Hexamethyldisilazane Research Articles

The Effect of Wettability on Confinement-Induced Phase Behavior and Storage of Alkane in Nanoporous Media.

The impact of wettability on the confined phase behavior of fluids is paramount for various applications, such as gas storage, carbon dioxide sequestration, and water purification. However, the understanding of the fluid-solid intermolecular interactions in confined systems is still limited and requires further investigation. This work investigates the effect of hydrophilic and hydrophobic nanoporous materials on the adsorption and desorption isotherms of n-butane. The hydrophilic samples in this research are MCM-41 silica powder with two different pore sizes (80 and 100 Å). MCM-41 samples were successfully treated with hexamethyldisilazane (HMDS) to create hydrophobic adsorbents. Isotherms of n-butane in materials with different wetting states were generated at various temperatures using an upgraded gravimetric apparatus. The results demonstrated that n-butane was adsorbed more onto the hydrophilic MCM-41 materials during the initial adsorption process. The lower affinity between n-butane and the modified MCM-41 samples slightly increased the capillary condensation and evaporation pressures in these materials compared to those in the original ones. However, it is noted that wettability's influence on the confined phase transitions of n-butane was not significant in this study. Interestingly, the hysteresis behavior of the vapor-liquid and liquid-vapor phase transitions due to confinement was independent of the surface's wetting properties. Kelvin's equation for a hemispherical meniscus was adopted to evaluate the capillary evaporation pressures of n-butane in nanopores. The calculated pressures showed agreement with experimental data when appropriate pore size and surface tension values were applied. These findings provide valuable insights into the impacts of surface chemistry and wettability on the phase behavior of hydrocarbon gas in nanoporous media. Furthermore, this study enriches the experimental database on confined fluids, which is essential for developing accurate theoretical and modeling tools for numerous industrial and scientific applications.

Fluorinated B-72 hybrid silver doped modified nanoparticle as a coating for biological corrosion protection of ancient bricks

In this paper, a superhydrophobic organic-inorganic composite coating containing fluorinated B72 hybrid methyl-modified silica/(Ag doped TiO2) by hexamethyldisilazane (HMDS) (H-SiO2/Ag/TiO2) was prepared by means of a mild and an environmental friendly method. Transparency, adhesion, hardness tests and photocatalytic performance were measured to determine the content of Ag in TiO2 which the TiO2/AgNO3 ratio is 0.008 g/mL. The synthesized Ag/TiO2 nanoparticles were characterized by X-ray diffraction (XRD), Raman spectra and transmission electron microscope (TEM). The highest contact angle of coated ancient bricks was 148.66° and the color change value of ΔE⁎ before and after coating was <5 which is within an acceptable range. The physical properties such as apparent porosity and water vapor permeability (ΔMp) were studied. After weathering from acid, alkali, salt, water and ultraviolet radiation, the bricks coated by the composite coatings still have good hydrophobicity that the contact angle were >120° and minor degree of surface corrosion comparing with the ancient bricks. The inhibitory effect of the composite coating on Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli), and that on algae (Chlamydomonas and Dunaliella) were studied through bacteriostasis test and algae comparative experiments, respectively. Finally, the mechanism of the composite coating on antibacterial and anti-algae was studied. The results showed that the appearance of the ancient bricks was not changed after coating, and the anti-weathering, antibacterial and anti-algae properties of the ancient transformation were increased.

Hydrophobic composite phase change coating: Preparation, performance and application

