Technische Universität Darmstadt

Materials with magnetic anisotropy can serve as a model object for exploring the multicaloric effect because their thermodynamic state alterations can be achieved either through the application of a magnetic field H or/and by mechanically rotating the sample in the magnetic field using torque τ. In such materials, the total entropy change __-mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"-__Δ S T arises from two distinct contributions: (1) the conventional magnetocaloric effect (MCE) or paraprocess __-mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"-__Δ S m and (2) the rotational MCE __-mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"-__Δ S φ . In this manuscript, using molecular field model which enables a separation of contributions to the total entropy change __-mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"-__Δ S T from conventional __-mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"-__Δ S m and rotational __-mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"-__Δ S φ , we have determined cross-coupling multicaloric coefficients __-mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"-__ χ τ , H = ∂τ ∂H T , θ and __-mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"-__ χ H , τ = - ∂m ∂θ T , H for anisotropic magnetic materials and show that they satisfy the basic thermodynamic identities. We also confirmed that the total multicaloric effect in the material with magnetic anisotropy can be accurately expressed as the sum of the individual magnetocaloric effects induced by separate application of the H and τ, minus the magnetic entropy change arising from thermodynamic cross-coupling between the subsystems of the solid: __-mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"-__   Δ S T = Δ S T , τ H + Δ S T , H θ -   Δ S coupling .

Measuring dynamic processes in responsive soft matter systems remains a critical frontier in bridging fundamental studies and applied sciences. In particular, determining structural changes of surface-grafted polymers due to the application of stimuli remains poorly examined due to historical instrument limitations. Herein, we exploit the high flux capabilities of the D17 neutron reflectometer (Institut Laue-Langevin, France) to examine kinetic changes in the internal nanostructure of a poly(N-isopropyl-acrylamide) (PNIPAM) brush with temperature or the presence of a common osmolyte (glucose).

Ellipsometry and neutron reflectometry (NR) was employed to examine changes in brush thickness as a function of temperature in water and aqueous glucose solutions under equilibrium conditions. NR captured the kinetics of brush swelling/collapse triggered by rapid temperature or glucose concentration changes.

Ellipsometry and NR revealed a decrease in the lower critical solution temperature (LCST) of a PNIPAM brush with increasing glucose concentration. Equilibrium NR measurements showed vertical phase separation within the brush when in a near-collapsed state. This stratified structure was expected for the thermally triggered conformation changes, but has not been observed for glucose-triggered collapse/swelling. Excellent statistics were achieved over intervals for the NR kinetic measurements with modelled profiles comparable to longer equilibrium measurements across a wider q range. A small hysteresis was observed in the temperature induced swelling/collapse, while a more pronounced hysteresis was observed in the glucose triggered conformational changes. This hysteresis was equivalent for both swelling and collapse transitions and is attributed to preferential adsorption of the glucose in the brush.

Abstract: The transition to sustainable hydrogen and carbon economies is essential for addressing critical global issues such as climate change, resource depletion, and waste management.A vital strategy for low-carbon sustainability in the energy and chem. sectors is the chem. conversion of greenhouse gas into fuels and platform chems.Effective waste management, including waste-to-energy conversion and recycling, plays a crucial role in reducing emissions and promoting a circular economy.A key aspect of this transition is the development of innovative technologies that can transform waste into valuable resources while minimizing environmental impacts.Plasma-based recycling presents a promising solution, offering remarkable versatility for applications like waste upcycling and greenhouse gas conversion.These processes play a crucial role in advancing the development of sustainable carbon and hydrogen economies.