Ultrahydrophobic melamine sponge via interfacial modification with reduced graphene oxide/titanium dioxide nanocomposite and polydimethylsiloxane for oily wastewater treatment

Three-dimensional(3D)porous absorbents have attracted significant attention in the oily wastewater treatment technology due to their high porosity and elasticity.Given their amphiphilic surface,they have a propensity to simultaneously absorb water and oil,which restricts their range of applications.In this study,a reduced graphene oxide and titanium dioxide nanocomposite(rGO/TiO_(2))was used to fabricate an ultra-hydrophobic melamine sponge(MS)through interfacial modification using a solution immersion technique.To further modify it,poly-dimethylsiloxane(PDMS)was grafted onto its surface to establish stronger covalent bonds with the composite.The water contact angle of the sponge(rGO/TiO_(2)/PDMS/MS)was 164.2°,which satisfies the condition for ultrahydrophobicity.The evidence of its water repellency was demonstrated by the Cassie-Baxter theory and the lotus leaf effect.As a result of the increased density of rGO/TiO_(2)/PDMS/MS,it recorded an initial capacity that was 2 g/g lower than the raw MS for crude oil absorption.The raw MS retained 53% of its initial absorption capacity after 20 cycles of absorption,while rGO/TiO_(2)/PDMS/MS retained 97%,suggesting good recyclability.Excellent oil and organic solvent recovery(90%-96%)was demonstrated by rGO/TiO_(2)/PDMS/MS in oil-water combinations.In a continuous separation system,it achieved a remarkable separation efficiency of 2.4×10^(6)L/(m^(3)·h),and in turbulent emulsion separation,it achieved a demulsification efficiency of 90%-91%.This study provides a practical substitute for massive oil spill cleaning.

Influence of water vapor on the separation of volatile organic compound/nitrogen mixture by polydimethylsiloxane membrane

In the industrial treatment of waste volatile organic compound(VOC)streams by membrane technology,a third impurity,generally,water vapor,coexists in the mixture of VOC and nitrogen or air,and can affect membrane performance and the design of the industrial process.This study focused on the investigation of the effect of water vapor on the separation performance of the separation of VOC/water/nitrogen mixtures by a polydimethylsiloxane(PDMS)membrane.Three types of VOCs:water-miscible ethanol,water-semi-miscible butanol,and water-immiscible cyclohexane,were selected for the study.Different operating parameters including,concentration of the feed VOC,feed temperature,and concentration of the feed water were compared for the separation of binary and ternary VOC/nitrogen mixtures.The interaction between the VOC and water was analyzed to explain the transportation mechanism after analyzing the difference in the membrane performance for the separation of binary and ternary mixtures.The results indicated that the interaction between the VOC(or nitrogen)and water is the key factor affecting membrane performance.Water can promote the permeation of hydrophilic VOC but prevent hydrophobic VOC through the membrane for the separation of ternary VOC/water/nitrogen mixtures.These results will provide fundamental insights for the design of the recovery application process for industrial membrane-based VOCs,and also guidance for the investigation of the separation mechanism in vapor permeation.

Impact of polydimethylsiloxanes on physicochemical and tribological properties of naphthenic mineral oil(KN 4010)-based titanium complex grease

Titanium complex greases were prepared by using naphthenic mineral oil and polydimethylsiloxane as the mixed base oil. The effect of polydimethylsiloxane molecular weight and polydimethylsiloxane content in mixed base oil on the physicochemical and tribological properties of titanium complex greases was investigated.As compared to the sole mineral oil-based titanium complex grease, the use of polydimethylsiloxane(H201-350)as a co-base oil increased the dropping point from 310 to 329℃, decreased the oil separation from 3.7% to 2.3%,reduced the corrosion extent, and obviously improved the tribological properties. When the mixed oil-based titanium complex grease was used as a lubricant, lubricating films of polydimethylsiloxane were probably formed on the surfaces of friction pairs, giving good lubricating property.

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 HIT of MAO/DLC coating from 15.96 to 8.34GPa;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 10min 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.

