Thermal Curing Research Articles

Facile synthesis of polyhedral oligomeric silsesquioxanes with excellent thermosetting, fibrous and crystalline properties

The development of multifunctional polyhedral oligomeric silsesquioxanes (POSS) that are more serialized than traditional POSS is essential to reduce the economic investment and expand the category of high-performance POSS. This work employed a simple one-step method to synthesize a series of different physical states of methacryloxypropyl-phenyl POSS (AcPhPOSS). The FTIR, NMR and MS results showed that the products were mainly composed of regular T8, T10 and T12 cage-like structures, and the outer periphery of the AcPhPOSS cage carried different proportions of flexible methacryloxypropyl (R1) and rigid phenyl (R2) groups. In addition, the curable, fibrous, and crystalline properties of liquid, semi-solid, and powder AcPhPOSS were studied through thermal curing, electrospinning, and crystallization methods, respectively. The results showed that AcPhPOSS in three different states, especially AcPhPOSS@1:0 (liquid), AcPhPOSS@1:3 (semi-solid) and AcPhPOSS@0:1 (powder), exhibited good thermal curing properties, fiber and crystallization, respectively. Hence, this work proposes a facile strategy for producing multifunctional materials with good curing properties, fiber-forming properties, and crystallinity, which have broad application potential in thermosetting resins, fiber materials, and single crystal materials.

Multifunctional superhydrophobic sugarcane bagasse capable of efficiently separating oil-water mixtures and degrading MB

Biodegradable and low-cost superhydrophobic absorption materials are still urgently required for the removal of organic compounds from sewage. In this study, sugarcane bagasse (SCB), an abundant and readily available byproduct from sugarcane industries, was used as substrate to fabricate the superhydrophobic adsorbent through a facile dip-coating technique. Firstly, β-FeOOH particles were in-situ grown on the SCB surface, which was further decorated with SiO2 particles. Next, the modified SCB were coated with benzoxazine based on cardanol and dodecylamine (CD) followed by a thermal curing to obtain a superhydrophobic SCB (PC-D/β-FeOOH@SiO2/SCB) with a water contact angle (WCA) of 154°. PC-D/β-FeOOH@SiO2/SCB not only exhibited excellent oil absorption capacities in the range of 11.8 to 22.6 g/g for various organic solvents and oils, but also could successfully separate immiscible oil-water mixtures and emulsions with a separation efficiency of over 99.1 %. After 30 cycles of use, the absorption capacity of the modified SCB only displayed a slight decrease and its separation efficiencies for immiscible oil-water mixture, water-in-oil and oil-in-water emulsions are all more than 99.2 %, meanwhile, all these repeatedly used SCB still maintained a superhydrophobicity, demonstrating an outstanding reusability. Moreover, the WCA of PC-D/β-FeOOH@SiO2/SCB was still higher than 150o after 48 h of immersion in HCl, NaOH and NaCl solutions, exhibiting a satisfactory chemical stability. Besides, the prepared SCB also possessed a high photocatalytic degradation activity to methylene blue. Therefore, this work not only provides a sustainable and cheap superhydrophobic absorbent for wastewater treatment, but also presents a route for the better utilization of SCB.

Phenylethynyl-Terminated Imide Oligomer-Based Thermoset Resins.

Phenylethynyl-terminated imide (PETI) oligomers are highly valued for their diverse applications in films, moldings, adhesives, and composite material matrices. PETIs can be synthesized at varying molecular weights, enabling the fine-tuning of their properties to meet specific application requirements. Upon thermal curing, these oligomers form super-rigid network structures that enhance solvent resistance, increase glass-transition temperatures, and improve elastic moduli. Their low molecular weights and melt viscosities further facilitate processing, making them particularly suitable for composites and adhesive bonding. This review examines recent advancements in developing ultra-high-temperature PETIs, focusing on their structure-processing-properties relationships. It begins with an overview of the historical background and key physicochemical characteristics of PETIs, followed by a detailed discussion of PETIs synthesized from monomers featuring noncoplanar configurations (including kink and cardo structures), fluorinated groups, flexible linkages, and liquid crystalline mesogenic structures. The review concludes by addressing current challenges in this research field and exploring potential future directions.

