Superlattices of lamellae in microporous oriented polyolefine films

Physics of the Solid State, 2012

Spatial correlations on the surface of microporous polyethylene films obtained by extrusion of the polymer melt with the subsequent stages of annealing, uniaxial extension, and thermal fixation have been studied using scanning electron microscopy. It has been shown that, as the degree of orientation of the melt increases, the formation of the periodic superlattice of oriented lamellae occurs in the films as a result of the disorder-order transition. This transition is preceded by the formation of two mutually complementary per colation clusters, which reflect the pores and the solid phase of the polymer.

Physics of the Solid State, 2012

The surface structure of polypropylene and polyethylene microporous films prepared by the extrusion of the polymer melt with the subsequent stages of annealing, uniaxial extension, and thermal fixa tion of the samples has been analyzed using scanning electron microscopy. It has been shown that percolation through pores corresponds to the axial texture of the surface with the channel structure described by the frac tal cluster model. The transition from open pores (through flow channels) to closed pores leads to the forma tion of surface regions with a biaxial texture. An increase in the density of the solid phase cluster is accompa nied by the formation of a homogeneous biaxial texture with a period of alternation of the density in two mutually perpendicular directions, one of which coincides with the direction of orientation of the films.

2010

Thin films (5-500 nm thick) of the linear aliphatic polyester (3,7) poly(propylene azelate) (PPAz) were prepared by spin-coating of CHCl 3 polymer solutions with different polymer concentrations. The morphology and structure of the spin-coated thin films were investigated by atomic force microscopy (AFM) and by grazing incidence wide-angle X-ray scattering (GIWAXS) techniques. AFM revealed the continuous nature of the flat, spherulitic films which are stable against dewetting even for polymer coatings as thin as 15 nm. GIWAXS patterns revealed a high crystal orientation of the films. A sharp reflection on the meridian whose spacing is related to the polymer chain unit length (c-axis) supports the presence of flat-on lamellae morphology in the whole range of film thicknesses investigated. The flat-on lamellae morphology is also supported by AFM images. A triclinic unit cell with the c*-axis perpendicular to the substrate is proposed for PPAz. The repulsion of the long aliphatic spacer by the Si-substrate is invoked as the main reason for the flat-on morphology observed.

Polymer International

Systematic studies based on well-controllable model systems aim at understanding how crystallization from a melt or solution of randomly coiled polymers leads to the formation of mono-lamellar crystals. However, besides mono-lamellar crystals also various other morphologically simple but yet not well understood structures are found. In particular, stacks of correlated lamellar crystals have been observed since the early days of polymer crystallization. Here, we demonstrate that a recently proposed mechanism of self-induced nucleation within lamellar crystals provides a possibility to explain how in such stacks lamellar crystals can be correlated. Examining various polymer systems, we show that the probability for generating self-induced nuclei depends on the morphology of an initiating dendritic basal lamellar crystal. In addition, we provide evidence that this self-induced nucleation mechanism, together with a high rate of transport of molten polymer to the fold This article is protected by copyright. All rights reserved. surface allows to form polymer crystals with similar size in all three dimensions, containing a large number of superposed correlated lamellae.

Macromolecules, 2011

We study the change of the size and structure of freely suspended single lamella nanoparticles of polyethylene during thermal annealing in aqueous solutions. Using small-angle x-ray scattering and cryogenic transmission electron microscopy, it is shown that a doubling of the crystalline lamella sandwiched between two amorphous polymer layers is obtained by annealing the nanoparticles at 125 • C. This thickening of the crystalline lamella can be understood in terms of an unlooping of

Nano Letters, 2007

We study the change of the size and structure of freely suspended single lamella nanoparticles of polyethylene during thermal annealing in aqueous solutions. Using small-angle x-ray scattering and cryogenic transmission electron microscopy, it is shown that a doubling of the crystalline lamella sandwiched between two amorphous polymer layers is obtained by annealing the nanoparticles at 125 • C. This thickening of the crystalline lamella can be understood in terms of an unlooping of

Sen'i Gakkaishi, 1992

A cryogenic transmission electron microscope with a superconducting objective lens was utilized to obtain high-resolution images of uniaxially oriented thin films of polyethylene and isotactic poly-(4-methyl-l-pentene). The resulting images successfully revealed the presence of tie-crystallites connecting crystalline lamellae in the stretching direction in both of the films.

The Journal of Chemical Physics, 2013

The dynamics of microphase separation and the orientation of lamellae in diblock copolymers is investigated in terms of a mean-field model. The formation of lamellar structures and their stable states are explored and it is shown that lamellae are stable not only for the period of the structure corresponding to the minimum of the free energy. The range of wavelengths of stable lamellae is determined by a functional approach, introduced with this work, which is in agreement with the results of a linear stability analysis. The effects of the interaction of block copolymers with confining plane boundaries on the lamellae orientation are studied by an extensive analysis of the free energy. By changing the surface property at one boundary, a transition from a preferentially perpendicular to a parallel lamellar orientation with respect to the boundaries is found, which is rather independent of the distance between the boundaries. Computer simulations reveal, that the time scale of the lamellar orientational order dynamics, which is quantitatively characterized in terms of an orientational order parameter and the structure factor, depends significantly on the properties of the confining boundaries as well as on the quench depth.

Macromolecules, 2008

Introduction. Diblock copolymers are composed of two different polymers that are spontaneously self-assembled into periodic nanostructures, of which the size and morphology can be easily controlled by the molecular weight and composition of copolymers. 1,2 When diblock copolymers are confined to physically or chemically defined patterns, the interfacial interaction and structural commensurability between the copolymer and the patterns strongly influence the assembly of copolymer chains. The confining of diblock copolymers in topographically or chemically patterned structures has frequently been employed to control the order and orientation of the nanostructures of the copolymers. 3-8 For example, Kramer and co-workers demonstrated the spherical nanodomains of diblock copolymers in long-range order by graphoepitaxy. 3 Thomas and co-workers also reported the well-ordered nanodomains of copolymers in topological patterns. 4 Lamellar nanodomains of diblock copolymers were also guided and oriented in large areas with chemically patterned substrates. 7 By confining diblock copolymers inside the cylindrical nanopores of anodized aluminum oxides, Russell and co-workers observed novel nanostructures such as helices and toroids that were not observed in bulk samples. 9,10 Since nanoimprint lithography is known to be an effective patterning method in nanometer scale, 11 Huck and coworkers recently demonstrated the ordered nanostructures of diblock copolymers when copolymers were patterned by nanoimprinting. 12 In this communication, we demonstrated a critical role of the kinetic process in lamellar ordering in confined geometry by investigating the lamellar nanostructures of diblock copolymers in patterned thin films by the visualization based on transmission electron microscopy. Depending on the initial morphology of a diblock copolymer film, which was prepared without or with preannealing, the orientation of lamellae inside the pattern was either parallel or perpendicular to the substrate. The discrepancy in the lamellar orientation after patterning was ascribed to the kinetic effect during the lamellar development inside the pattern.

Thin Solid Films, 2011

A simple method to create self-organized patterns of microparticles in polymer films is demonstrated. Dye-loaded zeolite crystals are used as model microparticles, allowing convenient imaging of the patterns by fluorescence microscopy. The pattern formation can be interpreted within the general framework of the model of local self-activation and lateral inhibition. Two starting parameters, namely the polymer concentration and the wet film thickness, control the size and shape of the particle aggregates in the patterns, as well as their spacing. The size of the aggregates ranges from 50 to 340 µm.