Sterically stabilized lock and key colloids: A self-consistent field theory study

A self-consistent field theory study of lock and key type interactions between sterically stabilized colloids in polymer solution is performed. Both the key particle and the lock cavity are assumed to have cylindrical shape, and their surfaces are uniformly grafted with polymer chains. The lock-key potential of mean force is computed for various model parameters, such as length of free and grafted chains, lock and key size matching, free chain volume fraction, grafting density, and various enthalpic interactions present in the system. The lock-key interaction is found to be highly tunable, which is important in the rapidly developing field of particle self-assembly

Adsorption of Externally Stretched Two-Dimensional Flexible and Semi-flexible Polymers near an Attractive Wall

We study analytically a model of a two dimensional, partially directed, flexible or semiflexible polymer, attached to an attractive wall which is perpendicular to the preferred direction. In addition, the polymer is stretched by an externally applied force. We find that the wall has a dramatic effect on the polymer. For wall attraction smaller than the non-sequential nearest neighbor attraction, the fraction of monomers at the wall is zero and the model is the same as that of a polymer without a wall. However, for greater than, the fraction of monomers at the wall undergoes a first order transition from unity at low temperature and small force, to zero at higher temperatures and forces. We present phase diagram for this transition. Our results are confirmed by Monte-Carlo simulations.Comment: 15 pages, 6 figure

Hard colloidal rods near a soft wall: wetting, drying, and symmetry breaking

Within an Onsager-like density functional theory we explore the thermodynamic and structural properties of an isotropic and nematic fluid of hard needle-like colloids in contact with a hard substrate coated with a soft short-ranged attractive or repulsive layer. As a function of the range and the strength of the soft interactions we find wetting and drying transitions, a pre-drying line, and a symmetry-breaking transition from uniaxial to biaxial in the wetting and drying film.Comment: 7 pages, 2 figure

Particle Monte Carlo simulation of string-like colloidal assembly in 2 dimensions

We simulate structural phase behavior of polymer-grafted colloidal particles by molecular Monte Carlo technique. Interparticle potential, which has a finite repulsive square-step outside a rigid core of the colloid, was previously confirmed via numerical self-consistent field calculation. This model potential is purely repulsive. We simulate these model colloids in the canonical ensemble in 2 dimensions and find that these particles containing no interparticle attraction self-assemble and align in a string-like assembly, at low temperature and high density. This string-like colloidal assembly is related to percolation phenomena. Analyzing the cluster size distribution and the average string length, we build phase diagrams and discover that the average string length diverges around the region where the melting transition line and the percolation transition line cross. This result is similar to Ising spin systems, in which the percolation transition line and the order-disorder line meet at a critical point.Comment: 11 pages, 14 figure

Monte-Carlo simulation of string-like colloidal assembly

We study structural phase transition of polymer-grafted colloidal particles by Monte Carlo simulations on hard spherical particles. The interaction potential, which has a weak repulsive step outside the hard core, was validated with use of the self-consistent field calculations. With this potential, canonical Monte Carlo simulations have been carried out in two and three dimensions using the Metropolis algorithm. At low temperature and high density, we find that the particles start to self-assemble and finally align in strings. By analyzing the cluster size distribution and string length distribution, we construct a phase diagram and find that this string-like assembly is related to the percolation phenomena. The average string length diverges in the region where the melting transition line and the percolation transition line cross, which is similar to Ising spin systems where the percolation transition line and the order-disorder line meet on the critical point.Comment: 7 pages, 6 figures, Accepted for Europhysics Letter

Polymer Brushes in Cylindrical Pores: Simulation versus Scaling Theory

The structure of flexible polymers endgrafted in cylindrical pores of diameter D is studied as a function of chain length N and grafting density \sigma, assuming good solvent conditions. A phenomenological scaling theory, describing the variation of the linear dimensions of the chains with \sigma, is developed and tested by Molecular Dynamics simulations of a bead-spring model.Comment: 35 pages, 38 figure

Why Do Adult Patients With Cancer Not Seek Help for Their Depressive Symptoms?:The Role of Illness Perceptions, Coping, and Social Support

Background: Up to 75% of cancer patients with depressive symptoms do not make use of psychological care.Objective: To examine how perceptions of and coping with depressive symptoms and perceived social support in adults with cancer are associated with their need for psychological care, concurrently and over time.Methods: In this longitudinal study, 127 participants who received a cancer diagnosis in the past 5 years, experienced at least moderate depressive symptoms, and were not receiving psychological help, completed 2 self-report questionnaires (3 months apart) including the brief Illness Perception Questionnaire and brief Coping Orientation to Problems Experienced Inventory and Social Support List.Results: Participants with stronger belief in the efficacy of psychological care and more likely to use avoidant coping reported a greater need for psychological care at both data points. Social support was not significantly associated with perceived need for psychological care.Conclusions: Stronger perceived treatment control and greater use of avoidant coping were significantly associated with a greater perceived need for psychological care.Implications for practice: People with cancer may benefit from being informed about the efficacy of depression treatment. Furthermore, health care professionals should be aware that avoidant coping may complicate psychological care seeking for a group of adults with cancer experiencing depressive symptoms and having a need for psychological care.Foundational: Illness perceptions and coping mechanisms can predict cancer patients’ need for psychological care. Providing information about treatment options and its efficacy, together with targeting avoidant coping may increase adequate decision-making and possibly the uptake of psychological care

Seasonal patterns in mindfulness in people with seasonal affective disorder (SAD)

Background: Mindfulness-based cognitive therapy (MBCT) is a well-known, effective treatment in the prevention of relapse in Major Depression Disorder (MDD). However, a recent study in people with Seasonal Affective Disorder (SAD) showed that MBCT given in spring was ineffective in preventing a next depressive episode. To test the hypothesis that people with SAD may experience sufficient levels of mindfulness in spring and therefore less benefit from MBCT, this study examines variations in levels of mindfulness over seasons. Methods: This longitudinal prospective study followed 77 people with SAD over a two-year period. Participants filled out a self-report questionnaire, Five Facet Mindfulness Questionnaire (FFMQ) on a quarterly basis. Results: Levels of mindfulness differed throughout the seasons, with overall results suggesting lower levels of mindfulness in winter. Limitations: The results are limited by the small sample size and varying levels of mindfulness over the two years of the study period. Conclusion: Findings suggest a seasonal component in levels of mindfulness exists, implying that people with SAD are less mindful during the winter compared to other seasons. Future research is needed to examine to what extent the motivation of people with SAD to participate in MBCT and benefit from it is higher in the winter