Increasing Hydrocarbon Chain Length Research Articles

Viscosity effects on the dynamics of diols and diol-based deep eutectic solvents.

Diols, characterized by the presence of two hydroxyl groups, form extended hydrogen-bonded networks. Increasing hydrocarbon chain length is known to elevate the viscosity of diols. Given the established influence of viscosity on solvent dynamics, it becomes imperative to comprehend the impact of viscosity on the fluctuation dynamics within diols and establish connections with hydrogen bond formation and breaking dynamics. In this study, we employ two-dimensional infrared spectroscopy to investigate the viscosity dependence of the structural evolution dynamics in three diols with varying chain lengths. Complementing our experimental approach, molecular dynamics simulations are conducted to extract hydrogen bond lifetimes. Our findings reveal a linear correlation between bulk viscosity, solvent fluctuation timescales, and hydrogen bond lifetimes. Notably, the selected diols exhibit the capability to form deep eutectic solvents upon mixing with choline chloride at specific molar ratios. In contrast to molecular solvents like diols, deep eutectic solvents are characterized by the formation of heterogeneous nanodomains, comprising various intercomponent hydrogen-bonded networks. Interestingly, our observations indicate that while the fluctuation dynamics decelerate with increasing bulk viscosity in diol-based deep eutectic solvents, the relationship between viscosity and dynamics is not linear, in contrast to the observed linearity in diols. This nuanced understanding contributes to the broader comprehension of the interplay between viscosity and dynamics in both molecular and deep eutectic solvents.

THERMODYNAMICS OF LIQUID–GAS PHASE EQUILIBRIA OF DIISOPROPYLSULFOXIDE–WATER SYSTEM

The saturated vapor pressure of diisopropylsulfoxide aqueous solutions was measered at temperatures of 303.15 K and 308.15 K. It was shown that the total saturated vapor pressure increases with decreasing diisopropylsulfoxide concentration in the solution and with increasing temperature. As in the cases of diethylsulfoxide and dipropylsulfoxide aqueous solutions, a negative deviation from Raoult’s law is also observed. This confirms the ability of diisopropylsulfoxide molecules to associate with water molecules. Based on the results obtained, the partial pressures, the activity coefficients of diisopropylsulfoxide and water and the excess Gibbs energy of their mixing, were calculated. It is shown that the excess Gibbs energy of mixing is negative and reaches its minimum value at a mole fraction of diisopropylsulfoxide equal to 0.38. The obtained data on the excess Gibbs energy of mixing DiPSO and water were treated using the Redlich–Kister equation. It has been established that the interaction between the molecules of diisopropylsulfoxide and water is stronger than in the diethylsulfoxide+water system, and weaker than in the dipropylsulf-oxide+water system. This fact can be explained by an increase in the electron-donating ability of the alkyl group with increasing hydrocarbon chain length, which increases the reactivity of the oxygen atom of the sulfoxide group. As a result, when moving from diethylsulfoxide to diisopropylsulfoxide or dipropylsulfoxide, the ability of their molecules to interact with water molecules to form hydrogen bonds increases. At the same time, a decrease in hydrophobic effects and dispersion forces between diisopropylsulfoxide molecules with a branched hydrocarbon chain leads to a weakening of the interaction between molecules in the diisopropylsulfoxide+water system compared to the dipropylsulfoxide+water system, which is also observed experimentally.

