Controlling domain orientation of liquid crystalline block copolymer in thin films through tuning mesogenic chemical structures

Controlling the macroscopic orientation of nanoscale periodic structures of amphiphilic liquid crystalline block copolymers (LC BCPs) is important to a variety of technical applications (e.g., lithium conducting polymer electrolytes). To study LC BCP domain orientation, a series of LC BCPs containing a poly(ethylene oxide) (PEO) block as a conventional hydrophilic coil block and LC blocks containing azobenzene mesogens is designed and synthesized. LC ordering in thin films of the BCP leads to the formation of highly ordered, microphase‐separated nanostructures, with hexagonally arranged PEO cylinders. Substitution on the tail of the azobenzene mesogen is shown to control the orientation of the PEO cylinders. When the substitution on the mesogenic tails is an alkyl chain, the PEO cylinders have a perpendicular orientation to the substrate surface, provided the thin film is above a critical thickness value. In contrast, when the substitution on the mesogenic tails has an ether group the PEO cylinders assemble parallel to the substrate surface regardless of the film thickness value. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55, 532–541     

Synthesis of bottlebrush block copolymers from bottlebrush polystyrene and bottlebrush random copolymer of ω-end-norbornyl polymethacrylates and their self-assembly

Six different bottlebrush block copolymers (BBCPs) (A-b-(B-co-C)) from bottlebrush polystyrene (A) and bottlebrush random copolymers (B-co-C) of polymethacrylates were synthesized through living anionic polymerization and ring-opening metathesis polymerization. To induce the phase separation of bottlebrush polystyrene (PNB-g-PS) (A) and bottlebrush poly(benzyl methacrylate) (PNB-g-PBzMA) (C)-based BBCP with an extremely low Flory–Huggins interaction parameter (χ), three kinds of bottlebrush polymethacrylates (B): poly(norbornene-g-methyl methacrylate) (PNB-g-PMMA), poly(norbornene-g-tert-butyl methacrylate) (PNB-g-PtBMA), and poly(norbornene-g-methacrylic acid) (PNB-g-PMAA), respectively, were randomly combined with C. An order–disorder phase transition of the BBCPs (A-b-(B-co-C)) was observed with a change in mole ratios of PMMA, PtBMA, or PMAA to PBzMA of 25, 50, and 75% in random copolymer blocks using field-emission scanning microscopy. While the BBCP with 25% of PMAA in the random copolymer block showed an ordered lamellar nanostructure, a disordered morphology was revealed at 75% PMAA. SEM showed that the incorporation of PtBMA and PBzMA showed better-ordered lamellar morphologies than was the case with PMMA and PBzMA at the same mole ratios.     

Doubly photoresponsive and water‐soluble block copolymers: Synthesis and thermosensitivity

We report the synthesis and investigation of a new type of photoresponsive block copolymers (BCPs). They were designed to comprise two water‐soluble polymers containing two different photoisomerizable moieties (either azobenzene and spiropyran or two different azobenzenes), with the two constituting blocks that, when separated, exhibit a lower critical solution temperature (LCST) in water and can shift their LCST in opposite directions upon photoisomerization (decrease of LCST for one polymer and increase for the other). A variety of such doubly photoresponsive BCPs were synthesized using either azobenzene‐ or spiropyran‐containing poly(N,N‐dimethylacrylamide) (PDMA), poly(N‐isopropylacrylamide) (PNIPAM) and poly[methoxydi(ethylene glycol) methacrylate] (PDEGMMA). Their thermal phase transition behaviors in aqueous solution before and after simultaneous photoreactions on the two blocks were investigated in comparison with their constituting blocks, by means of solution transmittance (turbidity) and variable‐temperature ¹H NMR measurements. The results show that BCPs displayed a single LCST whose shift upon two photoisomerizations appeared to be determined by the competing and opposing photoinduced effects on the two blocks. Moreover, optically controlling the relative photoisomerization degrees of trans azobenzene‐to‐cis azobenzene and spiropyran‐to‐merocyanine could be used to tune the LCST of BCP solution. This study demonstrates the potential of exploring a more complex photoreaction scheme to optically control the solution properties of water‐soluble thermosensitive BCPs. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 4055–4066, 2010     

Morphological transition of nanostructures of self-assembled block copolymers by stimuli-induced conformational changes in the hydrophilic block

