Behavior Of Semidilute Solutions Research Articles

Rheology of lyotropic cholesteric liquid crystal forming single-wall carbon nanotube dispersions stabilized by double-stranded DNA

The rheology of lyotropic cholesteric liquid crystalline phase forming double-stranded DNA (dsDNA) stabilized single-wall carbon nanotube (SWCNT) dispersions was analyzed over a wide range of SWCNT concentrations. In the semidilute regime, supernatant dispersions of dsDNA-SWCNTs showed the characteristic rheological behavior of semidilute solutions of rods predicted by the Doi-Edwards theory. These cholesterogenic liquid crystal dispersions exhibited some of the key rheological behaviors associated with lyotropic liquid crystalline polymers (LLCPs) including a non-monotonic relationship in the viscosity and moduli versus concentration curves, and the empirical Cox-Merz not being obeyed. However, the dsDNA-SWCNT viscosity versus shear rate curves exhibited an inflection point instead of the three distinct regions associated with many LLCPs and nanocylinder dispersions. This could be related to orientation defects and inherent secondary interactions between the dsDNA and the SWCNTs. Linear viscoelasticity measurements also showed similarities to other lyotropic systems.

Effect of surfactant on the viscoelastic behavior of semidilute solution of two different families of water-soluble copolymers prepared by solution polymerization

The interactions between hydrophobically modified polyacrylamides (HMPAM) and the anionic surfactant SDS (sodium dodecyl sulfate) and/or the cationic surfactant DTAB (dodecyltrimethylammonium bromide) were studied in aqueous solution using steady flows and oscillatory rheological experiments. The structure of the HMPAM used consisted of a telechelic polymer (with hydrophobic groups at the chain ends) and a multisticker polymer (with hydrophobic groups along the polymer chain). The multisticker polymer was prepared with acrylamide and N-hexadecylacrylamide (HDAM), whereas the telechelic polymer was prepared with acrylamide and a hydrophobic initiator that was derived from 4,4′-azobis(4-cyanopentanoic acid) (ACVA) and contained a long linear chain of 16 carbon atoms (ACVA16). In both polymers, the rheological behavior depended strongly on the amount of surfactant added. For the telechelic and multisticker polymers, the terminal relaxation time TR exhibited a maximum when the surfactant concentration was augmented (SDS or DTAB). An increase or decrease in the plateau modulus G0 was observed, depending on the structure of the polymer (telechelic or multisticker).

Synthesis, characterization, and aqueous solution behavior of copolymers of acrylamide and sodium 10-acryloyloxydecanoate

A new water-soluble monomer of sodium 10-Acryloyloxydecanoate (NaAD), which possesses a hydrophobic group and an ionizable group, was synthesized from acryloyl chloride and 10-hydroxydecanoic acid, and the series of copolymers of NaAD with acrylamide (AM) were prepared by the free radical polymerization in aqueous solution using ammonium persulfate as the initiator. The feed ratio of NaAD:AM was varied from 5:95 to 70:30 mol%, with the total monomer concentration held constant at 0.5 M. The copolymer compositions were determined from elemental analysis. The molecular weights of the copolymers were determined by gel permeation chromatography ranged from 0.76 × 106 to 1.37 × 106 g/mol. All copolymers were soluble in deionized water and salt solutions at pH > 5. The dilute and semidilute solution behavior of the copolymers was studied as a function of composition, pH, and added electrolytes, and the results indicated that NaAD30 exhibited much higher viscosity values. At moderate pH values, the copolymers coils become slightly more expanded and intermolecular association interactions occur, which was indicated by fluorescence and apparent viscosity measurements. Upon the addition of NaCl and in low pH, viscosities tended to decrease because of the disruption of the intermolecular associations.

