The influence of confinement and curvature on the morphology of block copolymers

In the bulk, at equilibrium, diblock copolymers microphase separated into nanoscopic morphologies ranging from body-centered cubic arrays of spheres to hexagonally packed cylinders to alternating lamellae, depending on the volume fraction of the components. However, when the block copolymers are forced into cylindrical pores, where the diameter of the pores are only several repeat periods of the copolymer morphology or less, then commensurability of the copolymer period and the pore diameter can impose a frustration on the microdomain morphology. In addition, due to the small pore diameter, a curvature is forced on the microdomain morphology. In combination with interfacial interactions between the blocks of the copolymer and the pore walls, the preferential segregation of one component to the walls, spatial confinement and forced curvature are shown to induce transitions in the fundamental morphology of the copolymers seen in the bulk. Lamellar morphologies transformed into torus-type morphologies, cylinders are forced into helices, and body-centered cubic arrays of spheres are force into helical arrays of spheres due to these restraints. The novel morphologies, not accesssible in the bulk, open a large array of nanoscopic structures that can be used as templates and scaffolds for the fabrication of inorganic nanostructured materials. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 3377–3383, 2005     

Molecular Springs: Integration of Complex Dynamic Architectures into Functional Devices

Molecular/supramolecular springs are artificial nanoscale objects possessing well‐defined structures and tunable physicochemical properties. Like a macroscopic spring, supramolecular springs are capable of switching their nanoscale conformation as a response to external stimuli by undergoing mechanical spring‐like motions. This dynamic action offers intriguing opportunities for engineering molecular nanomachines by translating the stimuli‐responsive nanoscopic motions into macroscopic work. These nanoscopic objects are reversible dynamic multifunctional architectures which can express a variety of novel properties and behave as adaptive nanoscopic systems. In this Minireview, we focus on the design and structure–property relationships of supramolecular springs and their (self‐)assembly as a prerequisite towards the generation of novel dynamic materials featuring controlled movements to be readily integrated into macroscopic devices for applications in sensing, robotics, and the internet of things.     

Functionalized block copolymers for preparation of reactive self‐assembled surface patterns

Two phase separating block copolymers equipped with functional groups (acid and alkyne) were synthesized via reversible addition‐fragmentation chain transfer (RAFT) polymerization. Thin films of these materials were prepared and examined with regard to surface morphology, surface composition, and film stability. Self‐assembled structures with domain sizes of about 40 nm were detected through atomik force microscopy (AFM) analysis while X‐ray photoelectron spectroscopy measurements revealed a balanced surface exposure of the two segregated phases. Thus, reactive groups being present in both phases are specifically provided within nanoscopic surface areas. The films showed good stability on exposure to various solvents but the self‐organized surface patterns were only resistant toward ethanol. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Nanoscopic Visualization of Cross‐Linking Density in Polymer Networks with Diarylethene Photoswitches

The in situ nanoscopic imaging of soft matter polymer structures is of importance to gain knowledge of the relationship between structure, properties, and functionality on the nanoscopic scale. Cross‐linking of polymer chains effects the viscoelastic properties of gels. The correlation of mechanical properties with the distribution and amount of cross‐linkers is relevant for applications and for a detailed understanding of polymers on the molecular scale. We introduce a super‐resolution fluorescence‐microscopy‐based method for visualizing and quantifying cross‐linker points in polymer systems. A novel diarylethene‐based photoswitch with a highly fluorescent closed and a non‐fluorescent open form is used as a photoswitchable cross‐linker in a polymer network. As an example for its capability to nanoscopically visualize cross‐linking, we investigate pNIPAM microgels as a system known with variations in internal cross‐linking density.     

Solvent Induced Sphere Development in Symmetric Diblock Copolymer Thin Films

Summary: We follow the time development of the microdomain structure in symmetric polystyrene‐block‐poly(methyl methacrylate) (PS‐b‐PMMA) diblock copolymer thin films during acetone vapor treatment. Besides the highly ordered nanoscopic spheres or stripes as reported previously, a novel so‐called flower‐like pattern, which comprises six PS spheres and each PS sphere belongs to three “flowers” is formed. This finding is very helpful to discuss the highly ordered nanoscopic sphere formation process.

