PDMS Solution Research Articles

Fabrication of Superhydrophobic (TiO2/PDMS) Coating For Oil-Water Separation

Oil-contaminated water as a result of oil spill disasters or industrial disposal is a threat to human health and environmental sustainability on a global scale. The rising need for efficient oil-water separation has led to a growing interest in superhydrophobic materials for this purpose. Due to the regeneration ability of nanoparticles of titanium dioxide (TiO2), superhydrophobic and superolephilic TiO2/PDMS were created using a simple, low cost dip coating procedure. TiO2 (NPs) was synthesised by hydrothermal method and modified with PDMS (FS-1200 silicon sealant) solution. The mesh coated had remarkable superhydrophobicity, as seen by a contact angle of 155° with water. Additionally, the surface displayed superoleophilicity, as indicated by an oil contact angle (OCA) of 0°. The coated mesh surface was characterized by X-ray diffraction analysis, contact angle measurement, field emissions scanning electron microscopy (FE-SEM), Fourier transform infrared spectroscopy (FTIR), and energy dispersive spectroscopy (EDS). The separation of kerosene-water, diesel oil-water combinations, and sunflower oil-water may be effectively achieved via a simple filtering approach using a coated mesh. This method demonstrates a notable separation efficiency of 91.6%.

Hydrophobicity and membrane distillation performance of glass fiber membranes modified by dip coating of pure PDMS

With growing concern for environmental issues associated with the use of chemicals and nanomaterials to achieve membrane hydrophobicity, polydimethylsiloxane has emerged as a promising and eco-friendly alternative. However, few studies have explored the application of pure PDMS solutions through dip coating to achieve hydrophobicity in membranes designed for membrane distillation; a process which demands the membranes possess specific porosity and pore size characteristics. This study explored how dip coating with different PDMS concentrations affected the hydrophobicity and physical properties of glass fiber membranes. Increasing the concentration of polydimethylsiloxane up to 15% resulted in a stepwise rise in hydrophobicity, but the functionality as a membrane was compromised when the concentration reached 20%. Hydrophobicity on the membrane surface was higher with 15% PDMS treatment than on the chemically grafted membrane, but the latter demonstrated superior performance in the membrane distillation process. Nevertheless, the study confirms the potential of the pure PDMS-coated membrane as a viable option for membrane distillation, with the possibility of enhancing performance through improvements in pore size and surface morphology.

Luminescence properties of Tb3+/Eu3+ ions activated LiLaSiO4 phosphors for solid-state lighting and flexible display applications

The synthesis and luminescence properties of Tb3+ and Eu3+ single- and co-doped LiLaSiO4 (LLSO) phosphors with energy transfer mechanisms were reported. The rare-earth ions doped LLSO phosphors were synthesized via a solid-state reaction method and their physical characterizations such as phase purity, surface morphology, and elemental analysis were investigated systematically. For the Tb3+ and Eu3+ single- and co-doped LLSO phosphors, their photoluminescence (PL) properties were studied in detail. The LLSO:Tb3+ and LLSO:Eu3+ single-doped phosphors showed superior red and green emissions due to 5D4→7F5 and 5D0→7F2 in the optimized characteristic electronic transitions under ultraviolet (UV) irradiation, respectively. The luminescence performances for both the LLSO:Tb3+ and LLSO:Eu3+ phosphors were optimized at 0.125 mol of doping ion concentration. Under UV excitation, by adjusting the Eu3+ ion concentration in LLSO:0.125Tb3+/Eu3+ phosphors, the tunable emissions from green to red via yellow-orange were obtained. Thus, the tunable emission spectra and luminescence decay lifetimes with increasing the doping content of acceptor ions (Eu3+) confirmed an efficient energy transfer from Tb3+ to Eu3+ ions in the co-doped samples. The critical distance between Tb3+ and Eu3+ was determined to be 13.26 Å and the energy transfer mechanism from Tb3+ to Eu3+ ions was demonstrated to be a dipole-dipole mechanism interaction. In addition, the temperature-dependent PL study was carried out for the LLSO:0.125Tb3+/0.025Eu3+ co-doped phosphor sample and it showed better thermal stability against the temperature quenching. The Tb3+ and Eu3+ single- and co-doped LLSO/polydimethylsiloxane (PDMS) flexible composite films were fabricated by mixing the phosphor powders and PDMS solution. Benefiting from the effective protection of the PDMS matrix, the luminescence stability of the composite films was greatly enhanced. Based on the excellent properties of the synthesized phosphors, Tb3+ and Eu3+ single-doped and Tb3+/Eu3+ co-doped LLSO phosphors could serve as a single-phase multicolor-emitting phosphor under UV excitations.