Studies on Methacryloyl Guar Gum: Surface Morphology, Crystallinity, Biodegradability and Viscosity Behavior of Semi-Dilute Solutions

Methacryloyl guar gum was investigated with respect to crystallinity, surface morphology, biodegradability and viscosity of semi-dilute solutions. It was studied that the shear-dependent viscosity behaviour could be well described by the Cross viscosity model, under various methacryloyl guar gum concentrations, salts addition and temperature. The zero-shear-rate viscosity was observed to change with different methacryloyl guar gum concentration and decease with the increase of temperature.

Rheological behavior of semidilute solutions of ultrahigh-molecular-weight polyethylene

The rheological behavior of spinning solutions of ultrahigh-molecular-weight polyethylene was investigated in stationary and dynamic conditions of shear flow. It was shown that at the shear rates characteristic of real spinning conditions, the elastic reaction of the solution is much higher than the viscous reaction. In conditions of constant shear stress that ensure non-Newtonian flow of the solution, the uniform decrease in the viscosity is replaced by an increase in time due to gradual formation of a cross-linked layer adjacent to the rotating disk of the working unit of the rheometer.

Interpolymer Complex between Hydroxypropyl Cellulose and Maleic Acid-Styrene Copolymer: Phase Behavior of Semi-Dilute Solutions

The phase behavior of a water/hydroxypropyl cellulose/maleic acid-styrene copolymer (H2O/HPC/MAc-S) system was investigated in the semi-dilute range by turbidimetry, rheology, and optical microscopy. The two polymers under investigation form interpolymer complexes via hydrogen bonding. In the case of a total polymer concentration of cpol = 5 mg . mL(-1) a second phase segregates upon heating the homogeneous ternary system. By applying a constant shear rate (gamma = 50 s(-1)) the phase separation temperature of the system is 10-15 degrees C lower than for an unsheared one. For cpol = 10 mg . mL(-1) phase separation has already occurred at room temperature when the two binary polymer solutions are mixed. The distribution of the partners among the coexisting phases was examined by FT-IR spectroscopy. The stoichiometry of the interpolymeric complex (IPC) was estimated to be HPC/MAc-S = 40:60 (w/w) independent of cpol.

Solution and bulk rheological behavior of poly(ethylenes) based on VERSIPOL™ catalysts

Palladium catalysts [(ArNC(Me)–C(Me)NAr)Pd(CH2)3(COOMe)]+BAr4′− (VERSIPOL™) or [(ArNC(Me)–C(Me)NAr)Pd(CH2)3(COOMe)]+BF4− (Ar=2,6-i-Pr2–C6H3, 2,6-Me2–C6H3 or C6H5 and Ar′=3,5-(CF3)2–C6H3) were synthesized and tested, in dichloromethane, for the polymerization of ethylene. The influence of the substituent present on the diimine ligand on the molar mass of the resulting polymers was examined first. Poly(ethylene)s obtained in the presence of catalysts containing the bulky 2,6-i-Pr2 group, prepared at different ethylene pressures, exhibited almost identical weight average molar mass values, but were characterized by great differences in hydrodynamic volume, radius of gyration and intrinsic viscosity values. These differences were attributed to the evolution of the topology going from hyperbranched to almost linear. Similar observations were made earlier. The major part of the work dealt with new results on the behavior of these PE samples examined in terms of particle scattering function q5/3I(q) (Kratky–Porod) plot based on small angle neutron scattering experiments and on the semi-dilute solution behavior. Some results on the bulk rheological properties of these polymers were presented in the last section and corroborated the results obtained in dilute or semi-dilute solution. The data were compared also to PE obtained with other catalysts.

