To take advantage of these conventional and unconventional methods, a great number of building blocks can be fabricated into multilayer thin films with a defined sequence structure in a designed way. It has been demonstrated that LbL methods provide new horizons for surface molecular engineering.     

Thickness and annealing temperature effects on the optical properties and surface morphology of layer‐by‐layer poly(p‐phenyline vinylene)+dodecylbenzenesulfonate films

The fabrication of controlled molecular architectures is essential for organic devices, as is the case of emission of polarized light for the information industry. In this study, we show that optimized conditions can be established to allow layer‐by‐layer (LbL) films of poly(p‐phenylene vinylene) (PPV)+dodecylbenzenesulfonate (DBS) to be obtained with anisotropic properties. Films with five layers and converted at 110 °C had a dichroic ratio δ = 2.3 and order parameter r = 34%, as indicated in optical spectroscopy and emission ellipsometry data. This anisotropy was decreased with the number of layers deposited, with δ = 1.0 for a 75‐layer LbL PPV + DBS film. The analysis with atomic force microscopy showed the formation of polymer clusters in a random growth process with the normalized height distribution being represented by a Gaussian function. In spite of this randomness in film growth, the self‐covariance function pointed to a correlation between clusters, especially for thick films. In summary, the LbL method may be exploited to obtain both anisotropic films with polarized emission and regular, nanostructured surfaces. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011