Reversible Morphological Transformation between Polymer Nanocapsules and Thin Films through Dynamic Covalent Self‐Assembly

A facile method has been developed for synthesizing polymer nanocapsules and thin films using multiple in‐plane stitching of monomers by the formation of reversible disulfide linkages. Owing to the reversibility of the disulfide linkages, the nanostructured materials readily transform their structures in response to environmental changes at room temperature. For example, in reducing environments, the polymer nanocapsules release loaded cargo molecules. Moreover, reversible morphological transformations between these structures can be achieved by simple solvent exchanges. This work is a novel approach for the formation of robust nano/microstructured materials that dynamically respond to environmental stimuli.     

Free‐Standing Gold‐Nanoparticle Monolayer Film Fabricated by Protein Self‐Assembly of α‐Synuclein

Free‐standing nanoparticle films are of great importance for developing future nano‐electronic devices. We introduce a protein‐based fabrication strategy of free‐standing nanoparticle monolayer films. α‐Synuclein, an amyloidogenic protein, was utilized to yield a tightly packed gold‐nanoparticle monolayer film interconnected by protein β‐sheet interactions. Owing to the stable protein–protein interaction, the film was successfully expanded to a 4‐inch diameter sheet, which has not been achieved with any other free‐standing nanoparticle monolayers. The film was flexible in solution, so it formed a conformal contact, surrounding even microspheres. Additionally, the monolayer film was readily patterned at micrometer‐scale and thus unprecedented double‐component nanoparticle films were fabricated. Therefore, the free‐floating gold‐nanoparticle monolayer sheets with these properties could make the film useful for the development of bio‐integrated nano‐devices and high‐performance sensors.     

Self‐Assembly of Differently Shaped Protein–Polymer Conjugates through Modification of the Bioconjugation Site

Self‐assembly of protein–polymer block copolymers is an attractive route for preparing biocatalytic materials. To clarify the effect of bioconjugate shape on self‐assembly without changing the chemical details of either block, four different conjugation sites are selected on the surface of the model globular protein mCherry at residues 3, 108, 131, and 222 to alter the colloidal shape of the bioconjugate. All four mCherry‐b‐poly(N‐isopropylacrylamide) bioconjugates show qualitatively similar phase diagrams, indicating that self‐assembly is robust with respect to changes in conjugation site. However, protein orientation has an effect on the location of the order–disorder transition concentration, and the stability of the disordered micellar phase is shown to be different for each conjugate. Differences in domain spacing also suggest changes in protein orientation within the lamellae.

     

A Self‐Assembly Approach to Temperature‐Responsive Polymer Nanocontainers

Summary: Thermosensitive polymer nanocontainers were formed by self‐assembly of diblock copolymers poly(2‐cinnamoylethyl methacrylate)‐block‐poly(N‐isopropylacrylamide) (PCEMA‐block‐PNIPAM) and subsequent photo‐crosslinking of the PCEMA shells. It was found that the diameter of the nanocontainers ranges from tens of nanometers to thousands of nanometers, depending on the self‐assembly conditions. The phase transition of the nanocontainers takes place at 32 °C; the structural changes are reversible in a heating and cooling cycle.

Schematic illustration of the structural transition behavior of the thermosensitive polymer nanocontainers.     

Ion‐Specific Self‐Assembly of Low‐Dimension Aggregate Structures of Conjugated Polymer at Two‐Phase Interface

A novel and facile approach to manipulate the morphology of Cu²⁺‐ion‐specific assembly of conjugated polymer by coordinative interaction at an oil–water two‐phase interface is present. The application of increasing importance is the use of π‐conjugated polymers as receptors, exploiting their ability to selectively form complexes, which can obviously change the optical properties in solution and induce the formation of varied solid nano/microstructures. By this method, microtubes are formed through self‐rolling of a strained ionic bilayer film at the oil/water interface.     

Kinetically Enhanced Approach for Rapid and Tunable Self‐Assembly of Rod–Coil Block Copolymers

A facile approach is reported to process rod–coil block copolymers (BCPs) into highly ordered nanostructures in a rapid, low‐energy process. By introducing a selective plasticizer into the rod–coil BCPs during annealing, both the annealing temperature and time to achieve thermodynamic equilibrium and highly ordered structures can be decreased. This process improvement is attributed to enhanced chain mobility, reduced rod–rod interaction, and decreased rod–coil interaction from the additive. The novel method is based on kinetically facilitating thermodynamic equilibrium. The process requires no modification of polymer structure, indicating that a wide variety of desired polymer functionalities can be designed into BCPs for specific applications.

