Increase In Contact Angle Research Articles

Dominant role of laser-generated nano-structures on enhancement of interfacial bonding strength by laser surface modification

Laser surface modification has been widely applied to the pre-treatment of material surfaces for interface bonding, however, laser-treated surfaces face an inevitable risk of environmental exposure during engineering application, and it remains unclear how laser-induced modifications change under environmental exposure. This study investigates the robustness of laser-treated aluminum surface under typical atmospheric and aqueous environments at different temperature from −40 °C to 80 °C. Although the carbon elemental content and water contact angle greatly fluctuate with exposure environments from 23 at.% to 33 at.%, and from 0° to 148°, respectively, laser-treated surfaces exhibit stable improvement of ∼25 % in bonding strength compared to untreated condition even after 30 days exposure. Notably, hygrothermal exposure of 80 °C and 95 %RH significantly declines bonding strength by ∼45 %, and this strength degradation is accompanied by 1.8 % increase of carbon elemental content and water contact angle of ∼150°. Results reveal that laser-generated nano-structures play crucial role in strength improvement, instead of carbonaceous contaminants and surface polarity, and nanostructure transformation causes an apparent strength degradation and change of fracture mode from cohesive to interface. This work uncovers the dominant role of laser-generated nano-structures in enhancing interfacial bonding strength, and provides supports for engineering application of laser surface modification.

Numerical investigation on cooperative evaporation from microdroplet array on heated substrate

The evaporative heat and mass transport characteristics from an array of continuously fed microdroplet on a heated substrate are investigated numerically by a Multiphysics model, which incorporates heat conduction, buoyant flow, Marangoni flow, Stefan flow, and vapor diffusion. The effects of droplet spacing, contact angle, and droplet size on the evaporation rate, heat flux, and convection strength were analyzed in detail with a fixed thermal and vapor concentration boundary condition. The results revealed the existence of extremely strong convection current in the ambient gas domain for evaporation from droplet array. This convection effect dominates the vapor transport process, overcomes the suppression effect from neighboring droplet, and causes the total evaporation rate to exceed the prediction from traditional diffusion-based model by up to ten times. The strength of the convective vapor transport is characterized by a dimensionless parameter, which increases first from 2.3 to 7 and then decrease to 4 with increasing contact angle from 30° to 150°, but remains invariant at 6.3 for hemispherical droplet irrespective of the change in droplet dimension. Finally, the numerical results demonstrate potential for microdroplet array evaporation to resolve the thermal management challenge of ultrahigh power electronics with heat flux up to 1 kW/cm2.

Impact of annealing temperature on optical, morphological, and surface characteristics of PC/PBT blend exposed to alpha particles

The induced modifications of the optical and surface characteristics in the annealed α-irradiated polycarbonate/polybutylene terephthalate (PC/PBT) blend have been studied in the temperature annealing range from 100 to 200 °C for 15 min. Several techniques have been used to study the changes in chemical composition, optical-electronic transitions, photoemission, contact angle, surface roughness, and hardness of annealed samples comparable to the pristine one. The FTIR spectra exhibit aggregate changes in the band intensities after annealing, indicating the scission and cross-linking of the polymer chains. The intensity of the peaks reduced with α-irradiation but began to increase with increasing annealing temperature. The trend of the function groups found in the annealed samples with the rise in annealing temperature supports the crosslinking mechanism. The UV/Vis spectra revealed that the absorption edges of annealed samples were shifted toward lower photon energy (red shift), reflecting the decrease of optical energy gap from 4 eV to 3.6 eV for direct transition and from 3.8 eV to 3.5 eV for indirect transition at the highest temperature. Further, the number of carbon atoms and the number of carbon clusters increases with the increase in the annealing temperature. The refractive index of the samples decreases from 1.5479 for the pristine sample to 1.4008 for the sample at the highest temperature. Moreover, the dielectric parameters and optical conductivity of the annealed samples were modified after thermal annealing. The PL emission yields are decreased with the increase in annealing temperatures that indicating an enhancement in the non-radiative recombination rate relative to the radiative recombination, which may be due to the increasing in the surface density states. The α-irradiated samples showed a notable increase in contact angle and a notable decrease in surface tension values with increasing the annealing temperatures. The side chain induction, which readily bundles and recombines the annealed parts by raising temperatures, also causes the surface roughness of annealed samples to decrease from 1.099 μm for the pristine sample to 0.696 μm for the annealed sample at the highest temperature. It is noteworthy that there is an increase in the hardness from 10.49 ΜPa for the pristine sample to 41.98 ΜPa for the annealed sample at the highest temperature. This is related to the results of changes in the polymer chains due to the active sites or branching points created by scission, which can lead to cross-linking.

