软三嵌段两面神胶体粒子自组装行为的模拟研究

采用软补丁粒子模型及相应的介观动力学模拟方法, 研究了软三嵌段两面神胶体粒子在稀溶液条件下的自组装行为. 通过合理调节补丁大小和补丁之间的吸引强度, 软三嵌段两面神胶体粒子能够自组装形成非常丰富的聚集结构, 包括线状结构、 六方柱状结构、 体心四方束状结构以及三维网络状结构. 此外, 分析了与纤维结构类似的体心四方束状结构形成的动力学机理. 模拟结果为实验上设计并制备新颖的超胶体纳米结构提供一定的理论支持.     

两亲性Janus粒子在蜂窝状多孔聚合物膜上的自组装性能

采用具有两亲性的两面体(Janus)粒子实现稳定的粒子界面组装与水滴模板法自组装过程相结合的方法获得了粒子在蜂窝状多孔聚合物薄膜内壁的高效定向修饰.通过与均质粒子组装形貌的对比,证明了Janus粒子因其特殊的界面自组装活性,可以获得高粒子加量条件下的规则多孔结构,解决了使用均质粒子时存在的结构有序性和粒子修饰密度之间的矛盾.而在较低粒子加量的条件下,Janus粒子也展示出与均质粒子极为不同的组装形貌.这一方法的建立,为新型表面功能化材料的制备提供了一个新的思路.     

Selective surface reactions for Janus ORMOSIL particles with multiple functional groups using an ordered monolayer film at liquid-liquid interface

Monodispersed, submicron-sized Janus ORMOSIL particles with multiple functional groups were prepared by the selective surface reaction of a monolayer film formed at a hexane-water interface. A well-ordered monolayer film was obtained by self-assembly of ORMOSIL particles with multiple functional groups at hexane-water interface. The photopolymerization of an ordered monolayer containing ORMOSIL particles yields a rigid film strong enough to maintain its integrity for transfer and further chemical reaction. The chemical reaction of this ordered film with organic and inorganic functional groups produced Janus ORMOSIL particles with multiple functional groups. The morphologies, structures, and chemical compositions of monolayer films and Janus ORMOSIL particles were characterized by FT-IR, solid state NMR, X-ray diffraction (XRD), optical microscopy (OM), electron microscopies (SEM and TEM), and confocal laser scanning microscopy.     

配体链包覆纳米粒子的表面相分离及自组装的模拟研究

通过耗散粒子动力学方法,模拟了二元配体链包覆的纳米粒子表面的相分离行为,并与现有的模拟和实验体系进行对比.研究结果印证了相分离驱动力是配体链错位所导致的构象熵的结论.进一步以相分离得到的Janus和三嵌段Janus结构纳米粒子作为构筑单元,研究了其在选择性溶剂中的自组装行为.结果表明,Janus粒子易自组装成为双层囊泡结构,而三嵌段Janus粒子则更易形成单层囊泡结构.对于从配体链包覆的纳米粒子出发,设计具有特殊功能的囊泡提供了理论支持.     

Self-assembled morphologies of monotethered polyhedral oligomeric silsesquioxane nanocubes from computer simulation

Self-assembly of functionalized nanoscale building blocks is a promising strategy for "bottom-up" materials design. Recent experiments have demonstrated that the self-assembly of polyhedral oligomeric silsesquioxane (POSS) "nanocubes" functionalized with organic tethers can be utilized to synthesize novel materials with highly ordered, complex nanostructures. We have performed molecular simulations for a simplified model of monotethered POSS nanocubes to investigate systematically how the parameters that control the assembly process and the resulting equilibrium structures, including concentration, temperature, tether lengths, and solvent conditions, can be manipulated to achieve useful structures via self-assembly. We report conventional lamellar and cylindrical structures that are typically found in block copolymer and surfactant systems, including a thermotropic order-order transition, but with interesting stabilization of the lamellar phase caused by the bulkiness and cubic geometry of the POSS nanocubes.     

两亲性Janus粒子的合成及其在Pickering乳液中的应用

Janus粒子由于在光、电、力、磁及表面亲/疏水性等方面表现出各向异性,因此在稳定乳液、生物医药及功能涂层等方面展现出广阔的应用价值.两亲性Janus粒子是指一侧具有亲水性、另一侧具有疏水性的不对称材料,由于同时具有表面活性剂的性质和固体颗粒的效应,在稳定Pickenng乳液方面极具优势.基于此,本文对两亲性Janus...     

