Silica Loading Research Articles

Improving the Mechanical, Thermoelectric Insulations, and Wettability Properties of Acrylic Polymers: Effect of Silica or Cement Nanoparticles Loading and Plasma Treatment

The acrylic polymer composites in this study are made up of various weight ratios of cement or silica nanoparticles (1, 3, 5, and 10 wt%) using the casting method. The effects of doping ratio/type on mechanical, dielectric, thermal, and hydrophobic properties were investigated. Acrylic polymer composites containing 5 wt% cement or silica nanoparticles had the lowest abrasion wear rates and the highest shore-D hardness and impact strength. The increase in the inclusion of cement or silica nanoparticles enhanced surface roughness, water contact angle (WCA), and thermal insulation. Acrylic/cement composites demonstrated higher mechanical, electrical, and thermal insulation properties than acrylic/silica composites because of their lower particle size and their low thermal/electrical conductivity. Furthermore, to improve the surface hydrophobic characteristics of acrylic composites, the surface was treated with a dielectric barrier discharge (DBD) plasma jet. The DBD plasma jet treatment significantly enhanced the hydrophobicity of acrylic polymer composites. For example, the WCA of acrylic composites containing 5 wt% silica or cement nanoparticles increased from 35.3° to 55° and 44.7° to 73°, respectively, by plasma treatment performed at an Ar flow rate of 5 L/min and for an exposure interval of 25 s. The DBD plasma jet treatment is an excellent and inexpensive technique for improving the hydrophobic properties of acrylic polymer composites. These findings offer important perspectives on the development of materials coating for technical applications.

Exposure to respirable silica contributes to lower airway inflammation in asthmatic horses.

Respirable mineral particles can induce lower airway inflammation, but the role they play in asthma of horses is unknown. Respirable mineral particles, particularly respirable silica, are an overlooked determinant of chronic lung inflammation (asthma) in horses. Twenty-three horses from an equine hospital population: 11 moderately affected (MEA), 7 severely asthmatic (SEA), and 5 control horses free from respiratory clinical signs. Prospective observational study. The quantity and quality of mineral particles found in bronchoalveolar lavage fluid (BALF) were characterized, with particular attention to silica content. Polarized light microscopy performed on cytospin slides identified intracellular birefringent particles as silica. Spectrometry-based analysis performed on whole BALF determined total mineral and silica percentage and concentration. Group-related differences in BALF mineral and silica load were investigated as well as associations with BALF cytology. Intracellular birefringent particles were increased in SEA vs MEA (median [interquartile range, IQR]), 12 [7] vs 4 [5] particles/30 high power fields [hpf], respectively; P = .01) and vs controls (4 [2] particles/30 hpf; P = .02). Total mineral concentration in BALF was similar between the groups studied, whereas silica concentration and percentage were increased in SEA vs MEA (1758 [887] particles/mL and 20 [10]% vs 867 [662] particles/mL and 8 [6]%; P = .009 and P = .001) and control group (355 [330] particles/mL and 6 [3]%; P = .0003 and P = .002). Silica load in BALF was associated with BALF neutrophilia in MEA and SEA. Respirable silica is associated with neutrophilic lower airway inflammation in horses and might contribute to asthma development.

Ballistic impact behavior of shear thickening fluid impregnated sisal fabrics

The study explores the ballistic impact performance of shear thickening fluid (STF) impregnated sisal fabric panels with varying nano silica loadings (10 wt%, 20 wt%, and 30 wt%). Rheological analysis indicated improved shear thickening behavior with increased nano-silica. FESEM, XRD, and FTIR analyses were conducted to assess changes in morphology, phase structure, and functional groups. The yarn pull-out test showed a higher pull-out force for STF-impregnated fabrics, with 30 wt% STF demonstrating the highest pull-out speed. Ballistic impact tests revealed significant improvements in energy absorption for STF-impregnated fabrics compared to neat fabrics, with energy absorption enhancements of 4.40% for 10 wt%, 45.09% for 20 wt%, and 50.17% for 30 wt%. The increased nano-silica loading resulted in greater energy absorption, attributed to enhanced inter-yarn friction and improved fabric integrity.

