Special Issue "Crystal Morphology and Assembly in Spherulites"

A special issue of Crystals (ISSN 2073-4352). This special issue belongs to the section "Crystal Engineering".

Deadline for manuscript submissions: closed (31 March 2017)

Special Issue Editor

Guest Editor
Prof. Dr. Eamor M. Woo

Department of Chemical Engineering, National Cheng Kung University
Website | E-Mail
Interests: polymer phases; morphology; crystallization; polymer blends and phase separation; nanocomposites; biodegradable polymers; structure–property characterization

Special Issue Information

Dear Colleagues,

A spherulite (organic/inorganic molecular compounds or polymers) is a hierarchically packed complex structure of a rounded aggregate composed of central nuclei usually with cavity/crack, lamellae bundles radiating from nuclei, crystal branches or dislocations, and interspersed with localized amorphous domains. The typical spherulite diameter can vary from micrometers to millimeters, depending on kinetic factors. As spherulites are viewed using a polarizing optical microscope, the directional alignment of the molecules within the lamellae results in optical birefringence with a variety of color patterns, sometimes with ordered repetitions, which have intrigued scientific investigators for centuries. However, crystal morphology and mechanisms of lamellae assembly in spherulites, owing to theire complexity, have yet to be better understood.

This Special Issue of Crystals aims to be a collection of high-caliber original/review papers focusing on recent progress on: (a) mechanisms of diversification of spherulite morphology; (b) micro-lamellar assembly leading to a variety of optical birefringence patterns in spherulites; (c) kinetics and thermodynamics theories/models for prediction of lamellae self-assembly patterns in spherulites; (d) novel interpretations for periodically repetitive crystal assembly in spherulites; and (e) special crystal morphology in spherulites that are associated with potential applications such as functional, biomedical, or photonic materials. However, other interesting topics are also welcome should they fall generally in the field of crystals and their self-ordering behavior in spherulites.

Prof. Dr. Eamor M. Woo
Guest Editor

Manuscript Submission Information

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Keywords

  • Spherulites
  • Lamellae assembly
  • Morphology
  • Crystal growth

Published Papers (6 papers)

