Unique Combination of Surface Energy and Lewis Acid-Base Characteristics of Superhydrophobic Cellulose Fibers

Comparison of Surface Properties of Sepiolite and Palygorskite: Surface Energy and Nanoroughness

The surface properties of two sepiolite samples and one palygorskite sample were compared using inverse gas chromatography (IGC). Samples were previously conditioned at appropriate temperatures for the removal of all zeolitic water. Dispersive (or Lifshitz–van der Waals) component of the surface energy (γ_s^d), specific interactions (−ΔG_a^s) with π electron donor bases (1-alkenes), and nanomorphology indices (IMχT) based on the injections of cycloalkanes and a branched alkane were measured. From IGC data, at 240 °C, it was found that the palygorskite was clearly distinguished from the sepiolites. The palygorskite possessed a lower γ_s^d, larger −ΔG_a^s with 1-alkenes, and remarkably higher IMχT. Slight differences could also be observed between the two sepiolite samples with the same origin. The results were rationalized in terms of the structural features of the two studied minerals. The larger channels of the sepiolite allow for a better insertion of the n-alkanes (longer retention times) while excluding the bulkier probes, such as cyclooctane or 2,2,4-trimethylpentane. Accordingly, the corresponding γ_s^d values were larger and the IMχT values were lower (higher surface nanoroughness) for the sepiolites. Regarding Lewis acid–base properties, all the sample’s surfaces evidenced a very strong amphoteric character. The present results highlight the potential of the evaluated samples for, e.g., adsorption processes with volatile organic compounds or matrix–filler interactions regarding the production of composite structures with Lewis acid–base matrices.

Effect of non-oxidative plasma treatments on the surface properties of poly(p-phenylene terephthalamide) (PPTA) and poly(p-phenylene benzobisoxazole) (PBO) fibres as measured by inverse gas chromatography

It has been shown in previous works that the interfacial adhesion in PPTA- and PBO-epoxy composites can be improved by modifying the surface properties of these high-performance fibres upon exposure to non-oxidative plasma treatments. In this work, the effects developed on both types of polymer surface were examined as a function of treatment gas nature (He or N₂) and exposure time (one or four minutes) using inverse gas chromatography at infinite dilution (IGC). From the adsorption of n-alkanes, it has been proved that non-oxidative plasma treatments led to energetically heterogeneous surfaces in the case of PPTA, and to low-energy surfaces in the case of PBO. Nevertheless, it was proved with the 1-min plasma treatments (either under helium or under nitrogen) that chemical reactivity was enhanced on the PBO surface. Such a behaviour was ascribed to the presence of low-molecular weight oxidized materials. The mechanisms involved in surface activation of PPTA were not equivalent under He or N₂ exposure. Nitrogen plasma exposure led to a PPTA surface that is chemically reactive as a result of polarity enhancement. Helium plasma-treated PPTA surface was characterized by the presence of branched arrangements that intensified the number of chemical contacts onto reactive sites. Finally, for both fibre sets, if the purpose is to enhance the chemical surface reactivity, it makes no sense to increase the plasma exposure time from 1 to 4 min.

Novel Low-Temperature Chemical Vapor Deposition of Hydrothermal Delignified Wood for Hydrophobic Property

As a hydrophilic material, wood is difficult to utilize for external applications due to the variable weather conditions. In this study, an efficient, facile, and low-cost method was developed to enhance the hydrophobicity of wood. By applying the low-temperature chemical vapor deposition (CVD) technology, the polydimethylsiloxane-coated wood (PDMS@wood) with hydrophobic surface was fabricated employing dichlorodimethylsilane as the CVD chemical resource. The result of water contact angle (i.e., 157.3°) revealed the hydrophobic behavior of the PDMS@wood. The microstructures of the wood samples were observed by scanning electron microscopy and energy dispersive X-ray spectroscopy (EDS) analysis verified PDMS successfully coated on wood surfaces. The chemical functional groups of the PDMS@wood were investigated by Fourier transform infrared (FT-IR) and Raman spectra. The thermogravimetric results indicated the enhanced thermal stability of the wood after PDMS coating. In addition, the stability test of PDMS@wood indicated that the hydrophobicity properties of the PDMS@wood samples were preserved after long-time storage (e.g., 30 days). The scratch test was carried out to examine the abrasion resistance of the hydrophobic coatings on PDMS@wood surface. It was suggested that low-temperature CVD process could be a successful approach for fabricating hydrophobic wood.

"Raincoat for explosives": Surface chemistry approach to control wetting of nitrocellulose with nitroglycerin

HYPOTHESIS

Wicking and percolation of a liquid in porous media is, among other factors, strongly affected by wettability of the pores. Nitrocellulose (NC) fibrous matrix impregnated with nitroglycerin (NG) is a main component of propellant formulations. Over time, NG, being a wetting liquid, leaks out from the matrix causing fires and explosions resulting from the storage. Here, we propose a chemical functionalization approach aimed at preparation of lyophobic coatings of NC to control wetting and to inhibit leakage of NG.

EXPERIMENTAL

NC was functionalized by a two-step process using the reaction of 3-(triethoxysilyl-propyl) isocyanate followed by reactions with either alkyl-, fluoroalkyl-, or phenyl-silane producing NC surfaces ranging in lyophobicity. The wettability of the NC pellets was characterized using water, hexadecane, and NG as probe fluids.

FINDINGS

FTIR and chemical analysis supported the covalent attachment of organosilanes to NC via robust carbamate and siloxane bonds. SEM and DSC of the modified NC materials suggested that the bulk properties of NC were not affected by the reactions with silanes. The contact angles of the modified NC changed over a wide range demonstrating surfaces with "tunable" wetting. NC grafted with fluoroalkyl-groups showed the most NG-repelling properties (θ_Adv/θ_Rec ∼ 90°/50°): NG beaded up and did not penetrate these surfaces.