Characterization of membrane pore size using statistical model by facile method of air bubbling in liquid media

Research has shown the correlation between porous membrane pore size and bubble formation including bubble size, frequency, and operating parameters. However, attempts to create a governing equation to establish this correlation have often suffered from low accuracy due to variable interactions. Therefore, it is necessary to identify the significant effects of membrane pore size on bubble formation to establish effective correlations. This study aimed to identify the significant effect of porous membrane pore size on bubble formation using analysis of variance (ANOVA) to establish a mathematical model that predicts porous membrane pore size using bubble formation. To achieve this, various porous membranes were fabricated by varying hydrophilic silica loadings. The resulting membranes were characterized regarding pore size and employed in an aeration device under variable air flow rates and inlet pressures to obtain bubble size and frequency data. JMP software developed a statistical model to characterize membrane pore sizes. The results show a significant effect of bubble formation information on pore size, with a p-value of 0.0089, R2 of 0.96, and root mean squared error (RMSE) value of 0.02. Validation of the model using three membranes demonstrated minor deviations of 0–6.5 %, emphasizing the model's effectiveness in predicting membrane pore size.

Mechanical reinforcement by bridging chains in polymer nanocomposites

The adsorption-induced bridging of polymer chains between adjacent nanoparticles was studied in poly(vinyl acetate)/silica nanocomposites with different polymer molecular weights, interaction strengths, nanoparticle sizes, and silica loading fractions. The polymer bridging contribution is successfully decoupled from the apparent rubbery plateau modulus by subtracting the hydrodynamic and trapped chain entanglement contributions. The bridging modulus depends on the nearest interparticle surface distance through a power-law relation with a universal exponent −3. Polymer molecular weight can enhance the bridging modulus only when nanoparticles have a high density of adsorption sites due to the emergence of direct bridging of multiple particles by one chain in addition to the regular bridging through self-similar carpets. Our results illustrate that bridging chains can dominate modulus enhancement at nanoparticle's loading at about 10 vol% in polymer nanocomposites with long polymer chains and high surface silanol density.

Filler Mixed Into Adhesives Does Not Necessarily Improve Their Mechanical Properties.

To investigate the influence of filler type/loading on the micro-tensile fracture strength (μTFS) of adhesive resins, as measured 'immediately' upon preparation and after 1-week water storage ('water-stored'). The morphology and particle-size distribution of three filler particles, referred to as 'Glass-S' (Esschem Europe), 'BioUnion' (GC), and 'CPC_Mont', were correlatively characterized by SEM, TEM, and particle-size analysis. These filler particles were incorporated into an unfilled adhesive resin ('BZF-29unfilled', GC) in different concentrations to measure the 'immediate' μTFS. After 1-week water storage, the 'water-stored' μTFS of the experimental particle-filled adhesive resins with the most optimum filler loading, specific for each filler type, was measured. In addition, the immediate and water-stored μTFS of the adhesive resins of three experimental two-step universal adhesives based on the same resin matrix but varying for filler type/loading, coded as 'BZF-21' (containing silica and bioglass), 'BZF-29' (containing solely silica), and 'BZF-29_hv' (highly viscous with a higher silica loading than BZF-29), and of the adhesive resins of the gold-standard adhesives OptiBond FL ('Opti-FL', Kerr) and Clearfil SE Bond 2 ('C-SE2', Kuraray Noritake) was measured along with that of BZF-29unfilled (GC) serving as control/reference. Statistics involved one-way and two-way ANOVA followed by post-hoc multiple comparisons (α<0.05). Glass-S, BioUnion, and CPC_Mont represent irregular fillers with an average particle size of 8.5-9.9 μm. Adding filler to BZF-29unfilled decreased μTFS regardless of filler type/loading. One-week water storage reduced μTFS of all adhesive resins except BZF-21, with the largest reduction in μTFS recorded for BZF-29unfilled. Among the three filler types, the μTFS of the 30 wt% Glass-S and 20 wt% BioUnion filled adhesive resin was not significantly different from the μTFS of BZF-29unfilled upon water storage. Adding filler particles into adhesive resin did not enhance its micro-tensile fracture strength but appeared to render it less sensitive to water storage as compared to the unfilled adhesive resin investigated.

