Thermochromic smart windows switch between transmitting and blocking solar infrared radiation (IR) based on temperature. These properties enable passive modulation of solar heat gain, which significantly lowers energy consumption in buildings and increases comfort levels for occupants via a balanced indoor climate. In this study, we set up a tailored test building in Eindhoven (The Netherlands) to monitor the real-life performance of a thermochromic smart window. We produced full sized double-glazed windows comprising a laminated outboard made from thermochromic interlayers, installed them in the test building and monitored their light transmission, solar heat gain and glass surface temperature over a full year. This enabled us to study the thermochromic phase transition of a smart window under real-life conditions for the first time. We demonstrated that the temperature of the smart window's outer glass pane regulated the phase transition and that the overall performance matched well with lab data. A glass surface temperature of 30 degrees C, influenced by the outdoor temperature and solar irradiance (photothermal heating), led to phase transition to the IR blocking state. During summer the smart window transitioned to its IR blocking state around 13:00, whereas in winter glass surface temperatures remained below 30 degrees C, retaining an IR transparent state of the smart window. In spring and autumn photo-thermal heating on cold, but sunny days led to undesired transitions to the IR blocking state, where glass surface temperatures exceeded outdoor temperatures by up to 20 degrees C. We studied the effect of photothermal heating in detail to conclude that optimized behavior of the smart window can be achieved with a phase transition temperature around 35-40 degrees C.

Abstract Vanadium is a transition metal widely used in steel production, batteries, and catalysis. It is a critical material and its disposal poses significant environmental challenges, making recovery and reuse a necessity. This study presents an innovative approach for the recovery and reuse of vanadium from spent catalysts, transforming it into high-purity V2O5 as the precursor for advanced VO2-based thermochromic coatings for smart windows. A multistep process comprising reductive acid leaching, oxidation, and selective precipitation was employed to develop two recovery pathways, resulting either in high-purity vanadium pentoxide (total metallic impurities of 2.14 ppm; extraction yield = 26%) or in a high extraction yield of 72% (total metallic impurities = 1.78%). The material was subsequently converted to monoclinic VO2 and applied for the production of a thermochromic solar control coating for smart windows. Optical measurements revealed a visible transmittance of 55% and a solar modulation of 4.4%, consistent with values for state-of-the-art VO2 coatings prepared by chemical reduction of virgin V2O5. This process demonstrates the technical feasibility of recovering vanadium from spent catalysts and reuse it in functional materials for smart windows, contributing to resource efficiency and environmental sustainability.

Monoclinic vanadium dioxide (VO2 (M)) is a promising material for various applications ranging from sensing to signature management and smart windows. Most applications rely on its reversible structural phase transition to rutile VO2 (VO2 (R)), which is accompanied by a metal-to-insulator transition. Bottom-up hydrothermal synthesis has proven to yield high quality monoclinic VO(2)but requires toxic and highly reactive reducing agents that cannot be used outside of a research lab. Here, we present a new hydrothermal synthesis method using nontoxic and safe-to-use oxalic acid as a reducing agent for V2O5 to produce VO2 (M). In early stages of the process, polymorphs VO2 (A) and VO2 (B) were formed, which subsequently recrystallized to VO2 (M). Without the presence of W6+, this recrystallization did not occur. After a reaction time of 96 h at 230 C-degrees in the presence of (NH4)(6)H(2)W(12)O(40 )in Teflon-lined rotated autoclaves, we realized highly crystalline, phase pure W-doped VO2 (M) microparticles of uniform size and asterisk shape (Delta H = 28.30 J center dot g(-1), arm length = 6.7 +/- 0.4 mu m, arm width = 0.46 +/- 0.06 mu m). We extensively investigated the role of W6+ in the kinetics of formation of VO2 (M) and the thermodynamics of its structural phase transition.

