The Glass Transition of Thin Polymer Films: Some Questions, and a Possible Answer

A simple and predictive model is put forward explaining the experimentally observed substantial shift of the glass transition temperature, Tg, of sufficiently thin polymer films. It focuses on the limit of small molecular weight, where geometrical `finite size' effects on the chain conformation can be ruled out. The model is based on the idea that the polymer freezes due to memory effects in the viscoelastic eigenmodes of the film, which are affected by the proximity of the boundaries. The elastic modulus of the polymer at the glass transition turns out to be the only fitting parameter. Quantitative agreement is obtained with our experimental results on short chain polystyrene (Mw = 2 kg/mol), as well as with earlier results obtained with larger molecules. Furthermore, the model naturally accounts for the weak dependence of the shift of Tg upon the molecular weight. It furthermore explains why supported films must be thinner than free standing ones to yield the same shift, and why the latter depends upon the chemical properties of the substrate. Generalizations for arbitrary experimental geometries are straightforward.Comment: 7 pages, 4 figure

A RESILIENCE LENS ON HOMELESS OLDER PERSONS IN THE CITY OF TSHWANE: AN ILLUMINATION THROUGH PHOTOVOICE

This qualitative study explores and describes the resilience of homeless older persons in the City of Tshwane, South Africa. Eleven participants, recruited purposively, participated in photovoice activities supplemented with semi-structured interviews. Data were analysed through reflexive thematic analysis and trustworthiness was ensured. Findings indicate that conflict, abuse, family disappointment, unemployment, mental health challenges, declining mobility, isolation and a lack of access to services are risk factors hindering resilience. Religion, support and socialisation, amongst other things, are identified as protective factors enabling resilience. Recommendations for resilience-informed biopsychosocial gerontological social services to homeless older persons are offered to navigate towards better-than-expected outcomes

Reducing Friction and Leakage by Means of Microstructured Sealing Surfaces – Example Mechanical Face Seal

By defined structuring of sliding surfaces at dynamic contact seals friction and leakage can be reduced. Compared to macro-structures, micro-structures have the advantage of a quasi-homogeneous influence on the fluid behavior in the sealing gap. The development of suitable microstructures based on prototypes, whose properties are studied on the test bench, is very expensive and time-consuming due to the challenging manufacturing process and measuring technologies, which are necessary to investigate the complex rheological behavior within the sealing gap. A simulation-based development of microstructured sealing surfaces offers a cost- and time-saving alternative. This paper presents a method for simulative design and optimization of microstructured sealing surfaces at the example of a microstructured mechanical face seal

TB158: Milk Processing and Distribution Costs: Maine 1993

The objective of this study is to provide an updated estimate of the theoretically lowest achievable costs of processing and distributing milk in Maine. Costs are estimated for a state-of-the-art processing plant assumed to be located in the Portland, Maine, area. The plant produces and distributes a full line of products, including white milk, chocolate milk, and orange juice, and distributes additional products such as cheeses and yogurts.https://digitalcommons.library.umaine.edu/aes_techbulletin/1058/thumbnail.jp