Hydrogel-Embedded Polydimethylsiloxane Contact Lens for Ocular Drug Delivery.

Topical administration is the commonly preferred method of administering ophthalmic formulations, with the majority of available medications in the form of eye drops or ointments. However, the topical application of ophthalmological medications has less bioavailability and a short residence time because of the physiological and anatomical constraints of the eye, making efficient ophthalmic drug delivery a challenging task. Microfluidic contact lenses have the advantage of delivering drugs into the eye in a controlled and on-demand manner. Here, we showcase the use of hydrogel-embedded microcavities on PDMS-based contact lenses for ocular drug delivery applications. The fabrication technique adopted here is the spontaneous formation of the spherical cavity by hydrogel monomer droplet, followed by the simultaneous thermal curing of hydrogel and PDMS, creating a spherical cavity as small as 150 μm. The spherical cavity is embedded with pH-responsive hydrogel for on-demand drug delivery. The drug loaded in the hydrogel matrix is released into the ocular environment by diffusion. The spherical cavity with a narrow opening restricts the diffusion to a minimum under normal ocular pH conditions(pH > 6). When the ocular pH reduces (pH < 6), the pH-responsive hydrogel inside the spherical cavity deswell and accelerates the drug release.

Photothermal synergistic curing of one-component epoxy resin adhesive based on active monomer mechanism

ABSTRACT One-component epoxy resin adhesives with Ethylamine-boron trifluoride (BF3-MEA) have become popular choices for electronic applications due to their lower curing temperatures and excellent storage stability. However, in the traditional thermal curing process for these adhesives, which relies on the Active Chain End (ACE) mechanism, the formation of cyclic oligomers can compromise their mechanical performance. In this study, we prepared a series of novel one-component adhesives using Diglycidyl-4,5-epoxy-cyclohexane-1,2-dicarboxylate (TDE-85) epoxy resin, Bis [4-(diphenylsulfonio) phenyl] sulfide bis (hexafluoroantimonate) (Photoinitiator 1176), and BF3-MEA through blending, and successfully achieved photothermal dual-curing. We systematically explored various adhesive ratios and curing conditions. Compared to adhesives treated solely by thermal curing, those subjected to photothermal dual-curing exhibited the best shear strength of 13.9 ± 0.7 MPa and a hardness of 88 ± 4 Shore A, representing improvements of 118.2% and 18.9%, respectively. Additionally, the study demonstrated that hydroxyl groups produced by photocuring effectively inhibit the ACE mechanism and promote the Active Monomer (AM) mechanism, which becomes dominant. In summary, the photothermal synergistic curing approach, with the AM mechanism as dominant, prevents the formation of cyclic oligomers and enhances mechanical performance. This study offers a new approach for adhesives used in electronic devices.

Bio-Based Self-Healing Epoxy Vitrimers with Dynamic Imine and Disulfide Bonds Derived from Vanillin, Cystamine, and Dimer Diamine.

The condensation reactions of 4,4'-(ethane-1,2-diylbis (oxy)) bis(3-methoxybenzaldehyde) (VV) with cystamine, 1,6-hexamenthylene diamine, and a dimer diamine (PriamineTM 1075) produced three types of vanillin-derived imine-and disulfide-containing diamines (VC, VH, and VD, respectively). Thermal curing reactions of polyglycerol polyglycidyl ether with VD and mixtures of VC/VD and VH/VD produced bio-based epoxy vitrimers (BEV-VD, BEV-VC/VD, and BEV-VH/VD, respectively). The degree of swelling and gel fraction tests revealed the formation of a network structure, and the crosslinking density increased with a decreasing VD fraction. The glass transition temperature, tensile strength, and tensile modulus of the cured films increased as the VD fraction decreased. In contrast, the thermal degradation temperature of the cured films increased as the VD fraction increased. All the cured films were healed by hot pressing at 120 °C for 2 h under 1 MPa at least three times. The healing efficiencies, based on tensile strength after the first healing treatment, were 75-78%, which gradually decreased as the healing cycle was repeated. When imine-and disulfide-containing BEV-VC/VD and imine-containing BEV-VH/VD with the same VC/VD and VH/VD ratios were used, the former exhibited a slightly higher healing efficiency.

