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Highly silanized cellulose biocomposites for sustainable insulation materials
Microfibrillated lignocellulose networks, derived from agricultural byproducts, represent an environmentally friendly biogenic material production due to their abundant availability to circular bioeconomy and inherent carbon sink in life cycle analysis. Yet, its vulnerability to moisture and flammability, coupled with challenges in creating highly reinforced insulation materials, poses challenges for the carbon-zero green building sector. Here we address these challenges with a new concept of in-situ grafting polymerization of nanoporous silica in pre-formed lignocellulosic fiber networks. The seamlessly integrating nanoporous silica with cellulose through hydrogen bonding networks enabled us to prepare highly reinforced biogenic composites for green building insulations. A high reinforcement biocomposite with hierarchal arrangements of nanoporous silica within the cellulose network exhibits remarkable attributes. It boasts a thermal conductivity of 24.2 mW·m –1 ·K –1 , a flexural modulus of 942 MPa, and soundproofing with a 20.8 % noise reduction, as well as the fire resistance characterized by an extended time to ignition and a reduced peak heat release rate of 144 kW·m –2 at 35 kW·m –2 of incident radiant heat flux. Furthermore, it demonstrates a reduced water absorption capacity, dropping from 5.12 g·g –1 to 0.75 g·g –1 . Altogether, this study opens the new pathways towards sustainable carbon-zero building materials in the context of circular bioeconomy.
Revealing the Singlet Fission Mechanism for a Silane-Bridged Thienotetracene Dimer
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Highly transparent silanized cellulose aerogels for boosting energy efficiency of glazing in buildings
Abstract To maintain comfortable indoor conditions, buildings consume ~40% of the energy generated globally. In terms of passively isolating building interiors from cold or hot outdoors, windows and skylights are the least-efficient parts of the building envelope because achieving simultaneously high transparency and thermal insulation of glazing remains a challenge. Here we describe highly transparent aerogels fabricated from cellulose, an Earth-abundant biopolymer, by utilizing approaches such as colloidal self assembly and procedures compatible with roll-to-roll processing. The aerogels have visible-range light transmission of 97–99% (better than glass), haze of ~1% and thermal conductivity lower than that of still air. These lightweight materials can be used as panes inside multi-pane insulating glass units and to retrofit existing windows. We demonstrate how aerogels boost energy efficiency and may enable advanced technical solutions for insulating glass units, skylights, daylighting and facade glazing, potentially increasing the role of glazing in building envelopes.
Long-range coupling in cyclic silanes
We report the synthesis of a mixed methyl- and hydro-substituted cyclosilane (1) possessing cis/trans stereoisomerism. Each diastereomer of 1 possesses distinct symmetry elements (cis-1: Cs-symmetric; trans-1: C 2 -symmetric). Cyclosilane 1 is a model system to probe configuration- and conformation-dependent long-range proton–proton coupling. Here, extensive NMR spectroscopic characterization is reported, including one-dimensional 1 H NMR and 29 Si DEPT and INEPT+ spectra and two-dimensional 1 H– 29 Si and 1 H– 1 H correlated spectroscopy (HSQC, HMBC, COSY). On the basis of these experiments, molecular connectivity consistent with four-bond 1 H– 1 H coupling is confirmed.
Fabrication, thermal analysis, and heavy ion irradiation resistance of epoxy matrix nanocomposites loaded with silane-functionalized ceria nanoparticles
This paper describes a detailed understanding of how nanofillers function as radiation barriers within the polymer matrix, and how their effectiveness is impacted by factors such as composition, size, loading, surface chemistry, and dispersion. Here, we designed a comprehensive investigation of heavy ion irradiation resistance in epoxy matrix composites loaded with surface-modified ceria nanofillers, utilizing tandem computational and experimental methods to elucidate radiolytic damage processes and relate them to chemical and structural changes observed through thermal analysis, vibrational spectroscopy, and electron microscopy. A detailed mechanistic examination supported by FTIR spectroscopy data identified the bisphenol A moiety as a primary target for degradation reactions. Results of computational modeling by the Stopping Range of Ions in Matter (SRIM) Monte Carlo simulation were in good agreement with damage analysis from surface and cross-sectional SEM imaging. All metrics indicated that ceria nanofillers reduce the damage area in polymer nanocomposites, and that nanofiller loading and homogeneity of dispersion are key to effective damage prevention. The results of this study represent a significant pathway for engineered irradiation tolerance in a diverse array of polymer nanocomposite materials. Numerous areas of materials science can benefit from utilizing this facile and effective method to extend the reliability of polymer materials.