ACID-BASE PROPERTIES OF ALKYLENE­DIAMINETETRA (METHYLENEPHOSPHONIC) ACIDS

The acid-base characteristics of ethylenediaminetetra(methylenephosphonic) (edtmp), tetramethylenediaminetetra(methylenephosphonic) (tetdtmp) and pentamethylenediaminetetra(methylenephosphonic) (pendtmp) acids were investigated by means of pH-potentiometry and 31P NMR spectroscopy. Calculated and estimated values of acid dissociation constants (pK) for edtmp (рК1<2, рК2<2, рК3=3.07, рК4=5.17, рК5=6.52, рК6=7.97, рК7=9.65, рК8=10.94), for tetdtmp (рК1<2, рК2=4.48, рК3=5.34, рК4=6.13, рК5=6.66, рК6=10.08, рК7~11.4, рК8~11.5) and for pendtmp (рК1<2, рК2=4.22, рК3=5.56, рК4=6.16, рК5=7.66, рК6=10.99, рК7~11.5, рК8~11.6) were obtained. The values of the acid dissociation constants indicate a decrease in the acidity of phosphonic groups and an increase in the basicity of amino groups with increasing hydrocarbon chain length between the two nitrogen atoms in the edtmp, tetdtmp, and pendtmpseries. Based on the values of the calculated constants for the formation of anions of tetra­phosphonic acids, diagrams of the distribution of their equilibrium concentrations depending on pH were constructed, which indicate the state of acid-base equilibrium, the charge and the ratio of concentrations between anions with different degrees of protonation at certain pH values.
 According to the data of 31P NMR spectro­scopy, the formation of intramolecular hydrogen bonds between the deprotonated oxygen atoms of one amino(methylphosphonic) group with protonated nitrogen atom of another amino(methylphosphonic) group was established in the case of edtmp. In the case of pendtmp and tetdtmp, the formation of intermolecular hydrogen bonds between distant amino(me­thyl­phosphonic) groups is impossible due to the presence of steric hindrances.

The effect and enhancement mechanism of hydrophobic interaction and electrostatic interaction on zwitterionic wormlike micelles

The effects of hydrophobic interaction and electrostatic interaction on the structure of zwitterionic wormlike micelles (WLMs) were studied. The change of the hydrocarbon chain length and addition of cetyl trimethyl ammonium chloride (CTAC) were employed to explore the effect of hydrophobic interaction and electrostatic interaction on the wormlike micelles constructed by zwitterionic viscoelastic surfactants and sodium p-toluene sulfonate (NaPts). The experimental results show that increasing hydrocarbon chain length of zwitterionic surfactant and the addition of CTAC can increase the viscoelasticity and zero-shear viscosity of the system. The calculated length of wormlike micelles also increases. This shows that the enhancement of hydrophobic interaction and electrostatic interaction can promote the growth and entanglement of wormlike micelles. In addition, scanning electron microscope (SEM) images confirmed that CTAC makes the connection between the zwitterionic micellar layer closer. This is undoubtedly beneficial to the growth of micellar structure. Finally, this work explores the enhancement mechanism of the hydrophobic interaction and electrostatic interaction on the micelle structure.

Micellization and thermodynamics study of n-alkyl-4-methylpyridinium bromides in water and mixed water–ethanol media

The micellization behaviors of n-decyl-4-methylpyridinium bromide, n-dodecyl-4-methylpyridinium bromide, and n-tetradecyl-4-methylpyridinium bromide were studied in water and mixed water–ethanol media by using conductivity measurements over the temperature range of 293.15–318.15 K. The critical micelle concentrations (CMC) of all n-alkyl-4-methyl pyridinium bromides studied increased with increasing temperature, but they decreased with increasing hydrocarbon chain length. Their CMC values of n-decyl-4-methylpyridinium bromide, n-dodecyl-4-methylpyridinium bromide, and n-tetradecyl-4-methylpyridinium bromide in water at the temperature range of 293.15–318.15 K were determined as in the range of 43.62–46.42, 10.45–11.57, and 2.78–3.20 mM, respectively. Moreover, the lowest CMC values of n-decyl-4-methylpyridinium bromide, n-dodecyl-4-methylpyridinium bromide, and n-tetradecyl-4-methylpyridinium bromide were found with 15, 5, and 5 vol% ethanol additions, respectively. The calculated negative ΔGm0 and ΔHm0 values proved that their micellizations in water and mixed water–ethanol media were spontaneous and exothermic. Also, ΔGm0 values became the more negative with the longer the hydrocarbon chain length. Furthermore, their micellization processes in water were determined to be entropy controlled, however enthalpic contributions in the mixed water–ethanol systems started to predominate with increasing ethanol concentrations and/or temperature.

Electrophoretic Deposition of Nanoporous Oxide Coatings from Concentrated CuO Nanoparticle Dispersions.

