Integrity and Structural Characteristics of the M6E8 (E=S, Se, Te) Cluster Core: Syntheses and Structures of [Co6S8(PR3)6] n+ (R=Me2Ph, n=1; R=OMe, n=0)

Two new members of the hexanuclear series [Co₆S₈(PR₃)₆] ⁿ⁺, complexes [Co₆S₈(PMe₂Ph)₆](ClO₄) (1) and [Co₆S₈P(OMe)_{3 6}] (2), have been synthesizes and characterized by X-ray diffraction analyses. Their formation process was postulated to go through trinuclear ₃--S bridged moieties. The structural characteristics of the M₆E₈P₆ skeleton of a whole series of [M₆E₈(PR₃)₆] ⁿ⁺ (M=Co, Cr, Fe, Mo; E=S, Se, Te) complexes are presented in terms of atomic distances and core volumes.     

十二烷基三甲基溴化铵在聚苯乙烯胶乳粒子上的吸附

实验测得C~1~2TAB在PS胶乳粒子表面的吸附等温线呈L型的二阶段吸附特征,这表明初始的C~1~2TA^+离子是将其季铵正电性头基吸引在PS链的负电性硫酸根端基上,并将碳氢链通过疏水相互作用吸附在PS链上。结合光子相关谱测得胶乳粒子流体力学半径R~H的变化,表明第I阶段围绕着这些初始吸附位的聚集吸附,产生平均聚集数为4.0的松散小聚集体,此时对应的浓度c/cmc=0.32是文献通常所指的临界表面胶团浓度csmc。其后的进一步聚集吸附最终生成了附着在PS链端基处且平均聚集数为19.5的球形吸附胶团。这一饱和吸附的结果增加了胶乳粒子在水溶液中的分散稳定性。     

Dependence of emulsion stability on particle size: Relative importance of drop concentration and destabilization rate on the half lifetimes of O/W nanoemulsions

This study reports the behavior of ionic dodecane-in-water nanoemulsions in distinct salt concentrations. Systems of smaller particle size (74–285 nm) were synthesized by a sudden dilution of an equilibrated mixture. Larger size systems (384–670 nm) were obtained from a set of formerly smaller nanoemulsions that evolved unperturbed for 2 weeks. Characteristic destabilization times for flocculation, coalescence, and Ostwald ripening were evaluated. In general, it was observed that stability increases with drop size. However, this size dependence is largely the consequence of the lower particle concentration of the coarser emulsions.     

Bis(phenothiazyl‐ethynylene)‐Based Organic Dyes Containing Di‐Anchoring Groups with Efficiency Comparable to N719 for Dye‐Sensitized Solar Cells

A new series of acetylene‐bridged phenothiazine‐based di‐anchoring dyes have been synthesized, fully characterized, and used as the photoactive layer for the fabrication of conventional dye‐sensitized solar cells (DSSCs). Tuning of their photophysical and electrochemical properties using different π‐conjugated aromatic rings as the central bridges has been demonstrated. This molecular design strategy successfully inhibits the undesirable charge recombination and prolongs the electron lifetime significantly to improve the power conversion efficiency (η ), which was proven by the detailed studies of electrochemical impedance spectroscopy (EIS) and open‐circuit voltage decay (OCVD). Under a standard air mass (AM) 1.5 irradiation (100 mW cm⁻²), the DSSC based on the dye with phenyl bridging unit exhibits the highest η of 7.44 % with open‐circuit photovoltage (V _oc) of 0.796 V, short‐circuit photocurrent density (J _sc) of 12.49 mA cm⁻² and fill factor (ff) of 0.748. This η value is comparable to that of the benchmark N719 under the same conditions.     