Synthesis and Characterization of Enhanced Proton-Conducting Nafion&lt;sup&gt;® &lt;/sup&gt;117- Silica Composite Membranes for Fuel Cell Applications

Nafion®/silica nanocomposite membranes were prepared by impregnation method from Nafion® 117 and sol-gel pre-synthesized n-octadecyl-trimethoxy silane (C18TMS) coated silica nanoparticles. The scanning electron microscope (SEM) of pristine silica particles displayed monodispersed nanospheres with diameters ranging from 150-350 nm; while Brunauer-Emmett-Teller (BET) analysis presented 760 m2/g BET surface area, a micropore-mesopore bimodal distribution of micropore systems with respective pore volume at 14.6 Å and 17.0 Å (2.01 x 10-3 cm3/g.Å), as well as the prolific mesopores centered at 29.5 Å (5.64 x 10-2 cm3/g.Å). Characterization of Nafion® 117 based membranes on SEM, Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), and x-ray diffraction (XRD), and tensile stress exhibited varying surface morphology with silica loadings, structural interaction between membrane support and the ion exchanger, thermal stabilities (up to 330 °C), crystalline nature, and reasonable mechanical stability of nanocomposite membranes. The maximum water uptake (44.8 %) and proton conductivity of (1.14 x10-2 S/cm) were obtained on low Nafion®/SiO2 (5%) loaded membrane. While both composite membranes displayed the improved reduction in methanol permeability, 2.43x10-07 cm2/s at 80 °C was obtained with high Nafion®/SiO2 (10%) loading. Improved water uptake and proton conductivity substantiate the high ion exchange capacity (IEC) of 1.81 meq.g-1 when compared to IEC of 0.93 meq.g-1 [pristine Nafion®] and 1.46 meq.g-1 [Nafion®/SiO2 (10%)]. The increase in IEC value may be due to the high acid functionalization of additional sulfonic acid groups surrounded by hydrophilic segments of nanosilica, which improves the properties of the membrane. The high proton conductivity coupled with great water retention capabilities indicated that the Nafion®/SiO2 nanocomposite membranes could be utilized as proton exchange membranes for medium temperature methanol fuel cells. Keywords: Fuel cells; nanocomposite membrane; SiO2 nanofillers; methanol permeability; ion exchange capacity

Synthesis and characterization of monodispersed silica‐based shear thickening fluid for impact resistance applications

AbstractShear thickening fluid (STF), a highly concentrated mixture of nanosized silica particles in polyethylene glycol (PEG) is characterized by its quick transition to a stiff, solid‐like form under high shear rates. In this study, the modified Stöber synthesis approach was used for synthesizing the monodispersed spherical 300 nm silica nanoparticles. The rheological properties of the STF formulated using different silica loading were characterized. The Takshak model was tested to assess the rheological properties. The effect of the STFs on the impact resistance and yarn pull‐out force of the Kevlar® 802 fabric was determined. The uniformity in size of the silica nanoparticles facilitated more efficient packing within the fluid matrix, resulting in the formation of networks or structures that enhance shear thickening behavior. The STF with 70% silica exhibited the best peak viscosity of 45.8 Pa.s. Upon impregnation of this STF onto the Kevlar, a significantly high energy absorption (478.4%) compared to neat Kevlar, was observed. Moreover, the yarn pull‐out force for this system was found to be very high (435.8%). The reasons for the enhancement of the properties are explained. The novelty of this work lies in the synthesis of silica particles, analysis of the rheological properties, and interrelating the rheological properties with the characteristic parameters to define the impact characteristics. The improved properties underscore the suitability of synthesized STF for impact resistance applications.

Simultaneously Improved Curing, Mechanical, Antioxidative Properties and Reduced ZnO Loading of Silica Filled NR Composites by Incorporation of Low-cost Crude Carbon Dots via Conventional Melt-milling Method

Simultaneously Improved Curing, Mechanical, Antioxidative Properties and Reduced ZnO Loading of Silica Filled NR Composites by Incorporation of Low-cost Crude Carbon Dots via Conventional Melt-milling Method

Coupling relationship between molecule structure at silica/silicone gel interfaces and ionic conductivity in polymer composites

Herein, the coupling relationship between molecule structure and ion conductivity in silica filled silicone gel are established. Based on the broadband dielectric spectrum, the concentration of ion charges and ions diffusion coefficients, two key roles for ion conductivity, are calculated. The concentration of ion charges is increased by about four orders of magnitude after the addition of silica. Because of the more short-length chains conformations and more amorphous regions at interfaces, the chains at interfaces are easier to rearrange with higher relaxation frequency, which enhances the ions diffusion process and contributes to negative decoupling exponents between the interface molecule relaxations and ion diffusion coefficients in silicone gel composites. With the increase of fumed silica loading, the ionic conductivity increases first and decreases owing to percolation phenomenon about silica dispersion. Meanwhile, decoupling exponents of the interface molecules are closer to 0. Our findings deepen the understanding how the interface structures act on ions conductivity in insulating polymer composites, which is critical to rationally design interface structures for manipulating the insulation performances.

