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A Schiff base bearing two methyl substituents, namely, 6,6'-((1

Psoriasis is a lingering inflammatory skin disease that attacks the immune system. The abnormal interactions between T cells, immune cells, and inflammatory cytokines causing the epidermal thickening. International guidelines have recommended topical treatments for mild to moderate psoriasis whilst systemic and phototherapy treatments for moderate to severe psoriasis. However, current therapeutic approaches have a wider extent to treat moderate to severe type of psoriasis especially since the emergence of diverse biologic agents. In the meantime, topical delivery of conventional treatments has prompted many unsatisfactory effects to penetrate through the skin (stratum corneum). By understanding the physiology of stratum corneum barrier functions, scientists have developed different types of lipid-based nanoparticles like solid lipid nanoparticles, nanostructured lipid carriers, nanovesicles, and nanoemulsions. These novel drug delivery systems help the poorly solubilised active pharmaceutical ingredient reaches the targeted site seamlessly because of the bioavailability feature of the nanosized molecules. Lipid-based nanoparticles for psoriasis treatments create a paradigm for topical drug delivery due to their lipids' amphiphilic feature to efficiently encapsulate both lipophilic and hydrophilic drugs. This review highlights different types of lipid-based nanoparticles and their recent works of nano formulated psoriasis treatments. The encapsulation of psoriasis drugs through lipid nanocarriers unfold numerous research opportunities in pharmaceutical applications but also draw challenges for the future development of nano drugs.

Graphical abstract, Highlights • Pandanus amaryllifolius extraction and encapsulation by simple ultrasonic procedure. • The sonoencapsulation using lysozyme and chitosan as shell materials. • Control on the size and size distribution of the pandan-encapsulated microspheres. • Stable Pandan encapsulated microspheres allow more pure Pandan extract in products., Pandan (Pandanus amaryllifolius) is commonly used as a food ingredient in Southeast Asia due to its delicious flavor, appetizing aroma and bright green colour. Pandan plant is uniquely found only in certain parts of the world. Despite its increasing popularity worldwide, its export market is limited by practical issues. One of the main problems for exporting Pandan to global market is its stability during transport. Due to the volatility of its active constituent, the functional properties of Pandan are lost during storage and shipment. In this study, we explored the ability of ultrasound processing technology to encapsulate the aromatic Pandan extract using lysozyme or chitosan as a shell material. 20 kHz ultrasonicator was used to encapsulate the pandan extract at 150 W of applied power. Two parameters, the ultrasonic probe tip and the core-to-shell ratio were varied to control the properties of the encapsulates. The diameters of the probe tip used were 0.3 and 1.0 cm. The core-to-shell volume ratios used were 1:160 and 1:40. The size distribution and the stability of the synthesized microspheres were characterized to understand and explore the possible parameters variation impact. Both size and size distribution of the microspheres were found to be influenced by the parameters varied to certain extent. The results showed that the mean size of the microspheres was generally smallest when using 1 cm probe tip with lower core-to-shell volume ratio but largest when using the 3 mm tip with higher core-to-shell volume ratio. This indicates that the sonication parameters could be fine-tuned to achieve the encapsulation of Pandan extract for storage and export. The pandan-encapsulated microspheres were also found to be stable during storage at least for one month.

Highlights • The validity of Weissler, Fricke and terephthalic acid dosimetry methods is reported. • Weissler and Fricke dosimetries provided comparable OH radical yields. • Terephthalic acid dosimetry provided very low OH radical yield. • Possible reasons and recommendations are discussed. • Opinion Paper may initiate further discussion among researchers working in sonochemistry., Acoustic cavitation and sonochemical reactions play a significant role in various applications of ultrasound. A number of dosimetry methods are in practice to quantify the amount of radicals generated by acoustic cavitation. In this study, hydroxyl radical (OH•) yields measured by Weissler, Fricke and terephthalic acid dosimetry methods have been compared to evaluate the validities of these methods using a 490 kHz high frequency sonochemical reactor. The OH• yields obtained after 5 min sonication at 490 kHz from Weissler and Fricke dosimetries were 200 µM and 289 µM, respectively. Whereas, the OH• yield was found to be very low (8 µM) when terephthalic acid dosimetry was used under similar experimental conditions. While the results agree with those reported by Iida et al. (Microchem. J., 80 (2005) 159), further mechanistic details and interfering reactions have been discussed in this study. For example, the amount of OH• determined by the Weissler and Fricke methods may have some uncertainty due to the formation of HO2• in the presence of oxygen. In order to account for the major discrepancy observed with the terephthalic acid dosimetry method, high performance liquid chromatography (HPLC) analysis was performed, where two additional products other than 2-hydroxy terephthalic acid were observed. Electrospray ionization mass spectrometry (ESI-MS) analysis showed the formation of 2,5-dihydroxyterephthalic acid as one of the by-products along with other unidentified by-products. Despite the formation of additional products consuming OH•, the reason for a very low OH• yield obtained by this dosimetry could not be justified, questioning the applicability of this method, which has been used to quantify OH• yields generated not only by acoustic cavitation, but also by other processes such as γ-radiolysis. The authors are hoping that this Opinion Paper may initiate further discussion among researchers working in sonochemistry area that could help resolve the uncertainties around using these dosimetry methods.