The utilization of composite phase change materials in energy storage and solar thermal applications is significantly restrained by their inherent non-hydrophobic surfaces and susceptibility to contamination. This study presents a novel synthesis of modified paraffin (Pa) @ silica (SiO2) nanocapsules through an efficient in situ hydrolysis and polycondensation reaction utilizing tetraethyl orthosilicate (TEOS) as the silicon source, paraffin as the phase change material, and hexamethyldisilazane (HMDS) as the surface modifier. These nanocapsules were then employed to formulate a composite phase change coating (PSC-1) by spraying onto a substrate of lithium silicate (Li2SiO3), a green inorganic binder. This coating combines self-cleaning and energy storage functionalities. The thermal characterization of PSC-1 revealed an enthalpy of phase transition of 92.95 J/g at a core-shell ratio of 1.5:1 and an HMDS to TEOS volume ratio of 1:1. Additionally, the thermal conductivity of PSC-1 was measured at 0.505 W/m∙K, which is approximately 53 % higher than that of pure paraffin. PSC-1 also demonstrated superior hydrophobicity, with a static water contact angle of 132.6°. Enhancing its practicality, the coating was subsequently dyed black and assessed for photothermal conversion efficiency, which was determined to be around 68 %. The integration of robust self-cleaning properties and high-efficiency thermal characteristics renders PSC-1 a highly promising material for broad applications in solar energy conversion and storage.

A Simple and User-Friendly Method for High-Quality Preparation of Pollen Grains for Scanning Electron Microscopy (SEM).

Pollen is becoming an increasingly important subject for molecular researchers in genetic engineering, plant breeding, and environmental monitoring. To broaden the scope of these studies, it is essential to develop accessible methods for scientists who are not specialized in palynology. The article presents a simplified technical procedure for preparing pollen grains for scanning electron microscopy (SEM). The protocol is convenient for any molecular laboratory due to its small set of reagents, ease of execution, low cost, does not require special equipment, and takes only one hour to complete. The high penetrating ability of formaldehyde and the final delicate dehydration using hexamethyldisilazane (HMDS) instead of critical point drying allow for sufficient preservation of the architecture of the aperture, which is considered a gateway for the passage of biomolecules. The method was successfully applied to pollen grains of representatives of dicotyledons (beetroot, petunia, radish, tomato and tobacco) and monocotyledons (lily, onion, corn, rye and wheat). Species studied included insect-pollinated (entomophilous) and wind-pollinated (anemophilous) species. A comparative analysis of the sizes of fresh living pollen grains under a light microscope and those prepared for SEM showed some shrinkage. Quantitative analysis of the degree of pollen grain shrinkage showed that this process depends on the initial shape of dry pollen grains, and the number and structure of apertures. The results support the theoretical model of the folding/unfolding pathways of pollen grains.

Microstructure, mechanical properties, and wettability of CrN and CrSiCN coatings with graded architectures

Protective CrN-based coatings are of interest for applications requiring a combination of corrosion resistance and toughness. Here, the processing-microstructure-properties relationships for metallic Cr, binary CrN, and quaternary CrSiCN coatings are reported. Hexamethyldisilazane (HMDS) was used as a single-source organosilicon precursor for Si and C during plasma-enhanced magnetron sputtering (PEMS). By varying the availability of reactive species during coating growth, graded coating architectures were produced. Scanning and transmission electron microscopy revealed that as Si and C content increased, the coating microstructure evolved from a coarse, columnar growth structure (0 at.% Si), to a nanocolumnar structure (3 at.% Si), and, finally, to a dense, nanoscale structure (6 at.% Si). Coating surface topography was characterized using optical microscopy and atomic force microscopy. While the CrSiCN coating deposited at the highest HMDS flow rate exhibited the lowest nanoscale surface roughness (Rq = 6.74 nm), it also had the greatest area fraction of microscopic surface defects. Evidence of the formation of secondary Cr2N phases within the graded interlayers of the coatings was acquired from selected area electron diffraction analysis. However, the practical adhesion of the coatings, as evaluated by the Rockwell C indentation test, was not adversely affected. Nanoindentation testing revealed that greater incorporation of Si and C into the CrN-based coatings increased coating hardness from 25.4 ± 1.6 GPa to 30.7 ± 1.8 GPa and decreased apparent elastic modulus from 295 ± 14 GPa to 284 ± 12 GPa. Contact angle goniometry was conducted to determine the wettability of the coatings. It was found that sessile water contact angles decreased from 86.5° ± 1.6° to 77.3° ± 2.1° as coating Si and C content increased.

