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In the search for a greater understanding of polymer crystallization,numerous experimental observations with regards to microscopic structures and macroscopic properties have been reported in the past half-century.There are genera...
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In the search for a greater understanding of polymer crystallization,numerous experimental observations with regards to microscopic structures and macroscopic properties have been reported in the past half-century.There are generally two types of experimental results to provide information about the mechanisms of polymer crystal growth,i.e.molecular dynamic/scattering and structural/morphological.Since we cannot follow the trajectory of individual chain molecules when they undergo the transition from liquid to solid state during the crystallization process,structural/morphological analysis of polymer crystals reveal information recorded during this process.Namely,the final structure and morphology of polymer crystals have atomic,stem and global chain conformation information embedded in them during crystallization which provides evidence which can be used to deduce molecular aspects of the polymer crystallization process.It is commonly understood that polymer crystallization,from the thermodynamic perspective,is a first-order transition involving the relaxation of a metastable undercooled melt towards the equilibrium state which is rarely reached in polymer crystals.This process is controlled by a free energy barrier.A molecular model is required to describe the landscape of the free energy barriers and to provide an analytical explanation concerning and predictions about polymer crystallization.The Hoffman-Lauritzen (HL) theory,which was put forward more than 40 years ago,was one of the first analytical theories to illustrate how polymers crystallize.Since then,modifications to the HL theory and suggestions for new approaches have been reported,but the core physical picture of the HL theory has largely remained intact.This article consists of four major parts:(1) we will compare the crystallization of small molecules and long chain molecules,and the relationship between crystallization and crystal habits.The diversity of crystalline structures and morphologies of semi-crystalline polymers must be taken into account when studying the crystallization mechanism of polymers (2) this article also serves as a brief review of the HL theory and its importance in our understanding of polymer crystallization (3) we have tried to answer the question:what is the nucleation barrier?Specifically,we will illustrate that the nucleation barrier in polymer crystallization consists of both enthalpic and entropic components as deduced from experimental results.This barrier,from our perspective,consists of selection processes taking place in different length- and time-scales (4) finally,there is a brief discussion on what issues remain,in particular,in the areas of undercooled liquid structures and the initial stages of crystallization.
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The use of appropriate flat-sided pyramidal containers to grow ordered foams allows single crystals to be formed. In the case of face-centred cubic crystals, these have been prepared with up to 500 bubbles. Strained and deliberate...
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The use of appropriate flat-sided pyramidal containers to grow ordered foams allows single crystals to be formed. In the case of face-centred cubic crystals, these have been prepared with up to 500 bubbles. Strained and deliberately defective crystals can also be grown. The growth of simple cubic and body-centred cubic crystals is limited by instability; preliminary results are presented for these, as well as ordered bidisperse foams.
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A crystallization monitoring system using a quartz crystal oscillator was utilized to predict different shapes of crystal formation by measuring crystal growth rate and to measure supersaturation. Applying different rates of cooli...
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A crystallization monitoring system using a quartz crystal oscillator was utilized to predict different shapes of crystal formation by measuring crystal growth rate and to measure supersaturation. Applying different rates of cooling, crystal formation of different shapes was induced, and the frequency variation of the oscillator and the crystal shape observed with an SEM were compared to determine how the frequency variation can be interpreted for the prediction of produced crystal shape. The experimental results obtained from the crystallization of potassium nitrate and cupric sul-fate solutions showed that the proposed frequency measurement technique could be applied in the prediction of crystal shape of cooling crystallization processes. In addition, supersaturation was determined from the measurements of solution and coolant temperatures.
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During the growth of organic crystals, crystal defects can be formed. Microscopic defects, which include point, line, and planar defects, appearing as vacancies, growth dislocations, striations, and others, play an important role ...
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During the growth of organic crystals, crystal defects can be formed. Microscopic defects, which include point, line, and planar defects, appearing as vacancies, growth dislocations, striations, and others, play an important role in the mechanical properties, optical properties, and electrical conductivity of organic crystals. In addition, macroscopic defects, such as fluid inclusions and cavities, may cause toxicity during crystal dehydration and degradation while favorable cavity defects can satisfy certain functions. Herein, this paper summarizes the growth defects of organic crystals from four perspectives;; formation mechanism, characterization methods, control methods, and applications. We conclude three kinds of formation mechanism which are related to diffusion of solute molecules, impurities participating in the crystal growth, and structure of solute molecules respectively. Next, the characterization methods are exhibited from the perspectives of microscopy, spectroscopy, and others for different research areas. Then, we offer some control methods of defects which include adjustment of crystallization operation parameters, assistant of ultrasound and additives, irradiation, and ion implantation. As for applications, organic crystal defects have application potential in the fields of pharmacy and materials, for example, nonlinear optical materials, energetic materials, and semiconductor materials. Finally, we put forward the fixture outlooks on the growth defects of organic crystals.
