Aqueous solution properties of polyampholytes: Effect of the net charge distribution

Viscometric and light scattering studies have been performed on aqueous solutions of polyampholyte terpolymers based on sodium-2-acrylamido-2-methylpropanesulfonate (Na-AMPS), 2-(methacryloyloxy)-ethyltrimethylammonium chloride (MADQUAT), and acrylamide (AM), prepared by an inverse microemulsion polymerization technique. The distribution of net charges among the chains was varied by adjusting the initial monomer composition and the degree of conversion. The effect of this distribution on the solubility of the samples and on the chain conformation was studied. It was found that samples with a narrow distribution of net charges were soluble in pure water even if the average net charge is small. Addition of salt induces a transition from an extended conformation to a more compact one, in qualitative agreement with theoretical predictions. A practically alternated NaAMPS-MADQUAT copolymer prepared by polymerization in homogeneous solution and with a small average net charge shows a behavior quite similar to that of the terpolymers. © 1996 John Wiley & Sons, Inc.     

Dynamic light scattering by weakly ionized gels: Effects of inhomogeneities and non-ergodicity

Small angle neutron scattering and light scattering experiments have been performed on partially neutralized poly(acrylic acid) solutions and gels. The structure factor obtained from small angle scattering and static light scattering reveals the absence of significant contribution from large scale inhomogeneities in the gels as soon as the ionization degree exceeds 9·10⁻³. The comparison of the time and ensemble averages of the autocorrelation function of scattered light intensity shows that the gels behave with respect to that experiment as ergodic media.     

Mechanism and kinetics of the radical polymerization of acrylamide in inverse micelles

A kinetic study of the photoinitiated polymerization of acrylamide in oil/AOT/H₂O reverse micelles has been investigated. Determinations of the dependence of the rates of polymerization and the molecular weights of the polymers on initiator and monomer concentrations, as well as the relative light intensity and the identity of the oil employed were performed. Rates of polymerization were measured by dilatometry, and polymer molecular weights were determined by viscometry. The polymerization was shown to be first order in monomer concentration, and the order of the termination step of the polymerization depended strongly upon the oil employed. When the oil was benzene, termination occurred by a biradical process. When benzene was replaced by toluene, a monoradical termination was shown to occur, suggesting that a degradative chain transfer to toluene is occurring in this case. The similarities and differences of polymerization in conventional emulsions and in micelles are discussed on the basis of these results.     

Effect of surface modification of colloidal silica nanoparticles on the rigid amorphous fraction and mechanical properties of amorphous polyurethane–urea–silica nanocomposites

Colloidal silica nanoparticles (NPs) modified with eight different silane coupling agents were incorporated into an amorphous poly(tetramethylene oxide)‐based polyurethane–urea copolymer matrix at a concentration of 10 wt % (4.4 vol %) in order to investigate the effect of their surface chemistry on the structure–property behavior of the resulting nanocomposites. The rigid amorphous fraction (RAF) of the nanocomposite matrix as determined by differential scanning calorimetry and dynamic mechanical analysis was confirmed to vary significantly with the surface chemistry of the NPs and to be strongly correlated with the bulk mechanical properties in simple tension. Hence, nanocomposites with an RAF of about 30 wt % showed a 120% increase in Young's modulus, a 25% increase in tensile strength, a 15% decrease in elongation at break with respect to the neat matrix, which had no detectable RAF, whereas nanocomposites with an RAF of less than 5% showed a 60% increase in Young's modulus, a 10% increase in tensile strength and a 5% decrease in the elongation at break. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, 2543–2556     

Solubilization of Immiscible Liquids Into Mesophases Formed from Amphiphilic Block Copolymers

Optical microscopy and X-ray diffraction studies reveal the presence of highly swollen mesophases in four-component systems containing amphiphilic triblock copolymers. According to the composition of the system, lamellar phases or hexagonal structures are produced. The polymeric mesophases exhibit textures very similar to those encountered in low molecular weight liquid crystalline phases.     

STRUCTURE AMD VISCDMETRIC BEHAVIOR OF GEL PHASES IN QUATERNARY SYSTEMS CONTAINING ANIONIC SURFACTANTS

The homogeneous viscous phases which form by mixing sodium dodecylsulphate, butanol, toluene and water in different proportions have been characterized through viscometric measurements and optical techniques. Abrupt increases in viscosity observed in some regions of the phase diagram have been correlated to the formation of birefringent phases which exhibit non-newtonian behavior. These highly swollen mesophases are shown to be of the lamellar type by the characteristic optical textures displayed under polarizing microscope. An addition of NaCl salt to the systems, upon decreasing the solubility of the surfactant in water, tends to destroy the organized structure and give rise to a diphasic system (Winsor II). Similarly, a rise in temperature increases the relative affinity of the tensio-active agent for water, producing a transition from the lamellar phase to an isotropic newtonian phase through a two-phase coexistence region.     

The true potential energy curves for different states of SiO and SiS molecules

The true potential energy curves forX ¹ Σ ⁺, a³ π _r,A ¹ π,e ³ Σ ⁻,E ¹ Σ ⁺,c ³ π _i states of astrophysically important molecule SiO, whose spectra were observed in the sunspots, have been constructed using the method of Lakshman and Rao. Dissociation energy and ionization potential have been estimated as 65,350 cm⁻¹ and 92,854 cm⁻¹ respectively and found to be in good agreement with the values cited in literature. The true potential energy curves forX ¹ Σ ⁺,D ¹ π andE ¹ Σ ⁺ states of SiS molecule have been constructed by the same method and its dissociation energy in the ground state has been estimated using Hulburt-Hirschfelder potential function as 54,765 cm⁻¹ in good agreement with 53,250.9 cm⁻¹ given by Herzberg.     

Structural and rheological properties of hydrophobically modified alkali‐soluble emulsion solutions

Scattering and rheological experiments were carried out on hydrophobically modified alkali‐soluble emulsion solutions at pH ～ 7.3 as a function of the polymer concentration. The light scattering experiments revealed the existence of a liquidlike order for concentrations below approximately 0.1 × 10^?2g cm^?3 corresponding approximately to the close packing of microgels particles. Above this concentration, the zero‐shear viscosity rose sharply, whereas the ordering disappeared progressively. The results are discussed within the framework of gelation models of associating polymers. Diffusing wave spectroscopy experiments provided estimates of the high‐frequency modulus. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 1985–1994, 2002