Steven Abbott

Broadband moth-eye antireflection coatings fabricated by low-cost nanoimprinting

Subwavelength scale antireflection moth-eye structures in silicon were fabricated by a wafer-scale nanoimprint technique and demonstrated an average reflection of 1% in the spectral range from 400 to 1000 nm at normal incidence. An excellent antireflection property out to large incident angles is shown with the average reflection below 8% at 60°. Pyramid array gave an almost constant average reflection of about 10% for an incident angle up to 45° and concave-wall column array produced an approximately linear relation between the average reflection and the incident angles. The technique is promising for improving conversion efficiencies of silicon solar cells.

Mechanism of hydrophobic drug solubilization by small molecule hydrotropes.

Drugs that are poorly soluble in water can be solubilized by the addition of hydrotropes. Albeit known for almost a century, how they work at a molecular basis is still controversial due to the lack of a rigorous theoretical basis. To clear up this situation, a combination of experimental data and Fluctuation Theory of Solutions (FTS) has been employed; information on the interactions between all the molecular species present in the solution has been evaluated directly. FTS has identified two major factors of hydrotrope-induced solubilization: preferential hydrotrope-solute interaction and water activity depression. The former is dominated by hydrotrope-solute association, and the latter is enhanced by ionic dissociation and hindered by the self-aggregation of the hydrotropes. Moreover, in stark contrast to previous hypotheses, neither the change of solute hydration nor the water structure accounts for hydrotropy. Indeed, the rigorous FTS poses serious doubts over the other common hypothesis: self-aggregation of the hydrotrope hinders, rather than promotes, solubilization.

Comparison of transient thermal conduction in tellurium and organic dye based digital optical storage media

Considerable research and development has been done, in recent years, on combinations of optically absorbing thin films and substrates for digital optical storage media. Recent theoretical models have considered the formation of pits, by laser heating, in such media in two stages: (i) a preinitiation stage before pit formation; (ii) a pit growth stage. To compare the validity of suggested mechanisms for initiation accurate temperature calculations are required. In this paper the full transient thermal conduction equation is solved by finite element methods for both a tellurium and an organic dye layer system and the results compared.

Mass production of bio-inspired structured surfaces

Abstract Bio-inspired surface structures offer significant commercial potential for the creation of antireflective, self-cleaning and drag reducing surfaces, as well as new types of adhesive systems. The current article explores how the current understanding of the basic science of the biological structures occurring on the surface of moth eyes, leaves, sharkskin, and the feet of reptiles can be transferred to functional man-made materials, some of the drawbacks of which are shown to offer a long-term challenge to engineers. Explored also is the related topic of how such surfaces can be mass-produced, encompassing the important areas of current surface replication techniques and the associated acquisition of good master structures.

7.3: Holographic Antiglare and Antireflection Films for Flat Panel Displays

Antiglare AG and low- or anti-reflection LR, AR are important optical features of the front surfaces of flat panel displays and other information displays. New types of holographic surface relief microstructures have been developed on large areas showing very good optical properties. Holographic exposure techniques give the freedom to carefully design AG properties. They also allow the superposition of different types of structures, e.g. a Motheye AR and an AG microstructure MARAG ™ 1, which can be produced very cost-effectively by mass UV precision nano-replication UV-PNR. As a bonus, the UV-PNR structures are hardcoat materials suitable for the real world.

Practical molecular thermodynamics for greener solution chemistry

We all know that to enhance solubility using greener chemistry we should harness sound principles of molecular-based thermodynamics. The problem is that even for simple systems it can be hard to know how to use fundamental tools for formulation benefit, and for the more complex systems that we must often use, calculations required for molecular thermodynamics can often be quite involved. In this paper we show that a fundamental, assumption-free statistical thermodynamics approach, the Kirkwood–Buff theory, can be used in practical, complex aqueous systems to provide the insights we need to optimise formulations. The theory itself is not that difficult, but its implementation, which requires many steps of thermodynamic calculations, has up to now not been straightforward. Taking full advantage of an interactive approach, here we review what the Kirkwood–Buff theory can provide for formulators; we use the power of modern web browsers to provide open-source, user-friendly, responsive-design apps to do the hard work of data analysis, leaving formulators to focus on the interpretation of the results for their specific optimisation task. Indeed the apps are intended to be used by researchers and formulators for specific systems of interest to them.

A theoretical and experimental investigation of reservoir-fed, rigid-roll coating

An industrially-important variant of reverse roll coating is studied in which the metering gap sits beneath a large, liquid reservoir, the influence of which is investigated via complimentary experimental, analytical (lubrication) and computational (finite element) methods, and for which gravitational effects are shown to be influential. Experimental measurements for both the flow rate and wetting line position are given over a wide range of roll speed ratio and capillary number and it is shown that, provided the wetting line is sufficiently far from the nip, the flow rate depends linearly on the reservoir level. A key feature of the mathematical models is that, unlike previous reverse roll coating studies, the variation of dynamic contact angle with metering roll speed has been accounted for. The lubrication model also uses boundary conditions which incorporate free surface, surface tension and wetting line effects and the predictions from both models are found to be in generally good agreement with experiment. Finally, streamlines obtained from Finite Element solutions of the flow in the reservoir and wetting line regions are found to compare well with corresponding experimental flow visualisations. The flow in the reservoir is recirculating in nature, the size and number of recirculations depending on the reservoir geometry.

An integrated approach to optimizing skin delivery of cosmetic and pharmaceutical actives

The academic literature on skin delivery provides countless examples of scientific insights into specific aspects of the overall process. For the practical formulator, however, it is difficult to know how to combine such insights in a way that fits into the realities of commercial formulations. In this study, five key principles are combined into an integrated approach that can be applied to real‐world formulations. Given the complexities of skin science, the integrated approach cannot be expected to be highly precise. Instead, it is intended as a way for a formulation team to balance the many conflicting issues. The predictions are sufficiently specific to be examined by those with the appropriate analytical resources and data on formulation efficacy. It is hoped that such challenges will allow the approach to be refined for the future.

Finite element analysis of thermal stresses in optical storage media

Finite element techniques are used to calculate the thermal stresses generated in single‐layer, optical storage thin films. The calculations predict that the thermal stresses generated by laser heating may reach values well beyond the strength of the media in times much less than that for pit formation by melting. Both dye‐polymer and metal‐based systems are considered with either air or substrate incident laser sources.

Finite element modeling of laser-induced hole formation in optical storage media

A finite element model has been used to solve the transient thermal conduction equation for multilayer dye-polymer optical storage media. An accurate computer model is required to determine the laser heat input throughout the absorbing layers due to optical interference effects through the thickness of the dye. Only by this technique can accurate temperature distributions be calculated. From the resulting temperature distributions finite element analysis is used to determine the resulting thermal stresses. These stresses may be sufficiently high to cause intcrlayer failure by fracture.