Electrophoretic deposition (EPD) of nanoporous oxide coatings is an interesting research avenue owing to the experimental simplicity and broad scope of applications and materials. In this study, the properties of concentrated (up to 5000 mg/L), nonaqueous CuO nanoparticle (NP) dispersions were tailored to produce micrometer-thick, nanoporous CuO films by EPD. In particular, we performed a systematic investigation of the electrophoretic mobilities and size distributions of dispersed CuO aggregates and developing agglomerates in different organic solvents for concentrations ranging from 50 to 5000 mg/L with and without surfactant addition. Time-resolved dynamic light scattering analyses showed that aggregate mobilities and agglomeration rates decrease with increasing hydrocarbon chain length of the organic solvent (from ethanol to hexanol) and thus with increasing viscosity. The highest electrophoretic mobility was obtained for CuO NP aggregates and agglomerates dispersed in ethanol as a solvent. However, the addition of ≥0.5 wt % acetylacetone as a surfactant is required to stabilize these dispersions for subsequent EPD and at the same time introduce a net attractive (electrostatic) interaction between neighboring agglomerates on the substrate to promote layer formation during the EPD step. The produced micrometer-thick nanoporous CuO coatings can serve as high surface area nanostructured materials or nanoporous scaffolds in catalysis, combustion, propellants, and nanojoining.

Aggregation behavior and reactivity of N-alkyl-N,N-dimethyl-N-(2,3-epoxy propyl) ammonium chloride

A series of epoxy-functionalized quaternary ammonium surfactants consisting of different alkyl chains (C10–C18) were synthesized. Their aggregation behaviors in aqueous solution, as well as antibacterial activity and reactivity were investigated. The cmc, γcmc, πcmc, pc20 and cmc/c20 suggested that the presence of epoxy group increased the surface activity of ADEAC. This is ascribed to the hydrogen bonding effect between the adjacent hydrophilic groups. The surface activity increased with the increase of hydrocarbon chain length. The thermodynamic parameters indicated that the micellization process was entropy-driven at high temperature, and enthalpy-driven at low temperature. The activation energy of conductance and micelle aggregation number were also calculated. The antibacterial activity of ADEAC against Gram-negative bacteria was stronger than that for Gram-positive ones, and N-dodecyl-N,N-dimethyl-N-(1,2-epoxy propyl) ammonium chloride showed the most effective antibacterial activity. The synthesis of N-hexadecyl-N,N-dimethyl-N-(1,2-epoxy propyl) ammonium chloride (HDEAC) modified chitosan demonstrated the reactivity of HDEAC.

Aggregation behavior and adsorption properties of salt-free catanionic surfactant mixtures containing tetradecyltrimethyl ammonium salts

ABSTRACTThe aggregation behavior of salt-free catanionic surfactants, tetradecyltrimethyl ammonium hydroxide (TTAOH)/fatty acid (FA) including octanoic acid (OA), decylic acid (DA) and lauric acid (LA) in aqueous solutions were studied. The critical micelle concentration(cmc), surface tension at cmc (γcmc), surface excess (Гmax), mean molecular surface area (Amin), adsorption efficiency (pc20) and surface tension reduction effectiveness (πcmc) were obtained from surface tension isotherms. The influence of temperature on the surface tension of salt-free TTAOH/FA (TTAOF) systems was investigated. Data of adsorption dynamics indicated that at fixed adsorption time, the order of adsorption capacity was TTAOH < TTAOH/OA (TTAOO) < TTAOH/DA (TTAOD) < TTAOH/LA (TTAOL). The adsorption process of salt-free TTAOF was adsorption-controlled. The complex and storage moduli increased with increasing oscillation frequency, however, the loss modulus showed the opposite trend. The complex modulus passed through a maximum value with increasing concentration of salt-free surfactant TTAOF. The adsorbed TTAOF layer was elastic, and the elasticity increased with increasing hydrocarbon chain length of FA.

