The surface modification of cellulose fibres to create super-hydrophobic, oleophobic and self-cleaning properties

The surface modification of cellulose fibres was performed with the use of low-pressure water vapour plasma, followed by the application of a pad-dry-cure sol–gel coating with the water- and oil-repellent organic–inorganic hybrid precursor fluoroalkyl-functional siloxane (FAS), with the aim of creating the “lotus effect” on the cotton fabric surface. The tailored “lotus effect” was confirmed by measurements of the contact angle of water (154°) and n-hexadecane (140°), as well as by measurements of the water sliding angle (7°), which were used to identify the super-hydrophobic, oleophobic and self-cleaning properties of the modified fibres. The chemical and morphological changes caused by modifications of the fibres were investigated by XPS, FTIR, AFM and SEM. The results show that the plasma pre-treatment simultaneously increased the surface polarity, average roughness, and surface area of the fabric. The application of the FAS coating after plasma pre-treatment caused only a slight increase in the surface roughness, accompanied by a decrease in the surface area, indicating that the architecture of the surface was significantly changed. This result suggests that the surface pattern affected the “lotus effect” more than the average surface roughness. The plasma pre-treatment increased the effective concentration of the FAS network on the fabric, which resulted in enhanced repellency before and after repetitive washing, compared with that of the FAS-coated fabric sample without the plasma pre-treatment. Despite the fact that the plasma pre-treatment increased the concentration of the oxygen-containing functional groups on the fabric surface, this phenomenon insignificantly contributed to the adhesion ability and, consequently, the washing fastness of the FAS coating.     

Creating cellulose fibres with excellent UV protective properties using moist CF4 plasma and ZnO nanoparticles

Weakly ionised gaseous plasma created in a moist tetrafluoromethane gas at a low pressure with an electrodeless radiofrequency discharge was applied to modify the surface properties of cellulose fibres. The plasma was used to increase the adsorption of zinc oxide (ZnO) nanoparticles such that cellulose fibres with good ultraviolet (UV) protective properties could be created. The UV protection factor (UPF) values of the ZnO-functionalised fibres were determined as a function of the plasma treatment time. The chemical and physical surface properties of the plasma-treated fibres were examined using scanning electron microscopy, X-ray photoelectron spectroscopy, and wettability tests. The quantity of zinc on the fibres was determined using inductively coupled plasma mass spectroscopy. The results indicated that 30 s of plasma treatment resulted in ZnO-functionalised samples with lower UPF values than samples without plasma treatment due to the creation of fluorine-rich functional groups on cellulose fibres and the agglomeration of ZnO nanoparticles. The highest UPF values (50+) were obtained when samples were treated with plasma for 10 s. These high UPF values were a result of the increased adsorption of uniformly distributed ZnO nanoparticles caused by fibres surface functionalization and roughening upon plasma treatment. Furthermore, the mechanical properties of textiles treated with moist CF₄ plasma for 10 s were slightly improved.     

Oxygen plasma functionalization of poly(p-phenilene sulphide)

Surface effects during plasma activation of poly(p-phenilene sulphide)—PPS have been studied. Samples that were exposed to weakly ionized highly dissociated oxygen plasma created an inductively coupled radiofrequency discharge with the power of 100 W. The electron density and temperature were measured with a double Langmuir probe and were 4 × 10¹⁵ m⁻³ and 3 eV, respectively, while the neutral atom density was measured with a fiber optics catalytic probe and was 4 × 10²¹ m⁻³. The surface tension was determined by measuring the contact angle of deionized water, while the appearance of surface functional groups was detected by XPS. The surface tension of untreated PPS was 7 × 10⁻³ N/m or/and increased to 7 × 10⁻² N/m in few seconds of plasma treatment. It remained fairly constant for longer plasma treatments. The XPS survey spectrum showed little oxygen on untreated samples, but its concentration increased to about 20 at.% in few seconds. Detailed high resolution XPS C 1s peak showed that the carbon was left fairly stable during plasma treatment. The main functional groups formed were rather sulphate in sulphite groups, as determined from high resolution S 2p peak. Namely, a strong transition from sulphide to sulphate state of sulfur was observed. The spontaneous deactivation of the polymer surface was measured as well. The deactivation was fairly logarithmic with the characteristic decay time of several hours.     

Synthesis and preliminary biological evaluation of 5-fluoro-5,8-dideazaisoaminopterin

The new folate antagonist, 5-fluoro-5,8-dideazaisoaminopterin was synthesized in four steps beginning with 2,4-diamino-5-fluoroquinazoline. It was found to be a potent inhibitor of human dihydrofolate reductase. Against L1210 leukemia in mice, 5-fluoro-5,8-dideazaisoaminopterin was equiactive with methotrexate at approximately one half of the total dose employed.     

