Light‐Induced Reversible Self‐Assembly of Gold Nanoparticles Surface‐Immobilized with Coumarin Ligands

A novel light‐induced reversible self‐assembly (LIRSA) system is based on the reversible photodimerization and photocleavage of coumarin groups on the surface of gold nanoparticles (AuNPs) in THF solution. Facilitated by coumarin groups, light irradiation at 365 nm triggers the stable assembly of monodisperse AuNPs; the resulting self‐assembly system can be disassembled back to the disassembled state by a relatively short exposure to benign UV light. The reversible self‐assembly cycle can be repeated 4 times. A specific concentration range of coumarin ligand and the THF solvent were identified to be the two predominant factors that contribute to the LIRSA of AuNPs. This is the first successful application of reversible photodimerization based on a coumarin derivative in the field of AuNP LIRSA. This LIRSA system may provide unique opportunities for the photoregulated synthesis of many adjustable nanostructures and devices.     

Evaporation‐Driven Self‐Assembly of Colloidal Silica Dispersion: New Insights on Janus Particles

The evaporation driven self‐assembly of novel colloidal silica Janus particles was evaluated by scanning electron microscopy in comparison to unfunctionalized silica particles. The cyclodextrin‐ and azobenzene‐modified compound was obtained utilizing Pickering emulsion approach, in which the particles were immobilized on solidified wax droplets and subsequently functionalized. Silica particles were modified with 3‐aminopropyl trimethoxysilane and afterward reacted with tosyl‐β‐CD or phenylazo(benzoic acid), respectively. Mesoscopic structures of the colloidal dispersions, as dried films from aqueous solution, have been investigated by scanning electron microscopy and dynamic light scattering. Interestingly, it has been observed that the Janus particles show a significantly different evaporation‐induced assembly than the unmodified particles.     

Single‐step process to produce functionalized multiresponsive polymeric particles

Monodisperse functional multiresponsive particles were prepared by encapsulation of an amphiphilic diblock copolymer during the precipitation polymerization of polystyrene and divinylbenzene in one single step. The amphiphilic diblock copolymer employed throughout this study, polystyrene‐b‐poly (dimethylaminoethyl methacrylate) (PS‐b‐PDMAEMA) has been synthesized by ATRP in two consecutive polymerization steps. After encapsulation of the block copolymer within the microsphere, the surface modification of the particle occurs spontaneously upon exposure to water by surface segregation of the hydrophilic PDMAEMA block, thus without any additional post‐polymerization and/or chemical modification steps. The response of the functionalized particles both to pH and temperature was analyzed by potential zeta and DSC measurements. Upon dispersion of the particles in acidic media, the PDMAEMA block in its charged state is soluble and does not exhibit any change by heating. At higher pH values and temperatures above 35 °C (Low Critical Solubility Temperature of the PDMAEMA block) the hydrophilic segment collapses as detected by differential scanning calorimetry. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3523–3533, 2010     

Combination of Episulfide Ring‐Opening Polymerization With ATRP for the Preparation of Amphiphilic Block Copolymers

We report for the first time the combination of ATRP and ring‐opening episulfide polymerization as a means to synthesize polysulfide‐based low‐dispersity amphiphilic block copolymers. The most significant finding is the possibility to perform ATRP under mild conditions using poly(propylene sulfide) macroinitiators, apparently without any significant copper sequestration by the polysulfides. Using glycerol monomethacrylate (GMMA) as a hydrophilic monomer, the polymers self‐assembled in colloidal structures with a morphology depending on the PS/GMMA ratio, but also probably on GMMA degree of polymerization. We here also present a new AFM‐based method to calculate the average number of amphiphilic macromolecules per micelle.     

