Crystallization precursor

Examples of polymers which form anisotropic polymer melts iaclude petroleum pitches, polyesters, polyethers, polyphosphaziaes, a-poly- -xyljlene, and polysdoxanes. Synthesis goals iaclude the iacorporation of a Hquid crystal-like entity iato the maia chaia of the polymer to iacrease the strength and thermal stabiHty of the materials that are formed from the Hquid crystal precursor, the locking ia of Hquid crystalline properties of the fluid iato the soHd phase, and the production of extended chain polymers that are soluble ia organic solvents rather than sulfuric acid. 

Mixtures of a nematic liquid crystal (LC or LC ) with small quantities of gold nanoparticles coated with alkylthiolates (<5 wt%) including an alkylthiolate functionalized with a chiral group have been studied (Figure 8.29) [72]. All mixtures show nematic mesophases with transition temperatures and phase stability very similar to those oftheliquid crystal precursors LC or LC. The introduction ofachiral center into the mixtures (mixtures of Au ) produce chiral nematic mesophases. A similar result is obtained in mixtures of Au and LC doped with the chiral dopant (s)-Naproxen. 

Dobbs, W., Suisse, J.-M., Douce, L. and Welter, R. (2006) Electrodeposition of Silver Partides and Gold Nanopartides from Ionic Liquid-Crystal Precursors. Angewandte Chemie (International Edition in English), 45, 4179-4182. 

High-Temperature Crystallization The size-tunable optical and electronic properties of semiconductor nanocrystals are attractive for a variety of optoelectronic applications. In solution-phase crystallization, precursors undergo chemical reaction to form nuclei, and particle growth is arrested with capping ligands that... 

Prominent exceptions are studies on the liquid crystal phase formation and self-assembly of two-dimensional disc- or sheet-like nanomaterials such as the organization of nanodiscs or nanoplatelets into nematic, smectic, or columnar morphologies [263-270] (see Fig. 2 for an example of the self-assembly of nanoclay in aqueous suspensions) or the synthesis of CuCl nanoplatelets from ionic liquid crystal precursors as described by Taubert and co-workers [271-273]. 

Shear breeding results when supersaturated solution flows by a crystal surface and carries with it crystal precursors believed formed in the region of the growing crystal surface. High supersaturation is required for shear breeding to produce significant numbers of nuclei. 

Uniform and small crystallites could be rapidly synthesized by milling of crystal precursor. The size and concentration profiles of precipitated particles affected not only the induction period and the rate of crystallization, but also the crystal structure and distribution of the acid sites. Accordingly, if the crystal precursor is as small and uniform as possible, the synthesis of a very small and uniform crystallites and very rapid crystallization would be expected. Such small particles would play the role of nuclei of the crystals. Therefore, in this study, the precipitated gel was milled by a motor driven mortar. The liquid phase separated from the gel by the progress of milling was removed twice by centrifuge (Method 3) ... 

Ceramics obtained from polymeric precursors are usually amorphous. Since substantial thermal activation is required for nucleation and crystallization, precursor-derived ceramics (PDCs) frequently remain amorphous or nanocrystalUne up to rather high temperatures. For example, crystallization of a number of quaternary Si-B-C-N ceramics is retarded even up to 1800°C, resulting in excellent thermomechanical properties. Nevertheless, crystalline materials are of great interest because their microstructure formation can be controlled during devitrification, providing a means for stabilizing nanosized morphologies. 

Khoury, F. The spherulitic crystallization of isotactic polypropylene from solution on the evolution of monoclinic spherulites from dendritic chain-folded crystal precursors. J. Res. Nat. Bur. Stand. 1966, A-70, 29. 

Taubert A (2004) CuCl nanoplatelets from an ionic Uquid-crystal precursor. Angew Chem Int Ed 43 5380-5382... 

Taubert A, Steiner P, Mantion A (2005) Ionic liquid crystal precursors for inorganic particles phase diagram and thermal properties of a CuCl nanoplatelet precursor. J Phys Chem B 109 15542-15547... 

Wang Q, Wang X, Lou W et al (2009) Stable blue- and green-emitting zinc oxide from ionic liquid crystal precursors. Chemphyschem 10 3201—3203... 

Dobbs W, Suisse J, Douce L et al (2006) Electrodeposition of silver particles and gold nanoparticles from ionic liquid-crystal precursors. Angew Chem Int Ed 45 4179 182... 

Several fibers based on liquid crystal precursors have been subsequently produced. Keller [23] postulates the existence of a liquid crystalline phase during the melt-crystalline transition in polyethylene (and other polymers). 

The epitaxial growth and the formation of a shish-kebab stmcture were also investigated in high molecular weight iPP (HMW-iPP)/low-molecular-weight LLDPE (LMW-LLDPE) blends [21]. The formation of the initial crystallization precursor structure was investigated by using synchrotron WAXS/SAXS techniques at 130 and 140 °C. Shear was applied at temperatures above the cloud points of these blends, and therefore, the HMW-iPP chains could form a flow-induced crystalline stmcture in the blends only at 6 and 9 wt% of HMW-iPP LMW-LLDPE merely served as the amorphous matrix (Fig. 5.3). When the HMW-iPP... 

Fig. 5.3 Schematic illustration of initial crystallization precursor structure (stable critical nucleus) formation in HMW-iPP/LMW-LLDPE blends after cessation of flow. Before flow, HMW-iPP chains solid lines) form a network with a given entanglement density in the LMW-LLDPE matrix blank area). During shear, stretched chain segments begin to form initial erystallization precursor structure via local parallel packing, r and t represent the sizes of initial precursor and critical nucleus for crystallization, respectively. When r > r, the precursors can furthta develop into crystals [21]...

J. K. Keum, Y. Mao, F. Zuo, B.S. Hsiao, Flow-induced crystallization precursor stmcture in high molecular weight isotactic polypropylene (HMW-iPP)/low molecular weight linear low density polyethylene (LMW-LLDPE) binary blends. Polymer 54, 1425-1431 (2013)... 

Solutions containing chelates with multidentate ligands (such as citrate ions OOC—CH2 C(0H)(C00 )—CH2—COO ) give an amorphous viscous deposit sticking to the support surface upon drying [51]. The phase obtained after thermal treatments is more dispersed than with crystallized precursors. 

Role of Chain Entanglement Network on Formation of Flow-Induced Crystallization Precursor Structure... 

B.S. Hsiao Role of Chain Entanglement Network on Formation of Flow-Induced Crystallization Precursor Structure, Lect. Notes Phys. 714, 133-149 (2007)... 

Current Opinions on Flow-Induced Crystallization Precursor Structures... 

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