Hierarchical assembly of uranyl metallacycles involving macrocyclic hosts

Actinide metallacycles are an emerging class of functional coordination assemblies, but multi-level assembly from metallacycle units toward hierarchical supramolecular structures are still rarely investigated. In this work, we put forward a novel supramolecular inclusion-based method through introducing two macrocyclic hosts, cucurbit[7]uril (CB[7]) and cucurbit[8]uril (CB[8]) to facilitate hierarchical assembly of uranyl metallacycles with higher complexity, and successfully prepare two different kinds of uranyl metallacycle-based complexes with intriguing hierarchical structures, a CB[7]-based four-member molecular necklace ([4]MN) and a CB[8]-involved ring-in-ring supramolecular polymer chain. The results obtained here prove the feasibility of supramolecular inclusion for regulating coordination assembly of uranyl metallacycles and related hierarchical structures. It is believed that this method can be used to achieve the construction of actinide coordination assemblies with higher structural complexity.     

Dispersion of carbon black in a continuous phase: Electrical, rheological, and morphological studies

This work investigates the dispersion of carbon black (CB) aggregates into various polymeric matrices to increase electric conductivity. The effect of matrix viscosity on CB morphology and, consequently, on the blend conductivity was thoroughly addressed. The electric conductivity increases from 10^-9 to 10^-4 when less than 3% CB aggregates were dispersed into the PDMS liquid of various viscosities. The CB threshold loading was found to increase from 1% to 3% as the viscosity rose from 10 cp to 60 000 cp. This finding shows that an ideal loading with CB aggregates is far below that (generally 15%) of a typical pelletized CB loading. Moreover, the microscope and RV tests reveal that CB aggregates diffuse and form an agglomerate-network when the conductivity threshold is reached in a low-viscosity matrix. However, a CB aggregate-network was observed when the threshold value was attained in a high-viscosity matrix. These two mechanisms can be distinguished at approximately 1000 cp. Finally, experimental observation shows that the increase of viscosity during curing does not influence the conductivity of the composite while the CB aggregates dispersed in a thermoset matrix. The minimum viscosity during curing, however, was found to be critical to CB dispersion morphology and, consequently, to ultimate electric conductivity.     

Solvent entrainment in and flocculation of asphaltenic aggregates probed by small-angle neutron scattering

While small-angle neutron scattering (SANS) has proven to be very useful for deducing the sizes and masses of asphaltenic aggregates in solution, care must be taken to account for solvation effects within the aggregates so as to not err in the characterization of these important systems. SANS measurements were performed on solutions of asphaltenes dispersed in deuterated solvents in which a broad spectrum of solute and solvent chemical compositions was represented. Fits to the scattering intensity curves were performed using the Guinier approximation, the Ornstein-Zernike (or Zimm) model, a mass-fractal model, and a polydisperse cylinder model. The mass-fractal model provided apparent fractal dimensions (2.2-3) for the aggregates that generally decreased with increasing aggregate size, indicating increased surface roughness for larger aggregates. The polydisperse cylinder model provided typical values of the particle thicknesses from 5 to 32 angstroms, the average particle radius from 25 to 125 angstroms, and approximately 30% radius polydispersity. Subsequent calculation of average aggregate molar masses suggested a range of solvent entrainment from 30 to 50% (v/v) within the aggregates that were consistent with previous viscosity measurements. Additional calculations were performed to estimate the proportion of microparticle to nanoparticle aggregates in the solutions. The results indicate that the inclusion of solvation effects is essential for the accurate determination of aggregate molecular weights and fractal dimensions.     