High-pressure phases of liquid silane studied using first-principles molecular dynamics simulations
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Fabrication, Thermal Analysis, and Heavy Ion Irradiation Resistance of Epoxy Matrix Nanocomposites Loaded with Silane-Functionalized Ceria Nanoparticles
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Silane-coupled Molecular Rebar® tested in EV tires: A Phase II DOE SBIR Project Review
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Promotion of epoxy/ceramic interfacial adhesion through chemical vapor deposition of silane coatings
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Aging of Limestones and Silane–Siloxane-Based Protective Hydrophobics: The Impact of Heating–Cooling and Freeze–Thaw Cycles
Stones are traditionally used in construction and architectural applications as building elements due to their aesthetic and technical/structural performance. Like other environmental factors (rain, humidity, moisture, salt presence, biological activity, etc.), heating–cooling and freeze–thaw cycles significantly threaten the longevity of stone materials. Hence, considering the socio-economic and cultural value of stones, preventive actions such as hydrophobic coatings are applied to prevent or mitigate damage. The scope of this study is the performance assessment of limestones with different characteristics and the efficiency of various commercial silane/siloxane-based hydrophobic coatings when exposed to thermal variation and freeze–thaw. For that purpose, the standards EN 14066:2013 (determination of resistance to aging by thermal shock) and EN 12371:2010 (determination of frost resistance) were followed. Open porosity and static contact angles were estimated to assess the stone durability and water protection capabilities of the hydrophobics. Additionally, sound speed propagation velocity, quality of building material index, elastic modulus and flexural strength were measured to evaluate the variation of mechanical properties. Static contact angle revealed that the coatings maintained an efficient level of hydrophobicity even after thermal-shock and freeze–thaw weathering tests. The study also revealed a critical interaction between freeze–thaw cycles, hydrophobic coatings and structural integrity of the stones, mostly on more porous ones. When they are subjected to harsh environmental conditions, untreated porous limestones keep structural cohesion, allowing for the natural absorption and release of water during freezing and thawing. On the contrary, when limestones are treated, the hydrophobic coatings can moderately obstruct the water release due to the partial saturation of the porous framework by the products. It also probably resulted from the different mechanical behavior between the inner matrix and layer of stone coated, resulting in a premature breakout and mechanical damage of the stone.
Design Considerations for Controlling Silicon Nanoparticle Nucleation and Growth in a Nonthermal Plasma
Controlling the nucleation and growth of nanoparticles in low temperature plasma systems is imperative for controlling nanoparticle size distributions; and for some applications such as deposition and etching in microelectronic processing, preventing particle contamination. In this work, silicon nanoparticle (NP) production from silane is used as a model system to investigate the nucleation process. Although the mechanisms responsible for silicon NP nucleation and growth have been studied, it is unclear how controllable system parameters (e.g., pressure, system geometry, and gas composition) can be used to inhibit or promote NP formation. For example, the transport of reactive silane species is expected to significantly affect the feed fraction of silane required to nucleate silicon NP (the nucleation onset fraction) due to losses at the reactor walls. In this work, NP mass density was determined as a function of system pressure, gas composition, and reactor diameter for a tubular flow-through radiofrequency (RF) plasma using Ar/H2/He/SiH4 gas mixtures. A quartz crystal microbalance (QCM) impactor was developed to measure the total aerosol mass density downstream of the plasma and thereby identify the nucleation onset and its dependence on process parameters. Finally, a reaction mechanism was developed and incorporated into a global plasma chemistry model to better understand the nucleation onset and NP growth.
Microscopic Origins of the Nonlinear Behavior of Particle-Filled Rubber Probed with Dynamic Strain XPCS
The underlying microscopic response of filler networks in reinforced rubber to dynamic strain is not well understood due to the experimental difficulty of directly measuring filler network behavior in samples undergoing dynamic strain. This difficulty can be overcome with in situ X-ray photon correlation spectroscopy (XPCS) measurements. The contrast between the silica filler and the rubber matrix for X-ray scattering allows us to isolate the filler network behavior from the overall response of the rubber. This in situ XPCS technique probes the microscopic breakdown and reforming of the filler network structure, which are responsible for the nonlinear dependence of modulus on strain, known in the rubber science community as the Payne effect. These microscopic changes in the filler network structure have consequences for the macroscopic material performance, especially for the fuel efficiency of tire tread compounds. In this work, we elucidate the behavior with in situ dynamic strain XPCS experiments on industrially relevant, vulcanized rubbers filled (13 vol %) with novel air-milled silica of ultrahigh-surface area (UHSA) (250 m 2 /g). The addition of a silane coupling agent to rubber containing this silica causes an unexpected and counterintuitive increase in the Payne effect and decrease in energy dissipation. For this rubber, we observe a nearly two-fold enhancement of the storage modulus and virtually equivalent loss tangent compared to a rubber containing a coupling agent and conventional silica. Interpretation of our in situ XPCS results simultaneously with interpretation of traditional dynamic mechanical analysis (DMA) strain sweep experiments reveals that the debonding or yielding of bridged bound rubber layers is key to understanding the behavior of rubber formulations containing the silane coupling agent and high-surface area silica. These results demonstrate that the combination of XPCS and DMA is a powerful method for unraveling the microscale filler response to strain which dictates the dynamic mechanical properties of reinforced soft matter composites. With this combination of techniques, we have elucidated the great promise of UHSA silica when used in concert with a silane coupling agent in filled rubber. Such composites simultaneously exhibit large moduli and low hysteresis under dynamic strain.