Study of three different families of water-soluble copolymers: synthesis, characterization and viscoelastic behavior of semidilute solutions of polymers prepared by solution polymerization

Polymer chains consisting of water-soluble polyacrylamides, hydrophobically modified with low amounts of N, N-dialkylacrylamides ( N, N-dihexylacrylamide (DHAM) and N, N-dioctylacrylamide (DOAM)) have been prepared via free radical solution polymerization, using two hydrophobic initiators derived from 4,4′-azobis(4-cyanopentanoic acid) (ACVA) containing long linear chains of 12 (C12) and 16 (C16) carbon atoms. This procedure resulted in polyacrylamides containing hydrophobic groups along the chain as well as at the chain ends. This class of polymers, termed ‘combined associative polymers’, has been studied and compared with the multisticker (with hydrophobic groups along the polymer chain) and telechelic (with hydrophobic groups at the chain ends) associative polymers, which were prepared with DHAM or DOAM and with the hydrophobic initiator (ACVA) modified with alkyl chains of two different lengths. The viscoelastic properties of these different families of associative polymers were investigated using steady-flow and oscillatory experiments. The effect of type, localization and concentration of the hydrophobic groups on the viscosity of the associative polymer solution was investigated. All viscosity curves clearly show two different regimes within the semidilute range: a first unentangled regime where the viscosity increases moderately; and a second entangled regime where the viscosity varies according to a power law, proportional to C 4. The relaxation time, T R, and the plateau modulus, G 0, showed relatively high values which increased with the number of carbon atoms in the hydrophobic groups. The combined associative polymer (PAM- co-DHAM/ACVA12) showed relaxation times that remained relatively constant along the concentrations studied, but very high values of G 0.

Direct measurement of polymer segment orientation and distortion in shear: semi-dilute solution behavior

The shear induced backbone segment orientation and deformation of the polymeric chromophore diacetylene 4-butoxycarbonylmethylurethane (4BCMU) in semi-dilute solution has been measured with an extended dichroism technique. At low shear rates the random coil, visco-elastic polymer shows orientation in the flow direction. At higher shear rates a reduction in the average conjugation length is observed with an increase in the number of segments orienting perpendicular to the flow direction. Novel behavior, which is not consistent with standard models, is observed for this visco-elastic polymer at high shear rates. The results presented are discussed in view of prior experimental and theoretical work.

The Effects of Concentration, Pressure, and Temperature on the Diffusion Coefficient and Correlation Length of SDS Micelles

The effects of sodium dodecyl sulfate (SDS) concentration (≤ 10 mass %), temperature (35 and 50 °C), and pressure (0.1 to 100 MPa) on the cooperative diffusion coefficient and static correlation length of micelles in solutions in 1 M NaCl were studied using static and dynamic light scattering. These data are interpreted in terms of models of dilute and semidilute solutions of rod-like polymers. The results indicate that the effects of pressure are most significant near the crossover concentration between dilute and semidilute solution behavior. This concentration is a function of temperature and pressure because both of these thermodynamic parameters affect the mean micellar size.

Solvent effects on aggregation behavior of polyvinyl alcohol solutions

The present study elucidates the effects of solvent quality and polymer concentration on the aggregation behavior of polyvinyl alcohol (PVA) solutions from the dilute solution to semi-dilute solution regions. Combination of the results in static and dynamic light scattering indicates that in dilute solution the thermodynamic driving forces primarily dominate the dynamic behavior of PVA/N-methylpyrrolidone (PVA/NMP) solution. In contrast with PVA/water solution, the hydrodynamic interaction would dominate the dynamic behavior of the solution. The concentration dependence on the dynamic behavior of semi-dilute solution has also been studied through DLS measurement. For PVA/water solutions, the hydrodynamic correlation length of fast mode has a concentration dependence given by ξD=[η]C−0.42, and the value of exponent is close to the predicted value from scaling theory in the marginal solvent. On the other hand, for PVA/NMP solutions the value of exponent is close to the predicted value from the scaling theory in good solvent limit: −0.75. However, contrary to the expectation, the gelation behavior could not occur in PVA/water solutions at the same condition of gelation in PVA/NMP solution even though the affinity of water to PVA is much lower than that of NMP. In this work, we considered that the PVA/NMP solution might possess a character that could form a homogeneous network structure. The intermolecular associations must play a dominant role as soon as the chains start to overlap in PVA/NMP solution. On the other hand, combining the DLS result with our previous work, the gelation of PVA/NMP solutions is considered due to complex formation in the transient network junctions, i.e. the formation of molecular complex is crucial to the physical gelation in a good solvent system.

