Insoluble Block Research Articles

Interfacial assembly and properties of amphiphilic polymer-grafted nanoparticles: Effect of chemical design and density of grafted polymers

Despite extensive research conducted on the polymer-grafted nanoparticle (PGNP) systems for the development of emulsifiers with enhanced performance, little is known about the effects of the grafting architecture and density on the interfacial assembly and interfacial tension reduction behavior of the oil/water (O/W) interface at the molecular level. We performed coarse-grained molecular simulations of both biphasic and emulsion droplet systems with emulsifiers, including Janus (grafting of hydrophilic (HI) and hydrophobic (HO) homopolymers onto two regions of the surface), HI–HO (grafting of diblock polymers with HI monomers as inner blocks and HO monomers as outer blocks), and HO–HI PGNPs, for various graft densities and volume fractions of PGNPs. Compared with the diblock PGNPs, the grafted HI and HO homopolymers of Janus PGNPs penetrate the oil or water phase, rather than assembling at the O/W interface. The depletion of the interface of grafted polymers increases the interfacial tension; consequently, the Janus PGNPs are not effective in reducing the interfacial tension for all the investigated graft densities. The interfacial assembly behavior of the HI–HO and HO–HI PGNPs, whose insoluble blocks have asymmetric interactions with the O/W phases, depends on the graft density and volume fraction. This is particularly the case for their dispersibility, which is an important factor for the interfacial tension. At low graft density, we observe a uniform distribution of HO–HI PGNPs at the O/W interface, resulting in an effective reduction in interfacial tension. At high volume fractions of PGNPs with high graft density, a more tightly packed distribution is observed between HO–HI PGNPs than between HI–HO PGNPs, and their changes in assembly behavior reverse the rate of decrease in the interfacial tension of HO–HI and HI–HO PGNPs. Our results indicate that the grafting architectures of diblock polymers have a significant influence on the assembly behavior at the interface and interfacial tension, and that the appropriate grafting architecture for effective emulsifiers that stabilize the interfaces is different depending on the graft density and volume fraction of the PGNPs. This study also provides new insights into the relation between the interfacial assembly and the stability of emulsion droplets covered by the PGNPs. We observe that the diblock PGNPs, which have the insoluble block as the inner block, are more promising candidates for stabilizing emulsions compared with Janus PGNPs. In the opposite case, the insoluble blocks become the “sticky” points for the adhesion of emulsion droplets, resulting in droplet–droplet coalescence even for effective emulsifiers in reducing interfacial tension. The findings of this study offer a theoretical guide for designing optimal PGNPs for specific volume fractions and optimal graft densities and volume fractions for the grafting architectures of synthesizable PGNPs, and they support the progression from the trial-and-error empirical approaches for developing improved emulsifiers.

Shape-Shifting Thermoresponsive Block Copolymer Nano-Objects

In this Feature Article, we review our recent progress in the design of shape-shifting thermoresponsive diblock copolymer nano-objects, which are prepared using various hydroxyl-functional (meth)acrylic monomers (e.g. 2‑hydroxypropyl methacrylate, 4‑hydroxybutyl acrylate or hydroxybutyl methacrylate) to generate the thermoresponsive block. Unlike traditional thermoresponsive polymers such as poly(N-isopropylacrylamide), there is no transition between soluble and insoluble polymer chains in aqueous solution. Instead, thermally driven transitions between a series of copolymer morphologies (e.g. spheres, worms, vesicles or lamellae) occur on adjusting the aqueous solution temperature owing to a subtle change in the partial degree of hydration of the permanently insoluble thermoresponsive block. Such remarkable self-assembly behavior is unprecedented in colloid science: no other amphiphilic diblock copolymer or surfactant system undergoes such behavior at a fixed chemical composition and concentration. Such shape-shifting nano-objects are characterized by transmission electron microscopy, dynamic light scattering, small-angle X-ray scattering, rheology and variable temperature 1H NMR spectroscopy. Potential applications for this fascinating new class of amphiphiles are briefly considered.

Selective Destruction of Soluble Polyurethaneimide as Novel Approach for Fabrication of Insoluble Polyimide Films.

