The influence of the oxyethylene spacer length between terminal hydrophobes of hydrophobically-modified ethoxylated urethanes (HEURs) is examined through the synthesis of two series of welldefined terminally-modified HEUR thickeners. In the first series, octadecyl isocyanate is reacted with poly (oxyethylene) (POE) of varying molecular weight. In the second synthesis, excess isophorone diisocyanate is reacted with POE to prepare an isocyanate functional precursor, followed by reaction of the terminal isocyanate group with nonylphenol. Viscous aqueous solutions are obtained with only partial terminal modification of POE; with full terminal modification swollen gels are realized. At moderate concentrations the phase separation of HEUR thickeners is dependent on the size of the hydrophobe and the number of oxyethylene units between the hydrophobes. In both series of HEURs, the critical aggregation concentration is lowest when 500 oxyethylene units separate the terminal hydrophobes. In the presence of surfactant, both anionic and nonionic, the fully-modified HEURs also exhibit a maximum in viscosity when the spacer is ~500 oxyethylene units. The viscosities realized in both HEUR series are equal or greater (with smaller HEUR oxyethylene spacings) with the nonionic surfactant relative to the anionic surfactant, sodium dodecyl sulfate.
Information and communication technologies (ICTs) are electronic tools used to convey, manipulate and store information. The exponential growth of Internet access and ICTs greatly influenced social, political, and economic processes in the United States, and worldwide. Regardless of the level of practice, ICTs will continue influencing the careers of social workers and the clients they serve. ICTs have received some attention in the social work literature and curriculum, but we argue that this level of attention is not adequate given their ubiquity, growth and influence, specifically as it relates to upholding social work ethics. Significant attention is needed to help ensure social workers are responsive to the technological changes in the health care system, including the health care infrastructure and use of technology among clients. Social workers also need ICT competencies in order to effectively lead different types of social change initiatives or collaborate with professionals of other disciplines who are using ICTs as part of existing strategies. This paper also identifies potential pitfalls and challenges with respect to the adoption of ICTs, with recommendations for advancing their use in practice, education, and research.
The synthesis, characterization, and solution rheology of well-characterized hydrophobically-modified, ethoxylated urethane (HEUR) water-soluble polymers are described for two types of model HEURs: linear polyloxyethylene) of M n = 26 200 with terminal hydrophobes of different sizes, and terminal hydrophobe groups separated by smaller oxyethylene spacing around a larger internal hydrophobe. In the first series, a terminal isocyanate telechelic prepolymer of poly(oxyethy1ene) is prepared and reacted with amine and alcohol containing hydrophobes of variable size. In the second, terminal hydrophobe HEURs varying in geometry around an internal hydrophobe are synthesized by a one-step addition of an ethoxylated nonylphenol surfactant to a diisocyanate or an isocyanato functional biuret or isocyanurate. Low shear rate viscosities and oscillatory responses of HEUR solutions are examined, alone and in the presence of anionic and nonionic surfactants. HEUR solutions exhibit a maximum inviscositywith increasing surfactant concentrations with both anionic and nonionic surfactants. The viscoelasticity of the solution in the area of the viscosity maximum and factors influencing the magnitude of the viscosity increase are addressed. The surfactant concentration necessary to achieve the viscosity maximum is observed to depend on the concentration and architecture of the HEUR as well as the structure of the surfactant. Differences in the phase separation behavior of aqueous solutions also are observed.
The surface tension characteristics of poly(ethy1ene ride) derivatives were examined as a function of concentration, time, temperature, and molecular weight. rne effects of the polymer's adsorption rheology and the degree of alkyl substitution upon the surface tension of ethylene oxide derivatives were also examined. A high (106) molecular weight material exhibits a slightly positive surface activity-temperature coefficient. The adsorption characteristics, as a function of concentration and time, remain approximately constant in the 104 to 106 molecular weight range. Below a molecular weight range of lo4 the surface activities of the aqueous solutions exhibit a marked dependence upon polymer molecular weight; i.e., the surface tension values decrease with decreasing degree of polymerization. In contrast to the high molecular weight material, an ethylene oxide polymer of 400 molecular weight exhibits exothermic adsorption characteristics. The marked surface activity dependence is characterized by a decreasing entropy factor and by an increasingly compact rheological structure. Both factors are independently associated with the polymer's decreasing molecular weight. An examination of alkyl-substituted triethylene glycol derivatives supports the above conclusions and provides insight into the adsorption rheology of poly(ethy1ene oxides) I Contrary to previous investigations, this study indicates that all ethylene oxide adducts from the trimeric to the 2.4 x 106 molecular weight polymer have portions of their structures oriented out of the interfacial region. The surface activity of ethylene oxide copolymers, as a function of concentration, reveals unique polynomial behaviors. These adsorption characteristics are interpreted as the first observed reorientations, by surface tension measurements, of interfacially adsorbed macromolecules. IntroductionI n studies of reactions related to carbohydrates and polysaccharides, Lovell and Hibbert2 studied the surface activity of aqueous poly(ethy1ene glycol) solutions via the capillary-rise method. This extensive investigation neglected the effects of polymer adsorption on the glass-capillary interface and the variation of contact angle with polymer molecular weight. The study observed the surface tension parameter as a function of concentration and molecular weight. Couper and Eley, employing the ring-balance procedure, recorded the aqueous surface tensions of four poly(ethylene glycols), ranging in molecular weight from 1000 to 6000. Both investigations were inconclusive in elucidating the principles governing the behavior of polymeric glyc01s.~ Lovell and Hibbert postulated that poly(ethy1ene oxide) entities with greater than 18 ethoxide units tended to orient out of the interface as in the case of fatty acids. Couper and Eley proposed that the adsorbed ethoxide macromolecules lie approximately flat at the aqueous surface. The data obtained in the present investigation strongly indicate that all poly(ethy1ene oxide) entities, ranging from the trimeric to the polymeric specie...
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