Self-assembly Of Copolymers Research Articles

Boundary-Directed Epitaxy of Block Copolymers Toward Sub-10 nm Fabrication

The directed self-assembly (DSA) of block copolymers (BCPs) can be used to produce nanoscale patterns without the cost and process complexity of state-of-the-art optical lithography. Thus, DSA may be useful in a wide variety of semiconductor applications such as fin field-effect transistors and biosensors. To create technologically useful patterns with aligned BCP domains, conventional DSA mechanisms often rely on topographically complex structures or high-resolution chemical patterns to direct the self-assembly, that are difficult to fabricate. In comparison, a newly discovered mechanism for DSA, termed boundary-directed epitaxy (BDE), utilizes chemical contrast at the boundaries between a substrate and relatively wide chemical stripe. Here, we demonstrate the use of BDE to template the fabrication of sub-10 nm features for the first time. BDE is used in conjunction with selective infiltration to create ultranarrow line-space arrays of alumina. These results demonstrate a proof-of-concept for BDE as a method for ultrahigh-resolution feature formation.

Improvements of Solubility and Bioavailability of Lutein Through Grafting with Hydrophilic Polyacrylic Acid

In this study, polyacrylic acid grafted lutein (PAA-g-lutein) was prepared by hydrophilic modification of lutein with polyacrylic acid (PAA) through Steglish esterification method. The unreacted lutein was loaded in micelles formed by self-assembly of graft copolymers in water to form composite nanoparticles. The bioaccessibility and bioavailability of lutein nanoparticles were studied by in vitro and in vivo digestion experiments. Compared with free lutein, the saturated solubility and bioaccessibility of lutein nanoparticles were increased by 78 times and 3.6 times, respectively. The pharmacokinetics results in the mice model showed that the maximum concentration (Cmax) and area under concentration-time curve (AUC) of plasma of mice were increased by 3.05 and 6.07 times with lutein nanoparticles compared with free lutein. Meanwhile, the prepared lutein nanoparticles also promoted the accumulation of lutein in the liver, mesenteric adipose, and eyeballs. These results indicate that graft copolymerization of lutein with water-soluble polymers to form nanoparticles is an effective method to promote the bioavailability of lutein in vivo. Moreover, this method is simple and applicable, and can also be used for the modification of other bioactive molecules.

Interpretable Machine Learning Models for Phase Prediction in Polymerization-Induced Self-Assembly.

While polymerization-induced self-assembly (PISA) has become a preferred synthetic route toward amphiphilic block copolymer self-assemblies, predicting their phase behavior from experimental design is extremely challenging, requiring time and work-intensive creation of empirical phase diagrams whenever self-assemblies of novel monomer pairs are sought for specific applications. To alleviate this burden, we develop here the first framework for a data-driven methodology for the probabilistic modeling of PISA morphologies based on a selection and suitable adaption of statistical machine learning methods. As the complexity of PISA precludes generating large volumes of training data with in silico simulations, we focus on interpretable low variance methods that can be interrogated for conformity with chemical intuition and that promise to work well with only 592 training data points which we curated from the PISA literature. We found that among the evaluated linear models, generalized additive models, and rule and tree ensembles, all but the linear models show a decent interpolation performance with around 0.2 estimated error rate and 1 bit expected cross entropy loss (surprisal) when predicting the mixture of morphologies formed from monomer pairs already encountered in the training data. When considering extrapolation to new monomer combinations, the model performance is weaker but the best model (random forest) still achieves highly nontrivial prediction performance (0.27 error rate, 1.6 bit surprisal), which renders it a good candidate to support the creation of empirical phase diagrams for new monomers and conditions. Indeed, we find in three case studies that, when used to actively learn phase diagrams, the model is able to select a smart set of experiments that lead to satisfactory phase diagrams after observing only relatively few data points (5-16) for the targeted conditions. The data set as well as all model training and evaluation codes are publicly available through the GitHub repository of the last author.

Stepwise self-assembly of bottlebrush random copolymers into uniform cylindrical structures

Stepwise self-assembly of bottlebrush random copolymers into uniform cylindrical structures

Non-Equilibrium Block Copolymer Self-Assembly Based Porous Membrane Formation Processes Employing Multicomponent Systems.

