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In general, temporary well plugging is essential for repairing of oil and gas wells due to their long life time. One of the newest methods used for this purpose is gel polymer plugging. The strength of the gel in the well conditions is one of the most important challenges in the application of gel polymer in the temporary well plugging in work over operation. In this study, silica nanoparticles were used to improve the strength of polymer hydrogels. The bottle and rheological tests were used to determine the gel strength in desired well conditions (high temperature and high salinity). Also, the gel strength properties and swelling behavior were studied in various conditions such as distilled water, formation water, tap water and oil. It was observed that the strength of the gel increased from 520Pa to about 36kPa (5000% increase) by adding nanoparticles. Also, the gel swelling in the aqueous solution has been significantly reduced. Based on the results obtained in this study, a polymer gel containing 9 wt.% of silica nanoparticles with structural strength and thermal stability at 90 °C was introduced for field studies.

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In this research, the rheological behavior of ribbon type Iranian gum tragacanth was investigated at different concentrations (1–5 g/L), temperatures (5–55°C with 10 degree intervals), pH (4, 7, and 10), and rotational speeds (up to 200 rpm). At first, the apparent viscosity of gum tragacanth solutions were measured at 3 concentrations (1, 3, and 5 g/L) during 28 hours in 2 hour intervals. The results showed that the soaking has no significant effect on the apparent viscosity of gum tragacanth solutions. Regarding the influence of the abovementioned factors, our findings revealed that increasing rotational speed or shear rate at low concentrations (1 and 2 g/L) has no effect on the apparent viscosity of the solutions and those samples behaved likewise Newtonian fluids whereas, at higher concentrations (3 to 5 g/L), with increasing the rotational speed the apparent viscosity diminished and the solution consequently showed a Pseudoplastic behavior. In all experiments, alongside increasing the concentration and temperature the apparent viscosity increased and decreased, respectively. In addition, pH had no considerable effect on apparent viscosity in most of our samples. For comparison purposes, using mathematical equations, experimental findings (namely rotational speed) were converted to fundamental parameters (shear rate and shear stress) as well.

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In order to develop the scope of application of polymer materials in the preparation of drilling fluids, in this study, various blends of wheat starch and copolymer of sulfonated polyacrylamide were prepared and the rheology and compatibility behavior of samples under different salinity and aging conditions were evaluated. The rheological behavior of starch-polyacrylamide blends in tap water and saturated brine water showed that the viscosity of the samples increased with increasing concentration of polyacrylamide copolymer in the both media. However, starch-polyacrylamide blends in saturated brine had less viscosity than tap water. It was observed that in both tap water and salt water saturated conditions after 4 hours of aging at 90 ° C, the viscosity of most samples increased. Comparison of the curves for empirical viscosity data and prediction of the mixing rule showed that in both of tap water and salt saturated water, positive deviation from the mixing rule is observed, which indicates the compatibility between the blend components. By performing the aging process, although positive deviation was still observed, this positive deviation slightly decreased, which means the negative effect of aging on the compatibility of the starch- copolymer of sulfonated polyacrylamide blend.
In conclusion, the results of this study showed that the blend of starch- sulfonated polyacrylamide copolymer is compatible at high temperature (90 °C) and saturated NaCl salt wate. Moreover, in some samples, this compatibility exists even after aging.
 

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Research Subject: Poor mechanical strengths and lack of thermal stabilities of hydrogels confine their extensive practical applications in many areas. The growing scientific need for solving this problem and achievement to the hydrogels with improved properties has led to the design and production of the nanocomposite hydrogels.
Research Approach: The polymeric networks of nanocomposite hydrogels compared to the ordinary hydrogels have improved elasticity and rheological properties. Other points that increase the importance of structural studies of nanocomposite hydrogels are the high strength of these materials versus the application of external forces, as well as maintaining its structure against increasing of temperatures. In this regard, the type and amounts of nanomaterial, the preparation method and formation of hydrogel network have a significant role in improving the physical, chemical and biological properties of hydrogels, and, it must be noted that these parameters will depend on the application of nanocomposite hydrogels. This also highlights the need for the production of nanocomposite tailored hydrogels. Therefore, orientation of the range of nanomaterials, the preparation method and product identification, along with sufficient information on the application of these materials, might have an important role in ensuring the success of these materials, requiring comprehensive library research and studies on polymerization processes, morphology and rheology.
Main Results: In this review article, the scientific advances in the field of nanocomposite hydrogels, focusing on its types based on the type of nanoparticles, its properties, preparation methods, identification methods with a new perspective on rheology, thermal analysis and morphology is investigated. Finally, the applicability of these materials is collected in a comprehensive table in various fields such as tissue engineering, enhanced oil recovery, agriculture, and etc…

