A Real-Time Study of Homogeneous Nucleation, Growth, and Phase Transformations in Nanodroplets of Low Molecular Weight Isotactic Polypropylene Using AFM

Department of Chemistry, The University of Sheffield, Sheffield, England, United Kingdom
Macromolecules (Impact Factor: 5.8). 10/2007; 40:7223-7230. DOI: 10.1021/ma070861t


Nanodroplets of isotactic polypropylene (iPP) were observed using temperature-controlled AFM in order to study the polymer's crystallization behavior. The nucleation, growth, and transformation of iPP crystals on heating have been directly imaged. The strong confinement of the polymer into nanoscale droplets has allowed the controlled observation of polymer nucleation as well as access to crystal growth at exceptionally high supercooling in iPP. Different modes of crystal growth were observed depending on the film thickness, including the formation of multiple independent homogeneous nuclei within single droplets. The temperature at which the onset of nucleation was observed in individual droplets was found to be dependent on the thickness as well as the volume of the droplets. For droplets with smaller thicknesses (<5 nm), the thickness of the droplets was found to be the dominating factor influencing the nucleation temperature. This is the first real-space, real-time observation of homogeneous nucleation in iPP, almost 125 degrees C below its melting point, which could signify crystal growth in the smectic form, and of the subsequent reorganization into the a-form.

Download full-text


Available from: Jean-Nicolas Audinot,
  • Source
    • "Their WAXS results indicate that the PP is crystallizing in a smectic phase within the nanodroplets. This type of crystallographic arrangement could be a consequence of the way the nanodroplets are prepared, since they come from the rupture and coalescence of nanolayers and therefore in agreement with the recent observation of Kailas et al. [38] who found similar results for droplets whose thickness were below 5 nm (see above). On the other hand, Arnal et al. [76] obtained PP droplets in the micron range (1e2 mm) in a PS matrix (by melt blending) and demonstrated by WAXS that the droplets crystallized in the typical a phase of PP, just as the bulk polymer. "
    [Show abstract] [Hide abstract]
    ABSTRACT: We review previous works on polymer confined crystallization employing strategies that allow confinement to go from the micron to the nanometer scale: droplets, blends, block copolymers and infiltration into alumina nanopores. We also present novel results, reporting homogeneous nucleation and first order crystallization kinetics, for the first time, in a homopolymer and a diblock copolymer infiltrated within alumina nanopores. Confinement can produce fractionated crystallization or exclusive crystallization at much higher supercoolings as compared to bulk polymers, as the degree of confinement increases. For highly confined heterogeneity free micro or nano-domains, the overall crystallization kinetics is dominated by nucleation and therefore becomes first order. The nucleation mechanism changes from heterogeneous nucleation for the bulk polymer to surface or homogeneous nucleation for ensembles of confined and isolated heterogeneity free micro or nanodomains. Surface nucleation is more commonly found than homogenous nucleation, although this fact is not frequently recognized in the literature.
    Polymer 07/2013; 54(16):4059-4077. DOI:10.1016/j.polymer.2013.05.029 · 3.56 Impact Factor

  • [Show abstract] [Hide abstract]
    ABSTRACT: Composite products of the agro-food industry are commonly obtained by blending two or more ingredients in order to improve the sensory quality of the final mixtures. In this paper four virgin olive oils coming from different cultivars and processes have been considered. The sensory evaluation of the tasters (panel test) has allowed the selection of the best mixture by using a mathematical model with linear parameters calculated by regression. The employed special cubic model has pointed out a net synergistic effect in the response contour plot of a three-component mixture when the worst olive oil's concentration is excluded. By increasing its concentration the sensory response's volume decreases slightly in the composition tetrahedron, and that indicates that the synergism among the three best olive oils can widely compensate the effect of the worst one.
    Chemometrics and Intelligent Laboratory Systems 02/1995; 27(2):205-210. DOI:10.1016/0169-7439(95)80024-4 · 2.32 Impact Factor
Show more