Polymer Single Crystals Research Articles

Exfoliation of two-dimensional polymer single crystals into thin sheets and investigations of their surface structure by high-resolution atomic force microscopy.

The acid-assisted wet-chemical and the adhesive-tape induced micromechanical exfoliation of differently sized single crystals of a 2D polymer (approx. 20 μm and 100 μm) is shown to result in thin sheet stacks. Tuning of the thickness is achieved via duration and frequency of the exfoliation, respectively. A color code is established that correlates interference colors of sheet stacks on SiO2(300 nm)/Si as observed under an optical microscope with their thicknesses measured by atomic force microscopy. This facilitates reliable monitoring of the exfoliation and quick identification of sheet stacks of a desired thickness. Furthermore, high resolution atomic force microscopy is applied to investigate the surfaces of starting crystals and both wet-chemically and micromechanically exfoliated sheet stacks aiming at exploring whether exfoliation proceeds with preservation of surface periodicity and with a low frequency of sheet rupturing. These investigations also aimed at uncovering possible point defects and domain (grain) boundaries in the surfaces. It appears that all investigated objects have a high molecular scale perfection and that both exfoliation methods proceed mild enough to largely preserve the molecular structure of the 2D polymer including the not covalently bonded template molecules being part of the crystal packing.

How temperatures affect the number of dislocations in polymer single crystals

The influence of crystallization temperature (Tc) on the number of spiral growths on poly(butylene succinate) (PBS) single crystals, obtained by self-seeding method, was systematically studied. The studies show that the statistical average number of spiral growths formed on the PBS single crystals decays exponentially with respect to the Tc. Inspired by BCF (Bruton, Cabrera and Frank) theory and L-H (Lauritzen and Hoffman) theory, a thermodynamic model has been proposed, in which the origin of spiral growth was treated as a nucleation process. The model suggests that the nucleation rate of spiral growth depends on the inverse square of super-cooling degree, which predicted the density of spiral growth formed on lamellae, and was consistent with the experiments very well.

New habits in branched polyethylene single crystals

Faceted polymer single crystals obtained from solution have been examined for decades. Most of the studies have been performed with linear polyethylene. It is well known that solution-grown linear polyethylene single crystals may exhibit different and often complex morphologies and habits. However, the effect of molecular architecture (i.e., short chain branching) in the morphology of the single crystals remains practically unexplored. At the highest crystallization temperature investigated, the shape of the crystals is lozenge-like, but with curved and slightly truncated {110} faces. As the crystallization temperature decreases, strong changes in the width-to-length ratio and, consequently in the characteristic angles of the single crystal occur. Interestingly, the single crystals obtained at the lowest crystallization temperature explored exhibit a nearly square shape. This phenomenon has not yet been observed in linear high molecular weight polyethylene, for which the characteristic lozenge habit with straight {110} faces is retained as crystallization temperature decreases. The application of the Shcherbina and Ungar approach to fit the unusual shapes of the branched PE single crystals obtained in this work requires a strong decrease in the ratio of the rates of propagation to the right and to the left of the growth edge. This result is probably linked to different steric conditions of chain attachments into non-equivalent niches induced by the presence of branches.

Towards controlled polymer brushes via a self-assembly-assisted-grafting-to approach.

Precise synthesis of polymer brushes to modify the surface of nanoparticles and nanodevices for targeted applications has been one of the major focuses in the community for decades. Here we report a self-assembly-assisted-grafting-to approach to synthesize polymer brushes on flat substrates. In this method, polymers are pre-assembled into two-dimensional polymer single crystals (PSCs) with functional groups on the surface. Chemically coupling the PSCs onto solid substrates leads to the formation of polymer brushes. Exquisite control of the chain folding in PSCs allows us to obtain polymer brushes with well-defined grafting density, tethering points and brush conformation. Extremely high grafting density (2.12 chains per nm2) has been achieved in the synthesized single-tethered polymer brushes. Moreover, polymer loop brushes have been successfully obtained using oddly folded PSCs from telechelic chains. Our approach combines some of the important advantages of conventional ‘grafting-to' and ‘grafting-from' methods, and is promising for tailored synthesis of polymer brushes.