The switching performance of W/VO2 nanoparticles in thermochromic glass laminates was investigated. W/VO2 powder was prepared, and displayed a phase transition temperature and switching enthalpy of 20.9 degrees C and 37.5 +/- 0.2 J g- 1, respectively. Using wet bead milling, the particle size was reduced from 24 +/- 2 mu m to 120 +/- 10 nm. In the same process, the switching enthalpy decreased to 18.2 +/- 0.6 J g-1 due to partial loss of crystallinity. The kinetics of the structural phase transition were studied using Friedman's differential isoconversional method. This demonstrated that the activation energy |E alpha| was inversely proportional to the square of the difference between the material's temperature and the critical switching temperature T0, pointing out that nucleation kinetics were determining the rate. Furthermore, |E alpha| decreased upon milling, and kinetic asymmetry was induced. The milled nanoparticles were compounded with PVB to produce thermo-chromic films, which were applied for laminating glass plates. The impact of nanoparticle size and concentration on the resulting optical properties of the laminate, viz. solar transmission and solar modulation, was studied in detail. The highest solar modulation obtained was 9.4%. The results obtained in this study are of direct importance for the application in smart windows, showing that (i) the W/VO2 particle size needs to be <= 100 nm to avoid excessive haze, (ii) both powder production and bead milling require further process optimization to minimize functional performance losses, and (iii) T0 should be set about 3 degrees C lower to ensure a sufficiently fast switch at the temperature of choice.

Thermochromic window coatings represent a promising technology to improve the energy efficiency of buildings in intermediate climates. With the technology approaching market introduction it is important to investigate its performance limits within smart windows and to identify existing development challenges. Here we analyze the theoretical maximum performance of thermochromic window coatings that modulate IR transmission whilst retaining high visible transparency. The set limitations lead to a theoretical maximum solar modulation of 39.1%. Within an insulated glazing unit (IGU), where at least 2 glass panes and a conventional low-e coating are required, this value is further reduced to 12.9%. We show that by carefully selecting a low-e coating with the highest compatibility to a thermochromic coated glass and by allowing 10% of modulation in the visible spectral range, the theoretical maximum can be increased to 23.1%, illustrating the importance to codesign and match both coatings within a smart window to reach optimum performance. Furthermore, we compared our current best-performing VO2:SiO2 composite coating within an IGU to the theoretical maximum. The analysis shows that with a solar modulation of 13.4%, the coating is currently at 59% of the theoretical maximum. Finally, we propose and discuss several strategies to proceed further toward the theoretical maximum.

The thermodynamics and kinetics of the structural phase transition from monoclinic VO2 (M) to rutile VO2 (R) and vice versa were studied for particulate materials obtained by bead milling of VO2 (M) powder. Using wet bead milling, we decreased the particle size of VO2 (M) powder from similar to 1 mu m to 129 nm. With progressive milling, the switching enthalpy decreased from 47 J g(-1) to 29 J g(-1) due to a loss of crystallinity. The switching kinetics were studied using Friedman's differential isoconversional method. The activation energy vertical bar E-alpha vertical bar decreases with increasing difference between the actual temperature of the material and its switching temperature (T-0). Furthermore, vertical bar E-alpha vertical bar decreases with progressive milling, and kinetic asymmetry is induced. For milled particulate materials, vertical bar E-alpha vertical bar is lower for the switch from VO2 (R) to VO2 (M) than for the opposite switch. For hydrothermally synthesized nanoparticles, vertical bar E-alpha vertical bar is in the same order of magnitude, albeit with inverse switching asymmetry. Latter may result from different defects that are introduced during both preparation techniques. Applying layers of milled particulate material to glass sheets yielded thermochromic coatings with luminous transmission of 40.7% and solar modulation of 8.3%. This demonstrates that milled VO2 particles have potential for use in energy efficient thermochromic windows.