A superhydrophobic graphene@copper mesh irradiated by laser for efficient oil/water separation

Oil/water separation has become a global task due to the worldwide increase of oily wastewater. As such, developing membranes that could separate oil from water is of high importance. The aim of this work is to develop a copper mesh with superhydrophobic properties that has a high oil/water separation efficiency. To achieve this, a copper mesh was coated with a monolayer graphene/polydimethylsiloxane (PDMS) mixture in a one-step immersion process. Combining a fixed percentage of graphene (3 %) with three different ratios of PDMS (10 %, 5 % and 2.5 %) allowed us to investigate the effect of PDMS on the contact angle of the fabricated meshes. The Cu-mesh prepared by a 2.5 % PDMS solution displayed the highest contact angle of 133.3o ± 0.5. Irradiating the samples with a Nd:YAG −1064 nm laser, that scans the whole area of the mesh, resulted in the improvement of the hydrophobic properties of the surface. It was also found that the laser-to-sample distance influenced the improvement of the contact angle. Graphene@Cu mesh, treated by laser at a distance of 1.5 mm above the laser focal point showed superhydrophobic characteristics with a contact angle of 155.6o ± 0.3. The oil/water separation efficiency was measured for the fabricated meshes. The best developed mesh showed potential in separating both thick oils, such as HD-40 engine oil, and thin oils, such as toluene, from water with separation efficiencies of 92 % and 95 %, respectively.

Fabrication, Properties, and Performance of Polymer-Clay Nanocomposites for Organic Dye Removal from Aqueous Media

Methylene blue dye (MB dye) is a harmful contaminant for wastewater streams of industries and is harmful to human and aquatic life. An ecofriendly sugar templating process was used to generate porous bentonite/polydimethylsiloxane (PB) and porous magnetite nanoparticles/bentonite/polydimethylsiloxane (PBNP) composite absorbents to remove MB dye in this study. During the infiltration of PDMS solution into the sugar template in the vacuum chamber, bentonite and magnetite particles were integrated on the surface of the PDMS, and the porous structure was generated during the leaching out of sugar particles in water. The absorbents were characterized using Fourier infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). The absence of the methyl bond at 2924 cm-1 and phenol bond at 3325 cm-1 in the FTIR spectra of the formed membrane proves that the food grade sugar was completely removed. The SEM images confirm that porosity was achieved as well as uniform mixing of the in the formation of composite. MB dye was effectively removed from wastewater using the as-prepared composite as absorbent. The removal efficiencies of the composite PBNP and PB were ~91% and ~85%, respectively. The experimental data was applied to pseudo-first-order (PFO) and pseudo-second-order (PSO) kinetic models as well as the Dubinin-Radushkevich, Harkins-Jura, and Elovich models for the adsorption isotherm. The data was found to fit the pseudo-second-order and Elovich models, respectively. The results show that the presence of magnetite nanoparticles improved MB dye removal significantly.

A Homogenous, Photocrosslinkable Poly(dimethylsiloxane‐co‐methylvinylsiloxane) Solution in an Acrylate Monomer

AbstractIn this study, a simple photocuring method is proposed for preparing PDMS elastomers using a homogenous poly(dimethylsiloxane) (PDMS) solution in tert‐butyl acrylate (tBA) as an alternative way of mechanically blending two kinds of PDMS respectively containing vinyl and hydridosilyl groups over a platinum catalyst. Poly(dimethylsiloxane‐co‐methylvinylsiloxane) (PDMSc) with 30 mol% of vinyl moieties is synthesized. The functionalized PDMS is estimated to be soluble in tBA from theoretical calculations of solubility parameters of PDMS and several liquid monomers. The PDMS solution is satisfactorily photocured under a conventional photoinitiator. Initial modulus and strain of the photocured films increase from 144 to 552 MPa and decrease from 3.96 to 1.84, respectively, as the tBA content rises from 5 to 30 wt%. They are extremely transparent in a visible region (T > 94%) regardless of the amount of tBA. The unreacted vinyl groups in PDMSc are inter‐ or intrareacted near 200 °C and γ‐hydrogen transfer reactions from the tert‐butyl groups in poly(tert‐butyl acrylate) occur over 250 °C. One of the photocrosslinked films exhibits outstanding performance as an electroactive polymer in application. In essence, this study will initiate a new methodological research into provision of PDMS elastomers using an easily formulated photocrosslinkable PDMS solution.