Preparation of non‐spherical particles from amphiphilic block copolymers

Simple self‐assembly techniques to fabricate non‐spherical polymer particles, where surface composition and shape can be tuned through temperature and the choice of non‐solvents was developed. A series of amphiphilic polystyrene‐b‐poly(2‐ethyl‐2‐oxazoline) block copolymers were prepared and through solvent exchange techniques using varying non‐solvent composition a range of non‐spherical particles were formed. Faceted phase separated particles approximately 300 nm in diameter were obtained when self‐assembled from tetrahydrofuran (THF) into water compared with unique large multivesicular particles of 1200 nm size being obtained when assembled from THF into ethanol (EtOH). A range of intermediate structures were also prepared from a three part solvent system THF/water/EtOH. These techniques present new tools to engineer the self‐assembly of non‐spherical polymer particles. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 750–757     

Mimicking Biological Membranes with Programmable Glycan Ligands Self‐Assembled from Amphiphilic Janus Glycodendrimers

An accelerated modular synthesis produced 18 amphiphilic Janus glycodendrimers with three different topologies formed from either two or one carbohydrate head groups or a mixed constellation with a noncarbohydrate hydrophilic arm. By simple injection of their THF solutions into water or buffer, all of the Janus compounds self‐assembled into uniform, stable, and soft unilamellar vesicles, denoted glycodendrimersomes. The mixed constellation topology glycodendrimersomes were demonstrated to be most efficient in binding plant, bacterial, and human lectins. This evidence with biomedically relevant receptors offers a promising perspective for the application of such glycodendrimersomes in targeted drug delivery, vaccines, and other areas of nanomedicine.     

Engineering Surface Patterning of Colloidal Rings through Plateau–Rayleigh Instability

Plateau–Rayleigh (P‐R) instability occurring on Brownian colloidal particles is presented. This instability can be used for the surface patterning of Brownian colloidal rings. This idea was realized by employing polystyrene(PS)/SiO₂ core/shell rings, for which PS layer was selectively grown onto the interior surface of SiO₂ rings. The P‐R instability was initiated in the ring's dispersion by adding a good solvent of PS. By using both experiments and theory, it is shown that the number of patches is tunable and that it is linearly related to a function of two variables, namely, solvent quantity and contact angle. In particular, one‐patch Janus rings and patchy disks were also synthesized at high yields. The patch size of all particles is tunable by step‐by‐step polymerization and the patches can be functionalized, for example by ATRP grafting with pH‐sensitive polymers. This approach can be adapted for the synthesis of other patchy colloids with designated complexity.     

Directed Self‐Assembly Pathways of Active Colloidal Clusters

Despite the mounting interest in synthetic active particles, too little is known about their assembly into higher‐order clusters. Here, mixing bare silica particles with Janus particles that are self‐propelled in electric fields, we assemble rotating chiral clusters of various sorts, their structures consisting of active particles wrapped around central “hub” particles. These clusters self‐assemble from the competition between standard energetic interactions and the need to be stable as the clusters rotate when the energy source is turned on, and fall apart when the energy input is off. This allows one to guide the formation of intended clusters, as the final structure depends notably on the sequence of steps in which the clusters form.     

In-situ polymerization at the interfaces of micelles: a "grafting from" method to prepare micelles with mixed coronal chains

Herein we describe a new strategy for producing micelles with mixed coronal chains. This method involves attachment of an atom transfer radical polymerization (ATRP) initiator at the interface of a micelle and preparation of poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA) brushes at the interface by a "grafting from" method. Poly(ethylene glycol)- block-polystyrene (PEG- b-PS) diblock copolymer was achieved by ATRP. After the sulfonation reaction PS blocks were partly sulfonated. In aqueous solution at low pH the sulfonated block copolymer self-assembled into micelles with PS cores and PEG coronae and sodium 4-styrenesulfonate groups were distributed at the interfaces of the micelles. An ATRP initiator consisting of a quaternary ammonium salt moiety and a 2-bromo-2-methyl propionate moiety was ion exchanged onto the interface of the micelle. ATRP of DMAEMA was initiated at the interface, and micelles with PEG/PDMAEMA mixed coronal chains were prepared by ATRP. The structures of the micelles were characterized by dynamic light scattering (DLS), transmission electron microscopy (TEM), and zeta potential measurements. The size and morphology of the micelles were controlled by pH in aqueous solution. At high pH, PDMAEMA brushes collapse, forming nanodomains on the surface of the micelles. PDMAEMA brushes in the coronae of the micelles could be used as a template for preparation of gold nanoparticles.     

