When superhydrophobic coatings are icephobic: Role of surface topology

Among different types of anti-icing coatings, superhydrophobic coatings have attracted considerable attention due to their water repellency and low heat-transfer rate. However, condensation on superhydrophobic surfaces at low temperatures usually causes an increase in ice adhesion because of the induced wetting of micro- and nanostructures. By tuning the weight ratio of surface-modified nanoparticles to unmodified ones, five superhydrophobic coatings with different structural features at the microscale were developed. Ice-adhesion strength and ice-nucleation temperature were studied, together with the effect of moisture condensation on ice adhesion. It was found that the ice-adhesion strength and icing temperature of these coatings do not necessarily follow the same order among these surfaces because of different mechanisms involved. Surface roughness is inadequate to describe the necessary surface features that critically affect the anti-icing behavior of the coatings. Detailed topology/geometry has to be considered when designing icephobic coatings. Superhydrophobic coatings can be adopted for icephobic applications once the surface topology is carefully designed

Braided textile composites for sports protection: Energy absorption and delamination in impact modelling

Composites reinforced with braided textiles exhibit high structural stability and excellent damage tolerance, making them ideal materials for use in sports-protection equipment. In sports impact scenarios, braided composites need to maintain their structure integrity and dissipate impact energy to protect a human body. Thus, it is crucial to study the dynamic response of a composite structure and its energy-dissipation mechanisms. Here, a multi-scale computational approach was explored to capture main damage modes of a braided textile composite; simulations were supported by experimental verification. A drop-weight test was performed with a spike-shape impactor to imitate real-life sports impact collision scenarios, followed by X-ray computed micro-tomography to characterize damage morphology of the specimen. The experimental results were compared with analytical models. The extent of delamination was quantified by applying surface- and element-based cohesive zone models. A ply-level model with three-dimensional continuum and shell elements was employed to explore the effect of through-thickness failure modes on energy absorption of the composite. The propagation mechanism of matrix cracks is also discussed. In addition, with the developed model, impact-attenuation performance of a shin-guard structure was simulated. The presented modelling capability can improve design of braided composite structures for sports and other protective and structural applications

Damage accumulation in braided textiles-reinforced composites under repeated impacts: Experimental and numerical studies

© 2018 Elsevier Ltd Composites reinforced with braided textiles exhibit high structural stability and excellent damage tolerance, making them very attractive for defence, aerospace, automotive and energy industries. Considering the real-life service environment, it is crucial to study a dynamic response of a composite structure and its energy-dissipation ability, especially under repeated low-velocity impacts. So, a series of drop-weight tests were carried out followed by X-ray computed micro-tomography to characterize damage morphology of braided composite specimens. Meanwhile, a multi-scale computational approach was explored and implemented as a user-defined-material subroutine (VUMAT) for ABAQUS/Explicit to capture main damage modes of a braided textile composite, while its delamination was modelled by employing cohesive-zone elements. Load- and energy-time curves were obtained both experimentally and numerically. The predicted levels of peak forces and absorbed energy were found to agree with the experimental data. An extent of delamination and damage accumulation in the braided composite was predicted numerically and analysed; it was found that material responses to repeated impacts had two types depending on the level of normalised impact energy. The presented modelling capability could contribute to design of braided composite structures for various applications

Strength prediction for bi-axial braided composites by a multi-scale modelling approach

Braided textile-reinforced composites have become increasingly attractive as protection materials thanks to their unique inter-weaving structures and excellent energy-absorption capacity. However, development of adequate models for simulation of failure processes in them remains a challenge. In this study, tensile strength and progressive damage behaviour of braided textile composites are predicted by a multi-scale modelling approach. First, a micro-scale model with hexagonal arrays of fibres was built to compute effective elastic constants and yarn strength under different loading conditions. Instead of using cited values, the input data for this micro-scale model were obtained experimentally. Subsequently, the results generated by this model were used as input for a meso-scale model. At meso-scale, Hashin’s 3D with Stassi’s failure criteria and a modified Murakami-type stiffness-degradation scheme was employed in a user-defined subroutine developed in the general-purpose finite-element software Abaqus/Standard. An overall stress–strain curve of a meso-scale representative unit cell was verified with the experimental data. Numerical studies show that bias yarns suffer continuous damage during an axial tension test. The magnitudes of ultimate strengths and Young’s moduli of the studied braided composites decreased with an increase in the braiding angle

