Thermal Characterization of PMMA Thin Films on Silica Using Modulated Differential Scanning Calorimetry

The number of studies of thin polymer films has increased over recent years as technological processes incorporate the use of nanomaterials. An enhanced understanding of these films would enable us to predict bound-polymer behavior and thus improve the efficiency of processes and the quality of products. This is especially true as the thickness of the films approach molecular dimensions. The glass transition temperature of a polymer is one of the most important properties for characterization because it indicates how the polymer might perform macroscopically. when a polymer is confined, such as one the surface of a substrate, its behavior is influenced by molecular interactions between the polymer and the substrate. These interactions may affect the polymer\u27s glass transition temperature and warrant scientific investigation. This study uses modulated differential scanning calorimetric (MDSC) to examine the glass transition of poly (methyl methacrylate) adsorbed onto silica. We varied the amount of polymer adsorbed, and found that the Tg center and its breadth increased with decreased coverage. T o our knowledge this is the first reported analysis of such very thin polymer films using MDSC

Dynamics of Adsorbed Poly(Methyl Acrylate) and Poly(Methyl Methacrylate) on Silica

Deuterium NMR and modulated differential scanning calorimetry (MDSC) were used to probe the behavior of ultrathin adsorbed poly(methyl acrylate) (PMA). The spectra for the bulk methyl-labeled PMA-d3 were consistent with the motions of the polymer segments being spatially homogeneous. For the polymers adsorbed on silica, multicomponent line shapes were observed. The segmental mobility of the surface polymers increased with increased adsorbed amounts. In contrast to the behavior of the polymers in bulk, the adsorbed lower-molecular-mass PMA-d3 was less mobile than the adsorbed high-molecular-mass polymer. The presence of a polymer overlayer was sufficient to suppress the enhanced mobility of the more-mobile segments of the adsorbed (inner) polymer. MDSC studies on adsorbed poly(methyl methacrylate) showed that the glass-transition temperature of the thin polymer films increased and broadened compared to the behavior of the polymer in bulk. The presence of a motional gradient with the less-mobile segments near the solid-polymer interface and the more-mobile segments near the polymer-air interface was consistent with the experimental observations

Graduated Segmental Mobility in Polymer Layers on Silica

The behavior of thin polymer layers on oxide substrates has gotten a great deal of attention as the size of materials, and hence polymer films, has gotten smaller. Indeed, the properties of adsorbed polymers are such that they can be different from those of bulk polymers, especially when the films are very thin. A wide variety of studies have been made on adsorbed polymers and sometimes the results seem contradictory. One of the properties often measured in thin films is the apparent glasstransition temperature, Tg. In principle, many techniques are sensitive to phenomenological changes occurring around Tg and, therefore, can be compared to each other. For polymer thin films there are two surfaces (often different) to consider. For example, a thin polymer film on a solid substrate, such as silica, has a polymer-silica interface and a polymer-air interface. In principle, these two interfaces would be expected to have different properties. In addition, it is not always clear if either of these would dominate the properties measured. In this paper, we provide support for the existence of graduated segmental mobility in thin polymer films. As examples we cite the behavior observed from both deuterium NMR of poly(methyl acrylate)-d3 (PMA-d3) and modulated differential scanning calorimetry (MDSC) of poly(methyl methacrylate) (PMMA), both on silica powder. In Figure 1, we depict a surface with which the polymer has a favorable interaction. We propose that the segments at the polymer-air interface have enhanced mobility while those at the polymer-silica interfect have reduced mobility

Unsettling planning theory

Recent political developments in many parts of the world seem likely to exacerbate rather than ameliorate the planetary-scale challenges of social polarization, inequality and environmental change societies face. In this unconventional multi-authored essay, we therefore seek to explore some of the ways in which planning theory might respond to the deeply unsettling times we live in. Taking the multiple, suggestive possibilities of the theme of unsettlement as a starting point, we aim to create space for reflection and debate about the state of the discipline and practice of planning theory, questioning what it means to produce knowledge capable of acting on the world today. Drawing on exchanges at a workshop attended by a group of emerging scholars in Portland, Oregon in late 2016, the essay begins with an introduction section exploring the contemporary resonances of ‘unsettling’ in, of and for planning theory. This is followed by four, individually authored responses which each connect the idea of unsettlement to key challenges and possible future directions. We end by calling for a reflective practice of theorizing that accepts unsettlement but seeks to act knowingly and compassionately on the uneven terrain that it creates

Measuring the predictability of life outcomes with a scientific mass collaboration.

