ory ramon | Technion Israel Institute of Technology (original) (raw)
Papers by ory ramon
Macromolecules, 2010
... Inna Shechter § , Ory ... Equally contributing authors. Abstract. Abstract Image. The LCST p... more ... Inna Shechter § , Ory ... Equally contributing authors. Abstract. Abstract Image. The LCST phase-transition of aqueous PNIPA solutions in rising concentrations of the strong chaotropic salt KSCN was studied microcalorimetrically by DSC and apparently for the first time by ITC. ...
Drying Technology
In the present research, an air-suspension fluidized-bed technique for generation of core and she... more In the present research, an air-suspension fluidized-bed technique for generation of core and shell microcapsules containing probiotic Lactobacillusparacasei cells was evaluated. The air-suspension process was performed in a Wu¨rster coater system with a bottomspraying atomizer. In the first stage, a solution containing trehalose, maltodextrin, and probiotic cells was spray-coated onto and absorbed by the inert carrier microcrystalline cellulose to produce nonagglomerating dry coated particles with high probiotic cell viability (109 colony-forming units [cfu]/g particles). The effect of inlet air temperature, spray flow rate, solids concentration, cell concentration, and encapsulation formulation on survival was investigated. The inlet air temperature had the most pronounced effect; a 15�C increase in inlet air temperature led to a 250-fold decrease in survival percentage. There was no agglomeration of the coated adsorbed particles at spray flow rates of 1 to 3.5 mL/min. Spraycoatin...
LWT - Food Science and Technology, 2011
Ultrasonic vacuum spray dryer was used to produce a dry powder of highly viable probiotic cells. ... more Ultrasonic vacuum spray dryer was used to produce a dry powder of highly viable probiotic cells. The drying was performed through two stages: Vacuum spray drying of the solution followed by fluidizedbed drying of the powder. The embedding matrix was a combination of trehalose and maltodextrin. The effects of external and internal variables on cell survival during the drying process and storage were investigated. The hypothesis was that by minimizing the oxidative and thermal stresses in the drying stages, in addition to adequate formulation choice, the cell viability during the drying and storage will increase. It was concluded that during the drying process the faster the embedding matrix reaches a glassy state the higher was the probiotic survival. Evaluating water activity and moisture limit of the glassy matrix concluded that maltodextrin DE5 is a better encapsulating matrix than maltodextrin DE19. Combining trehalose to maltodextrin in the encapsulating matrix resulted in a significant increase in the survival up to 70.6 AE 6.2%.
Food & function, 2014
This study evaluated the use of enzymatically synthesized dextran nanoparticles to entrap a hydro... more This study evaluated the use of enzymatically synthesized dextran nanoparticles to entrap a hydrophobic nutraceutical, the isoflavone genistein. The focus was on the synthesis of pure dextran as the material for the entire nanoparticle, and their inclusion-complexation of genistein. Under optimal conditions (pH 5.2-6 and sucrose concentration >0.5 M), dextransucrase generated spherical dextran nanoparticles (100-450 nm). The two nutraceutical inclusion methods were DMSO dilution in water and acidification. Optimization of the inclusion processes produced nanosized dextran particles containing genistein. The DMSO method was found to be more suitable for inclusion of genistein in dextran, resulting in a higher genistein load (5.6 ± 0.1 g genistein per 100 g particles), and a higher percentage of nanosized particles (85%, 105-400 nm). For both protocols, addition of a freeze-drying step exerted a positive effect presumably due to the formation of new hydrogen bonds and van der Waals...