Mechanically robust transparent anti-icing coatings: Roles of dispersion status of Titanate nanotubes

© 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Ice accretion on automobiles, aerospace components, precision instruments, and photovoltaic devices detrimentally affect their performance and increase the maintenance cost. Despite significant efforts devoted to the investigation of anti-icing coatings in the past decades, mechanically robust and transparent anti-icing coatings are rarely reported. In this study, titanate nanotubes are used as filler to prepare mechanically robust anti-icing coatings with a sol-gel method. Specially, the effect of dispersion status of nanotubes on the transmittance, surface roughness, and water repellency is investigated. The optimized smooth, transparent coating exhibits higher water repellency and better anti-icing performance in terms of ice-adhesion strength, icing delay time, and ice-nucleation temperature than the rough one. Much higher hardness and scratch resistance than that of commercially available icephobic or anti-icing coatings is obtained on the smooth, transparent sample; the coating also presents good adhesion to the substrate

Transparent icephobic coatings using bio-based epoxy resin

© 2017 Elsevier Ltd Ice accretion and accumulation pose serious challenges for maintaining the operation and performance of outdoor facilities in cold climate. Epoxy resin, with a wide range of formulation possibilities, is widely used as protective coatings for outdoor facilities. However, bisphenol A (BPA), a key ingredient of conventional epoxy, is known to interfere with human's natural hormones and cause various disorders in the body system. Reduction or complete elimination of the usage of BPA is therefore high in the agenda of the coatings industries. In this study, a transparent, anti-icing, bio-based ep oxy coating was developed for room-temperature processing. As a result of hydrophobic treatment with addition of silanes, the glass-transition temperature and anti-icing performance of bio-based epoxy resin increased significantly. The optimum coating exhibited good water repellency and ice-adhesion strength as low as 50 kPa at − 20°, which was half of the widely accepted threshold value of 100 kPa for icephobic coatings. The icing delay time was much delayed compared with that of an uncoated glass substrate. To further demonstrate the anti-icing performance of the optimized coating, supercooled-water dripping on coated wooden outdoor floors and wooded boards was conducted at − 15 °C, superior anti-icing performance was observed on the coated substrates

High-Resolution NMR Spectra in Inhomogeneous Fields via IDEAL (Intermolecular Dipolar-Interaction Enhanced All Lines) Method

Intermolecular double-quantum technique is used to yield high-resolution NMR spectra in inhomogeneous magnetic fields. The method exploits the distant dipolar interactions between the solvent and solute nuclear spins. Chemical shifts, J couplings, multiplicity patterns, and relative areas are retained with the method. Except for a 1.5-fold change in the scale factor of J couplings, other parameters are consistent with those extracted from one-dimensional spectra obtained in a homogeneous field

High-Resolution NMR Spectra in Inhomogeneous Fields via IDEAL (Intermolecular Dipolar-Interaction Enhanced All Lines) Method

Intermolecular double-quantum technique is used to yield high-resolution NMR spectra in inhomogeneous magnetic fields. The method exploits the distant dipolar interactions between the solvent and solute nuclear spins. Chemical shifts, J couplings, multiplicity patterns, and relative areas are retained with the method. Except for a 1.5-fold change in the scale factor of J couplings, other parameters are consistent with those extracted from one-dimensional spectra obtained in a homogeneous field

High-Resolution NMR Spectra in Inhomogeneous Fields via IDEAL (Intermolecular Dipolar-Interaction Enhanced All Lines) Method

Intermolecular double-quantum technique is used to yield high-resolution NMR spectra in inhomogeneous magnetic fields. The method exploits the distant dipolar interactions between the solvent and solute nuclear spins. Chemical shifts, J couplings, multiplicity patterns, and relative areas are retained with the method. Except for a 1.5-fold change in the scale factor of J couplings, other parameters are consistent with those extracted from one-dimensional spectra obtained in a homogeneous field

NGS data for DNA-based NGS for fusion-gene detection

The identification of the genomic sequence of the breakpoint flanking regions of the fusion gene translocation was sequenced by next-­generation sequencing (NGS).</p