Micro-Nano-Nanowire Triple Structure-Held PDMS Superhydrophobic Surfaces for Robust Ultra-Long-Term Icephobic Performance.

Anti-icing superhydrophobic surfaces have attracted tremendous interests due to their repellency to water and extremely low ice affinity, whereas the weak durability has been the bottleneck for further applications. Surface durability is especially important in long-term exposure to low-temperature and high-humidity environments. In this study, a robust micro-nano-nanowire triple structure-held PDMS superhydrophobic surface was fabricated via a hybrid process: ultrafast-laser-prepared periodic copper microstructures were chemically oxidized, followed by modification of PDMS. The hedgehog-like surface structure was composed of microcones, densely grown nanowires, and tightly combined PDMS. The capillary force difference in micro-nanostructures drove PDMS solutions to distribute evenly, bonding fragile nanowires to form stronger composite cones. PDMS replaced the commonly used fragile fluorosilanes and protected nanowires from breaking, which endowed the surfaces with higher robustness. The ductile PDMS-nanowire composites possessed higher resiliency than brittle nanowires under a load of 1 mN. The surface kept superhydrophobic and ice-resistant after 15 linear abrasion cycles under 1.2 kPa or 60 icing-deicing cycles under -20 °C or 500 tape peeling cycles. Under a higher pressure of 6.2 kPa, the contact angle (CA) was maintained above 150° until the abrasion distance exceeded 8 m. In addition, the surface exhibited a rare spontaneously optimized performance in the icing-deicing cycles. The ice adhesion strength of the surface reached its lowest value of 12.2 kPa in the 16th cycle. Evolution of surface roughness and morphology were combined to explain its unique U-shaped performance curves, which distinguished its unique degradation process from common surfaces. Thus, this triple-scale superhydrophobic surface showed a long-term anti-icing performance with high deicing robustness and low ice adhesion strength. The proposed nanostructure-facilitated uniform distribution strategy of PDMS is promising in future design of durable superhydrophobic anti-icing surfaces.

Fabrication of multilayer composite hollow fiber membrane comprising NH2-MIL-125 (Ti) for CO2 removal from CH4

The presence of CO2 has created significant challenges in natural gas processing in order to meet consumer’s specifications and pipeline transportation. Membrane separation is among the most effective approaches in CO2 separation from natural gas mainly to its energy efficiency. This study investigates the alternate technique for enhancing the performance of hollow fiber membrane in CO2 removal from CH4. A new type of composite hollow fiber membrane is fabricated by dip-coating of polymer solution comprising various loadings of NH2-MIL-125 (Ti) in PEBAX onto PDMS coated-polysulfone (PSf) hollow fiber. The morphology and elemental mapping analysis of the resultant membranes were characterized via scanning electron microscope (SEM) and energy dispersive X-ray (EDX), respectively. SEM images showed that no major voids or clusters were observed between the two phases of polymer and filler. Improved CO2 and CH4 gas permeance were found for composite membranes, as compared to PSf membrane coated only by PDMS and PEBAX solutions. Besides, highest improvement of CO2/CH4 ideal selectivity was obtained for composite membrane loaded with 10 wt% of filler. High porosity and high CO2 affinity of NH2-MIL- 125 (Ti) are the main reasons for the enhancement of CO2 removal from CH4. Hence, further research work is necessary to explore the performance of this membrane at various operating conditions such as temperature, flow rate, and CO2 feed concentration.