     

Bioreducible Nanocapsules Prepared from the Self‐assembly of Branched Polymer in Nanodroplet

Though great attention has been paid in constructing well‐defined nano‐structures via the self‐assembly of amphiphilic macromolecules, the self‐assembly of non‐amphiphilic macromolecules in nanodroplet has drawn less attention up to now. Recently, we prepared a temperature‐responsive PEG‐based branched polymer with disulfide bonds in its backbone via reversible addition–fragmentation chain transfer (RAFT) polymerization of 2‐(2‐methoxyethoxy) ethyl methacrylate, oligo(ethylene glycol) methacrylate, and N,N′‐cystamine bisacrylamide. Subsequently, we loaded the branched polymer into nanodroplets, and have found that the self‐assembly behaviors of this branched poly­mer in the nanodroplet are different from those in common solution. Bioreducible nanocapsules with tunable size can easily formed in nanodroplet even at high concentration.

     

Amphiphilic Janus Gold Nanoparticles Prepared by Interface‐Directed Self‐Assembly: Synthesis and Self‐Assembly

Materials with Janus structures are attractive for wide applications in materials science. Although extensive efforts in the synthesis of Janus particles have been reported, the synthesis of sub‐10 nm Janus nanoparticles is still challenging. Herein, the synthesis of Janus gold nanoparticles (AuNPs) based on interface‐directed self‐assembly is reported. Polystyrene (PS) colloidal particles with AuNPs on the surface were prepared by interface‐directed self‐assembly, and the colloidal particles were used as templates for the synthesis of Janus AuNPs. To prepare colloidal particles, thiol‐terminated polystyrene (PS‐SH) was dissolved in toluene and citrate‐stabilized AuNPs were dispersed in aqueous solution. Upon mixing the two solutions, PS‐SH chains were grafted to the surface of AuNPs and amphiphilic AuNPs were formed at the liquid–liquid interface. PS colloidal particles decorated with AuNPs on the surfaces were prepared by adding the emulsion to excess methanol. On the surface, AuNPs were partially embedded in the colloidal particles. The outer regions of the AuNPs were exposed to the solution and were functionalized through the grafting of atom‐transfer radical polymerization (ATRP) initiator. Poly[2‐(dimethamino)ethyl methacrylate] (PDMAEMA) on AuNPs were prepared by surface‐initiated ATRP. After centrifugation and dissolving the colloidal particles in tetrahydrofuran (THF), Janus AuNPs with PS and PDMAEMA on two hemispheres were obtained. In acidic pH, Janus AuNPs are amphiphilic and are able to emulsify oil droplets in water; in basic pH, the Janus AuNPs are hydrophobic. In mixtures of THF/methanol at a volume ratio of 1:5, the Janus AuNPs self‐assemble into bilayer structures with collapsed PS in the interiors and solvated PDMAEMA at the exteriors of the structures.     

Directed Self‐Assembly of Diblock Copolymer Thin Films on Prepatterned Metal Nanoarrays

The sequential layer by layer self‐assembly of block copolymer (BCP) nanopatterns is an effective approach to construct 3D nanostructures. Here large‐scale highly ordered metal nano­arrays prepared from solvent annealed thin films of polystyrene‐block‐poly(2‐vinylpyridine) (PS‐b‐P2VP) diblock copolymer are used to direct the assembly of the same BCP. The influence of initial loading concentration of metal precursor, the type of metal nanoparticle (gold, platinum, and silver), and the nanoparticle–substrate interaction on the directed assembly behavior of the upper BCP layer have been focused. It is found that the upper BCP film can be completely directed by the gold nanoarray with P2VP domain exclusively located between two adjacent gold nanowires or nanodots, which behaves the same way as on the platinum nanoarray. While the silver nanoarray can be destroyed during the upper BCP self‐assembly with the silver nanoparticles assembled into the P2VP domain. Based on the discussions of the surface energy of nanoparticles and the interplay between nanoparticle–substrate interaction and nanoparticle–polymer interaction, it is concluded that the effect of immobilization of nanoparticles on the substrate, together with entropy effect to minimize the energetically unfavorable chain stretching contributes to the most effective alignment between each layer.

