جستجوی مقالات مرتبط با کلیدواژه « اصلاح سطح » در نشریات گروه « مهندسی شیمی، نفت و پلیمر »

Plate and frame heat exchangers are widely used in the industry due to their high heat transfer coefficient. In this research, experimental studies was carried out on corrugated plates, because the corrugations result in reducing the liquid turbulence to the counter current liquid flow and increasing heat transfer efficiency.  Dendritic nanofins were synthesized on copper plates in a heat exchanger microchannel and the effect of the heat transfer coefficient behavior was investigated. Synthesis of dendritic nanofins performed by a standard two-electrode glass cell with a graphite electrode as a reference electrode on six corrugated copper plates with dimensions of 4.6 cm ×4.6 cm in a plate heat exchanger microchannel by electrodeposition method. The dendritic copper nanofin array grew on the copper plates from electrolyte solution consisting of CuSO4 (0.6M), H2SO4 (0.4M) and an increasing current starting from 1.2 to 4.8 A/cm2 in 300 seconds. Characterization of the coated surface was performed by FESEM method, and the adhesion of this coating to the surface was investigated by AAS method. The microchannel designed with two hot and cold inlet fluids and it was installed in a system with the ability to check the improvement of the heat transfer coefficient by applying copper nanofins coatings. In this system, water was selected as a circulating fluid with two hot and cold inlets and two hot and cold outlets in the microchannel. The cold water inlet temperature was 7°C and the hot water inlet temperature was set at 45, 50 and 55°C in separate experiments. The heat transfer coefficient was measured in two stages before coating with copper nanofins and after coating. The measured increase in heat transfer coefficient between 40% and 62% as a result.

Hypothesis: 

first, poly ether sulfone (PES)-based nanofiltration (NF) membranes were prepared through the phase inversion-immersion precipitation technique. Then, the surface of the membranes made of polymethyl methacrylate (PMMA)-graphene oxide nanoplates (GO NPs) was modified using dip-coating technique. The effect of the active coating layer on the morphology, physical-chemical properties, and antifouling performance and separation ability to remove metal ions from wastewater was studied.

The properties of prepared membranes were studied by scanning electron microscopy (SEM) and Fourier transform infrared (FTIR) analysis.  Also, the effect of the formed active layer on the physio-chemical properties of the membrane including water contact angle, water content, flux and sodium sulfate rejection, porosity, mean pore size, heavy metal rejection and anti-fouling performance was investigated. 

 The obtained results revealed that the surface-modified membrane with 1 % (by wt)  MM-0.5% (by wt) GO-NPs had a more appropriate separation performance and better antifouling properties compared to other membranes. SEM images of the cross-sectional area of the membranes showed the formation of a relatively uniform layer on the membrane surface, which became more dense with increase in the amount of GO-Nps. The performance of the modified membrane in the removal of Cu and Cr heavy metal ions was also evaluated and compared with the pristine membrane. The removal percentage of Cu and Cr ions was 51.4% and 49.3% for the neat membrane, whereas it was 81.7% and 75.3% for the superior modified membrane, respectively. Moreover, the total fouling resistance was measured to be 23% for the virgin membrane, while it was 13.2% (Pvalue<0.05) for the best modified one. The irreversible fouling parameter was obviously decreased from 20% for the pristine membrane to 3.2% for the optimum modified membrane that shows  a superior antifouling ability for them.

Hypothesis: 

The surface modification of a heterogeneous cation exchange membrane was carried out through a chitosan nanocomposite layer containing copper oxide nanoparticles in an electrodialysis process. The effect of the formed surface layer on the structure and transfer, separation and antibacterial properties of the membranes was investigated.   

Double layer membranes were produced by dip-coating method. Scanning electron microscopy (SEM), X-ray diffractometry (XRD) and Fourier transform infrared spectroscopy (FTIR-ATR), electrical resistance, ionic flux, ability to remove heavy metal ions, water content, water contact angle and antibacterial experiments were employed to examine the membranes.