The morphological control of nanostructures created by the self-assembly of macromolecular building blocks in solution has practical importance because the structural parameters of nanostructures greatly affect their physical and chemical behavior in solution, for example, pharmacokinetics. Herein, we report that the stimuli-induced changes to the conformation of the hydrophilic polymer block of a block copolymer (BCP), in this case branched-linear poly(ethylene glycol)-b-poly(styrene) BCPs, are translated to changes in the morphology of the BCP self-assemblies in solution. Specifically, the cone angle between the poly(ethylene glycol) arms in the tri-arm hydrophilic block equipped with pyridyl units in the scaffold can be changed by varying the self-assembly conditions, thus affecting the packing parameter (p) of the BCP. Upon increasing the cone angle by protonating the pyridyl units, the self-assembled BCP structures underwent changes consistent with a reduction in the p value. In contrast, the chelation of zinc metal cations (Zn²⁺) to the pyridyl groups resulted in the conformation of the hydrophilic block taking on a closed form, resulting in an apparent increase in the p value of the BCP. Our results could be applied to stimuli-dependent morphological transitions of other self-assembled BCP nanostructures in solution.     

Long-range ordered thin films of block copolymers prepared by zone-casting and their thermal conversion into ordered nanostructured carbon

Large-scale alignment of lamellae in thin films of diblock copolymers containing polyacrylonitrile and poly(n-butyl acrylate) was achieved by casting copolymer solution on a silicon substrate moved away at a constant speed from the casting nozzle (zone-casting). Grazing incidence small-angle X-ray scattering revealed that the lamellae, which were perpendicular to the substrate, were also aligned over macroscopic scale in the direction perpendicular to the casting direction. Such long-range ordered block copolymer films were then converted by pyrolysis into nanostructured carbons, with excellent preservation of lamellar morphology and orientation.     

MOLECULAR AND SUPRAMOLECULAR ORDERING IN CONFINED ENVIRONMENTS

Crystal and phase morphologies and structures determined by self-organization of crystalline-amorphous diblockcopolymers, crystallization of the crystallizable blocks, and vitrification of the amorphous blocks are reviewed through asystematic study on a series of poly(ethylene oxide)-b-polystyrene (PEO-b-PS) diblock copolymers. On the base ofcompetitions among these three processes, molecular and supramolecular ordering in confined environments can beinvestigated. In a concentration-fluctuation-induced disordered (D_(CF)) diblock copolymer, the competition between crystalli-zation of the PEO blocks and vitrification of the PS blocks is momtored by time-resolved simultaneous small angle X-rayscattering (SAXS) and wide angle X-ray diffraction (WAXD) techniques. In the case of T_c相似文献   

Highly oriented and ordered microstructures in block copolymer films

Block copolymer (BCP) films with long-range lateral ordering and orientation are crucial for many applications. Here, we report a simple, versatile strategy based on a solution casting procedure, to produce millimeter thick film of BCPs with highly oriented nanostructures. Transmission electron microscope (TEM), small angle X-ray scattering (SAXS), and Hansen solubility parameters were used to study the morphology and interactions of the system. A variety of BCP-solvent pairs were investigated. Factors including set-up geometry, BCP characteristics, solvent evaporation, surface tension, and interactions, such as solvent-BCP, solvent-substrate, and BCP-substrate were examined. A mechanism is proposed to describe the observed long-range lateral ordering and orientation in films up to 1 mm in thickness. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018 , 56, 1369–1375     

Macroscopic arrays of magnetic nanostructures from self-assembled nanosphere templates

We have extended the widely used technique of nanosphere lithography to produce nanosphere templates with significantly improved long-range order. Single, ordered domains stretching over areas greater than 1 cm2 have been achieved by assembling spheres with the correct surface chemistry on a water/air interface. Self-assembly over macroscopic areas is facilitated by a combination of electrostatic and capillary forces. The presented technique is easily implemented, and the assembled monolayers can be transferred onto almost any surface, thus making the procedure applicable to a broad range of nanoscale research. We demonstrate this through the fabrication of hexagonally ordered, macroscopic arrays of magnetic nanostructures with modified magnetic properties.     