Porous polymer-derived membranes are useful for applications ranging from filtration and separation technologies to energy storage and conversion. Combining block copolymer (BCP) self-assembly with the industrially scalable, non-equilibrium phase inversion technique (SNIPS) yields membranes comprising periodically ordered top surface structures supported by asymmetric, hierarchical substructures that together overcome performance tradeoffs typically faced by materials derived from equilibrium approaches. This review first reports on recent advances in understanding the top surface structural evolution of a model SNIPS-derived system during standard membrane formation. Subsequently, the application of SNIPS to multicomponent systems is described, enabling pore size modulation, chemical modification, and transformation to non-polymeric materials classes without compromising the structural features that define SNIPS membranes. Perspectives on future directions of both single-component and multicomponent membrane materials are provided. This points to a rich and fertile ground for the study of fundamental as well as applied problems using non-equilibrium-derived asymmetric porous materials with tunable chemistry, composition, and structure.

Biofilm microenvironment-responsive polymeric CO releasing micelles for enhanced amikacin efficacy

Biofilm-associated infections (BAI) have posed serious threats to public health. Novel therapy based on carbon monoxide (CO) is being increasingly appreciated. However, CO therapy like inhaled gas treatment was impeded owing to its low bioavailability. Besides, the direct use of CO releasing molecules (CORM) showed low therapeutic efficacy in BAI. Therefore, it is vital to improve the efficiency of CO therapy. Herein, we proposed polymeric CO releasing micelles (pCORM) from self-assembly of amphiphilic copolymers containing CORM bearing block as hydrophobic part and acryloylmorpholine block as hydrophilic part. The catechol modified CORM were conjugated through pH cleavable boronate ester bonds and releasing CO passively under biofilm microenvironment. When combined with subminimal inhibitory concentration antibiotic amikacin, pCORM could significantly enhance its bactericidal efficiency against biofilm-encapsulated multidrug-resistant bacteria, representing a promising approach to combat BAI.

Self-Assembly of Block Copolymers in Thin Films Swollen-Rich in Solvent Vapors.

In this study we have employed a polymer processing method based on solvent vapor annealing in order to condense relatively large amounts of solvent vapors onto thin films of block copolymers and thus to promote their self-assembly into ordered nanostructures. As revealed by the atomic force microscopy, a periodic lamellar morphology of poly(2-vinylpyridine)-b-polybutadiene and an ordered morphology comprised of hexagonally-packed structures made of poly(2-vinylpyridine)-b-poly(cyclohexyl methacrylate) were both successfully generated on solid substrates for the first time.

Direct Visualization of Polymerization-Induced Self-Assembly of Amphiphilic Copolymers

Direct Visualization of Polymerization-Induced Self-Assembly of Amphiphilic Copolymers

Selective solvent vapor induced self-assembly of silicon-containing bottlebrush block copolymer thin films to generate mesoporous silicon oxide patterns

Bottlebrush block copolymers (BBCPs) are intriguing architectures that can produce various anisotropic nanostructures dictated by the composition, length of the backbone and the lengths of side-chains. Here, we develop a facial approach toward ordered inorganic silicon oxide patterns and particles on substrates by solvent vapor induced thin film self-assembly of anisotropic bottlebrush block copolymers (BBCP) containing polydimethylsiloxane (PDMS) and polystyrene (PS) side chains. The in-plane cylindrical or stripes-like, spherical, and ordered porous morphologies as well as Janus particles-like morphology were fabricated on the substrate through solvent vapor annealing (SVA). The Janus particle-like morphology consisting of PS heads inserted in PDMS heads were directed to produce meso-to macroporous silicon oxide bowls after oxygen plasma etching. The effects of the solvent vapor on the molecular geometry and morphology of the BBCPs were described, and the influence of the backbone length on the self-assembly behavior of the thin film were discussed. This work demonstrates that silicon-containing BBCPs with a native etch contrast and a large difference in solubility parameters are potential candidates to generate ordered silicon oxide templates of different geometries with periodicity 80–150 nm providing access to length scales larger than linear block copolymers.

Formation of Size-Controllable Tetragonal Nanoprisms by Crystallization-Directed Ionic Self-Assembly of Anionic Porphyrin and PEO-Containing Triblock Cationic Copolymer.