The EDX and FTIR results confirmed the formation of chitosan-copper oxide nanocomposite layer on the surface of pristine membrane. The SEM images also showed the formation of a uniform layer on the modified membranes. The amount of water content for double-layer membranes showed an increasing trend compared to pristine membranes, although the contact angle results proved an increase in surface roughness for double-layer membranes. The results of ionic properties also showed that the electrical resistances of double-layer membranes decreased to 46% initially by utilizing CuO nanoparticles in the surface layer, whereas the monovalent ionic flux and bivalent flux for heavy metals were enhanced by 50% and >300%, respectively. At high ratios of CuO nanoparticles in the surface layer, the electrical resistance of membranes increased again and the flux showed a decreasing trend. Double-layer nanocomposite membranes showed a high ability to remove copper heavy metal ions and their antibacterial performance was suitable against Escherichia coli. Among the prepared membranes, the double-layer membrane containing 0.001% (by weight) copper oxide nanoparticles showed better performance compared to a pristine and other modified membranes.

In this study, thin film nanofiltration membranes were modified by using Ar-Air plasma. The effect of plasma time, power and the composition of plasma gases on physico-chemical properties and separation performance of membranes were investigated. The results showed that the plasma treatment caused to increase in membrane surface hydrophilicity considerably. The surface modification of membranes by using plasma treatment led to enhancement of water flux through the membrane obviously. The separation efficiency of membranes due to surface modification was also changed broadly compared to unmodified membrane. The separation efficiency of modified membranes at 35 W and 180 s, 25 W and 120 s, and 15 W and 60 s plasma treatment measured ~30%, 76%-92%  and 77%-89% respectively. The selectivity for un-modified membrane was also measured ~90%. Among all studied membranes, the modified membrane at 50-50 (v/v) Ar-Air plasma, 25 W and 120 s treatment with considerable enhancement of water flux compared to pristine membrane was selected as the optimum sample.

A thin film nanofiltration membrane was modified by poly(vinyl alcohol) (PVA) and chitosan-functionalized activated carbon nanoparticles. The effect of a surface layer formed on the structure and separation properties of prepared membranes was investigated.

Scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), water content, porosity and mean pore size measurements, Na2SO4 and NaCl rejection, water flux as well as membrane flux recovery ratio for the study of antifouling ability were used for characterization of the membranes.

The FTIR results confirmed the formation of hydroxyl and amine groups on the surface of modified membranes. The SEM images also showed the formation of a uniform layer on the modified membranes. As shown in the SEM images, adding functionalized activated carbon nanoparticles into PVA leads to a heterogeneous and dense structure on the surface of modified membranes. Modification of pristine membrane by PVA and modified activated carbon nanoparticles up to 0.25% wt initially increased the water content, and subsequently with increase in nanoparticles ratio from 0.25 to 1.0% (wt), the water content decreased. The obtained results showed a larger mean pore size for all modified membranes compared to pristine membrane. Moreover, all modified membranes showed a higher flux in comparison with virgin membrane. In addition, salt rejection revealed that the surface modification of nanofiltration membrane has a positive effect in preventing smaller rejection amount despite the increase in the amount of flux. Sodium sulfate salt rejection was also measured more than sodium chloride salt rejection. Flux recovery ratio was also measured more than 92% for the modified membranes whereas it was more than 66% for pristine membrane that confirms the antifouling ability for the modified membranes.

The fabrication of polypropylene composites using various types of reinforcements to improve the mechanical properties has received much attention in recent years. In this paper, enhancing the mechanical properties of polypropylene composites by adding different classes of natural and synthetic particle and fiber reinforcements were reviewed. Accordingly, it was found that the fabrication of polypropylene composites leads to an increase either in the strength of samples and corresponding mechanical properties. Moreover, surface modification and processing reinforcements, especially natural fibers via chemical and physical methods were studied. The results show an increase in the adhesion of reinforcements surface inside the polypropylene, which results in strength enhancement and improving the mechanical properties of polypropylene composites. The evidence from this study points towards the idea that the increased use of modified natural fibers in polylropylene composites and those natural or synthetic reinforcements which form hybrid composites provide promising research topics in the future.

