In general, when a crystal is molten, all molecules forget about their mutual correlations and long-range order is lost. Thus, a regrown crystal does not inherit any features from an initially present crystal. Such is true for materials exhibiting a well-defined melting point. However, polymer crystallites have a wide range of melting temperatures, enabling paradoxical phenomena such as the coexistence of melting and crystallization. Here, we report a self-seeding technique that enables the generation of arrays of orientation-correlated polymer crystals of uniform size and shape ('clones') with their orientation inherited from an initial single crystal. Moreover, the number density and locations of these cloned crystals can to some extent be predetermined through the thermal history of the starting crystal. We attribute this unique behaviour of polymers to the coexistence of variable fold lengths in metastable crystalline lamellae, typical for ordering of complex chain-like molecules.

A level-set method for the simulation of fluid interfaces with insoluble surfactant is presented in two-dimensions. The method can be straightforwardly extended to three-dimensions and to soluble surfactants. The method couples a semi-implicit discretization for solving the surfactant transport equation recently developed by Xu and Zhao [62] with the immersed interface method originally developed by LeVeque and Li and [31] for solving the fluid flow equations and the Laplace-Young boundary conditions across the interfaces. Novel techniques are developed to accurately conserve component mass and surfactant mass during the evolution. Convergence of the method is demonstrated numerically. The method is applied to study the effects of surfactant on single drops, dropdrop interactions and interactions among multiple drops in Stokes flow under a steady applied shear. Due to Marangoni forces and to nonuniform Capillary forces, the presence of surfactant results in larger drop deformations and more complex drop-drop interactions compared to the analogous cases for clean drops. The effects of surfactant are found to be most significant in flows with multiple drops. To our knowledge, this is the first time that the level-set method has been used to simulate fluid interfaces with surfactant.

No abstract

Morphology, phase composition, and molecular mobility for a series of semicommercial gel-spun UHMWPE fibers were studied using a combination of WAXS, SAXS, and 1 H solid-state NMR methods. The fibers show uncommon for this type of fibers decrease in the break load with increasing draw ratio, whereas their modulus and the tenacity reach very high ultimate values. The X-ray and NMR methods have provided complementary information about the fiber morphology and structural reorganizations occurring at the final stage of the fiber drawing. The results suggest that the fiber morphology can be described by a mixture of crystalline fibrils with long period of ∼35À45 nm, as shown by SAXS, and large, so-called, chain-extended crystals. The presence of large crystals with embedded defects is shown by NMR. The drawing causes increase in the crystallinity from ∼89 to ∼96 wt % and in chain orientation, while the long period of fibrils and the break load of fibers surprisingly decrease. The decrease in the long period with the drawing could indicate a partial reorganization of the amorphous phase and/or some fragmentation of the fibrils, while the decrease in the break load could correspond to a decrease in number of load-bearing chains. A disorder of the crystals and a small increase in chain mobility in the constrained amorphous fraction is also observed with increasing the drawing. Approximately 1 wt % of the chain fragments in the amorphous fraction has a high molecular mobility. It is assumed that these chain fragments reside in nanovoids, the presence of which was shown previously by a 129 Xe NMR study on the same fibers. The role of α-crystalline relaxation in structural reorganizations during fiber drawing is also discussed.

A reversibly cross‐linked epoxy resin with efficient reprocessing and intrinsic self‐healing was prepared from a diamine Diels‐Alder (DA) adduct cross‐linker and a commercial epoxy oligomer. The newly synthesized diamine cross‐linker, comprising a DA adduct of furan and maleimide moieties, can cure epoxy monomer/oligomer with thermal reversibility. The reversible transition between cross‐linked state and linear architecture endows the cured epoxy with rapid recyclability and repeated healability. The reversibly cross‐linked epoxy fundamentally behaves as typical thermosets at ambient conditions yet can be fast reprocessed at elevated temperature like thermoplastics. As a potential reversible adhesive, the epoxy polymer with adhesive strength values about 3 MPa showed full recovery after repeated fracture‐thermal healing processes. The methodology explored in this contribution provides new insights in modification of conventional engineering plastics as functional materials. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015, 53, 2094–2103

No abstract

An axisymmetric liquid bridge is surrounded by a passive gas. A steady shear flow is set up by imposing a temperature gradient along the bridge and driving the motion by thermocapillarity. This dynamic state is susceptible to convective instabilities that lead to propagating hydrothermal waves that feed on the underlying temperature gradients. The convective instabilities of this axisymmetric return-flow state are presented as functions of the Prandtl number of the liquid and the surface Biot number of the interface. Comparisons are made with the results of Smith and Davis for planar layers and with available experimental data.

The impact of nanoconfinement introduced by nanoparticles on polymer crystallization has attracted extensive attention because it plays an important role in the ultimate properties of polymer nanocomposites. In this study, interfacial and spatial confinement effects of silica (SiO2) nanoparticles on the crystallization behaviors of poly(ethylene oxide) (PEO)/SiO2 composites were systematically investigated by changing the size and concentration of SiO2 in PEO matrix. The composites with high silica loadings exhibit two crystallization peaks of PEO as determined by differential scanning calorimetry. The first peak at 7–43 °C is related to the bulk PEO, while the second peak at −20 to −30 °C is attributed to the restricted PEO segments. Three‐layer (amorphous, interfacial, and bulk) model is proposed to interpret the confined crystallization of PEO/SiO2 composites, which is supported by the results of thermogravimetric analysis and solid‐state 1H nuclear magnetic resonance. In amorphous layer, most PEO segments are directly adsorbed on SiO2 surface via hydrogen bonding. The interfacial PEO layer, which is nonuniform, is composed of crystallizable loops and tails extending from amorphous layer. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016, 54, 414–423