Correction for ‘Lipid-based nanoparticles for psoriasis treatment: a review on conventional treatments, recent works, and future prospects’ by Ummu Umaimah Mohd Nordin et al., RSC Adv., 2021, 11, 29080–29101, https://doi.org/10.1039/D1RA06087B.

Methods of NMR relaxation and differential scanning calorimetry (DSC) were used to study the crystallization of anhydrous milk fat (AMF) obtained from milk and subjected to ultrasonic (US) processing. Amongst the changes in the crystallization nature under the influence of ultrasound are the decrease in the crystallization temperature and the increase in the melting enthalpy of the anhydrous milk fat samples. The increase is ∼30% at 20 min of isothermal crystallization and is presumably explained by the additional formation of β'-form crystals from the melt. The parameters of the Avrami equation applied to the description of experimental data show an increase in the crystallization rate in samples with ultrasonic treatment and a change in the dimension of crystallization with a change in melting temperature.

A new semi-empirical kinetic (SEK) method has been used to calculate the values of KXBr or RXBr (X represents substituted iodobenzoates), with KX and KBr representing CTABr micellar binding constants of counterions X− (in the presence of either spherical or non-spherical micelles) and Br− (in the presence of only spherical micelles), respectively. Steady-shear rheological properties of mixed 0.015M CTABr/[MX] aqueous solutions reveal the presence of flexible wormlike micelles where MX represents sodium 3- and 4-iodobenzoates. The maxima of the plots of viscosity vs. [MX] at 0.015M CTABr for MX representing sodium 3- and 4-iodobenzoates support the presence of long linear and entangled wormlike micelles.

Acoustic cavitation in a liquid medium generates several physical and chemical effects. The oscillation and collapse of cavitation bubbles, driven at low ultrasonic frequencies (e.g., 20 kHz), can generate strong shear forces, microjets, microstreaming and shockwaves. Such strong physical forces have been used in cleaning and flux improvement of ultrafiltration processes. These physical effects have also been shown to deactivate pathogens. The efficiency of deactivation of pathogens is not only dependent on ultrasonic experimental parameters, but also on the properties of the pathogens themselves. Bacteria with thick shell wall are found to be resistant to ultrasonic deactivation process. Some evidence does suggest that the chemical effects (radicals) of acoustic cavitation are also effective in deactivating pathogens. Another aspect of cleaning, namely, purification of water contaminated with organic and inorganic pollutants, has also been discussed in detail. Strong oxidising agents produced within acoustic cavitation bubbles could be used to degrade organic pollutants and convert toxic inorganic pollutants to less harmful substances. The effect of ultrasonic frequency and surface activity of solutes on the sonochemical degradation efficiency has also been discussed in this overview.

A semi-empirical kinetic technique has been used to obtain the ratios of pure CTABr (cationic nanoparticle) and mixed CTABr–C16E20 (cationic–nonionic nanoparticle) micellar binding constants of counterions X and Br, KX/KBr (=KBrX or RBrX) for X = salicylate ion. The values of KBrX or RBrX for the salicylate ion remain typically independent of the concentration of pure micelles, [CTABr]T (0.006–0.015 M). These values are also independent of mixed [CTABr]T–[C16E20]T micelles under similar conditions. The presence of C16E20 decreases the average values of KBrX or RBrX from 42 to 16 for salicylate ions. Increase in concentration of cationic and cationic–nonionic nanoparticles at a fixed amount of CTABr reveals the monotonic increase in the value of kobs, which was explained using the PPM model together with an empirical equation. Rheological characteristics of 0.015 M CTABr solutions in the presence of disodium salicylate indirectly show the presence of branched elongated nanoparticles at 25 °C and 35 °C and [C16E20]T = 0. Contrarily, such findings reveal the existence of spherical micelles at 25 °C and 35 °C in the presence of ≥0.006 M [C16E20]. The values of KBrX or RBrX and rheological observations clearly demonstrate that 0.015 M CTABr/M2X/H2O (M2X = disodium salicylate, 2-NaOC6H4CO2Na) solutions contain wormlike and spherical micelles when KBrX or RBrX values are ≈42 and 16, respectively.