In recent years, hydrogels have been considered as one of the most promising materials due to their unique properties. Hydrogels are cross-linked hydrophilic polymer structures that are able to absorb and holding water or biological fluid. Thus, the hydrogel networks can extensively swell in water media without dissolution. In the last few decades, hydrogels been used in various industries such as food, packaging, pharmaceuticals and drug delivery systems, agriculture, biomedical and bioengineering applications, manufacturing of technical and electronic devices, and as adsorbents for the removal of pollutants in environmental applications. Superabsorbent polymer (SAP) hydrogels are a type of hydrogel that, due to the hydrophilic nature of polymer chains can absorb and retain extraordinary large amounts of water or aqueous solution up to hundreds of times their weight. In recent years, , new superabsorbent hydrogels have been developed for different applications. High demand for these substances, especially in personal hygiene, has led to an increase in their production (now over three million tons per year). Because the main components of commercial and widely used SAPs in industry are based on raw materials derived from fossil resources (oil, gas and coal), the widespread use of SAPs and their increasing production, on the one hand, have contributed to environmental concerns by contributing to water, soil and air pollution, and, on the other hand, have threatened global price fluctuations and the degradability of fossil resources. Therefore, the replacement of at least some components of SAPs with natural, biobased or renewable raw materials (such as lactic acid, succinic acid and itaconic acid) and the production of SAPs with hybrid structures have been considered. The purpose of this paper is to review the hybrid SAPs based on some biobased compounds that are used in three structural parts of the polymer network including crosslinker, surface modifier and monomer.

Nowadays, Due to the environmental pollution associated with synthetic dyes, the attention to the application of natural dyes in the textile industry is growing. Natural dyes are environmentally friendly and possess some advantages and disadvantages in comparison with synthetic dyes. One of the main drawbacks of natural dyes is the low exhaustion of textile fibers. To improve the dyeing of textiles with natural colorants, several methods, including metal mordanting, bio-mordanting, treatment with nano-clay, ultrasound, microwave, plasma, ultraviolet, and enzyme, besides the attachment of chitosan, cyclodextrins, and dendrimers to the fibers have been employed. Due to the toxicity of the majority of metallic mordants, the use of bio-mordants and surface modification of fibers by physical and chemical methods are considered as alternative strategies for promoting the natural dyeing of wool fibers. These methods usually improve the sorption of natural dyes by wool fibers and improve the fastness properties of the dyed fibers in most cases. In this paper, the different methods employed to enhance the dyeing of wool fibers with natural dyes are discussed and summarized.

The volume of studies conducted on biopolymeric materials emphasizes the high-consumption of polymers in biomaterial fields, especially in cosmetics industry which must be resistant to different kinds of microorganisms and bacteria. Polymers in this category include acrylate polymers, which are generally made by precipitation polymerization. Carbopol is a brand of acrylic polymer, based on poly(acrylic acid). This polymer is highly used as thickening and gelling agents for its rheological features. By chemically induced antimicrobial agents into the carbopol structure, microgels of inherently antimicrobial properties are obtained with effective applications in personal and public health applications, including combating and controlling corona epidemics (Covid 19).

In this study, it has been tried to improve the antibacterial nature of Carbopol by its bonding and surface modification with different amounts of cationic monomer acryloyl oxyethyl trimethyl ammonium chloride (A.Etac). In this work, for the first time, we attempted to modify the surface of carbopol by ultrasound. We also studied the swelling rate of the sample before and after surface modification in aqueous, alcoholic and salt solutions. Infrared spectroscopy (IR), scanning electron microscopy (SEM) with energy dispersive X-Ray analysis (SEM-EDX), antibacterial, rheometry and swelling tests were used to evaluate the chemical surface modification of Carbopol microparticles to achieve the stated goals. Antibacterial properties of the samples were evaluated by gram-negative bacteria (E. coli) and gram-positive bacteria (S. aureu) by plate count agar method.

