The design and synthesis of new linear-dendritic diblock copolymers with a linear PEO block and a dendrimeric PAMAM block are described. Two series with PEO molecular weights of 2000 and 5000 were synthesized. DSC results on the effect of diblock composition on the microphase segregation behavior of the diblocks are reported. Glass transition temperatures of the diblocks depend on the end group functionality of the dendrimer. The aqueous solution behavior of the hybrid copolymers at 30°C studied using intrinsic viscosity and GPC techniques is influenced by the length of the PEO block and the end group functionality of the dendrimer. The intrinsic viscosity trends exhibited by the diblocks with the shorter PEO chain length did not deviate greatly from that of linear polymers, and those exhibited by the diblocks with the longer PEO chain length indicate the formation of unimolecular micelles. IntroductionDendrimers have been of particular interest to the polymer science community in the past 20 years. These materials present a new, well-defined architecture and a large degree of functionality in a single macromolecule. A wide variety of dendrimers with different chemistries have been synthesized; 1-3 however, commercial applications of these materials have only recently begun to be realized. Many of the potential applications under investigation make use of two important properties of dendrimers, both of which are a direct consequence of their architecture: namely, the large number of end groups and the nanoporous nature of the interior at higher generations. 4 The interior regions may be used to sequester ions, to host molecules, or to act as catalytic sites for reaction of small molecules. When appropriately configured in consistent thin films, dendrimeric materials could prove to be useful as membranes for separations applications. Dendrimericlinear hybrid diblock copolymers present material systems which are suitable for the formation of selfassembled films in the bulk state, on surfaces, and at the air-water interface. Dendrimeric diblock copolymers with one linear block and one dendritic block have been synthesized by a number of different groups. Examples include PEO-poly(L-lysine) dendrimer, 5 PSpoly(propyleneimine) dendrimer, 6 PEO/PS-poly(benzyl ether) dendrimer, 7,8 and poly(oxazoline)-PAMAM dendrimer. 9 In some cases the aqueous solubility of the two blocks was dissimilar and the resulting diblocks have been shown to be amphiphilic. 5,6,9 We have chosen to investigate an amphiphilic dendrimeric diblock copolymer with a hydrophobic dendron unit and a water soluble linear tail.Thus far, limited information is available on the dilute solution behavior of dendrimeric diblocks. Deviations from traditional linear behavior of polymers has been observed for dendrimeric homopolymers and block copolymers by other researchers. 1,10 The exponential increase of molecular weight in dendrimeric homopolymers, when compared to a linear incremental increase of molecular diameter with generation, results in large variatio...
Contaminants from the soil surrounding drinking water distribution systems are thought to not enter the drinking water when sufficient internal pressure is maintained. Pressure transients may cause short intervals of negative pressure, and the soil near drinking water pipes often contains fecal material due to the proximity of sewage lines, so that a pressure event may cause intrusion of pathogens. This paper presents a risk model for predicting intrusion and dilution of viruses and their transport to consumers. Random entry and dilution of virus was simulated by embedding the hydraulic model into a Monte Carlo simulation. Special attention was given to adjusting for the coincidence of virus presence and use of tap water, as independently occurring short-term events within the longer interval that the virus is predicted to travel in any branch of the distribution system. The probability that a consumer drinks water contaminated with virus is small, but when this happens the virus concentration tends to be high and the risk of infection may be considerable. The spatial distribution of infection risk is highly heterogeneous. The presence of a chlorine residual reduces the infection risk.
In this article, nitrification potential curves are introduced as a possible operational strategy to prevent nitrification in chloraminated distribution systems. Nitrification potential curves are constructed based on the parameters that define growth and inactivation kinetics of ammoniaoxidizing bacteria in environments that contain chloramine and ammonia. To demonstrate the applicability of nitrification potential curves, long‐term, pilot‐scale studies that covered a range of chlorine‐to‐ammonia application ratios and chloramine residual concentrations that are typical of full‐scale chloraminated systems were conducted. The nitrification potential curve approach was effective in explaining why some of the pilot‐scale runs experienced nitrification while others did not based only on experimental measurements of total chlorine residual and free ammonia concentration. Because of the simplicity of the required measurements, nitrification potential curves can help define strategies to monitor and operate chloraminated distribution systems to prevent or minimize nitrification episodes.
Nitrification potential curves were recently introduced as a practical way of determining whether water quality conditions are conducive to the establishment of nitrification in chloraminated drinking water distribution systems. The innovative concept links the total chlorine and free ammonia concentrations found in chloraminated distribution systems to the growth and inactivation kinetics of the ammonia‐oxidizing bacteria responsible for nitrification. In this study, nitrification potential curves were developed for three full‐scale, chloraminated distribution systems. The curves were then used to evaluate the nitrification control strategies in effect at each system and show how operational changes such as reducing water age or increasing pH could affect nitrification potential.
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