The effect of polystyrene-block-poly(4-vinylpyridine) prepared by a RAFT method in the dispersion polymerization of styrene

The dispersion polymerization of styrene has been carried out using polystyrene-block-poly(4-vinylpyridine) copolymer [P(S-b-4VP)], prepared by a reversible addition-fragmentation chain transfer (RAFT) method, as a steric stabilizer in alcohol media. These block copolymer contains a long poly(4-vinylpyridine) block and a short polystyrene block. The stable spherical particles were obtained when the block copolymer concentrations increased from 2 to 20 wt.% relative to the monomer and the average particle sizes decreased from 340 to 200 nm with increasing concentration of the block copolymer. Alcoholic solvents, from methanol to n-hexanol, are responsible for the particle size. These results indicate that the poly(S-b-4VP) block copolymer is effective for providing polystyrene nano-sized particles with a low content of it working as a good stabilizer in any kind of alcoholic medium.     

Self-organization of triblock copolymer patterns obtained by drying and dewetting

Self-organized block copolymer structures derived from dewetting of thin films are becoming important in nanotechnology because of the various spontaneous and regular sub-micrometric surface patterns that may be obtained. Here, we report on the self-organization of a poly(styrene)-b-poly(ethene-co-butene-1)-b-poly(styrene) triblock copolymer during drying of its solution over a mica substrate. Regular submicrometric arrangements with long-range order were formed at critical polymer concentrations, consisting of parallel ribbons and hexagonal arrays of dots (droplets). This variety of highly ordered structures is explained by the interplay between forming mechanisms, mainly due to “fingering instabilities” at the three-phase line of the copolymer solution during drying. The thickness of the structures was “quantized” due to the microphase separation of the block copolymer. The formation of hexagonal patterns may be attributed to Marangoni instability at the liquid film surface prior to dewetting.     

Morphology of lamellae-forming block copolymer films between two orthogonal chemically nanopatterned striped surfaces

The structure of block copolymers results from the interplay between weak intermolecular forces, typically in the order of k(B)T per molecule. This is particularly true for block copolymer thin films in the presence of chemically patterned surfaces, where the different contributions to the total free energy, the interfacial and bulklike terms, have comparable magnitudes. Here, we report on the structures formed by block copolymers films equilibrated between two chemically patterned surfaces with orthogonal stripes. Our experiments and simulations reveal that the domains are continuous through the film and the interface between domains resembles the Scherk's first minimal surface. The impact of chemical patterns on block copolymer morphologies and the underlying physics gives insight into the nanofabrication of complex nanostructures with directed self-assembly using two engineered boundary conditions, as opposed to only one.     

Novel Route to Control Interfacial Properties of Glass Fiber-Reinforced Polystyrene Composites via a Photo-Cross-Linkable Block Copolymer Coupling Agent

A diblock copolymer of polystyrene–block–poly(2-hydroxyethyl acrylate) (PS-b-PHEA) was synthesized via atom transfer radical polymerization (ATRP) and reacted with cinnamoyl chloride in triethylamine to yield PS-b-(PCEA-co-PHEA) copolymer with photo-cross-linkable poly(2-cinnamoylethyl acrylate) (PCEA) moieties. Then the triblock copolymer of polystyrene–block–poly(2-cinnamoylethyl acrylate-co-2-hydroxyethyl acrylate)–block–poly(γ-methacryloxypropyltrimethoxysilane) (PS-b-(PCEA-co-PHEA)-b-PMPS) was synthesized viaATRP from PS-b-(PCEA-co-PHEA) copolymer. Using as-prepared triblock copolymer as a macromolecular coupling agent to modify glass fibers, via microbond tests, the interfacial bond strength between pretreated glass fiber and polystyrene was compared before and after copolymer photo-crosslinking. The partially crosslinked block copolymer coupling agent greatly improved the interfacial adhesion of glass fiber-reinforced polystyrene.     

Simulation of NEXAFS spectra of a photo-reactive copolymer with considerably large monomer units: An ab initio molecular orbital study

We performed the simulation of near edge X-ray absorption fine structure (NEXAFS) spectra of a photo-reactive copolymer with considerably large monomer units by ab initio molecular orbital calculation, in order to explain the spectral change induced by irradiation of the linearly polarized near ultra-violet (LPNUV) light. The “building block approach” is applied for the theoretical calculation to calculate the core-excited states of the polymer with such large monomer units; the monomer unit is divided into subunits, whose core-excited states are calculated individually, and the results are summed up to simulate the spectra of the polymer. With the result of the simulation, the peaks in the observed spectra were assigned. The spectral change after the LPNUV-irradiation is attributed to the change in the electronic structure caused by the breakdown of the π-conjugation system of chalconyl group after photo-dimerization.     