Study on hydrophobic modification of starch‐based foam with fumigating and spraying

AbstractTo enhance water resistance of starch‐based foam, based on the porous and irregular surface feature of foam, fumigating hexamethyldisilazane (HMDS) and spraying nano‐SiO2/ethanol solution were utilized to enhance hydrophobic properties of the starch‐based foam. Homemade starch‐molded foams were used for hydrophobic modification studies, the results showed that fumigating HMDS can lead to the formation of “Si‐O‐C” bonds between HMDS and starch. Additionally, it can form more stable “Si‐O‐Si” bonds with nano‐SiO2 in the original composites, which can better adhere to the surface of the starch foam to effectively create a waterproof barrier layer. On the basis of HMDS fumigation modification, hydrophobicity was significantly enhanced by further spraying of nano‐SiO2/ethanol solution. When the mass ratio of nano‐SiO2 to ethanol was 6:100, the combination of HMDS and nano‐SiO2 was optimal, while making the roughness of the foam surface suitable, at which time, the contact angle reached 155°, the maximum value under this system, indicating that the hydrophobicity was optimal. The fumigation and spraying method can evenly and comprehensively act on the surface of the porous and irregular starch‐based foam, which facilitates the waterproof post‐treatment process of the industrial application process and has strong practical significance.Highlights Fumigated with HMDS, the starch foam's exhibit some hydrophobic effect. Fumigation followed by spraying is effective in enhancing the hydrophobicity of starch foams. Both the fumigation method and the spray method are suitable for the post‐treatment of hydrophobic of starch foams.

Enhanced performance of MoS2/SiO2 field-effect transistors by hexamethyldisilazane (HMDS) encapsulation

Scalable methods for improving the performance and stability of a field-effect transistor (FET) based on two-dimensional materials are crucial for its real applications. A scalable method of encapsulating the exfoliated MoS2 on the SiO2/Si substrate by hexamethyldisilazane (HMDS) is explored here for reducing the influence of interface traps and ambient contaminants. This leads to 25 times reduction in trap density, three times decrease in subthreshold swing, three times increase in the peak field-effect mobility, and a drastic reduction in hysteresis. This performance remains nearly the same after several weeks of ambient exposure of the device. This is attributed to the superhydrophobic nature of HMDS and the SiO2 surface hydrophobization by the formation of covalent bonds between the methyl groups of HMDS and silanol groups of SiO2.

Effect of hydrophobic materials on alkali-silica reaction-induced deterioration of mortar: A comparative study

The deterioration of mortar or concrete caused by the alkali-silica reaction (ASR) significantly depends on its susceptibility to moisture imbibition and exposure. This study investigated how applying hydrophobic materials in cement mortar prevents ASR-induced deterioration. Three hydrophobic materials were used, including a hexamethyldisilazane (HMDS) treated fumed-silica, a silane-based emulsion, and a silane-based cream. These hydrophobic materials were applied by directly coating the aggregates before mortar preparation or added directly to the mixture as admixtures. The effect of the applied hydrophobic materials on mortar properties was evaluated based on compressive strength, dynamic modulus, water absorption, and linear expansion. Furthermore, the microstructure and ionic distribution of alkalis from the aggregates interface were appraised using scanning electron microscope (SEM) and energy-dispersive X-ray spectroscopy (EDS) tests. The results were compared to a mortar with no admixtures and a mortar with 20% cement replaced by fly ash (a traditional method of ASR mitigation). Coating aggregates with hydrophobic fumed silica were more effective at reducing ASR-induced expansion than directly integrating the hydrophobic materials, although at a lower degree than fly ash.

