Effect Of Hydrophobic Modification Research Articles

Effect of hydrophobic modification and dosage of long afterglow phosphors on the properties of self-luminescent cement-based materials

Both the hydrolysis instability of original long afterglow phosphors (OLP) and limited amount of reflective powders (RP) degraded the luminescent performance of self-luminescent cement-based materials (SLCM). This study novelty proposed a solution by coating organosilicon layer on the OLP surface to create hydrophobic effect for enhancing its water resistance. Furthermore, compared with typical SLCM with low content of LP and RP, SLCM mixtures were prepared through replacing cement by LP and containing higher volume of RP according to the modified Andreasen and Andersen (A&A) model. The effects of dosage and surface modification of LP on the strength, hydration kinetics, luminescent performance, phase composition and microstructure of SLCM were examined. Hydrophobic LP (HLP) achieved similar crystal structure but changed its surface morphology as well as enhanced its water resistance. Introduction of the OLP into SLCM was liable to generate the hydrolysis products. HLP performed better in generating more hydration products but less hydrolysis products, thus formed a compact microstructure and enhanced the thermal stability. Hydration kinetics revealed that the hydrolysis reaction of OLP decreased the heat of hydration, while the hydration process was promoted by HLP. Higher dosage of LP after hydrophobic modification in SLCM helped in obtaining a better luminescent performance but caused a drastic reduction in strength. Overall, the optimal dosage of HLP in SLCM including higher volume of RP was more effective in achieving a superior luminescent performance without degrading the strength.

The improvement of dispersity, thermal stability and mechanical properties of collagen fibers by silane modification: an exploration for developing new leather making technology

The effect of hydrophobic modification on the performances of collagen fibers (CFs) was investigated by using silane coupling agents with different alkyl chains as hydrophobic modifiers. It was found silane could be easily grafted onto CF surface through covalent bonds under 5% water content. This modification led to the transformation of surface wettability of CF from hydrophilic to hydrophobic. Interestingly, the change of surface wettability resulted in substantial improvement of the modified CF properties, presenting well dispersity of collagen fibers, higher thermal stability and enhanced mechanical properties in comparison with natural CF. The degree of improvement mainly depended on the length of alkyl chain in silane. Longer alkyl chain produced strong hydrophobicity and subsequently more superior performances of the modified CF. When the length of alkyl chain increased to 18 carbon atoms, the modified CF possessed durable superhydrophobicity even exposed to aqueous solutions of different pH, UV, and organic solvents, and had excellent thermal and mechanical properties like leather fibers. In general, this work clearly revealed that the properties of CF are closely and positively related to the hydrophobicity, which is suggestive in developing new leather making technology.Graphical

Application of filter media surface hydrophobic modification to reduce bioclogging in the infiltration system

ABSTRACT Bioclogging is a commonly encountered operational issue that lowers hydraulic conductivity and the overall performance of the infiltration systems. In this paper, a novel processing for alleviating bioclogging by filter media surface hydrophobic modification was presented. Two-dimensional porous media cells were used to observe the influence of hydrophobic modification on biofilm growth in the pore structure. Moreover, two continuous-flow columns packed with gravel, one of which half gravel was hydrophobically modified, were operated with artificial wastewater to verify the effect of hydrophobic modification on bioclogging alleviation. The results showed that the biofilm growth in the cell with hydrophobic modification was slow, and the biomass was less and liable to wipe off after hydrophobic treatment. Meanwhile, the hydraulic efficiency of the flow seepage field was also improved after hydrophobic treatment. The column tests results showed that the hydraulic conductivity of the filter bed with hydrophobic modification (Column B) decreased more slowly than that of another without hydrophobic modification (Column A). Column B had the hydraulic conductivity (k) of 0.66 cm/s in the final stage of the experiment, while the k of Column A was 0.14 cm/s. It verified that hydrophobic modification of partial filter media can alleviate the bioclogging problem of the infiltration systems to some extent. The results provide a new idea and potential technical support for solving bioclogging problem.