Light-induced orientation of the molecules of nematic liquid crystals doped with comb-shaped polymers with different spatial distributions of chromophores

The orienting effect of light on nematic liquid crystals (NLCs) doped with comb-shaped polymers with different spatial distributions of side absorbing azobenzene fragments, i.e., a homopolymer (containing only azofragments), a block copolymer (containing additionally a block of non-absorbing fragments), and a statistical copolymer (containing randomly arranged absorbing and non-absorbing fragments) is experimentally studied. The light-induced Freedericksz transition threshold for the block copolymer is two times lower than that for the homopolymer. For NLC with statistical copolymer dopant, the first-order orientation transition with an extremely wide optical bistability region is observed.     

An isothermal titration calorimetry study of the interactions between an oxyphenylethylene/oxyethylene diblock copolymer and sodium dodecyl sulfate

Interactions between the diblock copolymer S₁₅E₆₃ and the surfactant sodium dodecyl sulfate (SDS) have been investigated by isothermal titration calorimetry (ITC) in the temperature range 10–40°C. At 20°C, the block copolymer is associated into micelles with a hydrodynamic radius of 11.6?nm, which is composed of a hydrophobic styrene oxide (S) core and a water-swollen oxypolyethylene (PEO) corona. The copolymer/surfactant system has been studied at a constant copolymer concentration of 0.25?wt% and over a wide range of surfactant concentration, from 7.5?×?10^?6 up to 0.3?M. The titration calorimetric data for SDS in the temperature range 10–20°C presents a first endothermic increase indicating the formation of mixed copolymer rich-surfactant micelles. From that point, important differences in the ITC plots for surfactant titrations in the presence and in the absence of the copolymer are present. A shallow second endothermic peak is assigned to the interaction between SDS molecules and copolymer molecules resulting from the beginning of micelle disruption. An exothermic peak indicates the end of this disruption where only SDS micelles attached to single copolymer monomers are present, as shown by DLS in a previous paper. At higher temperatures in the range 25–40°C, the first endothermic maximum is not totally shown because interactions between surfactant and block copolymer start at very low SDS concentrations. Moreover, the second endothermic peak is absent and the exothermic minimum is less pronounced as a consequence of the increased micellization of the block copolymer.     

Mesostructures and properties of transparent block copolymer/silica nanocomposite monoliths

In this work, three different block copolymer/silica hybrid nanocomposite monoliths that possess mesostructured domains (hexagonal, cubic, and disordered) were prepared through the micellization of the block copolymer during the sol-gel process of a silica precursor. Transparent block copolymer/silica nanocomposite monoliths were obtained from the amphiphilic triblock copolymer poly(ethylene oxide)-b-poly(propylene oxide)-b-poly(ethylene oxide) (EO₁₀₆PO₇₀EO₁₀₆, Pluronic F127), which we used to organize the polymerizing silica networks; the ratio between the block copolymer and silica was fixed at 60:40 (wt%). Small-angle X-ray scattering (SAXS) and transmission electron microscopy (TEM) were used to observe the mesostructural ordering. Temperature-dependent SAXS patterns of the cubic structured nanocomposites showed that the calcination process takes place at 210°C. The transmittances of the nanocomposite monoliths over the range of wavelengths from 400 to 800 nm was >85%. From rheological measurements at low frequency, it was found that the hexagonally structured monoliths had higher storage and loss moduli relative to the monoliths possessing cubic and disordered structures.     

Phase behavior of triblock copolymers varying in molecular asymmetry

The transformation from A(1)B diblock copolymer to A(1)BA(2) triblock copolymers varying in molecular asymmetry is investigated as the A(2) end block is progressively grown via chemical synthesis. Dynamic rheological measurements show that the order-disorder transition (ODT) temperatures of two copolymer series differing in composition and molecular weight decrease when the A(2) block is short relative to the A(1) block, and then increase as the length of the A(2) block is increased further. The resultant ODT minimum, predicted by mean-field theory, is attributed to mixing between long B and short A(2) blocks.     