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The thermostable aspartyl-tRNA synthetase (AspRS-1) from Thermus thermophilus is a 132 kDa homodimer with a subunit composed of 580 amino acids. It catalyses the aminoacylation of tPNA~asp with aspartic acid in the process of tran...
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The thermostable aspartyl-tRNA synthetase (AspRS-1) from Thermus thermophilus is a 132 kDa homodimer with a subunit composed of 580 amino acids. It catalyses the aminoacylation of tPNA~asp with aspartic acid in the process of translating genetic information. Here we present data on crystals grown in the presence of two different crystallizing agents. A first crystal form (form A) grows in the presence of 0.8 M ammonium sulfate and exhibits the orthorhombic space group p2_12_12_1. Monoclinic plates (form B) grow in an aqueous solution of 6/100 (m/v) PEG-8000.
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New ionic liquid crystals of [n-CxH(2x+1)NEt3][BEt3Me] (abbreviated to [CxNEt3][BEt3Me]) were detected for species with even numbers of 8 ]]]]]]= 12) in the liquid-crystal phases. In the case of x = 4, 5, XRD analysis showed that the sa...
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New ionic liquid crystals of [n-CxH(2x+1)NEt3][BEt3Me] (abbreviated to [CxNEt3][BEt3Me]) were detected for species with even numbers of 8 ]]]]]]= 12) in the liquid-crystal phases. In the case of x = 4, 5, XRD analysis showed that the salts form cubic crystal structures. Furthermore, the NMR line shapes revealed that both the cation and anion underwent isotropic reorientation. In contrast, the NMR spectra showed that the cations rotated about their long axis in the [C6NEt(3)][BEt3Me] and [C7NEt(3)][BEt3Me] crystals.
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The compound bis(ethylenediamine-N,N')-(oxalato-O,O')-cobalt biphenyl-4,4'-disulfonate hydrate, refcode TIQHOR, crystallizes with four Co(III) cations in the asymmetric unit. Another pair of compounds, rac-bis(ethylenediamine-N,N'...
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The compound bis(ethylenediamine-N,N')-(oxalato-O,O')-cobalt biphenyl-4,4'-disulfonate hydrate, refcode TIQHOR, crystallizes with four Co(III) cations in the asymmetric unit. Another pair of compounds, rac-bis(ethylenediamine-N,N')-(oxalato-O,O')-cobalt(III) L-hydrogenaspartate, refcode VAGBOU, and tetra-ammine-(N-benzylethanediamine)-cobalt(III) trinitrate sesquihydrate, refcode ZIFHEB crystallize both as conglomerates and kryptoracemates. Their stereochemical characteristics are described, and the fact that they display more than one mode of crystallization in a single lattice, is illustrated numerically and visually. (C) 2015 Academie des sciences. Published by Elsevier Masson SAS. All rights reserved.
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Protein crystallization screens frequently yield salt crystals as well as protein crystals. A simple method for determining whether a crystal is composed of salt or macromolecules is suggested. A drop containing one or more crysta...
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Protein crystallization screens frequently yield salt crystals as well as protein crystals. A simple method for determining whether a crystal is composed of salt or macromolecules is suggested. A drop containing one or more crystals is transferred to a glass cover slip and the cover slip is then passed through the flame of a Bunsen burner. Macromolecule crystals are destroyed by this treatment, while salt crystals generally remain. The test can be performed after other commonly used tests such as crushing and staining.
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The 4-hydroxy benzaldehyde-N-methyl 4-stilbazolium tosylate (HBST), a good non-linear optical (NLO)crystal has been synthesized and the single crystal has been grown by slow evaporation method. In thiswork we have used ethyl aceta...
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The 4-hydroxy benzaldehyde-N-methyl 4-stilbazolium tosylate (HBST), a good non-linear optical (NLO)crystal has been synthesized and the single crystal has been grown by slow evaporation method. In thiswork we have used ethyl acetate mixed methanol (1:1 ratio) as solvent. The lattice parameters were cal-culated from the powder X-ray diffraction patterns and compared with previous reports. The crystallineperfection has been verified with multicrystal X-ray diffractometer. The functional groups were identi-fied from FTIR and NMR spectral studies. In order to know the optical quality of the grown crystal, theUV-Vis-NIR absorption spectrum was recorded and optical transition energy levels were also calculated.The thermal properties were analyzed from TG/DTA data. The relative SHG efficiency was compared withurea by Kurtz powder method.
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