Weak form equation–based finite-element modeling of viscoelastic asphalt mixtures

The objective of this study is to demonstrate using weak form partial differential equation (PDE) method for a finite-element (FE) modeling of a new constitutive relation without the need of user subroutine programming. The viscoelastic asphalt mixtures were modeled by the weak form PDE-based FE method as the examples in the paper. A solid-like generalized Maxwell model was used to represent the deforming mechanism of a viscoelastic material, the constitutive relations of which were derived and implemented in the weak form PDE module of Comsol Multiphysics, a commercial FE program. The weak form PDE modeling of viscoelasticity was verified by comparing Comsol and Abaqus simulations, which employed the same loading configurations and material property inputs in virtual laboratory test simulations. Both produced identical results in terms of axial and radial strain responses. The weak form PDE modeling of viscoelasticity was further validated by comparing the weak form PDE predictions with real laboratory test results of six types of asphalt mixtures with two air void contents and three aging periods. The viscoelastic material properties such as the coefficients of a Prony series model for the relaxation modulus were obtained by converting from the master curves of dynamic modulus and phase angle. Strain responses of compressive creep tests at three temperatures and cyclic load tests were predicted using the weak form PDE modeling and found to be comparable with the measurements of the real laboratory tests. It was demonstrated that the weak form PDE-based FE modeling can serve as an efficient method to implement new constitutive models and can free engineers from user subroutine programming.

Functionalised particles using dry powder coating in pharmaceutical drug delivery:promises and challenges

Introduction: Production of functionalised particles using dry powder coating is a one-step, environmentally friendly process that paves the way for the development of particles with targeted properties and diverse functionalities. Areas covered: Applying the first principles in physical science for powders, fine guest particles can be homogeneously dispersed over the surface of larger host particles to develop functionalised particles. Multiple functionalities can be modified including: flowability, dispersibility, fluidisation, homogeneity, content uniformity and dissolution profile. The current publication seeks to understand the fundamental underpinning principles and science governing dry coating process, evaluate key technologies developed to produce functionalised particles along with outlining their advantages, limitations and applications and discusses in detail the resultant functionalities and their applications. Expert opinion: Dry particle coating is a promising solvent-free manufacturing technology to produce particles with targeted functionalities. Progress within this area requires the development of continuous processing devices that can overcome challenges encountered with current technologies such as heat generation and particle attrition. Growth within this field requires extensive research to further understand the impact of process design and material properties on resultant functionalities.

Performance analysis of polymer optical fibre based Fabry-Perot sensor formed by two uniform Bragg gratings

The stress sensitivity of polymer optical fibre (POF) based Fabry-Perot sensors formed by two uniform Bragg gratings with finite dimensions is investigated. POF has received high interest in recent years due to its different material properties compared to its silica counterpart. Biocompatibility, a higher failure strain and the highly elastic nature of POF are some of the main advantages. The much lower Young’s modulus of polymer materials compared to silica offers enhanced stress sensitivity to POF based sensors which renders them great candidates for acoustic wave receivers and any kind of force detection. The main drawback in POF technology is perhaps the high fibre loss. In a lossless fibre the sensitivity of an interferometer is proportional to its cavity length. However, the presence of the attenuation along the optical path can significantly reduce the finesse of the Fabry-Perot interferometer and it can negatively affect its sensitivity at some point. The reflectivity of the two gratings used to form the interferometer can be also reduced as the fibre loss increases. In this work, a numerical model is developed to study the performance of POF based Fabry-Perot sensors formed by two uniform Bragg gratings with finite dimensions. Various optical and physical properties are considered such as grating physical length, grating effective length which indicates the point where the light is effectively reflected, refractive index modulation of the grating, cavity length of the interferometer, attenuation and operating wavelength. Using this model, we are able to identify the regimes in which the PMMA based sensor offer enhanced stress sensitivity compared to silica based one.

Protocol optimization for the mild detemplation of mesoporous silica nanoparticles resulting in enhanced texture and colloidal stability

Porosity development of mesostructured colloidal silica nanoparticles is related to the removal of the organic templates and co-templates which is often carried out by calcination at high temperatures, 500-600 °C. In this study a mild detemplation method based on the oxidative Fenton chemistry has been investigated. The Fenton reaction involves the generation of OH radicals following a redox Fe3+/Fe2+ cycle that is used as catalyst and H2O2 as oxidant source. Improved material properties are anticipated since the Fenton chemistry comprises milder conditions than calcination. However, the general application of this methodology is not straightforward due to limitations in the hydrothermal stability of the particular system under study. The objective of this work is three-fold: 1) reducing the residual Fe in the resulting solid as this can be detrimental for the application of the material, 2) shortening the reaction time by optimizing the reaction temperature to minimize possible particle agglomeration, and finally 3) investigating the structural and textural properties of the resulting material in comparison to the calcined counterparts. It appears that the Fenton detemplation can be optimized by shortening the reaction time significantly at low Fe concentration. The milder conditions of detemplation give rise to enhanced properties in terms of surface area, pore volume, structural preservation, low Fe residue and high degree of surface hydroxylation; the colloidal particles are stable during storage. A relative particle size increase, expressed as 0.11%·h-1, has been determined.

