Triblock Nanospheres with Amphiphilic Coronal Chains

Patchy Micelles with a Crystalline Core: Self-Assembly Concepts, Properties, and Applications

Crystallization-driven self-assembly (CDSA) of block copolymers bearing one crystallizable block has emerged to be a powerful and highly relevant method for the production of one- and two-dimensional micellar assemblies with controlled length, shape, and corona chemistries. This gives access to a multitude of potential applications, from hierarchical self-assembly to complex superstructures, catalysis, sensing, nanomedicine, nanoelectronics, and surface functionalization. Related to these applications, patchy crystalline-core micelles, with their unique, nanometer-sized, alternating corona segmentation, are highly interesting, as this feature provides striking advantages concerning interfacial activity, functionalization, and confinement effects. Hence, this review aims to provide an overview of the current state of the art with respect to self-assembly concepts, properties, and applications of patchy micelles with crystalline cores formed by CDSA. We have also included a more general discussion on the CDSA process and highlight block-type co-micelles as a special type of patchy micelle, due to similarities of the corona structure if the size of the blocks is well below 100 nm.

Self-assembly and morphological transitions of random amphiphilic poly(β-D-glucose-co-1-octyl) phosphazenes

The amphiphilic random copolymer poly(β-d-glucose-co-1-octyl)phosphazene (PGOP) can undergo continuous morphological transitions in DMF-water mixed solvents. In this study, the ratio of glucose moieties to octyl moieties was controlled via a two-step thiol-ene reaction. As a result, polyphosphazenes with glycosyl functionalization degrees of 58.1% (PGOP-1), 74.1% (PGOP-2) and 87.0% (PGOP-3) were obtained. These amphiphilic polyphosphazenes self-assemble in both water and water-DMF mixtures. Several self-assembled morphologies including spheres, rods and vesicles were formed though careful control of the water content (WC) in the DMF solvent as well as of the hydrophilicity or hydrophobicity of the copolymers. We also found that an increase in the hydrophobic proportion led to faster morphological transitions at a constant WC. The thermodynamics of micellization were also studied by Isothermal Titration Calorimetry (ITC), and the strong hydrophobic interactions in PGOP-1 were demonstrated by their highly exothermic nature. These self-assemblies have potential applications in biosensing, lectin adsorption and drug loading with controlled release.

Self-assembly and chemical processing of block copolymers: a roadmap towards a diverse array of block copolymer nanostructures

Block copolymers can yield a diverse array of nanostructures. Their assembly structures are influenced by their inherent structures, and the wide variety of structures that can be prepared especially becomes apparent when one considers the number of routes available to prepare block copolymer assemblies. Some examples include self-assembly, directed assembly, coupling, as well as hierarchical assembly, which can yield assemblies having even higher structural order. These assembly routes can also be complemented by processing techniques such as selective crosslinking and etching, the former technique leading to permanent structures, the latter towards sculpted and the combination of the two towards permanent sculpted structures. The combination of these pathways provides extremely versatile routes towards an exciting variety of architectures. This review will attempt to highlight destinations reached by LIU Guojun and coworkers following these pathways.

Simultaneous coating of silica particles by two diblock copolymers

Silica particles have been coated by two diblock copolymers, P1 and P2, through a one-pot reaction, and the resultant particles were characterized. The P1 and P2 used were synthesized by anionic polymerization and denote PIPSMA-b-PFOEMA and PIPSMA-b-PtBA, respectively. Here PIPSMA, PFOEMA, and PtBA correspond individually to poly[3-(triisopropyloxysilyl)propyl methacrylate], poly(perfluorooctylethyl methacrylate), and poly(tert-butyl acrylate). Catalyzed by HCl, the PIPSMA blocks of P1 and P2 co-condensed onto the surface of the same silica particles, exposing the PtBA and PFOEMA blocks. The relative amounts of grafted P1 and P2 could be tuned by changing the P1 to P2 weight ratio and were quantified by thermogravimetric analysis. The vertical segregation of the PFOEMA and PtBA chains could also be adjusted. Casting a dispersion of the coated particles in a solvent selective for either PFOEMA or PtBA onto glass plates or silicon wafers yielded films consisting of bumpy silica particles whose surfaces were enriched by the polymer that was soluble in the casting solvent. Particulate coatings with tunable surface wetting properties were obtained by changing either the proportion of grafted P1 and P2 or the casting solvent for coated silica. When a silica dispersion in perfluoromethylcychohexane (C(7)F(14)) was cast, films of coated silica that had P1 weight fractions of 25, 50, and 75% were all superhydrophobic because the particle surfaces were enriched by PFOEMA, which was selectively soluble in C(7)F(14).