Phase Behavior and Rheological Properties of Aqueous Solutions Containing Mixtures of Associating Polymers

The phase behavior and the rheological properties of aqueous solutions containing mixtures of multiblock hydrophobically modified polyacrylamides (HMPAM) have been investigated. Mixtures of a HMPAM with a homopolyacrylamide (PAM) phase separate above a given overall polymer concentration and a given PAM content. These results are in qualitative agreement with the predictions of a model based on the entropy changes due to the associations between the hydrophobic units [Annable, T.; Ettelaie, R. Macromolecules 1994, 27, 5616]. The viscoelastic behavior of semidilute solutions of various series of copolymer mixtures with variable molecular weights (Mw ≈ 105 to 2 × 106), hydrophobe contents ([H] = 0.5−2 mol %), and hydrophobic block lengths (NH ≈ 2−7 units per block) has been studied using steady-flow and oscillatory experiments. The linear viscoelasticity can be described by a slow relaxation process and other faster complex relaxation processes. When both HMPAM are mutually entangled, the slow relaxation is in agreement with the expectation from a hindered reptation model with in particular a plateau modulus that only depends on polymer concentration. When the two HMPAM are unentangled, the behavior is more complex, the properties being strongly dependent on the hydrophobe characteristics of the two copolymers. In particular, when there is a strong mismatch between the hydrophobic parameters, the viscosity of the system is depressed likely due to a local segregation between the two copolymers.

Effect of Surfactant on the Viscoelastic Behavior of Semidilute Solutions of Multisticker Associating Polyacrylamides

The interactions between well-defined hydrophobically modified polyacrylamides (HMPAM) and the anionic surfactant SDS (sodium dodecyl sulfate) or the cationic surfactant DTAB (dodecyltrimethylammonium bromide) were studied in aqueous solution using steady-flow and oscillatory rheological experiments. The structure of the HMPAM used consists of randomly distributed blocks of hydrophobic monomers (N,N-dihexylacrylamide) in the polyacrylamide backbone. A thorough investigation of the rheological behavior of HMPAM/surfactant mixtures as a function of polymer concentration and of different molecular parameters (molecular weight, hydrophobe content, and hydrophobic block length) provides some novel insight into the surfactant binding properties of multisticker chains. The experiments were performed on series of HMPAM located both in unentangled and entangled semidilute regimes. In both regimes, the rheological behavior strongly depends on the level of surfactant addition, with first an increase and then a decrease in the values of the zero-shear viscosity η0 and of the terminal relaxation time TR without significant change in the plateau modulus G0. The latter observation that differs from most of the other reported conclusions suggests that the viscosity enhancement is not due to the formation of additional mixed plurifunctional aggregates, but to an increase in the lifetime of the preexisting cross-links resulting from surfactant binding. At high surfactant concentrations (≳0.05 M), the solubilization of the individual hydrophobic blocks by the surfactant micelles leads to a decrease of G0, η0, and TR and the HMPAM lose their associative properties. The results also suggest that the maximum of viscosity corresponds to an optimum surfactant binding which is about the same, whatever the concentration of hydrophobic units in the HMPAM solution. SDS has a much larger effect on the η0 variation than DTAB, likely due to a different lifetime of the mixed aggregates.

