Slow dynamics near glass transitions in thin polymer films

The $\alpha$-process (segmental motion) of thin polystyrene films supported on glass substrate has been investigated in a wider frequency range from 10$^{-3}$ Hz to 10$^4$ Hz using dielectric relaxation spectroscopy and thermal expansion spectroscopy. The relaxation rate of the $\alpha$-process increases with decreasing film thickness at a given temperature above the glass transition. This increase in the relaxation rate with decreasing film thickness is much more enhanced near the glass transition temperature. The glass transition temperature determined as the temperature at which the relaxation time of the $\alpha$-process becomes a macroscopic time scale shows a distinct molecular weight dependence. It is also found that the Vogel temperature has the thickness dependence, i.e., the Vogel temperature decreases with decreasing film thickness. The expansion coefficient of the free volume $\alpha_f$ is extracted from the temperature dependence of the relaxation time within the free volume theory. The fragility index $m$ is also evaluated as a function of thickness. Both $\alpha_f$ and $m$ are found to decrease with decreasing film thickness.Comment: 9 pages, 7 figures, and 2 table

Dewetting of Glassy Polymer Films

Dynamics and morphology of hole growth in a film of power hardening viscoplastic solid (yield stress ~ [strain-rate]^n) is investigated. At short-times the growth is exponential and depends on the initial hole size. At long-times, for n > 1/3, the growth is exponential with a different exponent. However, for n < 1/3, the hole growth slows; the hole radius approaches an asymptotic value as time tends to infinity. The rim shape is highly asymmetric, the height of which has a power law dependence on the hole radius (exponent close to unity for 0.25 < n < 0.4). The above results explain recent intriguing experiments of Reiter, Phys. Rev. Lett, 87, 186101 (2001).Comment: 4 pages, 5 figures, RevTe

‘Why haven’t I got one of those?’ A consideration regarding the need to protect non-participant children in early years research

It is widely documented that young children participating in research should be protected from harm and that ethical considerations should be applied throughout a research project. What this paper strives to assert, however, is that protecting these participants is insufficient. A research project into children’s speech and language development, using audio–-visual methods, highlighted that children who are non-participants, those on the periphery of research, can also be affected by the research process. It is acknowledged throughout this paper that although ethical procedures were adhered to whilst undertaking a specific research project, this was insufficient. It is therefore argued that all children within a research environment, whether participatory or not, should be given equal consideration with regards to ethical protection when undertaking research. It is asserted that ‘“why haven’t I got one of those’”, or the equivalent, is a phrase to be avoided at all costs when undertaking research with children

'You were quiet - I did all the marching': Research processes involved in hearing the voices of South Asian girls

This article is available open access through the publisher’s website at the link below. Copyright @ 2011 A B Academic Publishers.This article provides insights into the outcomes of reflection following two interview approaches used to explore narratives of the lived, individual experiences of South-Asian girls living in West London. In attempting to illuminate and re-present the cultural experiences as told by these girls, the choice of interview approach became critical in allowing the voices to be effectively heard (Rogers, 2005). This article therefore considers how a semi-structured interview approach offered valuable insights into the girls' experiences but became constraining for both researcher and participant in unveiling the complexity and depth of their lives. These constraints emerged through reflection by both participants and researcher. As a result of reflexivity during the research process, the researcher moved towards the use of research conversations during the second phase of the study. Ultimately the study revealed how the girls felt empowered by the opportunity to narrate their individual experiences and tell of their lives. In narrating their reflections on being part of the research, there was a clear recognition that the process facilitated the articulation of new voices and ‘multi-voicedness’ (Moen, 2006

‘It’s never okay to say no to teachers’: children’s research consent and dissent in conforming schools contexts

This article examines the limits to children giving research consent in everyday school contexts that emphasises their conformity to comply with adult expectations, and highlights children’s competence and agency in navigating this conformity through different practices of dissent. It draws on research into children’s agency, using a multimodal ethnography of Year 1 classrooms in two English primary schools. The article includes a reflexive methodological focus, exploring the extent to which I counter the schools’ emphasis on conformity. This includes creating visuals for children to practice consent; positioning myself as the researcher in a non‐teacher role, as ‘least adult’ and the one who ‘least knows’; and designing interview spaces markedly different from classrooms. The article examines how children navigate conforming discourses by finding different ways to dissent in the research. Firstly, children demonstrate a sophisticated awareness of the cultural norms of indicating refusals beyond saying the word ‘No’. Secondly, children achieve unnoticeablity, by which they absent themselves from the ‘on‐task’ classroom culture, and by extension the research process. Thirdly, they engage in playful dissent, demonstrating their political knowingness of the classroom social order. The article discusses the implications for educational research when the values of consent are in conflict with a schooling focused on conformity. This includes emphasising the limits of consent procedures, paying closer attention to how researchers recognise and respond ethically to children’s multiple practices of dissent, and using research to disrupt problematic power structures in education settings that limit possibilities for children’s consent

Two-Photon Fluorescence Microscopy Imaging of Cellular Oxidative Stress Using Profluorescent Nitroxides

A range of varying chromophore nitroxide free radicals and their nonradical methoxyamine analogues were synthesized and their linear photophysical properties examined. The presence of the proximate free radical masks the chromophore’s usual fluorescence emission, and these species are described as profluorescent. Two nitroxides incorporating anthracene and fluorescein chromophores (compounds 7 and 19, respectively) exhibited two-photon absorption (2PA) cross sections of approximately 400 G.M. when excited at wavelengths greater than 800 nm. Both of these profluorescent nitroxides demonstrated low cytotoxicity toward Chinese hamster ovary (CHO) cells. Imaging colocalization experiments with the commercially available CellROX Deep Red oxidative stress monitor demonstrated good cellular uptake of the nitroxide probes. Sensitivity of the nitroxide probes to H2O2-induced damage was also demonstrated by both one- and two-photon fluorescence microscopy. These profluorescent nitroxide probes are potentially powerful tools for imaging oxidative stress in biological systems, and they essentially “light up” in the presence of certain species generated from oxidative stress. The high ratio of the fluorescence quantum yield between the profluorescent nitroxide species and their nonradical adducts provides the sensitivity required for measuring a range of cellular redox environments. Furthermore, their reasonable 2PA cross sections provide for the option of using two-photon fluorescence microscopy, which circumvents commonly encountered disadvantages associated with one-photon imaging such as photobleaching and poor tissue penetration