Corona Chains Research Articles

Planar Multilayer Assemblies Containing Block Copolymer Aggregates

The design, preparation, and properties of planar multilayer structures composed of various combinations of sequentially deposited polyelectrolyte (PE) chains and self-assembled layers of individual block copolymer aggregates (vesicles, micelles, or large compound micelles (LCMs)) are described. The aggregates contain negatively or positively charged corona chains while the PE multilayers contain alternating polyanionic or polycationic chains deposited on silicon wafers. The final structures consist of combinations of layers of various charged species: multilayers of alternating PEs of poly(allyl hydrochloride) (PAH) and poly(acrylic acid) (PAA) as well as vesicles, micelles, or large compound micelles of ionized poly(styrene)-b-poly(4-vinylpyridine) (PS-b-P4VP) or of poly(styrene)-b-poly(acrylic acid) (PS-b-PAA). Two types of layer-by-layer (LbL) multilayer structures were studied: individual aggregate layers sandwiched between PE multilayers and layers of individual aggregates of various morphologies and of different corona chain charges, deposited on top of each other without intermediate multilayers or individual layers of PEs. The strong interactions between the successive layers are achieved mainly by electrostatic attraction between the oppositely charged layers. The planar LbL multilayers containing block copolymer aggregates could, potentially, be used as carriers for multiple functional components; each aggregate layer could be loaded with hydrophobic (in the core of the micelles, LCMs, or vesicle walls) or hydrophilic functional molecules (in the vesicular cavities). The overall thickness of such planar LbL multilayers can be controlled precisely and can vary from tens of nanometers to several micrometers depending on the number of layers, the sizes of the aggregates, and the complexity of the structure.

Thermo-responsive properties of metallo-supramolecular block copolymer micellar hydrogels

Metallo-supramolecular micellar hydrogels exhibiting thermo-mechanical responsiveness are prepared through the hierarchical assembly of a heterotelechelic associating copolymer. The copolymer consists of a linear thermo-sensitive water-soluble sequence terminated by a short hydrophobic sticker at one end, the other being functionalized by a chelating ligand. As the first level of assembly, the associating copolymer is dissolved in aqueous solution to yield micellar nanostructures, bearing coordinative motifs at the end of the coronal chains. The second level of assembly is achieved when transition metal ions are added to the micellar solutions, resulting in almost instantaneous gelation. The thermo-mechanical response of those materials is investigated in detail by rotational rheometry, showing abrupt changes within the temperature boundaries corresponding to the phase transition of the polymer block located in the micellar corona.

PH-responsive layer-by-layer films of zwitterionic block copolymer micelles

We report a strategy to incorporate micelles of poly[3-dimethyl (methacryloyloxyethyl) ammonium propane sulfonate]-block-poly[2-(diisopropylamino)ethyl methacrylate] (βPDMA-b-PDPA) into electrostatic layer-by-layer (LbL) films. We obtained micelles with pH-responsive PDPA-cores and zwitterionic βPDMA-coronae at pH 8.5 through pH-induced self-assembly of βPDMA-b-PDPA in aqueous solution. To incorporate βPDMA-b-PDPA micelles into LbL films, we first obtained a net electrical charge on βPDMA-coronae. Negative charges of the zwitterionic units were screened through complexation of βPDMA-b-PDPA micelles and poly(allylamine hydrochloride) (PAH). Positively charged micellar complexes were then self-assembled at the surface using poly(sodium 4-styrenesulfonate) (PSS). The pH-stability of the multilayers was examined by exposing the films to decreasing pH values. Despite the disintegration of micellar complexes below pH 7, no change in film thickness was recorded between pH 8.5 and 3.5. Only ∼20% of the film released at pH < 3.5. Moreover, we demonstrated that when multilayers were exposed to decreasing pH at a temperature below the upper critical solution temperature (UCST) of betainized coronal chains, the film thickness increased by 20% between pH 4.5 and 3. This is probably due to phase separation of the corona block and formation of voids within the film, probably entrapping water molecules within the multilayers. Decreasing temperature also shifted the critical disintegration pH (onset of multilayer dissolution) to a slightly lower pH. By taking advantage of the pH-responsive cores, we showed that multilayers were capable of releasing functional molecules under moderately acidic conditions. Important biological properties of polybetaines, higher loading capacity of zwitterionic block copolymer micelles than linear polybetaines and pH-response of the multilayers at physiologically related pH values make such films promising for biomedical applications.