Competitive hydrogen bonding and self‐assembly in poly(2‐vinyl pyridine)‐block‐poly(methyl methacrylate)/poly(hydroxyether of bisphenol A) blends

Blends of poly(2‐vinyl pyridine)‐block‐poly(methyl methacrylate) (P2VP‐b‐PMMA) and poly(hydroxyether of bisphenol A) (phenoxy) were prepared by solvent casting from chloroform solution. The specific interactions, phase behavior and nanostructure morphologies of these blends were investigated by Fourier transform infrared (FTIR) spectroscopy, differential scanning calorimetry (DSC), dynamic light scattering (DLS), atomic force microscopy (AFM), and transmission electron microscopy (TEM). In this block copolymer/homopolymer blend system, it is established that competitive hydrogen bonding exists as both blocks of the P2VP‐b‐PMMA are capable of forming intermolecular hydrogen bonds with phenoxy. It was observed that the interaction between phenoxy and P2VP is stronger than that between phenoxy and PMMA. This imbalance in the intermolecular interactions and the repulsions between the two blocks of the diblock copolymer lead to a variety of phase morphologies. At low phenoxy concentration, spherical micelles are observed. As the concentration increases, PMMA begins to interact with phenoxy, leading to the changes of morphology from spherical to wormlike micelles and finally forms a homogenous system. A model is proposed to describe the self‐assembled nanostructures of the P2VP‐b‐PMMA/phenoxy blends, and the competitive hydrogen bonding is responsible for the morphological changes. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 1894–1905, 2009     

Kinetically Enhanced Approach for Rapid and Tunable Self‐Assembly of Rod–Coil Block Copolymers

A facile approach is reported to process rod–coil block copolymers (BCPs) into highly ordered nanostructures in a rapid, low‐energy process. By introducing a selective plasticizer into the rod–coil BCPs during annealing, both the annealing temperature and time to achieve thermodynamic equilibrium and highly ordered structures can be decreased. This process improvement is attributed to enhanced chain mobility, reduced rod–rod interaction, and decreased rod–coil interaction from the additive. The novel method is based on kinetically facilitating thermodynamic equilibrium. The process requires no modification of polymer structure, indicating that a wide variety of desired polymer functionalities can be designed into BCPs for specific applications.

     

PI-b-PMMA diblock copolymers: nanostructure development in thin films and nanostructuring of thermosetting epoxy systems

Poly(isoprene-block-methyl methacrylate) (PI-b-PMMA) block copolymers with different block ratios have been used to generate nanostructures both in thin films and by nanostructuring a thermosetting epoxy system. Obtained morphologies have been analyzed in terms of atomic force microscopy. The nanostructuring of thin films was carried out by thermal and solvent vapor annealing, in which the copolymer films were exposed to acetone vapors, selective solvent for methyl methacrylate (PMMA) block. By solvent vapor annealing thin films of both copolymers self-assembled into a hexagonally packed cylindrical morphology. Thermal annealing was carried out above the glass transition temperature of both blocks, obtaining worm-like and lamellar morphologies, depending on the block ratio. One of the copolymers has also been used for nanostructuring an epoxy thermosetting system. Morphologies consisting of spherical-shaped PI domains dispersed in a continuous epoxy matrix in which PMMA remained miscible were obtained, independently of the copolymer amount.     

Synthesis and self‐assembly of thermotropic block copolymer with long alkyl tethered cage silsesquioxane in the side chain

Thermotropic POSS‐containing poly(methacrylate) with long alkyl chain tethered polyhedral oligomeric silsesquioxane (POSS) in the side chain and the block copolymers (PMMA‐b‐PMAC11POSS) were developed by through living anionic polymerization. The resulting polymers indicated a phase transition temperature at 112 °C from spherocrystal to isotropic phase. The POSS‐containing polymer segments tended to form matrix of microphase‐separated nanostructures in the bulk even in the very low volume fraction, for instance, PMMA cylindrical nanostructure was obtained by PMMA₁₇₅‐b‐PMAC11POSS₁₁ (?_PMAC11POSS = 0.44). The control of thin film morphology was carried out by not only solvent annealing, but also thermal annealing, resulting in the formation of well‐ordered dot‐ and fingerprint‐type nanostructures. This is the first report in a series of POSS‐containing block polymers that are capable for thermal annealing to generate well‐ordered microphase‐separated nanostructures in thin films. The novel thermotropic POSS‐containing block copolymer offers a promising material for block copolymer lithography. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Synthesis of coil‐comb block copolymers containing polystyrene coil and poly(methyl methacrylate) side chains via atom transfer radical polymerization

A series of polystyrene‐b‐(poly(2‐(2‐bromopropionyloxy) styrene)‐g‐poly(methyl methacrylate)) (PS‐b‐(PBPS‐g‐PMMA)) and polystyrene‐b‐(poly(2‐(2‐bromopropionyloxy)ethyl acrylate)‐g‐poly(methyl methacrylate)) (PS‐b‐(PBPEA‐g‐PMMA)) as new coil‐comb block copolymers (CCBCPs) were synthesized by atom transfer radical polymerization (ATRP). The linear diblock copolymer polystyrene‐b‐poly(4‐acetoxystyrene) and polystyrene‐b‐poly(2‐(trimethylsilyloxy)ethyl acrylate) PS‐b‐P(HEA‐TMS) were obtained by combining ATRP and activators regenerated by electron transfer (ARGET) ATRP. Secondary bromide‐initiating sites for ATRP were introduced by liberation of hydroxyl groups via deprotection and subsequent esterification reaction with 2‐bromopropionyl bromide. Grafting of PMMA onto either the PBPS block or the PBPEA block via ATRP yielded the desired PS‐b‐(PBPS‐g‐PMMA) or PS‐b‐(PBPEA‐g‐PMMA). ¹H nuclear magnetic resonance spectroscopy and gel permeation chromatography data indicated the target CCBCPs were successfully synthesized. Preliminary investigation on selected CCBCPs suggests that they can form ordered nanostructures via microphase separation. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 2971–2983     

Defect-free nanoporous thin films from ABC triblock copolymers

The self-assembly of triblock copolymers of poly(ethylene oxide-b-methyl methacrylate-b-styrene) (PEO-b-PMMA-b-PS), where PS is the major component and PMMA and PEO are minor components, provides a robust route to highly ordered, nanoporous arrays with cylindrical pores of 10-15 nm that show promise in block copolymer lithography. These ABC triblock copolymers were synthesized by controlled living radical polymerization, and after solvent annealing, thin films showing defect-free cylindrical microdomains were obtained. The key to the successful generation of highly regular, porous thin films is the use of PMMA as a photodegradable mid-block which leads to nanoporous structures with an unprecedented degree of lateral order. The power of using a triblock copolymer when compared to a traditional diblock copolymer is evidenced by the ability to exploit and combine the advantages of two separate diblock copolymer systems, the high degree of lateral ordering inherent in PS-b-PEO diblocks plus the facile degradability of PS-b-PMMA diblock copolymer systems, while negating the corresponding disadvantages, poor degradability in PS-b-PEO systems and no long-range order for PS-b-PMMA diblocks.     

Thin film processing using S-layer proteins: biotemplated assembly of colloidal gold etch masks for fabrication of silicon nanopillar arrays

We explored the bionanofabrication of silicon nanopillar structures using ordered gold nanoparticle arrays generated from microbial surface layer (S-layer) protein templates. The S-layer template used for these thin film processing experiments was isolated from the Gram-positive bacterium Deinococcus radiodurans. In this preliminary work, S-layers preimmobilized onto chemically modified silicon substrates were initially used to template the fabrication of a nanolithographic hard mask pattern comprised of a hexagonally ordered array of 5-nm gold nanoparticles (lattice constant = 18 nm). Significantly, the use of the biotemplated gold nanoparticle mask patterns in an inductively coupled plasma (ICP) etching process successfully yielded silicon nanopillar structures. However, it was found that the resultant nanopillars (8–13 nm wide at the tip, 15–20 nm wide at half-height, 20–30 nm wide at the base, and 60–90 nm tall) appeared to lack any significant degree of translational ordering. The results suggest that further studies are needed in order to elucidate the optimal plasma processing parameters that will lead to the generation of long-range ordered arrays of silicon-based nanostructures using S-layer protein templates.     

中国嵌段共聚物受限自组装的研究进展

近年来,嵌段共聚物在受限空间中的自组装已成为高分子科学领域一个新的关注点.在受限条件下,嵌段共聚物展现出更多的可调控性,可获得复杂多样的微相分离结构.这些新颖的结构为实现嵌段共聚物更加丰富的功能奠定了材料基础.中国的学者们在嵌段共聚物受限自组装的理论模拟和实验研究方面取得了一系列重要创新成果,有力地推动了该领域的发展.本文总结和评述了中国学者在该领域的研究进展,并展望了嵌段共聚物受限自组装研究未来发展的机遇与挑战.     

Drying dissipative structures of cationic gel spheres of lightly cross-linked poly(2-vinyl pyridine) (170 ∼ 180 nm in diameter) in the deionized aqueous suspension

Drying dissipative patterns of cationic gel crystals of lightly cross-linked poly(2-vinyl pyridine) spheres (AIBA-P2VP, 170?～?180 nm in diameter) were observed on a cover glass, a watch glass, and a Petri glass dish. Convectional patterns were recognized with the naked eyes. Two kinds of the broad rings were observed at the outside edge and inner region in the macroscopic drying pattern, and their size at the inner regions first decreased and then turned to increase as gel concentration decreased. Formation of the similar-sized aggregates, i.e., hierarchical aggregation and their ordered arrays were observed. This work supported strongly the formation of the microscopic drying structures of (a) ordered rings, (b) flickering ordered spoke-lines, (c) net structure, and (d) lattice-like ordered structures of the aggregated particles. The ordering of the similar-sized aggregates of the cationic gel spheres (AIBA-P2VP) in this work is similar to that of the large cationic gel spheres of poly(2-vinyl pyridine) (385?～?400 nm in diameter) and further to that of the anionic thermosensitive gel spheres of poly(N-isopropyl acrylamide). Role of the electrical double layers around the aggregates and their interaction with the substrates during dryness are important for the ordering. The microscopic drying patterns of gel spheres were different from those of linear-type polymers and also from typical colloidal hard spheres, though the macroscopic patterns such as broad ring formation were similar to each other.     

Synthesis and spectroscopic characterization of symmetrical isoprene–methyl methacrylate diblock copolymers bearing different anthracene derivatives at the junctions

We describe the synthesis and characterization of 1‐(1‐anthryl)‐1‐phenylethylene (1‐An‐E) and 1‐(2‐anthryl)‐1‐phenylethylene (2‐An‐E). These species were used to end cap the living end group of polyisoprene (PI) obtained by anionic polymerization in tetrahydrofuran. The anions generated were used to initiate methyl methacrylate polymerization. In this way, we synthesized two symmetrical PI‐poly(methyl methacrylate) (PMMA) block copolymers each with a single dye at the junction. PI‐An1‐PMMA has an anthracene linked via its 1‐position. PI‐An2‐PMMA has the anthracene linked via its 2‐position. We compare the UV and fluorescence properties of the polymers to model compounds with similar chromophores. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 1225–1236, 2003     

Novel Nanostructures from Self‐Assembly of Chiral Block Copolymers

A diblock copolymer system constituting both achiral and chiral blocks, polystyrene‐block‐poly(L ‐lactide) (PS‐PLLA), was designed for the examination of chiral effects on the self‐assembly of block copolymers (BCPs). A unique phase with three‐dimensional hexagonally packed PLLA helices in PS matrix, a helical phase (H*), can be obtained from the self‐assembly of PS‐rich PS‐PLLA with volume fraction of PLLA f = 0.34, whereas no such phase was found in racemic polystyrene‐block‐poly(D .L ‐lactide) (PS‐PLA) BCPs. Moreover, various interesting crystalline PS‐PLLA nanostructures can be obtained by controlling the crystallization temperature of PLLA (T_c,PLLA), leading to the formation of crystalline helices (PLLA crystallization directed by helical confined microdomain) and crystalline cylinders (phase transformation of helical nanostructure dictated by crystallization) when T_c,PLLA < T_g,PS (the glass transition temperature of PS) and T_c,PLLA ≧ T_g,PS, respectively. As a result, a spring‐like behavior of the helical nanostructure can be driven by crystallization so as to dictate the transformation (i.e., stretching) of helices and to result in crystalline cylinders. For PS‐PLLA with PLLA‐rich fraction (f = 0.65), another unique phase, a hexagonally packed core‐shell cylinder phase with helical sense (CS*), in which the PS microdomains appear as shells and PLLA microdomains appear as matrix and cores, can be found in the self‐assembly of PLLA‐rich PS‐PLLA BCPs. The formation of those novel phases: helix and core‐shell cylinder is attributed to the chiral effect on the self‐assembly of BCPs, so we named this PS‐PLLA BCP as chiral BCP (BCP*). For potential applications of those materials, the spring‐like behavior with thermal reversibility might provide a method for the design of switchable nanodevices, such as nanoscale actuators. In addition, the PLLA blocks can be hydrolyzed. After hydrolysis, helical nanoporous PS bulk and PS tubular texture can be obtained and used as templates for the formation of nanocomposites.

     

Regioregular Poly(3‐hexylthiophene) in a Novel Conducting Amphiphilic Block Copolymer

Regioregular poly(3‐hexylthiophene) has been successfully incorporated into a novel amphiphilic block copolymer. The amphiphilic nature of poly(3‐hexylthiophene)‐block‐poly(acrylic acid) has been investigated using spectroscopic methods and has yielded solvatochromic behavior in several solvents of varying polarity. Evidence suggests that a supramolecular, long range ordering of block copolymer occurs in polar solvents, resulting in the formation of aggregates. Despite relatively large amounts of non‐conductive blocks, the poly(3‐hexylthiophene) diblock copolymer yields a high conductivity of 1 S · cm⁻¹, and atomic force microscopy shows the formation of a highly organized nanofibrilar morphology in the solid state.