Mechanism study of selected phenolic compounds determination using β-cyclodextrin-coated CdSe/ZnS quantum dots

β-Cyclodextrin (βCD)-coated CdSe/ZnS quantum dots (QDs), provide a sensitive method for the determination of phenolic compounds. The current study aimed to explain the mechanisms involved in photoluminescence quenching of CdSe/ZnS QDs, during the determination of quercetin and gallic acid, and select derivatives thereof. Quercetin, quercetin glycosides, gallic acid and gallate esters, were investigated to understand how the glycoside moiety in glycosides and the hydrocarbon chain in esters, affect the interactions of the investigated polyphenols with βCD-coated QDs. The phenomenon of βCD-coated CdSe/ZnS photoluminescence quenching, is caused by the effective formation of host-guest inclusion complexes between polyphenols and βCD. The presence of the glycoside moiety in the quercetin molecule reduced the effectiveness of the complex formation, while, in contrast, the efficiency of complexation increased with increasing hydrocarbon chain length of the gallate ester molecule. QD photoluminescence quenching may be a consequence of the proximity between the interacting phenolic compounds with the QD surface, rather than βCDs peeling off from the QD surface, resulting in structural destabilization. From the thermodynamic parameters, it was concluded that the formation of the complexes is based both on the van der Waals interactions forces and hydrophobic interactions between guest and host molecules. Ionic interactions may also play an important role in the effectiveness of polyphenol-βCD inclusion complex formation. In order to obtain QDs with long-term stability, there is a need to increase the zeta potential value of the QD surface. Recognition of the above-described mechanisms, should enable the optimization of existing methods and the development of new applications of βCD-coated CdSe/ZnS QDs, such as determination of octyl gallate in foodstuffs.

Efficient Mechanochemical Synthesis of MOF-5 for Linear Alkanes Adsorption

An efficient mechanochemical method was proposed to synthesize MOF-5 with high BET area within minutes. The effects of parameters such as solvents activation, the metal/ligand ratio, grinding speed and time were carefully studied and the optimized MOF-5-B was used to investigate its adsorption properties of linear alkanes (C1–nC7). The results showed that solvents activation played an important role in the formation of MOF-5. Besides, the Zn2+/BDC ratio had a great impact on the formation of crystalline MOF-5, and the appropriate Zn2+/BDC ratio was 3:1 for mechanochemical synthesis of MOF-5. Grinding for 60 min could lead to a better crystallinity and the highest surface area of MOF-5-B. The resulting MOF-5-B possessed BET area of 3465.9 m2·g–1. More importantly, MOF-5-B showed a preferential adsorption for long alkanes over short alkanes at low pressures. The saturated adsorption capacities of nC4–nC7 decreased with the increase of hydrocarbon chain length. The isosteric heats of C1–nC7 increased with th...

Synthesis and properties of biodegradable cationic gemini surfactants with diester and flexible spacers

A series of cationic gemini surfactants with diester and flexible spacers, namely C12-PG-C12, C14-PG-C14 and C16-PG-C16, were synthesized, purified and characterized. The surface properties and aggregation behavior of the gemini surfactants were investigated by surface tension, electrical conductivity, fluorescence and Krafft point. These gemini surfactants possess higher surface activity than the traditional monomeric surfactants. The thermodynamic parameters exhibited that the micellization was a spontaneous and exothermic process in environment. The micellization process became less favorable with the decrease of alkyl chain length and the increase of temperature. Steady-state fluorescence measurements revealed that the micropolarity and aggregation number of micelles decreased with the increase of hydrocarbon chain length. The Krafft points were taken as <0°C, which indicated the synthesized gemini surfactants had good water solubility. The biodegradability of the gemini surfactants were evaluated in river water using Closed Bottle tested and showed their high biodegradation ratio in the open environment due to the diester bond inserting in the flexible spacer of surfactant molecules.

Exhaustive and stable electromembrane extraction of acidic drugs from human plasma