Preparation of hyperbranched hydrophobic nano-silica and its superior needling-effect in PDMS defoam agent

Hydrophobic nano silica powder is a kind of important synergist to silicone defoaming agents. The large pore volume and branched chain conformation of silica nanoparticles present superior effects on defoaming properties. However, silica nanoparticles synthesized by liquid phase easily aggregate and pore collapse because of their high surface activity and polarity, leading to poorer dispersity and limited practicability. In this paper, a novel hydrophobic silica with a hyperbranched structure was designed through in-situ modifying method with hexamethyldisilazane (HMDS) and polydimethylsiloxane (PDMS) in the liquid phase. The trimethylsilanol generated by HMDS hydrolysis reacts quickly with the highly active hydroxyl groups on the silica, causing the surface properties of the nanoparticles to transform from polar to non-polar properties. The steric hindrance of the trimethyl silicon and the reduction of the surface polarity effectively prevent silica pores from collapsing and maintain the macropore structures to realize the hyperbranched silica. At the same time, the −Si (CH3)2− from PDMS endowed the hyperbranched silica with excellent hydrophobicity. When applied in the defoaming agent, the hydrophobicity of silica contributes to dewetting the foams, and the hyperbranched spatial structures play an enhanced needling effect. Therefore, this hydrophobic hyperbranched silica exhibited a surprising defoaming effect, which significantly reduced the defoaming time from 464.4 s to less than 2 s, superior to commercial defoaming silica (155.3 s). The defoaming efficiency reached 100 % within 2 s of the end of the shaking, and the defoamer antifoaming ability was improved to reach 27.5 min, which was 77 % higher than that of commercial defoamer.

Enhancing Electrochemical Sensing through Molecular Engineering of Reduced Graphene Oxide-Solution Interfaces and Remote Floating-Gate FET Analysis.

Two-dimensional nanomaterials such as reduced graphene oxide (rGO) have captured significant attention in the realm of field-effect transistor (FET) sensors due to their inherent high sensitivity and cost-effective manufacturing. Despite their attraction, a comprehensive understanding of rGO-solution interfaces (specifically, electrochemical interfacial properties influenced by linker molecules and surface chemistry) remains challenging, given the limited capability of analytical tools to directly measure intricate solution interface properties. In this study, we introduce an analytical tool designed to directly measure the surface charge density of the rGO-solution interface leveraging the remote floating-gate FET (RFGFET) platform. Our methodology involves characterizing the electrochemical properties of rGO, which are influenced by adhesion layers between SiO2 and rGO, such as (3-aminopropyl)trimethoxysilane (APTMS) and hexamethyldisilazane (HMDS). The hydrophilic nature of APTMS facilitates the acceptance of oxygen-rich rGO, resulting in a noteworthy pH sensitivity of 56.8 mV/pH at the rGO-solution interface. Conversely, hydrophobic HMDS significantly suppresses the pH sensitivity from the rGO-solution interface, attributed to the graphitic carbon-rich surface of rGO. Consequently, the carbon-rich surface facilitates a denser arrangement of 1-pyrenebutyric acid N-hydroxysuccinimide ester linkers for functionalizing capturing probes on rGO, resulting in an enhanced sensitivity of lead ions by 32% in our proof-of-concept test.

Cotton fabric surface treatment by plasma-deposited hexamethyldisilazane thin films

In the realm of fabric finishing, achieving the best wettability in cotton fabric is often a desired outcome. To accomplish this, a plasma-enhanced chemical vapor deposition (PECVD) system was used to deposit Hexamethyldisilazane (HMDSN) thin films onto cotton fabric for two different durations: 15 and 30 minutes. Various fabric properties were evaluated to determine the effectiveness of the treatment, including wettability, surface morphology, chemical structure, the effect of deposition on fabric stiffness, and the film fastness on the abrasion and washing. These properties were assessed using SEM, FTIR, and Martindale tester. Results indicated that both treatment durations improved the fabric's wicking ability. However, the film did not have a good fastness on abrasion and washing.

Preparation of Asymmetric Al2O3-SiO2 Janus Nanoparticles in Aqueous Phase and Its Interfacial Property.

