Morphology and crystalline structure of inclusion compounds formed between poly(ethylene glycol) and urea

Da-wei, Lin; Zhong, Zhihui; Tang, Yi-Ren; Gao, Yang; He, Yahao; Guo, Baohua; Xu, Jun

doi:10.1007/s10118-014-1496-8

Cited by 9 publications

(3 citation statements)

References 21 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The lamellar orientation of the PEN terrace‐like crystals, however, is not directly observable from the results in this study. We can only speculate that the terrace‐like crystals have flat‐on orientation based on their morphological features, that is, their height profiles are relatively flat, and the edges slightly fringed due to diffusion‐limited growth . Thus, PEN appears to favor an edge‐on embryo surface crystal, which, in thicker films, can directly give rise to edge‐on lamellae in all directions within the plane.…”

Section: Resultsmentioning

confidence: 98%

In situ AFM study of near‐surface crystallization in PET and PEN

Shinotsuka

Assender

2016

J of Applied Polymer Sci

View full text Add to dashboard Cite

The surface crystallization behavior of poly(ethylene terephthalate) (PET) and poly(ethylene 2,6-naphthalate) (PEN) spincoated thin films was compared by means of atomic force microscopy (AFM) with an in situ heating stage. As the films were heated up stepwise, characteristic surface crystals appeared at a crystallization temperature (T c ) in the near-surface region which is about 15 8C under the bulk T c , and were replaced by bulk crystals when the temperature was increased to the bulk T c . In the case of films whose thickness is less than 70 nm (PET) and 60 nm (PEN), significant increases in the bulk T c were observed. Scanning force microscopy (SFM) force-distance curve measurements showed that the glass transition temperature (T g ) of the near-surface region of PET and PEN were 22.0 and 26.6 8C below their bulk T g (obtained by DSC). After the onset of surface crystallization, edge-on and flat-on crystals appeared at the free surface of PET and PEN thin films, whose morphologies are very different to those of the bulk crystals. Although the same general behavior was observed for both polyesters, there are significant differences both the influence of the surface and substrate on the transition temperatures, and in morphology of the surface crystals. These phenomena are discussed in terms of the differences in the mobility of polymer chains near the surface.

show abstract

Section: Resultsmentioning

confidence: 98%

In situ AFM study of near‐surface crystallization in PET and PEN

Shinotsuka

Assender

2016

J of Applied Polymer Sci

View full text Add to dashboard Cite

show abstract

“…The inclusion compounds formed between poly(ethylene oxide) and urea (PEO-U-IC) have been widely studied. − Two types of crystal modifications have been reported. The PEO-U-IC α phase is a trigonal system, while the β phase is an orthorhombic system .…”

Section: Introductionmentioning

confidence: 99%

Study of the Crystal Growth Mechanism and Critical Secondary Nucleus Size of Poly(ethylene oxide)/Urea Inclusion Compound

Gao

Zhang

Shi

et al. 2019

Crystal Growth & Design

Self Cite

View full text Add to dashboard Cite

This study focuses on the crystal growth mechanism and the critical nucleus size of the inclusion compound formed between poly(ethylene oxide) and urea (PEO-U-IC) β spherulites crystallized from the melt. The surface nucleation mechanism during the crystal growth process is proposed based on the exponential dependence of the spherulite radial growth rate G on the negative reciprocal of product of the isothermal crystallization temperature multiplied by the degree of supercooling (−1/(T cΔT)). The radial growth rates G of PEO-U-IC β spherulites crystallized from the mixed melt with the gradual addition of the diluting agent N,N′-dimethyl urea (2MeU) were measured under a polarized optical microscope. On the basis of the first nucleation theorem proposed by Kashchiev, the critical secondary nucleus size n* during the surface nucleation is determined from the slope of linear fitting line of ln G versus ln x, where x is the mass fraction of urea in U/2MeU. The critical secondary nucleus consists of 3–9 entities with each entity of the inclusion compound crystal containing 1 urea and 1.5 ethylene oxide repeating units when the crystallization temperature ranges from 65 to 85 °C. The relationship that n* is proportional to 1/(ΔT)2 confirms that the critical secondary nuclei at the solid–melt interface are two-dimensional.