Viscoelastic properties of ionic polymer composites reinforced by soy protein isolate

Both linear and nonlinear viscoelastic properties of ionic polymer composites reinforced by soy protein isolate (SPI) were studied. Viscoelastic properties were related to the aggregate structure of fillers. The aggregate structure of SPI is consisted of submicron size of globule protein particles that form an open aggregate structure. SPI and carbon black (CB) aggregates characterized by scanning electron microscope and particle size analyzer indicate that CB aggregates have a smaller primary particle and aggregate size than SPI aggregates, but the SPI composites have a slightly greater elastic modulus in the linear viscoelastic region than the CB composites. The composite containing 3–40 wt % of SPI has a transition in the shear elastic modulus between 6 and 8 vol % filler, indicating a percolation threshold. CB composites also showed a modulus transition at <6 vol %. The change of fractional free volume with filler concentration as estimated from WLF fit of frequency shift factor also supports the existence of a percolation threshold. Nonlinear viscoelastic properties of filler, matrix, and composites suggested that the filler‐immobilized rubber network generated a G′ maximum in the modulus‐strain curves and the SPI formed a stronger filler network than the CB in these composites. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 3503–3518, 2005     

A new approach to visualizing the carbon black/natural rubber interaction layer in carbon black-filled natural rubber vulcanizates and to elucidating the dependence of mechanical properties on quantitative parameters

The viscoelastic behavior of carbon black (CB)-filled natural rubber (NR) vulcanizates is explained for the first time by applying a two-phase mixing law, excluding the CB phase, to the volume fraction of the CB/NR interaction layer (CNIL). For CB loadings of 20 phr or less, the CNIL of local CB aggregates induces the reinforcement effect of a series mechanical model of the mixing law. In contrast, for CB loadings of 30 phr or more, the CNIL that forms the CB network (CBN) generates the reinforcement effect of a parallel mechanical model of the mixing law. Therefore, the model of the mixing law presumably changes from a series mechanical model before CBN formation to a parallel one after the network forms. Additionally, employing this fraction, a transition caused by CBN formation was investigated.     

Highly Stable,Water‐Dispersible Metal‐Nanoparticle‐Decorated Polymer Nanocapsules and Their Catalytic Applications

A facile synthesis of highly stable, water‐dispersible metal‐nanoparticle‐decorated polymer nanocapsules (M@CB‐PNs: M=Pd, Au, and Pt) was achieved by a simple two‐step process employing a polymer nanocapsule (CB‐PN) made of cucurbit[6]uril (CB[6]) and metal salts. The CB‐PN serves as a versatile platform where various metal nanoparticles with a controlled size can be introduced on the surface and stabilized to prepare new water‐dispersible nanostructures useful for many applications. The Pd nanoparticles on CB‐PN exhibit high stability and dispersibility in water as well as excellent catalytic activity and recyclability in carbon–carbon and carbon–nitrogen bond‐forming reactions in aqueous medium suggesting potential applications as a green catalyst.     

PE/CB复合材料的辐照效应

研究了两种炭黑(CB)对PE的影响及PTC功能材料挤出后的特性，发现挤出后粒子和聚合物取向对材料电性能都有较大影响。经γ射线辐照后HDPE／CB功能复合材料稳定性大为提高，初步探讨了辐射对PTC功能材料稳定性的影响。结合辐射交联等方法提高材料的稳定性。用扫描电镜(SEM)观测了一系列PE／CB的形态、CB的分布、链段的分子运动，并结合Fisher的toy model对PE／CB机制做了较系统的解释。     

Highly Stable,Water‐Dispersible Metal‐Nanoparticle‐Decorated Polymer Nanocapsules and Their Catalytic Applications

A facile synthesis of highly stable, water‐dispersible metal‐nanoparticle‐decorated polymer nanocapsules (M@CB‐PNs: M=Pd, Au, and Pt) was achieved by a simple two‐step process employing a polymer nanocapsule (CB‐PN) made of cucurbit[6]uril (CB[6]) and metal salts. The CB‐PN serves as a versatile platform where various metal nanoparticles with a controlled size can be introduced on the surface and stabilized to prepare new water‐dispersible nanostructures useful for many applications. The Pd nanoparticles on CB‐PN exhibit high stability and dispersibility in water as well as excellent catalytic activity and recyclability in carbon–carbon and carbon–nitrogen bond‐forming reactions in aqueous medium suggesting potential applications as a green catalyst.     