Development of HEMA-Succinic Acid-PEG Bio-Based Monomers for High-Performance Hydrogels in Regenerative Medicine.

In recent years, hydrogels have found a special place in regenerative medicine for tissue repair, rehabilitation, and drug delivery. To be used in regenerative medicine, hydrogels must have desirable physical, chemical, and biological properties. In this study, a new biomonomer based on hydroxyethyl methacrylate-succinic acid-polyethylene glycol 200 (HEMA-Suc-PEG) was synthesized and characterized. Then, using the synthesized monomers and different ratios of polyethylene glycol diacrylate (PEGDA) as a crosslinker, biocompatible hydrogels were synthesized through thermal and UV curing methods. The mechanical, physical, chemical, and biological properties of the hydrogels and the behavior of endothelial cells, an essential component of the cardiovascular system, were evaluated. The results showed that the hydrogel synthesized with 0.2 g of PEGDA (UV curing) has desirable mechanical and physical properties. Biological tests showed that these hydrogels are not only nontoxic to cells but also enhance cell adhesion. Therefore, the hydrogel containing the synthesized monomer HEMA-Suc-PEG and 0.2 g of PEGDA has the potential to be used in the cardiovascular system.

Efficacy of Acacia Gum Biopolymer in Strength Improvement of Silty and Clay Soils under Varying Curing Conditions

Acacia gum (AG), a polysaccharide biopolymer, has been adopted to improve the strength of three cohesive soils by subjecting them to diverse environmental aging conditions. Being a polysaccharide and a potentially sustainable construction material, the AG yielded flexible film-like threads after 48 h upon hydration, and its pH value of 4.9 varied marginally with the aging of the stabilized soils. The soil samples for the geotechnical evaluation were subjected to wet mixing and were tested under their Optimum Moisture Content (OMC), as determined by the light compaction method. The addition of AG modified the consistency indices of the soils due to the presence of hydroxyl groups in AG, which also led to a rise in OMC and reduction in Maximum Dry Unit weight (MDU). The Unconfined Compressive Strength (UCS) and California Bearing Ratio (CBR) were determined under thermal curing at 333 K as well as on the same day of sample preparation. The least performing condition of the soil’s CBR was evaluated under submerged conditions after allowing the AG-stabilized specimens to air-cure for a period of 1 week. The UCS specimens tested after 7 days were subjected to the initial 7 days of thermal curing at 333 K. A dosage of 1.5% of AG yielded the UCS of 2530 kN/m2 and CBR of 98.3%, respectively, for the low compressible clay (LCC) after subjecting the sample to 333 K temperature for 1 week. The viscosity of the AG was found to be 214.7 cP at 2% dosage. Scanning Electron Microscopy (SEM), Fourier Transform Infrared Spectroscopy (FTIR), and average particle size determination revealed the filling of pores by AG gel solution, adsorption, and hydrogen bonding, which led to improvements in macroproperties.

UV/thermal dual-cured MWCNTs composites for pipeline rehabilitation: Mechanical properties and damage analysis