Scalable Synthesis of Two-dimensional Polymer Crystals and Exfoliation into Nanometer-thin Sheets.

Two-dimensional materials have moved into the spotlight of researchers. The isolation of single graphene sheets has shown that restricted dimensionality can lead to interesting properties. Bottom-up synthesis of organic, covalently-bonded structures is, however, still challenging. In this publication we give a synopsis of a recently published monomer that is easily accessible and reversibly provides chiral two-dimensional polymer single crystals, which can be exfoliated into nanometer-thin sheets and show promise for applications in, for example, nonlinear optics and ultrathin membranes.

Annealing-induced periodic patterns in solution grown polymer single crystals

Faceted polymer single crystals have been transformed into periodically branched patterns by applying a slow annealing procedure.

Nanoparticle mediated micromotor motion.

In this paper, we report the utilization of nanoparticles to mediate the motion of a polymer single crystal catalytic micromotor. Micromotors have been fabricated by directly self-assembling functional nanoparticles (platinum and iron oxide nanoparticles) onto one or both sides of two-dimensional polymer single crystals. We show that the moving velocity of these micromotors in fluids can be readily tuned by controlling the nanoparticles' surface wettability and catalytic activity. A 3 times velocity increase has been achieved for a hydrophobic micromotor as opposed to the hydrophilic ones. Furthermore, we demonstrate that the catalytic activity of platinum nanoparticles inside the micromotor can be enhanced by their synergetic interactions with iron oxide nanoparticles and an electric field. Both strategies lead to dramatically increased moving velocities, with the highest value reaching ∼200 μm s(-1). By decreasing the nanoparticles' surface wettability and increasing their catalytic activity, a maximum of a ∼10-fold increase in the moving speed of the nanoparticle based micromotor can be achieved. Our results demonstrate the advantages of using nanoparticles in micromotor systems.

Magnetically recyclable polymer single crystal supported silver nanocatalyst.

We report the immobilization of unprotected silver nanoparticle on the carboxylic acid abundant polymer single crystal surface with controllable size through photogenerated chemical reduction reaction. The resulting silver nanoparticle decorated polymer single crystal not only shows higher catalytic activity as compared to its counterpart bearing surface ligand but also exhibits size-dependent catalytic activity with the smallest size (∼1.5 nm) being the most active. By further introducing iron oxide nanoparticles onto its surface, the resulting catalyst system can be magnetically recycled for up to five times with little loss in catalytic activity. These, together with the high loading originated from the high surface area to volume ratio for a polymer single crystal, make current catalyst system attractive for many industrial important catalytic applications.

Molecular-weight-dependent changes in morphology of solution-grown polyethylene single crystals.

Polymer single crystals consisting of folded chains are always in a nonequilibrium state, even if they are faceted with a well-defined envelope reflecting the parameters of the crystal unit cell. Heterogeneities like small variations in the degree of chain folding within such crystals are responsible for a rather broad range in melting temperature. Consequently, upon annealing at a given temperature, some parts may be above and some below their respective melting temperatures, inducing a lamellar thickening process, which may vary locally. To emphasize such variations, controlled annealing experiments are performed at comparatively low temperatures and for long times. For single crystals of low-molecular-weight polyethylene, the formation of the well-known "Swiss-cheese"-like morphology with randomly distributed holes of varying sizes within the annealed single crystal is observed. However, for high-molecular-weight polyethylene, a regular pattern appeared upon annealing, characterized by branches of equal width that are oriented perpendicular to the crystal edge. All branches end at the nucleation site. Interestingly, the resulting pattern depends sensitively on both crystallization and annealing conditions. These thermally induced regular patterns within a single crystal are attributed to a stable crystalline framework formed within polyethylene single crystals in the course of growth.

“Raft” Formation by Two‐Dimensional Self‐Assembly of Block Copolymer Rod Micelles in Aqueous Solution

Block copolymers can form a broad range of self-assembled aggregates. In solution, planar assemblies usually form closed structures such as vesicles; thus, free-standing sheet formation can be challenging. While most polymer single crystals are planar, their growth usually occurs by uptake of individual chains. Here we report a novel lamella formation mechanism: core-crystalline spherical micelles link up to form rods in solution, which then associate to yield planar arrays. For the system of poly(ethylene oxide)-block-polycaprolactone in water, co-assembly with homopolycaprolactone can induce a series of morphological changes that yield either rods or lamellae. The underlying lamella formation mechanism was elucidated by electron microscopy, while light scattering was used to probe the kinetics. The hierarchical growth of lamellae from one-dimensional rod subunits, which had been formed from spherical assemblies, is novel and controllable in terms of product size and aspect ratio.