Fenton chemistry-based detemplation of an industrially relevant microcrystalline beta zeolite. Optimization and scaling-up studies

A mild template removal of microcrystalline beta zeolite, based on Fenton chemistry, was optimized. Fenton detemplation was studied in terms of applicability conditions window, reaction rate and scale up. TGA and CHN elemental analysis were used to evaluate the detemplation effectiveness, while ICP, XRD, LPHR-Ar physisorption, and 27Al MAS NMR were applied to characterize the structure and texture of the resulting materials. The material properties were compared to calcination. By understanding the interplay of relevant parameters of the Fenton chemistry, the process can be optimized in order to make it industrially attractive for scale-up. The H2O2 utilization can be minimized down to 15 mL H2O2/g (88 °C, 30 ppm Fe), implying a high solid concentration and low consumption of H2O2. When Fe concentration must be minimized, values as low as 5 ppm Fe can be applied (88 °C, 30 mL H2O2/g), to achieve full detemplation. The reaction time to completeness can be reduced to 5 h when combining a Fe-oxalate catalyst with UV radiation. The protocol was scaled up to 100 times larger its original recipe. In terms of the material's properties, the scaled material is structurally comparable to the calcined counterpart (comparable Si/Al and XRD patterns), while it displays benefits in terms of texture and Al-coordination, the latter with full preservation of the tetrahedral Al

Quantum dot materials for terahertz generation applications

Compact and tunable semiconductor terahertz sources providing direct electrical control, efficient operation at room temperatures and device integration opportunities are of great interest at the present time. One of the most well-established techniques for terahertz generation utilises photoconductive antennas driven by ultrafast pulsed or dual wavelength continuous wave laser systems, though some limitations, such as confined optical wavelength pumping range and thermal breakdown, still exist. The use of quantum dot-based semiconductor materials, having unique carrier dynamics and material properties, can help to overcome limitations and enable efficient optical-to-terahertz signal conversion at room temperatures. Here we discuss the construction of novel and versatile terahertz transceiver systems based on quantum dot semiconductor devices. Configurable, energy-dependent optical and electronic characteristics of quantum-dot-based semiconductors are described, and the resonant response to optical pump wavelength is revealed. Terahertz signal generation and detection at energies that resonantly excite only the implanted quantum dots opens the potential for using compact quantum dot-based semiconductor lasers as pump sources. Proof-of-concept experiments are demonstrated here that show quantum dot-based samples to have higher optical pump damage thresholds and reduced carrier lifetime with increasing pump power.

Effects in ultrafast laser micromachining PMMA-based optical fibre grating

Ultrafast laser owns extreme small beam size and high pulse intensity which enable spatial localised modification either on the surface or in the bulk of materials. Therefore, ultrafast laser has been widely used to micromachine optical fibres to alter optical structures. In order to do the precise control of the micromachining process to achieve the desired structure and modification, investigations on laser parameters control should be carried out to make better understanding of the effects in the laser micromachining process. These responses are important to laser machining, most of which are usually unknown during the process. In this work, we report the real time monitored results of the reflection of PMMA based optical fibre Bragg gratings (POFBGs) during excimer ultraviolet laser micromachining process. Photochemical and thermal effects have been observed during the process. The UV radiation was absorbed by the PMMA material, which consequently induced the modifications in both spatial structure and material properties of the POFBG. The POFBG showed a significant wavelength blue shift during laser micromachining. Part of it attributed to UV absorption converted thermal energy whilst the other did not disappear after POFBG cooling off, which attributed to UV induced photodegradation in POF.

Caking behaviour of spray-dried milk powders:using scanning probe microscopy to study nanoscale surface properties and material composition

Spray drying is widely used to manufacture many powdered products, with the drying process parameters having significant influence over the final powder's surface properties and propensity for unwanted caking. In most cases caking experiments are performed on bulk powders, but especially in multi-component powders, it is often difficult to interpret these results, where interaction effects between particles can be complex. Here the technique of scanning probe microscopy is used to characterize the nanoscale properties of spray dried model milk powders in order to investigate the surface properties of the powders.