Effect of Hydrophobic Modification on the Properties of Polymer‐Blended Microemulsion Gels

AbstractPhase behavior of sodium oleate (NaOl)/isoamyl alcohol‐based lamellar gel phase in cedar oil/water medium in the presence of the nonionic polymer hydroxyethyl cellulose (HEC) and its hydrophobic modified product (HMHEC) is investigated for the development of polymer‐embedded surfactant gels. HMHEC is more soluble in oil‐in‐water (o/w) microemulsions, but nonionic HEC shows limited solubility in the lamellar microemulsion (o/w type). Quantitative estimation of rate of adsorption of the polymer on lamellae bilayers can be easily done by Sudan solubilization and methylene blue complexation methods. Addition of HMHEC to the lamellar gel phase increases the polymer solubilization limit of lamellar gels as well as the viscoelasticity and thermal stability. The polymer‐embedded microemulsion gel acts as a “clean gel” since it exhibits good solubilization in different hydrocarbon media at ambient conditions. Elastic modulus of the polymer‐embedded gel influences directly the suspension performance of gels at high temperature and yields a reasonable sand‐settling velocity acceptable according to fracturing standards. The thermal characteristics and viscoelastic properties of polymer‐embedded gel were found to be suitable for moderate‐temperature reservoir stimulation where the bottom hole temperature is in the range 70–75 °C. Already a large amount of experimental data on pure microemulsions (without polymer) exists. Our studies indicate that the developed polymer‐embedded microemulsion gel has great potential as a model system for the study of polymer–microemulsion interactions.

Effect of Hydrophobic Modification on Mechanical Properties of Chinese Fir Wood

The water repellency, elastic modulus, and hardness of hydrophobic-treated and untreated wood cell walls were investigated. Chinese fir (CF; Cunninghamia lanceolata (Lamb.) Hook) wood was modified using polydimethylsiloxane (PDMS) and dimethyldichlorosilane (DMDCS) dissolved in n-hexane at 2%, 5%, and 8% (w/w) for 5 min, 30 min, and 2 h, respectively. A hydrophobic property was observed in the modified wood. The water contact angle value of the untreated wood surface was 85°, but after treatment this value increased to 147° and 143° for the PDMS- and DMDCS-treated wood, respectively. Increases in the elastic modulus and hardness of the wood cell wall were observed after PDMS treatment. These treatments also improved the water repellency of the wood surface, as verified by the reduction of the hydroxyl group O-H stretching vibrations at 3328 cm-1. Compared to DMDCS, the PDMS treatment improved the hydrophobicity of wood surfaces and increased the nanomechanical properties of the wood cell wall. When an 8% concentration of PDMS and a 2 h treatment time were used, the treated wood showed the best mechanical properties.

Effect of pH on the adsorption of dodecylamine on montmorillonite: Insights from experiments and molecular dynamics simulations

The hydrophobic aggregation in cationic surfactant suspension is an effective method to enhance the dewatering of clay-rich tailing. The solution pH can affect the adsorption behavior of cationic surfactant on clay mineral. The effect of pH on the adsorption of dodecylamine (DDA) on montmorillonite was investigated by the sedimentation test and the characterization of flocs images, contact angle, adsorption quantity, and fourier transform infrared (FTIR) spectroscopy, as well as molecular dynamics (MD) simulation. It was found that DDA ions were adsorbed on montmorillonite basal surfaces mainly by physical adsorption, including the electrostatic attraction and hydrogen bonding. A certain number of neutral DDA molecules can favor the adsorption of DDA. At pH around 8, the effect of hydrophobic modification was the best because DDA molecules and ions form compact and well-organized monolayer. The MD simulation results were in good agreement with that of contact angle, adsorption quantity and FTIR.

Effect of hydrophobic modification on the structure and rheology of aqueous and brine solutions of scleroglucan polymer

Amphiphilic scleroglucans were synthesized by grafting hydrophobic stearate groups in various densities onto the polysaccharide under its triple-helix conformation. Furthermore, a polyelectrolyte was obtained by attaching ionic-sulfonic groups to the hydrophobically modified scleroglucan. Rheological measurements demonstrated the role of grafted stearates in helix-coil transition of scleroglucan and in reducing the viscosity of scleroglucan in pure aqueous and brine solutions. Nevertheless, grafting the ionic-sulfonic groups caused a substantial recovery of the lost viscosity, especially in brine solution at 90 °C, while keeping the amphiphilic character of the hydrophobically modified scleroglucan. Additionally, the hydrophobic modification altered the adsorption behavior of scleroglucan on oil-reservoir rock surfaces: the higher the grafting density, the greater the adsorption amount. However, the polyelectrolyte sample showed the lowest adsorption among all modified samples. Finally, the modified scleroglucans are promising candidates for enhanced oil recovery applications.