Dual Modification of Cassava Starch Using Physical Treatments for Production of Pickering Stabilizers.

Cassava starch nanoparticles (SNP) were produced using the nanoprecipitation method after modification of starch granules using ultrasound (US) or heat-moisture treatment (HMT). To produce SNP, cassava starches were gelatinized (95 °C/30 min) and precipitated after cooling, using absolute ethanol. SNPs were isolated using centrifugation and lyophilized. The nanoparticles produced from native starch and starches modified using US or HMT, named NSNP, USNP and HSNP, respectively, were characterized in terms of their main physical or functional properties. The SNP showed cluster plate formats, which were smooth for particles produced from native starch (NSNP) and rough for particles from starch modified with US (USNP) or HMT (HSNP), with smaller size ranges presented by HSNP (~63-674 nm) than by USNP (~123-1300 nm) or NSNP (~25-1450 nm). SNP had low surface charge values and a V-type crystalline structure. FTIR and thermal analyses confirmed the reduction of crystallinity. The SNP produced after physical pretreatments (US, HMT) showed an improvement in lipophilicity, with their oil absorption capacity in decreasing order being HSNP > USNP > NSNP, which was confirmed by the significant increase in contact angles from ~68.4° (NSNP) to ~76° (USNP; HSNP). A concentration of SNP higher than 4% may be required to produce stability with 20% oil content. The emulsions produced with HSNP showed stability during the storage (7 days at 20 °C), whereas the emulsions prepared with NSNP exhibited phase separation after preparation. The results suggested that dual physical modifications could be used for the production of starch nanoparticles as stabilizers for Pickering emulsions with stable characteristics.

Improving the corrosion and wear resistance of CoCrNiSi0.3 Medium-Entropy Alloy by magnetron sputtered (CrN/Cr)x multilayer films

In this study, a medium entropy alloy (MEA) system consisting of Co, Cr, and Ni was selected to incorporate Si, resulting in the creation of CoCrNiSi0.3 MEA. The surface was coated with (CrN/Cr)x multilayer films to improve wear and corrosion resistance. The hardness, wear, corrosion, and nanoindentation tests were used to analyze the characteristics of CrN/Cr multilayer films and their protective performance. Low grazing angle X-ray diffraction (GIXRD), atomic force microscopy (AFM), scanning electron microscopy (SEM), electron probe microanalysis (EPMA), water contact angle analyzer, and transmission electron microscopy (TEM) were utilized to investigate the composition and structure of (CrN/Cr)x multilayer films. The intermediate Cr layer inhibits the columnar growth of the CrN layers and is progressively refined as the number of CrN/Cr bilayers increases. The Cr layer exhibits superior toughness in the multilayer structure and effectively hinders crack propagation. Therefore, the (CrN/Cr)3 multilayer film has the most outstanding anti-wear performance. The wear rates under 2 N and 4 N loads are 3.331 × 10−6 mm3•m−1•N−1 and 1.124 × 10−5 mm3•m−1•N−1, respectively. The growth of columnar crystals is suppressed and a more compact multilayer film is formed, resulting in a reduction in the defect density and an increase in the water contact angle, which retards the ingress of corrosive liquid and improves corrosion resistance. The corrosion current density of the (CrN/Cr)3 multilayer film is 0.73 μA•cm−2, while the corrosion polarization impedance is 962.35 Ω•cm2.

Surfactant-free fabrication of curcumin-loaded emulsion coatings on titanium for biomedical applications

Biofunctional emulsion coatings of curcumin-loaded poly(ɛ-caprolactone)/polyvinyl alcohol-hydroxyapatite (Cur-loaded PCL/PVA-HA) were developed on the titanium (Ti) plates without using any surfactant. Firstly, stable oil-in-water emulsions with different water/oil (W/O) ratios (9:1, 7:1, 5:1 and 3:1) were prepared by using the uniform PVA-HA slurry as a water phase and the Cur-loaded PCL solution as an oil phase. The diameter of the oil droplets in those emulsions mostly ranged from 4 to 6 µm. Subsequently, the emulsions were formulated into coatings on Ti through a spin-coating process. The obtained emulsion coatings consisted of Cur-loaded PCL microspheres that were evenly embedded in the PVA-HA matrix, and their phase composition was identified by the FT-IR analysis. The emulsion coatings were hydrophilic and displayed a gradual increase in water contact angles with the decrease of the W/O ratio. Moreover, abundant bone-like apatite aggregates were formed on the emulsion coatings, suggesting their excellent in vitro bioactivity. In addition, the emulsion coatings exhibited a sustained drug release behavior within 2–48 h, and the release process was mainly controlled by diffusion. The present study provides a new perspective on green and facile fabrication of functional emulsion coatings.