Influence of adsorbed polymers on the removal of mineral particles from a planar surface

 Experimental results on the role of adsorbed polymers on the particle adhesion are presented. Both Brownian (silica particles) and non-Brownian (glass beads) particles were used. The particles were deposited onto the internal surface of a glass parallelepiped cell, and then submitted to increasing laminar flow rates. The pH and the ionic strength of the electrolytes were fixed. The adhesive force was related to the hydrodynamic force required to dislodge 50% of the initially attached beads. We found that high molecular weight PEO had little effect on the adhesion of small silica beads due to the low affinity of the polymer for silica or glass surfaces. On the contrary, PEO greatly enhanced the adhesion of bigger glass beads forced to deposit on the capillary surface because of gravity. The increase was all the more pronounced as the molecular weight of the polymer was high. The effect of high molecular weight cationic copolymers on the adhesion of silica particles was drastic. The maximal force (1500 pN) applied by the device could not enable any particle detachment even using polymers of low cationicity rate (5%), showing the efficiency of electrostatic attractions. When copolymers were adsorbed on both surfaces (particles and plane), the adhesive force exhibited a maximum at intermediate coverage of particles. This optimum was related to the optimum flocculation concentration classically observed in flocculation of suspensions by polymers. Received: 16 February 1996 Accepted: 10 September 1996     

Measurement of Colloidal Stability in Solutions of Simple, Nonadsorbing Polyelectrolytes

The stability of a solution of charged polystyrene particles in the presence of nonadsorbing polyelectrolyte macromolecules is measured using optical light scattering. The particles were negatively charged polystyrene latex spheres (0.5–1 μm diameter) while the macromolecules were simulated using negatively charged colloidal silica spheres (5–7 nm diameter). Because of the electrostatic repulsion between the particles, the solution is found to be stable against primary flocculation (irreversible flocculation into a primary energy minima). However, because of long-range attractive depletion forces, reversible secondary flocculation of the particles occurs into a local potential energy minimum. As observed with uncharged macromolecules, the polyelectrolyte first induces flocculation at a critical flocculation concentration (v*), but later restabilizes the system at a critical restabilization concentration (v**). These critical concentrations are found to decrease with decreasing macromolecule size and increasing particle size. The restabilized solutions are found to remain suspended for periods greater than 20 days. Comparison of the measured flocculation and restabilization results to predictions made using a recently developed force-balance model show qualitative agreement.     

阳离子聚丙烯酰胺的制备及其絮凝性能

研究了氧化还原引发剂质量分数、偶氮类引发剂质量分数、阳离子度等因素对所制备的阳离子聚丙烯酰胺特性粘数的影响,探讨了pH值、阳离子聚丙烯酰胺特性粘数、阳离子度、用量等因素对污泥絮凝性能的影响. 较佳的制备条件为:复合引发体系中(NH4 )2 S2 O8 和CH3 NaO3 S·2H2 O总质量分数为0.015 0%、偶氮类引发剂质量分数为0.012 5%、单体质量分数为40%、阳离子度为40%,产物特性粘数为13.1 dL/g. 在污泥pH=6.0、阳离子聚丙烯酰胺特性粘数为11.9 dL/g、阳离子度为40%、用量为0.027%的较佳絮凝条件下,污水的透光率达98.0%,絮凝率达66.0%,脱水率达70.0%.     

Coordination/organometallic polymers based on diphosphine and diisocyanide ligands

This paper reviews various coordination/ organometallic polymers in which the metal atoms are incorporated in the backbone using diphosphine and diisocyanide ligands. Such ligands includes diphosphines of the type bis(diphenylphosphino)alkane where alkane is (CH₂)_m with m = 1, 3-6, bis(diphenylphosphino)acetylene (dpa), and bis(dimethylphosphino)methane (dmpm), and diisocyanides such as 1,8-diiso-cyano-p-menthane (dmb) and p-diisocyanotetra-methylbenzene (ditmb). The metal fragments are monocations such as Cu⁺, Ag⁺, and Au⁺, dinuclear species such as Pd₂(dmb)₂²⁺, Pd₂(dppm)₂²⁺, M₂(dmpm)₃²⁺ (M = Cu, Ag), and clusters such as M₄(dmb)₄²⁺ (M = Pd, Pt).