Influence of alkaline treatment and acetone extraction of natural rubber matrix on properties of carbon black filled natural rubber vulcanizates

In this study, air dried sheet (ADS) showed higher molecular weight, proteins, lipids and more gel content than the low protein natural rubber (LPNR) from alkaline treatment or acetone-extracted natural rubber (AENR). After removal of proteins and lipids, LPNR and AENR had shorter scorch and cure times among the rubber compounds observed. This is due to higher content of free fatty acids, glycerides and sodium salts of fatty acid that might act as cure activators with sulfur curing. Furthermore, a finer dispersion of CB was found in ADS, due to chemical interactions of CB with proteins and lipids at terminal ends of NR molecules. Also, high molecular weight and gel in ADS could induce a higher reinforcing index (α) resulting to superior mechanical, dynamic, thermo-mechanical, hardness and crosslink density. In contrast, CB agglomerates occurred in LPNR and AENR with low molecular weight and reduced proteins and lipids, causing inferior mechanical, dynamic, thermo-mechanical, along with loss of stiffness and crosslink density.     

天然橡胶原位接枝炭黑的分散性研究

采用原位固相接枝方法,使在高温和强剪切作用下降解的天然橡胶接枝到炭黑表面.采用透射电镜(TEM)、原子力显微镜(AFM)等方法观察了接枝前后的炭黑粒子形貌变化,发现未接枝炭黑以微米级的附聚体形式存在,而由于炭黑聚集体被强剪切力部分破坏,接枝炭黑的聚集程度明显减弱,粒子的尺寸减小.采用激光光散射粒度仪对接枝前后炭黑的粒度进行分析,接枝炭黑的体积平均粒径为164 nm,远小于测得的原炭黑的粒径797 nm.采用沉降法、透光率法及zeta电位测量研究了接枝改性对炭黑在溶剂中的分散性及分散稳定性的影响,结果表明,接枝炭黑在接枝分子的溶剂中的分散性变好,分散稳定性提高.     

Structure and properties of star‐shaped solution‐polymerized styrene‐butadiene rubber and its co‐coagulated rubber filled with silica/carbon black‐I: morphological structure and mechanical properties

The morphological structure and mechanical properties of the star‐shaped solution‐polymerized styrene‐butadiene rubber (SSBR) and organically modified nanosilica powder/star‐shaped SSBR co‐coagulated rubber (N‐SSBR) both filled with silica/carbon black (CB) were studied. The results showed that, compared with SSBR, silica powder could be mixed into N‐SSBR much more rapidly, and N‐SSBR/SiO₂ nanocomposite had better filler‐dispersion and processability. N‐SSBR/SiO₂/CB vulcanizates displayed higher glass‐transition temperature and lower peak value of internal friction loss than SSBR/SiO₂/CB vulcanizates. In the N‐SSBR/SiO₂/CB vulcanizates, filler was dispersed in nano‐scale resulting in good mechanical properties. Composites filled with silica/CB doped filler exhibited more excellent mechanical properties than those filled with a single filler because of the better filler‐dispersion and stronger interfacial interaction with macromolecular chains. N‐SSBR/SiO₂/CB vulcanizates exhibited preferable performance in abrasion resistance and higher bound rubber content as the blending ratio of silica to CB was 20:30. Copyright © 2008 John Wiley & Sons, Ltd.     

Supramolecular Inhibition of Amyloid Fibrillation by Cucurbit[7]uril

Amyloid fibrils are insoluble protein aggregates comprised of highly ordered β‐sheet structures and they are involved in the pathology of amyloidoses, such as Alzheimer’s disease. A supramolecular strategy is presented for inhibiting amyloid fibrillation by using cucurbit[7]uril (CB[7]). CB[7] prevents the fibrillation of insulin and β‐amyloid by capturing phenylalanine (Phe) residues, which are crucial to the hydrophobic interactions formed during amyloid fibrillation. These results suggest that the Phe‐specific binding of CB[7] can modulate the intermolecular interaction of amyloid proteins and prevent the transition from monomeric to multimeric states. CB[7] thus has potential for the development of a therapeutic strategy for amyloidosis.     