Interaction of silica with polystyrene: mechanical properties, polymer/filler adhesion and failure behavior

Composites of polystyrene with different loading of silica were prepared by melt mixing in a Brabender Plasticorder at a rotor speed of 60 rpm. The mechanical properties of the composites such as tensile behavior, impact strength, and flexural properties were studied as a function of filler loading. The tensile moduli of the composites increased with silica content. To improve adhesion between the filler and the matrix, an amino silane coupling agent was used. The composites with coupling agents showed enhanced mechanical properties. Thermal properties were measured using differential scanning calorimetry (DSC), thermogravimetry (TGA) and flammability tests. Composites with 15 wt.% and 0.5 wt.% coupling agent showed optimum properties. Scanning electron microscopy (SEM) studies of the tensile fractured samples revealed the extent of filler dispersion and filler/matrix interaction. Finally, experimental results were compared with theoretical predictions.

Enhanced Mechanical and Thermal Properties of Polyimide Films Using Hydrophobic Fumed Silica Fillers.

Polyimide (PI) composite films with enhanced mechanical properties were prepared by incorporating modified fumed silica (FS) particles while preserving their optical and thermal characteristics. The PI matrix was synthesized using a fluorinated diamine, a fluorinated dianhydride, and a rigid biphenyl dianhydride via chemical imidization. Commercially available FS particles, including unmodified FS particles (0-FS) and particles modified with dimethyl (2-FS), trimethyl (3-FS), octyl (8-FS), octamethylcyclotetrasiloxane (D4-FS), and polydimethylsiloxane (PDMS-FS) were used. Scanning electron microscope images and nitrogen adsorption-desorption isotherms revealed well-defined porous structures in the FS particles. The water contact angles on the composite films increased compared to those of the pristine PI films, indicating improved water resistance. The PI/0-FS films exhibited a typical trade-off relationship between tensile modulus and elongation at break, as observed in conventional composites. Owing to the poor compatibility and agglomeration of the PDMS-FS particles, the PI/PDMS-FS composite films exhibited poor mechanical performance and diminished optical characteristics. Although the longer-chained FS particles (8- and D4-FS) improved the tensile modulus of the PI film by up to 12%, a reduction of more than 20% in toughness was observed. The PI composite films containing the methylated FS particles (2- and 3-FS) outperformed 8- and D4-FS in terms of mechanical properties, with PI/3-FS films showing an over 10% increased tensile modulus (from 4.07 to 4.42 GPa) and 15% improved toughness (from 6.97 to 8.04 MJ/m3) at 7 wt. % silica loading. Except for the PI/PDMS-FS composites, all composite film samples exhibited more than 86% transmittance at 550 nm. Regarding thermal properties, the glass transition temperature (Tg) and thermal stability remained stable for most composite films. In addition, PI/3-FS films demonstrated enhanced dimensional stability with lower coefficients of thermal expansion (from 47.3 to 34.5 ppm/°C). Overall, this study highlights the potential of incorporating specific modified FS particles to tailor the mechanical, optical, and thermal properties of PI composite films.

Improving the stability of perovskite nanocrystals via SiO2 coating and their applications.

Lead halide perovskite nanocrystals (LHP NCs) with outstanding optical properties have been regarded as promising alternatives to traditional phosphors for lighting and next-generation display technology. However, the practical applications of LHP NCs are seriously hindered by their poor stability upon exposure to moisture, oxygen, light, and heat. Hence, various strategies have been proposed to solve this issue. In this review, we have focused our attention on improving the stability of LHP NCs via SiO2 coating because it has the advantages of simple operation, less toxicity, and easy repetition. SiO2 coating is classified into four types: (a) in situ hydrolytic coating, (b) mesoporous silica loading, (c) mediated anchoring, and (d) double coating. The potential applications of SiO2-coated LHP NCs in the field of optoelectronics, biology, and catalysis are presented to elucidate the reliability and availability of SiO2 coating. Finally, the future development and challenges in the preparation of SiO2-coated LHP NCs are analyzed in order to promote the commercialization process of LHP NC-related commodities.

