Relation Between the Adsorption Behavior and Bulk Complexation in Oppositely Charged Polyelectrolyte-Surfactant Systems: Effect of Polyelectrolyte Concentration, Molecular Weight, Charge Localization and Backbone Rigidity/Hydrophobicity

Due to a wide range of applications, much emphasis has been placed on understanding the physicochemical behavior of polyelectrolyte/surfactant complexes, both at air-water interface and in the bulk. However, the correlation between the adsorption behavior and complexation in the bulk is less explored. In this research, this correlation is investigated and its dependence on polyelectrolyte concentration, molecular weight, charge localization and backbone rigidity and hydrophobicity is studied. The polyelectrolyte concentration is normalized with respect to it critical overlap concentration in order to compare the polymer in same concentration regime. Different polyelectrolyte systems were used to analyze the polyelectrolyte structural effect: • The molecular weight effect was studied between low molecular weight cationic hydroxyethylcellulose (JR400)/SDS and high molecular weight hydroxyethylcellulose (JR30M)/SDS system • The charge localization effect was studied between the linearly charged poly(methacrylamidopropyltrimethylammonium chloride) (MAPTAC) and locally charged poly(methacrylamide propyl (methoxy-carbonyl-methyl) dimethyl ammonium chloride) (AMT) • The effect of rigidity and hydrophilicity/hydrophobicity of the polyelectrolyte backbone was studied by comparing and contrasting flexible/hydrophobic MAPTAC and semi rigid/hydrophilic JR30M All of these polyelectrolytes were interacted with sodium dodecyl sulfate (SDS) surfactant. The concentration of these polyelectrolytes was varied over a sufficient range to analyze the polyelectrolyte-surfactant interaction in different concentration regimes. The adsorption behavior was analyzed by surface tension measurements, while, the complexation in the bulk was examined by rheological measurements. Fluorescence measurement techniques were additionally used to analyze the effect of charge localization on the structure of the polyelectrolyte/surfactant complexes. In the molecular weight study, as a function of surfactant concentration, the surface tension at the interface varied in the one phase region above the surfactant’s critical aggregation concentration (CAC). The surface tension increased with increase in the SDS concentration and this became more pronounced with increase in polyelectrolyte molecular weight. This is counterintuitive. This increase can be explained by intermolecular association taking place in the bulk between the polymer and surfactant through hydrophobic association of the bound surfactants. This bulk intermolecular association was favored by the interfacial complex over the surface adsorption, thereby increasing desorption of the polyelectrolyte-surfactant complex from the surface. Increase in molecular weight increased this intermolecular association and the surface tension increased with increase in the molecular weight. Charge localization on the polyelectrolyte chain increased the surface tension in the two phase region. From fluorescence measurements it was observed that the charge localization enhances SDS aggregation. The charge localization of AMT causes an observed increase in the surface tension above the surfactant CAC and this can be interpreted as desorption of the surface complex as the bulk complex phase-separates. On the other hand, in the linearly charged MAPTAC/SDS complex the surface tension stays constant as SDS concentration is increased, signifying that the surface adsorbed complex cannot be desorbed by the formation of the MAPTAC/SDS complex in the bulk. Unlike the polyelectrolytes which have flexible hydrophobic backbones, the stiff, hydrophilic polymers were observed to increase the surface tension even while they remained in the one phase region. The association between the rigid and hydrophilic JR30M polymer and surfactant is higher than MAPTAC. For JR30M, pronounced desorption of the surface active species is observed in the one phase region above the CAC. On the other hand, in the case of flexible and hydrophobic MAPTAC, the association with SDS at the surfactant CAC causes the viscosity of the MAPTAC/SDS system reduces by addition of SDS. We deduce from this that the MAPTAC collapses with addition on surfactant in the one phase region. Thus, the surface tension stays Charge localization on the polyelectrolyte chain increased the surface tension in the two phase region. From fluorescence measurements it was observed that the charge localization enhances SDS aggregation. The charge localization of AMT causes an observed increase in the surface tension above the surfactant CAC and this can be interpreted as desorption of the surface complex as the bulk complex phase-separates. On the other hand, in the linearly charged MAPTAC/SDS complex the surface tension stays constant as SDS concentration is increased, signifying that the surface adsorbed complex cannot be desorbed by the formation of the MAPTAC/SDS complex in the bulk. Unlike the polyelectrolytes which have flexible hydrophobic backbones, the stiff, hydrophilic polymers were observed to increase the surface tension even while they remained in the one phase region. The association between the rigid and hydrophilic JR30M polymer and surfactant is higher than MAPTAC. For JR30M, pronounced desorption of the surface active species is observed in the one phase region above the CAC. On the other hand, in the case of flexible and hydrophobic MAPTAC, the association with SDS at the surfactant CAC causes the viscosity of the MAPTAC/SDS system reduces by addition of SDS. We deduce from this that the MAPTAC collapses with addition on surfactant in the one phase region. Thus, the surface tension stay