Reversible cross-linking of polyisoprene coronas in micelles, block comicelles, and hierarchical micelle architectures using Pt(0)-olefin coordination

Previous work has established that polyisoprene (PI) coronas in cylindrical block copolymer micelles with a poly(ferrocenyldimethylsilane) (PFS) core can be irreversibly cross-linked by hydrosilylation using (HSiMe(2))(2)O in the presence of Karstedt's catalyst. We now show that treatment of cylindrical PI-b-PFS micelles with Karstedt's catalyst alone, in the absence of any silanes, leads to PI coronal cross-linking through Pt(0)-olefin coordination. The cross-linking can be reversed through the addition of 2-bis(diphenylphosphino)ethane (dppe), a strong bidentate ligand, which removes the platinum from the PI to form Pt(dppe)(2). The Pt(0) cross-linking of PI was studied with self-assembled cylindrical PI-b-PFS block copolymer micelles, where the cross-linking was found to dramatically increase the stability of the micellar structures. The Pt(0)-alkene coordination-induced cross-linking can be used to provide transmission electron microscopy contrast between PI and poly(dimethylsiloxane) (PDMS) corona domains in block comicelles as the process selectively increases the electron density of the PI regions. Moreover, following the assembly of a hierarchical scarf-shaped comicelle consisting of a PFS-b-PDMS platelet template with PI-b-PFS tassels, Pt(0)-induced cross-linking of the PI coronal regions allowed for the selective removal of the PFS-b-PDMS center, leaving behind an unprecedented hollowed-out scarf structure. The addition of Karstedt's catalyst to PI or polybutadiene homopolymer toluene/xylene solutions resulted in the formation of polymer gels which underwent de-gelation upon the addition of dppe.

Engineering of amphiphilic block copolymers for polymeric micellar drug and gene delivery

The use of nano-delivery systems formed through assembly of synthetic amphiphilic block copolymers (ABCs) in experimental medicine and pharmaceutical sciences is experiencing rapid development. This rapid development is driven by a crucial need in improving the performance of existing therapeutic agents, as well as the necessity for the development of advanced delivery systems for complex new entities such as genes, proteins and other cellular components. The flexibility in the construction of appropriate carriers for the delivery requirements of these complex new "drugs" offered by versatile polymer chemistry provides an undeniable advantage for polymer based nano-delivery systems compared to other colloids in this regard. With seven formulations already in different stages of clinical trials, polymeric micelles are in the front line of drug development among different ABC-based nano-carriers. The success in rapid advancement of polymeric micelles from bench to bedside is owed to the rational engineering of core/shell structure so that the polymeric micellar carrier can meet the requirements for optimum delivery of specific drug(s) in certain disease condition(s). The engineering efforts in this regard have mostly been aimed at providing efficient drug loading, micellar stabilization, and sustained and/or site specific drug release. The objective of this review is to provide an update on different engineering strategies employed to achieve optimum polymeric micellar formulations.

Mixed, multicompartment, or Janus micelles? A systematic study of thermoresponsive bis-hydrophilic block terpolymers