Molecular Characterization of Mesoporous Silica (Un)loading by Gemcitabine and Ibuprofen – An Interplay of Salt-Bridges and Hydrogen Bonds

The molecular mechanisms of mesoporous silica nanomaterial (MSN) loading by gemcitabine and ibuprofen molecules, respectively, are elucidated as functions of pore geometry. Based on a small series of MSN archetypes, we use molecular dynamics simulations to systematically explore molecule-by-molecule loading of the carrier material. Apart from predicting the maximum active pharmaceutical ingredient (API) loading capacity, more detailed statistical analysis of the incorporation energy reveals dedicated profiles stemming from the interplay of guest-MSN salt-bridges/hydrogen bonding in concave and convex domains of the silica surfaces - which outcompete interactions among the drug molecules. Only after full coverage of the silica surface, we find secondary layer growth stabilized by guest-guest interactions exclusively. Based on molecular models, we thus outline a two-step type profile for drug release from MSN networks. Subject to the MSN structure, we find 50–75 % of the API within amorphous domains in the inner regions of the pores – from which drug release is provided at constant dissociation energy. In turn, the remaining 50–25 % of drug molecules are drastically hindered from dissociation.

Preparation and properties of rice husk ash silica filled natural rubber

AbstractRice husk ash silica obtained from the chemical purification of rice husk ash is a bio‐based silica. As a sustainable raw material, the bio‐based silica has attracted much attention in recent years. It can be used to replace traditional carbon black and silica in tire rubbers. Our experimental results show that the bio‐based silica can bring similar mechanical properties and higher wet grip to natural rubber in comparison with traditional silica. The wet mixing method is successfully used to disperse the bio‐based silica in natural rubber latex, obtaining a bio‐based silica/natural rubber composite with higher abrasion resistance and lower rolling resistance than the composite prepared by traditional dry mixing. The mechanical properties of bio‐based silica/natural rubber composites depend on the silica loading and mixing methods. Mixing natural rubber and bio‐based silica through wet‐mixing method is a green and sustainable approach to the tread rubbers with excellent mechanical properties, low rolling resistance, high abrasion resistance, and wet grip.

Quantifying the impact of silica hydrophilicity and loading on membrane surface properties through response surface methodology

Quantifying the impact of silica hydrophilicity and loading on membrane surface properties through response surface methodology

Rheological studies of nanocomposites based on hydrolyzed polyacrylamide with silica and alumina in saline media to enhance oil recovery

Many nanoparticles such as silicon dioxide (SiO2) and aluminum oxide (Al2O3) have been recently proposed to increase the performance of water-soluble polymers for use in oil recovery (EOR). However, nanoparticles in nanocomposites tend to precipitate, agglomerate, or even precipitate under harsh conditions such as high-temperature and high-salinity (HT-HS), which reduces their potential for field applications. In this work, silica and alumina nanoparticles were modified with 3-methoxysilyl-propyl-methacrylate (TMS) coupling agent containing a vinyl group to enhance better dispersibility in reaction media and much stronger adhesion with the polymer. Then, acrylamide (AM) and 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS) monomers were copolymerized in the presence of modified NPs via radical polymerization and were covalently bound to the NPs. In this study, the effect of AM/AMPS ratio and alumina as well silica loading amount on thermal stability, rheological properties and aging of composite solution was investigated and compared with commercial HPAM used for EOR. Results depicted that used method of synthesis could improve the rheological properties and better dispersion of nanoparticles in the polymer. It was found that the modified nanoparticles reduced the thermal degradation of the polymer and protect its original structure when compared to the neat copolymer. After 30 days of aging, the loss of viscosity in PAMS and HPAM was approximately 46% and 75% while PAMS10-Silica2% and PAMS10-Alumina2% exhibited a viscosity loss of 27%.

