Esam Z. Hamad

Synthesis and aqueous phase behaviour of homo- and copolymers of 1,1-diallyl-4-formylpiperazinium chloride

The quaternary ammonium salt, 1,1-diallyl-4-formylpiperazinium chloride (3) on cyclopolymerization in water solution in the presence of t-butylhydroperoxide gave water soluble polymer (5). The copolymers of (3) with sulfur dioxide have been prepared in DMSO solvent using ammonium persulfate as the initiator. The composition and phase diagram of the aqueous two-phase systems of the homopolymer (5) and copolymer (8) has been studied for the first time for this class of polymers. Synthesis of the polymer (8) paves the way for the preparation of a new class of polymers with a basic trivalent nitrogen as well as a quaternary nitrogen.

Surface and interfacial activities of hydrophobically modified poly(vinyl alcohol) (PVA)

Abstract In the present study, the air-liquid surface and liquid-liquid interfacial activities of hydrophobically modified poly(vinyl alcohol) (PVA) solutions were investigated to determine the effects of NaCl concentration, polymer concentration, time, polymer molecular weight, polymer modification and the average length of the hydrophobic side groups. The hydrophobically modified PVA exhibit high air-liquid surface and liquid-liquid interfacial activities which increase with increasing NaCl concentration, polymer concentration, molecular weight and average length of the hydrophobic side groups. The observed strong dependence of surface and interfacial activities on salt concentration for this non-polyelectrolyte polymer is explained in terms of the reduced polymer solubility or salting out with increasing salinity.

Contact pair correlation functions and equation of state for nonadditive hard‐sphere mixtures

We present some exact results for mixtures of nonadditive hard spheres and use them to derive two models for the contact values of the pair correlation functions and the equation of state. The new models are general in that they are not limited to binary mixtures, equal size components, or a certain range of the nonadditivity parameter. Comparison with the available computer simulation data for equal size components show that the new models predict satisfactory the equation of state data and the contact values. The prediction of the critical point of fluid–fluid phase separation is satisfactory at small and large values of the nonadditivity parameter, and less so at intermediate values.

Consistency test for mixture pair correlation function integrals

A consistency test for integrals of the mixture pair correlation functions is suggested. Testing of the Percus–Yevick expressions for hard sphere mixture reveals that the compressibility pair correlation functions are consistent, but the virial and the Carnahan–Starling expressions are not.

Cyclopolymerization studies of diallyl‐and tetraallylpiperazinium salts

The quaternary ammonium salt 1,1-diallyl-4-formylpiperazinium chloride (7) was synthesized in good yields. The monomer (7) on cyclopolymerization in the presence of ammonium persulfate in water solution at 90°C afforded water-soluble polymer (8) having excellent rheological properties. The synthesis of the polymer (8) paves the way for the preparation of a novel class of polymers : dicationic polyelectrolytes (9) and cationic polymer (10) with a basic nitrogen as well as a quaternary nitrogen. Effects of monomer, initiator, and additives concentration were studied. Cyclopolymerization of (7) with 1,1,4,4-tetraallylpiperazinium dichloride (12) gave ion-exchange resins with excellent swelling coefficients.

Solution behaviour of sodium maleate/1-alkene copolymers

Abstract In this study the rheological behaviour, air—liquid surface and liquid—liquid interfacial activities of solutions of water-soluble associative copolymers of sodium maleate/1-dodecene and sodium maleate/1-hexadecene are investigated with respect to the polymer concentration, temperature, salinity, shear rate and time. The copolymers have been found to exhibit good air—liquid surface and liquid—liquid interfacial activities. The viscosity of the copolymer solutions is characteristically low and invariant with shear rate. Adding salt to the solution results in an increase in the liquid—liquid interfacial activity and viscosity of the polymer solution. The magnitude of the viscosity and the behaviour of the air—liquid surface tension versus concentration indicate that the copolymers form small micelles, each containing a few polymer molecules. The factors that lead to an increase in viscosity also lead to an increase in air—liquid surface and liquid—liquid interfacial activities of these polymer solutions.

Synthesis, characterization, and solution properties of hydrophobically modified poly(vinyl alcohol)

A series of hydrophobically modified water-soluble poly(vinyl alcohol) (PVA) polymers was prepared by grafting urethanized PVA with varying fractions of fatty acid chlorides of various chain lengths. The objective of the synthesis was to prepare polymers that can be applied to enhanced oil recovery. The solution viscosity was investigated as a function of polymer concentration, temperature, shear rate, and salinity. Furthermore, the surface and decane-water interfacial tensions were investigated with respect to polymer and salt concentrations. Micelle formation was probed by measuring pyrene fluorescence as a function of polymer concentration. The solution viscosity was enhanced by the hydrophobic modification, compared with the unmodified PVA as a result of hydrophobic association. The viscosity of a 3% polymer solution decreased with increasing salt concentration from 0.0 to 6.0 wt %, above which some polymer precipitated from the solution. The solution viscosity decreased with both temperature and shear rate. Pyrene fluorescence measurements showed that hydrophobic micelles formed above a polymer concentration of 0.5%. The micelle formation was relatively insensitive to salt concentration. The surface tension decreased sharply with increasing polymer concentration to reach a minimum at a polymer concentration of 0.15% and then increased gradually up to a polymer concentration of 3%. Interfacial tension with n-decane showed a continuous decrease with polymer concentration.

A GENERAL MIXTURE THEORY. II. MIXTURES OF NONSPHERICAL MOLECULES

A recently suggested mixture theory for the prediction of mixture properties is formulated for nonspherical molecules. The theory is capable of handling equations of state that are not conformal (do not obey the corresponding states principle). The exact composition dependence of the density expansion of the mixture equations, plus other features of the original theory, are retained. Two methods for evaluating the cross molecular parameters for nonspherical molecules are suggested. They become identical for spherical molecules, and give similar predictions for mixture properties of nonspherical molecules at high densities. The two methods predict the properties of mixtures of convex bodies and fused hard spheres within simulation uncertainty. Properties of diatomic Lennard-Jones mixtures, and ethane–carbon dioxide are predicted fairly accurately.

Modeling and simulation of equation of state for nonadditive hard disk mixtures

We present exact results for mixtures of nonadditive hard disks and use some of them to derive a consistent model for the equation of state. We also performed molecular dynamics simulation for hard disks over a wide range of size ratios. Comparison of the model to the data shows that the model is accurate for all densities in the case of additive and slightly nonadditive (nonadditivity parameter within ±0.1) mixtures. For large nonadditivity, the model is accurate for low to moderate densities only, and starts to deteriorate at high densities.

Hard-sphere mixture excess free energy at infinite size ratio

This article presents the exact limiting value of the derivative of the excess Helmholtz energy, AE, with respect to molecular size at constant temperature, density and composition for a binary mixture of hard spheres with an infinite size ratio (σ11/σ22→∞); i.e., limσ22→0[(∂AhsE/RT)/∂σ22]T,ρ,x,σ11=(π/2)ρx1x2σ112/(1−(π/6)ρx1σ113). This limiting value is compared with the Mansoori–Carnahan–Starling–Leland (MCSL) and also used to test the limits of some commonly used models in estimating the excess free energy of solvents in mixtures or polymer solutions. The models evaluated include the van Laar, Wilson, Edmond–Ogston, Flory–Huggins, Lacome–Sanchez, Scott–Magat, and Chen et al. It is shown that while the MCSL equation of state produces the same limiting value as the exact value reported here the other mixture models deviate from the exact value. This expression may be utilized to correct the mixture theories at their infinite size ratio limits.