In this study, asymmetric Al2O3-SiO2 Janus nanoparticles with a dumbbell-like structure were synthesized by a facile chemical process in the aqueous phase. Prior to synthesis, Al2O3 nanoparticles in hydrosol were amino-modified using 3-aminopropyl triethoxysilane (KH550) and then carboxyl acid-functionalized using a ring-opening reaction of the amine functions with succinic anhydride, imparting unique anionic properties to the Al2O3 end. SiO2 nanoparticles were rendered hydrophobic through modification with hexamethyldisilazane (HMDS) and further functionalized with 3-chloropropyl triethoxysilane (KH230). The two nanoparticle hydrosols were then mixed, and the asymmetric Al2O3-SiO2 Janus nanoparticles were synthesized via the reaction between the -NH2 and -CH2Cl groups. The prepared Janus nanoparticles were primarily characterized by dynamic light scattering (DLS), Zeta potential (ZP), and transmission electron microscopy (TEM). The results indicated that about 90% of the modified Al2O3 and SiO2 nanoparticles were covalently coupled in a one-to-one manner to form the dominant dumbbell-like structure. These Janus nanoparticles exhibit amphiphilic properties, making them highly promising surfactants for emulsifying oil-water mixtures.

Izrada laminata upotrebom kompozita od drva i otpadne gume

This study aimed to develop laminate flooring composite using a combination of wood and waste tire rubber (WTR). Plywood panels were produced by using beech (Fagus orientalis), alder (Alnus glutinosa), and poplar (Populus) veneers in a 7-ply configuration. To enhance the physical-mechanical properties of the panels, three loadings of nano-SiO2 (0, 2, and 4 wt%) along with 2 wt% of hexamethyldisilazane (HMDS) were added. Commercial urea-formaldehyde (UF) resin and methylene diphenyl diisocyanate (MDI) were used to bind the wood layers and rubber layers together. The mechanical properties, including modulus of rupture (MOR), modulus of elasticity (MOE), impact strength (IS), hardness strength (HS), and physical properties, such as density (D), water uptake (WU), and thickness swelling (TS), were evaluated. The results showed that increasing the WTR content led to improvements in the physical properties (D, WU, and TS), while negatively affecting the mechanical properties (MOR, MOE, IS, and HS) of the resulting panels. However, the addition of nano-SiO2 improved both the physical and mechanical properties (MOR, MOE, and HS) of the panels. Furthermore, it was observed that the mechanical properties were enhanced with increasing the number of beech layers, although the WU of panels decreased compared to panels made with alder and poplar. Overall, the improvement in the physical properties of the panels followed the order of the arrangement of rubber layers &amp;gt; nano-SiO2 content &amp;gt; veneer layers.

Self-Assembled Organic Aerogel and Sponges for Rapid and Effective Absorption of Oil from Oil- Contaminated Soil Samples

Crude oil spills pose significant risks to both marine ecosystems and human populations. Traditional remediation techniques have their limitations, prompting the exploration of innovative approaches. This study introduces a novel method involving the synthesis of a self-assembled sponge and organic aerogel. These materials were further modified using hexamethyldisilazane (HMDS) and dodecyltrimethoxysilane (DTMS) to impart hydrophobic properties. Characterization via SEM examination and FTIR spectroscopy revealed distinctive features, including bands at approximately 1050 cm-1 and 790 cm-1, indicative of alkyl side chain stretching by Si-O-C and C-H, respectively, enhancing the hydrophobicity of the materials. The SEM images depicted a random rough surface with abundant pores, facilitating oil adsorption from contaminated samples. Notably, after seven cycles of use with contaminated soil samples, the organic aerogel exhibited exceptional oil removal capacity, achieving 100% efficiency according to the Sears method. This innovative sponge and organic aerogel-based approach represents a promising advancement in environmental remediation, offering a highly efficient and sustainable solution for oil spill cleanup.