Polystyrene‐Core–Silica‐Shell Hybrid Particles Containing Gold and Magnetic Nanoparticles

Polystyrene‐core–silica‐shell hybrid particles were synthesized by combining the self‐assembly of nanoparticles and the polymer with a silica coating strategy. The core–shell hybrid particles are composed of gold‐nanoparticle‐decorated polystyrene (PS‐AuNP) colloids as the core and silica particles as the shell. PS‐AuNP colloids were generated by the self‐assembly of the PS‐grafted AuNPs. The silica coating improved the thermal stability and dispersibility of the AuNPs. By removing the “free” PS of the core, hollow particles with a hydrophobic cage having a AuNP corona and an inert silica shell were obtained. Also, Fe₃O₄ nanoparticles were encapsulated in the core, which resulted in magnetic core–shell hybrid particles by the same strategy. These particles have potential applications in biomolecular separation and high‐temperature catalysis and as nanoreactors.     

Poly(dimethylaminoethyl methacrylate)‐b‐poly(hydroxypropyl methacrylate) copolymers: Synthesis and pH/thermo‐responsive behavior in aqueous solutions

The synthesis and self‐assembly properties in aqueous solutions of novel amphiphilic block copolymers composed of one hydrophilic, pH and temperature responsive poly(dimethyl amino ethyl methacrylate) (PDMAEMA) block and one weakly hydrophobic, water insoluble, potentially thermoresponsive poly(hydroxy propyl methacrylate) (PHPMA) block, are reported. The block copolymers were prepared by RAFT polymerization and were molecularly characterized by size exclusion chromatography, NMR, and FTIR spectroscopies. The PDMAEMA‐b‐PHPMA amphiphilic block copolymers self‐assemble in different nanostructured aggregates when inserted in aqueous media. The effects of different solubilization protocols, as well as the effects of solution temperature and pH on the structure of the aggregates, are studied by light scattering and fluorescence spectroscopy measurements. Experimental results indicate that there is a number of solution preparation and physicochemical parameters that allow the control and manipulation of the structure and thermoresponsive properties of PDMAEMA‐b‐PHPMA aggregates in aqueous media. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 1962–1977     

Peptide‐poly(2‐(dimethylamino)ethyl methacrylate) conjugates: Synthesis and aqueous/nonaqueous self‐aggregation into nanostructures of dendritic and spherical morphologies

Peptide–polymer conjugate consisting of a sequence‐defined tripeptide and poly(2‐(dimethylamino)ethyl methacrylate) (PDMAEMA) is synthesized by a simple “grafting from” atom transfer radical polymerization (ATRP) approach. The ATRP of PDMAEMA using peptide‐macroinitiator and CuBr/1,1,4,7,10,10‐hexamethyltriethylenetetramine system in anisole follows pseudo first order kinetics up to a conversion of about 25% within a time span of 125 min. The attachment of peptide moiety at the end of PDMAEMA chain is confirmed from MALDI‐TOF‐MS and circular dichroism analyses. The self‐assembly of as‐synthesized peptide‐PDMAEMA conjugate in organic solvents leads to the formation of spherical nanoparticles as observed through FESEM. Peptide‐PDMAEMA conjugate become soluble in water due to the protonation of the pendent —N(CH₃)₂ moiety of DMAEMA group of the conjugate. Owing to the amphiphilic nature of the protonated conjugate (peptide‐PDMAEMAH), it also undergoes self‐aggregation in water into nanostructures of various morphologies such as dendrite, small sphere and large sphere at pHs of 2, 8, and 10, respectively. Peptide‐PDMAEMA‐IBu conjugate obtained by the post‐modification of —N(CH₃)₂ moiety of DMAEMA group of the conjugate with n‐butylbromide also undergoes self‐aggregation into dendritic nanostructures in water. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 3286–3297     

Polyoxometalate‐Engineered Building Blocks with Gold Cores for the Self‐Assembly of Responsive Water‐Soluble Nanostructures

