Rheological Behavior Of Aqueous Solutions Research Articles

Study on the rheological behavior of aqueous solutions of polyacryloylglycinamide

Polyacryloylglycinamide exhibits an upper critical solution temperature (UCST) behaviour in aqueous solutions, and unlike typical polymers, dissolution is more sensitive to temperature and solutions may exhibit an extraordinary rheological behavior.

PH-Sensitive Poly(acrylic acid)-g-poly(L-lysine) Charge-Driven Self-Assembling Hydrogels with 3D-Printability and Self-Healing Properties.

We report the rheological behavior of aqueous solutions of a graft copolymer polyampholyte, constituted of polyacrylic acid (PAA) backbone grafted by Poly(L-lysine) (PAA-b-PLL). The graft copolymer self-assembles in aqueous media, forming a three-dimensional (3D) network through polyelectrolyte complexation of the oppositely charged PAA and PLL segments. Rheological investigations showed that the hydrogel exhibits interesting properties, namely, relatively low critical gel concentration, elastic response with slow dynamics, remarkable extended critical strain to flow, shear responsiveness, injectability, 3D printability and self-healing. Due to the weak nature of the involved polyelectrolyte segments, the hydrogel properties display pH-dependency, and they are affected by the presence of salt. Especially upon varying pH, the PLL secondary structure changes from random coil to α-helix, affecting the crosslinking structural mode and, in turn, the overall network structure as reflected in the rheological properties. Thanks to the biocompatibility of the copolymer constituents and the biodegradability of PLL, the designed gelator seems to exhibit potential for bioapplications.

A Research on Rheological Behavior of Aqueous Solutions of Pomegranate Peel Powder

Determining the viscosity of pomegranate peel powder (PPP) can aid in product development, process optimization, quality control, ingredient interactions, and scientific research related to pomegranate peel-based products or formulations. Therefore, in this study, the rheological behavior of dried and ground pomegranate peel has been investigated. The apparent viscosities of pomegranate peel solutions prepared with distilled water are measured by a rotational viscometer. The viscosity of the pomegranate peel solution at each concentration is measured at shear rates varying between 2.64 s-1 and 22 s-1 at constant temperature (25 °C). When the effect of concentration on apparent viscosity has been examined, it is observed that the viscosity rises with increasing concentration at a constant shear rate. Among the rheological models studied, Power model provides a good fit for the experimental viscosity data of aqueous solutions of pomegranate peel powder at different concentrations. The consistency coefficient and the flow behavior index are calculated using the power law model and the solutions have been found to exhibit pseudoplastic behavior.

Features of the rheological behavior of aqueous solutions of alumino-, aluminoboro- and aluminochromophosphates

Rheological studies carried out using rotational rheometer in the rotational and oscillatory modes at different temperatures and heating/cooling conditions revealed that the aqueous solutions of alumino-, aluminoboro- and aluminochromophosphates presented an unusual behavior. The largest increase in the viscosity of the studied systems was determined between 20 and 60 °C and was attributed to the formation of thermo-reversible inorganic gels in solutions of aluminophosphates due to interionic association. At the same time, the oscillation mode was found to be more sensitive to the process of polymer gel formation compared to the rotation mode. In addition, the process of polymer gel formation was more adequately studied from dynamic tests.

Viscosity Factor (VF) Complementary to the Statistical Indicators Associated with the Rheological Behavior of Aqueous Solutions of Polyvinyl Alcohol

The rheological behavior of aqueous solutions of polyvinyl alcohol at 4, 6, 8 and 10% by weight has been studied and evaluated at temperatures of 20, 25, 30 and 35 °C, using five non-Newtonian fluid models independent of time: Ferrys, Robertson-Stiff, Williamson, Sisko, and Ellis de Haven. The classical method consists in carrying out regression analysis. Using a comparative procedure of determination coefficients and variances, the model that most appropriately adjusts the experimental data to said model is selected. From the statistical point of view, the Sisko and Robertson-Stiff models present better regression parameters; to better specify the choice of the respective rheological model, a new factor has been proposed in the literature, the viscosity factor (VF), which expresses the relationship between apparent and dynamic viscosity. The analysis of this factor for the five models confirms the greater stability of the Ellis de Haven model in terms of the coefficient of variation of the VF. The value of VF fluctuates between 1 and 2 for all ranges of temperature and concentration experienced for vinyl alcohol solutions. As a consequence of the above, for the choice of the non-Newtonian fluid model associated with the rheology of the aqueous solution of polyvinyl alcohol, it is necessary to analyze the statistical parameters and the VF factor simultaneously.