Elucidating the mechanism of polymer/surfactant coacervate delivery/conditioning systems

For almost half a century, stimuli-responsive complexes formed by dilution of anionic surfactant/cationic polymer compositions have dominated conditioning shampoos and dilution-deposition delivery systems. There are a plethora of cationic polymers available but only a few are present in successful commercial products. Moreover, conditioning and delivery attributes are strongly dependent on compositional details and use conditions. In order to explore the reasons for the dominance of few polymers and the variability of performance with composition, we studied the effects on complex coacervate formation of polymer charge density and distribution, polymer backbone rigidity and hydrophilicity, and concentration relative to polymer overlap and entanglement concentrations and surfactant CMC by surface tensiometry, shear rheometry, and fluorescence spectroscopy. Our results show that, above the critical entanglement concentration, complex coacervates separate as shear-thinning gel networks that desorb anionic surfactant from the interface. Such networks are favored by polymers having relatively rigid hydrophilic backbones. Alternatively, systems below the critical overlap concentration separate as unconnected phase droplets which enhance interfacial adsorption. The importance of critical polymer concentrations on these delivery systems helps to provide a mechanistic scientific basis for better tailoring of compositions to confer optimal delivery of attributes

Mathematical Modelling and Cluster Analysis in Healthcare Analytics - The Case of Length of Stay Management

Length of Stay (LOS) is an important metric of care quality and efficiency in hospitals that has been studied for decades. Longer stays lead to increased costs and higher burdens on patients, caregivers, clinicians and facilities. Understanding characteristics of LOS outliers is important for developing actionable steps to address LOS reduction. Our study examines clustering of inpatients using key clinical and demographic attributes to identify LOS outliers and investigates the opportunity to reduce their LOS by comparing order sequences with similar non-outliers in the same cluster. Learning from retrospective data, we develop a mathematical model and a two-stage heuristic algorithm. Results indicate that switching orders in homogeneous inpatient sub-populations within the limits of clinical guidelines may be a promising decision support strategy for LOS management. These novel data-driven insights can be offered as suggestions for clinicians to apply new evidence-based, clinical guideline-compliant opportunities for LOS reduction through healthcare analytics

Response of Pacific-sector Antarctic ice shelves to the El Niño/Southern Oscillation.