Monoclinic VO2 (M) displays thermochromic properties based on its reversible metal-insulator transition. We studied the kinetics of the underlying structural phase transition (SPT) from monoclinic VO2 (M) to rutile VO2 (R) and vice versa both in powders and coatings, using isoconversional kinetic analysis based on datasets obtained through differential scanning calorimetry and UV-vis-NIR spectrophotometry. For VO2 powders, prepared via solution-phase reduction of V2O5 with oxalic acid and subsequent thermal anneal, we show that the activation energy vertical bar Ea vertical bar of the SPT is temperature dependent, and decreases with increasing difference between the material's temperature and the critical switching temperature T0. vertical bar Ea vertical bar for both VO2 (M) to VO2 (R) and VO2 (R) to VO2 (M) is similar, and ranges between 138 and 563 kJ mol(-1), depending on the temperature of the material. This indicates that similar defects play a key role in both SPTs. Upon doping with tungsten, T0 was lowered from 66.93 degrees C (0 at. % W) to -28.38 degrees C (3.5 at. % W). vertical bar Ea vertical bar, however, remained in the same range. Nonetheless, at W concentrations above 2 at. % a significant asymmetry was observed with higher vertical bar Ea vertical bar for the switch from VO2 (R) to VO2 (M). The SPT of VO2 (M) in coatings proceeded 4 times slower. This may result from the immobilization of the VO2 domains on the substrate surface and within the coating network, making the SPT more difficult to progress. The findings of this study have important implications for the application of VO2 (M) in energy efficient thermochromic glazing.

Vanadium dioxide displays thermochromic properties based on its structural phase transition from monoclinic VO2 (M) to rutile VO2 (R) and vice versa, and the accompanying reversible metal-insulator transition. We developed a single layer coating comprising VO2 (M) and SiO2. We applied the coating from an alcoholic solution comprising vanadium(IV) oxalate complex and pre-oligomerized tetra ethoxy silane to SiO2-coated float glass using dip coating, and thermally annealed the dried xerocoat in a two-step process. The addition of SiO2 as coating matrix resulted in non-scattering coatings with low surface roughness and random distribution of VO2 nanodomains ( 200 nm). Furthermore, the formation of the coating, comprising a phase separation yielding SiO2 and VO2 nanodomains during the thermal anneal, was studied in detail. The coating displays unrivalled optical properties, combining high visible light transmission Tvis 60% and large solar modulation Delta Tsol > 10%. When applied in insulating glass units, the coating has a positive impact on energy savings for heating and cooling of buildings in intermediate climates, which we demonstrated through building energy simulations. For a typical house in the Netherlands, energy savings up to 24% were obtained. In addition, we demonstrate a coating stability comparable to current energy-efficient window coatings during processing into and in insulating glass units through (accelerated) life time tests.

Reactive surfactants (surfmers), which are covalently attached to the surface of sub-micron sized polymer particles during emulsion polymerisation, are applied to tailor the surface functionality of polymer particles for an application of choice. We present a systematic study on the use of oligoglycidol-functionalised styrene macromolecules as surfmers in the emulsion polymerization of styrene. Firstly, we report the impact of the surfmer concentration on the particle size for polymerisations performed above and below the critical micelle concentration. Secondly, we report the influence of the oligoglycidol chain length on the particle size. Thirdly, we conducted experiments to analyse the influence of the surfmer concentration and its chain length on the colloidal stability of the aqueous polystyrene nanoparticles in sodium chloride solutions. We demonstrated that the size of polystyrene particles could be influenced by changing both the surfmer concentration and its chain length. Furthermore, we showed that the colloidal stability of the oligoglycidol-functionalized polystyrene particles is dependent on the particle size, and not directly related to the oligoglycidol chain length.

The building sector contributes approximately one third of the total energy consumption worldwide. A large part of this energy is used for the heating and cooling of buildings, which can be drastically reduced by use of energy-efficient glazing. In this study, we performed building energy simulations on a prototypical residential building, and compared commercially available static (low-e, solar IR blocking) to newly developed adaptive thermochromic glazing systems for various climate regions. The modeling results show that static energy-efficient glazing is mainly optimized for either hot climates, where low solar heat gain can reduce cooling demands drastically, or cold climates, where low-e properties have a huge influence on heating demands. For intermediate climates, we demonstrate that adaptive thermochromic glazing in combination with a low-e coating is perfectly suited. The newly developed thermochromic glazing can lead to annual energy consumption improvement of up to 22% in comparison to clear glass, which exceeds all other glazing systems. Furthermore, we demonstrate that in the Netherlands the use of this new glazing system can lead to annual cost savings of EU 638 per dwelling (172 m2, 25% window façade), and to annual nationwide CO2 savings of 4.5 Mt. Ergo, we show that further development of thermochromic smart windows into market-ready products can have a huge economic, ecological and societal impact on all intermediate climate region in the northern hemisphere.