Interaction of HPC with CTAB and Tween 40 at Water/Air and Water/Soya Oil Interfaces.

The bulk and interfacial shear rheological behavior of aqueous solutions of biocompatible polymer HPC has been investigated in the presence of cationic CTAB and nonionic Tween 40 having the same chain length but different head groups. Steady-state bulk experiments depict two distinct regions in the rheogram (Newtonian followed by pseudoplastic). Dynamic experiments suggest that the stability of HPC hydrogels decreases with the increase in surfactant concentration. Interfacial steady shear tests of 2D monolayers of 1 wt % HPC and 1 wt % HPC with varying concentrations of Tween 40/CTAB show a non-Newtonian dilatant behavior at the solution-air interface. However, two distinct dilatant regions separated by a Newtonian region were observed for the same films at the solution-soya oil interface. The strength of films formed at the two interfaces decreases with the increase of surfactant concentration as observed from oscillatory interfacial tests. HPC interacts more strongly with CTAB than Tween 40 both in bulk as well as at the interfaces studied.

PH-Responsive, Thermo-Resistant Poly(Acrylic Acid)-g-Poly(boc-L-Lysine) Hydrogel with Shear-Induced Injectability.

In this study we report the rheological behavior of aqueous solutions of an amphiphilic graft copolymer constituting a polyacrylic acid (PAA) grafted by poly(boc-L-lysine), P(b-LL). Due to the highly hydrophobic nature of the grafted chains, the copolymer self-assembles spontaneously in aqueous media forming three-dimensional (3D) finite size networks (microgels). The rheological analysis demonstrated that the copolymer behaves as a strong elastic hydrogel, showing characteristics of a "frozen" network. Moreover, it is noteworthy that the formulation shows the above-described characteristics in very small concentrations (0.25-1.20 wt%) compared to other naturally cross-linked hydrogels that have been studied so far. Concentration significantly affects the rheological properties of the hydrogel, showing considerable increase in elastic modulus, following the scaling law G'~C1.93. At the same time, the hydrogels can be described as intelligent stimuli-responsive systems, showing pH and shear responsiveness as well as stability with temperature changes. Thanks to the pH dependance of the degree of ionization of the weak polyelectrolyte PAA backbone, stiffness and swelling of the hydrogels can be tuned effectively by adjusting the pH conditions. Simulating conditions such as those of injection through a 28-gauge syringe needle, the gel demonstrates excellent response to shear, due to its remarkable shear thinning behavior. The combination of pH-sensitivity and shear responsiveness leads to excellent injectability and self-healing properties, given that it flows easily upon applying a low stress and recovers instantly in the site of injection. Therefore, the physically cross-linked PAA-g-P(b-LL) hydrogel exhibits remarkable features, namely biocompatibility, biodegradability of cross-links, pH responsiveness, shear-induced injectability and instantaneous self-healing, making it a potential candidate for various biomedical applications.

Effect of Sugars on Gelation Kinetics of Gelatin Gels

We investigate the rheological behavior of aqueous solutions containing animal gelatin, sugars and polyols. The aim is to study how the gelation kinetics, transition temperatures and gel strengths of an aqueous gelatin solution can be affected by the progressive addition of co-solutes. Aqueous solutions with a fixed mass percentage of gelatin of 6.8 wt% were prepared at various concentrations of sugars and polyols. Through Dynamic Temperature Ramp tests, performed at various ramp rates, and Dynamic Time Sweep and Dynamic Frequency Sweep tests, carried out at different temperatures, it was possible both to evaluate the transition temperatures and to monitor the gelation kinetics of the samples. It was found that the contribution of co-solutes positively affects both the gelation process and the thermal stability of the aqueous gelatin solution by reducing the gelation time and improving the mechanical properties of the gel in terms of network elasticity.