The first part of the current work systematically described the screening of different types of organic solvents as the supported liquid membrane (SLM) for electromembrane extraction (EME) of acidic drugs, including different alcohols, ketones, and ethers. Seven acidic drugs with a wide logP range (1.01–4.39) were selected as model substances. For the first time, the EME recovery of acidic drugs and system-current across the SLM with each organic solvent as SLM were investigated and correlated to relevant solvent properties such as viscosity and Kamlet and Taft solvatochromic parameters. Solvents with high hydrogen bonding acidity (α) and dipolarity–polarizability (π*) were found to be successful SLMs, and 1-heptanol was the most efficient candidate, which provided EME recovery in the range of 94–110%. Both hydrogen bonding interactions, dipole–dipole interactions, and hydrophobic interactions were involved in stabilizing the deprotonated acidic analytes (with high hydrogen bonding basicity and high dipole moment) during mass transfer across the SLM. The efficiency of the extraction normally decreased with increasing hydrocarbon chain length of the SLM, which was mainly due to increasing viscosity and decreasing α and π* values. The system-current during EME was found to be dependent on the type and the volume of the SLM. In contact with human plasma, an SLM of pure 1-heptanol was unstable, and to improve stability, 1-heptanol was mixed with 2-nitrophenyl octyl ether (NPOE). With this SLM, exhaustive EME was performed from diluted human plasma, and the recoveries of five out of seven analytes were over 91% after 10min EME. This approach was evaluated using HPLC-UV, and the evaluation data were found to be satisfactory.

Optimization Efficiency of Nano Emulsion Surfactants as Base Oil Antioxidants and Anti-wear Additives

N-hexadecyl-N-benzyl-N-methylglycine and N-Dodecyl-N-benzyl-N-methylglycine were studied as antioxidants and anti wear. The physico-chemical properties were investigated; the adsorption behavior of these compounds at oil interface was investigated by measuring the surface tension and interfacial tension as function of concentration. Surface properties, in particular the critical micelle, the maximum surface excess and the minimum surface area were measured. It is found that the surface and thermodynamic properties of the prepared surfactants depend on their chemical structure. Also it is found that there is a good relation between surface properties of the additive and their efficiency as antioxidants. The mechanism of the antioxidation action has been suggested according to the surface properties of each additive. Adsorption of the additive on the surface interface inhibits their free radicals trapped in micelle core. These compounds were added to oil in different concentrations. The antioxidants activities of different dosages were evaluated. The oxidation of the oil has been carried out for different time intervals. The degradation of the oil has been monitored by total acid formation. The anti wear characteristic of surfactants increase with increasing hydrocarbon chain length. This is due to the increase in chemisorptions of surfactants on the silicon carbide surface. These films provide lower wear and depend on amount Original Research Article Mehbad et al.; IRJPAC, 6(3): 128-134, 2015; Article no.IRJPAC.2015.041 129 of surfactants concentration adsorbed on silicon carbide and sliding speed. These studies have led to determine the effect of adsorbed surfactants in dispersion of nano particles of silicon carbide in oil phase. The anti wear characteristic of surfactants increase with increasing dispersed silicon carbide. These studies have led to much clear evidence of the intimate relationship between the chemical structure of the surfactants and dispersed silicon carbide.

Synthesis, surface activity and aggregation behavior of Gemini imidazolium surfactants 1,3-bis(3-alkylimidazolium-1-yl) propane bromide

Abstract A novel class of Gemini imidazolium surfactants 1,3-bis(3-alkylimidazolium-1-yl) propane bromide [C n -3-C n im]Br 2 ( n = 8, 10, 12) were synthesized and characterized by FT-IR, 1 H NMR and elemental analysis. The surface activity and aggregation behavior of [C n -3-C n im]Br 2 ( n = 8, 10, 12) were investigated by surface tension, conductivity and steady fluorescence methods. A series of surface active parameters, including cmc, Γ max , p C 20 , cmc/ C 20 , A min , γ cmc and Π cmc were obtained from surface tension measurement. It was indicated that Gemini imidazolium surfactants with the longer alkyl chain showed the higher surface activity. The thermodynamic parameters of micellization process, namely, standard Gibbs free energy (Δ G m ο ), enthalpy (Δ H m ο ) and entropy (Δ S m ο ) were derived from conductivity measurement at different temperatures. The micropolarity and the mean aggregation number ( N agg ) of micelles were evaluated from steady fluorescence spectra. The results revealed that the micropolarity and N agg of micelles decreased with the increase of hydrocarbon chain length.

