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Colloidal suspensions of charged latex microspheres in water exhibit liquid-like or crystalline ordering depending on particle interaction and concentration. By virtue of large particle spacing and slow dynamics, colloidal systems offer a unique opportunity to study interfacial structure and dynamics. This paper presents the first reported experimental study of the nucleation rate density, c, of an nonequilibrium (supercooled) colloidal liquid to colloidal crystal first order phase transition. Local and global observations of colloidal crystals growing from a metastable colloidal liquid were used to determine c. Microscopic local observations revealed homogeneous nucleation and constant interface velocity growth of quasispherical crystallites in the bulk and heterogeneous nucleation of a crystalline sheet with lower growth velocity at the cell wall. Complementary global observations of the recrystallization transition made by measuring the time dependence of the suspension transparency (the fraction of transmitted laser light) determined c by fitting this curve to a model based on an extension of Avrami's theory of crystallization. 相似文献
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Fabrication of Two-Dimensional Arrays of Micron-Sized Gold Rings Based on Preferential Nucleation at Reentrant Sites 下载免费PDF全文
A templating method for fabricating two-dimensional (2D) arrays of micron-sized goM rings is reported. The microstructures are formed by electroless plating in a through-porous polymer membrane on a silicon substrate obtained from a closed-packed silica colloidal crystal. Our results show that the sizes of gold rings can be altered by varying electroless plating conditions for the porous polystyrene membranes. Moreover, we explain the growth mechanism of gold rings using the classical crystal growth theory that is preferential nucleation at reentrant sites. 相似文献
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银纳米粒子阵列的自组装及其表面增强拉曼光谱应用 总被引:5,自引:0,他引:5
在以聚赖氨酸为表面耦联层分子的玻片基底制备了银纳米粒子阵列。SEM表征结果表明,银粒子以亚单层的形式排列在基底表面。比较银溶胶和纳米粒子阵列的紫外可见光谱可见聚赖氨酸耦联层对银纳米粒子的粒径具有一定的选择性,甲基紫精在银纳米粒子阵列上的表面增强FT拉曼光谱表明在近红外区拉曼散射的表面增强主要来自于化学增强效应。 相似文献
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文章报道了一种用紫外光引发还原制备金溶胶的新方法,其还原过程经历了自由基机理。用紫外可见光谱观察了不同反应时间溶胶状态的变化。结果表明,光照反应2h时明显出现金溶胶粒子,7h后氯金酸基本转化完毕。同时,研究了稳定剂聚乙烯吡咯烷酮(PVP)的加入对还原过程的影响,结果表明,PVP的加入不仅稳定了溶胶,而且降低了反应速率。用SEM观察了溶胶粒子聚集体的形貌。最后以1,4-bis(4-vinylpyridyl)phenylene为探针分子研究了这种溶胶的SERS活性。 相似文献
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晶体的熔化和结晶尽管有上百年的研究历史,但还缺乏基础层面上的理论,实验上则难以看到晶体内部单分子的运动。近二十年来,均匀微米大小的胶体粒子为研究这些问题提供了一个良好的实验平台。通过光学显微镜可以直接观察胶体粒子组成的晶体的表面和内部,研究相变在最初小尺度上的成核过程,并用图像处理得到单个粒子的运动轨迹,为复杂的结晶和熔化过程提供了丰富的微观信息。 相似文献
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Thin films of isotactic polystyrene partially crystallized from the glassy state were studied in detail by means of transmission electron microscopy and electron diffraction. Initial nucleation and growth stages of spherulitic fibrils (or lamellae) were illustrated clearly by using novel techniques, such as Au decoration, and novel specimens such as thin films containing holes. Spherulitic nucleation begins with the crystallization of a liquid-crystal-like nodule or a group of these nodules merging to form a spherulitic center. Fibrils or lamellae grow and fan out from the nucleus by additional incorporation of maturing nodules. Proliferation of fibrils is essentially a space-filling process through the crystallization of uncrystallized nodules or nodules that were left behind by growing fibrils which had initiated earlier. The deduced mechanism of spherulitic crystallization leads directly to the formation of interlamellar links between neighboring fibrils. However, no extended-chain-type interlamellar links were revealed by Au decoration. The application of the mechanism of spherulitic crystallization from the glass to that from the melt is also suggested; it is based primarily on recent studies which show remarkable similarities between structures existing in the glassy and the melt states prior to crystallization. 相似文献
