Interactions between charged and neutral self-assembled phospholipid membranes are well understood and take into account temperature dependence. Yet, the manner in which the structure of the membrane is affected by temperature was hardly studied. Here we study the effect of temperature on the thickness, area per lipid, and volume per lipid of charged membranes. Two types of membranes were studied: membranes composed of charged lipids and dipolar (neutral) membranes that adsorbed divalent cations and became charged. Small-angle X-ray scattering data demonstrate that the thickness of charged membranes decreases with temperature. Wide-angle X-ray scattering data show that the area per headgroup increases with temperature. Intrinsically charged membranes linearly thin with temperature, whereas neutral membranes that adsorb divalent ions and become charged show an exponential decrease of their thickness. The data indicate that, on average, the tails shorten as the temperature rises. We attribute this behavior to higher lipid tail entropy and to the weaker electrostatic screening of the charged headgroups, by their counterions, at elevated temperatures. The latter effect leads to stronger electrostatic repulsion between the charged headgroups that increases the area per headgroup and decreases the bilayer thickness.
A technically
simple, one-step process for the preparation of hydrophobic
cellulose-based fabrics via covalent surface modification is presented.
A small aliphatic molecule was grafted onto the surface of various
types of fabrics under mild processing conditions (room temperature,
few seconds), leading to alteration of the surface properties. The
modified fabrics displayed not only hydrophobic but also superoleophilic
properties, meaning that these fabrics are ideal candidates for separation
of oil–water mixtures. Separation efficiencies above 93% were
achieved for the removal of common organic solvents and oils from
aqueous solutions. In addition, separation efficiencies were unaffected
by the exposure of the modified fabrics to elevated temperature and
acidic conditions. Furthermore, all types of fabrics displayed high
recyclability: oil–water separation efficiency did not deteriorate
even after 30 separation cycles. The simplicity of the surface modification
combined with the use of readily available and low-cost materials
are promising characteristics for future practical applications.
A modular method for functionalization of nonwoven fabrics was developed using a two-step process. In the first step, the fabrics were grafted with a linker molecule, 10-undecenoyl chloride, via esterification, followed by attachment of a functional material under UV irradiation. Perfluorodecanethiol and 3-mercaptopropionic acid (MPA) were connected to the linker-modified fabrics using thiol-ene click chemistry. Perfluorodecanethiol modified fabrics exhibited hydrophobicity with water contact angle of about 140 while MPAmodified fabrics were able to lower the pH of a solution by about 1.6. We additionally demonstrated the possibility to connect functional polymers to the linker-modified fabrics by radical graft polymerization of acrylic acid; this produced a thin layer of the polymer on the surface of the fabric. Fabrics modified with poly(acrylic acid) exhibited increased hydrophilicity with water contact angle of 0 for both cotton and viscose-polyester fabrics, while the water absorption capability for polypropylene fabrics increased from about 50 to 1200%.
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