Recent advances in lithographic fabrication of micro-/nanostructured polydimethylsiloxanes and their soft electronic applications

The intensive development of micro-/nanotechnologies offers a new route to construct sophisticated architectures of emerging soft electronics.Among the many classes of stretchable materials,micro-/nanostructured poly(dimethylsiloxane)(PDMS)has emerged as a vital building block based on its merits of flexibility,stretchability,simple processing,and,more importantly,high degrees of freedom of incorporation with other functional materials,including metals and semiconductors.The artificially designed geometries play important roles in achieving the desired mechanical and electrical performances of devices and thus show great potential for applications in the fields of stretchable displays,sensors and actuators as well as in health-monitoring device platforms.Meanwhile,novel lithographic methods to produce stretchable platforms with superb reliability have recently attracted research interest.The aim of this review is to comprehensively summarize the progress regarding micro-/nanostructured PDMS and their promising soft electronic applications.This review is concluded with a brief outlook and further research directions.

A STUDY ON RADIATION CROSSLINKING OF POLYDIMETHYLSILOXANE (PDMS) RUBBER LATEX

Polydimethylsiloxane (PDMS) rubber latex with two sorts of sensitizers, trimethylol propane tri-methacrylate (TMPTMA) and diethylene glycol di-acrylate (DEGDA), was irradiated with γ-rays and electron beams in various conditions. The radiation crosslinking reaction of PDMS occurs in the inner phase of the latex and is relatively isolated from the water phase. Therefore the oxygen and the radicals produced by the radiolysis reaction of water almost have no effect on the crosslinking reaction of polymer. The experimental data correspond with the Charlesby-Pinner relationship in the main. The gelation doses, degree of crosslinking and degradation as well as G values of crosslinking were calculated. From them, the sensitization coefficients were derived to offer a quantitative measurement of the enhancing effect of sensitizer on the radiation crosslinking.

Polydimethylsiloxane (PDMS) Composite Membrane Fabricated on the Inner Surface of a Ceramic Hollow Fiber: From Single-Channel to Multi-Channel

The fabrication of a separation layer on the inner surface of a hollow fiber (HF) substrate to form an HF composite membrane offers exciting opportunities for industrial applications, although challenges remain. This work reports on the fabrication of a polydimethylsiloxane (PDMS) composite membrane on the inner surface of a single-channel or multi-channel ceramic HF via a proposed coating/crossflow approach. The nanostructures and transport properties of the PDMS HF composite membranes were optimized by controlling the polymer concentration and coating time. The morphology, surface chemistry, interfacial adhesion, and separation performance of the membranes were characterized by fieldemission scanning electron microscope (FE-SEM), attenuated total reflection Fourier-transform infrared (ATR-FTIR) spectroscopy, the nano-indentation/scratch technique, and pervaporation (PV) recovery of bio-butanol, respectively. The formation mechanism for the deposition of the PDMS layer onto the inner surface of the ceramic HF was studied in detail. The optimized inner surface of the PDMS/ceramic HF composite membranes with a thin and defect-free separation layer exhibited a high flux of ~1800 gm-2h-1 and an excellent separation factor of 35–38 for 1 wt% n-butanol/water mixtures at 60
C. The facile coating/cross-flow methodology proposed here shows great potential for fabricating inner-surface polymer-coated HFs that have broad applications including membranes, adsorbents, composite materials, and more.

Moth-eye Structured Polydimethylsiloxane Films for High-Efficiency Perovskite Solar Cells

Large-area polydimethylsiloxane(PDMS)films with variably sized moth-eye structures were fabricated to improve the efficiency of perovskite solar cells.An approach that incorporated photolithography,bilayer PDMS deposition and replication was used in the fabrication process.By simply attaching the moth-eye PDMS films to the transparent substrates of perovskite solar cells,the optical properties of the devices could be tuned by changing the size of the moth-eye structures.The device with 300-nm moth-eye PDMS films greatly enhanced power conversion efficiency of ~21 % due to the antireflective effect of the moth-eye structure.Furthermore,beautiful coloration was observed on the 1000-nm moth-eye PDMS films through optical interference caused by the diffraction grating effect.Our results imply that moth-eye PDMS films can greatly enhance the efficiency of perovskite solar cells and building-integrated photovoltaics.

INFLUENCE OF SURFACE-MODIFICATION FOR CALCIUM CARBONATE ON THE INTERACTION BETWEEN THE FILLERS AND POLYDIMETHYLSILOXANE

The surface of calcium carbonate(CaCO_3)particles was modified with stearic acid(SA)and the chemical structures of the product were characterized by FT-IR analysis.The interaction between polydimethylsiloxane(PDMS)and CaCO_3 fillers with different surface character was investigated by means of dynamic rheological and bound rubber tests for uncured compounds and mechanical properties measurements for the corresponding vulcanites.The results of dynamic tests indicate that with the increase of SA mass fraction...