show abstract

“…The work is expected to deepen our understanding of the nucleation of multi-component co-crystals.Entropy 2019, 21, 1032 2 of 12 compound (IC) during its crystal growth process [17]. The PEO/urea ICs consist of guest PEO chains residing in the cavities formed by the host urea molecules [18][19][20][21][22][23][24][25][26]. By replacing a small amount of urea with N,N -dimethyl urea with the PEO concentration unchanged, we could change the rate of secondary nucleation and determine the critical size of the secondary nuclei of the PEO/urea IC β crystal.…”

mentioning

confidence: 99%

Critical Size of Secondary Nuclei Determined via Nucleation Theorem Reveals Selective Nucleation in Three-Component Co-Crystals

Gao

Guo

2019

Entropy

Self Cite

View full text Add to dashboard Cite

The critical size of the secondary nuclei plays an important role in determining the crystal growth rate. In the past, the Nucleation Theorem has been applied to determine the number of molecules in the critical nuclei of a single-component crystal via variation of the crystal growth rate with dilution by the non-crystallizable component. In this work, we extend the method to the three-component co-crystal poly (ethylene oxide)/urea/thiourea inclusion compound. The theoretical crystal growth kinetics were deduced and the dependence of the radial growth rate of the inclusion compound spherulites on the mass fraction of urea in urea/thiourea was measured. The results reveal that the secondary nuclei of the poly (ethylene oxide)/urea/thiourea inclusion compound consist mainly of ethylene oxide repeating units and urea molecules. We propose that only urea molecules and ethylene oxide repeating units are selected to form the secondary nuclei while co-crystallization of the three components happens at the lateral spreading stage. As a result, the composition of the critical secondary nuclei is different from that of the bulk inclusion compound crystals. The work is expected to deepen our understanding of the nucleation of multi-component co-crystals.Entropy 2019, 21, 1032 2 of 12 compound (IC) during its crystal growth process [17]. The PEO/urea ICs consist of guest PEO chains residing in the cavities formed by the host urea molecules [18][19][20][21][22][23][24][25][26]. By replacing a small amount of urea with N,N -dimethyl urea with the PEO concentration unchanged, we could change the rate of secondary nucleation and determine the critical size of the secondary nuclei of the PEO/urea IC β crystal. Here, dimethylurea acted as a dilute agent, which was completely precluded from the crystal lattice. In the PEO/urea IC β crystal, the fixed stoichiometric ratio of 3/2 exists between ethylene oxide (EO) repeating units and urea molecules [22][23][24]27]; the crystallization unit is an entity containing 1 urea and 1.5 EO repeating units. Taking an entity as a unit of crystallization, the inclusion compound can be simplified as one-component crystal. A power-law relationship between the radial growth rate G and the mass fraction x of urea in the total mass of urea and the diluent was observed, and the exponent gave the critical size of the secondary nucleus. Our results revealed that a critical secondary nucleus of the PEO/urea IC β crystal consisted of 4 to 9 entities in the studied temperature range [17].In this work, we attempt to extend the Nucleation Theorem to determine the critical size of the secondary nuclei in a three-component co-crystal system poly (ethylene oxide)/urea/thiourea inclusion compound. Thiourea is an analogue molecule of urea, and as a result, the three components co-crystallize. PEO/urea/thiourea IC prepared by electrospinning was reported by Ye et al. [28], but the crystal growth kinetics were not examined. Here we find that the spherulites of PEO/urea/thiourea IC can form by isothermal crystalliz...

show abstract

Morphology and crystalline structure of inclusion compounds formed between poly(ethylene glycol) and urea

Cited by 9 publications

References 21 publications

In situ AFM study of near‐surface crystallization in PET and PEN

In situ AFM study of near‐surface crystallization in PET and PEN

Study of the Crystal Growth Mechanism and Critical Secondary Nucleus Size of Poly(ethylene oxide)/Urea Inclusion Compound

Critical Size of Secondary Nuclei Determined via Nucleation Theorem Reveals Selective Nucleation in Three-Component Co-Crystals

Contact Info

Product

Resources

About