Biomimetic aggrecan solutions show gel-like rheological behavior

Event Abstract Back to Event Biomimetic aggrecan solutions show gel-like rheological behavior Liam Vesey1, Harsh Patel1, Michele Marcolongo1 and Nicolas Alvarez1 1 Drexel University, Materials Science and Engineering and Chemical and Biological Engineering, United States Several cellular based medicine strategies exist to treat degenerative tissue and restore normal function. Over the past few years, it has been demonstrated that a novel family of biomimetic proteoglycans (BPs) is useful in modulating tissue mechanical properties by molecularly engineering the existing extracellular matrix. Biomimetic proteoglycans mimic the structure and composition of natural proteoglycans through a 3D bottle brush molecular architecture. The BPs of interest are composed of a poly(acrylic) acid core with bristles of chondroitin sulfate (CS) (BA-10-CS, 180kDa). We have observed that the starting CS precursor forms viscous solutions at low concentrations. Similar viscosities are also observed for solutions of synthesized BP. We present a systematic study of the rheological behavior of aqueous solutions of the CS precursor and final BPs as a function of aqueous concentration. We use small amplitude oscillatory shear (SAOS) on a DHR-3 rheometer to elucidate the underlying molecular structure of the bulk aqueous solution. Surprisingly, we find that both CS and BP show viscoelastic behavior typical of a gel and atypical for a solution of short chains. The observed rheological viscoelastic behavior is weakly dependent on CS and BP concentration. Furthermore, very little difference is observed between the CS precursor and the BP molecule. Our results suggest that CS molecules, which are composed of several acrylic acid and primary amine groups capable of hydrogen bonding, are forming a supramolecular network that span the sample volume. This is in agreement with other hydrogen bonding systems found in the literature. The surprising point is that the anchoring of CS molecules onto a poly(acrylic) acid core does not appear to alter the overall supramolecular structure. In addition to SAOS, the molecular structure of the CS aggregates are probed using large amplitude oscillatory shear and steady shear to determine the overall strength of the network and reformation time scales. The rheological study is presented alongside practical injection studies aimed at determining viability for injection of through needles between 16 and 33 gage under a controlled load of 1.8 N (less than thumb pressure to the plunger). Volumetric flow rates were calculated from video images of BP solutions of concentrations between 10 and 200mg/mL. Each solution was able to pass through each needle, regardless of solution concentration, material and needle gage. There was reduced volumetric flow rates for the higher concentrations and lower gage needles. The demonstration of flow through large to very small needles will offer minimally invasive injection strategies to a variety of soft tissues. Coulter Foundation Keywords: Biomimetic, mechanical property, polymer brush, biomacromolecule Conference: 10th World Biomaterials Congress, Montréal, Canada, 17 May - 22 May, 2016. Presentation Type: Poster Topic: Naturally-derived materials and biopolymers Citation: Vesey L, Patel H, Marcolongo M and Alvarez N (2016). Biomimetic aggrecan solutions show gel-like rheological behavior. Front. Bioeng. Biotechnol. Conference Abstract: 10th World Biomaterials Congress. doi: 10.3389/conf.FBIOE.2016.01.01381 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 27 Mar 2016; Published Online: 30 Mar 2016. Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Liam Vesey Harsh Patel Michele Marcolongo Nicolas Alvarez Google Liam Vesey Harsh Patel Michele Marcolongo Nicolas Alvarez Google Scholar Liam Vesey Harsh Patel Michele Marcolongo Nicolas Alvarez PubMed Liam Vesey Harsh Patel Michele Marcolongo Nicolas Alvarez Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

Extrusion of polysaccharide nanocrystal reinforced polymer nanocomposites through compatibilization with poly(ethylene oxide).

Polysaccharide nanocrystals with a rodlike shape but with different dimensions and specific surface area were prepared from cotton and capim dourado cellulose, and with a plateletlike morphology from waxy maize starch granules. The rheological behavior of aqueous solutions of poly(ethylene oxide) (PEO) with different molecular weights when adding these nanoparticles was investigated evidencing specific interactions between PEO chains and nanocrystals. Because PEO also bears hydrophobic moieties, it was employed as a compatibilizing agent for the melt processing of polymer nanocomposites. The freeze-dried mixtures were used to prepare nanocomposite materials with a low density polyethylene matrix by extrusion. The thermal and mechanical behavior of ensuing nanocomposites was studied.

