Fluoride-responsive debond on demand adhesives: manipulating polymercrystallinity and hydrogen bonding to optimise adhesion strength at lowbonding temperatures

This paper reports the solvent-free synthesis of a series of sixfluoride responsive debond-on-demand poly-urethane (PU) adhesives that contain a silyl functionalised degradable unit (DU). To optimise the adhesionstrength and debonding nature of the adhesives, the chemical composition of the PUs was varied according tothe structure of the polyol or the diisocyanate component in the polymer mainchain.1H NMR spectroscopy wasused to study the depolymerisation behaviour in solution state. It showed thattetra-butylammoniumfluoride(TBAF) triggered the breakdown of the DU unit without fragmenting the polyol mainchain indiscriminately. Onexposure tofluoride ions, the PUs underwent depolymerisation with reductions in Mnranging from 64 to 90% asmeasured by GPC analysis. The morphology and thermal properties of the PUs were characterised by differentialscanning calorimetry (DSC), rheology and variable temperature (VT) SAXS/WAXS analysis. Each techniquedemonstrated the reversibility of the supramolecular polymer network under thermal stimuli. PUs containingpoly(butadiene) soft segments were amorphous with glass transition and viscoelastic transition temperaturesdependent on the nature of the soft segment and diisocyanate starting materials. The PU containing a polyestersoft segment exhibited a defined melting point at 49 °C. Mechanical stress-strain analysis of the series of PUsshowed each exhibited greater than 70% reduction in toughness after treatment with TBAF for 30 min as aconsequence of the chemo-responsive degradation of the polymer mainchain. The material featuring an ester-based polyol demonstrated excellent adhesion at bonding temperatures as low as 60 °C. Moreover, this materialcould be thermally rebonded if broken by force without loss in adhesion strength over three debond-rebondcycles. Lap shear adhesion tests showed a reduction in adhesive strength of approximately 40% (from 11.4 MPato 7.3 MPa) on exposure tofluoride ion

Pre-pottery clay innovation in the Zagros foothills

Neolithic material engagements transformed the ways in which communities interacted with the physical world and one another. Based on evidence from the flanks of the Zagros Mountains, in western Iran and north‐eastern Iraq, Robert Braidwood initially proposed his ‘Hilly Flanks’ hypothesis for the origins of agriculture and sedentism. The evidence for multi‐centred developments in domestication has demonstrated that elements of these practices spanned south‐west Asia in the Early Neolithic. The Zagros Mountains (and the eastern branch of the Fertile Crescent as a whole) constituted an area of vibrant engagement with new ideas, materials, experimentation and innovation, participating in the networks of interaction and exchange that facilitated the spread of alternative lifeways. This research examines how engagements with clay influenced the development and spread of new ways of thinking about the physical world, highlighting the role of clay as a transformational material through sites in the Central Zagros

the effect of television image degradation on learning

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A Study of Personal Narratives in Community Energy

The community renewable energy movement is an active local response to the concerns posed by climate change, fossil fuel dependency and resource scarcity. Since 2011, there have been several policy changes disruptive to the progress of the movement, including: significant cuts to the Feed-in Tariff Scheme; a block to registration of new energy co-operatives, and the removal of investment eligibility under the Enterprise Investment Tax Relief Scheme. While previous research has explored community energy as a means of collective local action and the role it might play in the low-carbon transition, much of this work was undertaken during a time of emerging policy support. Accordingly, there is now a need to understand the effect of national policy changes at a local level and how community energy groups consequently adapt. The changing policy context has provided an opportunity to reconsider the dynamics of local renewable energy engagement during times of uncertainty.This thesis presents contemporary stories from the community energy movement at a pivotal moment of change. Twenty-four in-depth narrative interviews were conducted with individuals involved at the centre of the movement, a method that elicited different forms of storytelling in the interviews. These stories build new knowledge of low carbon transformation, and how the actions and narratives of individuals are intertwined with the evolution of wider societal themes and structures. The stories of community energy activists evidence creativity and resilience in response to uncertainty and have brought a new consideration of community energy project development and the connections of energy history, personal life, and group agency. The research argues the value of stories to illuminate meaningful perspectives of local transformation and the need for storytelling to connect these ideas to a wider audience. Such understandings can support the community energy movement as it continues to evolve through a changing context

Functionalised PEGs with photo-dimerisable, anthracenyl end-groups: new UV-curable materials for use in inkjet formulations

The synthesis and characterisation of two novel poly(ethylene glycol)-based materials featuring UV-dimerisable anthracenyl end-groups are described. These low molecular weight polymers exhibited good solubility (ca. 100 g/L) in common organic solvents and were deposited successfully using a drop-on-demand (DOD) inkjet printhead to produce clear prints. UV-vis irradiation of a linear bis-anthracene terminated PEG material resulted in polymerisation via photodimerisation of the anthracenyl end-groups, maintaining polymer solubility in common organic solvents and enabling solution state analysis of the polymerisation process using UV-vis and 1H NMR spectroscopies. In contrast, UV irradiation of a three-armed, tris-anthracenyl-terminated PEG resulted in the formation of an insoluble cross-linked network, which was characterised using rheometry, differential scanning calorimetry and lap shear tensiometry. It was found that the incorporation of solvent-soluble dyes into formulations of the tris-anthracenyl PEG resulted in an increase in UV-cure time when compared to the polymer alone, but did not prevent curing. The results highlight the suitability of this latter material as a UV-curable system for inclusion in inkjet formulations

Integrated micro-analysis of the built environment and resource use: high-resolution microscopy and geochemical, mineralogical, phytolith and biomolecular approaches

Peer reviewe

Fluoride-responsive debond on demand adhesives: manipulating polymer crystallinity and hydrogen bonding to optimise adhesion strength at low bonding temperatures

This paper reports the solvent-free synthesis of a series of six fluoride responsive debond-on-demand polyurethane (PU) adhesives that contain a silyl functionalised degradable unit (DU). To optimise the adhesion strength and debonding nature of the adhesives, the chemical composition of the PUs was varied according to the structure of the polyol or the diisocyanate component in the polymer mainchain. 1H NMR spectroscopy was used to study the depolymerisation behaviour in solution state. It showed that tetra-butylammonium fluoride (TBAF) triggered the breakdown of the DU unit without fragmenting the polyol mainchain indiscriminately. On exposure to fluoride ions, the PUs underwent depolymerisation with reductions in Mn ranging from 64 to 90% as measured by GPC analysis. The morphology and thermal properties of the PUs were characterised by differential scanning calorimetry (DSC), rheology and variable temperature (VT) SAXS/WAXS analysis. Each technique demonstrated the reversibility of the supramolecular polymer network under thermal stimuli. PUs containing poly(butadiene) soft segments were amorphous with glass transition and viscoelastic transition temperatures dependent on the nature of the soft segment and diisocyanate starting materials. The PU containing a polyester soft segment exhibited a defined melting point at 49 °C. Mechanical stress-strain analysis of the series of PUs showed each exhibited greater than 70% reduction in toughness after treatment with TBAF for 30 min as a consequence of the chemo-responsive degradation of the polymer mainchain. The material featuring an ester-based polyol demonstrated excellent adhesion at bonding temperatures as low as 60 °C. Moreover, this material could be thermally rebonded if broken by force without loss in adhesion strength over three debond-rebond cycles. Lap shear adhesion tests showed a reduction in adhesive strength of approximately 40% (from 11.4 MPa to 7.3 MPa) on exposure to fluoride ions