Phase transitions during membrane formation of polylactides. I. A morphological study of membranes obtained from the system polylactide-chloroform-methanol

The influence of solid-liquid demixing, liquid-liquid demixing and vitrification on the morphology of polylactide membranes has been investigated. To study the effects of crystallization of polylactides on the membrane and morphology, polylactides of varying stereoregularity were used. The polymers applied were poly--lactide (PLLA) and copolymers with different molar ratios of -lactide and -lactide [poly-L95/D5-lactide (PLA95), poly-L80/D20-lactide (PLA80) and poly-L50/D50-lactide (PDLLA)]. Solutions of polylactides in chloroform cast on a glass plate were immersed in methanol. From solutions containing the slowly crystallizing PLA80 or uncrystallizable PDLLA porous membranes were obtained if the phase separated system was removed from the nonsolvent bath within a few hours after immersion. After longer equilibration times in methanol the structure collapsed. The swelling in the nonsolvent methanol was too high to allow stabilization of the liquid-liquid demixed structure by vitrification. Stable membranes were easily obtained with more rapidly crystallizing polymers like PLLA. Casting solutions with low PLLA concentrations gave membranes with a cellular morphology due to liquid-liquid demixing by nucleation and growth of a polymer poor phase. Crystallization only played a role in the fixation of the liquid-liquid demixed structure. At increasing PLLA concentrations the demixing sequence gradually reversed to crystallization followed by liquid-liquid demixing. In these cases membranes with porous spherulites or spherulites surrounded with a cellular layer were obtained

A morphological study of membranes obtained from the systems polylactide-dioxane-methanol, polylactide-dioxane-water and polylactide-N-methyl pyrrolidone-water

The influence of liquid-liquid demixing, solid-liquid demixing, and vitrification on the membrane morphologies obtained from several polylactide-solvent-nonsolvent systems has been investigated. The polymers investigated were the semicrystalline poly-L-lactide (PLLA) and the amorphous poly-DL-lactide (PDLLA). The solvent-nonsolvent systems used were dioxane-water, N-methyl pyrrolidone-water and dioxane-methanol. For each of these systems it was attempted to relate the membrane morphology to the ternary phase diagram at 25°C. It was demonstrated that for the amorphous poly-DL-lactide the intersection of a glass transition and a liquid-liquid miscibility gap in the phase diagram was a prerequisite for the formation of stable membrane structures. For the semicrystalline PLLA a wide variety of morphologies could be obtained ranging from cellular to spherulitical structures. For membrane-forming combinations that show delayed demixing, trends expected on the basis of phase diagrams were in reasonable agreement with the observed membrane morphologies. Only for the rapidly precipitating system PLLA-N-methyl pyrrolidone-water were structures due to liquid-liquid demixing obtained when structures due to solid-liquid demixing were expected. Probably, rapid precipitation conditions promote solid-liquid demixing over liquid-liquid demixing, because the activation energy necessary for liquid-liquid demixing is lower than that for crystallization

Hoe zwart is Vlaanderen? Een exploratief onderzoek naar uiterst-rechtse denkbeelden in Vlaanderen in 1991

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The cognitive/affective distinction of job insecurity: Validation and differential relations

Job insecurity as a work-related stressor is well established through three decades of research. It has been related to outcomes such as decreased job satisfaction, organisational commitment and performance as well as increased ill-health and organisational turnover. However, some important conceptual and theoretical issues are still under discussion, with implications for the measurement of the construct. We administered a short version of the measure of job insecurity originally devised by De Witte (2000), which distinguishes between cognitive and affective job insecurity. Data on job satisfaction, commitment, psychological ill-health and emotional exhaustion were also gathered from employees in a variety of South African organisations (N=1925) by means of anonymous surveys. Exploratory and confirmatory factor analyses revealed that the cognitive and affective dimensions of job insecurity could be distinguished in this sample of South African employees, and the two dimensions evidenced adequate reliability. Equivalence analyses showed that the measurement properties of the scale were invariant across various demographic groups. The relationships with outcome variables were investigated by means of correlations and regression analyses. Cognitive job insecurity was predictive of all outcome variables, whereas affective job insecurity primarily played a role for emotional exhaustion. Norm data concerning levels of cognitive and affective job insecurity are presented to guide future South African studies.Key words: Job insecurity, job satisfaction, validation, equivalence analysis, factorial invarianc

Work locus of control and sense of coherence as antecedents of job insecurity

Previous research has highlighted various antecedents of job insecurity, both in cross-sectional research and in a recent meta-analysis. A review of this literature indicates that work locus of control actually is the only personality antecedent that has received considerable attention, while sense of coherence may also be an important factor to consider. Data on biographical variables, cognitive and affective job insecurity, work locus of control and sense of coherence were gathered from employees across 3 organisations (N=718), presenting two different sectors (chemical industry and financial services), by means of anonymous surveys. Data were analysed by means of correlations and regression analyses. Results indicate that both work locus of control and sense of coherence play a role in predicting job insecurity, even after controlling for biographical variables. Considering their individual contributions, it is suggested here that sense of coherence may be even more important than work locus of control as a personality antecedent of job insecurity

Stroke service in the Netherlands: an exploratory study on effectiveness, patient satisfaction and utilisation of healthcare

OBJECTIVE: To assess whether shared care for stroke patients results in better patient outcome, higher patient satisfaction and different use of healthcare services. DESIGN: Prospective, comparative cohort study. SETTING: Two regions in the Netherlands with different healthcare models for stroke patients: a shared care model (stroke service) and a usual care setting. PATIENTS: Stroke patients with a survival rate of more than six months, who initially were admitted to the Stroke Service of the University Hospital Maastricht (experimental group) in the second half of 1997 and to a middle sized hospital in the western part of the Netherlands between March 1997 and March 1999 (control group). MAIN OUTCOME MEASURES: Functional health status according to the SIP-68, EuroQol, Barthel Index and Rankin Scale, patient satisfaction and use of healthcare services. RESULTS: In total 103 patients were included in this study: 58 in the experimental group and 45 in the control group. Six months after stroke, 64% of the surviving patients in the experimental group had returned home, compared to 42% in the control group (p<0.05). This difference could not be explained by differences in health status, which was comparable at that time. Patients in the shared care model scored higher on patient satisfaction, whereas patients in the usual care group received a higher volume of home care. CONCLUSIONS: The Stroke Service Maastricht resulted in a higher number of patients who returned home after stroke, but not in a better health status. Since patients in the usual care group received a higher volume of healthcare in the period of rehabilitation, the Stroke Service Maastricht might be more efficient

In-gas-cell laser ionization spectroscopy in the vicinity of 100Sn: Magnetic moments and mean-square charge radii of N=50-54 Ag

In-gas-cell laser ionization spectroscopy studies on the neutron deficient 97-101Ag isotopes have been performed with the LISOL setup. Magnetic dipole moments and mean-square charge radii have been determined for the first time with the exception of 101Ag, which was found in good agreement with previous experimental values. The reported results allow tentatively assigning the spin of 97,99Ag to 9/2 and confirming the presence of an isomeric state in these two isotopes, whose collapsed hyperfine structure suggests a spin of 1/2 . The effect of the N=50 shell closure is not only manifested in the magnetic moments but also in the evolution of the mean-square charge radii of the isotopes investigated, in accordance with the spherical droplet model predictions