Hydrosilane σ‐Adduct Intermediates in an Adaptive Zinc‐Catalyzed Cross‐dehydrocoupling of Si−H and O−H Bonds
Abstract Three‐coordinate Ph BOX ZnR ( Ph BOX =phenyl‐(4,4‐dimethyl‐oxazolinato; R=Me: 2 a , Et: 2 b ) catalyzes the dehydrocoupling of primary or secondary silanes and alcohols to give silyl ethers and hydrogen, with high turnover numbers (TON; up to 10 7 ) under solvent‐free conditions. Primary and secondary silanes react with small, medium, and large alcohols to give various degrees of substitution, from mono‐ to tri‐alkoxylation, whereas tri‐substituted silanes do not react with MeOH under these conditions. The effect of coordinative unsaturation on the behavior of the Zn catalyst is revealed through a dramatic variation of both rate law and experimental rate constants, which depend on the concentrations of both the alcohol and hydrosilane reactants. That is, the catalyst adapts its mechanism to access the most facile and efficient conversion. In particular, either alcohol or hydrosilane binds to the open coordination site on the Ph BOX ZnOR catalyst to form a Ph BOX ZnOR(HOR) complex under one set of conditions or an unprecedented σ‐adduct Ph BOX ZnOR(H−SiR′ 3 ) under other conditions. Saturation kinetics provide evidence for the latter species, in support of the hypothesis that σ‐bond metathesis reactions involving four‐centered electrocyclic 2σ–2σ transition states are preceded by σ‐adducts.
Vapor-phase grafting of a model aminosilane compound to Al 2 O 3 , ZnO, and TiO 2 surfaces prepared by atomic layer deposition
Atomic layer deposition (ALD) is a highly versatile surface functionalization technique that can conformally coat both planar and porous substrates. Here we use ALD metal oxide layers to establish a well-defined starting surface for vapor-phase surface organic modification. Vapor-phase (3-aminopropyl)triethoxysilane (APTES) surface silanization of ALD Al 2 O 3 , ZnO and TiO 2 surfaces were studied at 100 °C, 150 °C and 200 °C. In situ quartz crystal microbalance (QCM) and Fourier-transform infrared (FTIR) spectroscopy measurements, and ex situ atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS) measurements showed uniform monolayer silane formation through self-limiting APTES reaction. We observed a higher surface density of grafted APTES species following silanization at 100 °C compared to 200 °C, and we attribute this to the temperature-dependent reactivity of the surface hydroxyls and changes in the mode of APTES reaction. The FTIR and XPS measurements revealed that APTES reacts with Al 2 O 3 and ZnO exclusively through metal siloxy bond formation. However, APTES reacts with TiO 2 through both siloxy bond formation and ammonium salt formation via the amine group.
Reliability of double probe measurements in nanodusty plasmas
Abstract Nonthermal plasmas are attractive sources for nanoparticles synthesis, however, their plasma properties are notoriously difficult to assess due to the chemically reactive environment and high nanoparticle concentrations. Here, we are using a floating double probe to measure the plasma properties of a nanoparticle-forming argon:silane plasma. We demonstrate good stability of current–voltage characteristics over several minutes of operation. However, unexpectedly larger electron temperatures are measured with increasing the silane mole fraction. To test the validity of these results, we developed a zero-dimensional global model to investigate the effect of the presence of nanoparticles on the plasma properties. Using this model, we show that increasing particle concentration leads to an increasing electronegativity of the plasma, causing an increase of the reduced electric field. However, this causes only a moderate increase in mean electron energy, in contrast to the much larger increase measured by the double probe. We argue that these large electron temperatures are based on the fact that a double probe measures an ‘apparent’ electron temperature, which is defined by the negative inverse slope of the logarithm of the electron energy probability function (EEPF) at an energy corresponding to the probe’s floating potential. As the silane mole fraction is increased, the plasma becomes more electronegative and the probe’s floating potential moves closer to the plasma potential. Combined with the strong non-Maxwellian EEPF, this leads to the large apparent electron temperatures obtained by the probe. Thus, the apparent electron temperatures measured with the double probe do not follow the trends in mean electron energy.