Mechanism for rapid self-assembly of block copolymer nanoparticles

Amphiphilic block copolymers in solution spontaneously self-assemble when the solvent quality for one block is selectively decreased. We demonstrate that, for supersaturation ratio changes [d(S)/dt] over 10(5) per second from equilibrium, nanoparticles are obtained with a formation mechanism and size dependent on the jumping rate and magnitude. The threshold rate for homogeneous precipitation is determined by the induction time of a particle, equivalent to the diffusion limited fusion of copolymer chains to form a corona of overlapping soluble brushes. Via determination of the induction time with a novel confined impinging jets mixer and use of a scaling relation, the interfacial free energy of a block copolymer nanoparticle was measured for the first time.     

Diblock and triblock copolymer thin films on a substrate with controlled selectivity

Using self-consistent field theory (SCFT), morphology development in symmetric linear ABC triblock copolymer films on neutral and selective substrates has been studied, and it is compared with the triblock copolymer morphologies in bulk. In particular, the effects of the substrate preferable to B (interior) block on nanopattern formation of the copolymer films are of our central interest. Here, we report various nanopatterns with tunable square morphologies. The domain patterns are much more diverse than those parallel to the substrate with substrate selectivity for end-block or those vertical to the substrate without substrate selectivity. Furthermore, in order to figure out an economical and efficient way to fabricate useful passive pattern transfer layers, which have potential applications in microelectronic processes and ultrahigh density storage media, we propose a two-step strategy and scrutinize the conditions for generating square symmetries using cylinder-forming or lamella-forming AB diblock copolymers deposited on substrates created from ABC triblock copolymer films. It is found that a thinner film with weak incompatibility can produce square patterns.     

Atomic force microscopy of the supramolecular organization and strength properties of ultrathin polysiloxane block copolymer films

Ultrathin films of polysiloxane block copolymers and their composites with modifying additives of the C₆₀ fullerene have been studied using atomic force microscopy. It has been revealed that, independently of the concentration of the additives, the surface relief of the films has an ordered structure with a period of approximately 35 nm, which is associated with the presence of a spatial network of rigid block domains of ladder phenylsilasesquioxane in the block copolymer. The mechanical properties of the films have been determined from indentation tests of their surface layers. Reliable quantitative measurements have been performed with specially fabricated spherical indenters of the calibrated submicron radius of curvature. The obtained values of the strength parameters correlate with the data derived from standard physical and mechanical tests of thick films. It has been found that the addition of the C₆₀ fullerene at a level of 0.01% significantly improves the elasticity of the surface layers of the block copolymer.     

Composition and molecular weight distribution of block copolymers

The composition distribution (CS) of diblock copolymers of styrene and methyl methacrylate, prepared anionically via a sequential addition procedure, has been investigated by two methods, one based on the theory of light scattering from copolymer solutions and the other on the principle of adsorption chromatography. Calculations were carried out to show that if the structure of the sample block copolymer is described by random coupling statistics, information of the molecular weight distribution (MWD) for either one of the block chains can be drawn from light scattering data obtained with one single solvent in which the solute is invisible. In practice, bromobenzene was used as a solvent appropriate for this purpose. Since the MWD for the precursor polystyrene is known, the MWD for the poly(methyl methacrylate) block was determined by this method. By using these data and assuming the Schulz distribution for MWD, the CD curve was calculated. Fractionation of the block copolymer sample by composition was made on a semipreparative scale (300 mg) by employing a glass cylinder packed with activated silica gel. The elution was carried out with a binary mixture of ethyl acetate and benzene. The fractionation was achieved without interference of molecular weight. Nine fractions having different styrene contents were recovered and analyzed to construct the CD curve. The CD curves obtained by the chromatographic method were in good agreement with those drawn from the light scattering data.     

Binary-component micelle and vesicle: Free energy and asymmetric distributions of amphiphiles between monolayers of vesicle

The real-space two-dimensional self-consistent field theory (SCFT) is employed to study the free energies of micelles and vesicles constituted by binary amphiphilic diblock copolymer AB in homopolymer A. With increasing volume fraction of copolymer AB, there are morphological transitions from the circle micelles to oblate circle-like micelles, to compound structure with inverted micelles in the inner center and micelles outer layer, and to vesicles. Special attentions are paid to the role of the copolymer AB in controlling free energies of the micelles and vesicles, by examining the effect of length ratio of A/B with the fixed whole chain length of AB copolymer, the length effect of A or B block with the corresponding fixed length of B or A block, for one component of copolymer, and the effect of different amphiphile compositions for binary-component copolymer system. The quantity η is provided to describe the asymmetric density distribution of amphiphiles between the inner and outer monolayers of vesicles, and to quantify the relative asymmetric extent of the density distribution between two species of copolymers in binary component vesicles.     