The creation of anisotropic nanostructures with precise size control is desirable for new properties and functions, but it is challenging for ionic self-assembly (ISA) because of the non-directional electrostatic interactions. Herein, the formation of size-controllable tetragonal nanoprisms is reported via crystallization-directed ionic self-assembly (CDISA) through evaporating a micellar solution on solid substrates. First, ISA is designed with a crystalline polyethylene oxide (PEO) containing cationic polymer poly(2-(2-guanidinoethoxy)ethyl methacrylate)-b-poly(ethyleneoxide)-b-poly(2-(2-guanidinoethoxy)-ethylmethacrylate) (PGn -PEO230 -PGn ) and an anionic 5,10,15,20-Tetrakis(4-sulfonatophenyl) porphyrin (TPPS) to form micelles in aqueous solution. The PG segments binds excessive TPPS with amplenet chargeto form hydrophilic corona, while the PEO segments are unprecedentedly dehydrated and tightly packed into cores. Upon naturally drying the micellar solution on a silicon wafer, PEO crystallizationdirects the micelles to aggregate into square nanoplates, which are further connected to nanoprisms. Length and width of the nanoprisms can be facilely tuned by varying the initial concentration. In this hierarchical process, the aqueous self-assembly is prerequisite and the water evaporation rate is crucial for the formation of nanostructures, which provides multiple factors for morphology regulating. Such precise size-control strategy is highly expected to provide a new vision for the design of advanced materials with size controllable anisotropic nanostructures.

Self-Assembled Copolymeric Nanowires as a New Class of 3D Scaffold for Stem Cells Growth and Proliferation

Stem cell therapy has emerged as the most vibrant area of research, due to the capacity of stem cells for self-renewal and differentiation into different types of cell lines upon their culture. But lately, scientists become increasingly aware of the limitations of conventional 2D culture and stem cell culture media, due to several key drawbacks associated with this model, such as immune response upon transplantation, animal pathogen contamination, and complication, during developmental studies due to undefined factors in the cultural media. In this study, an attempt has been made to develop a new type of polymeric 3D scaffold based on the self-assembly of a star-like amphiphilic copolymer of poly(caprolactone)–poly(ethylene oxide) unit into nanowires (nanofibers), that have a scale similar to the native extracellular matrix and are capable of mimicking the extracellular microenvironment where the functional properties of stem cells can be observed and manipulated. The obtained data showed that polymeric-based nanofibers can be used as a 3D scaffold for mouse embryonic stem cells (mESCs) growth without losing their stem cell phenotype. The results obtained suggest that the polymeric 3D scaffolds (nanofibers) not only support stem cells’ growth and proliferation but also preserve the mESC pluripotency.

Surface encapsulating UV filters based on self-assembly of an amphiphilic random copolymer by miniemulsion polymerization

A nanoparticles encapsulating UV filters were prepared by miniemulsion polymerization, in which methyl methacrylate (MMA) as the monomer, and ethylene glycol dimethacrylate (EGDMA) as the cross-linker. Scanning electron microscopy (SEM) and X-ray photoelectron spectrometry (XPS) confirmed that the amphiphilic random copolymers poly (styrene-co-methacrylic acid) P(St-co-MAA) not only acted as the stabilizer but also self-assembled on the surface of the P(MMA-EGDMA) polymers. During the miniemulsion polymerization, most UV filters were encapsulated in the P(St-co-MAA) self-assembly aggregates on the surface of nanoparticles, giving the nanoparticles a raspberry-like structure. As the mass ratio of P(St-co-MAA) to MMA and EGDMA at 1.0, the encapsulation efficiency of UV filters was 69.85%, whereas 70.7% of UV filters were located in the P(St-co-MAA) self-assembly layer. The leakage of UV filters from the raspberry-like nanoparticles was negligible after continuous stirring in isopropyl myristate (IPM) for 24 h. The sun protection factor (SPF) and UVA Protection Factor (UVAPF) value of sunscreen formulation incorporated with the raspberry-like nanoparticles could reach 58.8 and 6.82, respectively. It enhanced UV protection more efficiently than the nanoparticles with a smooth surface.