Investigating the impact of nanoparticle geothermal silica loading on the mechanical properties and vulcanization characteristics of rubber composites

The present study investigates the effects of nanoparticle geothermal silica (NGS) on the mechanical properties and vulcanization characteristics of rubber compounds with various filler loadings. The rubber compounds were filled with 0, 20, 30, and 40 phr of silica. The properties of NGS were analyzed using transmission electron microscopy, particle size analyzer, and BET surface area analysis to examine its morphology, size distribution, and surface area. The mechanical properties and vulcanization characteristics of the rubber compounds reinforced with NGS were evaluated using a universal testing machine and moving die rheometer. The results showed that NGS possessed the primary particle sizes below 20 nm and a surface area of 168.35 m2/g. The interaction between silica and rubber determined the modulus of the rubber composites and the vulcanization characteristics. The tensile strength of the rubber compounds, meanwhile, showed a significant increase more than threefold as the filler loading increased from 0 phr to 30 phr, followed by a slight decline at 40 phr loading. The addition of 20 phr of silica led to a prolonged scorch time compared to the filler-free compound due to the adsorption of activators and accelerators. However, the scorch time decreased after reaching 30 phr of silica loading, which could be attributed to the higher amount of bound rubber covering a portion of the silica surface, thereby reducing its ability to adsorb the activator. The presence of silica with good thermal conductivity enabled a better heat transfer during the vulcanization process, resulting in shorter curing times for higher loading. Rubber compounds with an NGS loading of 30 phr demonstrated a favorable balance between filler-rubber interactions, vulcanization characteristics, and mechanical properties in the rubber compounds.

Glassy and Rubbery Epoxy Composites with Mesoporous Silica

The reinforcing efficiency of SBA-15-type mesoporous silica, when used as additive in epoxy polymers, was evaluated in this study. The effects of silica loading and its physicochemical characteristics on the thermal, mechanical, and viscoelastic properties of glassy and rubbery epoxy mesocomposites were examined using SBA-15 mesoporous silicas with varying porosities (surface area, pore size, and volume), particle sizes, morphologies, and organo-functionalization. Three types of SBA-15 were used: SBA-15 (10) with 10 nm pore diameters and long particles, SBA-15 (5) with 5 nm pore diameters and short particles, and SBA-15 (sc) with 10 nm pore diameters and short particles (“sc” for short channel). SBA-15 (10) was modified with propyl-, epoxy-, and amino-groups to study the effect of functionalization. The glassy or rubbery epoxy polymers and mesocomposites were produced by the crosslinking of a diglycidyl ether of bisphenol A (DEGBA) epoxy resin with isophorone diamine (IPD) or Jeffaminje D-2000, respectively. Mesoporous silica was uniformly dispersed inside the polymer matrices; however, the opacity levels between the rubbery and glassy samples were different, with completely transparent rubbery composites being prepared with as high as a 9 wt. % addition of SBA-15. The mechanical and thermal performance properties of the mesocomposites were dependent on both the type of the curing agent, which affected the cross-linking density of the pristine polymer matrix, and the characteristics of the mesoporous silica variants, being, in general, improved by the addition of up to 6 wt. % silica for the glassy polymers and up to 9 wt. % for the rubbery polymers.

On the selection of rheological tests for the prediction of 3D printability

Direct ink writing is used to print multiple polydimethylsiloxane (PDMS) mixtures with fumed silica or as a two-part commercial liquid silicone rubber (LSR) mixed with polyethylene glycol (PEG) or as a two-part commercial vulcanizing (RTV) silicone. We correlate their printability into a hollow slump cone with rheological measurements, including (1) a shear rate up-ramp followed by (2) a down-ramp in the shear rate, (3) creep tests, and (4) large-amplitude oscillatory shear (LAOS) with increasing amplitude. The PDMS-fumed silica mixtures fail to print even at the highest fumed silica loading used (9 wt. %), while LSR-PEG with 4 or 6 wt. % PEG prints well, and one of the two RTV silicone components is printable, as is the mixture due in part to its rapid chemical curing. The large differences in printability of these materials do not correlate well with any single rheological test. They do correlate with a combination of a measure of material strength, given by either the yield stress σycr from creep tests or the “flow stress” σf at which G′ and G″ cross-over in LAOS, and of material recoverability given by the dynamic yield stress σy− in test 2. The latter is measured during a down-ramp in the shear rate after reaching a maximum shear rate of 1000 s−1, the highest shear rate in the print nozzle.