Janus Nanoparticles: Preparation,Characterization, and Applications

In chemical functionalization of colloidal particles, the functional moieties are generally distributed rather homogeneously on the particle surface. Recently, a variety of synthetic protocols have been developed in which particle functionalization may be carried out in a spatially controlled fashion, leading to the production of structurally asymmetrical particles. Janus particles represent the first example in which the two hemispheres exhibit distinctly different chemical and physical properties, which is analogous to the dual‐faced Roman god, Janus. Whereas a variety of methods have been reported for the preparation of (sub)micron‐sized polymeric Janus particles, it has remained challenging for the synthesis and (unambiguous) structural characterization of much smaller nanometer‐sized Janus particles. Herein, several leading methods for the preparation of nanometer‐sized Janus particles are discussed and the important properties and applications of these Janus nanoparticles in electrochemistry, sensing, and catalysis are highlighted. Some perspectives on research into functional patchy nanoparticles are also given.     

Janus粒子制备研究*

具有不对称双面结构的Janus粒子以其独特性能,在乳液稳定、光学、生物传感、药物输送、电子学等领域具有潜在的应用前景。本文就近年来Janus粒子制备技术的研究进展进行了总结,详细地介绍了Janus粒子主要制备方法,包括微流体合成、拓扑选择表面改性、模板导向自组装、可控相分离及可控表面成核,并指出了各种Janus粒子制备技术存在的问题及其发展方向,认为基于可控相分离及表面成核的合成方法成本较低,产率较大,有可能得到更为广泛的应用。     

Janus and multiblock colloidal particles

We review recent developments in the synthesis and self-assembly of Janus and multiblock colloidal particles, highlighting new opportunities for colloid science and technology that are enabled by encoding orientational order between particles as they self-assemble. Emphasizing the concepts of molecular colloids and colloid valence unique to such colloids, we describe their rational self-assembly into colloidal clusters, taking monodisperse tetrahedra as an example. We also introduce a simple method to lock clusters into permanent shapes. Extending this to 2D lattices, we also review recent progress in assembling new open colloidal networks including the kagome lattice. In each application, areas of opportunity are emphasized.     

非对称性Janus粒子的制备与可控组装

古罗马的双面神(Janus)常被用来描述具有两种不同化学结构或性质的不对称粒子, Janus粒子由于自身的特殊性能在药物载体、电子器件和乳液稳定等方面表现出良好的发展势头, 其应用前景日益受到人们的重视. 目前, Janus 粒子作为基本的组装基元受到越来越多的关注, 相关组装方法也被广泛地研究, 包括本体组装、界面组装和外界驱动力调控等, 特别是Janus 粒子的双亲修饰与功能化. 本文综述了现今Janus 粒子制备方法及对其进行修饰组装的最新研究进展, 详细讨论比较了一步合成法、聚合物自组装法和晶种直接生长等方法的特点及差异, 并对一些新型功能Janus粒子的设计及潜在的应用前景进行了展望.     

Dielectrophoretic assembly of metallodielectric Janus particles in AC electric fields

"Janus" particles with two hemispheres of different polarizability or charge demonstrate a multitude of interesting effects in external electric fields. We reported earlier how particles with one metallic hemisphere and one dielectric hemisphere self-propel in low-frequency alternating current (AC) electric fields. Here, we demonstrate the assembly of such Janus particles driven by AC electric fields at frequencies above 10 kHz. We investigated the relation between field-induced dielectrophoretic force, field distribution, and structure of the assemblies. The phase space for electric field intensity and frequency was explored for particle concentrations large enough to form a monolayer on a glass surface between two gold electrodes. A rich variety of metallodielectric particle structures and dynamics were uncovered, which are very different from those obtained from directed assembly of plain dielectric or plain conductive particles under the action of fields of similar frequency and intensity. The metallodielectric particles assemble into new types of chain structures, where the metallized halves of neighboring particles align into lanes along the direction of the electric field, while the dielectric halves face in alternating direction. The staggered chains may assemble in various orientations to form different types of two-dimensional metallodielectric crystals. The experimental results on the formation of staggered chains are interpreted by means of numerical simulations of the electric energy of the system. The assembly of Janus metallodielectric particles may find applications in liquid-borne microcircuits and materials with directional electric and heat transfer.     

Helical self-organization and hierarchical self-assembly of an oligoheterocyclic pyridine-pyridazine strand into extended supramolecular fibers

The synthesis and characterization of an alternating pyridine-pyridazine strand comprising thirteen heterocycles are described. Spontaneous folding into a helical secondary structure is based on a general molecular self-organization process enforced by the conformational information encoded within the primary structure of the molecular strand itself. Conformational control based on heterocyclic "helicity codons" illustrates a strategy for designing folding properties into synthetic oligomers (foldamers). Strong intermolecular interactions of the highly ordered lock-washer subunits of compound 3 results in hierarchical supramolecular self-assembly into protofibrils and fibrils. Compound 3 also forms mechanically stable two-dimensional Langmuir-Blodgett and cast thin films.     