Polymeric coatings and membranes with extended stability toward a wide range of organic solvents are practical for application in harsh environments; on the other hand, such stability makes their processing quite difficult. In this work, we propose a novel method for the fabrication of films based on non-soluble polymers. The film is made from the solution of block copolymer containing both soluble and insoluble blocks followed by selective decomposition of soluble blocks. To prove this concept, we synthesized copolymer [(imide)n-(polyurethane)]m, in which the imide blocks were combined with polyurethane blocks based on polycaprolactone. By selective hydrolysis of urethane blocks in the presence of acid, it was possible to obtain the insoluble polyimide film for the first time. It was shown that the combination of thermal and acid treatment allowed almost complete removal of urethane blocks from the initial copolymer chains. IR spectroscopy, TGA, DSC and DMA methods were used to study the evaluation of the structure and properties of polymeric material as a result of thermal oxidation and hydrolysis by acid. It was shown that the polymeric films obtained by controlled decomposition were not soluble in aprotic solvent, such as dimethylformamide, n-methylpyrrolidone and dimethyl sulfoxide, and showed very close similarity to the homopolymer consisting of the same imide monomer, poly-(4,4′oxydiphenylene)pyromellitimide, confirming the feasibility of the proposed concept and its perspectives for fabrication of organic solvent-resistant membranes.

Ultralight hybrid silica aerogels derived from supramolecular hydrogels self-assembled from insoluble nano building blocks.

Supramolecular hydrogels are a type of hydrogel cross-linked by non-chemical bonds and they have been widely applied in the field of smart systems, sensors, tissue engineering, and controlled drug delivery. Most supramolecular hydrogels are formed by soluble molecules, polymers, and metal ions. In this work, supramolecular hydrogels self-assembled between two insoluble nano building blocks (ISNBBs), graphene oxide (GO) and amino-functionalized silica nanoparticles (SiO2–NH2), have been discovered and synthesized. The gelation conditions of the two ISNBBs have been investigated. A step further, ultralight hybrid silica aerogels are obtained by supercritical drying of the physical hydrogels. No visible volume shrinkage is observed, due to the fact that the hydrogel networks are formed by rigid ISNBBs. Thus the hybrid aerogels possess ultralow density (down to 7.5 mg cm−3), high specific surface areas (178.6 m2 g−1), and extremely high porosity (99.6%). The present work shows an alternative strategy to design and synthesize supramolecular hydrogels and aerogels using predetermined building blocks, together with designable morphology and physical properties for the target aerogels.

Electrochemical Stimulation of Water-Oil Interfaces by Nonionic-Cationic Block Copolymer Systems.

Variable interfacial tension could be desirable for many applications. Beyond classical stimuli like temperature, we introduce an electrochemical approach employing polymers. Hence, aqueous solutions of the nonionic-cationic block copolymer poly(ethylene oxide)114-b-poly{[2-(methacryloyloxy)ethyl]diisopropylmethylammonium chloride}171 (i.e., PEO114-b-PDPAEMA171 with a quaternized poly(diisopropylaminoethyl methacrylate) block) were investigated by emerging drop measurements and dynamic light scattering, analyzing the PEO114-b-qPDPAEMA171 impact on the interfacial tension between water and n-decane and its micellar formation in the aqueous bulk phase. Potassium hexacyanoferrates (HCFs) were used as electroactive complexants for the charged block, which convert the bishydrophilic copolymer into amphiphilic species. Interestingly, ferricyanides ([Fe(CN)6]3-) act as stronger complexants than ferrocyanides ([Fe(CN)6]4-), leading to an insoluble qPDPAEMA block in the presence of ferricyanides. Hence, bulk micellization was demonstrated by light scattering. Due to their addressability, in situ redox experiments were performed to trace the interfacial tension under electrochemical control, directly utilizing a drop shape analyzer. Here, the open-circuit potential (OCP) was changed by electrolysis to vary the ratio between ferricyanides and ferrocyanides in the aqueous solution. While a chemical oxidation/reduction is feasible, also an electrochemical oxidation leads to a significant change in the interfacial tension properties. In contrast, a corresponding electrochemical reduction showed only a slight response after converting ferricyanides to ferrocyanides. Atomic force microscopy (AFM) images of the liquid/liquid interface transferred to a solid substrate showed particles that are in accordance with the diameter from light scattering experiments of the bulk phase. In conclusion, the present results could be an important step toward economic switching of interfaces suitable, e.g., for emulsion breakage.