Effect of hydrophobic modification on carbon dioxide absorption using porous alumina (Al2O3) hollow fiber membrane contactor

Porous alumina (Al2O3) hollow fiber membranes were successfully prepared using phase inversion spinning and sintering technique. Hydrophilic surface of porous Al2O3 hollow fiber membrane was modified with a fluoroalkylsilane (FAS) solution that was used as hydrophobic agent for treating the surface of Al2O3 hollow fiber membranes. The unmodified and modified porous Al2O3 membranes were characterized using scanning electron microscopy, mercury porosimetry, gas permeation testing equipment, energy-dispersive X-ray spectroscopy, thermogravimetric analysis, and the contact angle analyzer. The hydrophobicity of the porous Al2O3 hollow fiber membrane increased with increasing FAS coating time. The effect of the FAS coating on the CO2 absorption performance was also investigated. As a result, the CO2 absorption flux decreased with increasing FAS coating time. In particular, these experiments revealed that 2h coating was sufficient to obtain an optimal hydrophobic protection against the wetting process of the Al2O3 hollow fiber membrane pores. In addition, the best performance for CO2 absorption flux was achieved with the Al2O3 hollow fiber membrane modified for 2h coating. The maximum CO2 absorption flux of surface modified Al2O3 hollow fiber membrane was 6.022×10−3mol/m2s with a liquid flow rate of 50ml/min at room temperature. Finally, a 50-hours-long stability test demonstrates that the modified porous Al2O3 hollow fiber membranes are stable and promising for membrane contactors.

Effect of hydrophobic modification of hydroxypropyl methylcellulose on silicone oil emulsions

ABSTRACTTo study the effect of hydrophobic modification of the emulsifier on the relationship between emulsion stability and polymer emulsifier concentration, silicone oil emulsions were prepared using hydroxypropyl methylcellulose (original HPMC) and HPMC stearoxy ether (hydrophobic HPMC) at concentrations around their overlap concentrations. Both HPMC types completely emulsified the silicone oil. However, the volume fraction of silicone oil in the emulsion prepared using hydrophobic HPMC was less than that that by the original HPMC, and the average oil droplet size in the former emulsion was less than that in the latter emulsion. Increasing HPMC concentration led to increase in both the amount of adsorbed polymer emulsifier and the storage moduli in the linear region, irrespective of which HPMC was used. Stress-strain sweep curves obtained by a rheo-optical method showed that emulsions stabilized by the hydrophobic HPMC flowed slowly, even beyond the yield stress, whereas emulsions prepared using the original HPMC flowed quickly beyond the yield stress. The storage moduli of the emulsions prepared by the hydrophobic HPMC were larger than those prepared using the original HPMC.

Effect of Hydrophobic Modification on the Durability and Environmental Properties of Porous MgF2 Antireflective Films

Conventional porous MgF2 antireflective films show poor environmental durability due to its hydrophilic nature. To improve the film environmental durability, hydrophobic porous MgF2 antireflective films are prepared by a methyl silicone-modified MgF2 sol. Effects of the methyl silicone proportions on the film properties are examined in order to control the wettability, peak transmittance, and environmental durability of the films. The modification of methyl silicone can increase the film hydrophobicity, thus decreases the adsorption of water, and improves the environmental durability. However, large amounts of methyl silicone could increase the film refractive index, resulting in the decrease in peak transmittance for films on BK7 glass. Films with 40% silicone show water contact angle of 110°, peak transmittance of 98.7%, and good environmental durability. The results of accelerated test show that the environmental durability of the porous MgF2 films modified with 40% methyl silicone is six times higher than that of the conventional films.