     

Stacking of Self‐Assembled Surface Micelles in Ultrathin Films

Nonpolar fluorophilic/lipophilic tetrablock amphiphiles are investigated on the surface of water and on solid substrates using compression isotherms, Brewster angle microscopy, and atomic force microscopy. At low pressures, the tetrablocks form monolayers of closely packed surface hemimicelles. Further compression causes a 2D/3D transition. At the end of the plateau, half of the deposited material is expelled forming a second monolayer on top of the initially formed monolayer. Both layers of the films consist of surface micelles, thus providing the first example of spontaneous or compression‐driven stacking of self‐assembled nano‐objects.     

Temperature‐responsive “tadpole‐shaped” protein–polymer hybrids and their self‐assembly behavior

The temperature‐responsive poly (N, N‐diethylacrylamide) (pDEAAm) with narrower molecular weight distribution was prepared by the atom transfer radical polymerization and characterized by ¹HNMR and gel permeation chromatography. The temperature‐responsive “tadpole‐shaped” BSA–pDEAAm hybrids were fabricated via a free Cys‐34 residue of bovine serum albumin (BSA) site specifically binding to the end group disulfide bonds of pDEAAm and characterized by native‐polyacrylamide gel electrophoresis (Native‐PAGE) and matrix‐assisted laser desorption/ionization time of flight mass spectrometry. Their temperature‐responsive behaviors were measured by ultraviolet‐visible spectra (UV‐Vis). The lower critical solution temperature (LCST) of the pDEAAm was identified as 28°C, and the LCST of BSA–pDEAAm hybrids was identified as 31°C. The morphologies of BSA–pDEAAm hybrids self‐assembled in the aqueous solutions with two different temperatures at 25 °C and 40°C were investigated by transmission electron microscopy. Below the LCST of BSA–pDEAAm hybrids, the separate spherical nanoparticles were observed. In contrast, bundles and clusters were observed above the LCST of BSA–pDEAAm hybrids. The results suggested that the self‐assembly morphology of BSA–pDEAAm hybrids depended upon the pDEAAm block in BSA–pDEAAm hybrids, and the morphology transitions were effected by the LCST of BSA–pDEAAm hybrids. It would be expected to be used in biomedicine and materials science. Copyright © 2016 John Wiley & Sons, Ltd.     

Twisted Morphologies and Novel Chiral Macroporous Films from the Self‐Assembly of Optically Active Helical Polyphosphazene Block Copolymers

A series of optically active helical polyphosphazene block copolymers of general formula R? [N?P(O₂C₂₀H₁₂)]_n‐b‐[N?PMePh]_m (R‐ 7 a – c ) was synthesized and characterized. The polymers were prepared by sequential living cationic polycondensation of N‐silylphosphoranimines using the mono‐end‐capped initiator [Ph₃P?N?PCl₃][PCl₆] ( 5 ) and exhibit a low polydispersity index (ca. 1.3). The temperature dependence of the specific optical activity ([α]_D) of R‐ 7 a , b relative to that for the homopolymers R‐[N?P(O₂C₂₀H₁₂)]_n (R‐ 8 a ) and the R/S analogues (R/S‐ 7 a , b ), revealed that the binaphthoxy–phosphazene segments induce a preferential helical conformation in the [N?PMePh] blocks through a “sergeant‐and‐soldiers” mechanism, an effect that is unprecedented in polyphosphazenes. The self‐assembly of drop‐cast thin films of the chiral block copolymer R‐ 7 b (bearing a long chiral and rigid R? [N?P(O₂C₂₀H₁₂)] segment) evidenced a transfer of helicity mechanism, leading to the formation of twisted morphologies (twisted “pearl necklace”), not observed in the nonchiral R/S‐ 7 b . The chiral R‐ 7 a and the nonchiral R/S‐ 7 a , self‐assemble by a nondirected morphology reconstruction process into regular‐shaped macroporous films with chiral‐rich areas close to edge of the pore. This is the first nontemplate self‐assembly route to chiral macroporous polymeric films with pore size larger than 50 nm. The solvent annealing (THF) of these films leads to the formation of regular spherical nanostructures (ca. 50 nm), a rare example of nanospheres exclusively formed by synthetic helical polymers.     

A Novel Nanocage from the Cooperative Self‐Assembly of Coil–Rod–Coil Triblock Copolymers and Nanopartilces

A Dissipative particle dynamics (DPD) simulations are performed to study the cooperative self‐assembly of coil–rod–coil triblock copolymers and nanoparticles in solution. The results show that, when the nanoparticle concentration exceeds a given value, the ternary systems can form a novel nanocage composed of two‐end coil‐caps and middle rod‐linkers. The novel nanocage is very similar to the real bird cage and the captured nanoparticles like the bird. It is the first nanocage from the self‐assembly of coil–rod–coil triblock copolymers. This may be used for the release of drugs and fertilizers, or as nanoreactors.