A Method for Manufacturing Flexible Microfluidic Chip Based on Soluble Material

In this paper, a novel method for manufacturing flexible microfluidic chips without bonding process is proposed, which combines 3D printing technology and material dissolution technology. The manufacturing process of the microfluidic chip is as follows: a soluble HIPS mold with a preset shape is manufactured by 3D printing and placed in a molten PDMS solution for solidification. Soak in the limonene material to dissolve the mold and form a microchannel in the cured PDMS. Experimental studies have shown that the temperature and concentration of the limonene solution have an important effect on the dissolution rate. A 0.62 cm3 HIPS mold has the fastest dissolution rate at 100°C and 50% concentration. The proposed method provided a new idea for fabricating flexible microfluidic chip. Compared to bonding process, it has the characteristics of not relying on complicated processing conditions and low manufacturing cost.

Method for Inkjet-printing PEDOT:PSS polymer electrode arrays on piezoelectric PVDF-TrFE fibers.

We present a method for printing conductive polymers onto P(VDF-TrFE) nanofibers to create all-polymer piezoelectric devices. Inkjet printing is an attractive fabrication approach for rapid prototyping of flexible electronics, but until now with limited applications in developing P(VDF-TrFE) nanofiber-based devices. We have demonstrated an approach to infill the void space within a piezoelectric nanofibrous matrix to allow for the inkjet printing of aqueous inks while avoiding leakage that typically leads to electrical shorting and without significant loss of voltage output. This was done using a diluted PDMS solution and a commercially available conductive ink. The 1 cm2 devices showed a 254 mV/N sensitivity to impact as well as a sensitivity to bending. The device was shown to be able to detect breathing and pulse rate when placed superficially to the carotid and radial arteries. Using these techniques, flexible piezoelectric sensing can be done in an array format, shown with applications in foot movement sensing.

Anti-icing efficiency on bio-inspired slippery elastomer surface

In this study, we conducted a facile method to fabricate an anti-icing surface on elastomer thin film by combining the PDMS nanostructure with the low surface tension lubricant. PDMS solution was mixed with slippery lubricant Krytox 1506 in a rational concentration and followed by a plasma dry etching process to promote the anti-icing performance in terms of shear stress and water repellency ability. Experimental results were compared with the reference substrates and demonstrated the advantages of the slippery surface in all mentioned scenarios. In addition, the functionalized surfaces also present high durability and good transparency, demonstrating a new facile method and design for outdoor anti-icing devices.

Highly contrastive, real-time modulation of light intensity by reversible stress-whitening of spontaneously formed nanocomposites: application to wearable strain sensors

Reversible stress-whitening in a nanocomposite film spontaneously formed from a photocurable PDMS solution enables reliable and real-time monitoring of human motion in the form of a wearable interface.

Properties of polydimethylsiloxane hydrophobic modified duplex microarc oxidation/diamond-like carbon coatings on AZ31B Mg alloy

A reliable, high-performance coating procedure was developed using PDMS to modify a duplex MAO/DLC coating on an AZ31B Mg alloy. First, the duplex MAO/DLC coating was fabricated via a combined MAO and unbalanced magnetron sputter process. Subsequently, a PDMS solution was used to modify the MAO/DLC coating via a conventional dip-coating method. The surface characteristics, bond strength, hardness, tribological behaviour, and corrosion resistance of the coated samples were evaluated via SEM, CA, Raman spectroscopy, friction and wear behaviour, polarisation curve, and NSS tests. The PDMS modification reduced the H IT of MAO/DLC coating from 15.96 to 8.34 GPa; this is ascribed to the penetration of PDMS, which has good rheological properties to form a viscoelastic Si-based organic polymer layer on the MAO/DLC coating. However, the PDMS-modified MAO/DLC coating was denser, hydrophobic, and had higher bond strength compared with MAO- and MAO/DLC-coated samples. Moreover, the PDMS modification reduced the COF and wear rate of the duplex MAO/DLC coating. This indicates that the PDMS improved the tribological behaviour owing to the transferred Si oxide that originated from the Si-O network of the PDMS, as well as the low graphitisation of the DLC layer during sliding. Furthermore, the corrosion current density of the MAO/DLC-coated sample modified by PDMS for 10 min decreased by two order of magnitude compared with that of the MAO/DLC-coated sample but by five orders of magnitude compared with that of the bare substrate. The NSS tests proved that the PDMS layer slowed the corrosion of the Mg alloy under long-term service, enhancing the corrosion protection efficiency. The results are attributed to the high bond strength and lubricant MAO/DLC layer, and the dual role of sealing and hydrophobicity of PDMS. Therefore, PDMS modification is promising for the fabrication of protective materials for Mg alloys that require corrosion and wear resistance.

