Rod-like Growth Research Articles

Kinetics of phase transition of a liquid crystalline polymer

The kinetics of phase transition from the isotropic state to the nematic mesophase of a main-chain, thermotropic liquid crystalline polymer has been studied by DSC and optical microscopy. Avrami-type analysis of the data gives an exponent close to 1.0 which suggests nucleation followed by rod-like growth.

Viscosity and crystallization kinetics of As 2Se 3

The crystallization kinetics, viscosity, and temperature coefficient of expansion of amorphous As 2Se 3 were investigated. The crystallization kinetics of As 2Se 3 are characterized under isothermal conditions for undercoolings ranging from 37°C to 122°C using thermal analysis techniques. The crystallization kinetics can be accurately described by the Johnson-Mehl-Avrami transformation equation. At least at the lower observed temperatures As 2Se 3 exhibits an increasing nucleation rate with respect to time. Microscopic examination of partially crystallized specimens reveals constant isothermal growth rates with respect to time and a spherulitic growth habitat for the crystalline phase. All spherulites nucleated at free surfaces. The individual As 2Se 3 crystallites in the spherulites have a plate-like growth morphology at temperatures well below the crystalline melting point. At temperatures approaching the crystalline melting point the crystallites assume a rod-like growth morphology. The activation energy for the crystal growth rate was determined to be 1.6 eV by direct observation. A model for the crystallization kinetics consistent with the data is suggested which yields an activation energy of 2.7 eV for secondary nucleation within the spherulites for 240°C < T < 300°C. The viscosity of As 2Se 3 in the pure and doped states (1 at.% Ag) was measured in the glass transition region. Utilizing these data for pure As 2Se 3 and the high temperature data of previous investigators the interpolated activation energy for viscous flow in the temperature region of rapid crystallization was determined to be 2.7 eV. The linear temperature coefficient of expansion was determined to be 1.55 × 10 −5/°C for T < T g and 10.0 × 10 −5/°C for T < T g.

High speed spinning of poly(ethylene terephthalate)—II: Orientation induced mechanism of cold crystallization in pre-orientated yarns

The kinetics of the “cold crystallization” of poly(ethylene terephthalate) (PET) pre-orientated yarns are investigated both in isothermal and in non-isothermal dynamic conditions. The amorphous-crystalline, solid-solid transformation is analyzed in terms of the Avrami equation and of Ozawa's theory. The nucleation and growth mechanism is a function of PET amorphous molecular orientation and changes from a three dimensional ( n = 4) to a two dimensional and one dimensional disc-like or rod-like growth. The molecular orientation may be defined as the best “nucleating agent” for PET overall rate of crystallization in the low temperature region.

Reducing the grain size of polycrystalline lead films by the use of nucleants

Thin layers of La, Y, Au, Pd, Pt, Ag, and Sn were evaporated at room temperature as nucleants prior to the evaporation of 2000 Å Pb. The correlations of grain size, surface morphology, and the phase diagrams of lead nucleant showed that the grain size of lead was reduced only if the nucleant formed a compound with lead and a eutectic between the compound and lead. In such a case the surface morphology was hemispherical, indicating that crystallization from the vapor took place through the liquid phase. The various sources of undercooling explaining the presence of the liquid phase are discussed. It is shown that the necessary condition for heterogeneous nucleation is the same as the condition for lamellar or rodlike eutectic growth; therefore, the occurrence of such eutectic in the phase diagram indeed indicates the possibility of heterogeneous nucleation. A vapor-liquid-heterogeneous nucleation mechanism of crystallization is suggested. Factors affecting the surface morphology of nucleated films are discussed.

Transient electric birefringence study of CTAB micelles. Implications for rodlike growth

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTTransient electric birefringence study of CTAB micelles. Implications for rodlike growthD. F. Nicoli, John G. Elias, and Don EdenCite this: J. Phys. Chem. 1981, 85, 20, 2866–2869Publication Date (Print):October 1, 1981Publication History Published online1 May 2002Published inissue 1 October 1981https://doi.org/10.1021/j150620a002RIGHTS & PERMISSIONSArticle Views106Altmetric-Citations13LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (463 KB) Get e-Alerts

Quiescent crystallization in thermotropic polyesters

The crystallization event in a number of thermotropic polyesters containing hydroxybenzoic acid, naphthalene dicarboxylic acid, isophthalic acid, and hydroquinone has been followed by a variety of techniques including optical microscopy, calorimetry, and wide angle X-ray diffraction. The results indicate that massive structural rearrangements do not occur during crystallization and, hence, the structure of the crystal closely resembles that of the nematic melt. The Avrami plot gives an exponent of about 2 which suggests rod-like growth and is well within the range typical of semicrystalline polymers. Perhaps the most important point is that the standard techniques employed for gaining an understanding of the crystallization of semicrystalline polymers seem to give reasonable results on mesogenic polymers. Studies of quiescent crystallization on thermotropic systems can provide insight into the crystallization event in oriented flexible chain polymer melts.

Crystallization kinetics of gehlenite glass

Isothermal and non-isothermal kinetics of gehlenite glass devitrification have been studied. A Johnson—Mehl—Avrami rate equation was assumed. The values of kinetic parameters obtained from XRD patterns and DTA curves are in a good agreement. The crystallization process is thought to proceed by a rod-like growth controlled by diffusion from a fixed number of nuclei.

Metal-induced recrystallization of solution grown amorphous polyvinylchloride (PVC) films

Recrystallization has been induced in solution grown amorphous PVC films (∼ μ thick) by depositing a thin film (10–50 å) of aluminum and then heating the double layer in vacuum or in benzene at various temperatures for various lengths of time. The morphology of the crystallites was found to depend on the method of crystallization and the duration and temperature of crystallization. Dendritic growth at higher temperatures (above 180°C) and needle or rod-like growth at lower temperatures have been observed. The role of aluminium in initiating or promoting the crystallization is discussed.

Developments in eutectics

Some of the more important aspects of lamellar and rod-like eutectic growth are presented. Recent experimental work has cast serious doubt on current theory. It seems probable that difficulties arise because of an incorrect choice of the additional condition necessary to specify lamellar growth. Doubt must be cast on the theory in its present form, both for lamellar spacing determination and for the lamellar to rod breakdown. Recent experimental work on the extent of the eutectic range has shown that the range depends critically on the temperature gradient in the liquid. A review is made of the treatments proposed to explain the experimental results.