"Inversed" surface micelle array fabrication of an amphiphilic block copolymer on water surface

A mixed film of polystyrene-block-poly(4-vinylpyridine) (PS-b-P4VP) with 6-{4-[(4-hexylphenyl)azo]phenoxy}hexanoic acid (6Az5COOH) were prepared on water by co-spreading method. The resulting films were transferred onto mica at various surface pressures. Atomic force microscopy (AFM) and pi-A isotherm measurements revealed that both PS and p4VP blocks in PS-b-P4VP forms spread monolayer on water with the assist of 6Az5COOH at low surface pressures. Upon compression on water, we observed that the P4VP/6Az5COOH parts in the hybrid film are collapsed selectively at an early stage and form dot array morphology. In addition, gold cluster dots were deposited selectively on the dots in the dot array film by metallization based on deposition of HAuCl4 to the P4VP chain and reduction with dimethylamino borane. These results strongly support the fact that the "inversed" surface micelles are formed on water via hybridization of PS-b-P4VP with 6Az5COOH.     

Charging Effects on Nuclear Spin Relaxation in Quantum Dots

We study the mechanism of nuclear spin relaxation in quantum dots due to the electron exchange with 2D gas. We show that the nuclear spin relaxation rate T ₁ ^–1 is dramatically affected by the Coulomb blockade (CB) and can be controlled by gate voltage. In the case of strong spin–orbit (SO) coupling the relaxation rate is maximal in the CB valleys whereas for the weak SO coupling the maximum of 1/T ₁ is near the CB peaks. The physical mechanism of nuclear spin relaxation rate at strong SO coupling is identified as Debye–Mandelstam–Leontovich–Pollak–Geballe relaxational mechanism.     

Bridging the Gap in the Micellar Transformation from Cylinders to Vesicles

The micelles of polystyrene‐block‐poly(acrylic acid) (PS₁₅₄‐b‐PAA₄₉) are made to transform slowly in mixed solvent, allowing continual trapping of the various intermediates. During the transformation from cylindrical to vesicular micelles, it appears that a section of the cylinder first flattens to give a lamellar section, which then depresses to give a bowl‐like moiety, before finally converting to a fully enclosed vesicle. Most part of this transformation involves the “flow” of polymer domains without mingling of the hydrophobic and hydrophilic domains. On the bases of the literature and the observation in this work, it is proposed that the reduction of surface‐to‐volume ratio provides the thermodynamic driving force for the cylinder‐to‐vesicle transformation, whereas molecular reorganization within the polymer domains creates the kinetic barrier. From the point of view of molecular interactions, the “flow” of polymer domain involves a low barrier, whereas the merging of two micelles, the severing of cylindrical micelles, and the closing of partial vesicles encounter high barriers. Moreover, the kinetic barrier is reduced when PSPAA containing shorter PAA blocks is used, or when the PAA block are protonated. This mechanistic proposal explains the kinetically controlled transformation pathway and structural features of the observed intermediates.     

Thermal-sensitive PBMA-b-PNIPAAm amphiphilic block copolymers brushes and their assembling micelles

Brush-like block copolymers with poly(t-butyl methacrylate) (PBMA) and poly(N-ispropylacrylamide) (PNIPAAm) as side arms, PBMA-b-PNIPAAm, were designed and synthesized via a simple free radical polymerization route. The chemical structure of these polymer brushes was characterized and determined by nuclear magnetic resonance (1H NMR), and Fourier transform infrared spectrometry (FT-IR). The micellar formation by these polymer brushes in aqueous solutions were detected by a surface tension technique, and the critical micelle concentration (CMC) ranged from 1.53 to 8.06 mg L(-1). The morphology and geometry of polymer micelles were investigated by transmission electron microscope (TEM) and dynamic light scattering (DLS). The polymer micelles assume the regularly-spherical core-shell structure with well-dispersed individual nanoparticles, and the particle size was in the range from 36 to 93 nm. The PNIPAAm segments exhibited a thermoreversible phase transition, so the resulting block polymer brushes were temperature-sensitive and the low critical solution temperature (LCST) was determined by UV-vis spectrometer at about 28.82-29.40 degrees C. The characteristic parameters of the polymer micelles such as CMC, micellar size and LCST values were affected by their compositional ratios and the length of hydrophilic or hydrophobic chains. The self-assembled micelles are expected to be used in specific biomedical fields as a candidate of drug controlled release carrier.     