Robust amphiphobic coatings from bi-functional silica particles on flat substrates

Robust oil- and water-repellent or amphiphobic particulate coatings were prepared from epoxy glue and bi-functional silica particles bearing poly(2-perfluorooctylethyl methacrylate) (PFOEMA) and poly(acrylic acid) (PAA) coronal chains. To prepare the particles, silica was first co-grafted in a one-pot process by poly[3-(triisopropyloxysilyl)propyl methacrylate]-block-poly(2-perfluorooctylethyl methacrylate) (PIPSMA-b-PFOEMA or P1) and poly[3-(triisopropyloxysilyl)propyl methacrylate]-block-poly(tert-butyl acrylate) (PIPSMA-b-PtBA or P2). P1 and P2 grafted onto silica because of the sol–gel reactions between the surface silanol groups of silica and the PIPSMA blocks of the two polymers. The sol–gel reactions also occurred between the different PIPSMA blocks of P1 and P2, resulting in a crosslinked anchoring PIPSMA layer. This layer was topped by the PFOEMA and PtBA chains. Cleavage of the tert-butyl groups of the PtBA chains yielded PAA corona chains. The particles bearing both PAA and PFOEMA could be dispersed in trifluorotoluene and sprayed onto an epoxy film that was partially cured on a glass plate to yield a rough particulate coating. The curing of the particles with the glue at 120 °C for 30 min bonded the AA units and the glycidyl groups of the epoxy glue and exposed the low-surface-tension PFOEMA chains. At P1 mass fraction of f1 ≥ 80% relative to P1 and P2, the coatings were superhydrophobic and repelled diiodomethane strongly. Furthermore, the coatings resisted trifluorotoluene extraction and abrasion tests if the PAA chains existed in sufficient amounts with P2 weight fraction (f2) ≥ 5%.

Superhydrophobic Hierarchically Assembled Films of Diblock Copolymer Hollow Nanospheres and Nanotubes

Reported are the formation of rough particulate films from cross-linked diblock copolymer vesicles and nanotubes and the wetting properties of the resultant films. The diblock copolymers used were F66M200 and F95A135, where the subscripts denote the repeat unit numbers, whereas M, A, and F denote poly(2-cinnamoyloxyethyl methacrylate), poly(2-cinnamoyloxyethyl acrylate), and poly(2,2,2-trifluoroethyl methacrylate), respectively. The precursory polymers to F66M200 and F95A135 were prepared by atom transfer radical polymerization. In 2,2,2-trifluoroethyl methacrylate (FEMA), a selective solvent for F, vesicles and tubular micelles were prepared from F66M200 and F95A135, respectively. Photo-cross-linking the M and A blocks of these aggregates yielded hollow nanospheres and nanotubes bearing F coronal chains. These particles were dispersed into CH2Cl2/methanol, where CH2Cl2 was a good solvent for both blocks and methanol was a poor solvent for F. Casting CH2Cl2/methanol dispersions of these particles yielded films consisting of hierarchically assembled diblock copolymer nanoparticles. For example, the hollow nanospheres fused into microspheres bearing nanobumps after being cast from CH2Cl2/methanol at methanol volume fractions of 30 and 50%. The roughness of these films increased as the methanol volume fraction increased. The films that were cast at high methanol contents were superhydrophobic, possessing water contact angles of ∼160° and water sliding angles of ∼3°.