Rheological measurements on aqueous solutions containing a constant concentration of cetyltrimethylammonium bromide and increasing the concentration of counter ion additive, M2X, where X 2− represents 4-methoxysalicylate (4-MeOSa2−) and 3-, 4-methylsalicylate (3-, 4-MeSa2−), exhibit the presence of (i) spherical (SM), wormlike (WM) and branched (BWM) micelles for X 2− = 4-MeOSa2− and (ii) spherical, wormlike, branched micelles, small vesicles (SVs)/planar bilayer sheets (PBLS) and multilamellar vesicles (MLV) for X 2− = 3-, 4-MeSa2−. Zero shear viscosities measured with respect to M2X showed first and second maxima which were used to calculate flow activation energies (E a) at various M2X.

A comprehensive investigation on the effect of ultrasonic frequency and power on the structural transformation of CTABr/NaSal micelles has been carried out. Sonication of this micelle system at various ultrasonic frequencies and power resulted in the formation and separation of two types of micelles. High viscoelastic threadlike micelles of ∼ 2 nm in diameter and several μm in length and tubular micelles possessing a viscosity slightly above that of water with ∼ 30-50 nm diameter and few hundred nm length. The structural transformation of micelles was induced by the shear forces generated during acoustic cavitation. At a fixed acoustic power of 40 W, the structural transformation was found to decrease from 211 to 647 kHz frequency due to the decreasing shear forces generated, as evidenced by rheological measurements and cryo-TEM images. At 355 kHz, an increase in the structural transformation was observed with an increase in acoustic power. These findings provide a knowledge base that could be useful for the manipulation of viscosity of micelles that may have applications in oil industry.

The sonochemical synthesis of gold nanoparticles (GNPs) with different shapes and size distributions by using high-intensity focused ultrasound (HIFU) operating at 463 kHz is reported. GNP formation proceeds through the reduction of Au(3+) to Au(0) by radicals generated by acoustic cavitation. TEM images reveal that GNPs show irregular shapes at 30 W, are primarily icosahedral at 50 W and form a significant amount of nanorods at 70 W. The size of GNPs decreases with increasing acoustic power with a narrower size distribution. Sonochemiluminescence images help in the understanding of the effect of HIFU in controlling the size and shapes of GNPs. The number of radicals that form and the mechanical forces that are generated control the shape and size of the GNPs. UV/Vis spectra and TEM images are used to propose a possible mechanism for the observed effects. The results presented demonstrate, for the first time, that the HIFU system can be used to synthesise size- and shape-controlled metal nanoparticles.

Halo-substitutions at 3-position of benzene ring of the salts of aromatic carboxylate, MX, revealed the effect of two different halide ions (Br− and Cl−) on the counterion binding constants obtained from cationic nanoparticle catalyzed piperidinolysis of ionized phenyl salicylate (PhS−). The values of observed rate constant, kobs, determined at a constant total concentration of cetyltrimethylammonium bromide, [CTABr]T, piperidine, ([P]T), [PhS−]T, NaOH, and various concentration of MX (MX = 3-BrC6H4CO2Na and 3-ClC6H4CO2Na), were determined using UV-visible X spectrophotometric technique at 35 °C and 370 nm. The average value of nanoparticle binding constant, KXBr, for X− = 3-BrC6H4CO2− (RXBr = 57) was found to be about 2-fold larger than that for X− = 3-ClC6H4CO2− (RXBr = 30). These XX values were dependent of substituents 3-Br and 3-Cl, and independent of [CTABr]T. Both are related to the presence of different extent of viscoelastic worm-like nanoparticles formation in the [CTABr]T of 6 and 10 mM.