Morphology and ionic conductivity of solid polymer electrolytes based on polyurethanes with various topological structures

Polyurethanes with linear, hyperbranched and comb-crosslinked structures were synthesized and were used to prepare solid polymer electrolytes. The polymer electrolytes were characterized by means of Fourier transform Raman spectroscopy, impedance spectroscopy (IS) and atomic force microscopy (AFM). The results showed that salt concentration significantly influences the morphology and conductivity of the three kinds of polyurethane/LiClO₄ system. When the mole ratios of the ether oxygen atom to lithium ion were controlled to be 12, 4 and 4 respectively for linear, hyperbranched and comb cross-linking polyurethane, the electrolytes typically displayed micro-phase separated morphology and the ionic conductivity also reached maxima respectively at 2.2 × 10^–7 S/cm, 2.8 × 10^–6 S/cm and 2.8 × 10^–5 S/cm at room temperature.     

Controlled adhesion of human lymphocytes on electrically charged polymer surface having phosphorylcholine moiety

The human lymphocytes were interacted with polymer surfaces whose surface potential was controlled by the formation of a polyion complex (PIC) having a phosphorylcholine moiety. 3-(Methacryloyloxypropyl)-trimethyl ammonium iodide as the cationic unit or potassium 3-methacryloyloxypropyl sulfonate as the anionic unit was copolymerized with 2-methacryloyloxyethylphosphorylcholine (MPC) and _n-butyl methacrylate. PIC was made at the solid-liquid interface, that is, an aqueous solution containing an anionic polymer with different concentrations was contacted with a cationic polymer coated polymer membrane. The formation process of PIC was followed using a quartz crystal microbalance, and the PIC surfaces were analyzed by ζ potential and X-ray photoelectron spectroscopy. The surface potential on the PIC was controllable from +20 to -16 mV, which increased in the amount of adsorbed anionic copolymer as the ζ potential decreased toward the negative charge. The PIC surface in contact with human lymphocyte for 5 h was observed using ascanning electron microscopy and the density of the adherent human lymphocyte was determined by the lactate dehydrogenase method. The lymphocyte adhesion on the surface was gradually reduced with an increase in the negative value of the ζ potential. The morphological change in the adherent lymphocytes was not observed on the polymer surfaces with MPC units.The adherent lymphocytes were not activated on the PIC surface. The lymphocyte adhesion with reduced activation could be controlled by changing the surface potential on the polymer with the MPC unit.     

Corrosion performance of reinforced mortar in the presence of polymeric nano-aggregates: electrochemical behavior, surface analysis, and properties of the steel/cement paste interface

This study reports on the effect of admixed polyethylene oxide-b-polystyrene (PEO₁₁₃-b-PS₇₀) micelles on corrosion behavior of reinforced mortar. The electrochemical measurement shows that the corrosion performance of the reinforcing steel was not significantly improved. However, surface analysis and microstructural investigation at the steel/cement paste interface reveal that the admixed micelles lead to a steel surface layer with enhanced barrier properties in terms of morphology and composition. Therefore, the presence of micelles further minimized and halted the corrosion process, despite the very aggressive, chloride-containing environment of 5% NaCl. The reasons and mechanisms behind the hereby observed corrosion behavior of reinforced mortar in the presence of micelles are related to the influence of these nano-aggregates on microstructural properties. These further results in altered water/ion transport and chloride-binding mechanisms in the bulk mortar matrix and thus steel product layer modifications towards enhanced corrosion resistance.     

Morphology control of structured polymer brushes

The surface-initiated photopolymerization (SIPP) of vinyl monomers on structured self-assembled monolayers, as defined by two-dimensional (2D) initiator templates for polymer growth, is investigated. The 2D templates are prepared by electron-beam chemical lithography (EBCL) of 4'-nitro-4-mercaptobiphenyl (NBT) and chemical conversion to an asymmetric azo initiator (4'-azomethylmalonodinitrile-1,1'-biphenyl-4-thiol). Ex situ kinetic studies of the SIPP process reveal a linear increase in the thickness of the polymer layer with the irradiation/polymerization time. The effect of the applied electron dosage during the EBCL process upon the final thickness of the polymer layer is also studied. The correlation between the electron-induced conversion of the 4'-nitro to the 4'-amino group and the layer thickness of the resulting polymer brush indicates that the polymer-brush grafting density can be directly controlled by the EBCL process. NBT-based template arrays are used for the combinatorial study of the influence of the lateral structure size and the irradiation dosage on the morphology of the resulting polymer-brush layer. Analysis of the array topography reveals the dependence of the thickness of the dry polymer layer on both electron dosage and structure size. This unique combination of EBCL as a lithographic technique to locally manipulate the surface chemistry and SIPP to amplify the created differences allows the preparation of defined polymer-brush layers of controlled morphologies.     