Metal and metal oxide particles as modifiers for effective layer melting and Z-axis strength in 3D printing

This work concerns research on the use of inorganic chemical compounds Fe2O3, Fe3O4, and Al and organosilicon modifiers used as additives controlling the properties of PLA for material extrusion in 3D printing technology. The addition of inorganic compounds reduces the temperature at the beginning of the composite decomposition, which is related to the presence of metal and metal oxides. An effect of inhibition of catalytic activity was also noticed as a result of the addition of organosilicon compounds. An increase in the melt flow index parameter was observed, making improving the extrusion and 3D printing process possible. The presence of inorganic additives results in a better fusion of the print paths, which leads to reduced structure defects and better interlayer adhesion. The tensile strength of the obtained composite samples decreases with the increase in the concentration of the metal and metal oxides. The addition of organosilicon substances increases the tensile strength regardless of the inorganic compound concentration. The highest increase in tensile strength was obtained for the PLA/12.5% Fe3O4/OSS-5OD-3TMOS sample and it was 24.35% compared to the sample without the addition of organosilicon compounds. The use of organosilicon additives resulted in an increase in the water contact angle.

Wettability alterations of amorphous shales in geological carbon storage: Impact of acidic conditions in deep saline aquifers

The feasibility of Geological carbon storage (GCS) in deep saline aquifers is mainly determined by its ability to prevent CO2 leakage through caprock, which is most commonly shale. The wettability of the shale–CO2–brine system is one of the most essential petro-physical parameters in the assessment of the integrity of shale caprock. Current literature suggests that wettability measurements of the shale–CO2–brine system have many contradictory outcomes. Furthermore, previous applications of molecular dynamic simulation (MDS) to estimate wettability of the shale–CO2–brine system disregarded variations in shale composition and concentrated on just a single component. Moreover, there has been limited investigation into the effect of CO2 dissolution in brine and the resultant acidic conditions on the wettability of the shale–CO2–brine combination. In this study, MDS is implemented for evaluating the wettability of a system made up of amorphous shale, CO2, and brine under conditions representative of typical geological storage site. An amorphous shale molecular model has been developed through the integration of illite, quartz, and kerogen. The microscopic wetting and half-angle fitting approaches have been applied to establish the wettability. A qualitative investigation was also conducted to further examine the wettability of the studied systems. Additionally, a contrasting analysis was conducted to assess the conclusions of this study in relation to relevant literature data. The findings of this study demonstrate the wettability of an amorphous shale–CO2–brine system is significantly influenced by the composition of the shale and the presence of acidic conditions. The water contact angles for shales with TOC values of 5% and 10% were measured to be 42.1° and 52.5°, respectively, at a pressure of 10 MPa and a temperature of 333 K, without taking into account any acidic conditions. The addition of induced acidic conditions resulted in a 15% and 24% increase in the water contact angle, respectively, for high and low TOC shale systems, respectively. The findings of this study have significant implications on the containment of stored CO2, thereby contributing to the worldwide efforts of minimizing greenhouse gas emissions through enhancements in the performance of GCS processes.

Changes in the hydrophilicity of the surface of PADC under ionizing radiations: Anomalous increase of the contact angle of water droplets under protons

The contact angle of water droplets decreases above certain absorbed doses in the case of heavy ions (He, C and Kr ions). Similarly, monotonic decreases are seen due to exposures to corona discharge and UV lights. The present trends indicate that the hydrophilicity of PADC surface increases by the contribution of hydroxyl groups.In comparison, the contact angle increases due to proton irradiations up to 1.3×105 Gy. Then it begins to decrease monotonically with increasing the absorbed dose. The present anomalous trend is discussed based on the combination of the track overlapping model and the Young’s formula.