Delivery and Controlled Release of Bioactives in Foods and Nutraceuticals, 2008
![Research paper thumbnail of ATR-FTIR studies on the effect of strong salting-out salts on the phase separation scenario in aqueous solutions of poly(N-isopropylacrylamide) [PNIPA]](https://attachments.academia-assets.com/42065565/thumbnails/1.jpg)
](Polymers for Advanced Technologies, 2002
Attenuated total reflectance (ATR) FTIR spectroscopy was used to investigate the effect of two st... more Attenuated total reflectance (ATR) FTIR spectroscopy was used to investigate the effect of two strong saltingout salts (Na 2 SO 4 and K 2 SO 4 ) on the temperatureinduced phase separation process in aqueous solutions of poly(N-isopropylacrylamide) [PNIPA]. It was found that the addition of these salts not only depresses the phase transition temperature (as was pointed out by other groups in the past) but, in fact, changes the whole scenario below, at, and above the aggregation temperature. Deconvolution of the amide II peak into three subbands reflecting three types of populations that differ by their hydrogen bonding types revealed that the sulfate ions decreased the amount of amide±water hydrogen bonds, while increasing the amount of amide±amide intramolecular H-bond population. This led to a relatively compact structure even at low temperatures. Based on the behavior of the hydrophobic IR peaks it is suggested that addition of sulfate ions increases the importance of hydrophobic interactions below the phase separation temperature. This study demonstrates the potential of ATR-FTIR in providing information at a molecular level on phase separation phenomena in aqueous solutions of hydrophobic polymers and, in particular, on the effects of co-solutes in such systems.
Polymer Engineering and Science, 1994
ABSTRACT Cushioning curves for different plastic foams were determined using drop and shock tests... more ABSTRACT Cushioning curves for different plastic foams were determined using drop and shock tests. It was found that at intermediate static stresses the two methods give comparable results. At low and very high static stresses however, different results were obtained. An explanation was given why the shock test is more appropriate and reliable at low and the drop test at very high static stresses.
Polymer Engineering and Science, 1990
It is also possible that your web browser is not configured or not able to display style sheets. ... more It is also possible that your web browser is not configured or not able to display style sheets. In this case, although the visual presentation will be degraded, the site should continue to be functional. We recommend using the latest version of Microsoft or Mozilla web browser to ...
Physical Chemistry Chemical Physics, 2011
Amphiphilic block copolymers and mixtures of amphiphiles find broad applications in numerous tech... more Amphiphilic block copolymers and mixtures of amphiphiles find broad applications in numerous technologies, including pharma, food, cosmetic and detergency. Here we report on the interactions between a biological charged diblock copolymer, b-casein, and a synthetic uncharged triblock copolymer, Lutrol F-127 (EO 101 PO 56 EO 101 ), on their mixed micellization characteristics and the micelles' structure and morphology. Isothermal titration calorimetry (ITC) experiments indicate that mixed micelles form when Lutrol is added to monomeric as well as to assembled b-casein. The main driving force for the mixed micellization is the hydrophobic interactions. Above b-casein CMC, strong perturbations caused by penetration of the hydrophobic oxypropylene sections of Lutrol into the protein micellar core lead to disintegration of the micelles and reformation of mixed Lutrol/b-casein micelles. The negative enthalpy of micelle formation (DH) and cooperativity increase with raising b-casein concentration in solution. z-potential measurements show that Lutrol interacts with the protein micelles to form mixed micelles even below its critical micellization temperature (CMT). They further indicate that Lutrol effectively masks the protein charges, probably by forming a coating layer of the ethyleneoxide rich chains. Small-angle X-ray scattering (SAXS) and cryogenic-transmission electron microscopy (cryo-TEM) indicate relatively small changes in the oblate micellar shape, but do show swelling along the small axis of b-casein micelles in the presence of Lutrol, thereby confirming the formation of mixed micelles.
Macromolecules, 2010
... Inna Shechter § , Ory ... Equally contributing authors. Abstract. Abstract Image. The LCST p... more ... Inna Shechter § , Ory ... Equally contributing authors. Abstract. Abstract Image. The LCST phase-transition of aqueous PNIPA solutions in rising concentrations of the strong chaotropic salt KSCN was studied microcalorimetrically by DSC and apparently for the first time by ITC. ...