Deformation and damage in underground pipelines remain challenging to monitor over the long term due to sensor degradation caused by corrosive substances present in the pipelines. This study investigates the potential of incorporating multi-walled carbon nanotubes (MWCNTs) into ultraviolet-cured-in-place pipe (UV-CIPP) material, a widely adopted trenchless repair technique, to enhance performance and enable deformation monitoring. A UV/thermal dual-curing strategy is introduced to mitigate the significant reduction in light transmittance caused by the inclusion of MWCNTs in the composite material. The addition of MWCNTs led to a 94.86 % reduction in light transmittance through glass fibers. However, this issue was effectively resolved through the incorporation of thermal curing, allowing for the production of ultra-high-strength composites using only three layers of fibers within a short curing time. Under optimal conditions (0.2 wt% MWCNTs with the impregnation layer on top), the flexural strength and modulus reached 442.75 MPa and 15.58 GPa, respectively, marking improvements of 14.01 % and 45.2 % over the base material. Additionally, the hardness on the composite's backside increased by 10.95 % compared to the front, indicating enhanced reinforcement. The tensile strength of braided glass fibers improved by 42.31 % and 197.54 % with the addition of 0.2 wt% and 1.0 wt% MWCNTs, respectively. Failure modes varied based on the location of the sensing layer, but all specimens eventually failed due to resin cracking, delamination of the MWCNTs-impregnated layer, and fiber fractures. The UV/thermal dual-cured composite material developed for pipeline rehabilitation in this study exhibits ultra-high strength and shows significant potential for multifunctional sensing applications.

Impact of Different Substituents on Thermal Curing and Flame‐Retardant Behaviors of 2,2′‐Methylenebis(4‐nitrophenol)‐Based (Poly)benzoxazines

AbstractPolymerization of benzoxazine at low temperatures is important because the high‐temperature polymerization restricts its utilization in a wide range of applications, though the polybenzoxazines possess excellent properties. The effect of nitro functionality and various substituents on the thermal curing of benzoxazine and the flame‐retardant behavior are mainly focused in this study. In the present work, 2,2′‐methylenebis(4‐nitrophenol) (NBP) was synthesized from 4‐nitrophenol and is used for the synthesis of benzoxazine derivatives with five structurally different aromatic amines. As the synthesized benzoxazine contains nitro‐groups in the phenolic part and various substituted functional groups in different positions of the amine part, the curing temperatures significantly varied among each other. The effect of different substituents on the thermal ring‐opening polymerization (ROP) of benzoxazine was studied with exotherms of the DSC thermogram. The 4‐fluoroaniline and 2‐aminobenzotrifluoride‐based benzoxazines show the highest and lowest curing temperatures of 272 and 189 °C, respectively, which is based on their substituents and their position that can act as an internal catalyst. The resulting polybenzoxazines possess higher char yield (49% ≤ 63%) and higher values of LOI (37 ≤ 43) including excellent flame retardant (UL94‐V0) behaviors suggesting that the polybenzoxazine can be used as coatings for high‐performance industrial applications.

Efficient synthesis of main chain thermosetting polybenzoxazine resin containing tert-butylcyclohexanone and diphenylmethane units for supercapacitor energy storage

Ring-opening polymerization (ROP) can be utilized to synthesize polybenzoxazine (PBZ) precursors from their respective benzoxazine monomers, resulting in thermosetting phenolic resins. In this study, we synthesized DADCA-DADPM BZ using 4-(tert-butyl)-2,6-bis((E)-4-hydroxybenzalidene)cyclohexan-1-one (DADCA) and 4,4′-diamino-diphenylmethane (DADPM) with paraformaldehyde. The resulting DADCA-DADPM BZ and poly(DADCA-DADPM BZ)_X materials were obtained after thermal curing polymerization at temperatures ranging from 110 to 250 °C were employed as electroactive materials in electrode preparation for supercapacitors (SCs). Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) revealed a thermal curing temperature of 230 °C, a char yield of 35 wt%, and a decomposition temperature (Td10) of 288 °C. The electroactive material DADCA-DADPM BZ and poly(DADCA-DADPM BZ)_X materials were evaluated for their suitability in SCs, showing a specific capacitance ranging from 84.6 to 166.6 F g−1, depending on the thermal curing temperature (110–250 °C). Notably, the poly(DADCA-DADPM BZ)_250 retained 84 % of its efficiency after 5000 consecutive cycles at 10 A g−1, highlighting its potential for recyclability.