Wettability and surface composition of partly and fully regenerated cellulose thin films from trimethylsilyl cellulose

The wettability and surface free energy (SFE) of partly and fully regenerated cellulose model surfaces from spin coated trimethylsilyl cellulose were determined by static contact angle (SCA) measurements. In order to gain detailed insight into the desilylation reaction of the surfaces the results from SCA measurements were compared with data from other surface analytical methods, namely thickness measurements, X-ray photoelectron spectroscopy (XPS) and attenuated total reflectance infrared spectroscopy (ATR-IR). Additionally, the influence of ultra high vacuum treatment (UHV) during XPS measurements on the water wettability and surface morphology of regenerated cellulose thin films was investigated. The wetting of polar and non-polar liquids increased with prolonged regeneration time, which is reflected in the higher SFE values and polarities of the films. After UHV treatment the water SCA of partly regenerated films decreases, whereas fully regenerated cellulose shows a higher water SCA. Therefore it is assumed that volatile desilylation products tend to adsorb on partly regenerated films, which strongly influences their wettability.     

Effect of field direction on electrowetting in a nanopore

We manifest a significant influence of field direction and polarity on surface wetting, when the latter is tuned by application of an external electric field. Thermodynamics of field-induced filling of hydrocarbon-like nanopores with water is studied by open ensemble molecular simulation. Increased field strength consistently results in water-filling and electrostriction in hydrophobic nanopores. A threshold field commensurate with surface charge density of about one elementary charge per 10 nm2 suffices to render prototypical paraffin surfaces hydrophilic. When a field is applied in the direction perpendicular to the confining walls, the competition between orientational polarization and angle preferences of interfacial water molecules relative to the walls results in an asymmetric wettability of opposing surfaces (Janus interface). Reduction of surface free energy observed upon alignment of confinement walls with field direction suggests a novel mechanism whereby the applied electric field can operate selectively on water-filled nanotubes while empty ones remain unaffected.     

Synthesis of some novel halogenated 2,4-diaminoquinazolines

Three new 2,4-diaminoquinazolines, the 5,6-difluoro, 6,7-difluoro and 7,8-difluoro isomers were prepared by the reaction of the requisite trifluorobenzonitrile and guanidine carbonate. Surprisingly, 2,3,6-trifluorobenzonitriles gave 2,4-diamino-5,6-difluoroquinazoline exclusively as determined by high resolution nuclear magnetic resonance spectroscopy. On the other hand, 3-amino-2,6-difluorobenzonitrile on reaction with guanidine carbonate yielded only 5-fluoro-2,4,8-triaminoquinazoline. This compound was subsequently converted to 8-chloro-2,4-diamino-5-fluoroquinazoline using the Sandmeyer procedure. The nitration of 2,4-diamino-8-fluoroquinazoline occurred exclusively at position six yielding 2,4-diamino-8-fluoro-6-nitroquinazoline, which upon reduction with stannous chloride afforded 8-fluoro-2,4,6-triaminoquinazoline. In a similar fashion 7-fluoro-2,4-diaminoquinazoline underwent nitration at position six and was then reduced to give 7-fluoro-2,4,6-triaminoquinazoline. Finally, both of these triaminoquinazolines were converted to the 6-chloro derivatives under Sandmeyer conditions to yield 6-chloro-2,4-diamino-8-fluoroquinazoline and 6-chloro-2,4-diamino-7-fluoroquinazoline, respectively.     

Dynamics of capillary drying in water

We use atomistic simulations to address the question when capillary evaporation of water confined in a hydrocarbonlike slit is kinetically viable. Activation barriers and absolute rates of evaporation are estimated using open ensemble Monte Carlo-umbrella sampling and molecular dynamics simulations. At ambient conditions, the evaporation rate in a water film four molecular diameters thick is found to be of the order 10(5)(nm(2) s)(-1), meaning that water readily evaporates. Films more than a few nanometers thick will persist in a metastable liquid state. Dissolved atmospheric gas molecules do not significantly decrease the activation barrier.     

Synthesis and structure of [Rh4(CO)5(μ-PPh2)5]−, a completely phosphide bridged tetrarhodium cluster

The synthesis, ^pre31P {^pre1H} NMR spectrum, and structure of the first completely phosphide bridged rhodium cluster is described. This novel complex has an arachno (or “butterfly”) structure, with a dihedral angle of 124°, and contains only PPh₂^? groups as bridging ligands.