Langmuir, 2008
beta-Casein is one of the main proteins in milk, recently classified as an intrinsically unstruct... more beta-Casein is one of the main proteins in milk, recently classified as an intrinsically unstructured protein. At neutral pH, it is composed of a highly polar N-terminus domain and a hydrophobic C-terminus tail. This amphiphilic block-copolymer-like structure leads to self-organization of the protein monomers into defined micelles. Recently, it has been shown that at room temperature, beta-casein also self-organizes into micelles in an acidic environment, but the effect of temperature on the micelles' formation and properties at the low pH regime were not explored. In the present study, we used two complementary techniques, cryogenic-transmission electron microscopy (cryo-TEM) and small-angle X-ray scattering (SAXS), to characterize at high-resolution the micelles' shape, dimensions, and aggregation numbers and to determine how these properties are affected by temperature between 1 and 40 degrees C. Two different regimes were studied: highly acidic pH where the protein is cationic, and neutral pH, where it is anionic. We found that flat disk-like micelles with low aggregation numbers formed at low temperature in the two pH regimes. Close to neutral pH increase in temperature involves a transition in the micelles' shape and dimensions from flat disks to bulky, almost spheroidal micelles, coupled with a sharp increase in the micelles' aggregation number. In contrast, no effects on the micelles' morphology or aggregation number were detected in the acidic environment within the entire temperature range studied. The self-organization into disk micelles and the lack of effect of temperature in the acidic environment are linked to the unstructured character of the protein and to the charge distribution map. The latter indicates that below the isoelectric pH (pI), beta-casein loses the distinct separation of hydrophobic and hydrophilic domains, thereby suggesting that it may no longer be considered as a classical head-tail block-copolymer amphiphile as in neutral pH.
Langmuir, 2009
The rheology of wormlike micelles (&a... more The rheology of wormlike micelles ("worms") formed by surfactants in water often follows nonmonotonic trends as functions of composition. For example, a study by Raghavan et al. (Langmuir 2002, 18, 3797) on mixtures of the anionic surfactant sodium oleate (NaOA) and the cationic surfactant octyl trimethylammonium bromide (OTAB) reported a pronounced peak in the zero-shear viscosity eta0 as a function of NaOA/OTAB ratio at a constant surfactant concentration (3 wt %). In this work, we study the origins of rheological changes in the NaOA/OTAB system and the relations between the composition and structural characteristics using cryo-transmission electron microscopy (cryo-TEM). When either surfactant is in large excess, the dominating morphology is that of spherical micelles. As oppositely charged surfactant is added to the mixture, the spheres grow into linear worms and these continue to elongate as the viscosity peak (which occurs at a 70/30 NaOA/OTAB ratio) is approached from either end. At the viscosity peak, the sample shows numerous long worms as well as a small number of branched worms. Taken together, NaOA/OTAB rheology can be primarily understood on the basis of micellar growth, which is explained primarily by packing arguments. While the size of the hydrophobic micellar core continuously decreases as the short amphiphile OTAB is added at the expense of NaOA, screening of charges goes through a maximum, which contributes to the asymmetry of the viscosity curve. With regard to micellar branching, there is no significant difference in the density of branched worms on either side of the viscosity peak. Therefore, it appears that in contrast to the behavior of some surfactant/salt systems, branching does not have a significant influence on the rheology of this mixed catanionic surfactant system. Instead, our data clearly indicate that the origin of the viscosity peak is linked with micellar growth and micellar shortening.
