Synthesis, Surface, Thermodynamic Properties of Some Biodegradable Vanillin-Modified Polyoxyethylene Surfactants

Four water-soluble non-ionic ethoxylated surfactants based on vanillin were synthesized (VE₁₅, VE₂₀, VE₄₀, and VE₆₀). The chemical structures of these surfactants were confirmed using FT-IR and ¹H-NMR spectra. The molecular weights of the compounds were determined using viscosity measurements and gel permeation chromatography. Surface tension as a function of the concentration of the surfactant in aqueous solution was measured at 25, 40 and 55?°C. From these measurements, the critical micelle concentration (CMC), effectiveness (??_cmc), efficiency (pC₂₀), maximum surface (??_max) excess and minimum surface area (A _min), were calculated. The surface activity measurements showed their high tendency towards adsorption and micellization and their good surface tension reduction, and low interfacial tension. The emulsion stability measurements showed the applicability of these surfactants as emulsifying agents. The thermodynamic parameters of micellization (??G _mic, ??H _mic, ??S _mic) and adsorption (??G _ads, ??G _ads, ?S _ads) showed their tendency towards adsorption at the interfaces and also micellization in the bulk of their solutions. The biodegradability of the prepared surfactants was tested in river water using die-away method and showed their readily biodegradation in the open environment.     

Effects of Molecular Structure and Temperature on Micellization of Cationic Ammonium Gemini Surfactants in Aqueous Solution

Micellization of four cationic quaternary ammonium gemini surfactants, having a diethyl ether or hexyl spacer with the alkyl chain lengths of 12 and 16 carbon atoms, was studied using isothermal titration microcalorimetry (ITC) and electrical conductivity measurements in the temperature range from 298.15 to 313.15 K. In this temperature range, where surfactants are normally applied, the temperature almost does not influence the critical micelle concentration (CMC) and the degree of micelle ionization (α) values of the gemini surfactants, and the replacement of a hexyl spacer by a diethyl ether spacer leads to a slight decrease in the CMC and α values. However, as the alkyl chain length increases from 12 to 16 carbon atoms, the CMC values significantly decrease from 0.99–1.19 mM to 0.020–0.057 mM. In particular, the enthalpy of micellization (ΔH_mic ) and the associated thermodynamic parameters show obvious changes with varying temperature and molecular structure. ΔH_mic becomes much more exothermic at higher temperature or for the surfactants with a more hydrophilic spacer. Moreover, the heat capacity change of micellization (ΔC _{P, mic} ) is less exothermic for the surfactants with a more hydrophilic spacer or a longer alkyl chain. The enthalpy–entropy compensation data show that the surfactants with longer alkyl chains have a more stable micellar structure.     

Rhamnolipid–Metal Ions (CrVI and PbII) Complexes: Spectrophotometric,Conductometric, and Surface Tension Measurement Studies

The formation of rhamnolipid complexes with metal ions of chromium (VI) and lead (II) has been studied spectrophotometrically, conductometrically, and by surface tension measurement. The values of the critical micelle concentration (CMC) of rhamnolipid, obtained by spectroscopic, conductometric, and surface tension measurements, were 5.2 × 10⁵ , 5.0 × 10⁵ , and 5.3 × 10⁵ mol.dm⁻³, respectively, which are in close agreement. An increase in CMC on increasing metal ion content in the rhamnolipid solution and a shift in λ_max in the spectra of rhamnolipid indicated the formation of a complex between rhamnolipid and both the metal ions, namely, chromium (VI) and lead (II). The values of stability constants for the {rhamnolipid–chromium (VI)} and {rhamnolipid–lead (II)} complexes have been determined by spectroscopic data and were as 0.58 × 10⁴ and 0.50 × 10⁴ at 308 K, respectively. The thermodynamic parameters for micellization, namely, free energy change (∆G_mic) , entropy change (∆S_mic) , and heat enthalpy change (∆H_mic) , have been determined by conductivity measurements. An increase in the negative value of ∆G_mic and a decrease in the value of ∆S_mic on increasing metal ion content in the surfactant solution indicated lower micellization of rhamnolipid in the presence of metal ions. The electrostatic attractions and entrapment of chromium (VI) in the micelles of the biosurfactants were found to be responsible for {rhamnolipid–lead (II)} and {rhamnolipid–chromium (VI)} complexes, respectively.     