Transition from flower‐like structure to well‐ordered arrays of spheres, in which the flower‐like pattern, the transitional morphology, and the ordered spheres are in the portion A, B, and C, respectively.     

Orientation-dependent nanostructuring of titanium surfaces by low-energy ion beam erosion

Regular nanoscopic ripple and dot patterns are fabricated on poly-crystalline titanium samples by irradiation with 1.5 keV argon ions at normal incidence. The morphology of the nanostructures is investigated by scanning electron microscopy and scanning force microscopy. The ripple structures exhibit a saw-tooth cross-section profile. Electron backscatter diffraction experiments are performed to analyze the local grain structure. The study suggests a distinct correlation of the nanostructure morphology to the crystallographic orientation of the titanium surface.     

Synthesis of mesoporous silicas in alkaline and acidic media using the systems cetyltrimethylammonium tosylate (CTAT)-Pluronic F127 triblock copolymer and CTAT-Pluronic F68 triblock copolymer as templates

Mesoporous silica materials were synthesized in alkaline and acidic media, using cetyltrimethylammonium tosylate (CTAT), Pluronic triblock copolymers F127 and F68, and mixtures of CTAT with each copolymer in order to investigate the effects of pH, surfactant concentration, and CTAT/triblock copolymer molar ratios on the morphology and texture of the synthesized materials. The results show that the kind of mesoporous materials and their pore size can be tuned by changing not only the pH but also the proportion of components and the nature of the copolymer. In alkaline synthesis, microscopic bicontinuous materials are obtained, which are composed by nanoscopic plate-like particles having slit-shaped pores. In acidic synthesis, on the contrary, monolithic silicas are obtained. These materials are also composed by nanoscopic plate-like particles having slit-shaped pores, although in some cases, the microscopic structures are formed by fused spherical particles. The inclusion of the triblock copolymer in the template composition causes a transformation from a bimodal to a monomodal pore size distribution, leading to small and nearly round pores which are probably formed by copolymer or copolymer-CTAT mixed micelles. The differences between the systems synthesized by CTAT-Pluronic F127 and CTAT-Pluronic F68 are explained on the basis of the different interactions between each copolymer and CTAT.     

Phenomenon of the ousting of a monatomic ion from its hydration shell in flat nanopores

The structure and stability of hydrate shells of singly charged sodium and chlorine ions are studied by computer simulations under the conditions of nanoscopic flat pores with the use of the previously proposed detailed force field model containing polarization interactions, transferring charge effects as well as manybody interactions of covalent type. It is found that the effect of ousting a monatomic ion from its hydration shell, which has previously been observed by independent authors in bulk vapor, is also reproduced persistently in nanoscopic pores. Whereas the ousting of the ion from its hydration shell in bulk vapor is accompanied by the loss of thermodynamic stability of the system and at sufficiently high vapor pressure causes avalanche-like condensation, under the conditions of a nanoscopic pore the thermodynamic stability is retained. The obtained data show that the ousting of the ion from its hydration shell is a universal phenomenon covering the majority, if not all, of monatomic and, possibly, some of molecular ions.     

Role of Intramolecular Aromatic π–π Interactions in the Self‐Assembly of Di‐l‐Phenylalanine Dipeptide Driven by Intermolecular Interactions: Effect of Alanine Substitution

