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

Nucleated dewetting in supported ultra-thin liquid films with hydrodynamic slip

This study reveals the influence of the surface energy and solid/liquid boundary condition on the breakup mechanism of dewetting ultra-thin polymer films. Using silane self-assembled monolayers, SiO$_2$ substrates are rendered hydrophobic and provide a strong slip rather than a no-slip solid/liquid boundary condition. On undergoing these changes, the thin-film breakup morphology changes dramatically -- from a spinodal mechanism to a breakup which is governed by nucleation and growth. The experiments reveal a dependence of the hole density on film thickness and temperature. The combination of lowered surface energy and hydrodynamic slip brings the studied system closer to the conditions encountered in bursting unsupported films. As for unsupported polymer films, a critical nucleus size is inferred from a free energy model. This critical nucleus size is supported by the film breakup observed in the experiments using high speed \emph{in situ} atomic force microscopy.Comment: 8 pages, 9 figures, including supplementary materia

Dance for Life: Expressive Arts for Cultural Wellbeing with Young People: Research and Evaluation Report

Developing strong mental health and wellbeing of young people is one of the most pressing issues Australian Society is currently facing. Anxiety and depressive disorders are increasing worldwide in adolescents with social, political, and environmental causes implicated. In Australia a post pandemic report on youth mental health and wellbeing found that 51% had difficulty completing daily tasks with 34% experiencing high or very high levels of distress (Headspace 2021). Worldwide public health policy has gradually shifted from a deterministic set of individualised ill-health factors to include a more holistic view of health and wellbeing (Mackay 2016). The World Health Organisation’s definition of health has come to include social determinants such as education, income and social protection, food and job security, housing, social inclusion, structural conflict and affordable and accessible health services. Current research indicates that social determinants “can be more important than health care or lifestyle choices in influencing health” (WHO 2021). What is still missing from this definition of wellbeing is the role of creative expression, arts and cultural values as imperative to cultural wellbeing (Mackay 2016). This research evaluation was commissioned by Kulture Break, a dance company with a focus on inclusion and wellbeing for young people. The aim of the research was to identify how their creative arts programs were able to influence young people’s wellbeing; specifically, in terms of social inclusion, confidence, sense of belonging and life aspirations. Further to this the research aimed to find out how dance as an expressive art can improve wellbeing and social cohesion within communities and better inform understandings of how wellbeing is experiences to inform nation wellbeing policy. This evaluative research project reviewed how dance programs at Kulture Break are implicated in the cultural wellbeing of young people that attend their classes