The term superhydrophilicity is only 11–12 years old and was introduced just after the explosion of research on superhydrophobic surfaces, in response to the demand for surfaces and coatings with exceptionally strong affinity to water. The definition of superhydrophilic substrates has not been clarified yet, and unrestricted use of this term to hydrophilic surfaces has stirred controversy in the last few years in the surface chemistry community. In this review, we take a close look into major definitions of hydrophilic surfaces used in the past, before we review the physics behind the superhydrophilic phenomenon and make recommendation on defining superhydrophilic surfaces and coatings. We also review chemical and physical methods used in the fabrication of substrates on surfaces of which water spreads completely. Several applications of superhydrophilic surfaces, including examples from the authors' own research, conclude this review.

Hydrophilic and superhydrophilic surfaces and materials

The work is giving estimations of the discrepancy between solutions of the initial and the homogenized problems for a one{dimensional second order elliptic operators with random coeecients satisfying strong or uniform mixing conditions. We obtain several sharp estimates in terms of the corresponding mixing coeecient. Abstract. In the theory of homogenisation it is of particular interest to determine the classes of problems which are stable on taking the homogenisation limits. A notable situation where the limit enlarges the class of original problems is known as memory (nonlocal) eeects. A number of results in that direction has been obtained for linear problems. Tartar (1990) innitiated the study of the eeective equation corresponding to nonlinear equation: @ t u n + a n u 2 n = f: Signiicant progress has been hampered by the complexity of required computations needed in order to obtain the terms in power{series expansion. We propose a method which overcomes that diiculty by introducing graphs representing the domain of integration of the integrals in each term. The graphs are relatively simple, it is easy to calculate with them and they give us a clear image of the form of each term. The method allows us to discuss the form of the eeective equation and the convergence of power{series expansions. The feasibility of our method for other types of nonlinearities will be discussed as well.

Applied Mathematics and Computation

/pdf/philosophical-transactions-of-the-royal-society-4zs1ii7889.pdf

Philosophical Transactions of the Royal Society

Functional two-photon Ca(2+)-imaging is a versatile tool to study the dynamics of neuronal populations in brain slices and living animals. However, population imaging is typically restricted to a single two-dimensional image plane. By introducing an electrically tunable lens into the excitation path of a two-photon microscope we were able to realize fast axial focus shifts within 15 ms. The maximum axial scan range was 0.7 mm employing a 40x NA0.8 water immersion objective, plenty for typically required ranges of 0.2-0.3 mm. By combining the axial scanning method with 2D acousto-optic frame scanning and random-access scanning, we measured neuronal population activity of about 40 neurons across two imaging planes separated by 40 μm and achieved scan rates up to 20-30 Hz. The method presented is easily applicable and allows upgrading of existing two-photon microscopes for fast 3D scanning.

/pdf/fast-two-layer-two-photon-imaging-of-neuronal-cell-xts110ul8s.pdf

Fast two-layer two-photon imaging of neuronal cell populations using an electrically tunable lens

Since its emergence as a field, optofluidics has developed unique tools and techniques for enabling the simultaneous delivery of light and fluids with microscopic precision. In this Review, we describe the possibilities for applying these same capabilities to the field of energy. We focus in particular on optofluidic opportunities in sunlight-based fuel production in photobioreactors and photocatalytic systems, as well as optofluidically enabled solar energy collection and control. We then provide a series of physical and scaling arguments that demonstrate the potential benefits of incorporating optofluidic elements into energy systems. Throughout the Review we draw attention to the ways in which optofluidics must evolve to enable the up-scaling required to impact the energy field.

Optofluidics for energy applications

The meniscus between two immiscible liquids of different refractive indices can be used as a lens. A change in curvature of this meniscus by electrostatic control of the solid/liquid interfacial tension leads to a change in focal distance. It is demonstrated that two liquids in a tube form a self-centred variable-focus lens. The optical properties of this lens were investigated experimentally. We designed and constructed a miniature camera module based on this variable lens suitable for mobile applications. Furthermore, the liquid lens was applied in a Blu-ray Disc optical recording system to enable dual layer disc reading/writing.

Electrowetting-Based Variable-Focus Lens for Miniature Systems

In this article we introduce a novel numerical method to solve the problem of optimal transport and the related elliptic Monge--Ampere equation. It is one of the few numerical algorithms capable of solving this problem efficiently with the proper transport boundary condition. The computation time scales well with the grid size and has the additional advantage that the target domain may be nonconvex. We present the method and several numerical experiments.

/pdf/a-least-squares-method-for-optimal-transport-using-the-monge-4xmic9oq26.pdf

A Least-Squares Method for Optimal Transport Using the Monge--Ampère Equation

We study the diffuse transport of light through polymer slabs containing TiO2 scattering particles. The slabs are diffuser plates typical of a commercial white light-emitting diode (LED) module (Fortimo). We have measured the diffuse transmission and reflection properties over a broad wavelength range (470–840 nm) from which we derive the transport mean free path using the theory of light diffusion. With increasing scatterer density, the mean free path becomes shorter. The mean free path increases with wavelength; hence, blue light is scattered more strongly than red light. To interpret the results, we propose an ab initio model without adjustable parameters for the mean free path by using Mie theory. We include inhomogeneous broadening as a result of the size distribution of the scattering particles as measured by dynamic light scattering. Surprisingly, the calculated mean free path decreases with wavelength, at variance with our experiments, which is caused by particles with radii R in excess of 0.25 μm. Close inspection of the scatterers by electron microscopy reveals that large particles (R>0.4  μm) consist of clusters of small particles (R<0.13  μm). Therefore, we have improved our model by only taking into account the individual scatterers within the clusters. This model predicts mean free paths in good agreement with our experimental results. We discuss consequences of our results to white LED lighting modules.

https://ps.brillouinzone.com/sites/default/files/applopt5vos2013scattering_white_LED.pdf

Broadband mean free path of diffuse light in polydisperse ensembles of scatterers for white light-emitting diode lighting

The design, manufacturing and application of variable liquid lenses are discussed. The interface between the two immiscible liquids that forms the lens can be altered with a voltage. Results are presented of applying this lens in miniature autofocus and zoom cameras, in optical recording and in illumination systems.

Variable liquid lenses for electronic products

We compute numerical solutions of Liouville's equation with a discontinuous Hamiltonian. We assume that the underlying Hamiltonian system has a well-defined behaviour even when the Hamiltonian is discontinuous. In the case of geometrical optics such a discontinuity yields the familiar Snell's law or the law of specular reflection. Solutions to Liouville's equation should be constant along curves defined by the Hamiltonian system. This consideration allows us to derive a new jump condition, enabling us to construct a first-order accurate scheme. Essentially, the correct physics is built into the solver. The scheme is tested in a two-dimensional optical setting with two test cases, the first using a single jump in the refractive index and the second a compound parabolic concentrator. For these two situations, the scheme outperforms more conventional methods such as ray tracing. Keywords: Liouville's equation, Hamiltonian systems, jump condition, upwind scheme, geometrical optics, phase space

T.W. Tukker

Papers

Electrowetting-Based Variable-Focus Lens for Miniature Systems

A Least-Squares Method for Optimal Transport Using the Monge--Ampère Equation

Broadband mean free path of diffuse light in polydisperse ensembles of scatterers for white light-emitting diode lighting

Variable liquid lenses for electronic products

A novel scheme for Liouville's equation with a discontinuous Hamiltonian and applications to geometrical optics