ZnO decorated polydimethylsiloxane sponges as photocatalysts for effective removal of methylene blue dye

In this study, porous zinc oxide/polydimethylsiloxane (ZnO/PDMS) sponge-like photocatalysts were prepared by an eco-friendly sugar templating method. The ZnO particles were incorporated on the surface of the PDMS during the infiltration of PDMS solution into sugar template in the vacuum chamber and the porous structure was created during the leaching out of sugar particles in water. The as-prepared composite sponges were utilized as efficient photocatalysts for the effective removal of methylene blue dye from wastewater under visible, UV and UV–visible light. The photocatalytic efficiencies under UV–visible and visible light illumination were obtained ~93% and ~85% by the composite ZnO/PDMS with about 2.7- and 5.7-fold higher kinetics, respectively than the pure PDMS sponge. Importantly, a quicker kinetic reaction rate can be achieved by the composite sponges than pure sponge under UV light compared to other lights. Finally, the high recyclability demonstrates the potential applications of the PDMS based photocatalytic porous sponges for the mitigation of environmental issues.

Synthesis of superhydrophobic and high stable Zr-MOFs for oil-water separation

A universal strategy is developed to construct a superhydrophobic and superoleophilic metal-organic framework (MOF) by an amidation reaction between amino group and acid chloride of octadecanoyl chloride. The introduction of long alkyl chain reduced the surface free energy, yielding a superhydrophobic Zr-MOF (UiO-66-NH-C18) with a high water contact angle (WCA) of 151.7°. The adsorbed amount of water on the UiO-66-NH-C18 was only 5.59 mmol/g, which was just 28 % of that on the UiO-66-NH2. More importantly, the hydrophobic modification improved the stability of Zr-MOFs under strong alkaline conditions (e.g., pH = 13). Furthermore, the UiO-66-NH-C18 can selectively absorb organic solvent from water and achieve continuous oil-water separation. The oil-water separation efficiency could reach up to 99.9 %. In addition, the UiO-66-NH-C18@sponge was also prepared through dip-coating of UiO-66-NH-C18 on the melamine sponge in the presence of PDMS solution. The resulting composite shows high adsorption capacities for various oils and organic solvents ranging from 32.3–66.1 g/g. The superhydrophobic UiO-66-NH-C18@sponge has potential as a promising absorbent for treatment of oily wastewater.

Paraffin Oil Based Soft-Template Approach to Fabricate Reusable Porous PDMS Sponge for Effective Oil/Water Separation.

Three-dimensional porous material holds enormous potential in the field of life science and environmental protection. In this work, we proposed a facile route for the large-scale synthesis of porous poly(dimethylsiloxane) (PDMS) sponge via paraffin oil based emulsion technique. A stable emulsion could be formed by emulsifying water in the PDMS solution with the aid of paraffin oil. Moreover, the amount of emulsified water in 5 g of PDMS solution is as high as 35 g, and the skeleton of the prepared PDMS sponge is still in intact. This method is cost-effective, rapid, and easily scaled up. The water contact angle of the obtained PDMS sponge is 141.9 ± 1°, and the absorption capacities of the sponges are 13.5-33.3 g g-1 for various organic solvents. The PDMS sponge only needed 0.069 MPa force to realize the compression ratio of 90%, which it still maintained after over 50 cycles of compression. In addition, the porous PDMS sponge exhibited an excellent oil absorption and an outstanding reusability, which were potentially useful in water purification.

Analysis and experiments on the spreading dynamics of a viscoelastic drop

• Spreading dynamics of a sessile viscoelastic drop on a horizontal surface is studied. • Simplified Phan–Thien–Tanner model represents the rheology of the viscoelastic drop. • Theoretical results are validated with our experimental results. • Elastic nature of the viscoelastic fluids reduces the spreading rate of the drop. We study the spreading dynamics of a sessile viscoelastic drop on a horizontal surface, where a simplified Phan–Thien–Tanner (sPTT) model is considered to represent the rheology of viscoelastic drop. We have adopted a macroscopic approach to obtain the temporal evolution of the spreading drop, while to establish the efficacy of the theoretical model, we have validated the results obtained from the mathematical formulation with the experimental results for both the Newtonian (Si-oil) and viscoelastic (PDMS and aqueous solution of CMC and glycerin) drops. Following the framework of Seaver–Berg approximation, the spherical shape of the drop is assumed as a cylindrical disk here. We observe from this study that an increment in the elasticity of the fluid enhances the velocity gradient and increases the viscous dissipation in the drop volume, leading to a reduction in the spreading rate.

