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For the preparation of electrically conductive composites, various combinations of cellulose and conducting materials such as polymers, metals, metal oxides and carbon have been reported. The conductivity of these cellulose composites reported to date ranges from 10−6 to 103 S cm−1. Cellulose nanocrystals (CNCs) are excellent building blocks for the production of high added value coatings. The essential process steps for preparing such coatings, i.e. surface modification of CNCs dispersed in water and/or alcohol followed by application of the dispersion to substrate samples using dip coating, are low cost and easily scalable. Here, we present coatings consisting of Ag modified CNCs that form a percolated network upon solvent evaporation. After photonic sintering, the resulting coatings are electrically conductive with an unprecedented high conductivity of 2.9 × 104 S cm−1. Furthermore, we report the first colloidal synthesis that yields CNCs with a high degree of Ag coverage on the surface, which is a prerequisite for obtaining coatings with high electrical conductivity.

Antireflective coatings (ARCs) are applied to reduce surface reflections. We review coatings that reduce the reflection of the surface of the transparent substrates float glass, polyethylene terephthalate, poly(methyl methacrylate), and polycarbonate. Three main coating concepts exist to lower the reflection at the interface of a transparent substrate and air: multilayer interference coatings, graded index coatings, and quarter-wave coatings. We introduce and discuss these three concepts, and zoom in on porous quarter-wave coatings comprising colloidal particles. We extensively discuss the four routes for introducing porosity in quarter-wave coatings through the use of colloidal particles, which have the highest potential for application: (1) packing of dense nanospheres, (2) integration of voids through hollow nanospheres, (3) integration of voids through sacrificial particle templates, and (4) packing of nonspherical nanoparticles. Finally, we address the remaining challenges in the field of ARCs, and elaborate on potential strategies for future research in this area.

Environmental analysis should be performed early in the Research and Development (R&D) phases of new technologies to timely determine potential impact and, thereby, include prevention and minimization of unfavorable ecological impact into the innovation process. Here, we demonstrate the application of anticipatory Life Cycle Assessment (LCA) on novel anti-reflective coatings used for greenhouses in the Netherlands. Currently, these coating technologies are developed at the laboratory scale (lab-scale), but they have the potential to be transferred to commercial scale on the short term. What-if scenarios have been used to scale-up the coating production process to pilot and industrial scales. The scenarios were developed by optimizing the laboratory scale coating production parameters. A cradle-to-grave LCA has been done to compare novel coatings with conventional coatings. The functional unit has been defined as the production of 1692.30 kg of tomatoes in greenhouses during 30 years. Results indicate that the novel coating manufactured at industrial scale can compete with conventional coatings in terms of the environmental performance. Furthermore, LCA shows that the novel coating assessed does not bring environmental benefits as compared to employing uncoated glass. However, the use of the glass coating in the greenhouse may bring economic benefits during functional lifetime by means of increased yield of crop (e.g. tomatoes). Different pathways of the technological development of the novel coating have been considered in the sensitivity analysis. The option that includes glass manufacturing in the Netherlands rather than China has led to the best environmental impact results. © 2019 Elsevier Ltd

Correction to: npj 2D Materials and Applications https://doi.org/10.1038/s41699-018-0048-4, Published online 21 February 2018 The Author contributions section has been amended to account for the full contributions of two of the authors, K.M. and M.C.D.M. This has now been corrected in the HTML and PDF versions of this article.

The use of cellulose nanocrystals (CNCs) in optical materials has been extensively studied. Key in most applications reported to date is the chiral nematic ordering of CNCs. Here, we demonstrate that random packing of silicated CNCs can also yield materials with interesting optical properties, i.e., highly porous, ultra-low refractive index coatings. Needle-shaped CNCs with an aspect ratio of 25 were extracted from Avicel, and subsequently covered with a silica layer. In one single dip coating step, highly porous coatings of CNC-silica core–shell particles were deposited on glass slides and silicon wafers. The lowest refractive index achieved was 1.03, which corresponds to a porosity of 94%; the thickness of these coatings ranged from 101 nm to 239 nm. The substrates, coated with a layer of CNC-silica core–shell particles, were heated to 450 °C for two hours. Cellulose was removed through pyrolysis, which resulted in porous coatings of sub-micron sized hollow silica rods. The porosity increase generated through pyrolysis of cellulose, however, was largely compensated by the decrease in packing porosity due to shrinkage of the coating.