Interaction of a hydrophobic-functionalized PAMAM dendrimer with bovine serum albumin: thermodynamic and structural changes.

The interaction between a hydrophobic-functionalized PAMAM dendrimer (PAMAM-NH2-C12, 25%, G4) and bovine serum albumin (BSA) has been investigated by circular dichroism (CD), UV-vis, and fluorescence spectroscopic methods and molecular modeling. The analysis of the effects of dendrimer complexation on the stability and conformation of BSA indicated that the binding process of the hydrophobic-functionalized dendrimer with BSA induced the relatively large changes in secondary structure of protein. Thermal denaturation of BSA, when carried out in the presence of dendrimer, also indicated that this hydrophobic-functionalized dendrimer acted as a structure destabilizer for BSA. The hydrophobic, electrostatic, and hydrogen bonding forces played important roles in the complex formation. The putative binding site of PAMAM-NH2-C12 (25%) dendrimer on BSA was near to domain I and domain II. The effect of hydrophobic modification on the stability and structure of BSA would find useful information on the cytotoxicity of PAMAM dendrimer.

Effect of Hydrophobic Modification on the Catalytic Performance of PdCl2/Cu-HMS with Different Silylation Temperatures

A new class of organic–inorganic hybrid materials were prepared by combining Cu-HMS with a silylation agent, trimethylchlorosilane (TMCS) via a simple silylation process at different silylation temperatures. They were characterized by a series of techniques including FT-IR, powder XRD, Nitrogen adsorption–desorption, TG analysis and water adsorption capacity test. It was demonstrated that silylation of PdCl2/Cu-HMS catalysts with TMCS enhanced their hydrophobicity, improved their activity and stability and importantly kept the excellent selectivity to diethyl carbonate (DEC) by oxidative carbonylation of ethanol in the gas-phase reaction. Moreover, the silylated samples obtained at 60 °C showed a better conversion of EtOH of 6.1 % and STY of DEC of 140.8 mg g−1 h−1.

Rheology and nanostructure of hydrophobically modified alginate (HMA) gels and solutions.

The effect of hydrophobic modification on the mechanical and structural characteristics of hydrophobically modified alginate (HMA) solutions and hydrogels were evaluated. The HMA systems consisted of alkyl chains, C8, grafted onto alginate backbones. With an increase in degree of substitution of hydrophobic tails, the association became stronger in solution, but same was not true for gels. The contribution of ionic crosslinking was found to be the dominant factor in determining the mechanical strength of hydrogels. Rheological measurements of 2wt% HMA gels reveal formation of a strongly crosslinked network with an elastic modulus close to 100kPa. Small-angle X-ray scattering (SAXS) experiments indicate that HMA assembles into a disordered structure with regions rich in the hydrophobic domain surrounded by a crosslinked hydrophilic network.

Hydrophobic Modification and Regeneration of Shirasu Porous Glass Membranes on Membrane Emulsification Performance

AbstractThe effect of hydrophobic modification and regeneration of Shirasu porous glass (SPG) membranes was systematically investigated on the monodispersity of emulsions. The results showed that the hydrophobic modification and regeneration of SPG membranes had little influence on the monodispersity of emulsions, no matter how many modification and regeneration runs were operated. The emulsification runs affected the emulsification performance to a certain extent when hydrophobically‐modified SPG membranes were used for preparing water‐in‐oil (W/O) emulsions repeatedly. However, they almost did not affect the emulsification performance when regenerated hydrophilic SPG membranes were used for preparing oil‐in‐water (O/W) emulsions. The SPG membranes could be used repeatedly after hydrophobic modification or regeneration with almost the same emulsification performance as fresh or freshly‐modified ones. The results provided some valuable guidance for the repetitive use of SPG membranes to prepare monodisperse O/W and W/O emulsions.