Pickering Emulsifiers Based on Block Copolymer Nanoparticles Prepared by Polymerization-Induced Self-Assembly.

Block copolymer nanoparticles prepared via polymerization-induced self-assembly (PISA) represent an emerging class of organic Pickering emulsifiers. Such nanoparticles are readily prepared by chain-extending a soluble homopolymer precursor using a carefully selected second monomer that forms an insoluble block in the chosen solvent. As the second block grows, it undergoes phase separation that drives in situ self-assembly to form sterically stabilized nanoparticles. Conducting such PISA syntheses in aqueous solution leads to hydrophilic nanoparticles that enable the formation of oil-in-water emulsions. Alternatively, hydrophobic nanoparticles can be prepared in non-polar media (e.g., n-alkanes), which enables water-in-oil emulsions to be produced. In this review, the specific advantages of using PISA to prepare such bespoke Pickering emulsifiers are highlighted, which include fine control over particle size, copolymer morphology, and surface wettability. This has enabled various fundamental scientific questions regarding Pickering emulsions to be addressed. Moreover, block copolymer nanoparticles can be used to prepare Pickering emulsions over various length scales, with mean droplet diameters ranging from millimeters to less than 200 nm.

Phase Diagram for Ideal Diblock-Copolymer Micelles Compared to Polymerization-Induced Self Assembly.

In this work we constructed a detailed phase diagram for the solutions of ideal diblock-copolymers and compared such diagram with that obtained during polymerization-induced self-assembly (PISA); a wide range of polymer concentrations as well as chain compositions was studied. As the length of the solvophobic block nB increases (the length of the solvophilic block nA was fixed), the transition from spherical micelles to cylinders and further to vesicles (lamellae) occurs. We observed a rather wide transition region between the spherical and cylindrical morphology in which the system contains a mixture of spheres and short cylinders, which appear to be in dynamic equilibrium; the transition between the cylinders and vesicles was found to be rather sharp. Next, upon increasing the polymer concentration in the system, the transition region between the spheres and cylinders shifts towards lower nB/nA values; a similar shift but with less magnitude was observed for the transition between the cylinders and vesicles. Such behavior was attributed to the increased number of contacts between the micelles at higher polymer volume concentrations. We also found that the width of the stability region of the cylindrical micelles for small polymer volume concentrations is in good quantitative agreement with the predictions of analytical theory. The obtained phase diagram for PISA was similar to the case of presynthesized diblock copolymer; however, the positions of the transition lines for PISA are slightly shifted towards higher nB/nA values in comparison to the presynthesized diblock copolymers, which is more pronounced for the case of the cylinders-to-vesicles transition. We believe that the reason for such behavior is the polydispersity of the core-forming blocks: The presence of the short and long blocks being located at the micelle interface and in its center, respectively, helps to reduce the entropy losses due to the insoluble block stretching, which leads to the increased stability of more curved micelles.

FEATURES OF MOLECULAR AGGREGATION OF BLOCK COPOLYMER ON BASE OF STYRENE AND POLYETHYLENE GLYCOL IN SOLUTIONS

This article focuses on the study of behavior of macromolecules of block copolymer on the base of styrene and polyethylene glycol in toluene media. Unique property of block copolymers is the ability of chemical heterogeneous blocks to phase separation. This process leads to the formation of micelle similar structures in selective solvents. These aggregates have the core from soluble block and the micelles capsule from insoluble block. Similar structures (reverse micelles) would be used for the purpose of stabilization of metal organosols. In this work aggregative stable reverse micelles in such systems as "toluene - water" and "toluene - methanol" have been prepared. Block copolymer of styrene and polyethylene glycol was applied as stabilizer in solutions with polymer concentration from 2.5 g/ 100 ml to 1 g/ 100 ml. Block copolymer has been synthesized by means of isocyanate cure on the end hydroxyl groups. Its structure has been confirmed by differential calorimetry spectroscopy (DSC) method. Dimension of formed particles has been determined by methods of sedimental turbidimetry and dynamic light scattering (DLS). Existence of both individual macromolecules and molecular aggregates in initial solutions has been established by DLS method. It has been found that dimensional homogeneity of organosol particles enlarges with the increase in dispersed phase content to 10 mass. %. At that, the size of the micelles in presence methanol is less than in water presence. Particles size also depends on polymer concentration in solution. The sizes of micelles in both systems increase with increasing concentration of the block copolymer, and with an increase in the content of the dispersed phase, a gradual decrease in their sizes is observed. It was shown that the sedimentation turbidimetry method does not reflect the behavior of the copolymer molecules in solutions, which results in a large scatter of data on the determination of particle sizes of the organosol in the toluene-water system with a water content of less than 5 masses. % . Based on the data obtained, it is assumed that micelles stabilized by a block copolymer based on styrene and polyethylene glycol can be used to introduce metal particles into them, followed by the formation of a metal layer on a solid surface.