Apparent catalytic effects of varying concentration of CTABr/MX/H 2 O nanoparticles (at a constant [CTABr] and [Piperidine]) on pseudo-first-order rate constants ( k obs ) for the reaction of piperidine with ionized phenyl salicylate have been measured as k obs / k 0 where k obs and k 0 represent rate constants in the presence and absence of MX, respectively. Symbols CTABr and MX represent respectively cetyltrimethylammonium bromide and 2,3- or 3,5-Cl 2 BzNa with Bz ⿿ = C 6 H 3 CO 2 ⿿ . At 6 mM CTABr, the maximum values of k obs / k 0 are 7.9 and 9.0 at 300 mM 2,3-Cl 2 BzNa and 80 mM 3,5-Cl 2 BzNa respectively. Several-fold larger catalytic effects of 3,5-Cl 2 Bz ⿿ than that of 2,3-Cl 2 Bz ⿿ are attributed to ⿼8-fold larger CTABr binding constant of 3,5-Cl 2 Bz ⿿ than that of 2,3-Cl 2 Bz ⿿ . Origin of CTABr/MX/H 2 O nanoparticles catalytic effects is related to the ability and efficiency of the expulsion of another counterion S ⿿ by the counterion X ⿿ from the cationic nanoparticles to the aqueous phase by means of the ion exchange process X ⿿ / S ⿿ at the cationic surface of nanoparticles.

The fascinating and serendipitous discovery, in 1976, of the characteristic viscoelastic behavior of wormlike micelles of cetyltrimethylammonium salicylate (CTASa) surfactant solution at ~ 2 × 10− 4 M CTASa became a catalyst for an increasing interest in both industrial application and mechanism of the origin of micellar growth of this and related wormlike micellar systems. It has been perceived for more than three decades, based upon qualitative evidence, that the extent of the strength of the counterion (X) binding to ionic micelles determines the counterion-induced micellar structural transition from spherical-to-small rodlike-to-linear long stiff/flexible rodlike/wormlike-to-entangled wormlike micelles. This perception predicts the presence of a possible quantitative correlation of counterionic micellar binding constants (KX) with counterion-induced micellar growth. The quantitative estimation of counterion binding affinity to cationic micelles, in terms of the values of the degree of counterion binding (βX), is concluded to be either inefficient or unreliable for moderately hydrophobic counterions (such as substituted benzoate ions). The values of KX, measured in terms of conventional ion exchange constants (KXY), can provide a quantitative correlation between KX or KXY (with a reference counterion Y = Cl− or Br−) and counterion-induced ionic micellar growth. A recent new semi-empirical kinetic (SEK) method provides the estimation of KXY for Y = Br as well as ratio of counterionic micellar binding constants KX/KBr (= RXBr) where the values of KBr and KX have been derived from the kinetic parameters in the presence of cationic spherical and nonspherical micelles, respectively. The SEK method has been used to determine the values of KXBr or RXBr for X = 2-, 3- and 4-ClC6H4CO2−. Rheometric measurements on aqueous CTABr/MX (MX = 2-,3- and 4-ClBzNa) solutions containing 0.015 M CTABr and varying values of [MX] reveal the presence of spherical micelles for MX = 2-ClBzNa and long linear as well as entangled wormlike micelles for MX = 3- and 4-ClBzNa. The respective values of KXBr or RXBr of 5.7, 50 and 48 for X = 2-, 3- and 4-ClBz− give a quantitative correlation with the rheometric measurements of the structural features of micelles of 0.015 M CTABr solutions containing 2-, 3- and 4 ClBzNa.

A semi empirical kinetic (SEK) method has been used to determine the ratio of cetyltrimethylammonium bromide (CTABr) micellar binding constants of counterion X⁻ and Br⁻ (a reference counterion), i.e. K(X)/K(Br) (=R(X)(Br)). The values of K(X) and K(Br) have been derived from the kinetic parameters obtained in the presence spherical/non-spherical and spherical micelles, respectively. This rather new method gives the respective mean values of R(X)(Br) as 45±2, 25±3, 4.7±0.6 and 119±10 for X=2,4-, 2,5-, 2,6- and 3,4-Cl₂C₆H₃CO₂⁻ (Cl₂Bz'Na). Literature lacks the report on the values of R(X)(Br) for all X except for X=2,6-Cl₂C₆H₃CO₂⁻ (2,6-Cl2Bz'⁻) for which the reported value is 5.0. Rheological properties, such as shear thinning behavior, reveal indirectly the presence of wormlike micelles (WM) in the CTABr micellar solutions containing MX for all X except X=2,6-Cl₂Bz'⁻. The micelles remain spherical within [2,6-Cl₂Bz'⁻] range 0.01-0.34 M at 0.015 M CTABr. The maxima of the plots of zero shear viscosity, η₀, (obtained from the initial plateau region of flow curves, i.e. η vs. γ curve) vs. [MX] (MX=2,4-, 2,5- and 3,4-Cl₂Bz'Na) at 0.015 M CTABr also support indirectly the presence of linear, entangled and branched WM.