Comparison of superhydrophobic biodegradable PLA films with fluorine-free hexamethyldisilazane grafted silica and mesoporous silica particles

This study reports the surface coating of fluorine-free hexamethyldisilazane (HMDS) on non-porous silica particles (SPs) and mesoporous silica particles (MSPs), with nanopores arranged in the straight channels, and compares the degree of superhydrophobicity by coating them on biodegradable PLA film by gravure process. The particle sizes of SPs and MSPs are 50 nm and 800 nm, and the amount of HMDS grafted onto SPs and MSPs is 0.5% and 9.5%, respectively. The superhydrophobicity of these particles is confirmed by the measurement of water contact angle (WCA) as a function of HMDS concentration for SPs and MSPs from 0 to 1.6 M, respectively. The WCA of HMDS@SPs and HMDS@MSPs grafted with 1.6 M of HMDS is 152° and 151° (WCA of unmodified SPs and MSPs is 13.85° and 27.65°). To apply superhydrophobic PLA film coating, 5 wt% of HMDS@SPs and HMDS@MSPs were mixed with gravure solution and then coated on biodegradable polylactic acid (PLA) film. The results showed that the WCA of PLA film with HMDS@SPs and HMDS@MSPs were 98.40° and 152.31°, respectively. This remarkable difference in WCA is due to the dissociation of HMDS molecules grafted on the surface of SPs and MSPs, which are easily separated by the gravure solvent. For MSPs materials composed of many nanopores, the dissociated HMDS molecules are initially released into the solution but are retained within the nanopores. Therefore, the residual amount of HMDS molecules dissociated by the gravure solution is much higher in HMDS@MSPs than in HMDS@SPs.

Comparative investigation on organosilicon film growth by cyclonic plasma using hexamethyldisilazane and hexamethyldisilazane/nitrogen gas mixture

This study aimed to discover the surface characteristics of cyclonic plasma‐deposited films and the effect of nitrogen gas addition. The influence of nitrogen gas addition on the surface characteristics of organosilicon films in hexamethyldisilazane (HMDSN) and HMDSN/nitrogen (HMDSN/N2) cyclonic plasmas at atmospheric pressure was evaluated. It was found that the addition of nitrogen gas is a crucial factor affecting organosilicon film growth in the plasma cyclone in one atmosphere. SEM, AFM, and ATR‐FTIR results indicated that on adding nitrogen gas, the surface morphology became rougher, the peak corresponding to the Si–O–Si group was detected at approximately 1050 cm−1, the degree of porosity was relatively low, and the proportion of the SiCHx group decreased. In general, the surface energies of the films deposited in the HMDSN discharge and the HMDSN/N2 gas mixture discharge exhibited similar features. SEM and AFM evaluations showed high roughness values of 44.5 nm for the film formation in the HMDSN/N2 gas mixture discharge, while the films grown in the HMDSN discharge exhibited a relatively flat surface with a roughness of 24.5 nm. Based on ATR‐FTIR detection, cyclonic plasma‐deposited films deposited in the HMDSN discharge obtained organic moieties, while the films generated in the HMDSN/N2 gas mixture discharge exhibited strong Si–O–Si absorption signals. A possible nano‐organosilicon film growth that prevails in atmospheric pressure plasma deposition is proposed based on atmospheric‐pressure plasma chemistry, nitrogen gas addition, and experimental observations.

Fabrication of Sn(IV)porphyrin-Imbedded Silica Aerogel Composite

Optoelectronic functional composite materials with porous structures are of great importance in various fields. A hybrid composite (SnP@SiA) composed of (trans-dihydroxo)(5,10,15,20-tetraphenylporphyrinato)tin(IV) (SnP) in silica aerogel (SiA) was successfully fabricated through the reaction of SnP with silanol groups of SiA in the presence of hexamethyldisilazane (HMDS). SnP@SiA was then characterized using various instrumental techniques. The zeta potential for SnP@SiA (−11.62 mV) was found to be less negative than that for SiA (−18.26 mV), indicating that the surface of SnP@SiA is covered by hydrophobic species such as SnP and trimethylsilyl groups. The Brunauer–Emmett–Teller (BET) surface area, pore volume, and average pore size of SnP@SiA are 697.07 m2/g, 1.69 cm3/g, and 8.45 nm, respectively, making it a suitable composite for catalytic applications. SnP@SiA, a photocatalyst with high porosity and a large surface area, yields promising performance in the photodegradation of acid orange 7 (AO7) under visible light irradiation in aqueous solution. This hybrid composite exhibited the desirable properties of aerogels along with the photoelectronic features of porphyrins. Therefore, this porphyrin-imbedded mesoporous material has valuable potential in various applications such as photocatalysis, light energy conversion, biochemical sensors, and gas storage.