Self-organizable vesicular columns assembled from polymers dendronized with semifluorinated Janus dendrimers act as reverse thermal actuators

The synthesis and structural analysis of polymers dendronized with self-assembling Janus dendrimers containing one fluorinated and one hydrogenated dendrons are reported. Janus dendrimers were attached to the polymer backbone both from the hydrogenated and from the fluorinated parts of the Janus dendrimer. Structural analysis of these dendronized polymers and of their precursors by a combination of differential scanning calorimetry, X-ray diffraction experiments on powder and oriented fibers, and electron density maps have demonstrated that in both cases the dendronized polymer consists of a vesicular columnar structure containing fluorinated alkyl groups on its periphery. This vesicular columnar structure is generated by a mechanism that involves the intramolecular assembly of the Janus dendrimers into tapered dendrons followed by the intramolecular self-assembly of the resulting dendronized polymer in a vesicular column. By contrast with conventional polymers dendronized with self-assembling tapered dendrons this new class of dendronized polymers acts as thermal actuators that decrease the length of the supramolecular column when the temperature is increased and therefore, are called reverse thermal actuators. A mechanism for this reversed process was proposed.     

Janus balance of amphiphilic colloidal particles

We introduce the notion of "Janus balance" (J), defined as the dimensionless ratio of work to transfer an amphiphilic colloidal particle (a "Janus particle") from the oil-water interface into the oil phase, normalized by the work needed to move it into the water phase. The J value can be calculated simply from the interfacial contact angle and the geometry of Janus particles, without the need to know the interfacial energy. It is demonstrated that Janus particles of the same chemical composition but different geometries will have the highest adsorption energy when J = 1. Even for particles of homogeneous chemical makeup, the Janus balance concept can be applied when considering the contact angle hysteresis in desorbing the particle from equilibrium into the water or oil phase. The Janus balance concept may enable predictions of how a Janus particle behaves with respect to efficiency and function as a solid surfactant, as the Janus balance of solid surfactants is the analog of the classical hydrophile-lipophile balance of small surfactant molecules.     

Facile, solution-based synthesis of soft, nanoscale janus particles with tunable janus balance

We present a novel, versatile, and simple solution-based routine to produce soft, nanosized Janus particles with tunable structural and physical properties at high volume yield. This process is based on the cross-linking of compartments within precisely defined multicompartment micelles (MCMs), which are themselves formed by the self-assembly of ABC triblock terpolymers. Therein, the C blocks form the stabilizing corona emanating from B compartments, which in turn reside on an A core. Cross-linking of the B compartments allows to permanently fixate the phase-separated state and dissolution in a good solvent for all blocks breaks up the MCMs into single Janus particles. They now consist of a core of cross-linked B blocks and two phase-separated hemispheres of A and C. The process gives access to unprecedented structural features such as tunable core diameter and control over the Janus balance ranging from dominant A side to equal hemispheres to dominant C side. We demonstrate that this simple one-pot approach can be extended to a range of triblock terpolymers with different block lengths and block chemistries to furnish a library of tailor-made Janus particles with widely tunable physical properties. Such a diversity and simplicity has remained unreachable with our previously developed approach using the controlled cross-linking of bulk morphologies. We show that this new synthetic route can be upscaled to a high volume yield of 10 wt %, thereby enabling large-scale applications. We further demonstrate the effect of the Janus balance on colloidal self-assembly. Janus particles with a dominant hydrophobic and a small hydrophilic patch aggregate into large clusters in water, but merely di- or trimerize in chloroform.     

Chiral molecular nanosilicas

Molecular nanoparticles including polyoxometalates, proteins, fullerenes and polyhedral oligosiloxane (POSS) are nanosized objects with atomic precision, among which POSS derivatives are the smallest nanosilicas. Incorporation of molecular nanoparticles into chiral aggregates either by chiral matrices or self-assembly allows for the transfer of supramolecular chirality, yet the construction of intrinsic chirality with atomic precision in discrete molecules remains a great challenge. In this work, we present a molecular folding strategy to construct giant POSS molecules with inherent chirality. Ferrocenyl diamino acids are conjugated by two or four POSS segments. Hydrogen bonding-driven folding of diamino acid arms into parallel β-sheets facilitates the chirality transfer from amino acids to ferrocene and POSS respectively, disregarding the flexible alkyl spacers. Single crystal X-ray structures, density functional theory (DFT) calculations, circular dichroism and vibrational circular dichroism spectroscopy clearly verify the preferential formation of one enantiomer containing chiral molecular nanosilicas. The chiral orientation and chiroptical properties of POSS show pronounced dependence on the substituents of α-amino acids, affording an alternative way to control the folding behavior and POSS chirality in addition to the absolute configuration of amino acids. Through the kinetic nanoprecipitation protocol, one-dimensional aggregation enables chirality transfer from the molecular scale to the micrometer scale, self-assembling into helices in accordance with the packing propensity of POSS in a crystal phase. This work, by illustrating the construction of chiral molecular nanosilicas, paves a new way to obtain discrete chiral molecular nanoparticles for potential chiroptical applications.