How predictable are life trajectories? We investigated this question with a scientific mass collaboration using the common task method; 160 teams built predictive models for six life outcomes using data from the Fragile Families and Child Wellbeing Study, a high-quality birth cohort study. Despite using a rich dataset and applying machine-learning methods optimized for prediction, the best predictions were not very accurate and were only slightly better than those from a simple benchmark model. Within each outcome, prediction error was strongly associated with the family being predicted and weakly associated with the technique used to generate the prediction. Overall, these results suggest practical limits to the predictability of life outcomes in some settings and illustrate the value of mass collaborations in the social sciences

A call for transparent reporting to optimize the predictive value of preclinical research

The US National Institute of Neurological Disorders and Stroke convened major stakeholders in June 2012 to discuss how to improve the methodological reporting of animal studies in grant applications and publications. The main workshop recommendation is that at a minimum studies should report on sample-size estimation, whether and how animals were randomized, whether investigators were blind to the treatment, and the handling of data. We recognize that achieving a meaningful improvement in the quality of reporting will require a concerted effort by investigators, reviewers, funding agencies and journal editors. Requiring better reporting of animal studies will raise awareness of the importance of rigorous study design to accelerate scientific progress

Search For Exotic Tau-decays

The Crystal Ball detector at the Doris II storage ring at DESY was used to search for the exotic decay processes tau -> e gamma, tau -> e pi0, tau -> e eta. No signal was observed. We obtained the following 90% CL upper limits on the branching fractions:B(tau -> e gamma)< 2.0x10^(-4),B(tau -> e pi0) < 1.4x10^(-4),B(tau -> e eta) < 2.4x10^(-4)

Finishing the euchromatic sequence of the human genome

The sequence of the human genome encodes the genetic instructions for human physiology, as well as rich information about human evolution. In 2001, the International Human Genome Sequencing Consortium reported a draft sequence of the euchromatic portion of the human genome. Since then, the international collaboration has worked to convert this draft into a genome sequence with high accuracy and nearly complete coverage. Here, we report the result of this finishing process. The current genome sequence (Build 35) contains 2.85 billion nucleotides interrupted by only 341 gaps. It covers ∼99% of the euchromatic genome and is accurate to an error rate of ∼1 event per 100,000 bases. Many of the remaining euchromatic gaps are associated with segmental duplications and will require focused work with new methods. The near-complete sequence, the first for a vertebrate, greatly improves the precision of biological analyses of the human genome including studies of gene number, birth and death. Notably, the human enome seems to encode only 20,000-25,000 protein-coding genes. The genome sequence reported here should serve as a firm foundation for biomedical research in the decades ahead

Thermal characterization of polymer thin films using modulated differential scanning calorimetry

Modulated differential scanning calorimetry was used to thermally analyze separate thin films of poly( methyl methacrylate) (PMMA) and polystyrene (PS) that were adsorbed on silica and subsequently dried. The effects of surface coverage, adsorption medium, aging, and polymer/substrate interactions on the glass transition temperature (Tg) were investigated. For all of the treated samples, the half-height and the breadth of the Tg transitions increased with decreasing coverages compared to bulk and was the result of restrictions in mobility. PMMA-treated samples had an increase in the glass transitions\u27 onset and end temperatures whereas PS treated samples with the same coverages had a slight decrease in the onset temperature and an increase in the end temperature. In addition, the Tg span for the PS samples was not as broad as compared to PMMA-treated samples. The differences in the thermal behavior were due to the differences in the polymers\u27 interactions with the substrate. When PMMA was adsorbed from a polar solvent system, the Tg and its breadth increased compared to samples adsorbed from a poor solvent system. It was proposed that this was due to the polymer\u27s extended configuration on the substrate. After aging the polymer at room temperature for approximately a year, the thermal behavior of the low-coverage PMMA sample became more like that of the sample from the mixed solvent system. Presumably, the polymer chains rearranged into more stable configurations and attached more of their segments to the substrate --Abstract, page iv