Effect of hydrophobic modification on the rheological properties of poly(N‐vinyl pyrrolidone‐co‐dimethylaminopropylmethacrylamide)

AbstractThe viscoelastic properties of poly(N‐vinyl pyrrolidone‐co‐dimethylaminopropylmethacrylamide) (copolymer I) and its hydrophobically modified analogue, poly(N‐vinyl pyrrolidone–dimethylaminopropylmethacrylamide–dimethylaminopropylmethacrylamide⊕–C12H25Cl⊖) (copolymer II), were compared in the concentration range from 1 to 20% with dynamic and Brookfield rheometers. In addition, gel permeation chromatography/multi‐angle laser light scattering light scattering data were obtained to characterize the molecular weights and radii of gyration for the polymer samples. In general, the hydrophobically modified polymer copolymer II was characterized by a chain configuration that was more compact and a viscosity that was an order of magnitude lower than that of its unmodified counterpart, copolymer I (both polymers were characterized by similar molecular weights), in dilute (1% w/w) and semiconcentrated solutions (<5% w/w). The difference in the chain configurations resulted in significant differences in the measured viscosities of the polymer solutions as a function of polymer concentration and in the presence of added electrolyte. On the basis of dynamic rheological measurements for more concen‐trated solutions in the range of 5–10% for copolymer I and 5–20% for copolymer II, the viscous modulus predominated (loss modulus > storage modulus), with crossover points occurring at 10% (w/w) and 10 Hz for copolymer I and 20% (w/w) and 20 Hz for copolymer II. The mixtures of copolymer II with anionic surfactants, such as sodium dodecyl sulfate and polyoxyethylene (2) dodecyl ether sulfate (sodium laureth‐2‐sulfate), showed strong interactions by exhibiting viscosity maxima and flocculation points corresponding to the surfactant/polymer alkyl group and surfactant/polymer charge concentration ratios in the range of 1–2. Copolymer II showed network formation by significant viscosity buildup in combination with two nonionic surfactants, which included C14–15 Pareth‐7 and C12–13 Pareth‐3. On the basis of viscosity measurements, copolymer I was found not to interact with anionic and nonionic surfactants. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 105: 190–200, 2007

Effect of Hydrophobic Modification on Rheological and Swelling Features during Chemical Gelation of Aqueous Polysaccharides

Effect of Hydrophobic Modification on Rheological and Swelling Features during Chemical Gelation of Aqueous Polysaccharides

Effect of Hydrophobic Modification on Rheological and Swelling Features during Chemical Gelation of Aqueous Polysaccharides

Rheological characteristics during chemical gelation with the cross-linker ethylene glycol diglycidyl ether (EGDE) of semidilute aqueous solutions of hydroxyethylcellulose (HEC) and of two hydrophobically modified analogues (HM-1-HEC and HM-2-HEC) are reported. In addition, rheological features of gelling samples (dextran and its hydrophobically modified analogue (HM-dextran)) of a different structure have been examined. Some swelling experiments on these gels in the postgel region are also reported. The gelation time of the hydroxyethylcellulose systems decreased with increasing cross-linker concentration, and incorporation of hydrophobic units of HEC resulted in a slower gelation. The time of gelation for the dextran system was only slightly affected by the incorporation of hydrophobic groups (HM-dextran). At the gel point, a power law frequency dependence of the dynamic storage modulus (G' proportional to omegan') and loss modulus (G'' proportional to omegan'') was observed for all gelling systems with n' = n'' = n. The attachment of hydrophobic moieties on the dextran chains had virtually no impact on the value of n (n = 0.77), and the percolation model describes the incipient dextran gels. By increasing the number of hydrophobic groups of the HEC polymer, the value of n for the corresponding incipient gel drops significantly, and the value of the gel strength parameter increases strongly. Incorporation of hydrophobic units in the HEC chains promotes the formation of stronger incipient gels because of the contribution from the hydrophobic association effect. The frequency dependence of the complex viscosity reveals that all the investigated gels become more solidlike in the postgel domain. Far into the postgel region, the hydrophobicity of HEC plays a minor role for the strength of the gel network, whereas the values of the complex viscosity are significantly higher for HM-dextran than for the corresponding dextran gel. The swelling experiments on HEC, HM-1-HEC, and HM-2-HEC systems disclose that the degree of swelling of the postgels in water is quite different, depending on the relative distance from the gel point at which the cross-linker reaction is quenched. At a given distance from the gel point, the swelling of the HEC gel is less pronounced than for the corresponding hydrophobically modified samples. At this stage, the swelling of the HM-dextran gel is stronger than for the dextran gel.