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Regarding new researches on chemorheology of energetic composites,it is determined that HTPB slurry should have convenient viscosity for ease of casting. In the other word, available time for appropriate casting of energetic composite after curative addition called pot-life. Long pot-life of HTPB binder system is necessarily for good processability and non-defect production of energetic composite grains. In addition to long pot-life, the physical-mechanical properties of HTPB energetic composite are of at most important. In this research, effect of  curative type (structure), casting temperature and the amount of DBTDL as a curing catalyst on chemorheological behavior of HTPB binder system and physical-mechanical  properties of energetic composite were investigated. Toluene diisocyanate (TDI), Isophorone diisocyanate (IPDI) and Hexamethylene diisocyanate (HDI) were selected in order to investigate the role of molecular structure of curing agent on Chemorheology of binder system and its slurry and also on physical-mechanical  properties of energetic composite. Moreover, temperatures of 40, 50 and 60 ˚C, were selected to study the effect of casting temperature on chemorheology. By decreasing each 10˚C of casting temperature, pot-life of binder system (IPDI and TDI) was increased about 10 min. Pot-life of binder system and energetic composite slurry based on IPDI in the presence of 0.005% DBTDL (the optimum content) at similar temperatures, showed the longest pot-life. The elastomer and energetic composite based on IPDI showed the most crosslinking density (CLD) and modulus in comparison to other curing agents with retain of tensile strength and adequate elongation.
 

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Research Subject:

Polymer melts show complex response under the act of deformation. This response has direct relation to their molecular structure. The purpose of this study was to investigate the rheological behavior of branched polymers and the effect of branching on linear and nonlinear viscoelastic flow for usage in various industrial applications.

 
Research Approach:

For this purpose, the  tests such as frequency sweep and extensional for two polyethylene (LDPE) with long branches have been used. From these tests we obtained storage and loss moduli, complex viscosity and extensional viscosity. Molecular models in nonlinear  regions can also be used in this regard. 

Main Results:

Linear  tests can partly show the presence of branch in LDPE, while nonlinear  tests show strain hardening behavior for branched sample. One of the  models for branched polymers is the Multimode Pom-Pom (MPP) model which can be used to predict the strain hardening phenomenon in extensional flows. In this study, the average number of lateral branches was also calculated using this model.

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In this work, the effect of type and concentration of some sweeteners (sucrose, glucose, fructose, aspartame, acesulfame k and neotame) on the rheological properties of locust bean gum solutions in model system include sweeteners and hydrocolloid has been investigated . Two level of sweetener concentrations were used (10, 20% w/v for sucrose, glucose, fructose, and 0.1, 0.2% w/v for aspartame, acesulfame k, and 0.001, 0.002% w/v for neotame). The rheological properties were measured by oscillatory rheometer (model MCR-300). The results showed that the effect of sweeteners on rheological properties of locust bean gum depend on type and concentration of sweeteners. In these concentrations, the synthetic sweeteners had no effect on rheological properties of locust bean gum solution.

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    The high molecular weight polymeric fraction of gluten, glutenin macro-polymer (GMP) shows strong relation with breadmaking quality of wheat. In this study, GMP was extracted from different Iranian wheat cultivars with different breadmaking performances. The correlation was investigated between the wet weight and (small-strain deformation) rheological characteristic of GMP-gel with bread quality (loaf volume and height). The results showed a significant relation between gel amount and bread loaf volume and height. However, no positive and significant correlation was found between small-strain deformation rheological characteristics (storage modulus and tan delta) with breadmaking characteristics. Concluding, despite to GMP wet weight which is accepted as a predictive measure for breadmaking quality, small-strain deformation rheological analysis of GMP-gel can not be used for screening breadmaking quality between wheat cultivars.  

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  The effect of flour hydration on the rheological characteristics of bread dough was investigated. For this purpose, hydrated zero-developed (zero mechanical energy developed; ZD) doughs, which hydrated out side of the mixer were used. The influence of hydration temperature (5 and 25 °C) and time (1.5, 4 and 24 h) on hydration ability of doughs was investigated. Farinograph and Extensigraph experiments were used to study the behavior of hydrated doughs upon different hydration treatments. Results indicated that increasing hydration time and temperature led to an increase in hydration performance, thus hydration phase in Farinograms was decreased and finally disappeared. Comparing doughs prepared from ZD doughs versus those mixed from conventional flour-water mixtures showed that reduction in hydration phase (arrival time) in ZD doughs, especially upon hydration at 25 °C for 24 h, arrival time was totally disappeared. However, doughs prepared with ZD-dough had lower Farinograph "stability" and higher "degree of softening" values compared to those mixed from flour-water mixtures. Only hydration at 25 °C for 24 h gave suitable doughs for Extensigraph experiments. Evaluation of Extensigram of such dough compared with doughs mixed from flour-water mixer showed better rheological performance (higher Rmax , energy to extension and Ratio values).