Insights into the Payne Effect of Carbon Black Filled Styrene-butadiene Rubber Compounds

As a widely used reinforcing filler of rubber, carbon black(CB) often enhances the nonlinear Payne effect and its mechanism still remains controversial. We adopt simultaneous measurement of rheological and electrical behaviors for styrene-butadiene rubber(SBR)/CB compounds and CB gel(CBG) during large deformation/recovery to investigate the contribution of conductive CB network evolution to the Payne effect of the compounds. In the highly filled compounds, the frequency dependence of their strain softening behavior is much more remarkable than that of their CB network breakdown during loading, while during unloading the unrecoverable filler network hardly affects the complete recovery of modulus, both revealing that their Payne effect should be dominated by the disentanglement of SBR matrix. Furthermore,the bound rubber adjacent to CB particles can accelerate the reconstruction of continuous CB network and improve the reversibility of Payne effect. This may provide new insights into the effect of filler network, bound rubber, and free rubber on the Payne effect of CB filled SBR compounds.     

Understanding of morphology evolution in local aggregates and neighboring regions for organic photovoltaics

Fluorescence intensity and its ratio mapping combined with time-dependent optical microscopy and atomic force microscopy (AFM) were used to understand morphology evolution of local aggregates and neighboring regions for organic solar cells. Three solvents with different boiling points including chlorobenzene (CB), 1,3-dichlorobenzene (1,3-DCB) and 1,2-dichlorobenzene (1,2-DCB) were used to engineer morphology. These solvents affected morphology evolution factors such as solvent evaporation rate, formation (e.g., growth rate, size and/or quantity) of (6,6)-phenyl-C61-butric-acid methyl ester (PCBM)-rich aggregates, and packing/ordering of poly(3-hexylthiophene) (P3HT). Three local regions (1, 2 and 3) including microscale aggregates and their surrounding areas were identified to explore the mechanism of morphology evolution. Region 1 was the PCBM-rich aggregates; region 2 was the PCBM-deficient area; and region 3 was the area composed of a relatively normal P3HT/PCBM composite beyond region 2 for each solvent. The intensity of fluorescence spectra decreased as region 1 > region 2 > region 3 in thermally annealed (140 °C, 20 min) P3HT/PCBM blend film from each solvent. The highest fluorescence intensity in region 1 was probably caused by the relatively poor phase separation where both PCBM and P3HT formed large isolated domains. The higher fluorescence intensity ratio (720 nm/650 nm) suggested a larger relative amount of PCBM molecules, supported by similar morphologies in fluorescence intensity ratio mapping compared to those in optical images. The fluorescence intensity ratio was with the order of region 1 > region 3 > region 2 in both CB and 1,3-DCB based films, but with region 1 > region 2 > region 3 for the 1,2-DCB based film. The order of effective area taken up by aggregates was CB > 1,3-DCB > 1,2-DCB in annealed (140 °C, 10 min) bulk blend films. The final solar cell performance agreed with morphology results. This work is imperative with regards to revealing the mechanism of morphology evolution in local aggregates and surrounding regions for organic photovoltaic films.     

Influence of Carbon Black and Silica Filler on the Rheological and Mechanical Properties of Natural Rubber Compound