Enhanced Photoluminescence from Micellar Assemblies of Cadmium Sulfide Quantum Dots and Gold Nanoparticles

We report the preparation and characterization of well-defined hierarchically structured colloidal assemblies, consisting of a block copolymer micelle with a single photoluminescent cadmium sulfide (CdS) quantum dot (QD) in the core and various numbers of gold nanoparticles (GNPs, between 0.001 and 0.077 GNPs per micelle) chemically bonded to thiol groups at the terminus of the micelle coronal chains. These assemblies were prepared from tetrablock copolymer chains, poly(acrylic acid)-b-polystyrene-TTC-polystyrene-b-poly(acrylic acid) (PAA-b-PS-TTC-PS-b-PAA), where TTC represents a single trithiocarbonate group, synthesized using reversible addition–fragmentation chain transfer polymerization. The block copolymer chains were first self-assembled in 1,4-dioxane by adding cadmium acetate to form flower-like micelles, followed by templated synthesis of CdS QDs in the micelle cores. Then, the TTC groups in the micelle coronae were reductively transformed into thiol groups, which bonded to added GNPs. In the final structures, each GNP was anchored at a distance of a single solubilized PS block (∼20 nm) away from a CdS QDs. This precise spacing between QDs and GNPs prevented any quenching of QD photoluminescence (PL) by the colloidal metal and instead led to an apparent enhancement of QD PL emission relative to QD emission from micelles without GNPs. The observed enhancement increased as the number of GNPs per micelle increased, with a maximum observed emission amplification (EA) of ∼8 times the PL intensity in the absence of GNPs. The EA was also found to increase as the excitation wavelength increased toward the spectral region of the surface plasmon resonance of the GNPs. Lifetime measurements revealed no significant difference between QD emission lifetimes in the absence and presence of GNPs. These results suggest a mechanism of PL enhancement via an excitation antenna effect associated with proximal GNP surface plasmons.

Nanoparticle encapsulation in thin film micellar structures: a physical method for functional materials design

We investigate the confinement of gold nanoparticles, onto which poly(2-vinylpyridine) (P2VP) are end-tethered, within diblock copolymer polystyrene-b-poly(2-vinylpyridine) (PS-b-P2VP) micelles in a polystyrene (PS) host. The micellar nanocomposites were prepared by spin casting mixtures of the nanoparticles, the copolymer and the homopolymer chains onto a substrate, to form films approximately 110 nm thick. The samples were then annealed above the glass transitions of the polymers, resulting in the formation of spherical micelles, composed of inner cores of the P2VP segments and outer coronas comprising the PS blocks, throughout the PS homopolymer thin film host. All nanoparticles were encapsulated within micelle cores; on average each micelle contains one, or no, nanoparticle. The micelles exhibited a strong tendency to self-organize at interfaces when the PS homopolymer chain length is large compared to the PS corona chain length; they otherwise remain distributed throughout the film. In comparison to pure PS-b-P2VP/PS blends, the nanoparticle/PS-b-P2VP/PS blends contain a higher density of, on average, smaller micelles. This sample fabrication procedure is straightforward and compliments the current “toolbox” used to create functional materials from block copolymer–nanoparticle systems.

Interfacial activity of patchy worm-like micelles

The interfacial activity of self-assembled worm-like crystalline-core micelles (wCCMs) with a patchy polystyrene/poly(methyl methacrylate) (PS/PMMA) corona and a semi-crystalline polyethylene (PE) core is studied at the toluene–water interface. Strikingly, the interfacial activity is comparable to that of Janus cylinders with well-separated PS/PMMA hemishells and comparable length. From this finding an adaptation of the corona chains of the patchy wCCMs to the toluene–water interface is proposed.

Thermo-responsive metallo-supramolecular gels based on terpyridine end-functionalized amphiphilic diblock copolymers

ABSTRACTA thermo-responsive hydrogel was prepared on the basis of terpyridine endfunctionalized polystyrene-block-poly(N-isopropylacrylamide) diblock copolymer. As a first level of assembly, the copolymer was dissolved in a selective solvent to yield micelles bearing terpyridine ligands at the extremity of the coronal chains. The second level of self-assembly was triggered upon addition of metal ions to the micellar solution. Mechanical properties of the accordingly obtained micellar gel were finally characterized by rotational rheometry, below and above the lower critical solution temperature.