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  The effect of three hydrocolloids with different chemical structure and from different sources on the rheological properties of wheat flour dough , fresh baguette bread quality and its influence on bread staling were studied. The influence of the selected hydrocolloids( Guar, Pectin and Xanthan gum ) on rheological behavior of dough was tested by using extensograph and farinograph. Rheological characteristics of wheat flour doughs were modified to different extent by hydrocolloids of varying chemical structure. The greatest effects, but not the better ones, at dough level were promoted by xanthan followed by guar, these hydrocolloids strengthen the wheat flour dough. Hardness and sensory characteristics of bread after storing for 24 and 48 h. Hydrocolloids affected in different extent to stored bread. Although different improvements were observed associated to specific hydrocolloid , guar was the hydrocolloid with an improvement effect on all the parameters tested, specific volume index and crumb hardness. In addition , during storage, guar gum showed an anti staling effect, reducing the crumb hardening.  

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One of the problems related to oil recovery is water production, which reduces the production life of oil reservoirs and wells. Nowadays, the polymer gel injection method is used to control water production in the reservoir. In this study, an attempt has been made to investigate the rheological properties of xanthan-based hydrogels, considering Iran's reservoirs and also due to the existence of environmental problems in the field of synthetic polymers. The strength and stability of hydrogels can be applied by changing environmental conditions as a function of time and shear rate. For this purpose, the viscoelastic properties of hydrogels, including the elastic and viscous modulus, have been studied in relation to temperature, time and deformation rate for the gelant solution. Also, the effect of the composition of hydrogels, including the polymer concentration, the weight ratio of the crosslinking agent to the polymer, and the weight percentage of silica nanoparticles was considered in the study of rheological properties. Additionally, gelation time has been studied as one of the most important determining parameters of hydrogel during injection in porous medium. 

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Chocolate is a popular product for cunsumers in different ages . Chocolate sweetness  is related to the sucrose in its formula , it can be replaced by sweeteners like low digestible carbohydrates (LDCS) .The results would be reduction in calories and glycemic index and prevention of tooth decay. The aim of this study was to replace  the sucrose with the inulin (as dietary fiber) and tagatose (as natural keto hexose  with sweetness similar to sucrose). The ratio of the replacements were 100:0 , 75:25 , 50:50 , 25:75 and 0:100 inulin:tagatose in milk chocolate formula and the chemical and rheological properties of samples were tested. Results indicated that when the amount of inulin reduced and amount of tagatose  increased in chocolate formula, moisture contents reduced but aw values increased . The hardness of samples was related to the percentage of tagatose when tagatose added  to the formula, hardness was increased and the hardness of sample with 100% tagatose and control were comparable. In color parameters the least amounts of l^* ,a^*,b^*,c^* and hue° were observed in chocolate with 100% inulin which they went up when amount of tagatose was increased in formula. When inulin reduced in samples,  and  incresed and the lowest real and linear yield stress occurred in the sample with 100% inulin. By reduction of inulin, apparent and plastic viscosity were reduced. The least amount of apparent and plastic viscosity was observed in sample with 25%inulin-75% tagatose and the viscosity in formula with tagatose had no significant difference with control. Flow property index also reduced with reduction of inulin. Results showed that the samples with 50% inuin -50% tagatose and 25% inuin -75% tagatose  and 100% tagatose were the best ratio of the sugars as replacement of sucrose in formula, the two formers formulas are the best formula from nutrition point of view and are considered  as a functional food.  

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In this research, the effect of xanthan gum in three concentrations of 0.02, 0.05 and 0.07 g/kg of skim milk, containing 0.4% fat in production of Iranian white cheese was investigated. Two control cheeses was prepared, that one of them was full-fat control cheese without gum which was made of milk containing 3.2% fat and full milk. The other one was reduced fat control cheese that made of skim milk containing of 0.4% fat without adding any gum. The results of chemical, textural and rheological experiments showed the improvement of cheese's texture by increasing of xanthan gum. In this research, the full fat control one had the least quantity of rheological, textural features, and G^* that showing the softness and desirability of texture. The treated cheese with xanthan gum of 0.07g showed the maximum similarity to full fat control cheese which by increasing of xanthan concentration, the textural and rheological features reduced. The reduced fat control cheese had the highest quantity of and G^* which showing the hardness and undesirability of texture. This study shows the desirability of xanthan gum as fat replacer in order to lowering the energy- producing extent of cheese as well as an improving factor of texture.