Synthesis and characterization of a novel hydroxypolyether blocked polydimethylsiloxane PEO-b-PDMS-b-PEO

A novel hydroxypolyether blocked polydimethylsiloxane, poly（ethylene oxide） propyl-b-polydimethylsiloxane-b-propyl poly（ethylene oxide） （PEO-b-PDMS-b-PEO） was synthesized by simple hydrosilation reaction of poly（ethylene glycol） monoallyl ether with α,ω-dihydrogen terminated PDMS （HPDMS）. Fourier transform infrared spectroscopy （FTIR） and IH NMR were used to identify the structure of PEO-b-PDMS-b-PEO and intermediate product HPDMS. Based on the effect investigations of temperature, reactant molar ratio, catalyst and time on the hydrosilation, it was found that the conversion of Si-H bond to SiC bond increased with the increase of catalyst and time, and the reaction completed when the content of catalyst was 22μg/g and the time was 5 h, respectively. Urethane reaction of OH and NCO group confirms that PEO-b-PDMS-b-PEO is more reactive toward to diisocyanate than α,ω-dihydroxylbutyl terminated PDMS.

Synthesis and characterization of poly(phthalazinone ether nitrile) (PPEN)-polydimethylsiloxane (PDMS) block copolymers

Block copolymers with different backbone compositions have been prepared by the condensation of dimethylamino terminated poly（dimethylsiloxane） （PDMS） and hydroquinone terminated poly（phthalazinone ether nitrile） （PPEN） in the presence of chlorobenzcne/N-methyl pyrrolidone （NMP） as solvents. The products were characterized by FTIR, ^1H NMR and gel permeation chromatography. Differential scanning calorimetry analysis indicated that the block copolymers showed separated microphase.

Synthesis and characterization ofα-{3-[(2,3-dihydroxy) propoxy]propyl}-ω-butylpolydimethylsiloxanes

Hydrosilylation has been carried out between Si-H terminated polydimethylsiloxanes with narrow molecular weight distribution and protected 3-allyloxy-l,2-propanediol, and after subsequently alcoholyzed, α-{3-[（2,3-dihydroxy）propoxy]propyl}-ω- butyl-polydimethylsiloxanes with varying number of （（Si（CH3）2-O） unit were obtained. At each step, the produced compounds were carefully characterized. The results showed that each step was successfully carried out and target products were achieved.

Comparison of Apical Leakage in Root Canal Obturation Using Bioceramic and Polydimethylsiloxane Sealer (<i>In Vitro</i>)

Background: One of the ideal properties of a root canal sealer is to have a good sealing ability, especially at the apical third of the root. Objective: To evaluate the comparison of the apical leakage between obturation using bioceramic sealer (BS) and polydimethylsiloxane sealer (PS). Materials and Methods: Thirty-six mandibular premolars were equally divided into two groups and were obturated with single cone technique. The sealers used for Group I and Group II were BS and PS respectively. After obturation, the samples were incubated (37&deg;C, 24 h), sealed with two coats of nail polish except for 2 mm from the apex, submerged in the Indian ink for 7 days, decalcified, dehydrated, and made transparent according to Robertson technique. Dye penetration was evaluated under stereomicroscope. Samples without dye penetration were given score 0, dye penetration ≤ 0.5 mm were given score 1, 0.51 - 1 mm were given score 2, and >1 mm were given score 3. Result: The largest proportion distribution in BS group was at the score 1 (55.6%), whereas in PS group was at the score 2 (44.4%). Conclusion: Bioceramic sealer showed similar apical leakage to polydimethylsiloxane sealer. Clinical Relevance: Based on this study, bioceramic sealer can be recommended to be used as sealer with low level of apical leakage as well as polydimethylsiloxane sealer.