A comprehensive nanoscale understanding of layered double hydroxide (LDH) thermal evolution is critical for their current and future applications as catalysts, flame retardants and oxygen evolution performers. In this report, we applied in situ transmission electron microscopy (TEM) to extensively characterise the thermal progressions of nickel-iron containing (Ni-Fe) LDH nanomaterials. The combinative approach of TEM and selected area electron diffraction (SAED) yielded both a morphological and crystallographic understanding of such processes. As the Ni-Fe LDH nanomaterials are heated in situ, an amorphization occurred at 250 °C, followed by a transition to a heterogeneous structure of NiO particles embedded throughout a NiFe2O4 matrix at 850 °C, confirmed by high-resolution TEM and scanning TEM. Further electron microscopy characterisation methodologies of energy-filtered TEM were utilised to directly observe these mechanistic behaviours in real time, showing an evolution and nucleation to an array of spherical NiO nanoparticles on the platelet surfaces. The versatility of this characterisation approach was verified by the analogous behaviours of Ni-Fe LDH materials heated ex situ as well as parallel in situ TEM and SAED comparisons to that of an akin magnesium-aluminium containing (Mg-Al) LDH structure. The in situ TEM work hereby discussed allows for a state-of-the-art understanding of the Ni-Fe material thermal evolution. This is an important first, which reveals pivotal information, especially when considering LDH applications as catalysts and flame retardants.

To tailor the properties of nanoparticles and nanocomposites, precise control over particle size is of vital importance. Real-time monitoring of particle size during bottom-up synthesis in liquids would allow a detailed study of particle nucleation and growth, which provides valuable insights in the mechanism of formation of the nanoparticles. Furthermore, it facilitates a rational scale-up, and would enable adequate intervention in the production process of nanoparticle dispersions to minimize the number of off-spec batches. Since real-time monitoring requires particle size measurements on dispersions in flow, conventional dynamic light scattering (DLS) techniques are not suited: they rely on single scattering and measure the Brownian motion of particles dispersed in a liquid. Here, we present a set-up that allows accurate measurements in real-time on flowing dispersions using a DLS technique based on modulated 3D cross-correlation. This technique uses two simultaneous light scattering experiments performed at the same scattering vector on the same sample volume in order to extract only the single scattering information common to both. We connected the reactor to a flow-cell in the DLS equipment using a tailor-made analysis loop, and successfully demonstrated the complete set-up through monitoring of the size of spherical silica nanoparticles during Stober synthesis in a water-alcohol mixture starting from the molecular precursor tetraethyl orthosilicate. This work was supported by the European Commission and is part of the EU project COPILOT which has received funding from the European H2020 program under grant agreement no 645993. Solliance and the Dutch province of Noord Brabant are acknowledged for funding the TEM facility.

The effect of a nonspherical particle shape and shape polydispersity on the structure of densely packed hard colloidal particles was studied in real space by confocal microscopy. We show that the first layer at the wall of concentrated size-monodisperse but shape-polydisperse polyhedral colloids exhibits significant deviations from a hexagonal lattice. These deviations are identified as bond-orientational fluctuations which lead to percolating "mismatch lines." While the shape-induced geometrical frustration of the hexagonal symmetry suppresses translational order, bond-orientational order is clearly retained, indicating a hexaticlike structure of the polyhedral colloids.

We have discovered that the long-term aging of the hexagonal columnar liquid-crystal phase of polydisperse gibbsite platelets leads to fractionated crystallization, that is, to the formation of coexisting columnar crystals with different periods. This process was revealed by microradian X-ray diffraction demonstrating the splitting of the Bragg intercolumnar reflections into sequences of sharper reflections. The fractionated crystallization was observed in a number of samples of sterically stabilized as well as charge-stabilized polydisperse gibbsite platelets.

Gelation is a common effect in aqueous suspensions of charged colloidal clay platelets at concentrations as low as 1 wt%. However, in systems of charged gibbsite [Al(OH) 3 ] platelets, gelation can be delayed to concentrations as high as 50 wt% depending on the ionic strength. We investigated the phase behaviour of this system approaching the state of gelation in the delicate region between attractive and repulsive states that originate from competition between Coulomb repulsion and van der Waals attraction. As a function of the ionic strength, isotropic–nematic, nematic–columnar and isotropic–columnar phase separations were observed. Moreover, compression by gravitational forces allowed us to observe phase separation that is arrested by gelation in the homogeneous suspensions.