Although the role of intermolecular aromatic π–π interactions in the self‐assembly of di‐l ‐phenylalanine (l ‐Phe‐l ‐Phe, FF), a peptide that is known for hierarchical structure, is well established, the influence of intramolecular π–π interactions on the morphology of the self‐assembled structure of FF has not been studied. Herein, the role of intramolecular aromatic π–π interactions is investigated for FF and analogous alanine (Ala)‐containing dipeptides, namely, l ‐Phe‐l ‐Ala (FA) and l ‐Ala‐l ‐Phe (AF). The results reveal that these dipeptides not only form self‐assemblies, but also exhibit remarkable differences in structural morphology. The morphological differences between FF and the analogues indicate the importance of intramolecular π–π interactions, and the structural difference between FA and AF demonstrates the crucial role of the nature of intramolecular side‐chain interactions (aromatic–aliphatic or aliphatic–aromatic), in addition to intermolecular interactions, in deciding the final morphology of the self‐assembled structure. The current results emphasise that intramolecular aromatic π–π interaction may not be essential to induce self‐assembly in smaller peptides, and π (aromatic)–alkyl or alkyl–π (aromatic) interactions may be sufficient. This work also illustrates the versatility of aromatic and a combination of aromatic and aliphatic residues in dipeptides in the formation of structurally diverse self‐assembled structures.     

Colloidal behavior of nanoemulsions: Interactions,structure, and rheology

Nanoemulsions exhibit unique behavior due to their nanoscopic dimensions, including remarkable droplet stability, interactions, and rheology. These properties are significantly enhanced by nanoscopic droplet size, as well as the selection of surfactant and other molecular species in solution. Electrostatic and polymer-induced interdroplet interactions are particularly powerful tools for fine-tuning the interdroplet interactions, and have led to stimuli-responsive nanoemulsion systems that provide deep insight into their unique properties. As such, nanoemulsions have emerged as powerful model systems for studying a number of colloidal phenomena including suspension rheology, repulsive and attractive colloidal glasses, aggregation processes, colloidal gelation and phase instability, and associative network formation in polymer–colloid mixtures. This review summarizes recent advances in understanding the colloidal behavior of nanoemulsions, and provides a unifying framework for understanding the various complex states that emerge, as well as perspective on emerging challenges and opportunities that will advance the use of nanoemulsions in both fundamental colloid science and technological applications.     

Starburstr̀ dendrimers — Nanoscopic supermolecules according to dendritic rules and principles

Construction of dendritic macromolecules based on the mimicry of macroscopic branching patterns found in trees is reviewed. From this mimicry, synthetic strategies have been developed for the preparation of precise macromolecular building blocks referred to as Starburstr̀/Cascade dendrimers. These dendrimer constructions involve the amplifications of matter (mass) by organizing monomer units around initiator cores according to geometrically driven mathematical rules and principles. The predictable precision of mass and valency (i.e., number of reactive surface groups) displayed by these dendrimers, as a function of generation, validates their proposed role as fundamental nanoscopic building blocks (i.e., particle sizes of 10 −1000Å). This emerging area of “structure-controlled polymers” is defining a fourth new major class of macromolecular architecture. Ideal, defect free structures of Starburst^r̀ polyamidoamine (PAMAM) dendrimers (e.g., NH₃ core; generation = 2.0, MWt. 2,414) have been synthesized in kilogram quantities with overall yields of 60-70%. The precise masses and surface valencies associated with these dendrimer structures allow one to view these entities as “nanoscopic analogues” to atoms. As such, basic rules of chemical combination between dendrimers to give definite, stoichiometric compositions can be defined much as first noted by Dalton for atoms. The use of these nanoscopic building blocks (i.e., 10–1000Å species) to construct supramolecular/supermolecular structures such as nanoscopic compounds, clusters and macro-lattices will be reviewed. Registered trademark of Dendritech Inc.     

Strategies toward well‐defined polymer nanoparticles inspired by nature: Chemistry versus versatility

