The adsorption of non‐ionic polysaccharide guar gum (GG) in the presence of surfactants (anionic SDS, non‐ionic TX‐100, cationic CTAB and their equimolar mixtures) from their NaCl solutions onto an alumina surface (Al2O3) was studied spectrophotometrically. This study is important in light of the many disagreements concerning the structure and behaviour of mixtures containing polymers and surfactants at the surface of an adsorbent. The presence of surfactant caused an increase in the GG adsorption in all studied systems as a consequence of the formation of complexes. Among the single surfactants the highest increase in the GG adsorption was observed in the presence of CTAB. However, the usage of mixtures of the surfactants caused a much more effective increase in the GG adsorption on the alumina surface because of the synergistic effect of the surfactants. In order to get some information on the structure of the electrical double layer (edl), the surface charge density of alumina was determined and zeta potential measurements were conducted. The obtained data showed that the adsorption of GG or GG/surfactant complexes on the metal oxide surface strongly influences a diffused part of the edl, whereas a compact part of the edl is not affected. The colloidal stability of the alumina suspensions was measured in the presence and absence of GG and surfactants. It was found that GG and the mixtures of GG and surfactants can improve the stability of the suspensions. 相似文献
Corrosion inhibition of three new synthesized cationic surfactants, N‐(2‐(((Z)‐4‐(pyridin‐4‐yl)but‐3‐en‐1‐yl)amino)ethyl)‐N‐(2‐((E)‐(pyridin‐4‐ylmethylene)amino)ethyl)dodecan‐1‐aminium bromide I(4N), N1,N2‐didodecyl‐N1‐((Z)‐4‐(pyridin‐4‐yl)but‐3‐en‐1‐yl)‐N2‐(2‐((E)‐(pyridin‐4‐ylmethylene)amino)ethyl)ethane‐1,2‐diaminium bromide II(4N) and 1‐dodecyl‐4‐((E)‐((2‐(dodecyl(2‐(dodecyl((Z)‐4‐(1‐dodecylpyridin‐1‐ium‐4‐yl)but‐3‐en‐1‐yl)ammonio)ethyl)ammonio)ethyl)imino)methyl)pyridin‐1‐ium bromide IV(4N) on carbon steel was investigated by weight loss, electrochemical impedance spectroscopy and polarization measurements. Results show that the synthesized cationic surfactants inhibit corrosion of carbon steel in 1 M HCl. The inhibitive action occurs by virtue of adsorption on the metal surface following a Langmuir adsorption isotherm model. Polarization curves reveal that the investigated cationic surfactants can be classified as mixed inhibitor types. The variations in the corrosion inhibition efficiency between three cationic surfactants are correlated with their chemical structures, with more hydrophobic surfactants yielding higher inhibition efficiency. 相似文献
Surface properties of polyvinyl alcohol (nonionic polymer) and three synthesized cationic surfactants, namely, S‐alkyl isothiouronium bromide at different mole fractions of 1:9, 3:7, 5:5, 7:3, and 9:1, were investigated. The values of the surface parameters were discussed according to the type of interaction between the cationic surfactant and type of polymer studied. The S‐alkyl isothiouronium bromide surfactant molecules are positively charged molecules, and the PVA chains contain hydroxyl groups that are partially negatively charged centers. The comparison between the surface properties of the individual cationic surfactants and their mixture with PVA polymer showed that the mixed systems have some advantages over the individual cationic surfactants. 相似文献
Various occurrences in machining influence the machining dynamics and thus produce vibration in the cutting tool-workpiece arrangement. In this investigation, with tri-axial accelerometer mounted on the tool-holder in turning ASSAB-705 steel, vibration signals have been captured with and without cutting. The nature of vibrations arising in the cutting tool at different cutting conditions has been investigated. It has been observed that the RMS amplitude of vibration along all three axes for the increasing cutting speed was mixed in nature; however, an increasing trend was noticed in the vibrations along the feed, Vx and radial, Vy directions. The vibration along the main cutting direction, Vz was mixed, initiated by large vibration and then decreased until a particular cutting speed was reached and finally increased steadily. The feed vibration component, Vx has a similar response to the change of the workpiece surface roughness, while the other two components, Vy and Vz have the more coherent response to the rate of flank wear progression throughout the tool life. The natural frequency of different machine parts vibration has been found to be within the band of 0 Hz – 4.2 kHz, whereas the frequencies of different occurrences in turning varied between 98 Hz and 42 kHz. 相似文献
Site‐selectivity, differentiating members of the same functional group type on one substrate, is an emerging tactic for shortened advanced building block and biomolecule synthesis. Despite its potential, site‐selectivity remains less studied and especially so for ketone‐based substrates. During this work ketone site‐selectivity has been coupled with the chiral amine‐catalyzed aldol desymmetrization of 4‐keto‐substituted cyclohexanones, allowing three stereogenic centers to form in the aldol product while leaving the acyclic ketone unreacted. Unique here, compared to all previous 4‐substituted cyclohexanone desymmetrizations, is the first access to synthetically useful quantities of an epimeric (remote stereogenic center) aldol product. To demonstrate the value of these aldol products, we show their elaboration into eight keto‐acetonide and one keto‐lactone products. All compounds were isolated as single diastereomers and in high ee (≥96%). These efforts represent the first full characterization of aldol products with type III, Figure 2, relative stereochemistry, regardless of the enantiomer formed.