Journal of Polymer Science Part B: Polymer Physics, 2003
Livney, YD, Portnaya, I., Faupin, B., Fahoum, L., Ramon, O., Cohen, Y., Mizrahi, S. and Cogan, U.... more Livney, YD, Portnaya, I., Faupin, B., Fahoum, L., Ramon, O., Cohen, Y., Mizrahi, S. and Cogan, U.(2003), Interactions of glucose and polyacrylamide in solutions and gels. Journal of Polymer Science Part B: Polymer Physics, 41: 30533063. doi: 10.1002/polb. 10632
Journal of Polymer Science Part B: Polymer Physics, 2001
The swelling of dextran gels (Sephadex) in salt solutions with a water activity of 0.937, compare... more The swelling of dextran gels (Sephadex) in salt solutions with a water activity of 0.937, compared with the swelling in pure water, exhibited anion specificity as evidenced by an increased swelling ratio in the following order: Na 2 SO 4 Ͻ H 2 O Ͻ NaCl Ͻ NaSCN. The swelling ratio showed a good linear correlation with the osmotic pressure of dextran (500 kD) in these solutions. The salt-concentration difference (imbalance) between the polymer-solution side of the membrane and the polymer-free permeate side during the osmotic-pressure measurements positively correlated with the effect of the salt on the polymer osmotic pressure. These phenomena conform to Hofmeister-type (or lyotropic) behavior. The diminishing augmentation of dextran osmotic pressure and the change in the salt-concentration imbalance with rising NaSCN concentration imply a positive preferential interaction and adsorption of the salt onto the polymer.
Journal of Polymer Science Part B: Polymer Physics, 2004
The effect of two strong salting-out salts (Na 2 SO 4 and K 2 SO 4 ) on the temperature-induced p... more The effect of two strong salting-out salts (Na 2 SO 4 and K 2 SO 4 ) on the temperature-induced phase-separation process in aqueous solutions of poly(N-isopropylacrylamide) (PNIPA) was examined by attenuated total reflectance/Fourier transform infrared spectroscopy, differential scanning calorimetry, and viscosity measurements. On the basis of these measurements, a detailed scenario of the phase-separation process was deduced. The phase-separation scenario of solutions containing PNIPA and water was altered in the presence of sulfate ions. Here, the sulfate ions induced partial intrachain collapse, manifested by a relatively compact structure well below the lower critical solution temperature. This led to a more gradual, smooth phase transition, with temperature-resolved intrachain collapse and interchain aggregation and a lesser extent of hysteresis. Although at the macrolevel one may not be able to differentiate among various scenarios altering the solvent into a poor solvent, the aforementioned microlevel measurements provided a way to expose the difference between raising the temperature and adding cosolutes. Follow-up studies on the effect of salting-in salts will be presented.
Journal of Polymer Science Part B: Polymer Physics, 1997
Recent data on comparative osmotic deswelling of poly(acrylic acid) gels and solutions shows that... more Recent data on comparative osmotic deswelling of poly(acrylic acid) gels and solutions shows that the difference between osmotic pressure of the gel and of the solution, P gel (c, f ) 0 P solution (c, f ), taken at equal polymer concentration ( c) and fraction of the ionized acrylic acid monomers ( f ), changes its sign from negative to positive as the concentration c increases; this effect is enhanced with increasing f whereby it is shifted toward lower concentrations. In order to explain this effect, a model is suggested for the elastic pressure of the gel network which takes into account the effect of topological constraints combined with the effect of network ionization. According to the model, the sign-change of P gel 0 P solution originates from the topological constraints on conformations of the network; the ionization of the network chains enhances this effect and shifts it to the concentration range of the experiment.
Journal of Polymer Science Part B: Polymer Physics, 2008
Shpigelman, A., Portnaya, I., Ramon, O. and Livney, YD (2008), Saccharide-structure effects on po... more Shpigelman, A., Portnaya, I., Ramon, O. and Livney, YD (2008), Saccharide-structure effects on poly N-isopropylacrylamide phase transition in aqueous media; Reflections on protein stability. Journal of Polymer Science Part B: Polymer Physics, 46: 23072318. doi: ...