     

Interplay between H‐Bonding and Alkyl‐Chain Ordering in Self‐Assembly of Monodendritic L‐Alanine Derivatives

This paper reports on the synthesis and self‐organizing properties of monodendrons consisting of L ‐alanine at the focal point and alkyl chains with different length at the periphery. The structures of thin films and monolayers are studied by temperature‐resolved grazing‐incidence X‐ray diffraction and scanning force microscopy. The interplay between H‐bonding and ordering of the alkyl chains results in a rich temperature‐dependent phase behavior. The monodendrons form H‐bonded stabilized clusters with the number of molecules depending on the length of the aliphatic chains and temperature. The clusters play the role of constitutive units in the subsequent self‐assembly. Short alkyl chains allow the material to form thermodynamically stable crystalline phases. The molecules with longer side groups exhibit additional transitions from the crystalline phase to thermotropic columnar hexagonal or columnar rectangular liquid‐crystalline phases. In monolayers deposited on highly ordered pyrolytic graphite, the materials show ordering similar to thin films. However, for the compound bearing hexadecyl chains the affinity of the alkyl groups to graphite dominates the self‐assembly and thereby allows epitaxial growth of a 2D lattice with flat‐on oriented molecules.     

Self‐Assembly of Amphiphilic Nanocrystals

Amphiphilic hybrid materials are formed from polymer‐coated semiconductor nanoparticles that simulate a surfactant‐like response (see picture). The strength and density of the surface coating are the key assembling forces driving a transition from single particles to cylindrical or vesicular superstructures.

     

Self‐Assembly and Host–Guest Chemistry of a 3.5‐nm Coordination Nanotube

Upon complexation with Pd^II ions, precisely designed strandlike ligands with two tris(3,5‐pyridine) units at both terminals were assembled, with the aid of a linear template molecule, into a discrete tubular complex with a length of 3.5 nm. The high stability and the well‐defined structure of the coordination nanotube were revealed by NMR spectroscopy, cold‐spray ionization MS, and single‐crystal X‐ray analysis. Guest lengths were discriminated by the tube: When the association of strandlike guest molecules, in which two biphenylene units are linked with an (OCH₂CH₂)_n linker, were compared, the tube selectively recognized an appropriate guest whose length was comparable to that of the tube. Tetrathiafulvalene (TTF)‐terminated linear guests were directly oxidized to TTF²⁺ in the tube, but reduced stepwise via TTF^+? outside the tube.     

Layer‐by‐Layer Assembly of Metal–Organic Frameworks in Macroporous Polymer Monolith and Their Use for Enzyme Immobilization

New monolithic materials comprising zeolitic imidazolate framework (ZIF‐8) located on the pore surface of poly(glycidyl methacrylate‐co‐ethylene dimethacrylate) monolith previously functionalized with N‐(3‐aminopropyl)‐imidazole have been prepared via a layer‐by‐layer self‐assembly strategy. These new ZIF‐8@monolith hybrids are used as solid‐phase carriers for enzyme immobilization. Their performance is demonstrated with immobilization of a model proteolytic enzyme trypsin. The best of the conjugates enable very efficient digestion of proteins that can be achieved in mere 43 s.

     

Self‐Assembly of a Low‐Symmetry Monodendron Containing Two Asymmetrically Linked Molecular Wedges

Herein, we describe the synthesis of a low‐symmetry monodendron, 3,4‐bis(dodecyloxy)‐5‐[3,4,5‐tris(dodecyloxy)benzyloxy]benzoic acid, following a simple route which starts from gallic acid ethyl ester and does not require any protecting groups. The self‐assembled structures formed by the compound in 3D and 2D were investigated by synchrotron X‐ray scattering and scanning force microscopy (SFM). In 3D, the compound forms a stable crystalline phase with an orthorhombic lattice in which the alkyl chains connected to different benzene rings form crystalline and amorphous domains. Upon cooling from the isotropic melt the compound exhibits a monotropic smectic mesophase. In 100‐nm‐thick films on a neutral substrate the structure loses its biaxiality, adopting a hexagonal columnar structure with the columns oriented parallel to the substrate. By contrast, in ultrathin films on graphite the SFM likely reveals two crystal orientations, which can develop due to the epitaxial adsorption on the substrate of the alkyl chains pertinent to different benzene rings.