The tremendous attention given to micelle systems is due to its potential uses in many scientific, biomedical and industrial applications. Micellar aggregations possess unique ability to exhibit different physicochemical properties owing to their dynamic and reversible structural transformation. This flexibility is controllable by different stimuli. In this study, the possibility of designing a variety of micelle nanostructures using ultrasound is investigated. Using ultrasound as a stimulus is an advantage as it eliminates the needs of adding external chemicals to the micellar system, and experimental parameters could be easily controlled. The fundamental properties of micelles and various forces generated by ultrasound in liquids are discussed in Chapter 1. The second chapter on Literature Review is structured in line with Results and Discussion chapters. In the first section, the use of a fluorescence based technique for the determination of critical micelle concentration as well as reported attempts in monitoring micelle structural changes are outlined. In the second section, literature dealing with structural changes in micelle systems by different stimuli is reviewed. The Reptation Reaction Model is discussed in detail in the following section. This section provides theoretical arguments on the reptation process of micelle, as well as the different reaction (recombination) routes that result in the formation of different structures of micelle. In the last section, sonochemical synthesis of gold nanoparticles is reviewed. In Chapter 3, materials used, solution preparation methods, experimental approaches and analytical methods used are described. The micelle used in this study is cetyltrimethylammonium salicylate (CTASal) prepared by an ion exchange process between cetyltrimethylammonium bromide (CTAB) and sodium salicylate (NaSal). The ultrasonic settings chosen include different sonication reactors, frequency and applied power. In Chapter 4, a fluorescence based technique using fluorescein isothiocyanate (FITC) as a probe to monitor structural changes in micelle was successfully implemented. The method was found to be successful in detecting the critical micelle concentration (cmc) as well as for monitoring the concentration dependent structural growth of CTAB micelle system. It was then tested to the sonicated CTASal micelle system. The limitation of this technique is also discussed in this chapter. In Chapter 5, the first ultrasound-driven transformation of CTASal micelle structures is reported. The wormlike micelle formed from CTAB and NaSal was chosen due to the increasing interest of such viscoelastic micelles in recent technological applications. The sonication was carried out with a plate-type transducer at 211 kHz frequency. The wormlike micelle was found to transform to long threadlike micelle and vesicles/tubular micelle, simultaneously. These were confirmed by the cryo-TEM and rheological measurements. A mechanism for ultrasound induced micelle structural changes is proposed based on the Reptation Reaction Model. This study was also aimed to understand, and hence efficiently control CTASal micelle structural changes. This is accomplished by comparing the effect of sonication using different ultrasonic reactors as well as applying different frequencies and sonication power. This work is discussed in Chapter 6. Three types of ultrasonic transducers were used: (i) horn-type, (ii) plate-type, and (iii) high intensity focused ultrasound (HIFU). In Chapter 7, the sonochemical synthesis of gold nanoparticles using HIFU at 463 kHz is reported. This work was carried out to characterize the HIFU unit. Characterization of HIFU using snochemiluminescence imaging was also carried out. This system was then used to study the effect of HIFU on CTASal micelle structures. In Chapter 8, some concluding remarks have been provided.

A fluorescence-based method has been developed to detect the structural changes that occur in micelle systems. The sensitivity of fluorescein isothiocyanate (FITC) has been evaluated for (i) detecting the micellization of cetyltrimethyl ammonium bromide (CTAB) and (ii) probing the concentration dependent aggregation, leading to micro- structural changes that occur within CTAB micelles. The critical micelle concentration (cmc) of CTAB has been determined to be 1.35 ± 0.35 mM using the fluorescence spectral characteristics of FITC. Because the experimental conditions have been altered to optimize FITC probing, the cmc is also validated by surface tension and conductivity measurements. To make sure FITC does not affect the properties of micelles, we calculated the micelle binding constant, KM ,a t different concentrations of FITC using a nonlinear least-squares method. The average KM for (FITC)T ≤ 5m M is found to be 6575 ± 233. The optical properties of FITC have also been found to be sensitive in response to the changes in the polarity of the microenvironment, caused by the structural changes in CTAB/water system. Two significant observations are noticed from the fluorescence spectra of FITC in CTAB solutions: (i) a decrease followed by an increase in the maximum intensity (Imax )o ffluorescence and (ii) a red shift of maximum wavelength (λmax) with increasing concentrations of CTAB. These observations could be correlated with the concentration-dependent microstructural changes in CTAB micelles. On the basis of the experimental observations, FITC is found to be a suitable fluorescent probe for monitoring the changes in CTAB micelle structures.