Quasi block copolymers noncovalent bonded by stereocomplex crystals

Self-assembly of block copolymers (BCPs) yields unparalleled opportunities to integrate exquisite characteristics for preparation of advanced nanotechnology materials. The high-yield manufacturing of BCP is extremely desired, yet rarely exploited. Herein, we displayed that stereocomplex crystals (sc) of poly lactide (PLA) enantiomers, acting as pseudo linkage between adjacent polymer chains, enable formation of quasi-block copolymer (qBCPs) by straightforward melt compounding. Identical content of poly (D-lactide) (PDLA) and poly (L-lactide) (PLLA) were pre-grafted onto the backbones of poly styrene (PS) and poly (methyl methacrylate) (PMMA), respectively. Due to the complementary multiple hydrobonding interactions between PDLA and PLLA grafted moieties, PS-“block”-PMMA connected by cocrystallized sc was induced during the subsequent melt processing of PDLA-g-PS/PLLA-g-PMMA, thus allowing local segregation of PS-“block” and PMMA-“block” with nanometer size. The refined morphology, which was resembled with micro-phase separation of classical BCP, can be facilely tuned by varying the length and ratio of enantiomeric PDLA/PLLA grafts. More interestingly, the PS-“block”-PMMA typed qBCPs demonstrated superiority in compatibilizing immiscible PS/PMMA polymer blends, as compared with the classical compatibilizer (PS-block-PMMA) via reactive blending. Overall, our strategy represents a general method to construct noncovalent linked di-block copolymer via industrially relevant melt processing, which is quite challenging to achieve by existing synthetic technologies.

Precision Macro (molecular) Assemblies

Structural precision in hierarchical self-assembled architectures is ubiquitous in biological systems. For instance, DNA double helix, quaternary structures of proteins, tobacco mosaic virus, microtubules, and several other elegant systems are constituted through specific molecular recognitions that are responsible for regulating numerous complex functions in nature. Inspired by such elegant examples in living systems, the self-assembly of synthetic small molecules and macromolecules has been studied with great interest, especially in the past four decades since the concept of supramolecular chemistry had been established in a formal way. In this context, solution self-assembly of amphiphilic block copolymers (ABCPs) with amorphous core- forming blocks has been studied extensively in the past three decades owing to the possibility of generating different nanostructures in water,such as micelles, vesicles, fibers, lamella, and others.Despite the fact that self-assembly of ABCPs has proven to be an effective bottom- up approach for creating multilevel structures that are gateways to highly promising soft materials for diverse applications, attempts to improve specific and nontrivial functional utilities of these systems have been hampered by a number of significant problems. Aggregation of ABCPs in block-selective solvents is commonly catalyzed by the immiscibility-driven chain collapse of the amorphous core-forming blocks. Thus, the critical packing parameter, which in turn depends on the relative volume fraction of the hydrophobic and hydrophilic block segments, is the primary factor controlling the morphology of these polymer aggregates in solutions.This limits the ability to precisely tailor the internal order orsurface functional group display in such nanostructures or control their dimensions, shapes, and dispersity, which is crucial for their elegant biological functions. Moreover, for ABCPs with amorphous core- forming blocks, non-spherical structures are rarely accessible only within a limited window of block compositions and self-assembly environments. Sometimes, those are also contaminated with other undesired morphologies. Many studies have demonstrated that non-spherical, high aspect ratio nanostructures such as one- dimensional (1D) fibers and two- dimensional (2D) plateletperform superior functions in emerging applications, compared to their spherical analogues. This has paved the way for the emergence of new macromolecular designs toward the development of internally-ordered precision anisotropic structures.

Degradation-Influenced/Induced Self-Assembly of Copolymers with the Combinatory Effects of Changed Molecular Weight and Dispersity

Degradation-Influenced/Induced Self-Assembly of Copolymers with the Combinatory Effects of Changed Molecular Weight and Dispersity

Block copolymer interfaces investigated by means of NMR, atomic force microscopy and dielectric spectroscopy

Self-assembly of block copolymers (BC) is a key feature for bottom-up patterning that is applied in the fabrication of templates for nanostructured membranes, photonic nanodevices, or solar cells. The wide range of possible BC applications is because the dissimilar blocks can be appropriately selected to form distinct domains with controllable dimensions and functionalities. An important representative of these materials is polystyrene-b-poly(ethylene oxide) (PS-b-PEO) diblock copolymer. This copolymer is of considerable academic interest and therefore it is examined by a plethora of experimental techniques to elucidate its structure and molecular dynamics. Particularly worth investigating is the interphase, consisting of polymer chains located at the interface of crystallite-amorphous and inter-domain regions, which codetermines the properties of such a system. It is shown that below the melting point of the PEO, the majority of the amorphous PEO are occupying interfacial sites and are represented by the rigid amorphous fraction (RAF) which can be monitored by dielectric and nuclear magnetic resonance spectroscopies. Moreover, two independent NMR spin-diffusion experiments reveal the asymmetrical nature of PS-PEO interface indicating a significant fraction of the PEO phase under the influence of stiff, adjacent polystyrene. An analysis of complementary thermal calorimetry and X-ray scattering data confirms the presence of microphase-separated morphology as well as the semicrystalline nature of PEO component. Lamelar domain architecture was confirmed by atomic force microscopy data acquired in the case of thin copolymer film.