Antimicrobial coatings based on poly(dimethyl siloxane) and silver nanoparticles by solution blow spraying

Antimicrobial coatings of poly(dimethyl siloxane) with silver nanoparticles (PDMS/AgNPs) were produced by solution blow spraying (SBSp), an adaptation of the solution blow spinning technique (SBS). Firstly, AgNPs were synthesized by the Turkevich method and characterized by dynamic light scattering (DLS), ultraviolet-visible spectroscopy (UV–vis), agar disk diffusion tests against Escherichia coli and Staphylococcus aureus, and toxicity to Artemia salina. Further, the PDMS/AgNPs coating was prepared in two steps by deposition of PDMS solution in hexane (2:1) over the substrate, and then, five depositions, in intervals of 7.5 min each, of the colloidal dispersion of AgNPs onto partially cured PDMS surface. The neat PDMS and PDMS/AgNPs coatings were characterized by inductively coupled plasma atomic emission spectrometry (ICP-AES), atomic force microscopy (AFM), contact angle and scanning electron microscopy coupled with energy dispersive X-ray spectrometry (SEM/EDS). Furthermore, the antimicrobial activity against S. aureus and E. coli biofilm formation was evaluated by fluorescence. The results indicate that AgNPs were adhered near the PDMS coating surface, assuring antimicrobial activity against the studied microorganisms at a concentration of about 0.04 μg cm−2 and average particle size of 170.5 nm. Therefore, the SBSp technique, used to produce PDMS/AgNPs coating in two steps, proved to be a suitable method to produce antimicrobial coatings with potential applications in active packaging and self-disinfecting surfaces.

Biomimetic fabrication and photoelectric properties of superhydrophobic ZnO nanostructures on flexible PDMS substrates replicated from rose petal

Three-dimensional hierarchical ZnO nanostructures have been fabricated on flexible hierarchical PDMS substrates via a combination of facile PDMS casting process and solution growth routine. Fresh rose petal was used as template for the preparation of positive and negative hierarchical PDMS substrates. Morphologies, dimensions and orientation of ZnO nanostructures grown on rose-petal-like flexible PDMS surface can be controlled by adjusting the hydrothermal reaction parameters. ZnO nanostructures grown on the hierarchical PDMS substrate were found to highly influence the surface wetting behavior. Furthermore, the photoelectrical characterizations demonstrate that the flexible device based on superhydrophobic ZnO/PDMS films showed a high sensitivity of UV light and presented potential applications in optoelectronic applications.

Separation of CO2 and N2 from CH4 using modified DD3R zeolite membrane: A comparative study of synthesis procedures

The SiO2/H2O ratio of the synthesis solution has high importance in the synthesis of selective DD3R zeolite membrane. A DD3R membrane (M1) has been synthesized by procedure with a defined low SiO2/H2O ratio used mostly for the synthesis of DD3R powder. Another membrane (M2) has been synthesized by procedure with a defined high SiO2/H2O ratio that the synthesis of high selective DD3R membrane with this method is limited to NGK11Nippon (Japan) Gaishi (insulator) Kaisha (company).-insulators. XRD and SEM confirmed the formation of DD3R layer on the support with both methods. The surface of membranes were treated with polydimethyl siloxane solution. The results of pure gas permeation of CO2, N2 and CH4 and CO2/CH4 equimolar mixture showed that using the synthesis procedure with the low SiO2/H2O ratio leads to DD3R membrane with less defects, while the obtained membrane with the high SiO2/H2O ratio was so thick with low performance. Also, high separation performance of the membrane M1 (selectivity of 290 and 9 for CO2/CH4 and N2/CH4) reveals that the procedure with the low SiO2/H2O ratio following by the surface treatment with PDMS solution can be used as a high potential procedure to synthesize a selective DD3R zeolite membrane for separation of CO2 and N2 from CH4.