The polyoxometalates, or POMs (clusters comprising at least two metal and many oxygen atoms), have recently gained significant interest, owing to their versatile architecture and especially catalytic activities. Due to their high catalytic activity but low surface area, there is always a demand for making high-surface-area POMs, particularly high-surface-area Keggins. Our present work demonstrates the 'gluing' of the anionic phosphomolybdate Keggin on gibbsite nanoplatelets with a residual positive charge to form large-surface-area composites. The resulting composite reported here has been characterized using TEM imaging, EDX/TEM (elemental) analysis, FTIR spectroscopy, potentiometric titrations, electrophoretic mobility determination, and XRD. The composite reported here could be useful in catalysis.

We present designs for sharp bends in polymer waveguides using colloidal photonic crystal (PhC) structures. Both silica (SiO2) sphere based colloidal PhC and core-shell colloidal PhC structures having a titania (TiO 2) core inside silica (SiO2) shells are simulated. The simulation results show that core-shell Face Centered Cubic (FCC) colloidal crystals have a sufficient refractive index contrast to open up a bandgap in the desired direction when integrated into polymer waveguides and can achieve reflection >70% for the appropriate plane. Different crystal planes of the FCC structure are investigated for their reflection and compared with the calculated bandstructure. Different techniques for fabrication of PhC on rectangular seed layers namely slow sedimentation; spin coating and modified doctor blading are discussed and investigated. FCC and Random FCC silica structures are characterized optically to show realisation of (001) FCC. © 2014 SPIE.

We present a systematic study of the effect of variation of the zinc oxide (ZnO) and copper indium gallium (di)selenide (CIGS) layer thickness on the absorption characteristics of CIGS solar cells using a simulation program based on finite element method (FEM). We show that the absorption in the CIGS layer does not decrease monotonically with its layer thickness due to interference effects. Ergo, high precision is required in the CIGS production process, especially when using ultra-thin absorber layers, to accurately realize the required thickness of the ZnO, cadmium sulfide (CdS) and CIGS layer. We show that patterning the ZnO window layer can strongly suppress these interference effects allowing a higher tolerance in the production process. © 2014 Optical Society of America.

This paper describes the electro-optic response of a suspension of disk-like colloids. We have considered aqueous suspensions of Gibbsite platelets and measured the electrically induced birefringence in the broad frequency range 10 2-10 8 Hz. When simply dispersed in an electrolyte solution, these particles orient with their major axis parallel to the electric field at all frequencies. The spectral dependence of their Kerr coefficient features three regimes: an electrokinetic α-relaxation within the kHz range, a conductive Maxwell-Wagner-O'Konski (MWO) relaxation having characteristic frequency in the 1-10 MHz range, and a nonzero high frequency asymptote. We quantitatively analyze the MWO spectral component and the high-frequency asymptote on the basis of a model developed for oblate particles. This analysis enables us to obtain the relevant particle properties: surface conductivity, zeta potential, and intrinsic Gibbsite birefringence. When the particles are dispersed in a mixture that also contains smaller spherical particles that have a charge of the same sign, their electric birefringence becomes negative at low frequency. This anomalous orientation of the platelets is analogous to that observed in mixtures of prolate and spherical particles, and demonstrates the anomalous birefringence as a universal property of suspensions of nonspherical particles when surrounded by smaller charged particles. © 2011 American Chemical Society.

In this paper, we present a comprehensive study of the sol-gel transitions and liquid crystal phase transitions in aqueous suspensions of positively charged colloidal gibbsite platelets at pH 4-5 over a wide range of particle concentrations (50-600 g/L) and salt concentrations (10(-4)-10(-1) M NaCl). A detailed sol-gel diagram was established by oscillatory rheological experiments. These demonstrate the presence of kinetically arrested states both at high and at low salt concentrations, enclosing a sol region. Birefringence and iridescence show that in the sol state nematic and hexagonal columnar liquid crystal phases are formed. The gel and liquid crystal structures are studied in further detail using small-angle X-ray scattering (SAXS) and cryo-focused ion beam/scanning electron microscopy (cryo-FIB-SEM). The gel formed at high salt concentration shows signatures of a sponge-like structure and does not display birefringence. In the sol region, by lowering the salt concentration and/or increasing the gibbsite concentration, the nematic phase gradually transforms from the discotic nematic (ND) into the columnar nematic (NC) with much stronger side-to-side interparticle correlations. Subsequently, this NC structure can be either transformed into the hexagonal columnar phase or arrested into a birefringent repulsive gel state with NC structure.