Micellar Effects upon the Alkaline Hydrolysis of Acetaminophen Prodrugs: Carboxylic and Carbonic Acid Esters

The rates of alkaline hydrolysis for four carboxylate esters (4-acetaminophenyl acetate, 4-acetaminophenyl butyrate, 4-acetaminophenyl heptanoate and 4-acetaminophenyl benzoate) and three carbonate ester (4-acetaminophenyl methylcarbonate, 4-acetaminophenyl ethylcarbonates and 4-acetaminophenyl propylcarbonates) prodrugs of acetaminophen derivatives were determined in aqueous and micellar media. The cationic micelles of cetyltrimethylammonium bromide (CTABr) and cetyltrimethylammonium sulfate [(CTA)2SO4] catalyzed the rate of the reaction. The anionic sodium dodecyl sulphate (SDS) and non-ionic Brij-35 surfactants inhibited the rate of the reaction. Added salt did not influence the rate of the reaction in the aqueous medium but decreased the values of observed rate constant in the micellar media. The rate enhancement in cationic micelles was treated by applying the pseudophase ion exchange model while the inhibition effect on the rate of hydrolysis was described using the Poisson–Boltzman pseudophase model. The binding constant (K s ) for the acetaminophen derivatives increased with increasing hydrocarbon chain length while the values of micellar rate constant (k m ) decreased with the increase in chain length. The increase in values of K s and decrease in k m are ascribed to the hydrophobic interaction between the acetaminophen derivative and surfactant molecule and molecular orientation of the substrate in the micelles.

Dilational Rheological Properties of P-(n-alkyl)-benzyl Polyoxyethylene Ether Carboxybetaine at Water–Decane Interface

The dilational rheological behaviors of absorbed films of p-(n-alkyl)-benzyl polyoxyethylene ether carboxybetaine CxBE2CB (x = 8, 10, 12) at the water–decane interface have been investigated by the drop-shape analysis method. The influences of time, oscillation frequency, and bulk concentration on dilational modulus and phase angle have been expounded. The experimental results show that the phase angle of CxBE2CB (x = 10, 12) decreases with the increase of time, the slope of the log ϵ − log ω curve and phase angle of CxBE2CB (x = 10, 12) decrease in a wide concentration range. These phenomena become more and more apparent with the increase of hydrocarbon chain length and it cannot be attributed to the diffusion-exchange process between the bulk and the interface. It is reasonable to consider that ethylene oxide groups are flexible and can be compressed and expanded, just like a spring. Therefore, the compression and expansion of the ethylene oxide groups in the interfacial layer and the exchange between interface and sublayer play a more important role for CxBE2CB (x = 10, 12) adsorption film. The dependence of dilational modulus on interfacial pressure can support our provided mechanism strongly.

Syntheses and aggregation behavior of pyridine-based CH–CF hybrid surfactants

Five cationic CH–CF hybrid surfactants, each of which has a hydrocarbon chain (CnH2n+1, n=8, 10, 12, 14, 16) and a fluorocarbon one (C6F13), have been synthesized. Taking the advantage of the Grignard reaction and the subsequent quaternization, the hybrid surfactants were obtained with high synthetic yields over 65%. Their structures have been unambiguously confirmed by FTIR, 1H NMR, 19F NMR, 13C NMR and MS measurements. 19F NMR revealed that the presence of the chiral carbon center induced a nonequivalent magnetic resonance of the adjacent fluorine nuclei. The aggregation behavior of the hybrid surfactants were investigated by surface tension, conductivity and steady-state fluorescence measurements. Surface tension measurements revealed that the hybrid surfactants exhibited high surface activity. With increasing hydrocarbon chain length, the critical micellar concentration (cmc) decreased while the surface tension at the cmc (γcmc) increased. Both the results of conductivity and surface tension measurements showed there exists a stepwise aggregation behavior for the hybrid surfactants with n=8 and 10. Steady-state fluorescence measurements showed fairly good agreement with the results obtained from conductivity and surface tension measurements. Evaluation of the thermodynamic parameters (ΔGm0, ΔHm0, ΔSm0) showed that the aggregate formation of the hybrid surfactants with n<16 is enthalpy-driven at low temperature, which turns to entropy-driven at high temperature. While the aggregate formation of the hybrid surfactant with n=16 is entropy-driven within all the investigated temperature ranges.