Rheological Behavior of Aqueous Solutions of An Ionic Liquid As A Surfactant

The rheological properties of aqueous solutions of an ionic liquid as a surfactant, 1-tetradecyl-3-methylimidazolium bromide (C14mimBr), in the presence of sodium salicylate (NaSal), have been studied by rheological measurements. For these C14mimBr/NaSal systems, zero-shear viscosity as a function of NaSal concentration shows the maxima behavior. The effect of the concentration ratio, CNaSal/CC14mimBr, on the maximum was determined, and the scaling relations were obtained. Network structures could be formed in the aqueous C14mimBr solutions containing NaSal. 1H NMR spectra analysis indicates that the main interaction between C14mimBr and NaSal molecules is electrostatic attraction, which leads to the formation of an ion pair.

Synthesis and Characterization of Oligo(Ethylene Glycol)s Functionalized with Desaminotyrosine or Desaminotyrosyltyrosine

The aromatic compounds desaminotyrosine (DAT) and desaminotyrosyltyrosine (DATT) have been successfully used to functionalize gelatin in order to form physically crosslinked networks via π-π interactions and hydrogen bonds of the introduced phenol moieties. Here, it was explored whether this concept can be applied to a synthetic polymer not engaging in additional interactions such as triple helix formation in gelatin, enabling a network to form by physical interactions mainly related to the terminal functional groups. Oligo(ethylene glycol) (OEG) was chosen as hydrophilic synthetic polymer for the backbone structure. Linear OEG (MP = 3 kDa) and four-arm OEG (Mn = 5 kDa) with amino functionalities as endgroups were functionalized with DAT and DATT using EDC·HCl and NHS as activating agents. The compounds were characterized by NMR, IR spectroscopy, and MALDI. Rheological behavior of aqueous solutions of the polymers was studied. The critical micelle concentration (CMC) was determined by a fluorescence spectroscopic analysis using the hydrophobic fluorescent dye pyrene. DATT-functionalized linear OEG, four-arm DAT-functionalized OEG and four-arm DATT-functionalized OEG were synthesized with degrees of functionalization of 60-95 mol%. All compounds were water soluble, and rheological measurements revealed a decrease in storage modulus G' and loss modulus G'' compared to unfunctionalized OEG. Moreover, the CMC of linear OEG-DATT could be determined. The syntheses of OEG functionalized with the aromatic compounds DAT and DATT was reported. The polymers showed the properties of a surfactant.

Control of Rheological Behaviour with Oppositely Charged Polyelectrolyte Surfactant Mixtures

Abstract Mixtures of the cationic, cellulose based polyelectrolyte JR 400 and the anionic surfactant sodium dodecylbenzene sulfonate (LAS) have been used to control the rheological behaviour of aqueous solutions. Around charge equilibrium precipitation takes place, but both for the surfactant-rich and the polymer-rich side homogeneous solutions are formed. In these monophasic regions the rheology depends strongly on the mixing ratio between the two components and highly viscous systems can be obtained on the polyelectrolyte rich side upon the addition of relatively small amounts of surfactant. Here the viscosity increases by more than four orders of magnitude before reaching the phase boundary of precipitation. Small-angle neutron scattering (SANS) showed the formation of an interconnected network of rodlike aggregates composed of a polyelectrolyte/surfactant complex, which explains the observed high viscosity due to the high degree of interconnection by the polyelectrolyte.

Rheological Behavior of Aqueous Solutions of Cationic Guar in Presence of Oppositely Charged Surfactant