Stranded landscapes in the humid tropics: Earth's oldest land surfaces

Defying common expectations, some of the oldest landscapes on Earth are found in the humid tropics. 40Ar/39Ar dating shows that Fe-rich regolith that armors the ∼700–1000 m elevation banded iron-formation plateaus at Urucum, Mato Grosso do Sul, Brazil, results from chemical weathering that began at least 70 million years ago. Cosmogenic 3He concentrations in residual hematite clasts and the underlying saprolite on one plateau imply an extraordinarily slow surface lowering rate of 0.07–0.10 mMa−1 maintained over the last ∼17–70 Ma. Cosmogenic 10Be and 26Al concentrations in a quartz vein in the same plateau suggest a similarly low surface erosion rate of ∼0.11–0.18 mMa−1 over the past few million years. Cosmogenic 3He concentrations in goethite cementing a ∼200 m elevation indurated pediment ∼3 km northwest of the plateau escarpment yields a minimum exposure age of ∼2.6 Ma, revealing that some of the low-lying areas had already been incised and locally stabilized by goethite cementation by then. In contrast, 36Cl measurements on limestone outcrops at ∼170 m elevation and ∼6.5 km northwest of the Urucum plateau reveal short-term erosion rates of 7.1 ± 0.4 and 10.1 ± 0.5 mMa−1, showing that areas not stabilized by goethite cementation are undergoing erosion at a relatively fast pace. The ∼700 m of relief at Urucum is consistent with differential denudation over ∼70 Ma controlled by lithological differences in chemical and physical rates of weathering and erosion. Effective chemical weathering and protracted low rates of erosion for the high-elevation surface result in armoring by a resilient residue of hematite blocks that are relatively insoluble and too heavy to transport. Armoring by the surface lag of large chemically resilient hematite blocks and bedded hematite saprolite focuses meteoric water flow into the subsurface and along faults. Preferential subsurface flow along the permeable pathways between insoluble hematite blocks, combined with segmentation of the Urucum Surface into isolated catchments too small to host active drainage systems, brings physical erosion to a stand-still. The only effective erosive processes on the Urucum plateau are subsurface chemical erosion and scarp retreat. Non-steady-state landscapes in which elevation differences result from prolonged differential denudation are a common feature of Earth's southern hemisphere cratons, and they inherit their present form from underlying lithologies coupled with geomorphic processes active since the Mesozoic.

Self-Assembly of Linear-Dendritic and Double Dendritic Block Copolymers: From Dendromicelles to Dendrimersomes

Nanostructures formed upon self-assembly of amphiphilic block copolymers with linear and dendronized blocks are promising as nanocarriers for targeted drug and gene delivery. We propose a theoretical framework to predict how dimensions and morphologies of such nanostructures as well as the number of potentially functionalized terminal groups exposed to surrounding media can be controlled by adjusting molecular architecture parameters of dendronized blocks (i.e., number of generations and branching functionality). We demonstrate that dendronization of the soluble block stabilizes spherical micelles with a dendritic corona, whereas block copolymers with dendritic insoluble blocks give rise to cylindrical wormlike micelles or polymersomes even if homologous linear-linear block copolymers assemble into spherical micelles. Spherical micelles with a dendronized corona combine smaller hydrodynamic dimensions with a larger number of terminal groups as compared to micelles formed by homologous linear diblock copol...

