Lamellar arrangements of linear polyethylene in ultrathin films

Abstract

The crystal orientations of linear polyethylene films on silicon substrates are investigated using grazing incidence X-ray diffraction and atomic force microscopy. From diffraction analysis, we can identify the structural arrangement of PE crystals in ultrathin film. The orientation of lamellar crystal in PE films changes from edge-on to flat-on with the decrease of film thickness in the film thickness below $ 100 nm. The slightly inclined lamellae relative to the substrate are found to coexist with the flat-on lamellae in thin PE films that we have investigated. We find that the crystal orientation and structures is governed by the constraint imposed by film thickness rather than enthalpy gain as the film got thinner especially in the thickness below 200 nm.

Formation of Asymmetric Leaf-Shaped Crystals in Ultrathin Films of Oriented Polyethylene Molecules Resulting from High-Temperature Relaxation and Recrystallization

“…These results indicated that, after being annealed at 135 °C for 10 min and recrystallized by cooling to room temperature, the a -axis of PE in leaf-shaped crystals was preferentially oriented in two different directions at azimuthal angles ≈44° and ≈56° from the substrate plane. These results showed that the crystal orientation was similar with the structural arrangement of PE crystals in ultrathin films (with a thickness of about 52 nm) obtained by spin-coating . Considering the morphology revealed by AFM in Figure , we tentatively conclude that after recrystallization, both a - and c -axes of most crystals were tilted, resulting in slightly inclined terrace-like lamellae.…”

“…From the magnified images (Figure c,d), it became evident that these regions consisted of lamellae of different orientations, labeled by letters E and F. Region E was composed of lamellae in the edge-on orientation, whereas region F consisted of twisted and orderly stacked lamellae, most of them lying flat-on. This morphology reminds us of lamellar twisting, a common phenomenon for PE and other polymers. − Lamellar twisting has been established in banded spherulites, where the band spacing depends on crystallization temperature. In the present case, the band period was not constant but varied in different regions.…”

“…These results showed that the crystal orientation was similar with the structural arrangement of PE crystals in ultrathin films (with a thickness of about 52 nm) obtained by spin-coating. 32 Considering the morphology revealed by AFM in Figure 3, we tentatively conclude that after recrystallization, both a-and c-axes of most crystals were tilted, resulting in slightly inclined terrace-like lamellae.…”

Lamellar orientation of polyamide 6 thin film crystallization on solid substrates

“…For the film with the thickness approaching the radius of gyration of polymer M A N U S C R I P T A C C E P T E D ACCEPTED MANUSCRIPT 4 chains, flat-on lamellae are usually observed. This film thickness dependence of lamellar orientation is widely encountered in many polymer systems [9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28]. For example, Schönherret et al have found that for poly(ethylene oxide) thin films on the oxidized silicon substrate lamellae are oriented edge-on when the films are thicker than 1 µm, while in the films thinner than 300 nm lamellae are preferentially flat-on [9].…”

Ultrahigh Molecular Weight Polyethylene Lamellar‐Thin Framework on Square Meter Scale

“…[24] The thickness of PE films without and with porous structures reached down to 28 and 100 nm, with limited lateral size and absolute mechanical strength. [25,26] Towards a high aspect ratio, scalable PE microporous membranes driven by the application as lithium-ion battery separators have been intensively investigated., e.g., meter-square size of UHMWPE nanofibrous membranes with micrometer-level thickness, [27] and large-area UHMWPE membranes of 12-micrometer-thick used as radiative cooling fabric and electrocatalytic interface have been prepared. [28,29] Despite their outstanding properties and diverse applications, the simultaneous realization of low dimensionality down to lamellar thickness and large lateral size up to square-meter level is still to be accomplished.…”