Isothermal Growth and Reorganization upon Heating of a Single Poly(aryl−ether−ether−ketone) (PEEK) Spherulite, As Imaged by Atomic Force Microscopy

Ivanov, Dimitri A.; Jonas, Alain M.

doi:10.1021/ma961549e

Cited by 47 publications

(28 citation statements)

References 34 publications

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“…It is also observed that nodules develop to lath-like lamellae through merging or lateral aggregation [11,12]. At larger scale, the sheaf-like structures can be observed [14], and category 2 spherulites [6] are developed [15]. Crystal structures developed from the glassy state thus show distinct features from those developed from solution.…”

Section: Introductionmentioning

confidence: 98%

Effect of Film Formation Method and Annealing on Crystallinity of Poly(L-Lactic Acid) Films

Hsu

Yao

2011

ASME 2011 International Manufacturing Science and Engineering Conference, Volume 1

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Poly(L-lactic acid) (PLLA) has been shown to have potential medical usage such as in drug delivery because it can degrade into bioabsorbable products in physiological environments, and its degradation is affected by crystallinity. In this paper, the effect of film formation method and annealing on the crystallinity of PLLA are investigated. The films are made through solvent casting and spin coating methods, and subsequent annealing is conducted. The resulting crystalline morphology, structure, conformation, and intermolecular interaction are examined using optical microscopy, X-ray diffraction, and Fourier transform infrared spectroscopy. It is observed that solvent casting produces category 1 spherulites while annealed spin coated films leads to spherulites of category 2. Distinct lamellar structures and intermolecular interactions in the two kinds of films have been shown. The results enable better understanding of the crystallinity in PLLA, which is essential for its drug delivery application. INTRODUCTIONThere is a significant interest in use of biodegradable polymers due to their biocompatibility and biodegradability. Poly lactic acid (PLA) is a biodegradable polymer and can be obtained from renewable sources such as corn starch. It has a wide range of applications, such as in food packaging and tissue engineering. PLA is also of interest in drug delivery application because it can degrade into bioabsorbable products in physiological environments. Its degradation mainly comes from the cleavage of its ester groups, and is sensitive to chemical hydrolysis. In polymeric drug delivery system, drugs are encapsulated in polymer. As the polymer degrades, the drugs are released, and the release rate is determined by the polymer degradation rate. Crystallinity of polymer is a factor affecting the degradation rate. A good review on the effect of crystallinity on degradation and drug release can be found in [1]. In general, less crystallinity accelerates degradation and drug release rate. To create polymeric drug delivery system, drug molecules are dispersed or dissolved in the polymeric solution, formed through melting the polymer or dissolving it in a solvent. During the process the polymer may crystallize. The crystal structure also influences the degradation rate. Tsuji and Ikada [2] studied the hydrolysis of PLA films and proposed that it begins in the amorphous region between the crystalline lamellae, followed by the disorientation of the lamellae and disappearance of the spherulitic structure.

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Section: Introductionmentioning

confidence: 98%

Effect of Film Formation Method and Annealing on Crystallinity of Poly(L-Lactic Acid) Films

Hsu

Yao

2011

ASME 2011 International Manufacturing Science and Engineering Conference, Volume 1

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“…Recent advances in techniques of atomic-force microscopy (AFM) have added significant convenience in probing the surface topography, lamellar, and crystal structures in banded rings in various polymer spherulites. [15][16][17][18][19] There are still largely unresolved debates on origins or mechanism of ring-band patterns in polymer spherulite; however, there have been no attempts to evaluate and compare the thermal behavior of ring-band versus Maltesecross spherulites. Regardless of crystallization temperature, PEA possesses only a single type of crystal cell, i.e., no polymorphism in PEA; however, it can exhibit ring spherulites as well as typical Maltese-cross ones.…”

Section: Introductionmentioning

confidence: 99%

Thermal Behavior of Ring‐Band versus Maltese‐Cross Spherulites: Case of Monomorphic Poly(ethylene adipate)