Comparison of the behaviour of polymers in supercritical fluids and organic solvents via small-angle neutron scattering

Small-angle neutron scattering has been used to study the effect of temperature and pressure on the phase behaviour of semidilute solutions of polymers dissolved in organic and supercritical solvents. Above the theta temperature (TΘ), these systems exhibit a "good solvent" domain, where the molecules expand beyond the unperturbed dimensions in both organic solvents and in CO2. However, this transition can be made to occur at a critical "theta pressure" (PΘ) in CO2 and this represents a new concept in the physics of polymer-solvent systems. For T < TΘ, and P < PΘ, the system enters the "poor solvent" domain, where diverging concentration fluctuations prevent the chains from collapsing and allow them to maintain their unperturbed dimensions.

Viscoelastic Behavior of Semidilute Solutions of Multisticker Polymer Chains

Multisticker polymer chains consisting of water-soluble polyacrylamides hydrophobically modified with low amounts of N,N-dihexylacrylamide have been prepared by a free radical micellar polymerization technique. This process gives multiblock copolymers in which the number and length of the hydrophobic blocks can be tuned by varying the surfactant over hydrophobe molar ratio. The viscoelastic behavior of semidilute solutions of various series of copolymers with variable molecular weights (Mw ≈ 4.2 × 104−2.7 × 106), hydrophobe contents ([H] = 0.5−2 mol %), and hydrophobic block lengths (NH = 1−7 units per block) has been investigated as a function of polymer concentration, C, using steady-flow and oscillatory experiments. In the semidilute range, two different regimes can be clearly distinguished in the zero-shear viscosity η0 = f(C) curves: a first unentangled regime where the viscosity increase rate strongly depends on NH and [H]; a second entangled regime where the viscosity follows a scaling behavior of the polymer concentration with an exponent close to 4, whatever [H] or NH. The linear viscoelasticity can be described by (i) a slow relaxation process with a plateau modulus that only depends on polymer concentration and (ii) other faster complex relaxation processes. In the latter regime, the results can be quite well accounted for by a hindered reptation model.

The effect of amylose content from differing botanical sources on the nonlinear viscoelastic properties of semidilute solutions of maize starches* This article is a US Government work and, as such, is in the public domain in the United States of America. *Names are necessary to report factually on available data; however, the USDA neither guarantees nor warrants the standard of

The effect of the addition of potato or maize on the shear-thickening behavior of semidilute solutions of maize was examined. The experiments were conducted at 25°C using 90/10 weight–weight dimethyl sulfoxide (DMSO)–water as the solvent. The addition of amylose to maize amylopectin reduced and eventually eliminated the observed shear-thickening behavior of maize amylopectin. When potato amylose was combined with maize amylopectin, the shear-thickening phenomenon was observed up to a total amylose content of 10% by weight. For maize amylose, the shear-thickening behavior was eliminated at an amylose content of 5%. Maize amylose is thus more effective in inhibiting the formation of the structure formed after the shear-thickening region than potato amylose. This result indicates that the amylose obtained from potatoes interacts differently, or entangles differently, with maize amylopectin than does the amylose obtained from maize. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 2429–2436, 1999

Attractive interactions and phase transitions in solutions of similarly charged rod-like polyelectrolytes

We have calculated the effective interaction and thermodynamic behavior of semidilute solutions of rod-like polyelectrolytes. The model is based on a bare potential energy constructed from the Debye–Hückel potential but extended to include the anisotropic contributions arising from the rod-like conformation. We have calculated the bare and effective potential energy between two Kuhn segments in different polyelectrolyte rods, the isotropic-to-nematic transition, the orientational order parameter of the nematic phase and the phase diagram of the system. Moreover, the effects of molecular weight, monomer, and salt concentration on the different quantities are discussed.