The values of pseudo-first-order rate constants (k obs) for the acetolysis of phthalic anhydride (PAn) increase from 6.60 × 10−7 to 31.5 × 10−7 s−1 with the increase in temperature from 30 to 50 °C. These values of k obs give activation parameters ∆H* and ∆S* as 14.4 ± 0.4 kcal mol−1 and −39.1 ± 1.3 cal K−1 mol−1, respectively. The values of k obs remain essentially unchanged with the increase in the content of CS (CS = CH3CN or THF) from 0 to 40 % v/v in mixed AcOH–CS solvents. These observations have been explained qualitatively.

Pseudo-first-order rate constants (k(obs)) for alkaline hydrolysis of N-(2'-methoxyphenyl)phthalimide (1) decrease nonlinearly with increasing total concentration of nonionic surfactant C(m)E(n) (i.e. [C(m)E(n)](T) where m and n represent the respective number of methyl/methylene units in the tail and polyoxyethylene units in the headgroup of a surfactant molecule and m/n=16/20, 12/23 and 18/20) at constant 2% v/v CH(3)CN and 1.0 mM NaOH. The k(obs)vs. [C(m)E(n)](T) data follow the pseudophase micellar (PM) model at ≤ 50 mM C(16)E(20), ≤ 1.4 mM C(12)E(23) and ≤ 2.0 mM C(18)E(20) where rate of hydrolysis of 1 in micellar pseudophase could not be detected. The values of k(obs) fail to follow the PM model at > ∼50 mM C(16)E(20), > ∼1.4 mM C(12)E(23) and > ∼2.0 mM C(18)E(20) which has been attributed to a micellar structural transition from spherical to rodlike which in turn increases C(m)E(n) micellar binding constant (K(S)) of 1 with increasing values of [C(m)E(n)](T). Rheological measurements show the presence of spherical micelles at ≤ 50 mM C(16)E(20), ≤ 1.4 mM C(12)E(23) and ≤ 3.0 mM C(18)E(20). The presence of rodlike micelles is evident from rheological measurements at > ∼50 mM C(16)E(20), > ∼1.4 mM C(12)E(23) and > ∼3.0 mM C(18)E(20).

Pseudo-first-order rate constants (k(obs)) for the nucleophilic substitution reaction of piperidine (Pip) with ionized phenyl salicylate (PS(-)), obtained at a constant [Pip](T) (= 0.1 M), [PS(-)](T) (= 2 x 10(-4) M), [CTABr](T) (cetyltrimethylammonium bromide),or = 0.06 M NaOH, and a varying concentration of MX (= 3-FC(6)H(4)CO(2)Na, 3-FBzNa and 4-FC(6)H(4)CO(2)Na, 4-FBzNa), follow the kinetic relationship k(obs) = (k(0) + thetaK(X/S)[MX])/(1 + K(X/S)[MX]) which is derived by the use of the pseudophase micellar (PM) model coupled with an empirical equation. The empirical equation explains the effects of [MX] on CTABr micellar binding constant (K(S)) of PS(-) that occur through X(-)/PS(-) ion exchange. Empirical constants theta and K(X/S) give the parameters F(X/S) and K(X/S), respectively. The magnitude of F(X/S) gives the measure of the fraction of micellized PS(-) transferred to the aqueous phase by the limiting concentration of X(-) through X(-)/PS(-) ion exchange. The values of F(X/S) and K(X/S) have been used to determine the usual thermodynamic ion exchange constant (K(X)(Y)) for ion exchange process X(-)/Y(-) on the CTABr micellar surface. The values of K(X)(Br) (where Br = Y) have been calculated for X = 3-FBzNa and 4-FBzNa. The mean values of K(X)(Br) are 12.8 +/- 0.9 and 13.4 +/- 0.6 for X(-) = 3-FBz(-) and 4-FBz(-), respectively. Nearly 3-fold-larger values of K(X)(Br) for X = 3-FBz(-) and 4-FBz(-) than those for X = Bz(-), 2-ClBz(-), 2-CH(3)Bz(-), and the 2,6-dichlorobenzoate ion (2,6-Cl(2)Bz(-)) are attributed to the presence of wormlike micelles in the presence of50 mM 3-FBz(-) and 4-FBz(-) in the [CTABr](T) range of 5-15 mM. Rheological properties such as shear thinning behavior of plots of shear viscosity versus the shear rate at a constant [3-FBz(-)] or [4-FBz(-)] as well as shear viscosity (at a constant shear rate) maxima as a function of the concentrations of 3-FBz(-) and 4-FBz(-) support the conclusion, derived from the values of K(X)(Br), for the probable presence of wormlike/viscoelastic micellar solutions under the conditions of the present study.