Tailoring the morphology of raspberry-like carbon black/polystyrene composite microspheres for fabricating superhydrophobic surface

In our previous report, raspberry-like carbon black/polystyrene (CB/PS) composite microsphere was prepared through heterocoagulation process. Based on the previous study, in the present work, the morphology of raspberry-like CB/PS particle is tailored through adjusting the polarity and the concentration ratio of CB/PS colloidal suspension with the purpose to prepare particulate film for the fabrication of superhydrophobic surface. Scanning electron microscope (SEM) confirms the morphology of raspberry-like particle and the coverage of CB. Rough surfaces fabricated by raspberry-like particles with proper morphology are observed by SEM and clear evidence of superhydrophobic surface is shown. The structure of raspberry-like particle is analyzed by atom force microscope. The proposed relationship between the hydrophobicity and the structure of CB aggregates on the surface of PS microsphere is discussed in details.     

Controlled Fab installation onto polymeric micelle nanoparticles for tuned bioactivity

Abstract

Antibodies and antigen-binding fragments (Fabs) can be used to modify the surface of nanoparticles for enhanced target binding. In our previous work, site-specific conjugation of Fabs to polymeric micelles using conventional methods was limited to approximately 30% efficiency, possibly due to steric hindrance related to macromolecular reactants. Here, we report a new method that enables conjugation of Fabs onto a micelle surface in a controlled manner with up to quantitative conversion of nanoparticle reactive groups. Variation of (i) PEG spacer length in a heterofunctionalized cross-linker and (ii) Fab/polymer feed ratios resulted in production of nanoparticles with a range of Fab densities on the surface up to the theoretical maximum value. The biological impact of variable Fab density was evaluated in vitro with respect to cell uptake and cytotoxicity of a drug-loaded (SN38) targeted polymeric micelle bearing anti-EphA2 Fabs. Fab conjugation increased cell uptake and potency compared with non-targeted micelles, although a Fab density of 60% resulted in decreased uptake and potency of the targeted micelles. Altogether, our findings demonstrate that conjugation strategies can be optimized to allow control of Fab density on the surface of nanoparticles and also that Fab density may need to be optimized for a given cell-surface target to achieve the highest bioactivity.     

Observations of polyaniline surface morphology modification during doping and de-doping using atomic force microscopy

Chemically synthesized 30 m thick polyaniline films were studied during the doping and dedoping process by imaging the polymer surface using in situ atomic force microscopy (AFM). The polymer, which was initially in the base non-conducting form, was doped using aqueous solutions of both tosylic acid (pH = 0.2) and HCl (pH = 0.2 and 1.0). De-doping was accomplished by exposing the same doped polymer surface to NH₄OH (pH = 12) base solution. AFM images showed that it was necessary to cycle the polymer surface three times between acid and base before a reproducible surface morphology was established. For the case of doping with tosylic acid, AFM images showed that the polyaniline surface was immediately roughened; the changes in mean roughness for the base and acid conditions were ~ 5.4 and ~ 6.7 nm, respectively. In addition there appeared to be an increase in the size of surface channels and cracks. When doping with HCl (pH = 1.0), no change in surface morphology was observed; however, noticeable surface roughening occurred over 10 min for the case of the lower pH = 0.2 solution; mean roughness changes for the base and acid conditions were ~ 17.9 and 39.2 nm. Radio frequency measurements, which determined the polymer complex permittivity, and d.c. conductivity measurements were used to determine the level of doping in the samples studied by AFM which were exposed to acid solutions.     