Fabrication and characterization of highly hydrophobic PVDF membrane by phase inversion method with high anti-wettability characteristics

Membrane gas-liquid separation technology has garnered significant attention in applications such as membrane desalination, distillation, and gas absorption due to its operational flexibility, compact design, and large specific interfacial area. However, the currently used membranes are prone to pore wetting under high operational pressures, transitioning from a non-wetted state to partially or fully wetted conditions. This undesired wetting increases mass transfer resistance for water vapor molecules, ultimately leading to reduced removal efficiency. To address this issue and enhance wetting resistance, membrane hydrophobicity needs to be improved. In this study, a highly hydrophobic polyvinylidene fluoride (PVDF) membrane was developed using the phase inversion method for membrane distillation applications. We mixed a 16wt% polymer concentration with N-Methylpyrrolidone (NMP) as a solvent at 50°C for 24 hours. Subsequently, the polymer solution was cast and exposed to different non-solvents, namely water and methanol, to investigate their impact. Surface morphology and hydrophobic properties of the synthesized membranes were analyzed using Scanning Electron Microscope (SEM) and a Goniometer. Our findings indicate that the PVDF membrane fabricated with methanol as the non-solvent exhibited a significantly higher water contact angle of 126°, compared to 70° when deionized water was used as the non-solvent. This change from water to methanol as the non-solvent resulted in a more symmetrical membrane structure, enhancing the water contact angle from 70° to 126°. It is interesting to note that increase in the water contact angle increases the hydrophobicity of the PVDF membrane.

Effect of Different Ethylene Oxide Addition Numbers on the Performance of Polyoxyethylene Tallow Amine as a Pesticide Emulsifier.

Surfactant reduces the surface tension of liquids, resulting in improved emulsion stability, and there is great interest in pesticide additives. Ethoxylate is often used as a pesticide emulsifier. However, the degree of ethoxylation and the existence of dioxane byproducts can significantly affect the performance of emulsifiers. Here, a series of polyoxyethylene tallow amines with the addition of different numbers of ethylene oxide (EO) were synthesized and characterized. Their physical and chemical performances were measured. The ability of POEA as a surfactant to reduce water surface tension and the surface adsorption of molecules were assessed based on the static and dynamic surface tensions. The results show that the surfactant molecules preferentially form a saturated adsorption layer in solution, and the mixed-diffusion-kinetics mechanism dominates the adsorption process. With the increase of the EO addition number, the emulsifying property of POEA increases, while the wetting property gradually decreases and the contact angle increases. These results can provide a basis for the selection of pesticide additives. At the same time, the mechanism of removing dioxane by ethoxylate is described, and a simple and low-consumption method is put forward to reduce the dioxane content. It provides a new idea for the removal of dioxane.

The role of temperature on collector adsorption in galena flotation: Implications of seasonal temperature and climate change

This research focuses on studying the effects of the operating temperature and preconditioning time on the adsorption kinetics of sodium diisobutyl dithiophosphinate and sodium isopropyl xanthate collectors on the surface of galena, using contact angle measurements. The results indicate a strong correlation between higher operating water temperature and increased contact angles, suggesting faster adsorption kinetics and heightened hydrophobicity. Statistical analysis underscores the significance of temperature and preconditioning time, both factors being statistically significant. This study delves into the intricate interaction between temperature fluctuations and collector adsorption, contributing to a deeper understanding of flotation processes within the Pb/Cu circuit during seasonal temperature variations.Graphical abstract

Hierarchically porous silica particles: One-pot synthesis, tunable hydrophilic/hydrophobic properties, prospects for selective oil adsorption

Submicron spherical silica particles were synthesized via base hydrolysis of tetraethoxysilane (TEOS) and phenyltriethoxysilane (PTEOS) in a presence of cetyltrimethylammonium bromide. It was shown that the replacement of a part of TEOS with PTEOS in the reaction mixture led to formation of particles containing hierarchical micro-mesoporous structure with specific surface area of up to ∼ 1170 m2 g−1. The amount of PTEOS leads to the increase of water contact angle of the particles from 10° to 155° which causes a gradual change in their surface properties from hydrophilic to superhydrophobic. The static adsorption capacity of the particles was measured for water, toluene and methyl isobutyl ketone and was found to be affected by both the amount of OH- or C6H5-groups on the surface and the characteristics of porosity. In particular, the adsorption capacity for non-polar volatile organics increases with the increase of the hydrophobicity of particles. It was found that synthesized superhydrophobic silica particles efficiently and quickly absorb oil from water surface and then can be easily removed mechanically.