Self-assembly of block copolymers on surfaces exposed to space-confined solvent vapor annealing

We apply here an optimized polymer processing approach, based on solvent vapor annealing in a space-confined environment, to generate previously unrevealed self-assembled microstructures comprised of periodic lamellar or hexagonal nanostructures of molecular dimensions, depending on the type of block copolymer that is used.

Thermo-Responsive Injectable Hydrogels Formed by Self-Assembly of Alginate-Based Heterograft Copolymers.

Polysaccharide-based graft copolymers bearing thermo-responsive grafting chains, exhibiting LCST, have been designed to afford thermo-responsive injectable hydrogels. The good performance of the hydrogel requires control of the critical gelation temperature, Tgel. In the present article, we wish to show an alternative method to tune Tgel using an alginate-based thermo-responsive gelator bearing two kinds of grafting chains (heterograft copolymer topology) of P(NIPAM86-co-NtBAM14) random copolymers and pure PNIPAM, differing in their lower critical solution temperature (LCST) about 10 °C. Interestingly, the Tgel of the heterograft copolymer is controlled from the overall hydrophobic content, NtBAM, of both grafts, implying the formation of blended side chains in the crosslinked nanodomains of the formed network. Rheological investigation of the hydrogel showed excellent responsiveness to temperature and shear. Thus, a combination of shear-thinning and thermo-thickening effects provides the hydrogel with injectability and self-healing properties, making it a good candidate for biomedical applications.

Reduction-sensitive flower-like magnetomicelles based on PCL-ss-PEG-ss-PCL triblock copolymer as anti-cancer drug delivery system

Introducing an intelligent pharmaceutical nanocarrier for targeted drug release and reducing the side effects of chemotherapy is the main goal of many researchers. In this area, we synthesized amphiphilic triblock copolymer PCL-ss-PEG-ss-PCL consisting of cystamine as a reduction sensitive linkage. The aqueous self-assembly of triblock copolymer in the presence of magnetic iron oxide nanoparticles (Fe3O4) and doxorubicin (DOX) led to the formation of reduction-sensitive flower like magnetomicelle containing DOX and Fe3O4. The innovative design based on intelligent flower like structure led to high drug loading content, reduce drug release in physiologic condition, fast degradation at targeted site and burst release of more content of drug at earlier time. The DOX loading content was about 19% and DOX- loaded magnetomicelles (D-LMM) showed more triggered release under redox conditions at pH = 5. The efficiency of D-LMM was compared with non-reduction sensitive control group (CD-LMM), free DOX and commercial product of liposomal DOX (LD) in vitro. The D-LMM showed significant improvement in cellular uptake and toxicity behavior on human breast adenocarcinoma MCF-7 cells in comparison to commercial LD and also displayed better results in the cytotoxicity and apoptosis/necrosis assays in comparison to CD-LMM.

Controlling self-assembling co-polymer coatings of hydrophilic polysaccharide substrates via co-polymer block length ratio

HypothesisThe degree of polymerization of amphiphilic di-block co-polymers, which can be varied with ease in computer simulations, provides a means to control self-assembling di-block co-polymer coatings on hydrophilic substrates. SimulationsWe examine self-assembly of linear amphiphilic di-block co-polymers on hydrophilic surface via dissipative particle dynamics simulations. The system models a glucose based polysaccharide surface on which random co-polymers of styrene and n-butyl acrylate, as the hydrophobic block, and starch, as the hydrophilic block, forms a film. Such setups are common in e.g. hygiene, pharmaceutical, and paper product applications. FindingsVariation of the block length ratio (35 monomers in total) reveals that all examined compositions readily coat the substrate. However, strongly asymmetric block co-polymers with short hydrophobic segments are best in wetting the surface, whereas approximately symmetric composition leads to most stable films with highest internal order and well-defined internal stratification. At intermediate asymmetries, isolated hydrophobic domains form. We map the sensitivity and stability of the assembly response for a large variety of interaction parameters. The reported response persists for a wide polymer mixing interactions range, providing general means to tune surface coating films and their internal structure, including compartmentalization.