Solvent‐Induced Self‐Assembly Strategy to Synthesize Well‐Defined Hierarchically Porous Polymers

Porous polymers with well‐orchestrated nanomorphologies are useful in many fields, but high surface area, hierarchical structure, and ordered pores are difficult to be satisfied in one polymer simultaneously. Herein, a solvent‐induced self‐assembly strategy to synthesize hierarchical porous polymers with tunable morphology, mesoporous structure, and microporous pore wall is reported. The poly(ethylene oxide)‐b‐polystyrene (PEO‐b‐PS) diblock copolymer micelles are cross‐linked via Friedel–Crafts reaction, which is a new way to anchor micelles into porous polymers with well‐defined structure. Varying the polarity of the solvent has a dramatic effect upon the oleophobic/oleophylic interaction, and the self‐assembly structure of PEO‐b‐PS can be tailored from aggregated nanoparticles to hollow spheres even mesoporous bulk. A morphological phase diagram is accomplished to systematically evaluate the influence of the composition of PEO‐b‐PS and the mixed solvent component on the pore structure and morphology of products. The hypercrosslinked hollow polymer spheres provide a confined microenvironment for the in situ reduction of K₂PdCl₄ to ultrasmall Pd nanoparticles, which exhibit excellent catalytic performance in solvent‐free catalytic oxidation of hydrocarbons and alcohols.     

Orientation controlled preparation of nanoporous carbon nitride fibers and related composite for gas sensing under ambient conditions

Creating pores in suprastructures of two-dimensional (2D) materials while controlling the orientation of the 2D building blocks is important in achieving large specific surface areas and tuning the anisotropic properties of the obtained functional hierarchical structures.In this contribution,we report that arranging graphitic carbon nitride (g-C3N4) nanosheets into one-dimensional (1D) architectures with controlled orientation has been achieved by using 1D oriented melem hydrate fibers as the synthetic precursor via a polycondensation process,during which the removal of water molecules and release of ammonia gas led to the creation of pores without destroying the 1D morphology of the oriented structures.The resulting porous g-C3N4 fibers with both meso-and micro-sized pores and largely exposed edges exhibited good sensing sensitivity and selectivity towards NO2.The sensing performance was further improved by hybridization of the porous fibers with Au nanoparticles (Au NPs),leading to a detection limit of 60 ppb under ambient conditions.Our results suggest that the highly porous g-C3N4 fibers and the related hybrid structures with largely exposed graphitic layer edges are excellent sensing platforms and may also show promise in other electronic and electrochemical applications.     

Control of surface morphology of carbide coating on Co-Cr-Mo implant alloy

Wear of materials used in artificial joints is a common failure mode of artificial joints. A low wear rate for implants is believed to be critical for extending implant service time. We developed a carbide-coated Co-Cr-Mo implant alloy created in plasma of methane and hydrogen mixed gas by a microwave plasma-assisted surface reaction. The carbide-coated Co-Cr-Mo has a unique “brain coral-like” surface morphology and is much harder than uncoated Co-Cr-Mo. The effect of plasma processing time and temperature on the surface morphology of the top carbide layer was studied toward optimizing the surface coating. The ratios of average roughness, R_a, core roughness, R_k, and summation of core roughness, reduced peak height (R_pk) and reduced valley depth (R_vk), R_k+ R_pk+ R_vk, for the 6-h/985 ^∘C coating to those for the 0.5-h/985 ^∘C coating were 1.9, 1.7, and 1.9, respectively. The ratios of R_a, R_k, and R_k+ R_pk+ R_vk for the 4-h/1000 ^∘C coating to those for the 4-h/939 ^∘C coating were 2.3, 2.3, and 2.0, respectively. With the proper combination of plasma processing time and temperature, it may be possible to change the thickness of the peak-valley top cluster by fourfold from ∼ 0.6 μ m to ∼ 2.5 μ m. Finally, the growth mechanism of the carbide layers on Co-Cr-Mo was discussed in the context of atomic composition analysis.     

Controlling bubble density in MWNT/polymer nanocomposite foams by MWNT surface modification

Polymer nanocomposite foams are promising substitutes for polymeric foams. Carbon nanotube/polymer nanocomposite foams possess high strength, low density, and can be made conductive. Creating polymer foams with controlled foam morphology is of great importance for controlling foam properties. The foam morphology is influenced by the foaming conditions and filler properties. For carbon nanotube/polymer composite foams, dispersion state and aspect ratio of the carbon nanotubes have been shown to influence the bubble density and bubble size. In the current study, the influence of carbon nanotube surface chemistry on the bubble density of multi-walled carbon nanotube/poly(methyl methacrylate), MWNT/PMMA, nanocomposite foams was investigated. The surface of the MWNTs with controlled aspect ratio was covalently modified with glycidyl phenyl ether (GPE). Surface modified MWNT/PMMA nanocomposite foams were produced using a supercritical carbon dioxide foaming process. At constant MWNT concentration, the bubble density of polymer nanocomposite foams filled with GPE surface modified MWNT was found to be several times higher than that of polymer nanocomposite foams filled with nitric acid treated MWNT. After the MWNTs were modified with GPE, the surface chemistry of the MWNT became the dominant factor in determining the bubble density while the MWNT aspect ratio became less influential.     