Journal of Polymer Science Part B: Polymer Physics, 2003
The swelling of poly(acrylamide) (PAAm) gels and the osmotic pressure of linear PAAm in aqueous s... more The swelling of poly(acrylamide) (PAAm) gels and the osmotic pressure of linear PAAm in aqueous solutions were predominantly affected by anion type and increased according to the lyotropic series ranking of sodium halide anions:
Macromolecules, 2010
... Inna Shechter § , Ory ... Equally contributing authors. Abstract. Abstract Image. The LCST p... more ... Inna Shechter § , Ory ... Equally contributing authors. Abstract. Abstract Image. The LCST phase-transition of aqueous PNIPA solutions in rising concentrations of the strong chaotropic salt KSCN was studied microcalorimetrically by DSC and apparently for the first time by ITC. ...
Drying Technology
In the present research, an air-suspension fluidized-bed technique for generation of core and she... more In the present research, an air-suspension fluidized-bed technique for generation of core and shell microcapsules containing probiotic Lactobacillusparacasei cells was evaluated. The air-suspension process was performed in a Wu¨rster coater system with a bottomspraying atomizer. In the first stage, a solution containing trehalose, maltodextrin, and probiotic cells was spray-coated onto and absorbed by the inert carrier microcrystalline cellulose to produce nonagglomerating dry coated particles with high probiotic cell viability (109 colony-forming units [cfu]/g particles). The effect of inlet air temperature, spray flow rate, solids concentration, cell concentration, and encapsulation formulation on survival was investigated. The inlet air temperature had the most pronounced effect; a 15�C increase in inlet air temperature led to a 250-fold decrease in survival percentage. There was no agglomeration of the coated adsorbed particles at spray flow rates of 1 to 3.5 mL/min. Spraycoatin...
LWT - Food Science and Technology, 2011
Ultrasonic vacuum spray dryer was used to produce a dry powder of highly viable probiotic cells. ... more Ultrasonic vacuum spray dryer was used to produce a dry powder of highly viable probiotic cells. The drying was performed through two stages: Vacuum spray drying of the solution followed by fluidizedbed drying of the powder. The embedding matrix was a combination of trehalose and maltodextrin. The effects of external and internal variables on cell survival during the drying process and storage were investigated. The hypothesis was that by minimizing the oxidative and thermal stresses in the drying stages, in addition to adequate formulation choice, the cell viability during the drying and storage will increase. It was concluded that during the drying process the faster the embedding matrix reaches a glassy state the higher was the probiotic survival. Evaluating water activity and moisture limit of the glassy matrix concluded that maltodextrin DE5 is a better encapsulating matrix than maltodextrin DE19. Combining trehalose to maltodextrin in the encapsulating matrix resulted in a significant increase in the survival up to 70.6 AE 6.2%.
Food & function, 2014
This study evaluated the use of enzymatically synthesized dextran nanoparticles to entrap a hydro... more This study evaluated the use of enzymatically synthesized dextran nanoparticles to entrap a hydrophobic nutraceutical, the isoflavone genistein. The focus was on the synthesis of pure dextran as the material for the entire nanoparticle, and their inclusion-complexation of genistein. Under optimal conditions (pH 5.2-6 and sucrose concentration >0.5 M), dextransucrase generated spherical dextran nanoparticles (100-450 nm). The two nutraceutical inclusion methods were DMSO dilution in water and acidification. Optimization of the inclusion processes produced nanosized dextran particles containing genistein. The DMSO method was found to be more suitable for inclusion of genistein in dextran, resulting in a higher genistein load (5.6 ± 0.1 g genistein per 100 g particles), and a higher percentage of nanosized particles (85%, 105-400 nm). For both protocols, addition of a freeze-drying step exerted a positive effect presumably due to the formation of new hydrogen bonds and van der Waals...