Amphiphilic antidepressant drug amitriptyline hydrochloride under the influence of ionic and nonionic hydrotropes; micellization and phase separation

Herein we report the micellization and cloud point of an amitriptyline hydrochloride (AMT) under the influence of cationic, anionic and nonionic hydrotropes. Anionic hydrotropes were employed to know the micellar and surface behaviors, besides studying the clouding behavior of AMT drug with cationic, anionic and nonionic hydrotropes. Tensiometric study has been performed and the properties studied include the critical micelle concentration (cmc), maximum surface excess at the air/water interface (Γ_max), the minimum area per of amphiphilic molecule at air/water interface (A_min), and the different thermodynamic parameters, besides clouding phenomenon. Interaction parameters of micelles (β^m) and monolayer (β^σ) indicate that drug-hydrotrope systems show better interaction at the interface than in micelles.     

Counter-ion Effect on Micellization of Ionic Surfactants: A Comprehensive Understanding with Two Representatives, Sodium Dodecyl Sulfate (SDS) and Dodecyltrimethylammonium Bromide (DTAB)

Various micelle parameters viz., critical micelle concentration (CMC), counter-ion binding (β), aggregation number (N), hydrodynamic radius (R _h), micelle zeta potential (ζ) and energetic parameters, free energy of micellization ( $ \Updelta G_{\text{m}}^{0} $ ), enthalpy of micellization ( $ \Updelta H_{\text{m}}^{0} $ ) and entropy of micelle formation ( $ \Updelta S_{\text{m}}^{0} $ ) were determined for sodium dodecylsulfate, and dodecyltrimethylammonium bromide in the presence of NaCl for the former and NaBr for the latter. Conductometry and calorimetry methods were used for the measurements of CMC and energetic parameters. The fluorimetric (static quenching) method was employed to determine N and dynamic light scattering to estimate R _h and ζ. The conductometrically determined β was verified from the CMC values by calorimetry using the Corrin–Harkins equation. The results found for the two surfactants of identical tails but different head groups have been presented and discussed. A detailed report on the salt effect using salts containing counter-ions the same as those in the surfactant is found only limitedly in the literature.     

Synthesis and Physico-Chemical Properties of Sodium 3-Oxo-2-(3-(4-sulphonatophenyl)triaz-2-enyl)octadecanoate Anionic Surfactant

The novel anionic surfactant sodium 3‐oxo‐2‐(3‐(4‐sulphonatophenyl)triaz‐2‐enyl)octadecanoate (SSTO) was prepared from renewable raw materials; glycine and palmitic acid. Surface and bulk properties of SSTO were investigated by surface tension and electrical conductivity techniques at 298, 308, 318 and 328 K. Surface properties including critical micelle concentration (CMC), maximum surface excess concentration (Γ_max), minimum area per molecule (A_min), surface tension at CMC (γ_CMC), effectiveness of surface tension reduction (Π_CMC), efficiency of surface adsorption (pC₂₀), and degree of counterion dissociation (α) were determined. The thermodynamic parameters of micellization (ΔG°_mic, ΔH°_mic and ΔS°_mic) and adsorption (ΔG°_ad, ΔH°_ad and ΔS°_ad) were also investigated at 298, 308, 318 and 328 K. The effect of 3 wt% n‐propanol, n‐butanol and n‐pentanol on surface tension and conductivity at 298 K was also determined.     

Micellar and Interfacial Behavior of Cationic Benzalkonium Chloride and Nonionic Polyoxyethylene Alkyl Ether Based Mixed Surfactant Systems

Micellar and interfacial properties of mixed surfactant systems comprising benzalkonium chloride, a cationic surfactant and nonionic polyoxyethylene alkyl ether surfactants (POE: C₁₀E₇, C₁₀E₈, C₁₀E₉, C₁₀E₁₀) have been investigated by surface tension, fluorescence and dynamic light scattering techniques. Critical micelle concentration (CMC) for different mixing mole fractions has been investigated by surface tension and fluorescence measurements. Ideal CMC, mixed micellar composition (X ₁ ^m , X ₁ ^σ ), interaction parameters for mixed micelles (β ^m) and adsorption monolayer (β ^σ ), surface excess concentration (Г_max), minimum area per molecule (A _min) and related thermodynamic properties have also been determined. Lowering of the CMC and negative interaction parameter values indicate synergism in the mixed micelle and monolayer formed, whereas, thermodynamic parameters evaluated for the proposed mixed systems indicate stability of the resulting micelles and monolayer. Micellar aggregation number (N _agg) and hydrodynamic diameter (D _h) computed from fluorescence and dynamic light scattering measurements respectively illustrate micellar growth in the mixed state. Results obtained for the proposed mixed systems can be helpful in designing smart materials for industrial surfactant based formulations.     