Single-crystal diffraction from two-dimensional block copolymer arrays

The structure of oriented 2D block copolymer single crystals is characterized by grazing-incidence small-angle x-ray diffraction, demonstrating long-range sixfold orientational order. From line shape analysis of the higher-order Bragg diffraction peaks, we determine that translational order decays algebraically with a decay exponent eta=0.2, consistent with the Kosterlitz-Thouless-Halperin-Nelson-Young theory for a 2D crystal with a shear modulus mu=2 x 10(-4) N/m.     

Optimization of components in high-yield synthesis of block copolymer-mediated gold nanoparticles

The optimization to achieve stable and high-yield gold nanoparticles in block copolymer-mediated synthesis has been examined. Gold nanoparticles are synthesized using block copolymer P85 in gold salt HAuCl₄·3H₂O solution. This method usually has a very limited yield which does not simply increase with the increase in the gold salt concentration. We show that the yield can be enhanced by increasing the block copolymer concentration but is limited to the factor by which the concentration is increased. On the other hand, the presence of an additional reductant (trisodium citrate) in 1:1 molar ratio with gold salt enhances the yield by manyfold. In this case (with additional reductant), the stable and high-yield nanoparticles having size about 14 nm can be synthesized at very low block copolymer concentrations. These nanoparticles thus can be efficiently used for their application such as for adsorption of proteins.     

一种基于空间一致性降元的高光谱图像非监督分类

为了提高分类精度和边缘辨识性,该文引入图像空间一致性降元(pixels reduction with spatial coherence property, PRSCP)及线性回归分析,提出了一种基于空间一致性降元的非监督分类。该方法从像元光谱相似性出发,利用像元最小关联窗口合并相邻相似像元为像块完成降元。使用线性关系建模像块内像元的光谱向量,并利用F检验判断像块数据的线性显著性。利用一元线性回归(one dimensional linear regression, ODLR)估计出像块的基准向量,根据基准向量合并相似(同类)像块完成分类。利用AVIRIS数据评估了该方法性能,实验结果表明：与K-MEANS和ISODATA方法相比,该方法精度高、边缘辨识度好及鲁棒性强。     

The packing of soft materials: Molecular asymmetry,geometric frustration and optimal lattices in block copolymer melts

Block copolymer systems are well known for their ability to self-assemble into a wide array of periodic structures. Due to the abundance and adaptability of physical theories describing polymers, this system is ideal for the development of robust and testible predictions about amphiphilic self-assembly phenomena at large. We review the results of field-theoretic treatments of block copolymer melts, with the aim of understanding how self-assembly in this system can be understood in terms of optimal lattice geometry. The self-consistent (mean) field theory of block copolymer melts as well as its low temperature limit, strong-segregation theory, are presented in detail, highlighting the special role played by asymmetry in the copolymer architecture. Special attention is paid to micellar configurations, where a well-defined and simple notion of optimal lattice geometry emerges from a particular asymptotic limit of the full self-consistent field theory. In this limit, the stability of competing arrangements of copolymer micelles can be assessed in terms of two discrete measures of the lattice geometry, emphasizing the non-trivial coupling between the internal configurations of the fundamentally soft micelles and the periodic symmetry of the lattice.     

Surface morphology of siloxane block copolymer crystals: (Tetramethyl-p-silphenylenejsiloxane—dimethylsiloxane

The metal decoration technique was applied to solution grown crystals and cast thin films of (tetramethyl-p-silphenylene) siloxane and dimethylsiloxane (DMS) block copolymers in order to elucidate their surface textures as a function of copolymer composition. Electron diffraction and microscopy studies were used. Metal-free zones are observed at surface steps of single crystals, and decorating particles occasionally form spiral growths in the inner regions of crystals. However, the decorating particles form regular patterns, particularly on the copolymer crystal surfaces. In the case of solution-cast thin films, deposition of metallic particles occurs along lamellar crystal edges or where a fibrillar morphology occurs. The nucleation density of metallic particles depends on the copolymer composition and increases with increasing crystallinity of the samples. Probable models are suggested to account for this surface texture. The propensity for screw-dislocations crystal growths on the crystal surfaces decreases as the noncrystallizable DMS component increases.