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Wheat flour was substituted with oat flour by 0, 10, 20, 30, and 40% to investigate the effect on dough rheology and bread sensory quality and texture. Water absorption and dough development time in oat composite doughs increased with an increasing level of oat flour, whereas dough resistance, extensibility and bread firmness decreased. Dough sof-tening increased with an increased level of oat flour while the addition of oat flour im-proved bread shelf life and reduced the yellowness of bread. Breads produced with up to 20% oat flour were stable and with good quality as indicated by sensory evaluation. Oat flour had larger particle size in comparison to wheat flour. Breads produced with 30% and 40% oat flour had a bitter after taste, unacceptable to the sensory panelists.

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In this paper, the effect of type and concentration of  some sweeteners (sucrose, glucose, fructose, aspartame, acesulfame k and neotame) has been investigated on the reheological properties of guar gum solutions in a model system include sweeteners and hydrocolloid. Two level of sweetener concentrations were used (10, 20% for sucrose, glucose, fructose, and 0.1, 0.2% for aspartame, acesulfame k, and 0.001, 0.002% for neotame). The rheological properties were measured by oscillatory rheometer (model MCR-300). The results showed that the effect of sweeteners on rheological properties of guar gum depend on type and concentration of sweeteners. In these concentrations, the synthetic sweeteners had no effect on rheological properties of guar gum solution.     

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Rheological behavior of fig juice concentrates was studied with the objective of defining suitable models for use in evaporation and other processing procedures. The flow properties were determined for juice concentrate with solid content of 70° Brix containing different concentrations of pectin from 0.2 to 0.8% over the temperature range of 5 to 65°C using response surface methodology. A rotational viscometer was used to characterize the flow behavior of concentrates. Samples were subjected to a programmed shear rate increasing from 0-100 s^-1 in 10 min. The flow of all combinations was adequately described by Herschel Bulkely model and the consistency coefficient (m), the flow behavior index (n), yield stress (τ₀) and apparent viscosity (η) were obtained. m and τ₀ increased with pectin concentration and decreased with temperature, while pectin concentration and temperature had opposite effects on n and (η). All parameters were sensitive to changes in temperature and pectin concentration.    

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Yoghurt is one of the fermented dairy products with high nutritional value and short shelf life where its shelf-life can be prolonged by drying. Therefore, in the present study, the fresh yoghurt with different amounts of dry matter (10, 20 and 28% w/w) was dehydrated by microwave–vacuum dryer at different levels of microwave powers (35, 135, and 260 W) and definite absolute pressure (125± 5 mbar). Then, the effects of type (gum tragacanth, guar gum, locust bean gum, Persian gum, and casein powder), quantity (0.25, 0.5, 0.75 and 1% w/w) in singular and combined forms (tragacanth:guar, Tragacanth:locust been gum, and guar: locust been gum), combination ratio (80:20, 50:50),and adding stage (pre/post drying) of hydroclloids over sensory and rheological properties of instant yoghurt were evaluated. Results showed that higher microwave powers and dry matter percent led to the shorter and higher drying rate, respectively. Regarding rheological properties, the storage modulus was significantly higher than loss modulus (G'>G'')  and elastic behavior was observed in majority of samples. However, sample with Guar:locust bean gums showed inverse features, also Complex viscosity and loss tangent of most samples (pre drying method) were similar to control, except one  with guar: locust been gum. Furthermore, the most accepted reconstituted yoghurt was one containing gum tragacanth, and baking powder followed by one with 0.6% tragacanth:locust bean gum (80:20, 0.6%) which were prepared with pre-drying method. Moreover, it was found that the adding stage of hydrocolloids had significant effect on the evaluated properties of instant yoghurt where pre-drying method was recognized as the most appropriate one.  

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Flaxseed is one of the oilseeds that use as ingredient in food product due to its considerable nutritional and beneficial health effects. In this study in order to produce functional Taftoon bread, ground flaxseed was incubated at 30 ºc and microwaved for 2.5  minutes in order to reduce cyanogenic glycosides compound. Wheat flour replaced with treated ground flaxseed at 5, 15 and 25 percent levels. Results showed that cyanogenic compound reduced 84/6%. Result of rheological properties test of dough showed that, with replacing wheat flour with ground flaxseed, water absorption of dough and expansion of dough during fermentation decreased and stability time of dough increased and the difference between them was significant (p<0.01). Results of stress relaxation test showed that addition of ground flaxseed to wheat flour, increases the viscoelasticity of dough. Results of oxidative stability test showed that with replacing wheat flour with ground flaxseed, peroxide and thiobarbituric acid value increased and highest value was at 15% ground flaxseed and had significant difference(p<0.01). Results showed that bread containing flaxseed had darker color and softer texture and staling of bread containing flaxseed was lower. Results of organoleptic test showed that bread containing flaxseed had better flavor, aroma, texture and overall acceptability by panelist, although color of bread had less acceptance at 15% and 25% level of replacing ground flaxseeds.  

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