Pressure Jump Kinetics of Disorder to BCC Ordering in Diblock Copolymer Micelles in a Selective Solvent

We present time-resolved small-angle X-ray scattering (SAXS) measurements of the kinetics of a barotropic disorder–order transition in polystyrene–polyisoprene (SI) diblock micelles in diethyl phthalate (DEP), a styrene selective solvent. Because of the fast equilibration in a pressure jump we were able to observe the initial induction stage during which the short-range order of the micellar fluid increases, followed by a sharp first-order nucleation and growth of the BCC phase and eventual late stage coarsening. The time evolution of intensity from individual diffraction spots of a crystallite was obtained from the analysis of 2-dimensional SAXS patterns and shows late stage power-law growth. The time evolution of the SAXS intensity profiles was analyzed by fitting the contribution to the scattering from the ordered Bragg peaks by Gaussians and analyzing the contribution to the scattering from the disordered micellar liquid in terms of the Percus–Yevick interacting hard-sphere model. The time evolution of the micellar structural parameters obtained from this analysis reveals that the disorder to order transition occurs when the volume fraction of micelles reaches 0.53, and the effective hard sphere radius and volume fraction of micelles increases upon ordering while the core radius is unaffected. In both the ordered and disordered states the hard sphere radius and volume fraction of micelles increase with increasing pressure indicating increased swelling of the micellar corona. In the ordered state there is considerable penetration of the corona chains from neighboring micelles.

Rheo-Optical Study of Viscoelastic Relaxation Modes in Block Copolymer Micellar Lattice System

Dynamic birefringence and viscoelasticity of a diblock copolymer micellar solution were measured in order to clarify the molecular origin of viscoelastic response of the macrolattice structure formed by micelles. The complex strain-optical ratio changed its sign with angular frequency ω and exhibited very complicated ω dependence, suggesting that the stress emerged/relaxed through several mechanisms. With an assumption of the stress-optical rule for each mechanism, the complex shear modulus was separated into four components corresponding, from high to low ω, to the reorientation of corona chains, reorientation of core chains, deformation of core, and deformation of the micellar lattice. Values of the stress optical coefficients for respective components lent support to these assignments.

Hydrogen-bonded multilayers of micelles of a dually responsive dicationic block copolymer

We report the fabrication of hydrogen-bonded multilayers of micelles of a dually responsive, dicationic block copolymer, poly[2-(N-morpholino)ethyl methacrylate-block-2-(diisopropylamino)ethyl methacrylate] (PMEMA-b-PDPA). By taking advantage of the difference in the hydrophilicity of PMEMA and PDPA blocks, micelles with a PMEMA-corona and a PDPA-core were obtained above pH 6.5 and were assembled layer-by-layer at the surface with tannic acid (TA) at pH 7.4 through hydrogen bonding interactions between morpholino units of PMEMA and hydroxyl groups of TA. Destruction of PMEMA-b-PDPA micelles/TA films could be controlled at both acidic and basic conditions. At basic pH (pH = 8.75), multilayers disintegrated due to ionization of TA and disruption of hydrogen bonding interactions between layers of micelles and TA. At moderately acidic pH values, partially dissolved PMEMA-b-PDPA micelles and monomers underwent a restructuring with TA molecules and remained adsorbed at the surface. Complete dissolution of the multilayers occurred at around pH 3.6 due to further protonation of the tertiary amino groups on both blocks of PMEMA-b-PDPA, resulting in a charge imbalance between PMEMA-b-PDPA and TA layers followed by disintegration of the films. We have also encapsulated pyrene in the micellar cores and found that pyrene released from PMEMA-b-PDPA micelles/TA films increased 1.5- and 2.5-fold when the pH was decreased from 7.5 to 6 and 5, respectively. Such an increase in the amount of pyrene released was due to pH-controlled dissolution of the micellar cores. We have also found that at pH 7.5, increasing the temperature to 40 °C enhanced the release of pyrene by approximately 2-fold. Such an increase is due to lower critical solution temperature (LCST) behaviour of coronal PMEMA chains leading to temperature-induced conformational changes on the coronal chains, facilitating the release of pyrene through the coronal chains into the solution. Hydrogen bonded multilayers of micelles of a dicationic block copolymer are interesting due to the response of both multilayers and micellar cores at different pH paving the way for multiple pH-controlled delivery of functional molecules from surfaces.