The effect of amylose content from differing botanical sources on the nonlinear viscoelastic properties of semidilute solutions of maize starches*

The effect of the addition of potato or maize on the shear-thickening behavior of semidilute solutions of maize was examined. The experiments were con- ducted at 25°C using 90/10 weight-weight dimethyl sulfoxide (DMSO)-water as the solvent. The addition of amylose to maize amylopectin reduced and eventually elimi- nated the observed shear-thickening behavior of maize amylopectin. When potato amylose was combined with maize amylopectin, the shear-thickening phenomenon was observed up to a total amylose content of 10% by weight. For maize amylose, the shear-thickening behavior was eliminated at an amylose content of 5%. Maize amylose is thus more effective in inhibiting the formation of the structure formed after the shear-thickening region than potato amylose. This result indicates that the amylose obtained from potatoes interacts differently, or entangles differently, with maize amy- lopectin than does the amylose obtained from maize. © 1999 John Wiley & Sons, Inc.* J Appl Polym Sci 73: 2429 -2436, 1999

Water-soluble polymers. 71. pH responsive behavior of terpolymers of sodium acrylate, acrylamide, and the zwitterionic monomer 4-(2-acrylamido-2-methylpropanedimethylammonio)butanoate

Terpolymers of sodium acrylate (NaA), acrylamide (AM), and the zwitterionic monomer 4-(2-acrylamido-2-methylpropanedimethylammonio) butanoate (AMPDAB) were prepared by the free radical polymerization in 0.5M NaBr aqueous solution using potassium persulfate as the initiator. The feed ratio of AMPDAB : NaA : AM was varied from 5 : 5 : 90 to 40 : 40 : 20 mol %, with the total monomer concentration held constant at 0.45M. Terpolymer compositions were determined by 13C NMR. Molecular weights varied from 3.0 × 105 to 9.7 × 106 g/mol. All terpolymers were soluble in deionized water and salt solutions at all pH values. The dilute and semidilute solution behavior of the terpolymers was studied as a function of composition, pH, and added electrolytes. Polyelectrolyte behavior was observed for all terpolymers at pH 8.5, as evidenced by high viscosity values at low polymer concentrations and viscosity decrease in the presence of added electrolytes. The reduced viscosity as a function of decreasing pH exhibits a minimum as the terpolymer undergoes a polyanion/polyzwitterion/polycation transition. Comparison of the solution behavior of the terpolymers to terpolymers of 3-(2-acrylamido-2-methylpropane dimethylammonio)-1-propane sulfonate (AMPDAPS), AM, and NaA (AADAPS series) as well as copolymers of AMPDAB and AM (AMPDAB series) have been made. © 1997 John Wiley & Sons, Inc.

Water‐soluble polymers. 71. pH responsive behavior of terpolymers of sodium acrylate, acrylamide, and the zwitterionic monomer 4‐(2‐acrylamido‐2‐methylpropanedimethylammonio)butanoate

Terpolymers of sodium acrylate (NaA), acrylamide (AM), and the zwitterionic monomer 4-(2-acrylamido-2-methylpropanedimethylammonio) butanoate (AMPDAB) were prepared by the free radical polymerization in 0.5M NaBr aqueous solution using potassium persulfate as the initiator. The feed ratio of AMPDAB : NaA : AM was varied from 5 : 5 : 90 to 40 : 40 : 20 mol %, with the total monomer concentration held constant at 0.45M. Terpolymer compositions were determined by 13C NMR. Molecular weights varied from 3.0 × 105 to 9.7 × 106 g/mol. All terpolymers were soluble in deionized water and salt solutions at all pH values. The dilute and semidilute solution behavior of the terpolymers was studied as a function of composition, pH, and added electrolytes. Polyelectrolyte behavior was observed for all terpolymers at pH 8.5, as evidenced by high viscosity values at low polymer concentrations and viscosity decrease in the presence of added electrolytes. The reduced viscosity as a function of decreasing pH exhibits a minimum as the terpolymer undergoes a polyanion/polyzwitterion/polycation transition. Comparison of the solution behavior of the terpolymers to terpolymers of 3-(2-acrylamido-2-methylpropane dimethylammonio)-1-propane sulfonate (AMPDAPS), AM, and NaA (AADAPS series) as well as copolymers of AMPDAB and AM (AMPDAB series) have been made. © 1997 John Wiley & Sons, Inc.