Theoretical and experimental investigations of the flocculation of charged particles in aqueous solutions by polyelectrolytes of opposite charge

An electrostatic mechanism for the flocculation of charged particles by polyelectrolytes of opposite charge is proposed. The difference between this and previous electrostatic coagulation mechanisms is the formation of charged polyion patches on the oppositely charged surfaces. The size of a patch is primarily a function of polymer molecular weight and the total patch area is a function of the amount of polymer adsorbed. The theoretical predictions of the model agree with the experimental dependence of the polymer dose required for flocculation on polymer molecular weight and solution ionic strength.

A theoretical analysis based on the Derjaguin-Landau, Verwey- Overbeek electrical double layer theory and statistical mechanical treatments of adsorbed polymer configurations indicates that flocculation of charged particles in aqueous solutions by polyelectrolytes of opposite charge does not occur by the commonly accepted polymerbridge mechanism.

A series of 1, 2-dimethyl-5 -vinylpyridinium bromide polymers with a molecular weight range of 6x10^3 to 5x10^6 was synthesized and used to flocculate dilute polystyrene latex and silica suspensions in solutions of various ionic strengths. It was found that with high molecular weight polymers and/or high ionic strengths the polymer dose required for flocculation is independent of molecular weight. With low molecular weights and/or low ionic strengths, the flocculation dose decreases with increasing molecular weight.

Three essays on economics and information shocks

A person living in an industrialized society has almost no choice but to receive information daily with negative implications for himself or others. His attention will often be drawn to the ups and downs of economic indicators or the alleged misdeeds of leaders and organizations. Reacting to new information is central to economics, but economics typically ignores the affective aspect of the response, for example, of stress or anger. These essays present the results of considering how the affective aspect of the response can influence economic outcomes.

The first chapter presents an experiment in which individuals were presented with information about various non-profit organizations and allowed to take actions that rewarded or punished those organizations. When social interaction was introduced into this environment an asymmetry between rewarding and punishing appeared. The net effects of punishment became greater and more variable, whereas the effects of reward were unchanged. The individuals were more strongly influenced by negative social information and used that information to target unpopular organizations. These behaviors contributed to an increase in inequality among the outcomes of the organizations.

The second and third chapters present empirical studies of reactions to negative information about local economic conditions. Economic factors are among the most prevalent stressors, and stress is known to have numerous negative effects on health. These chapters document localized, transient effects of the announcement of information about large-scale job losses. News of mass layoffs and shut downs of large military bases are found to decrease birth weights and gestational ages among babies born in the affected regions. The effect magnitudes are close to those estimated in similar studies of disasters.