“Raft” Formation by Two‐Dimensional Self‐Assembly of Block Copolymer Rod Micelles in Aqueous Solution

AbstractBlock copolymers can form a broad range of self‐assembled aggregates. In solution, planar assemblies usually form closed structures such as vesicles; thus, free‐standing sheet formation can be challenging. While most polymer single crystals are planar, their growth usually occurs by uptake of individual chains. Here we report a novel lamella formation mechanism: core‐crystalline spherical micelles link up to form rods in solution, which then associate to yield planar arrays. For the system of poly(ethylene oxide)‐block‐polycaprolactone in water, co‐assembly with homopolycaprolactone can induce a series of morphological changes that yield either rods or lamellae. The underlying lamella formation mechanism was elucidated by electron microscopy, while light scattering was used to probe the kinetics. The hierarchical growth of lamellae from one‐dimensional rod subunits, which had been formed from spherical assemblies, is novel and controllable in terms of product size and aspect ratio.

Janus Polymer Single Crystal Nanosheet via Evaporative Crystallization.

We show that liquid/liquid interface can guide polymer chain folding during crystallization. Evaporation-induced crystallization of telechelic dicarboxyl end-functionalized poly(ε-caprolactone) (COOH-PCL-COOH) at a water/pentyl acetate interface produced millimeter-scale, uniform polymer single crystal (PSC) films. Due to the asymmetric nature at the interface, the PSC nanosheets exhibited a Janus structure: the two surfaces of the crystal showed distinct water contact angle, which are quantitatively confirmed by in situ nanocondensation using environmental scanning electron microscopy (ESEM).

Characterization and Structural Analysis of Solution-Grown Polyacrylonitrile-co-Methacrylic Acid (PAN-co-MAA) Single Crystals

To date studies regarding the growth and characterization of polyacrylonitrile (PAN)-based polymer single crystals have been limited. Polyacrylonitrile-co-methacrylic acid (PAN-co-MAA) was used in this work, which outlines the conditions for three major types of solution-grown crystals. Electron microscopy and diffraction are used to provide a comprehensive study for chain arrangement and growth characteristics for all crystal morphologies. The three major morphological types included polyhedral and polygonal (i.e., parallelogram and elongated rhombus) crystals. Lower crystallization temperatures (65 °C) resulted in more even growth along all facets, while crystals formed at both intermediate (75 °C) and higher (85–95 °C) temperatures exhibited preferential growth along a specific growth plane. Overall crystal size also increased with elevated crystallization temperature (Tc). On the basis of the experimental d-spacing measured by electron diffraction for the (h00) and (0k0) planes, the crystal unit cell ...

How Does Nanoscale Crystalline Structure Affect Ion Transport in Solid Polymer Electrolytes?

Polymer electrolytes have attracted intensive attention due to their potential applications in all-solid-state lithium batteries. Ion conduction in this system is generally considered to be confined in the amorphous polymer/ion phase, where segmental relaxation of the polymer above glass transition temperature facilitates ion transport. In this article, we show quantitatively that the effect of polymer crystallization on ion transport is twofold: structural (tortuosity) and dynamic (tethered chain confinement). We decouple these two effects by designing and fabricating a model polymer single crystal electrolyte system with controlled crystal structure, size, crystallinity, and orientation. Ion conduction is confined within the chain fold region and guided by the crystalline lamellae. We show that, at low content, due to the tortuosity effect, the in-plane conductivity is 2000 times greater than through-plane one. Contradictory to the general view, the dynamic effect is negligible at moderate ion contents....

One-step formation of responsive “dumbbell” nanoparticle dimers via quasi-two-dimensional polymer single crystals

We present a facile approach to synthesize "dumbbell" nanoparticle dimers via one-step coupling of nanoparticles and quasi-two-dimensional polymer single crystals. These dimers exhibit responsive properties enabled by flexible polymeric linkers.