Polymeric nanoparticles are promising delivery platforms for various biomedical applications. One of the main challenges toward the development of therapeutic nanoparticles is the premature disassembly and release of the encapsulated drug. Among the different strategies to enhance the kinetic stability of polymeric nanoparticles, shell‐ and core‐crosslinking have been shown to provide robust character, while creating a suitable environment for encapsulation of a wide range of therapeutics, including hydrophilic, hydrophobic, metallic, and small and large biomolecules, with gating of their release as well. The versatility of shell‐ and core‐crosslinked nanoparticles is driven from the ease by which the structures of the shell‐ and core‐forming polymers and crosslinkers can be modified. In addition, postmodification with cell‐recognition moieties, grafting of antibiofouling polymers, or chemical degradation of the core to yield nanocages allow the use of these robust nanostructures as “smart” nanocarriers. The building principles of these multifunctional nanoparticles borrow analogy from the synthesis, supramolecular assembly, stabilization, and dynamic activity of the naturally driven biological nanoparticles such as proteins, lipoproteins, and viruses. In this review, the chemistry involved during the buildup from small molecules to polymers to covalently stabilized nanoscopic objects is detailed, with contrast of the strategies of the supramolecular assembly of polymer building blocks followed by intramicellar stabilization into shell‐, core‐, or core–shell‐crosslinked knedel‐like nanoparticles versus polymerization of polymers into nanoscopic molecular brushes followed by further intramolecular covalent stabilization events. The rational design of shell‐crosslinked knedel‐like nanoparticles is then elaborated for therapeutic packaging and delivery, with emphasis on the polymer chemistry aspects to accomplish the synthesis of such nanoparticulate systems. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Coordination-driven self-assembly of supramolecular cages: heteroatom-containing and complementary trigonal prisms

The self-assembly of three nanoscopic prisms of approximate size 1 x 4 nm is reported. Tetrahedral carbon, silicon, and phosphorus were used as structure-defining elements in these coordination-based cages. A carbon-based assembly completes a pair of nanoscopic complementary 3-D structures. The formation of the structures is supported by multinuclear NMR, ESI FT-ICR mass spectrometry, and elemental analysis data.     

Starburst® dendrimers: A conceptual approach to nanoscopic chemistry and architecture

The nanoscopic domain of structural complexity, which ranges from 1 to 100 run on a particle size scale includes a relatively unexplored area of science which resides between classical chemistry and molecular biology. This rapidly growing area of science is referred to as nanoscopic chemistry and architecture. Concepts evolving in this area lead to a rich variety of precise structures, architecture and properties. These concepts are based on dendritic macromolecules in general and on Starburst® dendrimers in particular. They envision dendrimers as fundamental building blocks which may be used to synthesize nanoscopic compounds, clusters, polymers, etc. Accordingly, dendrimers are regarded architecturally as functional analogues of atoms; therefore, their potential role in nanoscopic chemistry may be compared to that of the atoms in classical chemistry.     

Nanoscopic confinement effects on ethylene polymerization by intercalated silicate with metallocene catalyst

In this article we report a study of in situ polymerization of ethylene by intercalated montmorillonite (MMT) with metallocene, allowing an investigation of the nanoscopic confinement effect of olefin polymerization and of the structure of polymer prepared in situ. Ethylene polymerization by intercalated MMT with metallocene and the varied aggregation morphology of the resulting polymer during polymerization were studied by X‐ray diffraction (XRD), differential scanning calorimetry (DSC), and gel permeation chromatography (GPC). The polymerization kinetics and the resulting polymer before and after destruction of the silicate registry were different. The laminated structure of silicate lowered the all‐reaction rate, including the propagation, chain transfer, and termination reactions, producing polymer of a high molecular weight. Moreover, the melting point of the polymer gradually increased during the in situ polymerization, indicating that nanoscopic confinement between solid surfaces affects the crystallization behavior of polyethylene via in situ polymerization. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 38–43, 2004     

Photoactivated Polymersome Nanomotors: Traversing Biological Barriers

Synthetic nanomotors are appealing delivery vehicles for the dynamic transport of functional cargo. Their translation toward biological applications is limited owing to the use of non‐degradable components. Furthermore, size has been an impediment owing to the importance of achieving nanoscale (ca. 100 nm) dimensions, as opposed to microscale examples that are prevalent. Herein, we present a hybrid nanomotor that can be activated by near‐infrared (NIR)‐irradiation for the triggered delivery of internal cargo and facilitated transport of external agents to the cell. Utilizing biodegradable poly(ethylene glycol)‐b‐poly(d,l ‐lactide) (PEG‐PDLLA) block copolymers, with the two blocks connected via a pH sensitive imine bond, we generate nanoscopic polymersomes that are then modified with a hemispherical gold nanocoat. This Janus morphology allows such hybrid polymersomes to undergoing photothermal motility in response to thermal gradients generated by plasmonic absorbance of NIR irradiation, with velocities ranging up to 6.2±1.10 μm s^?1. These polymersome nanomotors (PNMs) are capable of traversing cellular membranes allowing intracellular delivery of molecular and macromolecular cargo.     