Alcohols responsive photonic crystals prepared by self-assembly of dendronized block copolymers

Photonic crystals are widely used in chemical sensing for their visually color change. In this work, by proper design of the dendronized brush block copolymers, one dimensional photonic crystals (1D PCs) films that turned to different colors with different alkyl alcohols, alcohols isomers and alcohols mixtures were reported. Specifically, dendronized block copolymer (P(NAM-r-NDMA)-b-PNBM) with alcohols soluble PNAM block and alcohols insoluble PNBM block was prepared by sequential ring-opening metathesis polymerization of the corresponding monomers. The 1D PCs films with lamellar structures were prepared by self-assembly of P(NAM-r-NDMA)-b-PNBM. By swollen in alcohols and alcohol isomers with carbon numbers less than 8, the domain size of the 1D PCs changed, and the reflected wavelength red shifted to show different color as a result. Furthermore, in the binary alcohols mixtures and the alcohol aqueous solution, the color of the film changes with variation of the component, which can be used in semi-quantitative analyses. The alcohols responsive 1D PCs are very promising in visual, portable and reusable detection of alkyl alcohols.

Development of amphiphilic block copolymers as silica optical fiber overlayers for BSA protein detection

Novel amphiphilic block copolymers having both hydrophobic poly(methyl methacrylate) (PMMA) and hydrophilic poly[2-(dimethylamino)ethyl methacrylate] (PDMAEMA) blocks have been designed and synthesized for efficient protein detection in photonic-based sensing. Both the cationic PMMA117-b-PDMAEMA16 and the cationic vinyl-sulfone functionalized PMMA117-b-P(DMAEMA17-VSTEMA2) block copolymers, where VSTEMA is 2-(2-(vinylsulfonyl)ethylthio)ethyl methacrylate, were synthesized from a water insoluble hydrophobic PMMA block, which facilitated the formation of stable overlayers on the silica optical fibers surface. The well-defined structure of the co-polymers was confirmed by gel permeation chromatography (GPC). The presence of the cationic PDMAEMA block and the vinyl-sulfone double bonds led to reversible electrostatic binding of negatively charged proteins like bovine serum albumin (BSA) and non-reversible chemical binding by thiol-ene reactions with cysteine in proteins, respectively. The sensing properties of these materials were assessed and confirmed by ATR-FTIR analysis and by the characterization of fabricated sensing heads on silica optical fibers functionalized with suitably deposited overlayers. The sensing assessment revealed the requirements for deposited overlayer characteristics towards proteins' detection sensitivity and selectivity enhancement.

Poly(hydroxyl propyl methacrylate)‐b‐Poly(oligo ethylene glycol methacrylate) Thermoresponsive Block Copolymers by RAFT Polymerization

AbstractThermoresponsive amphiphilic poly(hydroxyl propyl methacrylate)‐b‐poly(oligo ethylene glycol methacrylate) block copolymers (PHPMA‐b‐POEGMA) are synthesized by RAFT polymerization, with different compositions and molecular weights. The copolymers are molecularly characterized by size‐exclusion chromophotography, and 1H NMR spectroscopy. Dynamic light scattering (DLS) and static light scattering (SLS) experiments in aqueous solutions show that the copolymers respond to temperature variations via formation of self‐organized nanoscale aggregates. Aggregate structural characteristics depend on copolymer composition, molecular weight, and ionic strength of the solution. Fluorescence spectroscopy experiments confirm the presence of less hydrophilic domains within the aggregates at higher temperatures. The thermoresponsive behavior of the PHPMA‐b‐POEGMA block copolymers is attributed to the particular solubility characteristics of the hydrophilic, water insoluble PHPMA block that are modulated by the presence of the water soluble POEGMA block.

Polymer Self-Assembly into Unique Fractal Nanostructures in Solution by a One-Shot Synthetic Procedure.