The controlled assembly of gold nanoparticles (AuNPs) with the size of quantum dots into predictable structures is extremely challenging as it requires the quantitatively and topologically precise placement of anisotropic domains on their small, approximately spherical surfaces. We herein address this problem by using polyoxometalate leaving groups to transform 2 nm diameter gold cores into reactive building blocks with hydrophilic and hydrophobic surface domains whose relative sizes can be precisely tuned to give dimers, clusters, and larger micelle‐like organizations. Using cryo‐TEM imaging and ¹H DOSY NMR spectroscopy, we then provide an unprecedented “solution‐state” picture of how the micelle‐like structures respond to hydrophobic guests by encapsulating them within 250 nm diameter vesicles whose walls are comprised of amphiphilic AuNP membranes. These findings provide a versatile new option for transforming very small AuNPs into precisely tailored building blocks for the rational design of functional water‐soluble assemblies.     

Self‐Assembly of Fullerene‐Based Janus Particles in Solution: Effects of Molecular Architecture and Solvent

Two molecular Janus particles based on amphiphilic [60]fullerene (C₆₀) derivatives were designed and synthesized by using the regioselective Bingel–Hirsh reaction and the click reaction. These particles contain carboxylic acid functional groups, a hydrophilic fullerene (AC₆₀), and a hydrophobic C₆₀ in different ratios and have distinct molecular architectures: 1:1 (AC₆₀–C₆₀) and 1:2 (AC₆₀–2C₆₀). These molecular Janus particles can self‐assemble in solution to form aggregates with various types of micellar morphology. Whereas vesicular morphology was observed for both AC₆₀–C₆₀ and AC₆₀–2C₆₀ in tetrahydrofuran, in a mixture of N,N‐dimethylformamide (DMF)/water, spherical micelles and cylindrical micelles were observed for AC₆₀–C₆₀ and AC₆₀–2C₆₀, respectively. A mechanism of formation was tentatively proposed based on the effects of molecular architecture and solvent polarity on self‐assembly.     

Synthesis of Linear ABC Triblock Copolymers and Their Self‐Assembly in Solution

The self‐assembly of amphiphilic block copolymers has attracted the interest of a large number of research groups in the past two decades. Many examples have been reported using AB diblock copolymers, but the self‐assembly becomes more complex and shows a greater variety if ABC triblock copolymers are used. However, the synthesis of the polymer becomes more demanding since end‐group modifications or chain extensions become necessary. Using various kinds of polymerization techniques, pure triblock copolymers have been reported and their synthesis is covered in this review. Following the synthesis, a detailed and thorough analysis of the self‐assembly behaviour is the next step. We have selected promising and well characterized examples to show the range of self‐assembled structures possible, covering novel shapes of micelles but also polymersomes with an asymmetric membrane. Our selection of current examples in literature show the challenges and chances associated with amphiphilic ABC triblock copolymers.     

Synthesis of poly(tetrahydrofuran)‐b‐polystyrene block copolymers from dual initiators for cationic ring‐opening polymerization and atom transfer radical polymerization

A dual initiator (4‐hydroxy‐butyl‐2‐bromoisobutyrate), that is, a molecule containing two functional groups capable of initiating two polymerizations occurring by different mechanisms, has been prepared. It has been used for the sequential two‐step synthesis of well‐defined block copolymers of polystyrene (PS) and poly(tetrahydrofuran) (PTHF) by atom transfer radical polymerization (ATRP) and cationic ring‐opening polymerization (CROP). This dual initiator contains a bromoisobutyrate group, which is an efficient initiator for the ATRP of styrene in combination with the Cu(0)/Cu(II)/N,N,N′,N″,N″‐pentamethyldiethylenetriamine catalyst system. In this way, PS with hydroxyl groups (PS‐OH) is formed. The in situ reaction of the hydroxyl groups originating from the dual initiator with trifluoromethane sulfonic anhydride gives a triflate ester initiating group for the CROP of tetrahydrofuran (THF), leading to PTHF with a tertiary bromide end group (PTHF‐Br). PS‐OH and PTHF‐Br homopolymers have been applied as macroinitiators for the CROP of THF and the ATRP of styrene, respectively. PS‐OH, used as a macroinitiator, results in a mixture of the block copolymer and remaining macroinitiator. With PTHF‐Br as a macroinitiator for the ATRP of styrene, well‐defined PTHF‐b‐PS block copolymers can be prepared. The efficiency of PS‐OH or PTHF‐Br as a macroinitiator has been investigated with matrix‐assisted laser desorption/ionization time‐of‐flight spectroscopy, gel permeation chromatography, and NMR. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 3206–3217, 2003     

