Self-assembly of various guest substrates in natural cellulose substances to functional nanostructured materials

Biological organisms are produced from self-assembly of highly ordered functional units and are inherently complex and hierarchical, possessing macro-to-nanoscale features. It is a facile, low-cost and environmentally benign short-cut to artificial functional materials with unique multilevel structures and morphologies employing biological substances as platform for the self-assembly of various guest substrates. This review summarizes the recent advances in the fabrication of nanostructured materials with designed properties and functionalities by means of self-assembly of different guest substrates (such as metal oxide thin films, small molecules, polymers, biomacromolecules, nanoparticles, carbon nanotubes and colloidal spheres) on the surfaces of cellulose nanofibers of bulk natural cellulose substances. The combination of the specific chemical properties of the guest substrates and the unique physical features of the natural cellulose substances sheds new light on the design and syntheses of new functional nanomaterials.     

聚苯乙烯胶晶的组装

采用自然沉降法、离心法和垂直沉积法组装了聚苯乙烯胶晶。实验结果表明,所得胶晶都具有面心立方结构,结构有序性相当高。自然沉降法和离心法适用于块体胶晶的组装,自然沉降法适用于胶晶膜的组装。     

Inverting structures: from micelles via emulsions to internally self-assembled water and oil continuous nanocarriers

Fluid-like colloidal structures are key components in nature's own functional materials and important for various applications. For instance, self-assembled structures are formed spontaneously by amphiphilic molecules in solvent, tailored by directional noncovalent intermolecular forces. These structures form the framework of cells defining their geometry and microenvironments for chemical reactions, for maintaining concentration gradients, and for nutrient exchange. Knowledge on the mechanisms at play that underlie the self-assembly of amphiphilic molecules into nanostructures in aqueous and nonaqueous solvents and their dispersion into particles can have direct implications for the rational design of new advanced and nature-inspired materials. These colloidal materials could help to deliver drug molecules and nutrients in a tailored manner to the body, or act as sustainable solvents for chemical or biotechnological processes. This contribution summarizes the recent progress in understanding the self-assembly structure formation in polar and nonpolar solvents and discusses the advances in hierarchically organized systems. Furthermore, it discusses challenges in the characterization of structure and dynamics in these biomimetic materials and highlights selected applications in the fields of drug delivery, food, and biotechnology.     

Active structuring of colloids through field-driven self-assembly

In recent years self-assembly has become progressively more “active”, i.e. the focus of research gradually has shifted towards field-manipulation of matter in order to form temporary states rather than creating static architectures. The desire for time-programmed control of materials certainly originates from the unmatched complexity of natural systems that orchestrate multiple components across length scales. Although artificial self-assembly still lacks control comparable to natural systems, there has been impressive progress in a concerted approach from physicists, chemists, biologists, and engineers. This review summarizes the current trend in colloidal assembly advancing from static assembly of isotropic particles towards active structuring of anisotropic particles with heterogeneous (patchy) surfaces, and ultimately, to complex behavior in dissipative dynamic systems. We focus both on the formation of static structures and on temporary states due to response to magnetic, electric, or optic stimulation. We give examples of nano- and microparticle assembly where the temporary state may adopt equilibrium order or a continuously changing dynamic pattern.     

The Two-Dimensional Electrides XONa (X=Mg,Ca) as Novel Natural Hyperbolic Materials

In two-dimensional electrides, anionic electrons are spatially confined in interlayer regions with high density, comparable to metals, and they are highly mobile, just as free electrons, resembling hyperbolic metamaterials with metal-dielectric multilayered structures. In this work, two-dimensional electride materials MgONa and CaONa are proposed as good natural hyperbolic materials. By using the first-principles calculations based on density functional theory (DFT), the electronic structures, stabilities, and optical properties of two-dimensional electride materials XONa (X=Mg, Ca) are investigated. Our results show that they are stable in 1-monolayer (1-ML) structures as well as in bulk states. They exhibit hyperbolic dispersions from visible to near infrared spectral range with high qualities up to about 700, which is two orders-of-magnitude larger than the preceding bulk hyperbolic materials. Numerical results reveal that they exhibit negative refraction with low losses. Their high-quality hyperbolic responses over a wide spectral range pave the way of broad photonic applications as natural hyperbolic materials.     

