Dynamics and thermodynamics of polymer glasses

The fate of matter when decreasing the temperature at constant pressure is that of passing from gas to liquid and, subsequently, from liquid to crystal. However, a class of materials can exist in an amorphous phase below the melting temperature. On cooling such materials, a glass is formed; that is, a material with the rigidity of a solid but exhibiting no long-range order. The study of the thermodynamics and dynamics of glass-forming systems is the subject of continuous research. Within the wide variety of glass formers, an important sub-class is represented by glass forming polymers. The presence of chain connectivity and, in some cases, conformational disorder are unfavourable factors from the point of view of crystallization. Furthermore, many of them, such as amorphous thermoplastics, thermosets and rubbers, are widely employed in many applications. In this review, the peculiarities of the thermodynamics and dynamics of glass-forming polymers are discussed, with particular emphasis on those topics currently the subject of debate. In particular, the following aspects will be reviewed in the present work: (i) the connection between the pronounced slowing down of glassy dynamics on cooling towards the glass transition temperature (Tg) and the thermodynamics; and, (ii) the fate of the dynamics and thermodynamics below Tg. Both aspects are reviewed in light of the possible presence of a singularity at a finite temperature with diverging relaxation time and zero configurational entropy. In this context, the specificity of glass-forming polymers is emphasized.The author acknowledges the University of the Basque Country and Basque Country Government (Ref. No IT-654-13 (GV)), Depto Educacion, Universidades e investigacion and the Spanish Government (Grant No MAT2012-31088) for their financial support.Peer Reviewe

A Novel Route to Calculate the Length Scale for the Glass Transition in Polymers

The occurrence of glass transition is believed to be associated to cooperative motion with a growing length scale with decreasing temperature. We provide a novel route to calculate the size of cooperatively rearranging regions CRR of glass-forming polymers combining the Adam-Gibbs theory of the glass transition with the self-concentration concept. To do so we explore the dynamics of glass-forming polymers in different environments. The material specific parameter $\alpha$ connecting the size of the CRR to the configurational entropy is obtained in this way. Thereby, the size of CRR can be precisely quantified in absolute values. This size results to be in the range 1 $\div$ 3 nm at the glass transition temperature depending on the glass-forming polymer

Teaching in the Open

Teaching in the Open is about building connections and community. It is about contextualizing learning in a larger world outside of the classroom, and making education more relevant, inclusive, equitable and accessible. Open helps us address the question: How can my role as a teacher or professional in higher education have a greater impact in influencing our larger culture? Open Pedagogy deeply prioritizes the empowerment of learners to take greater ownership of how and what they learn, and encourages them to “not just be consumers of, but contributors to the knowledge commons.” While it involves the use of the web, OER, and some easy-to-learn technological tools, it is not about the technology itself. Instead, practitioners of open pedagogy leverage the open license, and utilize the web for uncontrolled discovery, creativity and analysis, and as a venue for dialogue with the wider public

Leveraging RFID in hospitals: patient life cycle and mobility perspectives

The application of Radio Frequency Identification (RFID) to patient care in hospitals and healthcare facilities has only just begun to be accepted. This article develops a set of frameworks based on patient life cycle and time-and-motion perspectives for how RFID can be leveraged atop existing information systems to offer many benefits for patient care and hospital operations. It examines how patients are processed from admission to discharge, and considers where RFID can be applied. From a time-and-motion perspective, it shows how hospitals can apply RFID in three ways: fixed RFID readers interrogate mobile objects; mobile, handheld readers interrogate fixed objects; and mobile, handheld readers interrogate mobile objects. Implemented properly, RFID can significantly aid the medical staff in performing their duties. It can greatly reduce the need for manual entry of records, increase security for both patient and hospital, and reduce errors in administering medication. Hospitals are likely to encounter challenges, however, when integrating the technology into their day-to-day operations. What we present here can help hospital administrators determine where RFID can be deployed to add the most value

Semi-Conductors Lab

This write-up for a chemistry lab at Parkland College details the student\u27s experiences in a semi-conductor lab, in which the student learned what positive and negative biases are, how semiconductors work, how to treat them in a lab setting, how to make a functioning circuit, how to take accurate readings at different points in a circuit

DNA PROGRAMMABLE SOFT MATTER DEVICES

The ability to program soft materials to undergo observable shape transformations in response to environmental stimuli is critical to the development soft programmable matter. In recent years, chemomechanical shape-changing hydrogels have garnered interest because they do not require wires or batteries and can operate untethered at smaller size scales. Devices comprised of these materials can respond to only a limited set of spatially non-specific stimuli such as temperature or pH - and are therefore restricted to a small set of final states. On the other hand, due to the large sequence space and programmable interactions of DNA molecules, devices comprised of DNA-conjugated hydrogel domains can potentially access a much larger set of final configurations through sequence-specific, addressable actuation of individual domains. To investigate the shape-changing properties of single domain DNA-conjugated hydrogels, we first determine the swelling extent of DNA-crosslinked acrylamide networks in response to sequence-specific DNA stimuli. By coupling the DNA crosslinks to a DNA hybridization chain reaction that enables further incorporation of DNA to the crosslink sites, we demonstrate that specific DNA molecules can induce up to 100-fold volumetric hydrogel expansion. This large degree of swelling is then used to actuate approximately centimeter-sized gels containing multiple DNA-sensitive gel domains that each change shape in response to different DNA sequences. From swelling experiments and finite-element simulations we develop a simple design rule for the DNA-controlled shape change of a hydrogel bilayer. The next generation of soft programmable matter and robotics will require materials that not only respond to distinct chemical species, but mechanical forces as well. Prior work in developing mechanochemically responsive polymers makes use of mechanophores - molecules that change configuration and initiate chemical reactions in response to mechanical forces - to instill bulk materials with force sensing properties. In this work, we use established thermodynamic models to design two DNA mechanophore complexes capable of responding to two distinct ranges of applied force. We micromold PEGDA copolymer hydrogels containing DNA mechanophore complexes and examine the force-sensing properties of the bulk material through the use of a multifunctional force microscope and a DNA-based fluorescence reporting scheme. Because DNA molecules can be coupled to molecular sensors, amplifiers, and logic circuits, the incorporation of DNA complexes into hydrogel networks - whether as mechanophores or chemical crosslinkers -introduces the possibility of building soft matter devices that respond to numerous, distinct inputs and autonomously implement chemical control programs. These soft matter constructs have the potential to exhibit the multistage, goal-directed behaviors that are currently impossible to achieve in other soft robotic devices