Morphological transition of triblock copolymer cylindrical micelles responding to solvent change

Reported is the morphological transition of micelles of a BCA triblock copolymer after the solvation medium was changed from one that was selective for B and A to one that was selective for A only. Here B, C, and A denote poly(tert-butyl acrylate), poly(2-cinnamoyloxyethyl methacrylate), and the amine-bearing poly(N,N-dimethylaminoethyl methacrylate) blocks respectively. In methanol, BCA formed cylindrical micelles with the insoluble C block as the core and the soluble A and B blocks as the corona. Adding water reduced the solubility of the B coronal chains. The micellar morphological evolution was followed using transmission electron microscopy (TEM) by analyzing samples, which were taken at different times after water addition to the water volume fractions (fw) of 2.7% and 10.7%, respectively. Also reported are the stabilized morphologies of the micelles formed in methanol/water mixtures with fw ranging from 2.9% to 23%.

Dynamic birefringence and non-linear rheology of diblock copolymer micellar solutions

Dynamic viscoelasticity, dynamic birefringence, and non-linear rheology of styrene–ethylenepropylene diblock copolymer, SEP, in isotridecyl isononanoate solution were examined in order to clarify the rheology–structure relationship for block copolymer micellar solutions. SAXS experiments at room temperature indicated formation of the BCC super-lattice of the micelles, composed of S chain core and EP chain corona. The complex strain-optical coefficient, being the complex ratio of birefringence to strain in dynamic measurements, changed its sign with angular frequency, ω, and exhibited a very complicated ω dependence, indicating that the stress relaxed through several relaxation mechanisms. Assuming the stress-optical rule for each mechanism, the complex shear modulus was separated into three components. The three components could be assigned to the reorientation of corona chains, reorientation of core chains, and deformation of the lattice. Steady shear viscosity, η, showed strong thinning behavior. Shear rate dependence of η and the first normal stress difference were described well with the BKZ constitutive equation composed of the above three mechanisms having different damping parameters.

Synthesis, characterization, micellization and metal coordination polymerization of pentacyanoferrate-coordinated block copolymers for monodispersed soluble Prussian blue nanospheres

Monodispersed soluble prussian blue (PB) metal-coordination nanospheres are synthesized via a confined metal coordination polymerization within the cores of block copolymer micelles. Pentacyanoferrate-coordinated block copolymers of P(4VPFe-co-4VP)-b-PDMA (P4VPFe: pentacyanoferrate coordinated poly(4-vinylpyridine); PDMA: poly(dimethylacrylamide)) were synthesized through a ligand exchange reaction of [Fe(CN)5NH3]3− with pyridyl moieties in P4VP-b-PDMA. The polymers were isolated and characterized using UV-Vis, FT-IR, NMR and elemental analysis. In H2O/EtOH, selective solvents for PDMA, the polymers self-assembled into monodispersed nanospheres with P(4VPFe-co-4VP) forming cores and PDMA acting as the corona. Subsequent metal coordination polymerization of Fe3+ with ferrate confined within the cores of the micelles led to monodispersed PB nanospheres as confirmed by DLS, TEM, HRTEM and SEM. The particles are soluble both in water and organic solvents as a result of the robust solubility of PDMA corona chains. Several parameters, including the solvent used, the concentration of the block copolymers, the amount of FeCl3 added and the amount of water involved in the systems, have been found to be important in order to obtain well-defined monodispersed PB nanospheres.

Layer-by-layer films of stimuli-responsive block copolymer micelles

The recently introduced approach of using stimuli-responsive block copolymer micelles (BCMs) as building blocks for layer-by-layer (LbL) assemblies has greatly enhanced the functionality of LbL films. Responsive BCMs supply films with hydrophobic ‘pockets’ that can be ‘opened’ through external triggers. This is enabled by the use of amphiphilic polymers as constituents of micellar cores which undergo dissolution/collapse transitions as a function of environmental stimuli. Whereas the application of these stimuli in solution results in reversible disintegration of stimuli-responsive BCMs to unimers, such disintegration is inhibited within LbL films because of binding of BCM coronal chains with their polymer counterparts. Upon application of environmental stimuli, dissolution/collapse of micellar cores of assembled BCMs results in large-amplitude, reversible swelling/deswelling transitions of the entire film. In addition to the mechanical actuation response, the newly developed BCM-containing films demonstrated efficient control of the uptake and release of small hydrophobic molecules. This approach to constructing responsive assemblies is versatile, can be applied to a wide set of block copolymers with various composition and architecture, and extended to several types of environmental stimuli.