Orientation-dependent surface tension functions for surface energy minimizing calculations

Previous numerical methods that calculate equilibrium particle shape to study thermodynamic and kinetic processes depend on interfacial (surface) free energy functions γ( ) that have cubic symmetry and thus produce Wulff shapes W of cubic symmetry. This work introduces a construction yielding the minimal surface energy density γ^convex(W) that can be determined for any W. Each γ( ) that belongs to the equivalence class γ(W) bounded by γ^convex(W) can be used in an energy-minimizing calculation that depends only on W. For practical numerical calculations, this work gives two methods taking directional distance from specified orientation minima as a parameter to produce analytic forms of γ( ) giving W as the equilibrium shape for (an otherwise unconstrained) fixed volume. Included are several two- and three-dimensional examples that demonstrate the application and utility of the model γ( ) functions.     

Dispersion of micelle-encapsulated fluorophores in a polymer matrix for control of color of light emitted by light-emitting diodes

In the present study, we demonstrated that fluorescent dyes could be nanoscopically dispersed in a polymer matrix that was immiscible with the dyes; the dyes were encapsulated in micelles. Using a model polymer composite, we also showed that the color of light emitted by light-emitting diodes (LEDs) could be controlled by coating fluorescent polymer composites onto the LEDs. For this purpose, fluorophores that were insoluble in toluene were solubilized into a solution of block copolymer micelles in toluene by the selective incorporation of fluorescent dyes into micellar cores. Because the micelles could be dispersed well in the polymer matrix without the formation of aggregates, fluorescent dyes encapsulated in the micelles were also effectively dispersed in the polymer matrix without macroscopic separation. The polymer composite can be evenly coated onto most substrates, regardless of their surface characteristics. Thus, light-emitting devices with well-controlled emission wavelengths and emission intensities can be fabricated by coating the polymer composite onto the surface of the device.     

Unconventional layer-by-layer assembly: surface molecular imprinting and its applications

Layer-by-layer assembly (LbL) is a rich, versatile, and powerful technique for fabricating multilayer thin films with controlled architecture and functions. Singly charged, uncharged, or water-repellent molecules cannot be used directly in conventional LbL assembly. This problem can be solved with unconventional LbL methods, by employing the preassembly of building blocks in solution and the use of these assemblies for LbL formation at the interface. This Concept summarizes different methods of unconventional LbL assembly, including electrostatic complex formation, hydrogen-bonded complexes, block-copolymer micelles, and π-π interaction complexes. These preassembly treatments endow the building blocks with enhanced abilities for advanced functionality, in particular, surface molecular imprinting, a new concept emerging from unconventional LbL. Molecular imprinting approaches are thus conceptually described based on different types of interactions and their great potential in applications is demonstrated by examples such as selective surface patterning and selective filtration.     

The influence of surface roughness and pre-oxidation state on the wettability of aluminium nitride by commercial brazes

The effects of roughness (Ra = 0.17–0.20 m) and of pre-oxidation of the AlN ceramic surface on its wettability and contact interaction with commercial brazing alloys CB4 and CB5 of Ag-Cu-Ti composition have been studied. Wettability has been determined by the sessile drop method at three holding temperatures (810, 900 and 950°C). Particularities of the interface interaction have been identified by microprobe analysis for pre-oxidized samples. Experimental data are compared with data for samples polished to Ra = 0.02–0.03 m not subjected to pre-oxidation. The results show that, for the systems under study, surface roughness does not influence the contact angle value significantly. Pre-oxidation of the AlN in air at 1250°C, however, tends to reduce wettability as a result of the replacement of braze-aluminium nitride interaction by braze-surface aluminium oxide interaction.     

Determination of effective surface energy of dynamic failure

A method is presented for determining the effective surface energy under dynamic loading. It is based on combining the effect of a valuewise different static tensile load and similar tensile pulses on identical specimens. It is shown that the method is insensitive to the sharpness of the originally made notch. This facilitates the form of the moving crack front to be controlled and eliminates the need to set up a fatigue crack. Graphs of variation in time of the SIF and length and velocity of the crack are given.Translated from Problemy Prochnosti, No. 7, pp. 10–14, July, 1992.