Effect of Hydrophobic Modification on Sustained-Release Properties of Alachlor/MCM-41

The herbicide of alachlor was incorporated into the channels of MCM-41-type mesoporous silica (M41) by using an impregnation wetness method. Surface hydrophobic modification of the assembly of alachlor-MCM-41 (Ach/M41),via a gas-solid reaction with 1,1,1,3,3,3-hexamethyldisilazane (HMDS),gave rise to an efficient sustained-release system (Ach/TMS-M41). The resulting Ach/TMS-M41 not only retained high alachlor loading capacity but also possessed prolonged alachlor release time. The characterization results of XRD,nitrogen adsorption/desorption,FT-IR,and TG analysis showed that the M41 retained its structural integrity during the alachlor-loading process and alachlor was dispersed completely in the channels of MCM-41 with a mass ratio of alachlor [m(alachlor)/m(alachlor-MCM-41)] as high as 0.381 g·g-1 (mass fraction 27.6%). The release properties of Ach/M41 and Ach/TMS-M41 in water were investigated. 62% and 38.1% of alachlor were released from Ach/M41 and Ach/TMS-M41 after 6 days,respectively,which indicated that hydrophobic modification of MCM-41 was conducive to sustained-release of alachlor. Furthermore,the framework of the mesoporous silica protected the encapsulated alachlor against ultraviolet light irradiation.

Fluorocarbon‐containing hydrophobically modified poly(acrylic acid) gels: Gel structure and water state

AbstractA series of hydrophobically modified poly(acrylic acid) gels (HM‐PAA gels) were prepared by radical copolymerization of acrylic acid and a small amount of hydrophobic comonomers, 2‐(N‐ethyl perfluorooctane‐sulfonamido)ethyl methacrylate and lauryl acrylate, respectively, in tert‐butanol. The effects of hydrophobic modification on the structure and water state in hydrogels were studied by atomic force microscopy, differential scanning calorimetry, and thermogravimetric analyses. Significant differences in the enthalpy of dissociation of water per molar polymer unit were found between unmodified gel and hydrophobically modified gels (HM gels). Three states of water molecules—free water, nonfreezing water, and freezing bound water—were proven to exist in HM gels. The number of nonfreezing and freezing bound water molecules associated with a polymer unit, n0 and n1, increased with the hydrophobe content and the hydrophobicity of the hydrophobes. The roles of these water molecules are discussed in relation to hydrophobic association. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 1258–1265, 2003

Associations in Mixtures of Hydrophobically Modified Polymer and Surfactant in Dilute and Semidilute Aqueous Solutions. A Rheology and PFG NMR Self-Diffusion Investigation

Viscosity (dilute regime) and surfactant and polymer NMR self-diffusion (dilute and semidilute regime) measurements were carried out on aqueous solutions of ethyl(hydroxyethyl)cellulose (EHEC) and of a hydrophobically modified analogue, with (HM4-EHEC) and without (HM0-EHEC) a spacer, in the presence of various amounts of sodium dodecyl sulfate (SDS). Strong polymer−surfactant interactions were revealed. From the binding isotherm the critical aggregation concentration (cac ≈ 3 mm) was obtained for the EHEC/SDS system. By comparing the results from the binding isotherms with those from the rheological measurements, molecular interactions could be correlated to macroscopic properties. The polymer self-diffusion results suggest that the spin-echo attenuation can be described by a log-normal distribution (distribution of self-diffusion coefficients), giving a median polymer self-diffusion coefficient DME. There is no difference in the trend of DME between EHEC and the hydrophobically modified analogues at various SDS concentrations. The NMR signal decays of highly viscous samples of the modified analogues are initially described by a distribution mode followed by a single exponential (slow component). The effect of hydrophobic modification is seen in the existence of a slowly diffusing component (Dnet≈ 10-14 m2 s-1) (not observed for the unmodified analogue) that is related to a strong and long-lived network, at least of the order of the NMR time scale (ca. 0.5 s).