SYNTHESIS AND CHARACTERIZATION OF POLYDIMETHYLSILOXANE/POLYSTYRENE SEMIINTERPENETRATING POLYMER NETWORKS

The synthesis of pseudo- and semi-interpenetrating polymer networks (IPNs) based on polydimethylsiloxane (PDMS) and polystyrene (PS) is described. IPNs were obtained by simultaneous and in situ sequential synthesis procedure. The preliminary studies on IPNs properties such as transition temperature, microphase separation and mechanical behaviors have been carried out by using differential scanning calorimetry (DSC) and scanning electron microscopy (SEM). The experimental evidence clearly showed that semi-IPNs obtained by sequential synthesis procedure have higher interpenetrating extent than pseudo-IPNs synthesized by simultaneous procedure. Over the full composition, the PDMS/PS IPNs are immiscible. The pseudo-IPNs microphase separation can be greatly subdued through the formation of grafting bonds between two networks as well as the kinetic rate-matching of the individual network crosslinking.

Regulatable pervaporation performance of Zn-MOFs/polydimethylsiloxane mixed matrix pervaporation membranes

Pervaporation(PV)is an emerging separation technique for liquid mixture.Mixed matrix membranes(MMMs)often demonstrate trade-off relationship between separation factor and flux.In this study,by changing the organic linkers(2-methyl imidazolate,imidazole-2-carboxaldehyde,2-ethyl imidazolate),ZIF-8,ZIF-90 and MAF-6 were prepared and filled in polydimethylsiloxane(PDMS)membranes for dealcoholization of 5%(mass)n-butanol solution,and the membranes properties and pervaporation performances were adjusted.Compared with the pure PDMS membrane,the addition of ZIF-8 resulted in a 9%increase in flux(1136 g·m^(-2)·h^(-1))and a 22.5%increase in separation factor(28.3),displaying antitrade-off effect.For the MAF-6/PDMS MMMs(2.0%mass loading),the pervaporation separation index(PSI)and separation factor were 32347 g·m^(-2)·h^(-1) and 58.6 respectively(increased by 34%and 154%in contrast with that of the pure PDMS membrane),and the corresponding permeation flux was 552 g·m^(-2)·h^(-1),presenting great potential in the removal butanol from water.It was deduced that the large aperture size combined with moderate hydrophobicity of metal–organic frameworks(MOFs)favor the concurrent increase in permeability and selectivity.

Investigation on Thermal and Dimensional Stability of Epoxy Resin In-Situ Modified by Cyanate Ester Resin and Polydimethylsiloxane

The thermal and dimensional stability of epoxy resin(EP)in-situ modified by cyanate ester(CE)and polydimethylsiloxane(PDMS)are investigated by means of experiments and numerical simulation.Thermal gravimetric analysis(TGA)and differential scanning calorimeter(DSC)are used to analyze the heat resistance of the modified EP.The dimensional stability is characterized by the volume shrinkage of the series PDMS/CE/EP obtained by the density method.The chemical structure of the PDMS/CE/EP is analyzed by Fourier transform infrared spectroscopy(FTIR).The results of TGA and DSC indicate that the thermal stability of PDMS/CE/EP decreases firstly and then increases with the increase in the amount of CE.The addition of PDMS shows a slight effect on the thermal stability.The 40%CE makes the blending system exhibit the lowest initial decomposition temperature,which reduces by 15.5%and 40.8%compared with pure EP and CE,respectively.The FTIR results suggested that the influence of CE on the thermal stability of the modified EP is mainly ascribed to the generation of oxazolidinone ring with low thermal stability and the increase in the triazine ring with high thermal stability.The volume shrinkage measurement results show that the introduction of CE and PDMS are both beneficial to the improvement of the dimensional stability of the blending systems.The in-situ addition of 80%CE shows the lowest volume shrinkage of6.11%.The thermal stress distribution of PDMS/CE/EP generated during the solidification process is simulated by the finite element analysis.The results suggested that the introduction of 80%CE into EP results in the lowest thermal stress in the blending system,which indicates that the system has the lowest volume shrinkage,which agrees well with the experimental results.

Polydimethylsiloxane Microchip Capillary Electrophoresis for Determination of Cholesterol

Microchip capillary electrophoresis （MCE） has significant impact on diagnostic testing. One of the most importance in clinical analysis test is the determination of cholesterol level in blood, because its increase is associated with coronary heart disease which is a major cause of death world over. Polydimethylsiloxane （PDMS） was material used to make a MCE for determination of cholesterol. Hydrogen peroxide was generated from the oxidation of cholesterol with cholesterol oxidase （ChOx） and was detected electrochemically at a downstream gold （Au） wire electrode by amperometry. Various parameters, such as the detection potential, concentration of running buffer, pH of running buffer, separation voltage, injection time, and concentration of ChOx, were studied. The migration time of cholesterol is less than 100s and the calibration curve is linear from 50 mg.dL-1 to 250 mg-dL-1 with the coefficient of determination （R2） of 0.9955. Therefore, this proposed assay is very rapid and sensitive for the detection of cholesterol.

