Synthesis of monodispersed organic-inorganic hybrid spheres

This paper describes the attempt to prepare a new group of monodispersed silica-polymer hybrid particles, which consists of silica and amide polymer: poly(vinylpyrrolidone) (PVP) and poly(2-ethyloxazoline) (POXZ). Preparation method is based on the growth of hybrid seeds by the addition of TEOS-polymer solution.Monodispersed PVP-silica hybrid particles of 1.24 µm in diameter were prepared by growing the hybrid seeds of 0.54 µm by the addition of TEOS-PVP solution with ammonia catalyst. In the case of POXZ-silica particles, addition of TEOS-POXZ solution to the solution containing 0.54 µm seeds resulted in monodispersed POXZ-silica hybrid particles and four times repetition of the addition for particle growth gave the hybrid particles of the diameter of 1.6 µm.Improvement of mechanical properties of hybrid particles was observed when the particles were heated at 100 200°C.     

广义簇合物在均匀几率密度场下的生长

通过对广义簇合物生长的自调整模型的解析,得出了粒子在均匀几率密度场下簇合物生长形态的变化特征,揭示了表征其生长形态结构分式维数D的物理意义,同时考查了格子模型对簇合物生长形态的影响以及自调整模型的动力学行为。     

Kinetics of the transformation process of PbSO4 to PbO2 in a lead anodic film

The kinetics of the nucleation and growth of PbO₂ during the potentiostatic oxidation of PbSO₄ in a lead anodic film was studied using linear sweep voltammetry, potential-step and ac impedance tracing methods. The film investigated is the partially reduced anodic PbO₂ film formed by polarizing a lead electrode in 4.5 M H₂SO₄ solution first at 1.3 V vs. Hg|HgSO₄ for 20 min and then at 0.9 V for 5 min. The nucleation and growth process begins some time after the potential step and is completed within 60 s. The pre- and post-nucleation and growth processes correspond to the growth of the anodic film formed by the oxidation of the lead substrate. The mathematical equations representing the current-time and capacitance-time transients are derived taking the background oxidation current into account. The experimental results are well fitted by these equations. The process obeys the laws of two-dimensional instantaneous nucleation and growth.     

Dynamics of the formation of two-dimensional ordered structures

The growth of ordered domains in lattice gas models, which occurs after the system is quenched from infinite temperature to a state below the critical temperatureT _c, is studied by Monte Carlo simulation. For a square lattice with repulsion between nearest and next-nearest neighbors, which in equilibrium exhibits fourfold degenerate (2×1) superstructures, the time-dependent energy E(t), domain size L(t), and structure functionS(q, t) are obtained, both for Glauber dynamics (no conservation law) and the case with conserved density (Kawasaki dynamics). At late times the energy excess and halfwidth of the structure factor decrease proportional tot ^–x, whileL(t) t ^x, where the exponent x=1/2 for Glauber dynamics and x1/3 for Kawasaki dynamics. In addition, the structure factor satisfies a scaling lawS(k,t)=t ^2xS(kt^x). The smaller exponent for the conserved density case is traced back to the excess density contained in the walls between ordered domains which must be redistributed during growth. Quenches toT>T _c, T=T_c (where we estimate dynamic critical exponents) andT=0 are also considered. In the latter case, the system becomes frozen in a glasslike domain pattern far from equilibrium when using Kawasaki dynamics. The generalization of our results to other lattices and structures also is briefly discussed.     

Multiparticle fractal aggregation

Kinetic fractal aggregation in a particle bath where a fractionf of the sites are initially occupied is studied withd=2 computer simulations. Independent particles diffusing to a fixed cluster produce an aggregate with fractal dimensionD 1.7 up to a correlation length(f). At larger lengthsD2.(f) asf 0. When the particles remain fixed but the cluster undergoes a rigid random walkD appears constant at larger scales but varies withf. D 1.95 at largef andD 1.7 asf 0. In both cases, the aggregate sizeN(t) grows with timet ^(f) . Aggregation on a surface by independently diffusing particles produces shapes reminiscent of electrochemical dendritic growth. The dependence of growth rate and geometry is studied as a function of particle concentration and sticking probability.     

Palladium-catalyzed ortho-C(sp2)H bromination of benzaldehydes via a monodentate transient directing group strategy

A facile and efficient monodentate transient directing group strategy was developed to enable the palladium-catalyzed ortho-C(sp²)H bromination of benzaldehydes. A broad scope of benzaldehydes were transformed into the desired products by employing 2-amino-5-chlorobenzotrifluoride as a monodentate transient directing group, demonstrating good functional group tolerance. Mild reaction conditions and no requirement for a silver salt are also features of this strategy.     

Using a new solvation model for thermodynamic study on the interaction of nickel with human growth hormone

Thermodynamics of the interaction between Ni²⁺ and human growth hormone (hGH) were determined at 27 °C in Nail solution by isothermal titration calorimetry. A new method to predict protein penetration and the effect of metal ions on the stability of proteins is introduced. The new solvation model was used to reproduce the enthalpies of Ni²⁺-hGH interaction over the whole range of Ni²⁺ concentrations. The solvation parameters recovered from the new equation, attributed to the structural change of hGH and its biological activity.     

氟的离子选择电极瞬时电位法测定

研究了氟离子选择电极瞬时电位分析法，其检出限和Nernst响应下限均低于传统电位分析法，空白液切换到试液时瞬时电位达到稳定的峰电位Vp比传统电位法的响应快得多，可以实现小体积试液的快速准确分析；用该法测定了自来水和矿泉水中氟的含量；利用校正曲线的截距和检出限计算了LaF3的溶度积，在0.1mol/L KNO3介质中Ksp(LaF3)=10^-28.45，在0.001mol/L柠檬酸钠＋HAc-NaAc缓冲液（pH=5.50，离子强度I＝0.10mol/L)介质中溶度积K′sp(LaF3)=10^-26.26；据此，计算得柠檬酸与La^3 络合物的稳定常数K1=10^5.46和K2=10^3.99；用离子水合吉氏自由能ΔGh(F^-,g)解释了不同浓度F^-试液瞬时电位的跃迁时间。     

Growth of clusters in a first-order phase transition

The results of computer simulations of phase separation kinetics in a binary alloy quenched from a high temperature are analyzed in detail, using the ideas of Lifshitz and Slyozov. The alloy was modeled by a three-dimensional Ising model with Kawasaki dynamics. The temperature after quenching was 0.59T _c, whereT _c is the critical temperature, and the concentration of minority atoms was=0.075, which is about five times their largest possible single-phase equilibrium concentration at that temperature. The time interval covered by our analysis goes from about 1000 to 6000 attempted interchanges per site. The size distribution of small clusters of minority atoms is fitted approximately byc ₁(1-)³ w(t),c ₁ (1–)⁴ Q _l w(t)^l(2l10); wherec _l is the concentration of clusters of sizel;Q ₂,...,Q ₁₀ are known constants, the cluster partition functions;t is the time; andw(t)=0.015(1+7.17t ^–1/3). The distribution of large clusters (l20) is fitted approximately by the type of distribution proposed by Lifshitz and Slyozov,c _l ,(t)=–(d/dl) [lnt+p (l/t)], where is a function given by those authors and is defined by(x)=C _o e–x-C ₁ e ^–4x/3-C ₂ e ^–5x/3;C ₀,C ₁,C ₂ are constants determined by considering how the total number of particles in large clusters changes with time.Supported by the U.S. Air Force Office of Scientific Research under Grant No. 78-3522 and by the U.S. Department of Energy under Contract No. EY-76-C-02-3077*000.