Pickering乳液模板法制备Janus粒子

本文以SiO₂粒子稳定的水包油(O/W)型Pickering乳液作为模板, 在乳液连续相进行SI-ATRP, 将聚合物刷接枝到SiO₂粒子外半表面, 破乳得到半修饰的Janus粒子.     

End‐to‐End Self‐Assembly of Semiconductor Nanorods in Water by Using an Amphiphilic Surface Design

One‐dimensional (1D) self‐assemblies of nanocrystals are of interest because of their vectorial and polymer‐like dynamic properties. Herein, we report a simple method to prepare elongated assemblies of semiconductor nanorods (NRs) through end‐to‐end self‐assembly. Short‐chained water‐soluble thiols were employed as surface ligands for CdSe NRs having a wurtzite crystal structure. The site‐specific capping of NRs with these ligands rendered the surface of the NRs amphiphilic. The amphiphilic CdSe NRs self‐assembled to form elongated wires by end‐to‐end attachment driven by the hydrophobic effect operating between uncapped NR ends. The end‐to‐end assembly technique was further applied to CdS NRs and CdSe tetrapods (TPs) with a wurtzite structure.     

Synthesis,characterization, and self‐assembly of comb‐dendronized amphiphilic block copolymers

Novel amphiphilic comb‐dendronized diblock copolymers composed of hydrophobic Percec‐type dendronized polystyrene block and hydrophilic comb‐like poly(ethylene oxide) grafted polymethacrylate P(PEOMA) block were designed and synthesized via two steps of atom transfer radical polymerization (ATRP). The comb‐like P(PEOMA) prepared by ATRP of macromonomers (PEOMA) with two different molecular weights (M_n = 300 and 475) were used to initiate the sequent ATRP of dendritic styrene macromonomer (DS). The molecular weights and compositions of the obtained block copolymers were determined by ¹H NMR analysis. The copolymers with relatively narrow polydispersities (1.27–1.38) were thus obtained. The bulk properties of comb‐dendronized block copolymers were studied by using differential scanning calorimetry, polarized optical microscopy and wide‐angle X‐ray diffraction (WAXD). Similar to dendronized homopolymers, the block copolymers exhibited hexagonal columnar liquid‐crystalline phase structure. By using such amphiphilic comb‐dendronized block copolymers as building blocks, the rich self‐assembly morphologies, such as twisted string, vesicle, and large compound micelle (LCM), were obtained in a mixture of CH₃OH and THF. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4205–4217, 2008     

Supramolecular Self‐Assembly of Polymer‐Functionalized Carbon Nanotubes on Surfaces

Summary: Supramolecular self‐assembly of poly(methyl methacrylate)‐grafted multiwalled carbon nanotubes (MWNT‐g‐PMMA) was reported herein. The MWNT‐g‐PMMA (85 wt.‐% PMMA) dispersed in tetrahydrofuran could self‐assemble into suprastructures on surfaces such as gold, mica, silicon, quartz, or carbon films. With decreasing concentration of the MWNT‐g‐PMMA from 3 to 0.1 mg · mL⁻¹, the assembled structures changed from cellular and basketwork‐like forms to multilayer cellular networks and individual needles. SEM, AFM, and TEM measurements confirmed the morphology of the assembled suprastructures, and revealed the assembly mechanism. Phase separation during evaporation of the solvent drives the MWNT‐g‐PMMA nanohybrids to assemble and form the suprastructures, and the rigid MWNTs stabilize the structures.

SEM images of self‐assembled suprastructures of basketwork (a), cellular network (b), and needles (c) from the THF solution of the PMMA‐grafted MWNTs on gold surface.