Accelerated carbonation of alkali-activated vibro-compacted pervious concrete paving blocks

This study explores the use of an accelerated carbonation curing method to enhance the performance of non-structural precast alkali-activated fly ash pervious concrete paving blocks. Using a predefined production process, pervious paving blocks measuring 200 mm × 100 mm × 60 mm were manufactured and subjected to a 3-stage curing process. The blocks were produced with a dry consistence to allow for vibrocompaction, closely mirroring the manufacturing techniques used in the precast industry and enabling immediate demoulding. Initially, all blocks underwent thermal curing at 70 °C for 24 hours, followed by storage in a climatic chamber (20 ± 3 °C, 65 ± 10 % relative humidity) for 7–14 days. Finally, they were exposed to a carbonation chamber with 5 % CO2 at 23 ± 2 °C, and 60 ± 10 % RH for up to 7 days. Blocks cured without carbonation served as control specimens. All blocks were tested following the European standard EN 1338, which governs the conformity of conventional concrete pavement blocks. Additional properties such as water permeability and water stability were also assessed. The results demonstrated that the accelerated carbonation curing significantly improved the performance of the blocks. Increases of 30 % and 60 % in compressive and splitting tensile strengths, respectively, were reported for the 7-day CO2-cured blocks when compared to their control counterparts. The 7-day carbon-cured blocks showed significantly improved abrasion resistance, with mass loss due to abrasion decreasing from 8.2 % to 5.6 % with 7 days of CO2 exposure. Additionally, microstructural enhancements were observed for the carbonated specimens, positively impacting their overall performance and making them compliant with the standard for practical paving block applications. However, further research is recommended to explore automation in the production process to ensure consistent results and facilitate future standardisation and certification of these blocks.

Characterization and application of fine aggregate from Rio Branco do Sul – PR with quartz filler additions: innovations in concrete performance

Understanding the properties of a material is essential to ensure its efficient application and achieve good results. This study addresses the characterization and applicability of quartz sand from the Rio Branco do Sul region, Paraná (PR), Brazil, in civil construction, focusing on procedures such as ceramic block laying, plastering, and rendering. Additionally, quartz filler (quartz powder) was added as a pozzolanic additive in fractions of 10% and 20% relative to the weight of the cement, along with samples without additives, to compare the results. To evaluate performance, the test specimens were subjected to two curing processes: thermal curing, aimed at activating pozzolanic reactions between the quartz powder and the chemical components of the concrete; and wet curing, which, although it does not stimulate chemical reactions, preserves the physical effects of the addition, such as reducing the concrete’s porosity and increasing its compressive strength. The specimens were analyzed at 7, 14, 21, and 28 days of age.

Evaluation of the effect of curing conditions on compressive strength and microstructure of alkali-activated binders

Alkali-activated binders (AABs) are increasingly researched as sustainable alternatives to ordinary Portland cement (OPC), providing comparable strength. In recent years there has been a growing interest in studies focusing on the development of suitable composites and their fabrication methods. Composites' properties are significantly affected by temperature, humidity, formulations, and constituent types. Therefore, it is essential to understand these factors comprehensively to obtain the desired adequacy to use. This article aims to assess the impact of (i) temperature through ambient curing (25°C) and thermal curing (50°C for 24 hours), (ii) exposure to air (isolated or exposed to the air atmosphere), and (iii) susceptible to external humidity (air contacted or submerged) as curing conditions. The evaluation encompassed compressive strength tests at 1, 28, 63, and 91 days, along with microstructural evaluation through morphology analysis and incidence of voids. Digital image processing (DIP) through ImageJ software was employed. The AAB proposed consisted of fly ash (FA) and steel slag from the Basic Oxygen Furnace (BOF) process as precursors, with sodium hydroxide (NaOH) and sodium silicate (NaSi2O3) as alkali activators, applied in mortar production. Compressive strength results revealed that mortar subjected to thermal curing, isolated from air contact and external humidity, exhibited the highest strength outcome, with 46.05 MPa. Microstructural analysis indicated the formation of hydrated aluminosilicate gels and the presence of voids, including partially reacted particles and microcracks. The DIP analysis of the sectional area demonstrated that void incidence under 50 µm2 predominantly did not affect compressive strength.