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Research

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Open AccessArticle Atomic-Force Microscopy Analyses on Dislocation in Extinction Bands of Poly(dodecamethylene terephthalate) Spherulites Solely Packed of Single-Crystal-Like Lamellae
Crystals 2017, 7(9), 274; doi:10.3390/cryst7090274
Received: 25 June 2017 / Revised: 8 September 2017 / Accepted: 8 September 2017 / Published: 11 September 2017
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Abstract
This study, using atomic-force and polarized-optical light (AFM and POM) microscopies on the extinction banded spherulites of poly(dodecamethylene terephthalate) (P12T) at high Tc = 110 °C with a film thickness kept at 1–3 µm, has verified that banded spherulites can be composed
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This study, using atomic-force and polarized-optical light (AFM and POM) microscopies on the extinction banded spherulites of poly(dodecamethylene terephthalate) (P12T) at high Tc = 110 °C with a film thickness kept at 1–3 µm, has verified that banded spherulites can be composed of stacks of entirely single-crystal-like lamellae free of any twisting, flipping, or bending, and no branching of lamellae. Defects in the crystal packing of extinction bands are present in both intra-band and inter-band regions. The intra-band defects originate from the miss-match in spiral-circling into circular bands while the inter-band defects are in the interfaces between successive bands where single crystals in the ridge are jammed to deformation, then suddenly precipitate prior to initiating another cycle of banding. The fish-scale lamellae, at the initiation of a cycle, are orderly packed as terrace-like single crystals; conversely, near or on the defected regions, they are highly jammed or squeezed and deformed to beyond recognition of their original single-crystal nature. Full article
(This article belongs to the Special Issue Crystal Morphology and Assembly in Spherulites)
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Open AccessArticle Morphology of Spherulites in Rapidly Solidified Ni3Ge Droplets
Crystals 2017, 7(4), 100; doi:10.3390/cryst7040100
Received: 26 January 2017 / Revised: 22 March 2017 / Accepted: 29 March 2017 / Published: 1 April 2017
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Abstract
The congruently melting, single phase, L12 intermetallic β-Ni3Ge has been subject to rapid solidification via drop-tube processing. Four different cooling rates are used in this process, at very low cooling rates (≥850 μm diameter particles, ≥700 K s−1)
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The congruently melting, single phase, L12 intermetallic β-Ni3Ge has been subject to rapid solidification via drop-tube processing. Four different cooling rates are used in this process, at very low cooling rates (≥850 μm diameter particles, ≥700 K s−1) and slightly higher cooling rates (850–500 μm diameter particles, 700–1386 K s−1) the dominant solidification morphology, revealed after etching, is that of isolated spherulites in an otherwise featureless matrix. At higher cooling rates, (500–300 μm diameter particles, 1386–2790 K s−1 and (300–212 μm diameter particles, 2790–4600 K s−1) mixed spherulite and dendritic morphologies are observed. Indeed, at the higher cooling rate dendrites with side-branches composed of numerous small spherulites are observed. Selected area diffraction analysis in the TEM indicate that the formation of spherulites is due to an order-disorder transformation. Dark-field TEM imaging has confirmed that the spherulites appear to consist of lamellae of the ordered phase, with disordered material in the space between the lamellae. The lamellar width within a given spherulite is constant, but the width is a function of cooling rate, with higher cooling rates giving finer lamellae. As such, there are many parallels with spherulite growth in polymers. Full article
(This article belongs to the Special Issue Crystal Morphology and Assembly in Spherulites)
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Open AccessArticle Interior Lamellar Assembly and Optical Birefringence in Poly(trimethylene terephthalate) Spherulites: Mechanisms from Past to Present
Crystals 2017, 7(2), 56; doi:10.3390/cryst7020056
Received: 29 November 2016 / Accepted: 12 February 2017 / Published: 15 February 2017
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Abstract
Poly(trimethylene terephthalate) (PTT) with its unique spherulitic morphologies, highly birefringent features, and crystal stability serves as a good candidate to study polymer crystallization and assembly. This review compiles the main findings on crystallization in PTT, including birefringence and morphology, thermal behavior, as well
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Poly(trimethylene terephthalate) (PTT) with its unique spherulitic morphologies, highly birefringent features, and crystal stability serves as a good candidate to study polymer crystallization and assembly. This review compiles the main findings on crystallization in PTT, including birefringence and morphology, thermal behavior, as well as the interior structure of PTT banded spherulites, in order to elucidate the origin and formation mechanism of banded spherulites. Interior observation through the inner anatomy of crystal assembly in banded spherulites hidden under the top surface is necessary to provide a complete picture for the unsettled arguments about formation mechanism. Careful attention should be taken when selecting the etching agent for exposing the lamellar structure of polymer spherulite, otherwise, misinterpretation could result Full article
(This article belongs to the Special Issue Crystal Morphology and Assembly in Spherulites)
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Review