We present a systematic investigation of the extent of compartmentalization in micelles formed by a series of bis-hydrophilic block terpolymers with two outer water-soluble segments. The corona blocks are constructed from poly(ethylene oxide) (PEO) and the thermoresponsive poly(N-isopropyl-acrylamide) (PNiPAAm). The fraction of PNiPAAm is varied to establish its influence on the supramicellar aggregation and corona phase behavior. We demonstrate that--when the collapse of PNiPAAm is triggered--a clustering of micelles into superstructures only occurs when the contour length of the thermoresponsive block is longer than that of the PEO chains. The volume fractions play a minor role. The extent of superstructure formation increases with the amount of heating cycles, pointing to a rearrangement of micelles with a mixed corona into a phase-segregated corona. The collapse of PNiPAAm is exploited to artificially raise the incompatibility and drive phase segregation. A uniform population of biphasic Janus micelles cannot be obtained. After repeated heating cycles, the mixture consists of a range of multicompartment architectures, whose patch distribution can be derived from aggregate structures found in cryo-TEM obtained at high temperature. In the last section, we relate our results to previously studied systems and attempt to derive some generalities. First, we try to answer the question of how likely it is in terms of thermodynamics to obtain truly self-assembled Janus micelles. Furthermore, our results can provide an estimation for the volume ratio or/and block lengths required in micelles composed out of two corona blocks to induce supramicellar aggregation when a hydrophilic-to-hydrophobic phase transition is triggered in one of the blocks.

Core-shell-corona au-micelle composites with a tunable smart hybrid shell

Micelles having a core of polystyrene and a mixed shell of poly(ethylene glycol) and poly(4-vinylpyridine) were formed through self-assembly of a triblock copolymer poly(ethylene glycol)- block-polystyrene- block-poly(4-vinylpyridine) in acidic water (pH 2). Reducing the HAuCl(4)-treated micelle solution leads to the formation of the Au-micelle composites with a core of polystyrene, a hybrid shell of poly(4-vinylpyridine)/Au/poly(ethylene glycol), and a corona of poly(ethylene glycol). The gold nanoparticles with controlled sizes were anchored to poly(4-vinylpyridine) to form the physically cross-linked hybrid shell. In aqueous solution, the hybrid shell is swollen and the swollen degree is sensitive to the pH condition. Under basic conditions, the channel in the hybrid shells of the composite is produced, which renders the composites a good catalytic activity. In addition, the composites also show good stability, unchanged hydrodynamic diameter, and surface plasmon absorption under different pH conditions.

Self-organization and pattern formation of janus particles in two dimensions by computer simulations

The phase behavior and associated pattern formation of two-dimensional systems of hard disks decorated with amphiphilic coronae (Janus disks) are studied by means of Monte Carlo computer simulations. A primitive interaction potential that captures the essential interparticle interactions is introduced. Despite its simplicity, the system exhibits a very rich phase polymorphism. Apart from the isotropic phase and depending upon the coronal thickness, the simulated systems self-organize in a number of two-dimensional mesophases of various symmetries exhibiting a variety of novel patterns. The results of these simulations suggest that 2D Janus particles are promising candidates for bottom-up design of precise two-dimensional templates.

Environmentally Responsive “Hairy” Nanoparticles: Mixed Homopolymer Brushes on Silica Nanoparticles Synthesized by Living Radical Polymerization Techniques

This article reports on the preparation of environmentally responsive "hairy" nanoparticles by growth of mixed poly(tert-butyl acrylate) (PtBA)/polystyrene (PS) brushes from silica particles using living radical polymerization techniques and subsequent hydrolysis of PtBA to produce amphiphilic mixed poly(acrylic acid) (PAA)/PS brushes. Silica particles were synthesized by the Stober process and were functionalized with an asymmetric difunctional initiator-terminated monolayer. Surface-initiated atom transfer radical polymerization of tBA was carried out in the presence of a free initiator. Kinetics study showed that the polymerization was well controlled. By cleaving PtBA off the particles, the molecular weights of the grafted and free polymers were found to be essentially identical. Mixed PtBA/PS brushes were obtained by the nitroxide-mediated radical polymerization of styrene from PtBA particles. The M(n) of the grafted PS was found to be the same as that of the free PS formed in the solution from the free initiator. Amphiphilic mixed PAA/PS brush-coated nanoparticles were synthesized from mixed PtBA/PS particles by hydrolysis of PtBA with iodotrimethylsilane. Tyndall scattering experiments and (1)H NMR study showed that the mixed PAA/PS particles can be dispersed and form a stable suspension in CHCl(3), a selective solvent for PS, and also in CH(3)OH, a selective solvent for PAA, demonstrating the capability of these hairy nanoparticles to undergo chain reorganization in response to environmental changes.