胶体晶体微球及其生物医学应用

光子晶体(PhCs)是由单分散纳米粒子周期性排列形成的材料,具有光子禁带,频率落在光子禁带内的光被禁止传播,这个特性激起了研究者对其制备和应用的研究热情。然而,一般的光子晶体材料都具有角度有偏性质,限制了其在宽视角光学材料和设备上的应用。近几年有一系列围绕球形胶体光子晶体材料的研究成果问世,由于球形的对称性,球形胶体晶体的衍射峰不会随着光的入射角变化而发生变化,从而拓宽了胶体晶体的应用范围。随着微流控技术被用于制备液滴模板,球形胶体晶体的制备取得了巨大的进步。微流控技术不仅保证了液滴模板的单分散性,还增加了胶体晶体微球的结构与功能的多样性。胶体晶体微球这些特有的性质,可以很好地将光子晶体材料与编码、非标记检测、细胞培养以及载药等生物医学领域连接起来,为其应用提供了广阔的前景。本文总结了球形光子晶体的研究进展,包括球形光子晶体的设计、制备及其生物医学应用,最后,对球形光子晶体未来的发展方向作了展望。     

Continuous flow structuring of anisotropic biopolymer particles

We review concepts and provide examples for the controlled structuring of biopolymer particles in hydrodynamic flow fields. The structuring concepts are grouped by the physical mechanisms governing drop deformation and shaping: (i) capillary structuring, (ii) shear and elongational structuring and (iii) confined flow methods. Non-spherical drops can be permanently structured if a solidification process, such as gelation or glass formation in the bulk or at the interface, is superimposed to the flow field. The physical and engineering properties of these processes critically depend on an elaborate balance between capillary phenomena, rheology, gel or glass formation kinetics, and bulk heat, mass and momentum transfer in multiphase fluids. This overview is motivated by the potential of non-spherical suspension particles, in particular those formed from ‘natural’ and ‘sustainable’ biopolymers, as rheology modifiers in food materials, consumer products, cosmetics or pharmaceuticals.     

Protein nanocage-stabilized Pickering emulsions

The utilization of surface-active engineered protein nanocages as stabilizers for emulsions provides avenues for the design of new tailor-made functional materials in various fields including food, pharmaceutical, and biotechnology. They can be used to codeliver bioactive molecules of different polarities in a tailored manner to the body, act as a platform for screening cells or enzymes, or function as targeted drug delivery systems. Knowledge on the mechanisms that underlie the protein nanocage-driven stabilization of emulsions and their colloidal structure can have direct implications for the rational design of the new advanced functional colloids.This contribution summarizes the recent progress in protein nanocage-stabilized emulsions. It discusses the advances in the precision bioengineering of protein nanocages for emulsion design, highlights challenges in the characterization of structure and dynamics in these materials, and demonstrates selected applications in the field of functional food materials.     

Colloidal assembly: the road from particles to colloidal molecules and crystals

Colloidal particles may be considered as building blocks for materials, just like atoms are the bricks of molecules, macromolecules, and crystals. Periodic arrays of colloids (colloidal crystals) have attracted much interest over the last two decades, largely because of their unique photonic properties. The archetype opal structures are based on close-packed arrays of spheres of submicrometer diameter. Interest in structuring materials at this length scale, but with more complex features and ideally by self-assembly processes, has led to much progress in controlling features of both building blocks and assemblies. The necessary ingredients include colloids, colloidal clusters, and colloidal "molecules" which have special shapes and the ability to bind directionally, the control over short-range and long-range interactions, and the capability to place and orientate these bricks. This Review highlights recent experimental and theoretical progress in the assembly of colloids larger than 50 nm.     

Uniform Colloidal Polymer Rods by Stabilizer-Assisted Liquid-Crystallization-Driven Self-Assembly

The synthesis of anisotropic colloidal building blocks is essential for their self-assembly into hierarchical materials. Here, a highly efficient stabilizer-assisted liquid-crystallization-driven self-assembly (SA-LCDSA) strategy was developed to achieve monodisperse colloidal polymer rods. This strategy does not require the use of block copolymers, but only homopolymers or random copolymers. The resulting rods have tunable size and aspect ratios, as well as well-defined columnar liquid crystal structures. The integrated triphenylene units enable the rods to exhibit unusual photo-induced fluorescence enhancement and accompanying irradiation memory effect, which, as demonstrated, are attractive for information encryption/decryption of paper documents. In particular, unwanted document decryption during delivery can be examined by fluorescence kinetics. This SA-LCDSA-based approach can be extended to synthesize other functional particles with desired π-molecular units.     

