Chiral nematic liquid crystalline sensors containing responsive dopants

In his 1990 book, Peter Collings refers to liquid crystals (LCs) as “Nature’s delicate phase of matter.”1 This is perhaps most apparent when looking at the use of LCs as sensors. Due to the inherent fragility of the phase, LCs make ideal candidates for sensors, as small disruptions to the localized order are propagated and ampli-ed throughout the bulk material. This responsiveness, coupled with the attractive optical properties of liquid crystalline materials, has been the focus of much of the investigation into the applications of the liquid crystalline phase

Switchable surface structured hydrogel coatings

\u3cp\u3eSwitchable surface structures based on hydrogels are an emerging field in material science, microfluidics, soft robotics and anti-fouling. Here, we describe a novel method that uses a photo-cross-linkable terpolymer to create a hydrogel coating with a switchable surface structure. The terpolymer is based on poly(N-isopropylacrylamide) (PNIPAm) and it is shown that simple coating technologies like slit die coating can be used under ambient conditions. It is also shown that the swelling ratio of the coating is controlled by the energy dose of ultraviolet (UV) light. Simple and complex surface structures were created using respectively single or multiple UV illumination steps through masks and it is shown that the hydrogel coatings can be reversibly switched from a structured state to a flat state with temperature.\u3c/p\u3

Tunable surface topography in fluoropolymers using photo-embossing

\u3cp\u3eNovel methods that allow creation and tunable control of surface relief in polymer films are of key interest in the search for novel low surface energy materials. For example, photochemically cross-linked (UV-cured) high-performance fluoropolymer films with an engineered surface relief of precisely defined shapes and dimensions could have widespread applications. Here, we report a fabrication method based on photo-embossing that provides the ability to create surface relief in fluorinated elastomers. The height and shape of the surface relief structures can be altered as desired by changing the processing conditions such as energy dose, monomer composition and the added solvent volumes. Surface relief structures with heights of up to 9 μm have been obtained using a photomask with a 40 μm pitch. We demonstrate that surface relief structures with a broad range of shapes and dimensions can be created if appropriate photomasks are available.\u3c/p\u3

Improving visible-light transparency of drawn melt-crystallized linear polyethylenes:influence of molecular weight distribution

\u3cp\u3eA series of drawn melt-crystallized linear polyethylenes (LPEs) with different molecular weight distributions (MWD = M\u3csub\u3ew\u3c/sub\u3e/M\u3csub\u3en\u3c/sub\u3e) ranging from 2 to 25 are investigated with respect to the visible-light transparency. The results indicate that the MWD of the LPEs significantly influences the visible-light transparency of drawn melt-crystallized LPEs. At a high MWD, drawn melt-crystallized LPEs films are transparent and glass-like, this in contrast to the LPEs with a low MWD. A mechanism behind the observed results is proposed based on differential scanning calorimetry (DSC) analysis, small-angle X-ray scattering, wide-angle X-ray scattering, and small-angle light scattering experiments. A correlation between the molecular characteristics, especially the MWD, and the visible-light transparency of the drawn melt-crystallized LPEs is proposed. (Figure presented.).\u3c/p\u3

Transparent drawn article

\u3cp\u3eThe invention relates to a stretched molded article comprising a polymer A and a compound B, wherein the polymer A is a polyamide or a polyolefin and is at least partially oriented and comprises a crystalline phase and a non-crystalline phase, wherein the mass of compound B is from 0.25 to 10 mass% relative to the mass of polymer A, and wherein the compound B has a refractive index (nB) higher than the isotropic refractive index of polymer A (nA). The invention further relates to a process for manufacturing such stretch molded article, the use of such stretch molded articles and a product comprising such stretch molded article.\u3c/p\u3

High strength and high modulus electrospun nanofibers

\u3cp\u3eElectrospinning is a rapidly growing polymer processing technology as it provides a viable and simple method to create ultra-fine continuous fibers. This paper presents an in-depth review of the mechanical properties of electrospun fibers and particularly focuses on methodologies to generate high strength and high modulus nanofibers. As such, it aims to provide some guidance to future research activities in the area of high performance electrospun fibers.\u3c/p\u3

Memory effects in polyethylenes : influence of processing and crystallization history

The experimental timescale of memory effects related to restoring equilibrium viscoelastic properties in solution-cast linear and long-chain branched polyethylenes has been investigated. It was found that the crystallization history of low-density polyethylene and ultra-high-molecular-weight polyethylene, with respect to solid-state and melt properties, is lost after heating into the melt after a short period of time. The experimental timescale of memory effects is at least one order of magnitude shorter than the longest relaxation times in these materials, which correspond to reptative motion of macromolecules. The experimental results indicate that long-term memory effects related to the physical entanglement network in polyethylenes are absent and that equilibrium viscoelastic properties of polyethylene melts and solids and the concept of entanglement coupling are related to segmental rather than to macromolecular mobility