Delivery and Controlled Release of Bioactives in Foods and Nutraceuticals, 2008
Polymers for Advanced Technologies, 2002
Attenuated total reflectance (ATR) FTIR spectroscopy was used to investigate the effect of two st... more Attenuated total reflectance (ATR) FTIR spectroscopy was used to investigate the effect of two strong saltingout salts (Na 2 SO 4 and K 2 SO 4 ) on the temperatureinduced phase separation process in aqueous solutions of poly(N-isopropylacrylamide) [PNIPA]. It was found that the addition of these salts not only depresses the phase transition temperature (as was pointed out by other groups in the past) but, in fact, changes the whole scenario below, at, and above the aggregation temperature. Deconvolution of the amide II peak into three subbands reflecting three types of populations that differ by their hydrogen bonding types revealed that the sulfate ions decreased the amount of amide±water hydrogen bonds, while increasing the amount of amide±amide intramolecular H-bond population. This led to a relatively compact structure even at low temperatures. Based on the behavior of the hydrophobic IR peaks it is suggested that addition of sulfate ions increases the importance of hydrophobic interactions below the phase separation temperature. This study demonstrates the potential of ATR-FTIR in providing information at a molecular level on phase separation phenomena in aqueous solutions of hydrophobic polymers and, in particular, on the effects of co-solutes in such systems.
Polymer Engineering and Science, 1994
ABSTRACT Cushioning curves for different plastic foams were determined using drop and shock tests... more ABSTRACT Cushioning curves for different plastic foams were determined using drop and shock tests. It was found that at intermediate static stresses the two methods give comparable results. At low and very high static stresses however, different results were obtained. An explanation was given why the shock test is more appropriate and reliable at low and the drop test at very high static stresses.
Polymer Engineering and Science, 1990
It is also possible that your web browser is not configured or not able to display style sheets. ... more It is also possible that your web browser is not configured or not able to display style sheets. In this case, although the visual presentation will be degraded, the site should continue to be functional. We recommend using the latest version of Microsoft or Mozilla web browser to ...
Physical Chemistry Chemical Physics, 2011
Amphiphilic block copolymers and mixtures of amphiphiles find broad applications in numerous tech... more Amphiphilic block copolymers and mixtures of amphiphiles find broad applications in numerous technologies, including pharma, food, cosmetic and detergency. Here we report on the interactions between a biological charged diblock copolymer, b-casein, and a synthetic uncharged triblock copolymer, Lutrol F-127 (EO 101 PO 56 EO 101 ), on their mixed micellization characteristics and the micelles' structure and morphology. Isothermal titration calorimetry (ITC) experiments indicate that mixed micelles form when Lutrol is added to monomeric as well as to assembled b-casein. The main driving force for the mixed micellization is the hydrophobic interactions. Above b-casein CMC, strong perturbations caused by penetration of the hydrophobic oxypropylene sections of Lutrol into the protein micellar core lead to disintegration of the micelles and reformation of mixed Lutrol/b-casein micelles. The negative enthalpy of micelle formation (DH) and cooperativity increase with raising b-casein concentration in solution. z-potential measurements show that Lutrol interacts with the protein micelles to form mixed micelles even below its critical micellization temperature (CMT). They further indicate that Lutrol effectively masks the protein charges, probably by forming a coating layer of the ethyleneoxide rich chains. Small-angle X-ray scattering (SAXS) and cryogenic-transmission electron microscopy (cryo-TEM) indicate relatively small changes in the oblate micellar shape, but do show swelling along the small axis of b-casein micelles in the presence of Lutrol, thereby confirming the formation of mixed micelles.
Macromolecules, 2010
... Inna Shechter § , Ory ... Equally contributing authors. Abstract. Abstract Image. The LCST p... more ... Inna Shechter § , Ory ... Equally contributing authors. Abstract. Abstract Image. The LCST phase-transition of aqueous PNIPA solutions in rising concentrations of the strong chaotropic salt KSCN was studied microcalorimetrically by DSC and apparently for the first time by ITC. ...