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Yuzhen Wang Zhaobin Chen Jiayue Chen Yunpeng Qu Xiaoniu Yang 《Journal of Macromolecular Science: Physics》2013,52(10):1388-1404
A series of crystalline semiconducting poly(3-butylthiophene) (P3BT)/crystalline insulating polyethylene (PE) blends were prepared and the miscibility, crystallization, and structure/morphology were investigated. Even though phase separation was observed by transmission electron microscopy (TEM) and small-angle X-ray scattering (SAXS), several pieces of evidence indicated that limited miscibility should be present in PE/P3BT blends: small changes in both Tm and crystallinity of PE phase and a small portion of PE being dissolved in P3BT. The study of PE isothermal crystallization kinetics revealed that the introduction of P3BT significantly influenced the nucleation mechanism and growth geometry, i.e., PE was transformed from three-dimensional (3D) spherulitic to two-dimensional (2D) disc crystals. A striking reduction of nucleation density and an obvious ringed morphology of PE spherulites (2D) in PE/P3BT blends were also observed by polarized optical microscopy; it is proposed that the limited miscibility between PE and crystalline P3BT favors the formation of ringed PE spherulite in the blends. Additionally, preferred orientation of PE lamellae, with their b-axis largely constrained to the thin film plane, was observed by X-ray diffraction in PE/P3BT blend films. It is evidenced that the PE orientation was due to the b-axis being the crystal growth direction, which can only be in film plane. 相似文献
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Mei-Ling Xue Yong-Liang Yu Jun-Ping Zhang 《Journal of Macromolecular Science: Physics》2013,52(10):1955-1971
Organic montmorillonite (MMT) reinforced poly(trimethylene terephthalate) (PTT)/ polypropylene (PP) nanocomposites were prepared by melt blending. The effects of MMT on the nonisothermal crystallization of the matrix polymers were investigated using differential scanning colorimetry (DSC) and analyzed by the Avrami equation. The DSC results indicated that the effects of MMT on the crystallization processes of the two polymers exhibited great disparity. The PTT's crystallization was accelerated significantly by MMT no matter whether PTT was the continuous phase or not, but the thermal nucleation mode and three-dimensional growth mechanism remained unchanged. However, in the presence of MMT, the PP's crystallization was slightly retarded with PP as the dispersed phase, and was influenced little with PTT as the dispersed phase. When the MMT content was increased from 2_wt% to 7_wt%, the crystallization of the PTT phase was slightly accelerated, whereas the crystallization of the PP phase was severely retarded, especially at lower temperatures. Moreover, the nucleation mechanism for the PP's crystallization changed from a thermal mode to an athermal one. In the polypropylene-graft-maleic anhydride (PP-g-MAH) compatibilized PTT/PP blends, with the addition of 2_wt% MMT during melt blending, the T c (PTT) shifted 7.8°C to lower temperature and had a broadened exotherm, whereas the T c (PP) shifted 17.1°C to higher temperature, with a narrowed exotherm. TEM analysis confirmed that part of the PP-g-MAH was combined with MMT during blending. 相似文献
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Summary The process of colloidal crystallization has already been separately investigated by light scattering mearurements of the
crystalline order (Bragg peaks) and of long-ranged density fluctuations (small-angle scattering). We present the firstsimultaneous small- and large-angle light scattering experiment. Our measurements have been performed on hard-sphere colloids of different
particle densities. We show results for the temporal evolution of crystallization and find two distinct regimes: homogeneous
nucleation and diffusion- or reaction-limited growth at early times, followed by ripening of the Lifshitz-Slyozov or Lifshitz-Allen-Cahn
type. To our preliminary experience, we can already state that the results are always consistent in both partial experiments.
Paper presented at the I International Conference on Scaling Concepts and Complex Fluids, Copanello, Italy, July 4–8, 1994.
With deep regret we have to announce that Prof. Klaus Sch?tzel, who inspired and guided the work presented here, has died
in October 1994. 相似文献
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Y. Nakamura N. Ikeda S. Ohkouchi Y. Sugimoto H. Nakamura K. Asakawa 《Physica E: Low-dimensional Systems and Nanostructures》2004,21(2-4):551
Regular arrays of InGaAs quantum dots (QDs) with a 100-nm-periodicity have been successfully fabricated by controlling the nucleation sites on artificially prepared nano-hole arrays. The nucleation probability of a single QD at each nano-hole reached 100% by depositing InGaAs at low temperature and subsequent annealing. Four InGaAs QD layers were vertically stacked while conserving the regularity, and the stacked QD array has shown a clear photoluminescence peak at room temperature. We discuss the effects of several growth conditions on the nucleation probability of QDs. 相似文献
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We study the conditions under which and how an imposed cluster of fixed colloidal particles at prescribed positions triggers crystal nucleation from a metastable colloidal fluid. Dynamical density functional theory of freezing and Brownian dynamics simulations are applied to a two-dimensional colloidal system with dipolar interactions. The externally imposed nucleation clusters involve colloidal particles either on a rhombic lattice or along two linear arrays separated by a gap. Crystal growth occurs after the peaks of the nucleation cluster have first relaxed to a cutout of the stable bulk crystal. 相似文献
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《Journal of Macromolecular Science: Physics》2013,52(4):531-547
The crystallization behavior of poly(trimethylene terephthalate (PTT) in compatibilized and uncompatibilized PTT/polycarbonate (PC) blends are investigated in the research reported in this paper. The differential scanning calorimetry (DSC) results showed that the crystallization behaviors of PTT/PC blends were very sensitive to PC content. The onset (Tci) and the peak (Tc) crystallization temperatures shifted to lower temperatures whereas the area of the exotherm decreased quickly as the PC content was increased. The Avrami exponent, n, decreased from 4.32 to 3.61 as the PC content was increased from 0 to 20 wt %, and the growth rate constant, Z c , decreased gradually as well. This suggests that the nucleation mechanism exhibits the tendency of changing gradually from a thermal nucleation to an athermal mode although the growth mechanism still remains three‐dimensional. When epoxy (2.7 phr) was added as a compatibilizer during melt blending, the Tci and Tc shifted slightly to higher temperature (≤2°C), and the crystallization enthalpy, however, exhibited an increased crystallinity with the exception of the 90/10/2.7 phr PTT/PC/Epoxy. This suggests that the epoxy make a positive contribution to the PTT crystallization. Moreover, the influences of epoxy on the crystallization behaviors of PTT/PC blends are related to the epoxy content. By contrast, the compatibilizer of ethylene‐propylene‐diene copolymer graft glycidyl methacrylate (EPDM‐g‐GMA, ≤6.3 phr) had little effect on the crystallization behavior of PTT/PC blends. For PTT/PC/Epoxy (2.7 phr) blends, the Avrami exponent, n, decreased to near 3, while the growth rate constant, Z c , increased slightly as PC content was increased from 0 to 20 wt %. It is suggested that epoxy accelerated the process of the nucleation mechanism changing from thermal nucleation to an athermal mode. The EPDM‐g‐GMA had little effect on the nucleation mode and spherical growth mechanism. The PTT spherulite morphologies in PTT/PC blends were very sensitive to blend composition. Completely different morphologies were observed in pure PTT, PTT/PC, PTT/PC/Epoxy, and PTT/PC/EPDM‐g‐GMA blends. 相似文献
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The crystallization kinetics of colloidal hard spheres was studied using a special Bragg spectrometer with high sensitivity. In contrast with the classical scenario we observe a two-step nucleation process: the number of crystallites increases slowly at early times, followed by a dramatic reduction at intermediate times, prior to undergoing a rapid increase at late times. We explain these results in terms of a polydispersity limited growth of crystallites, where the crystallization at early times is governed by local fractionation processes, leading to a long delay prior to final crystallization. 相似文献
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D.M. Herlach 《The European physical journal. Special topics》2014,223(3):591-608
Metallic systems are widely used as materials in daily human life. Their properties depend very much on the production route. In order to improve the production process and even develop novel materials a detailed knowledge of all physical processes involved in crystallization is mandatory. Atomic systems like metals are characterized by very high relaxation rates, which make direct investigations of crystallization very difficult and in some cases impossible. In contrast, phase transitions in colloidal systems are very sluggish and colloidal suspensions are optically transparent. Therefore, colloidal systems are often discussed as model systems for metals. In the present work, we study the crystallization process of charged colloidal systems from the very beginning. Charged colloids offer the advantage that the interaction potential can be systematically tuned by a variation of the particle number density and the salt concentration. We apply light scattering and ultra-small angle x-ray scattering to investigate the formation of short-range order in the liquid state even far from equilibrium, crystal nucleation and crystal growth. The results are compared with equivalent studies on metallic systems. 相似文献
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Xingyou Tian Changjiu Ruan Wentao Liu Jin Zheng Xian Zhang 《Journal of Macromolecular Science: Physics》2013,52(5):835-848
The crystallization process of poly(ethylene terephthalate)/silica nanocomposites were investigated by differential scanning calorimetry (DSC) and then analyzed using the Avrami method. The results indicated that the crystallization of pure poly(ethylene terephthalate) (PET) was fitted for thermal nucleation and three‐dimensional spherical growth throughout the whole process, whereas the crystallization of PET/silica nanocomposites exhibits two stages. The first stage corresponds to athermal nucleation and three‐dimensional spherical growth, and the second stage corresponds to recrystallization caused by the earlier spherulites impingement. The crystallization rate increases remarkably and the activation energies decrease considerably when silica nanoparticles are added. The subsequent melting behavior of the crystallized samples shows that the melting point (T m) of nanocomposites is higher than that of pure PET, which might be caused by two factors: (1) The higher melting point might be due to some hindrance to the PET chains caused by the nanoparticles at the beginning of the melting process; (2) it might also be the case that more perfect crystals can be formed due to the higher crystallization temperatures and lower activation energies of PET/silica nanocomposites. 相似文献