A fractal nanostructure having a high surface area is potentially useful in sensors, catalysts, functional coatings, and biomedical and electronic applications. Preparation of fractal nanostructures on solid substrates has been reported using various inorganic or organic compounds. However, achieving such a process using polymers in solution has been extremely challenging. Here, we report a simple one-shot preparation of polymer fractal nanostructures in solution via an unprecedented assembly mechanism controlled by polymerization and self-assembly kinetics. This was possible only because one monomer was significantly more reactive than the other, thereby easily forming a diblock copolymer microstructure. Then, the second insoluble block containing poly(p-phenylenevinylene) (PPV) without any side chains spontaneously underwent self-assembly during polymerization by an in situ nanoparticlization of conjugated polymers (INCP) method. The formation of fractal structures in solution was confirmed by various imaging techniques such as atomic force microscopy, transmission electron microscopy (TEM), and cryogenic TEM. The diffusion-limited aggregation theory was adopted to explain the branching patterns of the fractal nanostructures according to the changes in polymerization conditions such as the monomer concentration and the presence of additives. Finally, after detailed kinetic analyses, we proposed a plausible mechanism for the formation of unique fractal nanostructures, where the gradual formation and continuous growth of micelles in a chain-growth-like manner were accounted for.

Theory of Linear-Dendritic Block Copolymer Micelles.

A self-consistent field theory is applied to study structural properties of micelles formed upon spontaneous assembly of diblock copolymers comprising soluble dendron block covalently linked to insoluble linear block in selective solvent. The structure of spherical micelles is analyzed as a function of degrees of polymerization of the blocks and number of generations and branching functionality of the dendron block. We demonstrate that for a given molecular mass of blocks both the hydrodynamic dimensions of the micelles and the aggregation number decrease as a function of the degree of branching of the dendron block. However, the number of potentially functionalizable terminal segments of dendrons in the corona exposed to the solution increases compared to the number of terminal groups in the corona of linear diblock copolymer micelle. This result may have important implications for construction of linear-dendritic block copolymer micelles with smart functionalities for targeted drug and gene delivery.

Effect of Architecture on Micelle Formation and Liquid-Crystalline Ordering in Solutions of Block Copolymers Comprising Flexible and Rigid Blocks: Rod-Coil vs Y-Shaped vs Comblike Copolymers.

Micelle formation of amphiphilic block copolymers of various architectures comprising both flexible and rodlike blocks were studied in a selective solvent via dissipative particle dynamics (DPD) simulations. Peculiarities of self-assembly of Y-shaped (insoluble rigid block and two flexible soluble arms) and comblike (soluble flexible backbone with insoluble rigid side chains) copolymers are compared with those of equivalent rod-coil diblock copolymers. We have shown that aggregation of the rigid blocks into the dense core of the micelles is accompanied by their nematic ordering. However, the orientation order parameter and aggregation number of the micelles are strongly dependent on macromolecular architecture. Relatively small micelles of pretty high nematic order parameter, S2 ≈ 0.5-0.8, are the features of the Y-shaped and rod-coil copolymer micelles. They are characterized by different responses to the solvent quality worsening. The aggregation number of the rod-coil diblock copolymer micelles increases and that of the Y-shaped copolymer micelles decreases at the solvent quality worsening. However, the order parameter grows in both cases, achieving a maximum value for the Y-shaped copolymer micelles. Herewith, the core elongates. On the contrary, comblike copolymers self-assemble into bigger spherical micelles whose core possesses a lower nematic order of the rods, S2 ≈ 0.3-0.4. The aggregation number is shown to depend on the length of the combs (on the number of repeating elements in the architecture). Possible physical reasons for such behavior of the systems are discussed.

Orthogonal solubility in fully conjugated donor-acceptor block copolymers: Compatibilizers for polymer/fullerene bulk-heterojunction solar cells