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Open AccessReview Organization of Twisting Lamellar Crystals in Birefringent Banded Polymer Spherulites: A Mini-Review
Crystals 2017, 7(8), 241; doi:10.3390/cryst7080241
Received: 12 July 2017 / Revised: 2 August 2017 / Accepted: 2 August 2017 / Published: 4 August 2017
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Abstract
In this mini-review, we summarize the evidences of lamellar twisting in the birefringent banded polymer spherulites demonstrated by various characterization techniques, such as polarized optical microscopy, real-time atomic force microscopy, micro-focus wide angle X-ray diffraction, etc. The real-time observation of lamellar growth under
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In this mini-review, we summarize the evidences of lamellar twisting in the birefringent banded polymer spherulites demonstrated by various characterization techniques, such as polarized optical microscopy, real-time atomic force microscopy, micro-focus wide angle X-ray diffraction, etc. The real-time observation of lamellar growth under atomic force microscopy unveiled the fine details of lamellar twisting and branching in the banded spherulites of poly(R-3-hydroxybutyrate-co-17 mol% R-3-hydroxyhexanoate). Organization of the twisting lamellar crystals in the banded spherulites was revealed as well. The lamellar crystals change the orientation via twisting rather than the macro screw dislocations. In fact, macro screw dislocation provides the mechanism of synchronous twisting of neighboring lamellar crystals. The driving force of lamellar twisting is attributed to the anisotropic and unbalanced surface stresses. Besides molecular chirality, variation of the growth axis and the chemical groups on lamellar surface can change the distribution of the surface stresses, and thus may invert the handedness of lamellar twisting. Thus, based on both experimental results and physical reasoning, the relation between crystal chirality and chemical molecular structures has been suggested, via the bridge of the distribution of surface stresses. The factors affecting band spacing are briefly discussed. Some remaining questions and the perspective of the topic are highlighted. Full article
(This article belongs to the Special Issue Crystal Morphology and Assembly in Spherulites)
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Open AccessReview Crystalline and Spherulitic Morphology of Polymers Crystallized in Confined Systems
Crystals 2017, 7(5), 147; doi:10.3390/cryst7050147
Received: 10 April 2017 / Revised: 15 May 2017 / Accepted: 15 May 2017 / Published: 19 May 2017
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Abstract
Due to the effects of microphase separation and physical dimensions, confinement widely exists in the multi-component polymer systems (e.g., polymer blends, copolymers) and the polymers having nanoscale dimensions, such as thin films and nanofibers. Semicrystalline polymers usually show different crystallization kinetics, crystalline structure
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Due to the effects of microphase separation and physical dimensions, confinement widely exists in the multi-component polymer systems (e.g., polymer blends, copolymers) and the polymers having nanoscale dimensions, such as thin films and nanofibers. Semicrystalline polymers usually show different crystallization kinetics, crystalline structure and morphology from the bulk when they are confined in the nanoscale environments; this may dramatically influence the physical performances of the resulting materials. Therefore, investigations on the crystalline and spherulitic morphology of semicrystalline polymers in confined systems are essential from both scientific and technological viewpoints; significant progresses have been achieved in this field in recent years. In this article, we will review the recent research progresses on the crystalline and spherulitic morphology of polymers crystallized in the nanoscale confined environments. According to the types of confined systems, crystalline, spherulitic morphology and morphological evolution of semicrystalline polymers in the ultrathin films, miscible polymer blends and block copolymers will be summarized and reviewed. Full article
(This article belongs to the Special Issue Crystal Morphology and Assembly in Spherulites)
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Open AccessReview Morphological Control of Polymer Spherulites via Manipulating Radial Lamellar Organization upon Evaporative Crystallization: A Mini Review
Crystals 2017, 7(4), 115; doi:10.3390/cryst7040115
Received: 21 March 2017 / Revised: 17 April 2017 / Accepted: 17 April 2017 / Published: 19 April 2017
Cited by 1 | PDF Full-text (16715 KB) | HTML Full-text | XML Full-text
Abstract
Various spherulites or spherulitic crystals are widely encountered in polymeric materials when crystallized from viscous melts or concentrated solutions. However, the microstructures and growth processes are quite complicated and remain unclear and, thus, the formation mechanisms are rather elusive. Here, diverse kinds of
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Various spherulites or spherulitic crystals are widely encountered in polymeric materials when crystallized from viscous melts or concentrated solutions. However, the microstructures and growth processes are quite complicated and remain unclear and, thus, the formation mechanisms are rather elusive. Here, diverse kinds of spherulitic growths and patterns of typical polyesters via evaporative crystallization of solution-cast thin films are delineated after detailed investigating the microstructures and in situ following the developing processes. The spherulitic crystals produced under different evaporation conditions reflect variously optical features, such as the usual Maltese Cross, non-birefringent or half-birefringent concentric-rings, extinction spiral banding, and even a nested ring-banded pattern. Polymer spherulites are composed of stacks of radial fibrillar lamellae, and the diversity of bewitchingly spherulitic morphologies is dominated by the arrangement and organization of radial lamellae, which is predicted to be tunable by modulating the evaporative crystallization processes. The emergence of various types of spherulitic morphologies of the same polymer is attributed to a precise manipulation of the radial lamellar organization by a coupling of structural features and specific crystal evolving courses under confined evaporation environments. The present findings improve dramatically the understanding of the structural development and crystallization mechanism for emergence of diverse polymer spherulitic morphologies. Full article
(This article belongs to the Special Issue Crystal Morphology and Assembly in Spherulites)
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