Interface cross-linked polymeric micelles with mixed coronal chains prepared by RAFT polymerization at the interface

Poly(ethylene glycol-block-2-hydroxyethyl methacrylate-block-tert-butyl acrylate) (PEG-b-PHEMA-b-PtBA) triblock copolymer was synthesized by the sequential atom transfer radical polymerization (ATRP) of HEMA and tBA using an ATRP initiator terminated PEG (PEG-Br) as the macroinitiator. Azide groups were introduced to the short mid-blocks by reactions of the triblock copolymer with 2-bromoisobutyryl bromide and sodium azide. In aqueous solution, the triblock copolymer self-assembled into micelles with azide groups at the interfaces. Reactive polymeric micelles with reversible addition–fragmentation chain transfer agents (RAFT CTAs) at the interfaces were prepared by a click cross-linking reaction between dialkynetrithiocarbonate and the azide groups. FT-IR, 1H NMR, dynamic light scattering (DLS) and transmission electron microscopy (TEM) were used to characterize the interface cross-linked (ICL) micelles and the grafting of the RAFT CTAs to the interfaces. Polymeric micelles with PEG–poly(N-isopropylacrylamide) (PNIPAM) mixed coronal chains were prepared by the in situ RAFT polymerization of NIPAM at the interfaces. The TEM results demonstrate that the mixed coronal chains have nano-sized phase separation on the surfaces of the micelles. The use of the polymeric micelles as particulate emulsifiers was also investigated in this research. These ICL micelles with mixed coronal chains produce relatively fine 1-undecanol-in-water (o/w) emulsions compared to emulsions stabilized by the PEG homopolymer under the same conditions.

Temperature‐Responsive Aqueous Micelles From Terpyridine End‐Capped Poly(N‐Isopropylacrylamide)‐Block‐Polystyrene Diblock Copolymers

An attractive concept for designing "smart materials" is the combination of supramolecular interactions with thermoresponsive polymers. Here, this concept is illustrated by preparing aqueous micelles from poly(N-isopropylacrylamide)-block-polystyrene copolymers functionalized at the extremity of their poly(N-isopropylacrylamide) coronal chains by terpyridine ligands. The effect of temperature and of the addition of Zn(II) ions on the self-assembling properties is then studied.

Structure of solvent-free grafted nanoparticles: Molecular dynamics and density-functional theory

The structure of solvent-free oligomer-grafted nanoparticles has been investigated using molecular dynamics simulations and density-functional theory. At low temperatures and moderate to high oligomer lengths, the qualitative features of the core particle pair probability, structure factor, and the oligomer brush configuration obtained from the simulations can be explained by a density-functional theory that incorporates the configurational entropy of the space-filling oligomers. In particular, the structure factor at small wave numbers attains a value much smaller than the corresponding hard-sphere suspension, the first peak of the pair distribution function is enhanced due to entropic attractions among the particles, and the oligomer brush expands with decreasing particle volume fraction to fill the interstitial space. At higher temperatures, the simulations reveal effects that differ from the theory and are likely caused by steric repulsions of the expanded corona chains.

Effect of block compositions of amphiphilic block copolymers on the physicochemical properties of polymeric micelles

Amphiphilic block copolymers with various chain lengths of poly( n-butyl methacrylate) blocks (PBMA) and poly( N-acryloylmorpholine) blocks (PAM) were prepared by RAFT polymerization. Packing parameter of block polymers in water ( β < 0.2) indicated the formation of core-corona structures, which was further confirmed from a difference between core- and corona-forming chain surface areas. Hydrodynamic micellar size was related with the numbers of BMA ( N BMA) and AM ( N AM), and their ratios ( N BMA/ N AM). With increasing N BMA/ N AM value, the polymer aggregation numbers and inner core sizes increased, while the critical micelle concentrations, the corona thickness, and the second virial coefficient of block copolymer micelles decreased. These properties changed with increasing N BMA/ N AM value resulted in a linear increase in corona chain unit density ( ρ AM) that limited chain mobility. Thus, the interaction between the micelles and serum protein at low ρ AM disappeared at a higher value. Consequently, both micellar properties and biocompatible effect can be regulated by tailoring the block compositions of amphiphilic polymers.