Colloidal platelets of hydrotalcite, a layered double hydroxide, have been prepared by coprecipitation at pH 11-12 of magnesium nitrate and aluminum nitrate at two different magnesium to aluminum ratios. Changing the temperature and ionic strength during hydrothermal treatment, the platelets were tailored to different sizes and aspect ratios. Amino-modified polyisobutylene molecules were grafted onto the platelets following a convenient new route involving freeze-drying. Organic dispersions in toluene were prepared of the particles with the largest size and highest aspect ratio. The colloidal dispersions prepared in this way showed isotropic-nematic phase transitions above a limiting concentration in a matter of days. The number density at the transition and the width of the biphasic region were determined and compared to theory. The orientation of the platelets in nematic droplets (tactoids) and at the isotropic-nematic interface were analyzed by polarization microscopy. It was observed that sedimentation induces a nematic layer in samples that are below the limiting concentration for isotropic-nematic phase separation. No nematic phase was observed in the initial aqueous suspensions of the ungrafted particles.

In this paper we describe the use of columnar liquid crystals of silica coated colloidal gibbsite platelets as templates for the generation of ordered silica structures. The colloidal liquid crystal phases can be formed in a few hours by modest centrifugation forces (100–200g). Base catalysed hydrolysis of tetraethoxysilane (TEOS) is used to deposit silica in the space between the silica coated gibbsite particles. The size of the gibbsite platelets is varied between 200 and 500 nm and the thickness of the silica coating between 5 and 15 nm making the system a very versatile templating material. Acid leaching is used to selectively remove the gibbsite material.

The polyoxometalates, or POMs (clusters comprising at least two metal and many oxygen atoms), have recently gained significant interest, owing to their versatile architecture and especially catalytic activities. Due to their high catalytic activity but low surface area, there is always a demand for making high-surface-area POMs, particularly high-surface-area Keggins. Our present work demonstrates the 'gluing' of the anionic phosphomolybdate Keggin on gibbsite nanoplatelets with a residual positive charge to form large-surface-area composites. The resulting composite reported here has been characterized using TEM imaging, EDX/TEM (elemental) analysis, FTIR spectroscopy, potentiometric titrations, electrophoretic mobility determination, and XRD. The composite reported here could be useful in catalysis.

The activation of synthetic hydrotalcite, the carbonated layered double hydroxide (LDH) with ratio Mg 2+/Al 3+ = 3 and structural formula [Mg 6Al 2(OH) 16] 2+· CO 3 2-n(H 2O), has been investigated using neutron and X-ray diffraction. In situ neutron diffraction was used to follow the structural phase transformations during the thermal decomposition (calcination) of hydrotalcite under vacuum in the temperature range 298-723 K, and during which the residual gas evolved by the sample was analysed by mass spectrometry. Detailed structural information of the LDH and mixed metal oxides (MMOs) was extracted from both the Bragg peaks and the total scattering. These two analysis techniques provide complementary insight into the relevant transition mechanisms, since Bragg diffraction originates from long-range periodicities within the samples while total scattering reveals the subtleties of the local atomic environment. This latter information is particularly important for our understanding of catalytic activity since it elucidates the local metal coordination. We find that, during the calcination process, the local environment around the metal centres is robust, as the various stages during the phase transition have identical local structures. The implications of these new results for the nature of the MMOs is discussed in relation to the well-studied, reverse, rehydration reaction, and the high propensity of trivalent Al ions to migrate to tetrahedrally-coordinated lattice sites.

Colloidal suspensions of charged gibbsite platelets at salt concentrations of 10(-2) M and below and with a sufficiently high particle concentration form a kinetically arrested, glassy state. We study the evolution of the glassy state in suspensions of three different gibbsite systems. Despite differences in size and polydispersity, we observe small, iridescent grains of the hexagonal columnar phase, for all these systems after periods of months to years. The connections between this devitrification phenomenon and the structure of the glassy state are discussed.

Rheological, optical and structural properties of colloidal suspensions of charge-stabilized gibbsite platelets across the sol–gel transition region are investigated. In this work we focus on samples with a low salt content (10−4 M). While at a gibbsite concentration of 300 g l−1, a nematic–columnar phase separation is observed, an arrested state with a nematic signature and highly elastic response has been observed for a concentration of 400 g l−1. A temporal evolution of the structure of the arrested state, which leads to stronger interparticle correlations, has been observed on a timescale of 20 months. The results suggest that the arrested state develops into a glass with a columnar nematic structure.