Pseudo-first-order rate constants (kobs) for the nucleophilic reaction of piperidine (Pip) with anionic phenyl salicylate (S−) in aqueous solution, obtained at constant content (=2%, v/v) of CH3CN, [Pip]T (=0.1 M), [S−]T (=2 × 10−4 M), [CTABr]T (total concentration of cetyltrimethylammonium bromide), NaOH (≤0.10 M) and varying concentration of inert salts, MX (=2-NaOC6H4CO2Na and 3-NaOC6H4CO2Na), follow the relationship: kobs = (k0 + θKX/S[MX])/(1 + KX/S[MX]), derived from an empirical equation coupled with the pseudophase model of micelle. The empirical constants θ and KX/S provide the respective parameters FX/S and KX/S. The magnitude of FX/S gives the measure of the fraction of cationic micellized S− transferred to the aqueous phase by the limiting concentration of co-ions X− through the ion-exchange process X−/S−. In other words, the value of FX/S shows the cationic micellar penetration of ions X− relative to co-ions S−. The values of FX/S and KX/S have been used to determine usual thermodynamic ion-exchange constant ( K X Y ). The values of K X Y (Y = Br) have been calculated for X = 2-−OC6H4CO2− (2-OBz2−) and 3-−OC6H4CO2− (3-OBz2−). The mean values of K X Br are 44 ± 7 and 4.9 ± 0.7 for X− = 2-OBz2− and 3-OBz2−, respectively. The value of K X Br for 2-OBz2− is nearly 9- and 16-fold larger than those for respective 3-OBz2−and 4-−OC6H4CO2− (4-OBz2−). These results are attributed to the presence and absence of viscoelasticity in CTABr aqueous solution with 2-OBz2− and 3-OBz2− as well as 4-OBz2−, respectively. The mean values of FX/S are 0.98 ± 0.10, 0.24 ± 0.07 and 0.14 ± 0.02 for X− = 2-OBz2−, 3-OBz2− and 4-OBz2−, respectively. The change in kinetic probe from piperidinolysis to hydrolysis of S− gives nearly same value, within the limits of experimental uncertainties, of K X Br for 2-OBz2−. The mean value of FX/S × KX/S for 2-OBz2− is decreased by 40-fold in the presence than in the absence of 0.05 M C16E20.

The semi-empirical spectrophotometric (SESp) method, for the indirect determination of ion exchange constants (K(X)(Br)) of ion exchange processes occurring between counterions (X⁻ and Br⁻) at the cationic micellar surface, is described in this article. The method uses an anionic spectrophotometric probe molecule, N-(2-methoxyphenyl)phthalamate ion (1⁻), which measures the effects of varying concentrations of inert inorganic or organic salt (Na(v)X, v = 1, 2) on absorbance, (A(ob)) at 310 nm, of samples containing constant concentrations of 1⁻, NaOH and cationic micelles. The observed data fit satisfactorily to an empirical equation which gives the values of two empirical constants. These empirical constants lead to the determination of K(X)(Br) (= K(X)/K(Br) with K(X) and K(Br) representing cationic micellar binding constants of counterions X and Br⁻). This method gives values of K(X)(Br) for both moderately hydrophobic and hydrophilic X⁻. The values of K(X)(Br), obtained by using this method, are comparable with the corresponding values of K(X)(Br), obtained by the use of semi-empirical kinetic (SEK) method, for different moderately hydrophobic X. The values of K(X)(Br) for X = Cl⁻ and 2,6-Cl₂C6H₃CO₂⁻, obtained by the use of SESp and SEK methods, are similar to those obtained by the use of other different conventional methods.

The semiempirical kinetic method has been used to determine the ratio of cetyltrimethylammonium bromide, CTABr, micellar binding constants of counterions X (K(X)) and Br (K(Br)), i.e., K(X)/K(Br) (= R(X)(Br)) for X = dianionic 5-methyl- and 5-methoxysalicylate ions. The values of K(X) and K(Br) have been derived from the kinetic parameters obtained in the presence of spherical/nonspherical and spherical micelles, respectively. The values of R(X)(Br) remain essentially independent of [CTABr] within its range 0.005-0.015 M for both dianionic 5-methyl- and 5-methoxysalicylate ions. The increase in temperature from 35 to 55 °C decreases the values of R(X)(Br) from 796 to 53 for 5-methylsalicylate ions and from 89 to 7.0 for 5-methoxysalicylate ions. Rheological properties of 0.015 M CTABr solutions containing ≥0.01 M counterionic salt, M(2)X, show indirectly the presence of unilamellar vesicles, ULV, and long linear, entangled, and branched wormlike micelles, WM, at, respectively, 35 and 55 °C for X = dianionic 5-methylsalicylate ion. However, such studies show WM and probable spherical micelles, SM, at, respectively, 35 and 55 °C for X = dianionic 5-methoxysalicylate ions. It has been shown that, at a constant [CTABr], the micellar structural transitions from SM-to-WM-to-vesicles may be correlated quantitatively with the values of R(X)(Br) regardless of whether such micellar structural transitions occur due to variation in the values of [M(2)X] at a constant temperature or due to variation in temperature at a constant [M(2)X].