Experimental results showed that the modified carbopol was significantly resistant to the bacteria. It should be noted that the samples showed more resistance to gram-positive bacteria than gram-negative bacteria. The results of rheological analysis also showed that the gel strength significantly increased after surface chemical modification. In addition, modified samples showed higher swelling in water and biological media (0.9% brine)

The change in the wetting of rock from hydrophobic to hydrophilic is named "wettability alteration". This is an important factor for enhanced oil recovery (EOR). Because of their unique properties, nanoparticles have attracted much attention for enhanced oil recovery. Despite promising results, the main challenges of using nanoparticles are related to colloidal stability and poor absorption of nanofluids under harsh conditions. In recent years, polymer-grafted nanoparticles have been considered as emerging materials for enhanced oil recovery.

In this study, wettability and absorption of polymer-grafted nanoparticles including silica nanoparticles modified by polyethylene glycol methyl ether (mean molecular weight 2000), silica nanoparticles modified by two polymers: polyethylene glycol methyl ether (mean molecular weights 2000 and 5000) and propyl chains are investigated. Fourier transform infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA) were used to investigate the chemical bonding and polymer content on the silica surface. Scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), water contact angle measurement, and UV-Vis spectroscopy were also used to study morphology, material composition, wettability, and absorption of the substrate, respectively.

Best performance for silica nanoparticles modified by polyethylene glycol methyl ether (average molecular weight 5000) and propyl chains at 1000 ppm concentration and salinity range 20000-40000 ppm was obtained. This study shows that silica nanoparticles bonded to different polymers can be considered as an effective and novel approach for enhanced oil recovery.

Nowadays, natural fibers are widely used for reinforcing polymer composites. Research investigations on such polymer composites have become widespread due to the low weight, low cost, environmental compatibility, abundance, and acceptable physical and mechanical properties of plant fibers. These polymer composites normally suffer from the incompatibility of natural fibers with the polymer matrix. To improve compatibility, various surface treatments can be used. In this study, the effects of different surface treatments on shear, flexural, tensile, and impact strengths of plant fiber-reinforced polymer composites have been reviewed. The mechanical properties of plant fiber-reinforced composites depend on the type of plant fibers, polymer matrix, production techniques, surface treatment methods, and materials. The chemical treatments can have undesirable effects on the impact strength of plant fiber composites with few exceptions, such as silanization.

Generally, polymer surface engineering has vast applications in biotechnology,membranes, self-cleaning and electronic devices. These applications are based oncontrollable changing in some properties such as surface energy, surface topography, andbiocompatibility of polymer. For choosing a proper method for the surface modificationof polymer, three parameters should be considered carefully. These parameters include:chemical structure of polymer which is focused on strengths and weaknesses of demandedpolymer, the surface properties that we need to achieve after treatment and finally surfacegeometry which is related to the presence or absence of porosity and or chemical andphysical heterogeneity of polymer surface. This research investigates the popular surfacemodification methods like wet chemistry, flame, plasma, UV radiation, laser and grafting.Furthermore, for accurate understanding of quantitative and qualitative changes of surfaceproperties of polymers, the general characteristics of used methods (depth analyzed,resolution, and analytical sensitivity) were briefly mentioned. Some of the popularmethods for include contact angle measurement, Fourier-transform infrared spectroscopy(FTIR), scanning electron microscopy (SEM), atomic force microscopy (AFM), X-rayphotoelectron spectroscopy (XPS), secondary-ion mass spectrometry (SIMS), Augerelectron spectroscopy (AES) and scanning tunnelling microscopy (STM).

