Early-Stage Formation of Helical Single Crystals and Their Confined Growth in Thin Film

Lamellar Assembly Mechanism on Dendritic Ring-Banded Spherulites of Poly(ε-caprolactone)

The self-assembly structures of lamellae in optical ring bands have a critical effect on their optical and physical arrangements. Two different types of dendritic banded spherulites (namely ring-banded and zigzag ring-banded) are formed in poly(ε-caprolactone)/poly (phenyl methacrylate) blend at crystallization temperatures of 42 and 46 °C, respectively. The difference in optical birefringence of ring bands in two types of spherulites is resolved by means of direct morphological comparison. Banded spherulites are fractured carefully to facilitate lamellar orientation analyses of both the top surface and the interior surface. The results have revealed the existence of tree-like dendritic fractal growth lamellar assemblies in both banded spherulites. The optical ring patterns of the banded spherulites are differentiated mainly by the fractal orientation of the edge-on crystal branches in the ridge region. On the basis of detailed morphological analysis, 3D-lamellar assembly mechanisms are proposed to explain the growth of dendritic ring-banded spherulites at 42 °C and dendritic zigzag ring-banded spherulites at 46 °C.

Structure and Morphology of Poly(vinylidene fluoride) Nanoscrolls

To date the scrolled morphology of γ-phase poly(vinylidene fluoride) (PVDF) has been witnessed via high temperature melt crystallization of crystalline thin films and through imaging of chemical etched PVDF bulk films. Here we show the first growth and characterization of free-standing γ-phase PVDF scrolls via solution crystallization. Scanning electron microscopy, transmission electron microscopy, and atomic force microscopy have been used to characterize and to further understand the fundamental preferred crystalline habit of the γ-phase of PVDF.

Responsive Shape Change of Sub-5 nm Thin, Janus Polymer Nanoplates

Responsive shape changes in soft materials have attracted significant attention in recent years. Despite extensive studies, it is still challenging to prepare nanoscale assemblies with responsive behaviors. Herein we report on the fabrication and pH-responsive properties of sub-5 nm thin, Janus polymer nanoplates prepared via crystallization-driven self-assembly of poly(ε-caprolactone)-b-poly(acrylic acid) (PCL-b-PAA) followed by cross-linking and disassembly. The resultant Janus nanoplate is comprised of partially cross-linked PAA and tethered PCL brush layers with an overall thickness of ∼4 nm. We show that pronounced and reversible shape changes from nanoplates to nanobowls can be realized in such a thin free-standing film. This shape change is achieved by exceptionally small stress-a few orders of magnitude smaller than conventional hydrogel bilayers. These three-dimensional ultrathin nanobowls are also mechanically stable, which is attributed to the tortoise-shell-like crystalline domains formed in the nanoconfined curved space. Our results pave a way to a new class of free-standing, ultrathin polymer Janus nanoplates that may find applications in nanomotors and nanoactuators.

Single-Walled Carbon Nanotube-Induced Orthogonal Growth of Polyethylene Single Crystals at a Curved Liquid/Liquid Interface

We report herein single-walled carbon nanotube-induced polyethylene crystallization at the curved liquid/liquid interface. A Pickering emulsion system comprised of polyethylene (PE)/single-walled carbon nanotubes (SWCNTs)/1,2-dichlorobenzene (DCB)/water is formed using probe sonication at an elevated temperature. SWCNTs are used as the Pickering agents, and they are bent into nanosized rings by the curved DCB/water interface. Upon cooling, PE crystallizes onto SWCNTs, forming kebab single crystals, and the PE lamellae are orthogonal to the DCB/water interface. The unique structure resembles nanohybrid shish kebab (NHSK) rings.

On the circular birefringence of polycrystalline polymers: polylactide

The circular birefringence of polycrystalline polymers is invariably obscured by strong linear birefringence. To parse the two mechanisms of light retardation, polycrystalline spherulites of polylactide enantiomers were analyzed by Mueller matrix microscopy. Polymer films are barely optically active in normal incidence, but if illuminated obliquely they become strongly optically active. Opposite hemispheres have oppositely signed circular birefringence. The sign is independent of the enantiomer but dependent on the sense of the sample's tilt. These observations are consistent with light path inhomogeneities resulting from stacked, mis-oriented lamellae. Chiroptical commonalities based on symmetry arguments are discussed among polylactide, a single oriented water molecule, and microfabricated metamaterial arrays, as well as the first physical model of optical activity, Reusch's pile of mica plates. The latter model provides the best explanation of the circular birefringence of polylactide spherulites. The only data on the optical rotation of crystalline polymers to date come from ostensible single crystals of polylactide. The enormous, anisotropic optical rotations observed previously are in quantitative agreement with misoriented lamellae observed here. Limitations of parsing circularly birefringent systems into those showing 'natural optical activity' and those others, somehow 'unnatural', are discussed.

Polymer decoration on carbon nanotubes via physical vapor deposition

The polymer decoration technique has been widely used to study the chain folding behavior of polymer single crystals. In this article, we demonstrate that this method can be successfully adopted to pattern a variety of polymers on carbon nanotubes (CNTs). The resulting structure is a two-dimensional nanohybrid shish kebab (2D NHSK), wherein the CNT forms the shish and the polymer crystals form the kebabs. 2D NHSKs consisting of CNTs and polymers such as polyethylene, nylon 66, polyvinylidene fluoride and poly(L-lysine) have been achieved. Transmission electron microscopy and atomic force microscopy were used to study the nanoscale morphology of these hybrid materials. Relatively periodic decoration of polymers on both single-walled and multi-walled CNTs was observed. It is envisaged that this unique method offers a facile means to achieve patterned CNTs for nanodevice applications.