Role of Chain Length and Type on the Adsorption Behavior of Cationic Surfactants and the Silica Floatability

In this study, we investigated the adsorption isotherms of cationic surfactants (i.e., distearyl dimethyl ammonium chloride (DDAC), behenyl trimethyl ammonium chloride (BTAC), and stearyl trimethyl ammonium chloride (STAC)) onto silica surface and the corresponding silica floatability according to chain type and length of cationic surfactants. The results for the adsorption isotherms of cationic surfactants showed that the adsorptive amounts increased with increasing surfactant concentration, but differences in the position of the adsorption isotherms existed between DDAC, BTAC, and STAC. Specifically, in the high range of initial surfactant concentrations (i.e., 10 ¹5 ­10 ¹3 M), the adsorptive amounts increased with increasing hydrocarbon chain length. In addition, in the presence of DDAC, the adsorptive amounts were much greater than those in the presence of BTAC and STAC. The results were attributed to the fact that the increase in the hydrocarbon chain group of surfactants decreased the Gibbs free energy of the system, resulting in a shift of hemimicelle concentration toward lower concentration. Meanwhile, in the low range of initial surfactant concentrations (i.e., 5 © 10¹7­5 © 10¹6M), the adsorptive amounts were comparable regardless of surfactant type, which was due to the fact that the interaction between the cationic surfactants and the silica surface was mainly governed by electrostatic attractive force. The results from silica flotation and hydrophobicity tests showed that silica floatability increased with increasing hydrocarbon chain group of surfactants (i.e., floatability was in the order of DDAC > BTAC > STAC) under the conditions where the adsorptive amounts of the surfactants were comparable and that floatability results were consistent with those for the hydrophobicity of silica surface. Overall, the findings from the present study suggested that the hydrocarbon chain length and type of cationic surfactants play a significant role in both the adsorption behavior of surfactants and the silica floatability. [doi:10.2320/matertrans.M2014088]

The effect of perfluoroalkyl and hydrocarbon liquid chain lengths on oleophobic behaviors of copolymer surfaces

In this work, the effect of wt.% of perfluoroalkyl content and also hydrocarbon chain length on oleophobic properties of perfluoroethyl alkyl methacrylate-methyl methacrylate (Zonyl-TM-MMA) copolymers was investigated. The wetting performance of p(Zonyl-TM-ran-MMA) copolymer films by hydrocarbon liquids was found to be strongly depended on perfluoroalkyl chain lengths. Besides, increase in hydrocarbon chain length also caused an increase in contact angle results of p(Zonyl-TM-ran-MMA) copolymer films due to the stronger cohesion interactions of liquid molecules and this resulted in weaker adhesion interactions between copolymer surface and hydrocarbon drop. It was also discovered that contact angle hysteresis, Δcosθ, values of copolymers depend on both wt.% Zonyl-TM content and also hydrocarbon chain length of liquids.

Synthesis of Ag Nanocubes 18–32 nm in Edge Length: The Effects of Polyol on Reduction Kinetics, Size Control, and Reproducibility

This article describes a robust method for the facile synthesis of small Ag nanocubes with edge lengths controlled in the range of 18-32 nm. The success of this new method relies on the substitution of ethylene glycol (EG)--the solvent most commonly used in a polyol synthesis--with diethylene glycol (DEG). Owing to the increase in hydrocarbon chain length, DEG possesses a higher viscosity and a lower reducing power relative to EG. As a result, we were able to achieve a nucleation burst in the early stage to generate a large number of seeds and a relatively slow growth rate thereafter; both factors were critical to the formation of Ag nanocubes with small sizes and in high purity (>95%). The edge length of the Ag nanocubes could be easily tailored in the range of 18-32 nm by quenching the reaction at different time points. For the first time, we were able to produce uniform sub-20 nm Ag nanocubes in a hydrophilic medium and on a scale of ∼20 mg per batch. It is also worth pointing out that the present protocol was remarkably robust, showing good reproducibility between different batches and even for DEGs obtained from different vendors. Our results suggest that the high sensitivity of synthesis outcomes to the trace amounts of impurities in a polyol, a major issue for reproducibility and scale up synthesis, did not exist in the present system.