Janus particles are of great research interest because of their reduced symmetry, which provides them with unique physical and chemical properties. Such particles can be prepared from spherical structures through colloidal assembly. Whilst colloidal assembly has the potential to be a low cost and scalable process, it typically lacks selectivity. As a consequence, it results in a complex mixture of particles of different architectures, which is tedious to purify. Very recently, we reported the colloidal synthesis of Au semishells, making use of polystyrene–polyphenylsiloxane Janus particles as an intermediate product (Chem. Commun. 2017, 53, 3898–3901). Here, we demonstrate that these Janus particles are realized through colloidal assembly of spherical glucose-functionalized polystyrene particles and an emulsion of phenyltrimethoxysilane in aqueous ammonia, followed by interfacial polycondensation to form the polyphenylsiloxane patch. Both the polystyrene spheres and the emulsion of Ph-TMS in aqueous ammonia are stabilized by a surfmer—a reactive surfactant. The colloidal assembly reported in this manuscript proceeds with an unexpected high selectivity, which makes this process exceptionally interesting for the synthesis of Janus particles. Furthermore, we report insights into the details of the mechanism of formation of these Janus particles, and apply those to adapt the synthesis conditions to produce polystyrene particles selectively decorated with multiple polyphenylsiloxane patches, e.g., raspberry particles.

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 10 3 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 × 10 4 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.

Protecting groups are commonly applied in multi-step molecular syntheses to protect one ormultiple functional groups from reacting. After the reaction, they are removed from the molecule. In full analogy to this concept, we report the practical and scalable colloidal synthesis of Au semishells using polyphenylsiloxane protecting patches to prevent part of the surface of polystyrene nanoparticles from being covered with Au. After Au deposition, the patches are removed yielding Au semishells. We anticipate that this strategy can be extended to the synthesis of other types of non-centrosymmetric nanoparticles.

Chloroauric acid (≥99.9 %), sodium borohydride (99 %), poly(ethylene glycol) methyl ether thiol (average Mn 6000), Trimethoxyphenylsilane (Ph-TMS) and ammonia solution (2.0 M in ethanol) were purchased from Sigma Aldrich. Toluene was purchased from Acros Organics. Tin(II) chloride (anhydrous) was purchased from Merck. Hydrochloric acid was purchased from TH Geyer. Formaldehyde was purchased from KFM optiChem. Potassium carbonate was purchased from Fluka. Glucose-functionalized polystyrene particles were synthesized according to a previously published procedure.34

Au and Ag nanoshells are of interest for a wide range of applications. The plasmon resonance of such nanoshells is the property of interest and can be tuned in a broad spectral regime, ranging from the ultraviolet to the mid-infrared. To date, a large number of manuscripts have been published on the optics of such nanoshells. Few of these, however, address the effect of particle size distribution and metal shell imperfections on the plasmon resonance. Both are inherent to the chemical synthesis of metal nanoshells and therefore to a large extent unavoidable. It is of vital importance to understand their effect on the plasmon resonance, since this determines the scope and limitations of the technology and may have a direct impact on the application of such particles. Here, we elucidate the effect of particle size distribution and imperfections in the metal shell on the plasmon resonance of Au and Ag nanoshells. The size of the polystyrene core and the thickness of the Au and Ag shells are systematically varied to study their influence on the plasmon resonance, and the results are compared to values obtained through optical simulations using extended Mie theory and finite element method. Discrepancies between theory and practice are studied in detail and discussed extensively. Quantitative information on the minimum thickness of the metal shell, which is required to realize a satisfactory plasmon resonance of a metal nanoshell, is provided for Au and Ag.

We present the synthesis of glucose-functionalized polystyrene particles through emulsion polymerisation using glucose acrylate as reactive surfactant. Additionally, we present the selective deposition of silver on the surface of these particles yielding well-defined polystyrene–silver composites.