The cationic guar (CG) is synthesized and the rheological behavior of aqueous solutions of CG in the presence of sodium dodecyl sulfate (SDS) is studied in detail. The steady viscosity measurements show that the zero shear viscosity enhancement can be almost 3 orders of magnitude as the concentration of SDS increases from 0 to 0.043%. The gel-like formation is observed as the concentration of SDS is greater than 0.016%. The oscillatory rheological measurements of CG solutions in the presence of SDS show that the crossover modulus is almost independent of the concentration of SDS whereas the apparent relaxation time increases swiftly upon increasing the concentration of SDS. The experimental results indicate that the strength rather than the number of the cross-links is greatly affected by SDS molecules. The mechanism concerning the effect of SDS upon the rheology of CG solutions can be coined by the two-stage model. Before the formation of cross-links at the critical concentration, the electrostatic interaction between SDS and cationic site of CG chains plays a key role and the SDS molecules bind to CG chains through the electrostatic interaction. After the formation of cross-links at the concentration greater than the critical concentration, the cooperative hydrophobic interaction become dominant and SDS molecules bind to the cross-links through the hydrophobic interaction. The rheological behavior of aqueous solutions of CG in the presence of SDS is chiefly determined by the micelle-like cross-links between CG chains. In fact, the flow activation energy of CG solution, obtained from the temperature dependence of the apparent relaxation time, falls in the range of transferring a hydrophobic tail of SDS from the micelle to an aqueous environment.

Solution properties of targacanthin (water-soluble part of gum tragacanth exudate from Astragalus gossypinus)

Solution properties of tragacanthin (the water-soluble part of gum tragacanth) were studied by gel permeation chromatography (GPC) combined with multi-angle light scattering and viscometry at 25 °C. Photon correlation spectroscopy was used to determine the hydrodynamic radius. Ultrasonic degradation was applied to obtain biopolymer fractions of different molecular weights. The dependence of intrinsic viscosity [ η] and radius of gyration 〈 s 2 〉 z 1 / 2 on weight average molecular mass M w for this biopolymer were found to be [ η ] = 9.077 × 10 − 5 M w 0.87 ( dL g − 1 ) and 〈 s 2 〉 z 1 / 2 = 0.021 M w 0.59 ( nm ) in the range of M w from 1.8 × 10 5 to 1.6 × 10 6. The conformational parameters of tragacanthin were calculated to be 1111 nm for molar mass per unit contour length ( M L ), 26 nm for persistence length ( q) and 1.87 ratio of R g/ R h. It was found that the Smidsrød parameter B, the empirical stiffness parameter was 0.013, which is lower than that of several polysaccharides indicating the stiff backbone for tragacanthin. The rheological behavior of aqueous solutions of gum tragacanth and its insoluble and soluble fractions (bassorin and tragacanthin, respectively) were studied. For concentrations equal to 1%, at 25 °C and in the absence of salt, bassorin solution showed the highest viscosity and shear thinning behaviour. Power law and Williamson models were used to describe the rheological behaviour of bassorin and tragacanthin, respectively. Oscillatory shear experiments showed a gel like structure for the bassorin but for tragacanthin the oscillatory data were as would be expected for semi-dilute to concentrated solution of entangled, random coil polymers. NaCl changed the steady and oscillatory rheological properties of both fractions and in this way the final viscosity of bassorin was even less than tragacanthin. The calculated activation energy for bassorin and tragacanthin indicated a more rapid decrease in viscosity with temperature for tragacanthin. The plot of η sp, 0 versus C[η] revealed that the transition from dilute to semi-dilute regime occurs at C *[ η] = 2.82 for tragacanthin.

Capillary thinning of filaments of polymer solutions with surfactants

We present an investigation of the influence of a surfactant content on the rheological behaviour of aqueous solutions of a flexible polyacrylamide in strong uniaxial elongational flow. The flow is produced by the capillary thinning of a liquid filament in an elongational rheometer. Measurement data consist in the temporal evolution of the filament diameter. The data is interpreted in the light of a theoretical analysis, which assumes that the surfactant causes the relaxation time of the solution to become time dependent, which is due to scission and formation of micelles in the solution on a certain time scale. The evaluation of the experimental results allows for determination of this time scale and leads to conclusions about its consequences on the rheological behaviour of these solutions.

Effect of Ethanol on the Rheological Properties of Water‐Rich Gels of Diblock Copolymer E43B11

AbstractSummary: The effect of added ethanol on the rheological behaviour of aqueous solutions of diblock copolymer E43B11 (E = oxyethylene unit, B = oxybutylene unit) has been investigated. Thermally reversible sol‐gel transitions were observed for concentrated solutions of the copolymer in solutions containing 0–30 wt.‐% ethanol. Storage (G′) and loss (G″) moduli and yield stress (σy) were used to define hard and soft gel phases. The introduction of 10 wt.‐% ethanol did not alter the phase behaviour greatly, whereas higher ethanol concentrations had a large effect, which differed in kind from that reported for triblock copolymers of ethylene oxide and propylene oxide, type EPE.Temperature dependence of the logarithm of (•) storage and (○) loss modulus for 20 wt.‐% copolymer in 10 wt.‐% ethanol.magnified imageTemperature dependence of the logarithm of (•) storage and (○) loss modulus for 20 wt.‐% copolymer in 10 wt.‐% ethanol.

