Civilization continues to be transformed by our ability to harness energy beyond human and animal power. A series of industrial and agricultural revolutions have allowed an increasing fraction of the world population to heat and light their homes, fertilize and irrigate their crops, connect to one another and travel around the world. All of this progress is fuelled by our ability to find, extract and use energy with ever increasing dexterity. Research in materials science is contributing to progress towards a sustainable future based on clean energy generation, transmission and distribution, the storage of electrical and chemical energy, energy efficiency, and better energy management systems.

The path towards sustainable energy

4. Survey of Novel Multiphoton Active Materials 1257 4.1. Multiphoton Absorbing Systems 1257 4.2. Organic Molecules 1257 4.3. Organic Liquids and Liquid Crystals 1259 4.4. Conjugated Polymers 1259 4.4.1. Polydiacetylenes 1261 4.4.2. Polyphenylenevinylenes (PPVs) 1261 4.4.3. Polythiophenes 1263 4.4.4. Other Conjugated Polymers 1265 4.4.5. Dendrimers 1265 4.4.6. Hyperbranched Polymers 1267 4.5. Fullerenes 1267 4.6. Coordination and Organometallic Compounds 1271 4.6.1. Metal Dithiolenes 1271 4.6.2. Pyridine-Based Multidentate Ligands 1272 4.6.3. Other Transition-Metal Complexes 1273 4.6.4. Lanthanide Complexes 1275 4.6.5. Ferrocene Derivatives 1275 4.6.6. Alkynylruthenium Complexes 1279 4.6.7. Platinum Acetylides 1279 4.7. Porphyrins and Metallophophyrins 1279 4.8. Nanoparticles 1281 4.9. Biomolecules and Derivatives 1282 5. Nonlinear Optical Characterizations of Multiphoton Active Materials 1282

Multiphoton Absorbing Materials : Molecular Designs, Characterizations, and Applications

Research into extreme water-repellent surfaces began many decades ago, although it was only relatively recently that the term superhydrophobicity appeared in literature Here we review the work on the preparation of superhydrophobic surfaces, with focus on the different techniques used and how they have developed over the years, with particular focus on the last two years We discuss the origins of water-repellent surfaces, examining how size and shape of surface features are used to control surface characteristics, in particular how techniques have progressed to form multi-scaled roughness to mimic the lotus leaf effect There are notable differences in the terminology used to describe the varying properties of water-repellent surfaces, so we suggest some key definitions

Progess in superhydrophobic surface development.

Micromachining technology was used to prepare chemical analysis systems on glass chips (1 centimeter by 2 centimeters or larger) that utilize electroosmotic pumping to drive fluid flow and electrophoretic separation to distinguish sample components. Capillaries 1 to 10 centimeters long etched in the glass (cross section, 10 micrometers by 30 micrometers) allow for capillary electrophoresis-based separations of amino acids with up to 75,000 theoretical plates in about 15 seconds, and separations of about 600 plates can be effected within 4 seconds. Sample treatment steps within a manifold of intersecting capillaries were demonstrated for a simple sample dilution process. Manipulation of the applied voltages controlled the directions of fluid flow within the manifold. The principles demonstrated in this study can be used to develop a miniaturized system for sample handling and separation with no moving parts.

Micromachining a miniaturized capillary electrophoresis-based chemical analysis system on a chip

We review transport characteristics of pressure-driven, multiphase flows through microchannel networks tens of nanometres to several hundred of micrometres wide with emphasis on conditions resulting in enhanced mixing and reduced axial dispersion. Dimensionless scaling parameters useful in characterizing multiphase flows are summarized along with experimental flow visualization techniques. Static and dynamic stability considerations are also included along with methods for stabilizing multiphase flows through surface modifications. Observed gas–liquid and immiscible liquid–liquid flows are summarized in terms of flow regime diagrams and the different flows are related to applications in chemistry and materials synthesis. Means to completely separate multiphase flows on the microscale and guidelines for design of scalable multiphase systems are also discussed.

Multiphase microfluidics: from flow characteristics to chemical and materials synthesis

Plasma processing is used to fabricate super hydrophilic or super hydrophobic polymeric surfaces by means of O-2 plasma etching of two organic polymers, namely, poly(methyl methacrylate) (PMMA) and poly(ether ether ketone) (PEEK); a C4F8 plasma deposition follows O-2 plasma etching, if surface hydrophobization is desired. We demonstrate high aspect ratio pillars with height ranging from 16 nm to several micrometers depending oil the processing time, and contact angle (CA) close to 0 degrees after O-2-Plasma treatment or CA of 153 degrees (with CA hysteresis lower than 5 degrees) after fluorocarbon deposition. Super hydrophobic surfaces are robust and stable in time; in addition, aging of super hydrophilic surfaces is significantly retarded because of the beneficial effect of the nanotextured topography. The mechanisms responsible for the plasma-induced PMMA and PEEK surface nanotexturing are unveiled through intelligent experiments involving intentional modification of the reactor wall material and X-ray photoelectron spectroscopy, which is also used to study the surface chemical modification in the plasma. We prove that control of plasma nanotexture call be achieved by carefully choosing the reactor wall material.

