Polyelectrolytes Adsorption: Chemical and Electrostatic Interactions

Mean-field theory is used to model polyelectrolyte adsorption and the possibility of overcompensation of charged surfaces. For charged surfaces that are also chemically attractive, the overcharging is large in high salt conditions, amounting to 20-40% of the bare surface charge. However, full charge inversion is not obtained in thermodynamical equilibrium for physical values of the parameters. The overcharging increases with addition of salt, but does not have a simple scaling form with the bare surface charge. Our results indicate that more evolved explanation is needed in order to understand polyelectrolyte multilayer built-up. For strong polymer-repulsive surfaces, we derive simple scaling laws for the polyelectrolyte adsorption and overcharging. We show that the overcharging scales linearly with the bare surface charge, but its magnitude is very small in comparison to the surface charge. In contrast with the attractive surface, here the overcharging is found to decrease substantially with addition of salt. In the intermediate range of weak repulsive surfaces, the behavior with addition of salt crosses over from increasing overcharging (at low ionic strength) to decreasing one (at high ionic strength). Our results for all types of surfaces are supported by full numerical solutions of the mean-field equations.Comment: 17 pages, 7 figures, final version. to be published in PR

Phase Behavior of Polyelectrolyte-Surfactant Complexes at Planar Surfaces

We investigate theoretically the phase diagram of an insoluble charged surfactant monolayer in contact with a semi-dilute polyelectrolyte solution (of opposite charge). The polyelectrolytes are assumed to have long-range and attractive (electrostatic) interaction with the surfactant molecules. In addition, we introduce a short-range (chemical) interaction which is either attractive or repulsive. The surfactant monolayer can have a lateral phase separation between dilute and condensed phases. Three different regimes of the coupled system are investigated depending on system parameters. A regime where the polyelectrolyte is depleted due to short range repulsion from the surface, and two adsorption regimes, one being dominated by electrostatics, whereas the other by short range chemical attraction (similar to neutral polymers). When the polyelectrolyte is more attracted (or at least less repelled) by the surfactant molecules as compared with the bare water/air interface, it will shift upwards the surfactant critical temperature. For repulsive short-range interactions the effect is opposite. Finally, the addition of salt to the solution is found to increase the critical temperature for attractive surfaces, but does not show any significant effect for repulsive surfaces.Comment: 23 pages, 10 figure

"Captive by the Uncertainty"-Experiences with Anticipatory Guidance for People Living with Dementia and Their Caregivers at a Specialty Dementia Clinic.

BackgroundAfter a diagnosis of Alzheimer's disease and related disorders, people living with dementia (PWD) and caregivers wonder what disease trajectory to expect and how to plan for functional and cognitive decline. This qualitative study aimed to identify patient and caregiver experiences receiving anticipatory guidance about dementia from a specialty dementia clinic.ObjectiveTo examine PWD and caregiver perspectives on receiving anticipatory guidance from a specialty dementia clinic.MethodsWe conducted semi-structured interviews with PWD, and active and bereaved family caregivers, recruited from a specialty dementia clinic. Interviews were recorded, transcribed, and systematically summarized. Thematic analysis identified anticipatory guidance received from clinical or non-clinical sources and areas where respondents wanted additional guidance.ResultsOf 40 participants, 9 were PWD, 16 were active caregivers, and 15 were bereaved caregivers. PWD had a mean age of 75 and were primarily male (n = 6/9); caregivers had a mean age of 67 and were primarily female (n = 21/31). Participants felt they received incomplete or "hesitant" guidance on prognosis and expected disease course via their clinicians and filled the gap with information they found via the internet, books, and support groups. They appreciated guidance on behavioral, safety, and communication issues from clinicians, but found more timely and advance guidance from other non-clinical sources. Guidance on legal and financial planning was primarily identified through non-clinical sources.ConclusionPWD and caregivers want more information about expected disease course, prognosis, and help planning after diagnosis. Clinicians have an opportunity to improve anticipatory guidance communication and subsequent care provision