The effects of the concentration of inert organic salts, [MX], (MX=2-, 3- and 4-BrBzNa with BrBzNa=BrC(6)H(4)CO(2)Na) on the rate of piperidinolysis of ionized phenyl salicylate (PS(-)) have been rationalized in terms of pseudophase micellar (PM) coupled with an empirical equation. The appearance of induction concentration in the plots of k(obs) versus [MX] (where k(obs) is pseudo-first-order rate constants for the reaction of piperidine (Pip) with PS(-)) is attributed to the occurrence of two or more than two independent ion exchange processes between different counterions at the cationic micellar surface. The derived kinetic equation, in terms of PM model coupled with an empirical equation, gives empirical parameters F(X/S) and K(X/S) whose magnitudes lead to the calculation of usual ion exchange constant K(X)(Br) (=K(X)/K(Br) with K(X) and K(Br) representing cationic micellar binding constants of counterions X(-) and Br(-), respectively). The value of F(X/S) measures the fraction of S(-) (=PS(-)) ions transferred from the cationic micellar pseudophase to the aqueous phase by the optimum value of [MX] due to ion exchange X(-)/S(-). Similarly, the value of K(X/S) measures the ability of X(-) ions to expel S(-) ions from cationic micellar pseudophase to aqueous phase through ion exchange X(-)/S(-). This rather new technique gives the respective values of K(X)(Br) as 8.8±0.3, 71±6 and 62±5 for X(-)=2-, 3- and 4-BrBz(-). Rheological measurements reveal the shear thinning behavior of all the surfactant solutions at 15mM CTABr (cetyltrimethylammonium bromide) indicating indirectly the presence of rodlike micelles. The plots of shear viscosity (η) at a constant shear rate (γ), i.e. η(γ), versus [MX] at 15 mM CTABr exhibit maxima for MX=3-BrBzNa and 4-BrBzNa while for MX=2-BrBzNa, the viscosity maximum appears to be missing. Such viscosity maxima are generally formed in surfactant solutions containing long stiff and flexible rodlike micelles with entangled and branched/multiconnected networks. Thus, 15 mM CTABr solutions at different [MX] contain long stiff and flexible rodlike micelles for MX=3- and 4-BrBzNa and short rodlike micelles for MX=2-BrBzNa.

The development of generic large-scale sonochemical reactors requires a fundamental understanding of how various experimental parameters affect the acoustic cavitation efficiency. With a view to expand the experimental database and knowledge, the changes to acoustic cavitation bubble structures, caused by covering the air–solution interface with a lid at various frequencies and power levels, have been investigated. The accompanying effects have been quantified using sonochemiluminescence and sonoluminescence as probes. It has been observed that the chemically active cavitation bubble population is dominant in the “open” (without lid) configuration and the sonoluminescing bubble population is dominant in the “closed” (with lid) configuration. A possible reason for such differences is the existence of a well-defined standing wave pattern in the closed system.

We report on the unprecedented ultrasound-driven engineering of typical wormlike micelles to well-aligned, much higher viscoelastic threadlike micelles and lower viscoelastic tubular micelles that have potential practical applications in medicine and oilfield industries. The sonication of the CTAB/salicylate micelle system at 211 kHz in aqueous solutions generated two nanostructures with specific but contradicting properties: stably aligned threadlike micelles of ∼2 nm in diameter and several μm in length with a high viscoelasticity and low viscoelastic tubular micelles of ∼30 nm in diameter and a few hundred nanometres in length. The tubular micelles are relatively unstable structures formed by the coalescence of vesicular intermediates generated during sonication. Acoustic cavitation-generated physical effects are primarily responsible for the generation of these novel nanostructures. This study also provides the first ever experimental evidence in support of a well-known theoretical model that was proposed in the 1990s on the structural transformation of micelles.