Highly Thermally Conductive Polydimethylsiloxane Composites with Controllable 3D GO@f-CNTs Networks via Self-sacrificing Template Method

Constructing controllable thermal conduction networks is the key to efficiently improve thermal conductivities of polymer composites.In this work,graphite oxide(GO)and functionalized carbon nanotubes(f-CNTs)are combined to prepare“Line-Plane”-like hetero-structured thermally conductive GO@f-CNTs fillers,which are then performed to construct controllable 3D GO@f-CNTs thermal conduction networks via selfsacrificing template method based on oxalic acid.Subsequently,thermally conductive GO@f-CNTs/polydimethylsiloxane(PDMS)composites are fabricated via casting method.When the size of oxalic acid is 0.24 mm and the volume fraction of GO@f-CNTs is 60 vol%,GO@f-CNTs/PDMS composites present the optimal thermal conductivity coefficient(λ,4.00 W·m^(-1)·K^(-1)),about 20 times that of theλof neat PDMS(0.20 W·m^(-1)·K^(-1)),also much higher than theλ(2.44 W·m^(-1)·K^(-1))of GO/f-CNTs/PDMS composites with the same amount of randomly dispersed fillers.Meanwhile,the obtained GO@f-CNTs/PDMS composites have excellent thermal stability,whoseλdeviation is only about 3%after 500 thermal cycles(20-200℃).

Ultrapermeable membranes based on connected cluster of hollow polydimethylsiloxane nanoparticles for gas separation

Mixed matrix membranes(MMMs)with the performance between the matrix and the filler is a promising strategy for membranes with excellent gas permeability-selectivity.In this study,the hollow polydimethylsiloxane nanoparticles were synthesized and then incorporated with the poly(oxide ethylene)monomer and tri-functional cross-linker to form mixed matrix membranes by in situ poly-merization.The hollow nanoparticles formed the independent closed nanocavities in membranes,which enhanced the gas permeability contributed by both the improved diffusivity and solubility.At high loading,the hollow polydimethylsiloxane nanoparticle was converted into the continuous phase with the cross-linked poly(oxide ethylene)as the dispersed phase.Gases preferred to permeate through the connected cluster of hollow polydimethylsiloxane nanoparticles,finally leading to ultrahigh gas per-meabilities far going beyond the instinct values of polydimethylsiloxane and the cross-linked poly(oxide ethylene).The optimized membrane with 34 wt%hollow nanoparticles loadings exhibited ultrahigh permeabilities with the values of 44186 Barrer for CO_(2) and 11506 Barrer for O_(2),accompanied with a CO_(2)/N_(2) selectivity of 9.9 and an O_(2)/N_(2) selectivity of 2.6,which exceeded the 2008 Robeson upper bound for O_(2)/N_(2) and located at the 2008 Robeson upper bound for CO_(2)/N_(2).

Polydopamine and collagen coated micro-grated polydimethylsiloxane for human mesenchymal stem cell culture

Natural tissues contain highly organized cellular architecture.One of the major challenges in tissue engineering is to develop engineered tissue constructs that promote cellular growth in physiological directionality.To address this issue,micro-patterned polydimethylsiloxane(PDMS)substrates have been widely used in cell sheet engineering due to their low microfabrication cost,higher stability,excellent biocompatibility,and most importantly,ability to guide cellular growth and patterning.However,the current methods for PDMS surface modification either require a complicated procedure or generate a non-uniform surface coating,leading to the production of poor-quality cell layers.A simple and efficient surface coating method is critically needed to improve the uniformity and quality of the generated cell layers.Herein,a fast,simple and inexpensive surface coating method was analyzed for its ability to uniformly coat polydopamine(PD)with or without collagen on micro-grated PDMS substrates without altering essential surface topographical features.Topographical feature,stiffness and cytotoxicity of these PD and/or collagen based surface coatings were further analyzed.Results showed that the PD-based coating method facilitated aligned and uniform cell growth,therefore holds great promise for cell sheet engineering as well as completely biological tissue biomanufacturing.