Surface morphology and microstructure of Bauhinia variegata L. flowers and leaves

The main purpose of this research is to characterize the wettability and microstructure of Bauhinia variegata L. flowers and leaves, aiming to provide a biological template for the preparation of hydrophobic surfaces. The contact angle test results show that the surfaces of flowers and leaves are hydrophobic, and the contact angle of the adaxial side and abaxial side of the leaves is highly significant difference, which is mainly affected by the topological morphology of the surface microstructure. The topological structure of flower and leaf surface morphology was revealed by scanning electron microscopy (SEM) and super-depth of field three-dimensional microscope. The results showed that the cell structure of flower surface array was the main factor leading to the hydrophobicity of flowers. The snowflake-like structure on the leaf surface is the main factor leading to hydrophobicity of leaves, and the burr structure of the micro-nano dual-level structure unique to the abaxial side of the leaf further enhances the hydrophobicity of the abaxial side, and the contact angle increases, resulting in a highly significant difference in wettability between the adaxial side and abaxial side. This provides an important biological template and reference value for the preparation of biomimetic materials.

Preparation and characterization of quaternary bacterial cellulose composites for antimicrobial oil‐absorbing materials

AbstractThe treatment of various types of oily wastewater is paramount for environmental protection. Bacterial cellulose (BC) stands out as a highly promising material for oil/water separation, owing to its exceptional mechanical properties and three‐dimensional porous structures. However, excessive hydroxyl groups on BC make it highly hydrophilic, reducing oil absorption and promoting bacterial growth, affecting its stability. To address these challenges, we developed a straightforward in situ polymerization method for the preparation of BC‐DMC composites. The innovation lies in the concurrent enhancement of BC's hydrophobicity and antimicrobial properties only through the addition of 2‐(Methacryloyloxy)ethyltrimethylammonium chloride (DMC), considerably simplifying the synthesis of materials possessing oil‐absorbing and antimicrobial properties. Morphological and structural characterization results confirmed the successful combination of DMC onto BC while maintaining its porous structure. After process parameter optimization, the BC‐DMC composites exhibited a remarkable increase in contact angle (117.7° compared with pure BC's 19.5°). It also demonstrated excellent oil absorption performance, with maximum capacities exceeding 30 g/g for different oils, maintaining values above 20 g/g even after eight cycles. In addition, the BC‐DMC composites exhibited strong antibacterial activity, with rates of 82.4% against Escherichia coli and 97.5% against Staphylococcus aureus. The antibacterial mechanism of the BC‐DMC composites was also discussed. Our novel BC‐DMC composites provides excellent oil absorption and antibacterial properties, making it highly applicable in the field of oily wastewater treatment and serving as a valuable reference for other researchers.

Effect of the chain length of geraniol esters on the plasticization efficiency with poly(lactide)

This work reports on the development of environmentally friendly PLA formulations utilizing different esters derived from geraniol as plasticizers. Geranyl formate, acetate, propionate, butyrate, isovalerate and caproate at 10 wt% were combined with PLA in formulations that were produced through extrusion and injection moulding processes. Theoretical solubility parameter studies predicted good miscibility between PLA and all the plasticizers. This was confirmed by tensile test, which showed elongation at break values between 200 and 300 %, totally in contrast with the 8 % value of neat PLA. Geranyl acetate and geranyl formate exhibited the highest elongation at break behavior. These values of elongation at break were supported by FESEM images, which showed clear signs of plasticization. The plasticization effect was further corroborated by DSC and DMTA analysis, where a clear decrease in the glass transition temperature was observed from a typical value of 60 °C for neat PLA down to 40–50 °C for the plasticized blends. This was related to an enhanced chain mobility of the amorphous regions of PLA. Moreover, the plasticizers slightly increased the water absorption capabilities of PLA, as demonstrated by an increase in the water contact angle and water uptake for 11 weeks.

Development, performance research and shape memory multifunctional exploration of epoxy/PEG shape memory nanofibers