Biomorphic porous ceramics obtained by infiltration of a Si-based preceramic polymer into poplar wood templates

In this work, a comprehensive and detailed study about the development and characterization of biomorphic porous SiOC/SiC/Si3N4/C-based ceramics was addressed with an integral approach. The materials were obtained using a novel processing route involving the infiltration of a Si-based preceramic polymer into activated poplar wood templates, thermal curing and N2 pyrolysis. The physical, structural, microstructural, and textural properties mostly depended on the degree of infiltration reached and the pyrolysis temperature used. All the developed porous microstructures exhibited the poplar wood´s features. It is worth noting the development of macropores with confined Si3N4 crystals, and particularly in the samples pyrolyzed at 1500 and 1600 °C, one-dimensional Si-based nanostructures, and micro- and mesopores located in cavity walls and within arrangements of the one-dimensional structures, mainly in the materials pyrolyzed at 1400 and 1500 °C. The last materials presented the highest specific surface area values, thus making them potential candidates in catalysts.

Thermal stability and thermal degradation kinetics of urea-formaldehyde resin modified by sodium lignosulfonate

ABSTRACT In this paper, an environmentally friendly urea-formaldehyde resin (UF) was prepared by using sodium lignosulfonate (SL) as a modifier. According to the basic properties of the resin, the strength of the plywood and the formaldehyde emission, the optimum addition amount of SL was determined. At the same time, the thermal curing and thermal degradation behavior of the resin were studied. The results show that the addition of SL can significantly reduce the formaldehyde emission of plywood. When the addition amount of SL was 1%, the wet bonding strength and formaldehyde emission of SL-modified UF (SL-UF) resin were 1.28 MPa and 0.35 mg·L−1, respectively, which were 23% higher and 71% lower than those of UF resin. Moreover, the initial curing temperature of SL-UF resin is lower, but the thermal curing activation energy is higher. SL also has a significant effect on the thermal degradation performance of UF resin. SL is a modifier that can effectively improve the performance of UF.

Enhanced oxidation resistance and electrochemical performance of PEMFC gas diffusion layer through [EMIM][TFSI] ionic liquid coating

The performance and durability of Proton Exchange Membrane Fuel Cells (PEMFCs) are critically hindered by the oxidation susceptibility of graphite felt gas diffusion layers (GDLs). This study addresses this challenge by employing a protective coating of 1-Ethyl-3-methylimidazolium Bis(trifluoromethyl sulfonyl)imide ([EMIM][TFSI]) on the GDL through a dip-coating method, followed by thermal curing to ensure uniform distribution and strong adherence. Comprehensive characterization, including Scanning Electron Microscopy (SEM), X-ray Diffraction (XRD), X-ray Photoelectron Spectroscopy (XPS), and Fourier-Transform Infrared Spectroscopy (FTIR), confirmed the homogeneous coating, adhesion, and maintained porosity and gas diffusion properties of the GDL. The coated GDL exhibited a substantial increase in oxidation resistance, resulting in higher hydrophobicity with a contact angle of approximately 131°, compared to 96° for the uncoated GDL. Electrochemical analyses revealed that the [EMIM][TFSI]-coated GDL achieved a current density of 27 mA cm−2 at 0.925 V, surpassing the 19 mA cm−2 of the uncoated GDL at 0.91 V during cyclic voltammetry (CV) analysis. This study is limited by the short-term stability tests and the specific environmental conditions under which the experiments were conducted. Future work will focus on optimizing the coating process for varied environmental conditions and exploring the scalability of this technique for practical applications.

