The interaction between surfaces displaying end-grafted hydrophilic polymer brushes plays important roles in biology and in many wet-technological applications. In this context, the conformation of the brushes upon their mutual approach is crucial, because it affects interaction forces and the brushes' shear-tribological properties. While this aspect has been addressed by theory, experimental data on polymer conformations under confinement are difficult to obtain. Here, we study interacting planar brushes of hydrophilic polymers with defined length and grafting density. Via ellipsometry and neutron reflectometry we obtain pressure-distance curves and determine distance-dependent polymer conformations in terms of brush compression and reciprocative interpenetration. While the pressure-distance curves are satisfactorily described by the Alexander-de-Gennes model, the pronounced brush interpenetration as seen by neutron reflectometry motivates detailed simulation-based studies capable of treating brush interpenetration on a quantitative level.
Here, the development
of highly porous colorimetric indicators
that are able to rapidly sense the presence of amine vapors is presented.
Specifically, porous, curcumin-loaded polycaprolactone fibers are
formed by electrospinning through non-solvent-induced phase separation.
In comparison to the non-porous fibers, the developed system shows
significantly higher sensitivity and responsivity to the presence
of dimethylamine vapors, with a distinct color change at very low
vapor concentrations (2.33 ppm compared to 9.26 ppm) within the first
5 s of exposure. Indeed, CIELAB analysis proves that the induced color
changes can be easily perceived visually, as the differences between
the initial and the final color of the indicator after its interaction
with the modified environment are well above the limit for visual
perception, even by inexperienced users. Furthermore, the color changes
are reversible, enabling the use of the same indicator several times,
making it, thus, a sustainable colorimetric indicator system that
can be used in applications where the rapid detection of low concentration
of alkaline vapors is necessary.
The effects of salt impregnation are studied within wood cell walls, occurring upon soaking from concentrated salt solutions. Osmotic deswelling is in some cases followed by ion specific swelling linked to Hofmeister effects. Taking into account microstructure, this study models the free energy changes associated with the ions and water uptake at molecular, colloidal, and macroscopic mechanical scales, to show that slow swelling until osmotic equilibrium originates from charge separation of the salt diffused into wood cell wall material. Kinetic effects as well as mechanical effects linked to transfer of species and swelling of the interstitial matrix between cellulose crystals are discussed. Predictions by minimal models taking into account nonelectrostatic ion complexation allow to estimate the order of magnitude of the nonelectrostatic binding free energy of adsorbed chaotropic anions and complexed divalent cations to be 8 and 10 kJ mole–1, respectively
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