In the current study, prepared PES nanofiltration membranes with phase inversion method were modified by the novel composite chitosan/GO (graphene oxide) nano-sheets coating process and the effect of coating on performance and membrane antifouling properties was investigated. The results revealed that the salt rejection strongly improved, and their hydrophilicity enhanced rather than PES. The rejection increased from 68% for PES to 94% due to pore size reduction and improvement in adsorption. But permeability flux was decreased by increasing skin layer after coating. In addition, contact angle was decreased because of chitosan and GO nano-sheets hydrophilic nature. The surface morphology was changed from rough surface to smoother one by coating. Finally, flux recovery ratio and total fouling ratio were in good agreement with contact angle results and roughness parameters. Moreover, an increase in flux recovery ratio and reduction of total fouling ratio indicated successfully enhancement of antifouling properties of membrane by coating of chitosan/GO nan-osheets.

The surface modification of polyvinylchloride-based heterogeneous cation exchange membranes was carried out using chitosan-co-polyaniline/graphene oxide nanocomposite layer for the application in electrodialysis process. The PANI/GO nanocomposites were prepared by in situ chemical oxidative polymerization of aniline in the presence of graphene oxide nanoplates. Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), water content, flux and permeability, areal ionic resistance, water softening ability and fouling measurements were used to characterize the membrane. The FTIR analysis results and SEM images demonstrated successful formation of polyaniline on the graphene oxide nanoplates. The scanning electron microscope images of membranes also exhibited a uniform layer of chitosan-co-PANI/graphene oxide nanoplates on the membrane surface. The water content of modified membranes was higher than that of pristine membrane. The sodium flux and sodium permeability were improved about 20% by 0.1 %wt PANI/graphene oxide nanocomposite. The areal ionic resistance of modified membranes also showed a decreasing trend by utilizing composite nanoplates in the membrane matrix. The prepared membranes showed good ability for Ca and Mg removal from water. The removal efficiency of Ca and Mg by membrane containing 0.5 %wt PANI/graphene oxide composite nanoplates was, respectively, 61 and 79% during 15 min. Moreover, the pollutant and foulant formed on the membrane surface were totally removed by sonication technique. The modified membranes showed suitable electrochemical characteristics compared to membranes reported by other researchers and made by industries.

In patients suffering from peripheral arterial disease; where vessels narrow and/or lose their efficiency and kidney failure; where hemodialysis is performed through an arteriovenous (AV) fistula that connects an artery to a vein, to purify blood, three types of surgical treatment; namely angioplasty, endarterectomy, and bypass grafting are vigorously considered. In cases like acute artery stenosis and multi-focal stenosis, a bypass is generally used. In addition, burns can damage blood vessels and cause fluid loss. This may result in low blood volume (hypovolemia) and in this case a bypass graft surgery is inevitable. However, in some cases, patients lack appropriate vessels for autologous grafting (autologous grafting includes grafting of a tissue from one site to another site of the same body). Furthermore, in autologous transplantation, a patient undergoes two surgeries simultaneously. In this respect, researchers have focused on designing artificial blood vessels as vascular implants. A class of materials that is highly regarded promising is polyurethanes, due to a number of outstanding properties including blood compatibility, biocompatibility, and most importantly, capability to tailor desirable properties. This report focuses on application of polyurethanes as artificial blood vessels while the impact of key parameters such as design of the polyurethane backbone, surface modification, and bulk modification, on the polymer key properties including: toxicity, endothelialization, and platelets adhesion are reviewed

Various approaches are available for the reduction of scale formation on heat transfer surfaces. Among these methods, though, the surface modification is considered as an innovative and efficient, environmentally-friendly approach to mitigate fouling. The notion here is to reduce the interactions between the precursors and the modified surface thus least wetting of the surface by the precursors would be expected leading to mitigation of scale formation. In this study, previous studies on the respective subject is surveyed to in order relate the effect of surface characteristics on fouling. It is shown though that previous studies have sometimes made conflicting conclusions for which the reasons are discussed in details. The paper goes on to conclude that there exists no robust and general criterion to relate surface energy and its sub-components to fouling propensity of various coatings.