Rheological properties of multisticker associative polyelectrolytes in semidilute aqueous solutions

AbstractMultisticker associative polyelectrolytes of acrylamide (≈86 mol %) and sodium 2‐acrylamido‐2‐methylpropanesulfonate (≈12 mol %), hydrophobically modified with N,N‐dihexylacrylamide groups (≈2 mol %), were prepared with a micellar radical polymerization technique. This process led to multiblock polymers in which the length of the hydrophobic blocks could be controlled through variations in the surfactant‐to‐hydrophobe molar ratio, that is, the number of hydrophobes per micelle (NH). The rheological behavior of aqueous solutions of polymers with the same molecular weight and the same composition but with two different hydrophobic block lengths (NH = 7 or 3 monomer units per block) was investigated as a function of the polymer concentration with steady‐flow, creep, and oscillatory experiments. The critical concentration at the onset of the viscosity enhancement decreased as the length of the hydrophobic segments in the polymers increased. Also, an increase in the NH value significantly enhanced the thickening ability of the polymers and affected the structure of the transient network. In the semidilute unentangled regime, the behavior of the polymer with long hydrophobic segments (NH = 7) was studied in detail. The results were well explained by the sticky Rouse theory of associative polymer dynamics. Finally, the viscosity decreased with an increase in the temperature, mainly because of a lowering of the sample relaxation time. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1640–1655, 2004

Mass Transfer in a Flat Gas/Liquid Interface using non‐Newtonian Media

AbstractGas/liquid mass transfer has been investigated using a stirred vessel gas/liquid contactor using non‐Newtonian media and carbon dioxide as absorbent and gas phase, respectively. The volumetric mass transfer coefficients at different operational variables have been determined. Non‐Newtonian media (liquid phase) were prepared as aqueous solutions of sodium carboxymethyl cellulose salt. The influence of the rheological properties, polymer concentration, stirring rate, and gas flow rate on mass transfer was studied for these liquid phases. Kinematic viscosity and density experimental data were used to calculate the average molecular weight corresponding to the polymer employed. The Ostwald model has been used to fit the rheological behavior of aqueous solutions of the polymer employed as absorbent phase. Reasonably good agreement was found between the predictions of the proposed models and the experimental data of mass transfer coefficients.

Shear Induced Demixing and Rheological Behavior of Aqueous Solutions of Poly(N‐isopropylacrylamide)

AbstractThe interrelation between the phase separation behavior and the rheological performance of aqueous solutions of high molecular weight (Mw = 1 600 kg/mol) poly(N‐isopropylacrylamide) was investigated. The system demixes upon heating and the cloud point temperature, Tcp decreases steadily with rising polymer concentration up to 10 wt.‐%. The application of shear supports phase separation and reduces Tcp markedly. This observation is interpreted in terms of destruction of intersegmental clusters formed in the quiescent state owing to favorable interactions. Intrinsic viscosities and Huggins coefficients as well as the viscosities, η at higher polymer concentrations are closely connected with the thermodynamic conditions. [η] decreases by almost two orders of magnitude upon heating, whereas the corresponding increase of kH is less pronounced. The η values (constant shear rate) of the moderately concentrated solutions as function of T pass a maximum at the corresponding phase separation temperatures. The existence of clusters also manifests in terms of stress overshoot and of particularities observed with solutions that are sheared for the first time. Transmittance (ratio of intensities of the transmitted light and the incidence light) of a 2.0 wt.‐% PNIPAm solution in water as a function of temperature at different shear rates indicated. Heating rate is 0.22 °C/min.imageTransmittance (ratio of intensities of the transmitted light and the incidence light) of a 2.0 wt.‐% PNIPAm solution in water as a function of temperature at different shear rates indicated. Heating rate is 0.22 °C/min.