Woo

et al. 2006

Macro Chemistry & Physics

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Summary: Two types of spherulites, extinction‐ring and Maltese‐cross, in poly(ethylene adipate) (PEA) were identified, isolated, and separately characterized using DSC and polarized‐light optical microscopy (POM). Ring‐band spherulites in PEA occurred only in a very narrow temperature range roughly between 25 and 30 °C, while Maltese‐cross spherulites at 35 °C and above or at 20 °C and below. Thermal behavior of ring‐spherulites is interpreted, analyzed, and compared to that of Maltese‐cross spherulites. The thermal behavior, like the morphology, was found to be significantly different between these two types of spherulites. Among the three multiple melting peaks in PEA, the highest P3 is proven to be related to melting of lamellae in the ring‐band spherulites; P1 and P2, whose relative extent of overlapping is dependent on the temperature of crystallization, are related to melting of lamellae in the regular ringless spherulites. This study has provided urgent and timely evidence for one major step further in the interpretation of relationships between the thermal behavior, melting, and extinction‐ring versus Maltese‐cross spherulites in semi‐crystalline polymers.DSC curves (10 °C · min−1, scanned from where the trace begins) for: (a) ring‐spherulites in PEA crystallized at 30 °C for 90 min, (b) sample‐(a) heated to 50 °C for 1 min, and (c) sample‐(a) heated to 50 °C, then quenched to 20 °C.magnified imageDSC curves (10 °C · min−1, scanned from where the trace begins) for: (a) ring‐spherulites in PEA crystallized at 30 °C for 90 min, (b) sample‐(a) heated to 50 °C for 1 min, and (c) sample‐(a) heated to 50 °C, then quenched to 20 °C.

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“…More recently, atomic force microscopy (AFM) has been utilized to study the organization of spherulites and the crystallization process of polymers. 10,11 A copolymer, poly(bisphenol A-co-octane), 12 was synthesized with the following structure:…”

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confidence: 99%

A Direct Observation of the Formation of Nuclei and the Development of Lamellae in Polymer Spherulites

Lin

Chan

et al. 1999

Macromolecules

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Since polymer spherulites were observed using optical microscopy and single polymer crystals were prepared from solution, 1,2 the internal structure of polymer spherulites has been investigated widely with electron microscopy. [3][4][5][6][7][8][9] For most crystalline polymers, it is generally accepted that spherulites are developed from a single crystal through unidirectional growth, and the spherical shape is attained through continuous splaying apart and occasional branching of lamellae, 5 though there are ongoing debates concerning the details of the branching in the literature. More recently, atomic force microscopy (AFM) has been utilized to study the organization of spherulites and the crystallization process of polymers. 10,11 A copolymer, poly(bisphenol A-co-octane), 12 was synthesized with the following structure:This polymer is attractive for analyses of the formation of nuclei and growth of lamellae because its glass transition temperature is close to room temperature, and it crystallizes at room temperature at a rate that allows imaging of the crystallization process by AFM without a hot stage. The glass transition temperature, melting point, and number-average molecular weight for this polymer were respectively measured to be 6.9°C, 83.5°C, and 5.7 × 10 3 g/mol. The crystallized sample exhibited several X-ray diffraction peaks at 2θ ) 5.6°, 15.2°, 18.6°, and 19.8°. A thin film of about 300 nm was prepared by spin-coating the polymer solution on a silicon chip, and the crystallization process was observed directly under tapping-mode AFM phase imaging.Embryos of the lamellae, as fine dots, with a dimension smaller than 10 nm, appeared and disappeared on the surface of the initially amorphous polymer film during scanning (Figure 1a,b). Figure 1a shows the presence of two embryos. In Figure 1b, which was obtained approximately 8.7 min after the image shown in Figure 1a, one of the embryos disappeared. We believe that this is the first experimental evidence in a polymer to show that, as predicted by thermodynamics, embryos smaller than a critical dimension are unstable and may not ultimately grow. The initial nucleating lamella grows along the length of the lamella at both ends (Figure 1c). During the growth stage, it breeds more lamellae (Figure 1d). When their lengths are longer than 0.5-1.0 µm, the lamellae begin to form branches (Figure 1e), and some lamellae splay apart from each other (Figure 1f). As a result of continual splaying and branching of the lamellae, the initial lamellae gradually develop into a lamella sheaf and a spherulite skeleton (Figure 1g,h). Figure 1. Nucleation, growth, and formation of a spherulite: (a) formation of lamella embryos; (b) disintegration of one of the lamella embryos; (c) growth of a lamella embryo; (d) breeding of more lamellae from the initial nucleating lamella; (e) branching of the growing lamellae; (f) splaying apart of the lamellae; (g) a lamella sheaf; and (h) a spherulite skeleton. 8240Macromolecules 1999, 32,[8240][8241][8242] 10.

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Isothermal Growth and Reorganization upon Heating of a Single Poly(aryl−ether−ether−ketone) (PEEK) Spherulite, As Imaged by Atomic Force Microscopy

Cited by 47 publications

References 34 publications

Effect of Film Formation Method and Annealing on Crystallinity of Poly(L-Lactic Acid) Films

Effect of Film Formation Method and Annealing on Crystallinity of Poly(L-Lactic Acid) Films

Thermal Behavior of Ring‐Band versus Maltese‐Cross Spherulites: Case of Monomorphic Poly(ethylene adipate)

A Direct Observation of the Formation of Nuclei and the Development of Lamellae in Polymer Spherulites

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