Supramolecular architectures assembled from amphiphilic hybrid polyoxometalates

Polyoxometalate (POM)-based inorganic-organic molecular hybrid clusters have been recently recognized as good candidates to design novel multi-functional materials. Tremendous efforts have been invested in synthesizing many interesting hybrid structures with exceptional chemical and physical properties. Grafting organic ligands to the POM clusters render these functional clusters amphiphilic properties. Here we summarize the current progresses and provide some perspectives, from colloidal chemists' point of view, on the self-assembly of the amphiphilic POM-organic hybrids in solution and at interfaces, as well as the related consequent novel features such as enhanced fluorescent properties.     

Electron Microscopic Study on Aerosol-Assisted Synthesis of Aluminum Organophosphonates Using Flexible Colloidal PS-b-PEO Templates

A wide variety of synthetic approaches from homogeneous precursor solutions have so far been developed for precise structural design of materials in multiscale. In organic templating approaches for porous materials design, we have recently developed a new approach to fabricate colloidal polystyrene-block-poly(oxyethylene) (PS-b-PEO) templated large pores that can be controlled in thick films of aluminum organophosphonate (AOP). In this study, we extended this approach using colloidal PS-b-PEO aggregates to aerosol-assisted synthesis for the fabrication of spherical particles. Structural variations (morphology and porous structure) depended on the synthetic conditions, which were mainly investigated by using electron microscopies (SEM and TEM). In addition to the insight on the colloidal PS-b-PEO templating of spherical pores in AOP spheres, it was found that colloidal PS-b-PEO aggregates were flexible for further design of pore shape that was strongly affected by external morphology. In this context, we proposed this method as flexible colloidal PS-b-PEO templating to fabricate unusual macroporous structures during morphological control from precursor solutions containing colloidal PS-b-PEO aggregates. The insights will be promising for precise construction of unique devices using porous materials templated by colloidal organic aggregates. In addition, we found a useful water adsorption-desorption behavior over the macroporous AOP bulky powders when the macropores were connected through large pores, which is also significant for future development of AOP-based porous materials.     

Colloidal crystals as templates for porous materials

Close-packed colloidal crystals are promising precursors for novel materials, but only after appropriate methods are developed to fix their structure. A wide range of advanced materials has recently been synthesized by replicating the structure of colloidal crystals into durable solid matrices. Such materials with structured pores have promise as photonic crystals, catalysts, and membranes, and in a variety of other applications. This paper reviews the methods used in the formation of these materials and likely future trends in the field.     

Porous Solids from Rigid Colloidal Templates: Morphogenesis

Modern research is increasingly focusing on structuring matter on a nanometer length scale rather than producing molecularly new species. This article describes a method for synthesizing porous solids from rigid colloidal templates in three steps (see scheme): a) assembly of colloidal particles into a regular array, b) impregnation of the template with monomer(s) and polymerization, and c) removal of the template. For the materials prepared there is a vast number of potential applications ranging from robust catalysts and supports over size- and shape-selective membranes to photovoltaic devices.     

Stimuli-responsive colloids: From stratified to self-repairing Polymeric Films and Beyond

Although stratification in polymeric colloids and films has been known for a long time, its significance has not been recognized until surface-interfacial properties driven by mobility of dispersing agents became one of the key features that impact structure–property relationships. Learning from these studies, the last decade resulted in significant advances that have led to the development of a new generation of polymeric materials in general, and colloids in particular, that exhibit stimuli-responsive attributes. As significant as hydrophobic interactions are in biological systems, the abundance of these and other interactions can be found in colloids that are capable of recognition and dynamic responsiveness leading to life-like materials with significant technological applications. Recent advances in the development of stimuli-responsive colloidal materials are discussed in the context of surface and bulk responsive morphologies, from dynamic shape and color changing colloidal nanoparticles to expandable nanotubes and polymer-modified metal nanoparticles. Stimuli-responsive and signaling attributes of macromolecular segments of colloids along with dispersing components will play key roles during colloidal film formation. Concurrently, the development of heterogeneous functional objects that can exhibit dimensional change initiated by light or other environmental factors will form a new platform of amazing and sparkling technologies for the 21st century capable of producing on-demand self-repairing colloid-based materials.     