Donor-acceptor (D-A) type fully conjugated block copolymer systems have been rarely reported due to the challenges in synthetic approaches to prepare well-defined low-polydispersity products. In this work, fully conjugated block copolymers are synthesized in a one-pot reaction through Stille coupling polycondensation, by utilizing the end-functional polymer copolymerization method. End-functional P3HT are copolymerized with AA (2,7-dibromo-9-(heptadecan-9-yl)-9H-carbazole) and BB (4,7-bis(5-(trimethylstannyl)thiophen-2-yl)benzo[c][1,2,5]thiadiazole, TBT) type monomers, respectively. The orthogonal solubility between the very soluble P3HT donor and the insoluble PCDTBT acceptor block improves the purity of block copolymers as well as distinct nano-scale phase-separation compared with other reports on miscibility of donor and acceptor polymer block. Further purification via preparative GPC is carried out to remove the excess of unreacted P3HT and free PCDTBT as well as to achieve low polydispersity of block copolymers. The chemical structure of the P3HT-b-PCDTBT block copolymers are verified via 1H-NMR, and further confirmed by FTIR spectra. The block copolymer shows broad absorption and moderate optical band gap of 1.8 eV. Furthermore, the fully conjugated block copolymer films exhibit significant fine structures, much smoother film morphology compared to P3HT/PCDTBT polymer blends. By adding a small amount of block copolymer P3HT-b-PCDTBT as a compatibilizer into the bulk-heterojunction of P3HT:PC61BM blends, polymer solar cells with an 8% increase of short circuit current (J sc and 10% increase of power conversion efficiency (PCE) are achieved owing to the improvement of the active-layer film morphology. To the best of our knowledge, this is the first report on donor-acceptor type fully conjugated block copolymer as an effective ternary additive in polymer: fullerene bulk heterojunction solar cells.

Controlling Multicompartment Morphologies Using Solvent Conditions and Chemical Modification.

The solution self-assembly of amphiphilic diblock copolymers into spheres, cylinders, and vesicles (polymersomes) has been intensely studied over the past two decades, and their morphological behavior is well understood. Linear ABC triblock terpolymers with two insoluble blocks A/B, on the other hand, display a richer and more complex morphological spectrum that has been recently explored by synthetic block length variations. Here, we describe facile postpolymerization routes to tailor ABC triblock terpolymer solution morphologies by altering block solubility (solvent mixtures), blending with homopolymers, and block-selective chemical reactions. The feasibility of these processes is demonstrated on polystyrene-block-polybutadiene-block-poly(methyl methacrylate) (SBM) that assembles to patchy spherical micelles, which can be modified to evolve into double and triple helices or patchy and striped vesicles. These results demonstrate that postpolymerization treatments give access to a broad range of morphologies from single triblock terpolymers without the need for multiple polymer syntheses.

Molecular Exchange Kinetics of Micelles: Corona Chain Length Dependence.

The rate of molecular exchange in diblock copolymer micelles is strongly dependent on the chain length of the core-forming insoluble block. Less is known about the influence of the soluble block forming the micellar corona. In this study we present a time-resolved small angle neutron scattering (TR-SANS) study exploring systematically the effect of corona chain length on the dynamics of chain exchange. As a model system we have taken amphiphilic AB diblock copolymers of the type C27H55-poly(ethylene oxide)x (C27-PEOx) with varying x between 4 and 36 kg/mol in aqueous solution in which well-defined spherical micelles with partially crystalline cores are formed. The TR-SANS results show that the chain exchange slows down considerably upon increasing PEO molecular weight, while the characteristic "attempt time" constant, τ0, was found to increase with a power law dependence τ0 ∼ MPEO9/5. The results are in excellent agreement with the Halperin and Alexander model1 and can be attributed to a reduced diffusion rate through the micellar corona. Our results clearly demonstrate that the rate for molecular exchange is not directly coupled to the solubility of the amphiphile and the critical micellar concentration, as has previously been indicated.

Rational design of ABC triblock terpolymer solution nanostructures with controlled patch morphology.

Block copolymers self-assemble into a variety of nanostructures that are relevant for science and technology. While the assembly of diblock copolymers is largely understood, predicting the solution assembly of triblock terpolymers remains challenging due to complex interplay of block/block and block/solvent interactions. Here we provide guidelines for the self-assembly of linear ABC triblock terpolymers into a large variety of multicompartment nanostructures with C corona and A/B cores. The ratio of block lengths NC/NA thereby controls micelle geometry to spheres, cylinders, bilayer sheets and vesicles. The insoluble blocks then microphase separate to core A and surface patch B, where NB controls the patch morphology to spherical, cylindrical, bicontinuous and lamellar. The independent control over both parameters allows constructing combinatorial libraries of unprecedented solution nanostructures, including spheres-on-cylinders/sheets/vesicles, cylinders-on-sheets/vesicles, and sheets/vesicles with bicontinuous or lamellar membrane morphology (patchy polymersomes). The derived parameters provide a logical toolbox towards complex self-assemblies for soft matter nanotechnologies.