Satellite observations over the past two decades have revealed increasing loss of grounded ice in West Antarctica, associated with floating ice shelves that have been thinning. Thinning reduces an ice-shelf's ability to restrain grounded-ice discharge, yet our understanding of the climate processes that drive mass changes is limited. Here, we use ice-shelf height data from four satellite altimeter missions (1994-2017) to show a direct link between ice-shelf-height variability in the Antarctic Pacific sector and changes in regional atmospheric circulation driven by the El Niño-Southern Oscillation. This link is strongest from Dotson to Ross ice shelves and weaker elsewhere. During intense El Niño years, height increase by accumulation exceeds the height decrease by basal melting, but net ice-shelf mass declines as basal ice loss exceeds lower-density snow gain. Our results demonstrate a substantial response of Amundsen Sea ice shelves to global and regional climate variability, with rates of change in height and mass on interannual timescales that can be comparable to the longer-term trend, and with mass changes from surface accumulation offsetting a significant fraction of the changes in basal melting. This implies that ice-shelf height and mass variability will increase as interannual atmospheric variability increases in a warming climate

Flexible hospital-wide elective patient scheduling

In this paper, we build on and extend Gartner and Kolisch (2014)’s hospital-wide patient scheduling problem. Their contribution margin maximizing model decides on the patients' discharge date and therefore the length of stay. Decisions such as the allocation of scarce hospital resources along the clinical pathways are taken. Our extensions which are modeled as a mathematical program include admission decisions and flexible patient-to-specialty assignments to account for multi-morbid patients. Another flexibility extension is that one out of multiple surgical teams can be assigned to each patient. Furthermore, we consider overtime availability of human resources such as residents and nurses. Finally, we include these extensions in the rolling-horizon approach and account for lognormal distributed recovery times and remaining resource capacity for elective patients. Our computational study on real-world instances reveals that, if overtime flexibility is allowed, up to 5% increase in contribution margin can be achieved by reducing length of stay by up to 30%. At the same time, allowing for overtime can reduce waiting times by up to 33%. Our model can be applied in and generalized towards other patient scheduling problems, for example in cancer care where patients may follow defined cancer pathways

Physician’s Usage Of Mobile Clinical Applications In A Community Hospital: A Longitudinal Analysis Of Adoption Behavior

It is widely believed that mobile clinical information systems can facilitate patient care, increase treatment capacity, reduce healthcare costs, and improve efficiency. Yet, there is limited research to substantiate these claims in healthcare delivery settings, partly due to lack of widespread adoption and use. This study summarizes our results on the adoption and usage trends in a community hospital which deployed several mobile clinical applications for daily patient care. We analyze twenty-two months of usage data to understand trends in physicians’ adoption and use of specific mobile applications. Applying a novel, semi-parametric, group-based, statistical methodology, we obtain developmental trajectories depicting how usage evolves from initial ‘trial’ adoption to long-term institutionalization. We examine this longitudinal developmental pattern to understand how users can be clustered and profiled, and provide insights indicating that the potential impact of social influence needs to be further explored to develop new approaches to facilitate adoption

Cognitive workload reduction in hospital information systems

Order sets are a critical component in hospital information systems that are expected to substantially reduce physicians’ physical and cognitive workload and improve patient safety. Order sets represent time intervalclustered order items, such as medications prescribed at hospital admission, that are administered to patients during their hospital stay. In this paper, we develop a mathematical programming model and an exact and a heuristic solution procedure with the objective of minimizing physicians’ cognitive workload associated with prescribing order sets. Furthermore, we provide structural insights into the problem which lead us to a valid lower bound on the order set size. In a case study using order data on Asthma patients with moderate complexity from a major pediatric hospital, we compare the hospital’s current solution with the exact and heuristic solutions on a variety of performance metrics. Our computational results confirm our lower bound and reveal that using a time interval decomposition approach substantially reduces computation times for the mathematical program, as does a K−means clustering based decomposition approach which, however, does not guarantee optimality because it violates the lower bound. The results of comparing the mathematical program with the current order set configuration in the hospital indicates that cognitive workload can be reduced by about 20.2% by allowing 1 to 5 order sets, respectively. The comparison of the K−means based decomposition with the hospital’s current configuration reveals a cognitive workload reduction of about 19.5%, also by allowing 1 to 5 order sets, respectively. We finally provide a decision support system to help practitioners analyse the current order set configuration, the results of the mathematical program and the heuristic approach