Ordered patterns and structures via interfacial self-assembly: superlattices, honeycomb structures and coffee rings

Self-assembly is now being intensively studied in chemistry, physics, biology, and materials engineering and has become an important "bottom-up" approach to create intriguing structures for different applications. Self-assembly is not only a practical approach for creating a variety of nanostructures, but also shows great superiority in building hierarchical structures with orders on different length scales. The early work in self-assembly focused on molecular self-assembly in bulk solution, including the resultant dye aggregates, liposomes, vesicles, liquid crystals, gels and so on. Interfacial self-assembly has been a great concern over the last two decades, largely because of the unique and ingenious roles of this method for constructing materials at interfaces, such as self-assembled monolayers, Langmuir-Blodgett films, and capsules. Nanocrystal superlattices, honeycomb films and coffee rings are intriguing structural materials with more complex features and can be prepared by interfacial self-assembly on different length scales. In this critical review, we outline the recent development in the preparation and application of colloidal nanocrystal superlattices, honeycomb-patterned macroporous structures by the breath figure method, and coffee-ring-like patterns (247 references).     

Sedimentation equilibrium of colloidal suspensions in a planar pore based on density functional theory and the hard-core attractive Yukawa model

The sedimentation equilibrium of colloidal suspensions modeled by hard-core attractive Yukawa (HCAY) fluids in a planar pore is studied. The density profile of the HCAY fluid in a gravitational field and its distribution between the pore and uniform phases are investigated by a density functional theory (DFT) approach, which results from employing a recently proposed parameter-free version of the Lagrangian theorem-based density functional approximation (Zhou, S. Phys. Lett. A 2003, 319, 279) for hard-sphere fluids to the hard-core part of the HCAY fluid, and the second-order functional perturbation expansion approximation to the tail part as was done in a recent partitioned density functional approximation (Zhou, S. Phys. Rev. E: Stat. Phys., Plasmas, Fluids, Relat. Interdiscip. Top. 2003, 68, 061201). The resultant DFT approach is, thus, the first adjustable parameter-free DFT for HCAY fluids. The validity of the present DFT for HCAY fluids of reduced range parameter z(red) = 1.8 under various external potentials is established in the first of the papers cited previously. The present DFT for HCAY fluids can predict the radial distribution function for the bulk HCAY fluid accurately in the colloidal limit (large value of z(red)), and in the hard-sphere limit, its prediction for the density profile of the hard-sphere fluid in a gravitational field is in very good agreement with the existing simulation data. The dependence of the density profile and distribution coefficient on the magnitude of the interparticle attraction, gravitational field, and degree of confinement is investigated in detail by the present DFT approach. Intuitive and qualitative analyses are also compared with the quantitative DFT calculational results.     

Functionalized Carbon Nanomaterials Derived from Carbohydrates

A tremendous growth in the field of carbon nanomaterials has led to the emergence of carbon nanotubes, fullerenes, mesoporous carbon and more recently graphene. Some of these materials have found applications in electronics, sensors, catalysis, drug delivery, composites, and so forth. The high temperatures and hydrocarbon precursors involved in their synthesis usually yield highly inert graphitic surfaces. As some of the applications require functionalization of their inert graphitic surface with groups like ? COOH, ? OH, and ? NH₂, treatment of these materials in oxidizing agents and concentrated acids become inevitable. More recent works have involved using precursors like carbohydrates to produce carbon nanostructures rich in functional groups in a single‐step under hydrothermal conditions. These carbon nanostructures have already found many applications in composites, drug delivery, materials synthesis, and Li ion batteries. The review aims to highlight some of the recent developments in the application of carbohydrate derived carbon nanostructures and also provide an outlook of their future prospects.     

Nanoparticulate Functional Materials

Nanoparticulate functional materials offer manifold perspectives for the increasing miniaturization and complexity of technical developments. Nanoparticles also make a major contribution to utilization of materials that is sparing of natural resources. Besides these obvious aspects, however, the importance of nanoparticles is due to their fundamentally novel properties and functions. These include photonic crystals and efficient luminophors, single particles and thin films for electronic storage media and switching elements, magnetic fluids and highly selective catalysts, a wide variety of possibilities for surface treatments, novel materials and concepts for energy conversion and storage, contrast agents for molecular biology and medical diagnosis, and fundamentally novel forms and structures of materials, such as nanocontainers and supercrystals. Creating high‐quality nanoparticles requires that numerous parameters, involving the particle core and surface, colloidal properties, and particle deposition, are taken into consideration during synthesis of the material. An appropriate characterization and evaluation of the properties requires the incorporation of a wide range of expertise from widely differing areas. These circumstances are what challenges and appeals to the nanoscientist.