Rubber compounds are reinforced with fillers such as carbon black and silica. In general, filled rubber compounds shows smooth rheological behavior and mechanical properties. Variation in rheological behavior and mechanical properties was studied in terms of the filler composition using natural rubber compounds filled with both carbon black and silica CB/Si = 0/60, 20/40, 30/30, 40/20 and 60/0 phr (parts per hundred rubber is parts of any non-rubbery material per hundred parts of raw gum elastomer (rubbery material)). The rheological behaviour can be showed in measurement of Mooney viscosity and cure time. The Mooney viscosity of rubber compounds increase with the increasing the carbon black in the compounds. The compound filled with CB/Si of 30/30 and 60/0 showed abnormal rheological behaviour in which the cure time decreased suddenly and the increased at certain ratio during the measurement. The mechanical properties such as hardness, abrasion resistance and tensile stress at 300% elongation were studied. In the hardness and abrasion resistance measurement, the higher ratio CB/Si decrease contribution of silica, which resulting smaller of hardness value. Ratio CB/Si 40/20 gives an optimum filler blended. It is also clearly understood that higher abrasion resistance mainly due to the lower hardness value under the same condition. The tensile stress at 300% elongation of rubber compound increased with the increasing carbon black filler.     

Thermally Tunable Hydrogels Displaying Angle‐Independent Structural Colors

We report the preparation of thermally tunable hydrogels displaying angle‐independent structural colors. The porous structures were formed with short‐range order using colloidal amorphous array templates and a small amount of carbon black (CB). The resultant porous hydrogels prepared using colloidal amorphous arrays without CB appeared white, whereas the hydrogels with CB revealed bright structural colors. The brightly colored hydrogels rapidly changed hues in a reversible manner, and the hues varied widely depending on the water temperature. Moreover, the structural colors were angle‐independent under diffusive lighting because of the isotropic nanostructure generated from the colloidal amorphous arrays.     

Dispersing behavior of recycled rubber particles

The hydrophobic nature of recycled rubber particles presently limits their use only in non-aqueous media. Recycled rubber particles were chemically modified by preparation of amphiphilic semi-interpenetrating polymer networks using poly(acrylic acid) as the hydrophilic polymer. The resulting composite particles are water dispersible and suitable for various aqueous media applications.     

IR spectroscopic study of molecular aggregation in condensate films of polar liquid crystals

Molecular association in polar liquid crystals influences almost all physical and chemical properties of these compounds and is of great importance for their use as materials for molecular electronics. There are only few reports available that present estimations of the degree of dimerization and enthalpy via dielectric measurements of bulk samples and of solutions in non-polar solvents. In the present work, the molecular aggregation of liquid-crystalline 4-pentyl-4′-cyanobiphenyl (5CB), 4-pentyl-4′-cyanophenyl pyridine (5Py), 4-pentyl-4′-cyanophenylcyclohexane (5CH), 4-octyl-4′cyanobiphenyl (8CB) and 4-octyloxy-4′-cyanobiphenyl (8OCB) in molecular condensate films and inert matrices has been studied by low-temperature reflection and transmission vibrational spectroscopy in a wide temperature range from 80 to 330 K. A red shift of the CN stretching vibration band was considered to be due to the formation of molecular aggregates. The factors affecting their thermodynamic stability are considered.     

Mechanical and thermodynamic properties of surfactant aggregates at the solid-liquid interface

Surfactants are widely used to stabilize colloidal systems in a variety of industrial applications through the formation of self-assembled aggregates at the solid-liquid interface. Previous studies have reported that the control of surfactant-mediated slurry stability can be achieved through the manipulation of surfactant chain length and concentration. However, a fundamental understanding of the mechanical and energetic properties of these aggregates, which may aid in the molecular-level design of these systems, is still lacking. In this study, experimentally measured force/distance curves between an atomic force microscope (AFM) tip and self-assembled surfactant aggregates on mica or silica substrates at concentrations higher than the bulk critical micelle concentration (CMC) were used to determine their mechanical and thermodynamic properties. The experimental curves were fitted to a model which describes the interaction between a hard sphere (tip) and a soft substrate (surfactant structures) based on a modified Hertz theory for the case of a thin elastic layer on a rigid substrate. The calculated mechanical properties were found to be in the same order of magnitude as those reported for rubber-like materials (e.g., polydimethylsiloxane (PDMS)). By integrating the force/distance curves, the energy required for breaking the surface aggregates was also calculated. These values are close to those reported for bulk-micelle formation.