Co‐Assembled Supramolecular Nanostructure of Platinum(II) Complex through Helical Ribbon to Helical Tubes with Helical Inversion

We demonstrated the morphology transformation of co‐assemblies based on terpyridine‐based ligands ( 1R and 1S ) possessing R‐ or S‐alanine analogues and their platinum(II) complex ( 2R‐Pt and 2S‐Pt ). The right‐handed helical ribbon of the co‐assembly formed with 0.5 equivalents of 2R‐Pt to 1R was converted into the left‐handed helical ribbon with 0.6 equivalents of 2R‐Pt . The left‐handed helical ribbon structure of the co‐assembly became a tubular structure in the presence of 0.8–1.0 equivalents of 2R‐Pt . The morphology transformation via helical inversion at the supramolecular level was due to an orientation change of the amide groups caused by non‐covalent Pt???Pt interactions between the terpyridine of 2R‐Pt and that of 2R‐Pt . This study provides insights into controlling the morphology of the transformation of helical ribbons into tubular structures through helicity inversion in co‐assembled supramolecular nanostructures based on platinum(II) complexes.     

Tuning nanoscopic self‐assembly of diblock copolymer blends on a two‐dimensional interface

Spreading amphiphilic diblock copolymers on a two‐dimensional liquid interface has been observed to produce nanoscale features via self‐assembly. Here, we develop a model that incorporates the effects of polymer entanglement and surface diffusion in polymer blends to quantitatively predict the size of experimentally observed structures. Simulations show that different polymers in the blend cooperate to self‐assemble into nanoscale features of varying sizes. Characteristic nanoscopic dimensions can be tuned by adjusting two easily controllable macroscopic quantities: the blend composition and the initial surface concentration. Theoretical predictions are in agreement with experimentally measured feature dimensions. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011     

Aqueous self-assembly of aromatic rod building blocks

One of the most fascinating subjects in areas such as nanoscience and biomimetic chemistry is concerned with the construction of novel supramolecular nanoscopic architectures with well defined shapes and functions. Supramolecular assemblies of aromatic rod molecules provide a facile entry into this area. Aromatic rigid rod molecules consisting of hydrophilic flexible chains, in aqueous solution can self-assemble into a variety of supramolecular structures through mutual interactions between aromatic rod molecules and water, including hydrophobic and hydrophilic interactions and pi-pi interaction. The supramolecular architecture in water can be manipulated by variation of the shape of the rigid segments, as well as the relative volume fraction of the flexible segment. The rigid aromatic segments have significant photonic and electronic properties. The self-assembly of aromatic rod molecules in water, therefore, can provide a strategy for the construction of well-defined and stable nanometer-size structures with chemical functionalities and physical properties as advanced materials for photonic, electronic and biological applications.     

Polymeric Janus Particles

Since de Gennes’ Nobel lecture in 1991, in which he coined the term “Janus grains”, research into asymmetric particles has boomed. Macroscopic, microscopic and nanoscopic particles have been prepared in which certain parts of their surface differ in chemical composition, polarity, color, or any other property. Spherical, cylindrical, disc‐like, snowman‐, hamburger‐, and raspberry‐like structures have been synthesized from organic or inorganic materials or even as hybrids of both. Synthetic strategies towards such particles vary greatly from simple polymer mixtures to the bulk self‐assembly of sophisticated terpolymers to immobilization methods of symmetric particles. Polymeric Janus particles are particularly promising, as they can often be prepared cheaply and sometimes even on larger scales.