A micromotor based on polymer single crystals and nanoparticles: toward functional versatility.

We report a multifunctional micromotor fabricated by the self-assembly technique using multifunctional materials, i.e. polymer single crystals and nanoparticles, as basic building blocks. Not only can this micromotor achieve autonomous and directed movement, it also possesses unprecedented functions, including enzymatic degradation-induced micromotor disassembly, sustained release and molecular detection.

Some unique features of polymer crystallisation

Mono-lamellar single crystals in thin films provide suitable model systems for studying crystallisation of long chain polymers, making distinct differences with respect to small molecules visible. Due to the high viscosity of polymeric melts, transport toward the growth front is slow and the corresponding crystal growth can suitably be followed in time. Besides being able to investigate generic processes in controlling crystal morphology like epitaxial growth or growth front instabilities, thin film studies reveal unique features of polymer crystallisation. In particular, it is possible to observe a logarithmic spatio-temporal evolution of the lamellar crystal thickness, caused by continuous rearrangements leading to regions of differing degrees of meta-stability within polymer single crystals. As a consequence of the kinetically determined lamellar thickness and the corresponding variations in melting temperature, polymer crystals allow for self-seeding, i.e., crystals can be re-grown from a melt which contains a few thermodynamically stable remnants of pre-existing crystals acting as seeds. Hence, when a single crystal is molten, all remnants have a unique orientation and thus also the crystals re-grown from these seeds. The logarithmic time-dependence of the variation in crystal thickness is reflected in a number of seeds decreasing exponentially with increasing seeding temperature. Despite their molecular complexity and some unique features, polymers proved to be valuable systems for detailed studies of crystal growth, allowing testing of theoretical concepts of morphology development.

Single Crystals of a 2-Dimensional Metal Coordination Polymer Containing Pendant Carbazole Groups

Department of Chemistry & Division of Energy Systems Research, Ajou University, Suwon 443-749, KoreaReceived August 20, 2013, Accepted September 25, 2013Key Words : Coordination polymers, Polymer single crystals, CarbazoleCoordination polymers consisting of metal cations andorganic linkers are widely used in fundamental supramole-cular approaches as well as various other practical appli-cations.

Electric Field-Induced, Reversible Lotus-to-Rose Transition in Nanohybrid Shish Kebab Paper with Hierarchical Roughness

Nature uses a variety of strategies to tune wetting behavior for biological applications. By artificially mimicking these strategies, a variety of different wetting conditions can be achieved. Numerous examples exist of designed surfaces that can mimic the wetting behavior of lotus leaves or rose petals, but few surfaces that may reversibly transition between the two have been reported. In this paper, a combination of topological control over conductive, carbon-based nanomaterials and low surface energy coating was used to tune the wetting properties between "lotus" and "rose." The topological control was imparted by a hierarchical "nanohybrid shish kebab" structure, which uses solution-grown polymer single crystals on carbon nanotubes to tune the surface roughness of the latter. The low surface energy polytetrafluoroethylene (PTFE) coating was deposited by the initiated chemical vapor deposition technique. Application of electric potential on these unique nanostructures allows the surfaces to reversibly transition between "lotus" and "rose" behavior. A further irreversible transition between "rose" and the fully wetted Wenzel wetting state was also predicted and shown. These materials show remarkable promise for lab-on-a-chip devices and surface passivation for biological studies.

Directed Self-Assembly of Nanoparticles for Nanomotors

We report, for the first time, the design and fabrication of a nanoparticle-based nanomotor system by directly self-assembling nanoparticles onto functional, nanometer-thin lamellae, such as polymer single crystals. Tens of thousands of judiciously selected nanoparticles (gold, iron oxide, and platinum nanoparticles) with sizes ranging from <5 to a few tens of nanometers have been introduced into a single nanomotor via directed self-assembly. The resulting nanomotor realizes functions such as autonomous movement, remote control, and cargo transportation by utilizing the advantages offered by nanoparticles, such as the small size, surface plasmon resonance, catalytic and magnetic properties. Because of the structural and functional versatility of nanoparticles, the facile fabricating procedure, and the potential for mass production, our strategy shows a key step toward the development of next generation multifunctional nanomotors.