Mechanisms of oxygen plasma nanotexturing of organic polymer surfaces: from stable super hydrophilic to super hydrophobic surfaces.

Ordered, hierarchical (triple-scale), superhydrophobic, oleophobic, superoleophobic, and amphiphilic surfaces on poly(methyl methacrylate) PMMA polymer substrates are fabricated using polystyrene (PS) microparticle colloidal lithography, followed by oxygen plasma etching-nanotexturing (for amphiphilic surfaces) and optional subsequent fluorocarbon plasma deposition (for amphiphobic surfaces). The PS colloidal microparticles were assembled by spin-coating. After etching/nanotexturing, the PMMA plates are amphiphilic and exhibit hierarchical (triple-scale) roughness with microscale ordered columns, and dual-scale (hundred nano/ten nano meter) nanoscale texture on the particles (top of the column) and on the etched PMMA surface. The spacing, diameter, height, and reentrant profile of the microcolumns are controlled with the etching process. Following the design requirements for superamphiphobic surfaces, we demonstrate enhancement of both hydrophobicity and oleophobicity as a result of hierarchical (triple-scale) and re-entrant topography. After fluorocarbon film deposition, we demonstrate superhydrophobic surfaces (contact angle for water 168°, compared to 110° for a flat surface), as well as superoleophobic surfaces (153° for diiodomethane, compared to 80° for a flat surface).

From superamphiphobic to amphiphilic polymeric surfaces with ordered hierarchical roughness fabricated with colloidal lithography and plasma nanotexturing.

A rapid, easy-to-implement, and potentially large-scale production method for fabricating high-aspect-ratio columnar-like nanostructures on poly(dimethylsiloxane) (PDMS) is demonstrated. Plasma treatment of PDMS under appropriate conditions in SF6 gas, followed by plasma-induced fluorocarbon film deposition, results in PDMS surfaces of fully controlled wetting properties, geometrical characteristics leading to robust superhydrophobic surfaces, and transparency. Potential applications to microfluidic devices are outlined.

https://iopscience.iop.org/article/10.1088/0957-4484/17/15/062/pdf

Nanotexturing of poly(dimethylsiloxane) in plasmas for creating robust super-hydrophobic surfaces

Durable superhydrophobic and superamphiphobic polymeric surfaces and their applications: A review

We demonstrate a mass-production-amenable technology for fabrication, surface modification and multifunction integration in polymeric microfluidic devices, namely direct lithography on the polymeric substrate followed by polymer plasma etching, and selective plasma deposition. We apply the plasma processing technology to fabricate polymeric microfluidics in poly(methyl methacrylate) (PMMA) and poly(ether ether ketone) (PEEK). First, deep anisotropic O2 plasma etching is utilized to pattern the polymer via an in situ, highly etch-resistant, thin, Si-containing photoresist, or via a thick organic photoresist. Absolute control of surface roughness (from smooth to very rough), and the production of stable-in-time (slowly ageing) superhydrophilic microchannels are demonstrated. Second, we demonstrate the spontaneous capillary pumping through such rough, superhydrophilic plasma-etched microchannels in contrast to smooth ones, even 5 weeks after fabrication. Third, by using C4F8 fluorocarbon plasma deposition through a stencil mask, we produce superhydrophobic patches inside the microchannels, and use them as passive valves. Our approach proposes “smart” multifunctional microfluidics fabricated by a plasma technology toolbox.

Angeliki Tserepi

Papers

Mechanisms of oxygen plasma nanotexturing of organic polymer surfaces: from stable super hydrophilic to super hydrophobic surfaces.

From superamphiphobic to amphiphilic polymeric surfaces with ordered hierarchical roughness fabricated with colloidal lithography and plasma nanotexturing.

Nanotexturing of poly(dimethylsiloxane) in plasmas for creating robust super-hydrophobic surfaces

Durable superhydrophobic and superamphiphobic polymeric surfaces and their applications: A review

“Smart” polymeric microfluidics fabricated by plasma processing: controlled wetting, capillary filling and hydrophobic valving