Impacts of Curing-Induced Phase Segregation in Silicon Nanoparticle-Based Electrodes

We report the investigation of silicon nanoparticle composite anodes for Li-ion batteries, using a combination of two nm-scale atomic force microscopy-based techniques: scanning spreading resistance microscopy for electrical conduction mapping and contact resonance and force volume for elastic modulus mapping, along with scanning electron microscopy-based energy dispersion spectroscopy, nanoindentation, and electrochemical analysis. Thermally curing the composite anode—made of polyethylene oxide-treated Si nanoparticles, carbon black, and polyimide binder—reportedly improves the anode electrochemical performance significantly. This work demonstrates phase segregation resulting from thermal curing, where alternating bands of carbon and silicon active material are observed. This electrode morphology is retained after extensive cycling, where the electrical conduction of the carbon-rich bands remains relatively unchanged, but the mechanical modulus of the bands decreases distinctly. These electrical and mechanical factors may contribute to performance improvement, with carbon bands serving as a mechanical buffer for Si deformation and providing electrical conduction pathways. This work motivates future efforts to engineer similar morphologies for mitigating capacity loss in silicon electrodes.

Biomass ash (BA) waste as an activator to produce carbon-negative cement

The use of biomass, as a renewable energy source, to run heating and power plants is propelled by sustainable European policy. Olive is an important resource in Mediterranean countries. The residues from the extraction of olive oil are used as biomass, either to produce the oil or to generate heat or electricity. The disposal of ash residue poses an important burden. This study uses olive pit bottom ash waste (OBA) to produce carbon-negative cement. The OBA is mixed with waste GGBS (GGBS), and neither calcination nor thermal curing are used to lower environmental impact.The cements produced contain up to 60 %OBA and have a carbon sequestration capacity up to -97.45 kg CO2e/m3. An optimum mix with 40 %OBA is developed (using auxiliary activator), with compressive strength of 36–44 MPa and a carbon sequestration capacity of 40–45 kg CO2/m3. A modified loss on ignition test is proposed to evaluate the embodied carbon of biomass ash.The OBA's main chemical constituents: K2O and CaO, afford outstanding activation and alkalinity to release Ca2+ Si4+ and Al3+ from GGBS to form calcite, hydrotalcite, C-(A)-S-H and amorphous cements. Using sodium carbonate (NC) and lime as supplementary activators enhanced the mechanical properties of the cements and slightly changed their composition and microstructure. NC is the most efficient activator, it increased dissolution, and produced a denser and stronger cement with higher Si and K concentration that includes gaylussite, N-A-S-H and C(K)-A-S-H. Pre-dissolving the NC prior to mixing increases the activator's efficiency, producing less calcite cement for the same amount of NC. By adding 4 % pre-dissolved NC, the compressive strength increased by 138.76 % (compared to OBA-GGBS mortar without auxiliary activators) and 113.94 % compared to the material with NC in powder form.

BioTrojans: viscoelastic microvalve-based attacks in flow-based microfluidic biochips and their countermeasures

Flow-based microfluidic biochips (FMBs) are widely used in biomedical research and diagnostics. However, their security against potential material-level cyber-physical attacks remains inadequately explored, posing a significant future challenge. One of the main components, polydimethylsiloxane (PDMS) microvalves, is pivotal to FMBs' functionality. However, their fabrication, which involves thermal curing, makes them susceptible to chemical tampering-induced material degradation attacks. Here, we demonstrate one such material-based attack termed “BioTrojans,” which are chemically tampered and optically stealthy microvalves that can be ruptured through low-frequency actuations. To chemically tamper with the microvalves, we altered the associated PDMS curing ratio. Attack demonstrations showed that BioTrojan valves with 30:1 and 50:1 curing ratios ruptured quickly under 2 Hz frequency actuations, while authentic microvalves with a 10:1 ratio remained intact even after being actuated at the same frequency for 2 days (345,600 cycles). Dynamic mechanical analyzer (DMA) results and associated finite element analysis revealed that a BioTrojan valve stores three orders of magnitude more mechanical energy than the authentic one, making it highly susceptible to low-frequency-induced ruptures. To counter BioTrojan attacks, we propose a security-by-design approach using smooth peripheral fillets to reduce stress concentration by over 50% and a spectral authentication method using fluorescent microvalves capable of effectively detecting BioTrojans.