Langmuir, 2008
beta-Casein is one of the main proteins in milk, recently classified as an intrinsically unstruct... more beta-Casein is one of the main proteins in milk, recently classified as an intrinsically unstructured protein. At neutral pH, it is composed of a highly polar N-terminus domain and a hydrophobic C-terminus tail. This amphiphilic block-copolymer-like structure leads to self-organization of the protein monomers into defined micelles. Recently, it has been shown that at room temperature, beta-casein also self-organizes into micelles in an acidic environment, but the effect of temperature on the micelles' formation and properties at the low pH regime were not explored. In the present study, we used two complementary techniques, cryogenic-transmission electron microscopy (cryo-TEM) and small-angle X-ray scattering (SAXS), to characterize at high-resolution the micelles' shape, dimensions, and aggregation numbers and to determine how these properties are affected by temperature between 1 and 40 degrees C. Two different regimes were studied: highly acidic pH where the protein is cationic, and neutral pH, where it is anionic. We found that flat disk-like micelles with low aggregation numbers formed at low temperature in the two pH regimes. Close to neutral pH increase in temperature involves a transition in the micelles' shape and dimensions from flat disks to bulky, almost spheroidal micelles, coupled with a sharp increase in the micelles' aggregation number. In contrast, no effects on the micelles' morphology or aggregation number were detected in the acidic environment within the entire temperature range studied. The self-organization into disk micelles and the lack of effect of temperature in the acidic environment are linked to the unstructured character of the protein and to the charge distribution map. The latter indicates that below the isoelectric pH (pI), beta-casein loses the distinct separation of hydrophobic and hydrophilic domains, thereby suggesting that it may no longer be considered as a classical head-tail block-copolymer amphiphile as in neutral pH.
Langmuir, 2009
The rheology of wormlike micelles (&a... more The rheology of wormlike micelles ("worms") formed by surfactants in water often follows nonmonotonic trends as functions of composition. For example, a study by Raghavan et al. (Langmuir 2002, 18, 3797) on mixtures of the anionic surfactant sodium oleate (NaOA) and the cationic surfactant octyl trimethylammonium bromide (OTAB) reported a pronounced peak in the zero-shear viscosity eta0 as a function of NaOA/OTAB ratio at a constant surfactant concentration (3 wt %). In this work, we study the origins of rheological changes in the NaOA/OTAB system and the relations between the composition and structural characteristics using cryo-transmission electron microscopy (cryo-TEM). When either surfactant is in large excess, the dominating morphology is that of spherical micelles. As oppositely charged surfactant is added to the mixture, the spheres grow into linear worms and these continue to elongate as the viscosity peak (which occurs at a 70/30 NaOA/OTAB ratio) is approached from either end. At the viscosity peak, the sample shows numerous long worms as well as a small number of branched worms. Taken together, NaOA/OTAB rheology can be primarily understood on the basis of micellar growth, which is explained primarily by packing arguments. While the size of the hydrophobic micellar core continuously decreases as the short amphiphile OTAB is added at the expense of NaOA, screening of charges goes through a maximum, which contributes to the asymmetry of the viscosity curve. With regard to micellar branching, there is no significant difference in the density of branched worms on either side of the viscosity peak. Therefore, it appears that in contrast to the behavior of some surfactant/salt systems, branching does not have a significant influence on the rheology of this mixed catanionic surfactant system. Instead, our data clearly indicate that the origin of the viscosity peak is linked with micellar growth and micellar shortening.