Mixed Micellization Behavior of (Chlorpromazine Hydrochloride + Cetyltrimethylammonium Bromide) System in Aqueous Solutions of Glycine

We have examined the mixed micellar behavior of {amphiphilic drug; chlorpromazine hydrochloride (CPZ) + cationic surfactant; cetyltrimethylammonium bromide (CTAB)} at varying mole fractions of CPZ (α_CPZ = 0.2, 0.4, 0.6, and 0.8) in (0.1, 0.3, and 0.5) mol kg⁻¹ glycine_(aq) solutions at 298.15, 308.15, and 318.15 K, by using conductometric, volumetric, isentropic compressibility, UV–visible absorbance, fluorescence, and dynamic light scattering (DLS) techniques. The critical micelle concentration (CMC) values obtained from above measurements have been utilized to calculate the thermodynamic parameters (ΔG^°_m, ΔH^°_m, and ΔS^°_m) and degree of ionization (α) at studied temperatures and concentrations. The partial specific volume (φ_v), partial specific isentropic compression (φ_κ), and isentropic compressibility (κ_s) have been calculated from the experimental density and speed of sound measurements and the results have been used to elucidate different interactions occurring in these systems. These results are further supported by UV–visible absorbance and fluorescence spectroscopic studies. The hydrodynamic diameters (D_h) of the mixed micellar system have been measured from the DLS studies. Thermodynamic and spectroscopic studies depict the dominance of hydrophobic/hydrophilic-hydrophobic interactions between the alkyl (R = C₁₆H₃₃) chain of CTAB or hydrophobic tricyclic scaffolding of CPZ/Br⁻/N⁺-CH₃ group of CTAB or hydrophilic group i.e., tertiary amine portion of CPZ with hydrophobic group of glycine.     

Mixed Micellization and Mixed Monolayer Formation of Sodium Cholate and Sodium Deoxycholate in Presence of Hydrophobic Salts Under Physiological Conditions

Mixed micellization and mixed monolayer formation of two bile salts namely sodium cholate (NaC) and sodium deoxycholate (NaDC), in the presence of sodium chloride (NaCl) and three hydrophobic salts including sodium acetate (NaAc), sodium butanoate (NaBu) and sodium hexanoate (NaHx) in 10 mM phosphate buffer (pH 6.5) at 37 °C were investigated by means of surface tension measurements. The experimental results were utilized to evaluate various parameters like critical micellar concentration (CMC), micellar and monolayer interaction parameter (β and β ^σ), micellar and monolayer mole fractions (X and Z), activity coefficients of two bile salts in mixed micelles and monolayer (f and f _(σ)), surface excess (Γ_max) and minimum surface area per molecule of bile salt (A _min). Mixed micelles and mixed monolayer were found to show slight non-ideality and both these phenomena have been found to be affected differently in the presence of various additive salts with NaHx showing larger effects. Higher efficiency of NaHx in affecting both phenomena has been attributed to its appreciable hydrophobicity and surface activity, thus showing stronger interactions with bile salt molecules.     

Polymeric surfactants for enhanced oil recovery. Part V: Prediction models for the effect of temperature and length of polyoxyethylene chain or hlb on surface and thermodynamic properties of some ethoxylated polymeric nonionics

Several equation models were investigated to find the relationship between temperature (T). number of ethylene oxide (EO) units (n) or the hydrophile-lipophile balance (HLB) and the surface and thermodynamic properties of some ethoxylated alkylphenol-formaldehyde polymeric nonionic surfactants. These properties include critical micelle concentration (CMC), free energy of micellization (ΔG_mic), surface tension at CMC (7_CMC), effectiveness (γ_CMC) and efficiency (pC₂₀) of surfactant to reduce the surface tension of water. The values of the ratio CMC/C_{2(π = 20)} were also considered. The linear multiple regression technique was employed to determine the parameters of the equations and to choose the best forms with the highest values of R² and F-ratio which reflect the goodness and the reliability of the fit.     