Targeted Chemical Processing Initiating Biosome Action-Potential-Matched Artificial Synapses for the Brain-Machine Interface.

A great gap still exists between artificial synapses and their biological counterparts in operation voltage or stimulation duration. Here, an artificial synaptic device based on a thin-film transistor with an operating voltage (-50-50 mV) analogous to biological action potential is developed by targeted chemical processing with the help of supercritical fluids. Chemical molecules [hexamethyldisilazane (HMDS)] are elaborately chosen and brought into the target interface to form charge receptors through supercritical processing. These charge receptors with the ability of capturing electrons mimic neurotransmitter receptors in terms of mechanism and constitute key players accounting for the synaptic behaviors. The relatively lower electrical barrier height contributes to an action-potential-matched operating voltage and considerably low power consumption (∼1 pJ/synaptic event), minimizing the divide with biological synapse for a seamless linkage to the biosystem or brain-machine interface. The stable synaptic behaviors also lead to near-ideal accuracy in pattern recognition. Moreover, this methodology that introduces chemical groups into a target interface can be viewed as a platform technology that could be adapted to other conventional devices with suitable chemical molecules to reach designed synaptic behaviors. This environmentally friendly and low-temperature processing method, which can be performed even after device fabrication, has the potential to play an important role in the future development of bionic devices.

Preventing ASR-induced deteriorations with hydrophobic aggregates- a feasibility study

Concrete deterioration due to alkali-silica reaction (ASR) is one of the main durability concerns. This study explores the feasibility of minimizing ASR-induced deterioration by enhancing aggregates' hydrophobicity. Mortar samples with highly reactive aggregates were prepared. The aggregates were modified through coating with hexamethyldisilazane (HMDS) pretreated fumed silica for improved hydrophobicity. The ASR progression of the specimens prepared with nontreated (control-NHA), washed-coated (WHA), and non-washed coated aggregates (HA) was assessed using compressive strength, linear expansion, and dynamic modulus of elasticity tests. In addition, an ASR detection reagent was used to study the extent of deterioration of the mortar specimens. Furthermore, the microstructure and chemical compositions of the ASR-affected mortar were studied using scanning electron microscopy (SEM) and energy-dispersed X-ray analysis (EDX). The research found that although using hydrophobic aggregates may reduce the compressive strength, increasing the hydrophobicity of aggregates can significantly reduce ASR-induced expansion, minimize cracking, and prevent warping.

Phosphorus fluoride exchange: Multidimensional catalytic click chemistry from phosphorus connective hubs

Phosphorus Fluoride Exchange (PFEx) represents a cutting-edge advancement in catalytic click-reaction technology. Drawing inspiration from Nature's phosphate connectors, PFEx facilitates the reliable coupling of P(V)-F loaded hubs with aryl alcohols, alkyl alcohols, and amines to produce stable, multidimensional P(V)-O and P(V)-N linked products. The rate of P-F exchange is significantly enhanced by Lewis amine base catalysis, such as 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD). PFEx substrates containing multiple P-F bonds are capable of selective, serial exchange reactions via judicious catalyst selection. In fewer than four synthetic steps, controlled projections can be deliberately incorporated along three of the four tetrahedral axes departing from the P(V) central hub, thus taking full advantage of the potential for generating three-dimensional diversity. Furthermore, late-stage functionalization of drugs and drug fragments can be achieved with the polyvalent PFEx hub, hexafluorocyclotriphosphazene (HFP), as has been demonstrated in prior research.