To improve the spinnability of thermoplastic epoxy resin and develop epoxy resin-based shape memory nanofiber materials, polyethylene glycol (PEG) was utilized to regulate the properties of thermoplastic epoxy. The process involved the preparation of thermoplastic epoxy/PEG nanofibers using melt-dispersion and electrospinning techniques. The addition of PEG has enabled the electrospinning of the thermoplastic epoxy, with EPP-5 having the smallest average diameter (227 nm) and EPP-10 showing the most uniform morphology. FTIR analysis confirmed sufficient polymerization of epoxy resin. The water contact angle analysis revealed that an appropriate amount of PEG reduced the hydrophilicity of the nanofiber membranes, with the EPP-10 showing a 14.9 ° increase in water contact angle compared to the EPP-5. The mechanical analysis demonstrated that an appropriate amount of PEG improved the nanofibers’ yield stress, breaking strain, and maximum tensile stress. The EPP-10 exhibited a 3.27 MPa increase in yield stress, a 19.54 % increase in breaking strain, and a 1.17 MPa increase in maximum tensile stress compared to the EPP-5. Thermal analysis showed that epoxy/PEG nanofibers decomposed mainly between 400 ℃ and 500 ℃. Thermomechanical analysis revealed a reduction in the Tg of epoxy/PEG films with the addition of PEG, among which the Tg of EPP-25 was 55.1 ℃ lower than that of EPP-0. The epoxy/PEG nanofiber membrane exhibits excellent shape memory performance, among which the EPP-10 exhibits the best shape recovery effect. In addition, the EPP-10 yarn stretched to 160 % of original length recovered within 25 s, and EPP-10 yarn tied in a temporary shape recovered to original shape within 15 s. In conclusion, by modulating the properties of thermoplastic epoxy through PEG, the spinnability of thermoplastic epoxy was achieved, and shape memory epoxy/PEG nanofibers with potential applications in the field of smart textiles were developed.

A study on the model of solar radiation transfer in multi-layer glass facade with attached droplets

To obtain the optical properties of the spray cooling double skin façade (SC-DSF), a solar radiation transfer model of the multi-layer glass system with attached droplets is proposed in this study. The solar radiation is segmented into direct and diffuse radiation, and the monte carlo ray tracing method and angle discretization method are used to obtain the optical properties of the single layer glass with attached droplets. And then, the energy balance equation of the multilayer glass system is established based on the net-radiation method, and the transmittance, reflectance and absorptance of the multilayer glass system are calculated. The effectiveness of the proposed method is verified by the experimental results, which shows the numerical results are in good agreement with the experimental data. In addition, some important influence factors are analyzed and discussed, including the solar incidence angle, the droplet contact angle, the droplet coverage rate, and the average droplet diameter. It is found that there is little influence on the system transmittance when the incidence angle is smaller than 40°. However, the transmittance decreases with the increase of the incidence angle when the solar incidence angle is greater than 40°. When the droplet contact angle is small (less than 40°) or large (larger than 140°), its influence on the transmittance of the system is negligible. Subsequently, with the increase in the droplet contact angle within 40–140°, the transmittance firstly decreases and then increases. Adjusting the droplet coverage rate and droplet size is an effective measure to decrease transmittance and solar heat gain.

Adaptation of application of drop area method to characterize hydrophobicity of materials

The drop area can characterize hydrophobicity of materials. To improve accuracy of the drop area method, a large number of drop profiles with different contact angles, drop volumes and liquid parameters (Δρ/γ) are numerically generated. Based on the generated profiles, the influences of contact angle, drop volume and liquid parameter on the drop area and its sensitivity dS/dθ are systematically investigated. The results reveal that the sensitivity of the drop area method reduces with increasing contact angle, and increases with increasing drop volume and liquid parameter. The drop area method is particularly suitable for application in the case with small contact angle and at the same time, the drop volume and liquid parameter should be not so low. The relationship between water drop area and contact angle at some common drop volumes is obtained by numerical calculation. The concept of critical contact angle for the drop area method is proposed and the values of critical contact angle corresponding to different water drop volumes are presented. And it can be used to determine whether the drop area method or the static contact angle method should be selected. Finally, the contact angle method and the drop area method are used to measure hydrophobicity of glass and silicone rubber with different water drop volumes. The results validate the above analysis and at the same time it is consistent with the corresponding numerical calculation. This work is helpful to improve the accuracy in the drop area method and to generalize the use of it.

Solvent-free surface modification of milled carbon fiber using resonant acoustic mixing

Resonant Acoustic Mixing (RAM) is used to rapidly modify the surface of milled carbon fiber using diazonium salts in solvent free conditions. This novel method allows tuning of the surface properties of this material and reduces the environmental footprint usually associated with surface modification of carbon fiber (discontinuous or otherwise). As a proof of concept, fluorine-containing diazonium salts were successfully grafted as determined by X-ray photoelectron spectroscopy (XPS), scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDX) and an increase in water contact angle (WCA) of the milled carbon fiber samples (+15°). Atomic Force Microscopy (AFM) together with SEM revealed the surface structure and integrity of the milled carbon fibers could be maintained despite vigorous mixing conditions. Using RAM proved more efficient than positive controls produced under thermal conditions in solvent.