Journal of Polymer Science Part B: Polymer Physics, 2003
Livney, YD, Portnaya, I., Faupin, B., Fahoum, L., Ramon, O., Cohen, Y., Mizrahi, S. and Cogan, U.... more Livney, YD, Portnaya, I., Faupin, B., Fahoum, L., Ramon, O., Cohen, Y., Mizrahi, S. and Cogan, U.(2003), Interactions of glucose and polyacrylamide in solutions and gels. Journal of Polymer Science Part B: Polymer Physics, 41: 30533063. doi: 10.1002/polb. 10632
Journal of Polymer Science Part B: Polymer Physics, 2001
The swelling of dextran gels (Sephadex) in salt solutions with a water activity of 0.937, compare... more The swelling of dextran gels (Sephadex) in salt solutions with a water activity of 0.937, compared with the swelling in pure water, exhibited anion specificity as evidenced by an increased swelling ratio in the following order: Na 2 SO 4 Ͻ H 2 O Ͻ NaCl Ͻ NaSCN. The swelling ratio showed a good linear correlation with the osmotic pressure of dextran (500 kD) in these solutions. The salt-concentration difference (imbalance) between the polymer-solution side of the membrane and the polymer-free permeate side during the osmotic-pressure measurements positively correlated with the effect of the salt on the polymer osmotic pressure. These phenomena conform to Hofmeister-type (or lyotropic) behavior. The diminishing augmentation of dextran osmotic pressure and the change in the salt-concentration imbalance with rising NaSCN concentration imply a positive preferential interaction and adsorption of the salt onto the polymer.
Journal of Polymer Science Part B: Polymer Physics, 2004
The effect of two strong salting-out salts (Na 2 SO 4 and K 2 SO 4 ) on the temperature-induced p... more The effect of two strong salting-out salts (Na 2 SO 4 and K 2 SO 4 ) on the temperature-induced phase-separation process in aqueous solutions of poly(N-isopropylacrylamide) (PNIPA) was examined by attenuated total reflectance/Fourier transform infrared spectroscopy, differential scanning calorimetry, and viscosity measurements. On the basis of these measurements, a detailed scenario of the phase-separation process was deduced. The phase-separation scenario of solutions containing PNIPA and water was altered in the presence of sulfate ions. Here, the sulfate ions induced partial intrachain collapse, manifested by a relatively compact structure well below the lower critical solution temperature. This led to a more gradual, smooth phase transition, with temperature-resolved intrachain collapse and interchain aggregation and a lesser extent of hysteresis. Although at the macrolevel one may not be able to differentiate among various scenarios altering the solvent into a poor solvent, the aforementioned microlevel measurements provided a way to expose the difference between raising the temperature and adding cosolutes. Follow-up studies on the effect of salting-in salts will be presented.
Journal of Polymer Science Part B: Polymer Physics, 1997
Recent data on comparative osmotic deswelling of poly(acrylic acid) gels and solutions shows that... more Recent data on comparative osmotic deswelling of poly(acrylic acid) gels and solutions shows that the difference between osmotic pressure of the gel and of the solution, P gel (c, f ) 0 P solution (c, f ), taken at equal polymer concentration ( c) and fraction of the ionized acrylic acid monomers ( f ), changes its sign from negative to positive as the concentration c increases; this effect is enhanced with increasing f whereby it is shifted toward lower concentrations. In order to explain this effect, a model is suggested for the elastic pressure of the gel network which takes into account the effect of topological constraints combined with the effect of network ionization. According to the model, the sign-change of P gel 0 P solution originates from the topological constraints on conformations of the network; the ionization of the network chains enhances this effect and shifts it to the concentration range of the experiment.
Journal of Polymer Science Part B: Polymer Physics, 2008
Shpigelman, A., Portnaya, I., Ramon, O. and Livney, YD (2008), Saccharide-structure effects on po... more Shpigelman, A., Portnaya, I., Ramon, O. and Livney, YD (2008), Saccharide-structure effects on poly N-isopropylacrylamide phase transition in aqueous media; Reflections on protein stability. Journal of Polymer Science Part B: Polymer Physics, 46: 23072318. doi: ...
Journal of Polymer Science Part B: Polymer Physics, 2003
The swelling of poly(acrylamide) (PAAm) gels and the osmotic pressure of linear PAAm in aqueous s... more The swelling of poly(acrylamide) (PAAm) gels and the osmotic pressure of linear PAAm in aqueous solutions were predominantly affected by anion type and increased according to the lyotropic series ranking of sodium halide anions: