Selective distribution of interacting magnetic nanoparticles into block copolymer domains based on the facile inversion of micelles

We demonstrate a simple methodology to incorporate interacting magnetic nanoparticles (mNPs) into cylinder forming block copolymer templates. Poly(styrene-block-isoprene) (PS-b-PI) with PI cylinders and poly(styrene-block-4vinylpyridine) (PS-b-P4VP) with PS cylinders were used as the block copolymer templates and γ-Fe₂O₃ NPs coated with oleic acids were pre-synthesized for the interacting mNPs. Regardless of the template block copolymers, the selective location of mNPs and the size of mNP aggregates are clearly altered by changing casting solvents. When good solvents for both blocks were used as casting solvents, mNPs are readily aggregated during the solvent evaporation. In contrast, under selective casting solvents for the minor blocks, the mNPs were selectively trapped into the cylinder domains through the facile inversion of micelles during solvent evaporation. The interplay between mNPs and block copolymers was also tested with different molecular weights of block copolymers.     

Large organized surface domains self-assembled from nonpolar amphiphiles

For years, researchers had presumed that Langmuir monolayers of small C(n)F(2n+1)C(m)H(2m+1) (FnHm) diblock molecules (such as F8H16) consisted of continuous, featureless films. Recently we have discovered that they instead form ordered arrays of unusually large (~30-60 nm), discrete self-assembled surface domains or hemimicelles both at the surface of water and on solid substrates. These surface micelles differ in several essential ways from all previously reported or predicted molecular surface aggregates. They self-assemble spontaneously, even at zero surface pressure, depending solely on a critical surface concentration. They are very large (~100 times the length of the diblock) and involve thousands of molecules (orders of magnitude more than classical micelles). At the same time, the surface micelles are highly monodisperse and self-organize in close-packed hexagonal patterns (two-dimensional crystals). Their size is essentially independent from pressure, and they do not coalesce and are unexpectedly sturdy for soft matter (persisting even beyond surface film collapse). We and other researchers have observed large surface micelles for numerous diblocks, using Langmuir-Blodgett (LB) transfer, spin-coating and dip-coating techniques, or expulsion from mixed monolayers, and on diverse supports, establishing that hemimicelle formation and ordering are intrinsic properties of (perfluoroalkyl)alkanes. Notably, they involve "incomplete" surfactants with limited amphiphilic character, which further illustrates the outstanding capacity for perfluoroalkyl chains to promote self-assembly and interfacial film structuring. Using X-ray reflectivity, we determined a perfluoroalkyl-chain-up orientation. Theoretical investigations assigned self-assembly and hemimicelle stability to electrostatic dipole-dipole interactions at the interface between Fn- and Hm-sublayers. Grazing-incidence small-angle X-ray scattering (GISAXS) data collected directly on the surface of water unambiguously demonstrated the presence of surface micelles in monolayers of diblocks prior to LB transfer for atomic force microscopy imaging. We characterized an almost perfect two-dimensional crystal, with 12 assignable diffraction peaks, which established that self-assembly and regular nanopatterning were not caused by transfer or induced by the solid support. These experiments also provide the first direct identification of surface micelles on water, and the first identification of such large-size domains using GISAXS. Revisiting Langmuir film compression behavior after we realized that it actually was a compression of nanometric objects led to further unanticipated observations. These films could be compressed far beyond the documented film "collapse", eventually leading to the buildup of two superimposed, less-organized bilayers of diblocks on top of the initially formed monolayer of hemimicelles. Remarkably, the latter withstood the final, irreversible collapse of the composite films. "Gemini" tetrablocks, di(FnHm), with two Fn-chains and two Hm-chains, provided two superposed layers of discrete micelles, apparently the first example of thin films made of stacked discrete self-assembled nanoobjects. Decoration of solid surfaces with domains of predetermined size of these small "nonpolar" molecules is straightforward. Initial examples of applications include deposition of metal dots and catalytic oxidation of CO, and nanopatterning of SiO(2) films.     

Aggregation in Langmuir and Langmuir-Blodgett films of azopolymers and its role for optically induced birefringence

Aggregation in azopolymers is reported to affect the Langmuir monolayer characteristics and the optically induced birefringence of Langmuir-Blodgett (LB) films from DR19 isophorone polyurethane (PIPDI) and DR19 4,4′ diphenylmethane polyurethane (PMDI). In mixed monolayers with cadmium stearate (CdSt), the folding of PMDI molecules appears to be substantially changed compared to the monolayer of the pure polymer, leading to a surface potential that is higher than observed for monolayers of pure PMDI and of pure CdSt. UV-Vis spectroscopy data of the deposited mixed LB films indicate H-type aggregation for PMDI/CdSt, in contrast to PIPDI/CdSt and other azopolymers investigated earlier. The H-type aggregation precludes photoisomerization, thus requiring a higher laser power for the maximum induced birefringence to be achieved in LB films of PMDI/CdSt.     

Fullerene- and porphyrin-appended crown ethers: Synthesis and preparation of stable langmuir and langmuir-blodgett films

The synthesis of a series (1–5) of fullerene and Zn(II)-porphyrin amphiphiles with polar dibenzo[24]crown-8 headgroups is described. Their ability to form Langmuir monolayers at the air-water interface was investigated in a systematic study. The Langmuir films were characterized by their surface pressure versus molecular area isotherms, compression and expansion cycles, and Brewsterangle microscopy. Complexation of larger alkali metal cations (K⁺ and Cs⁺) by the polar headgroups leads to higher molecular area requirements and a better anchoring to the aqueous subphase. The monolayers of the porphyrin-(dibenzo[24]crown-8) conjugates were transferred as Langmuir—Blodgett films onto glass slides and the films characterized by UV-vis spectroscopy and grazing-incidence X-ray diffraction. Good evidence was obtained that the porphyrin-fullerene-crown ether triad 5 adopts a sandwich geometry in the LB films. In such an arrangement, the electron-attracting carbon sphere benefits from attractive interactions with the sandwiching electron-rich porphyrin and crown ether chromophores. The described films could have potential applications as functional materials in optical and electronic technology.     

High-throughput preparation of complex multi-scale patterns from block copolymer/homopolymer blend films

A simple, straightforward process for fabricating multi-scale micro- and nanostructured patterns from polystyrene-block-poly(2-vinylpyridine) (PS-b-P2VP)/poly(methyl methacrylate) (PMMA) homopolymer in a preferential solvent for PS and PMMA is demonstrated. When the PS-b-P2VP/PMMA blend films were spin-coated onto a silicon wafer, PS-b-P2VP micellar arrays consisting of a PS corona and a P2VP core were formed, while the PMMA macrodomains were isolated, due to the macrophase separation caused by the incompatibility between block copolymer micelles and PMMA homopolymer during the spin-coating process. With an increase of PMMA composition, the size of PMMA macrodomains increased. Moreover, the P2VP blocks have a strong interaction with a native oxide of the surface of the silicon wafer, so that the P2VP wetting layer was first formed during spin-coating, and PS nanoclusters were observed on the PMMA macrodomains beneath. Whereas when a silicon surface was modified with a PS brush layer, the PS nanoclusters underlying PMMA domains were not formed. The multi-scale patterns prepared from copolymer micelle/homopolymer blend films are used as templates for the fabrication of gold nanoparticle arrays by incorporating the gold precursor into the P2VP chains. The combination of nanostructures prepared from block copolymer micellar arrays and macrostructures induced by incompatibility between the copolymer and the homopolymer leads to the formation of complex, multi-scale surface patterns by a simple casting process.     

Langmuir and Langmuir-Blodgett Films of Polyfluorenes and Their Use in Polymer Light-Emitting Diodes

The Langmuir and Langmuir-Blodgett (LB) film properties of two polyfluorene derivatives, namely poly(2,7-9,9′-dihexylfluorene-dyil) (PDHF) and poly(9,9 dihexylfluorene-dyil-vynilene-alt-1,4-phenylene-vyninele) (PDHF-PV), are reported. Surface pressure (П-A) and surface potential (ΔV-A) isotherms indicated that PDHF-PV forms true monolayers at the air/water interface, but PDHF does not. LB films could be transferred onto various types of substrate for both PDHF and PDHF-PV. Only the LB films from PDHF-PV could withstand deposition of a layer of evaporated metal to form a light-emitting diode (PLED), which had typical rectifying characteristics and emitted blue light. It is inferred that the ability of the polymer to form true monomolecular layers at the air/water interface seems to be associated with the viability of the LB films in PLEDs.     

Characteristics of Polypeptide/Phospholipid Monolayers on Water and the Plasma-Activated Polyetheretherketone Support

Polyetheretherketone (PEEK) is a highly biocompatible polymer widely used in medicine as an implant production material. In this article, the PEEK surface was characterized in terms of its wettabillity properties after the physicochemical modifications by treatment with the low-temperature air plasma and covering with the Langmuir–Blodgett (LB) monolayers of polypeptide (cyclosporine A, CsA) and/or phospholipid (1,2-dipalmitoyl-sn-glycero-3-phosphocholine, DPPC). The LB deposition was preceded by the analysis of miscibility and morphology of monolayers at the air/water interface by means of the Langmuir technique and Brewster angle microscopy (BAM). Then, wettability of the polymer-supported films was evaluated by the contact angle measurements of three probe liquids of different characters (two polar—water and formamide, one apolar—diiodomethane). The measured contact angles allowed for determination of the surface free energy and its components based on the Lifshitz-van der Waals/acid–base (LWAB) approach. Some relations between the kind and magnitude of interactions within the model membranes on the water subphase and those of the PEEK-supported membranes with the liquids were found out. The results allowed obtaining the interesting models of biological coatings with potential applications.     

Nanostructure and hydrogen bonding in interpolyelectrolyte complexes of poly(?-caprolactone)-block-poly(2-vinyl pyridine) and poly(acrylic acid)

Nanostructured poly(?-caprolactone)-block-poly(2-vinyl pyridine) (PCL-b-P2VP)/poly(acrylic acid) (PAA) interpolyelectrolyte complexes (IPECs) were prepared by casting from THF/ethanol solution. The morphological behaviour of this amphiphilic block copolymer/polyelectrolyte complexes with respect to the composition was investigated in a solvent mixture. The phase behaviour, specific interactions and morphology were investigated using differential scanning calorimetry (DSC), Fourier transform infrared (FTIR) spectroscopy, optical microscopy (OM), dynamic light scattering (DLS) and atomic force microscopy (AFM). Micelle formation occurred due to the aggregation of hydrogen bonded P2VP block and polyelectrolyte (PAA) from non-interacted PCL blocks. It was observed that the hydrodynamic diameter (D_h) of the micelles in solution decreased with increasing PAA content up to 40 wt%. After 50 wt% PAA content, D_h again increased. The micelle formation in PCL-b-P2VP/PAA IPECs was due to the strong intermolecular hydrogen bonding between PAA homopolymer units and P2VP blocks of the block copolymer. The penetration of PAA homopolymers into the shell of the PCL-b-P2VP block copolymer micelles resulted in the folding of the P2VP chains, which in turn reduced the hydrodynamic size of the micelles. After the saturation of the shell with PAA homopolymers, the size of the micelles increased due to the absorption of added PAA onto the surface of the micelles.     

Self-assembly of polystyrene-b-poly(4-vinylpyridine) in deoxycholic acid melt

It is well known that amphiphilic block copolymers in selective solvents self-assemble into micellar structures, where solvophilic blocks tend to contact with solvents while solvophobic blocks are shielded from the solvents. Different from the conventional micellization in liquid systems, we report that the block copolymer, polystyrene-b-(4-vinylpyridine) (PS-b-P4VP), can self-assemble in melted deoxycholic acid (DCA) at high temperatures and the structures are retained in “solid state” after being cooled down to room temperature. Probing by transmission electron microscopy (TEM), we found that a series of self-assembled structures, including spherical micelles, wormlike micelles and vesicles can be obtained by varying the length of the block copolymers and the morphologies are dependent on the annealing temperature and time. We also demonstrate how to extract the structures that are trapped in solid state by removing DCA using appropriate solvents. The extracted vesicles, which are loaded with solid molecules, are potential for applications in nanocapsules and controlled release.     

Synthesis and characterization of novel graft copolymers by radiation‐induced grafting

The radiation‐induced graft copolymerization of N‐vinyl‐2‐pyrrolidone (NVP), 4‐vinyl pyridine (4VP), and 2‐vinyl pyridine (2VP) monomers onto poly (ethylene‐alt‐tetrafluoroethylene) (ETFE) was investigated. The influence of synthesis conditions particularly the solvent was studied. Various solvents, such as n‐propanol, isoproponol, benzyl alcohol, methanol, ethanol, cyclohexanone, tetrahydrofuran (THF), nitromethane, 1,4‐dioxane, and n‐heptane were examined for this purpose. Graft copolymers were characterized by Fourier transform infrared (FTIR) spectroscopy, dynamic mechanical analysis (DMA), and scanning electron microscopy‐energy dispersive spectroscopy (SEM‐EDAX). It was found that the nature of the solvent had profound influence over the grafting reaction. Cyclohexanone, n‐propanol, and isoproponol for 4VP/ETFE grafting, THF and 1,4‐dioxane for NVP/ETFE grafting, and benzyl alcohol and methanol for 2VP/ETFE grafting were found to be the suitable solvents yielding highest graft levels. Isoproponol and n‐propanol are promising in terms of both graft level and mechanical properties for 4VP/ETFE. Grafting of NVP, 4VP, and 2VP onto ETFE were verified through FTIR spectroscopy. Storage modulus and glass transition temperature of the copolymers were found to increase as graft level increased. Surface profile of representative films was also investigated by viewing the distribution of elemental nitrogen using SEM‐EDAX. Results indicated that copolymers of 4VP, NVP, and 2VP are considerably different from each other. 4VP‐based copolymers exhibited relatively more homogenous grafting over the surface compared with NVP‐ and 2VP‐based copolymers. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Block copolymers containing pyridine moieties: Precise synthesis and applications

This review highlights the precise synthesis and application of various well-defined rod–coil and coil–coil block copolymers composed of poly(2-(or 4-)vinylpyridine) (P2VP or P4VP) block(s) with pyridine moieties. These polymers were synthesized by means of living anionic polymerization. Poly(hexyl isocyanate) (PHIC) was used as the rod-like segment, because hexyl isocyanate undergoes living anionic polymerization under carefully selected conditions. This review describes the syntheses of the block copolymers, polystyrene-b-P2VP, polystyrene-b-P4VP, polyisoprene-b-P2VP, P2VP-b-poly(methyl methacrylate), P2VP-b-poly(ethylene oxide), P2VP-b-poly(2-(N-carbazolyl)ethyl methacrylate), P2VP-b-PHIC, P2VP-b-PHIC-b-P2VP, and PHIC-b-P2VP-b-PHIC. The formation of self-organized nanostructured materials and molecular assemblies by such block copolymers and their possible applications are also described. These assemblies include monolayers, microphase-separated periodic-ordered nanostructures, micelles, polymer–metal complexes, nanoparticles, inorganic and metal layers, and nanoporous films with nanoparticles.     

PS-b-P4VP的合成及其薄膜的微相分离形貌

通过原子转移自由基聚合（ATRP）方法制备了聚苯乙烯-b-聚（4-乙烯基吡啶）二嵌段共聚物（PS-b-P4VP）,使用核磁共振（1H NMR）和凝胶渗透色谱（GPC）对嵌段共聚物进行了表征。将PS-b-P4VP/三氯甲烷溶液旋涂成膜,使用原子力显微镜（AFM）观察热处理条件对薄膜微相分离形貌的影响。结果表明,PS-b-P4VP薄膜会发生微相分离,形成以PS链段为分散相、P4VP链段为连续相基体的纳米尺度微相分离形貌。热处理条件的改变使薄膜呈现不同程度的微相分离形貌结构,提高热处理温度以及延长热处理时间均有利于促进嵌段共聚物的微相分离,使微相分离程度加大。在150℃、24 h的热处理条件下,PS-b-P4VP薄膜形成了PS微相区以规则的柱状形态在薄膜表面突起的微相分离形貌,且分布均匀,界面清晰。     

双亲嵌段共聚物PSt-b-P(St-alt-MA)-b-PAA的自组装行为

以三硫代碳酸二(α, α'-二甲基-α-乙酸)酯(BDATC)为链转移剂, 以苯乙烯、马来酸酐、丙烯酸为原料, 通过可逆加成-断裂链转移(RAFT)合成了双亲嵌段共聚物PSt-b-P(St-alt-MA)-b-PAA。通过选择性溶剂N, N-二甲基甲酰胺(DMF)诱导聚合物进行自组装, 利用紫外-可见光光度仪、纳米激光粒度仪详细研究了共聚物中亲疏水嵌段长度、初始浓度、体系pH值对聚合物自组装行为的影响。通过化学交联的方法制备得到了聚合物交联胶束, 利用透射电镜表征了形貌与尺寸, 研究明确了其形状和尺寸的稳定性。结果表明, 上述因素均会影响共聚物的自组装行为和自组装胶束的形态, 经乙二胺交联得到的交联自组装胶束平均粒径为145.4nm, 并具有良好的形状和尺寸稳定性。     

Adhesion of Polymer Monolayers to the Water Subphase. Effect of Solvents and Polymer Functionality

The properties and the organization of poly (D, L-lactic acid) monolayers spread at the air/water interface were shown to be dramatically dependent on whether these monolayers have been spread from a good or a bad solvent. Whereas a good solvent, such as chloroform, favored the deployment of polymer chains from their coiled structure in solution to the unfolded structure, a bad solvent, as exemplified by acetone, enhanced strong intersegment interactions resulting in the formation of microdomains capable of respreading and favored adhesion of the polymer monolayer to water.

Independently carried out experiments with monolayers of ester derivatives of hyaluronic acid demonstrated that the nature of a chemical group substituted on the glucuronic acid moieties of the polymer can considerably influence surface properties of these monolayers. Thus, if monolayers of the ethyl ester derivative were shown to be rather compressible, those of the benzyl ester derivative were more rigid and, relative to the ethyl ester derivative, they exhibited increased adhesion to the water subphase within a wide range of areas.

It has been shown that the van Oss-Chaudhury-Good theoretical approach applied to the calculation of interfacial free energies of these monolayers with water, obtained from the contact angle data on their Langmuir-Blodgett films, was perfectly adapted to explain the observed differences in their adhesion properties.     

Poly[2,7-(9,9-dihexylfluorene)]-block-poly[3-(trimethoxysilyl)propyl methacrylate] (PF-b-PTMSPMA) rod-coil block copolymers: Synthesis,morphology and photophysical properties in mixed solvents

We report the synthesis, morphology, and photophysical properties of poly[2,7-(9,9-dihexylfluorene)]-block-poly[3-(trimethoxysilyl)propyl methacrylate] (PF-b-PTMSPMA) with two different coil lengths. Ethyl acetate (EA) and methanol (MeOH) are used as selective solvents for the PF rod and PTMSPMA coil blocks, respectively, while THF as the common solvent. Micelle morphologies of the PF-b-PTMSPMA in THF/MeOH or THF/EA mixed solvents are characterized by transmission electron microscopy (TEM) and scanning force microscopy (SFM). In the THF/MeOH mixed solvent, PF-b-PTMSPMA assembles into diverse morphologies of sphere, short cylinder, cylinder, and cylinder bundles. Besides the selective effects, the strong π–π interaction of PF contributes partially to the above morphologies. In the THF/EA mixed solvent, morphologies of the PF-b-PTMSPMA changes from large compound micelles (LCM) to hollow spherical micelles due to the strong core chain stretching. Stable micelles are obtained by crosslink Si(OR)₃ groups of the PTMSPMA block by triethylamine (TEA). The micellar morphology significantly affects the photophysical properties. In the THF/MeOH mixed solvent, blue shifts on the UV-vis and fluorescence spectra are observed probably attributed to the formation of the H-aggregation in the PF core. However, the photophysical properties are insensitive to the different ratios of THF/EA, due to the insignificant aggregation of short PF corona. The present study reveals that the morphology and photophysical properties of fluorene-based rod-coil polymers could be significantly manipulated through solvent, rod/coil ratio, and π–π interaction.     

A simple method for creating nanoporous block-copolymer thin films

We introduce a simple method to create block copolymer films with controlled porosity. We show that the pore structure can be varied over a broad range of length scales not obtainable in homopolymer blend films. The morphology is a random two phase kinetically trapped structure that is not limited by the equilibrium block copolymer structure. The morphology is obtained through blending homopolymer poly(4-vinylpyridine) (P4VP) with block copolymer polystyrene-b-poly(4-vinylpyridine) (PS-b-P4VP) and then removing the homopolymer P4VP by washing with ethanol. The structure obtained prior to washing (which templates the nanoporous structure) is stabilized in the kinetically trapped morphology during spincoating and is not obtainable from either homopolymer blends or the pure block copolymer. When PS/P4VP blend solutions in tetrahydrofuran were spincoated at 25% relative humidity, continuous films with raised P4VP nanodomains were formed due to a preferential affinity of the spinning solvent for polystyrene. In a similar manner, when PS-b-P4VP/P4VP block copolymer/homopolymer solutions were spincoated, the P4VP homopolymer was solubilized in the P4VP block domains during spincoating, suppressing macro-phase separation. The film morphology is generated at the air surface and then propagates through the film, resulting in P4VP nanodomains oriented vertically to the substrate. In the resulting films, the size of P4VP nanodomains were varied by increasing the amount of P4VP homopolymer. The subsequent extraction of P4VP homopolymer from the PS-b-P4VP/P4VP blend films in ethanol resulted in nanopores with a distribution of length scales. The morphology of these materials makes the films potentially suitable for a range of applications such as anti-reflective coatings, nanoporous membranes and low-k materials. An illustrative example of an anti-reflective coating will be presented.     

SEBS三嵌段共聚物膜的形态研究

Surface morphologies of the films of poly [styrene-b-（ethylene-co-butene）-b-styrene] （SEBS） have been studied by using tapping-mode atomic force microscopy （TM-AFM）. The films of block copolymer were prepared both by spin-coating on mica and by solvent-casting on different solution surfaces. For spin-coating samples, the effect of solution concentration, solvent, and annealing temperature are investigated. It is shown that changing the concentration of the solution makes no difference on the morphology of the film of the block copolymer. The microstructures are quite stable during thermal annealing; only the size of the domains changes toward the equilibrium configuration. However, solvent annealing can notably change the microstructures. When different selective solvents are used for film spin-coating, different morphologies can be obtained and explained by the different solubility parameters of the solvents. As expected, significant different morphologies in the top and the bottom surfaces of the casting films were observed. The images of the top surfaces reveal cylinder microdomains, while those of the bottom surfaces were spherical morphologies.     

Preparation and electrical conductivity of Langmuir–Blodgett films of poly(3-alkylthiophene)s

Five poly(3-alkylthiophene)s (P3ATs) with different alkyl side chains were synthesized. Pure P3ATs alone are not well suited for manipulation by the Langmuir–Blodgett (LB) technique, but their mixed systems with arachidic acid can be used to prepare high-quality Y-type films with the vertical dipping method, which was proved by UV-visible spectra and small-angle X-ray diffraction patterns. Conductivities of the LB films were measured using a two-probe method at room temperature. The conductivities exhibited obvious anisotropy and could increase by 2–4 orders of magnitude after iodine vapor doping. The influence of alkyl chain length on the conductivity in the LB films was revealed. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 1–6, 1998     

Block copolymer photonic mesogels exhibiting dual volume phase transitions

Photonic mesogel films exhibiting brilliant photonic colors were prepared by selective swelling of polystyrene-b-quaternized poly(2-vinyl pyridine) (PS-b-QP2VP) block copolymers, and their volume phase transition behaviors were investigated in various solvent mixtures. The swollen PS-b-QP2VP lamellae segregate into mesophased gels where the highly swollen QP2VP gel layers are alternating with the glassy PS layers and exhibit strong responsive photonic colors in visible regime. Utilizing the changes of photonic stop bands, the swelling behaviors of the photonic mesogels were able to be monitored with sub-nanometer accuracy. Unusual dual volume phase transitions were observed at certain conditions where hydrogen bonding became significantly strong.