A molecular folding strategy is developed to construct ferrocenyl diamino acid conjugated polyhedral oligosiloxane molecules. Hydrogen bonding-driven folding facilitates the chirality transfer from the molecular scale to the micrometer scale.     

Preparation of hemispherical particles by cleavage of micrometer-sized,spherical poly(methyl methacrylate)/polystyrene composite particle with Janus structure: effect of molecular weight

Micrometer-sized, hemispherical polymer particles were prepared as a result of cleavage of spherical Janus poly(methyl methacrylate) (PMMA)/polystyrene (PS) composite particle by treating particles with acetone/water solutions. The original PMMA/PS composite particles were prepared by the slow evaporation of toluene from homogeneous PMMA/PS/toluene droplets dispersed in aqueous solution of sodium dodecyl sulfate in advance. Appropriate molecular weights of PMMA and PS were necessary for occurrence of the cleavage of the Janus composite particle, resulting in PMMA and PS hemispherical particles. The cleavage depended on the composition of the acetone/water solution, which was explained by selective solvent absorption into the polymer phases. The results strongly support the cleavage mechanism of Janus composite polymer particles that had been proposed earlier.     

One-step fabrication of polymeric Janus nanoparticles for drug delivery

With its unique structure of two compartments, Janus particles can be used for many applications for which monomorphic particles are inadequate, including to be used as a drug delivery system to deliver multiple payloads with widely different solubility. Here we report on a fluidic nanoprecipitation system (FNPS), capable of fabricating biocompatible Janus polymeric nanoparticles comprised of the FDA-approved polymer poly(lactic-co-glycolic acid) (PLGA). The FNPS contains dual inlets, one for each half of the particle, that insert into the precipitation stream. The system provides a one-step approach for production of Janus polymeric particles with submicrometer diameters and is likely amenable to substantial scale-up. To the best of our knowledge, this is the first demonstration of biocompatible Janus nanoparticles that encapsulate a hydrophobic drug (paclitaxel) on one side and a hydrophilic drug (doxorubicin hydrochloride) on the other.     

Janus and patchy colloids at fluid interfaces

Understanding the fundamental behavior of chemically anisotropic Janus and patchy particles at fluid interfaces enables utilization of these colloids as solid surfactants for stabilization of emulsions and as building blocks for fabrication of functional and responsive materials. Here, we review recent progress on understanding the combined effects of particle–interface and particle–particle interactions on the surface activity and organization of Janus and patchy particles at fluid interfaces. We also highlight recent developments that harness these fundamental properties for applications in self-assembly and emulsion stabilization, and discuss some of the outstanding questions that warrant future investigation. The progress in the field opens new opportunities to pursue techniques for controlling interfacial rheology, directed motion, and the formulation of novel soft materials.     

pH-responsive amphiphilic hybrid random-type copolymers of poly(acrylic acid) and poly(acrylate-POSS): synthesis by ATRP and self-assembly in aqueous solution

The synthesis and subsequent self-assembly of novel, random-type amphiphilic pH-responsive hybrid copolymers, having acrylic acid as pH-responsive hydrophilic and acrylate-polyhedral oligomeric silsesquioxane (POSS) as hydrophobic constituents are reported. The synthesis was carried out in two steps: first, t-butylacrylate and acrylate-POSS are copolymerized by ATRP, followed by the acid hydrolysis of t-butyl acrylate constituents of the synthesized poly(t-butylacrylate)-co-poly(acrylate-POSS) copolymers to achieve poly(acrylic acid)-co-poly(acrylate-POSS). It was found that POSS is a powerful hydrophobic unit. With very low POSS concentration in the copolymers, i.e., one POSS unit per 40 to 110 acrylic acid repeat units, the obtained amphiphilic hybrid copolymers could self-assemble in aqueous solution to form nanoaggregates, as revealed by the laser light scattering and fluorescence studies on the aqueous solutions of the obtained copolymers. The formation of hydrophobic core in the self-assembled aggregates is verified by the solubilization of pyrene (used as probe in fluorescence measurements) in aqueous solution of the copolymers. In addition to pH-dependent self-assembly behavior, it is also demonstrated that the particle size and aggregation number of the aggregates can be tuned simply by varying the composition of the copolymer, i.e., by changing the molar ratio of poly(acrylic acid) to poly(acrylate-POSS) in the copolymer. Finally, preliminary results on the influence of salt (NaCl) on the self-assembly of poly(acrylic acid)-co-poly(acrylate-POSS) in aqueous solution are also presented.