Surface activity and micellar behavior of dimethylamino‐ and trimethylammonium‐ tipped oxyethylene–oxybutylene diblock copolymers in aqueous media

Surface activity and micellar behavior in aqueous media in the temperature range 20–50°C of the two block copolymers, Me₂N(CH₂)₂OE₃₉B₁₈, (DE₄₀B₁₈) and I^?Me₃N⁺(CH₂)₂OE₃₉B₁₈, (TE₄₀B₁₈) in the premicellar and postmicellar regions have been studied by surface tensiometry, viscometry, and densitometry. Where E represents an oxyethylene unit while B an oxybutylene unit. Various fundamental parameters such as, surface excess concentrations (Γ_m), area per molecule (a) at air/water interface and standard Gibbs free energy for adsorption, ΔG have been investigated for the premicellar region at several temperatures. The thermodynamic parameters of micellization such as, critical micelle concentrations, CMC, enthalpy of micellization, ΔH, standard free energy of micellization ΔG, and entropy of micellization ΔS have also been calculated from surface tension measurements. Dilute solution viscosities have been used to estimate the intrinsic viscosities, solute‐solvent interaction parameter and hydration of micelle. Partial specific volume and density of the micelle were obtained from the density measurements at various temperatures. The effect of modifying the end group of the hydrophilic block was investigated by comparing the behavior of trimethylammonium‐ and dimethylamino‐tipped copolymers, designated TE₄₀B₁₈, and DE₄₀B₁₈, respectively. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Controlled one-pot synthesis of pH-sensitive self-assembled diblock copolymers and their aggregation behavior

Diblock copolymers of t-butyl methacrylate (tBMA) and 2-(diethylamino)ethyl methacrylate (DEAEMA) were successfully synthesized by one-pot strategy via the atom transfer radical polymerization (ATRP). Kinetic results clearly demonstrated the controlled/‘living’ character of the polymerization. The zwitterionic block copolymers of poly(methacrylic acid-b-DEAEMA), obtained by hydrolysis of poly(tBMA-b-DEAEMA), showed pH-dependent reverse micellization behavior. Micellar aggregates formed from poly(MAA₃₀-b-DEAEMA₇₁), poly(MAA₆₈-b-DEAEMA₅₅) and poly(MAA₆₄-b-DEAEMA₄₄) had fairly low polydispersity index at both solutions of low pH of 2 and high pH of 12. Micelles formed at pH 2 were larger (R_h∼40-61 nm) with looser core due to hydration of the MAA. In the presence of simple electrolyte (0.3 mol dm⁻³ NaCl solution), the size of the micelles reduced by almost half while the aggregation number was little changed. This is attributed to the draining of the hydrated micellar core due to osmotic pressure. On the other hand, DEAEMA-core micelles formed at pH 12 were compact and much smaller (R_h∼14-22 nm). Addition of NaCl had only a small effect. The micellar size reduced only slightly due to the electrostatic screening effect and the aggregation number was almost unchanged.     

Associative properties of hydrophilic tip modified oxyethylene‐oxybutylene diblock copolymers in aqueous media: Effect of end‐group

The associative properties of Me₂N (CH₂)₂OE₅₈B₇ and I^?Me₃N⁺(CH₂)₂OE₅₈B₇ in aqueous solution in the temperature range of 20–50°C have been investigated by dynamic and static laser light scattering. Here E represents an oxyethylene unit and B an oxybutylene unit. The results obtained were compared with results for E_mB_n analog. Our result shows that for micelles of dimethylamino‐tipped, the hydrodynamic radius, was large as compared with the thermodynamic radius r_t, suggesting a “soft” micelle. For the trimethylammonium‐tipped copolymer, r_h decreases and r_t increase with the increase in temperature. Also the values of association number, N_w, were low but increase with increase in temperature, indicating a change from soft micelle at low temperature to small, less swollen micelles at high temperature. The high values of thermodynamic volume per molecule, r_t/N_w, for a polymer with charged tip could be attributed to intermicellar charge effect. The effect of salt on various micellar parameters has also been discussed. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Theoretical Approaches on the Synergistic Interaction between Double-Headed Anionic Amino Acid-Based Surfactants and Hexadecyltrimethylammonium Bromide

Theoretical investigations on the micellization of mixtures of (i) amino acid-based anionic surfactants [AAS: N-dodecyl derivatives of aminomalonate, −aspartate, and -glutamate] and (ii) hexadecyltrimethylammonium bromide (HTAB), were carried out at different mole ratios. Variation in the theoretical values of critical micelle concentration (CMC), mole fraction of surfactants in the micellar phase (X), at the interface (X^σ), interaction parameters at the bulk/interface (β^R/β^σ), ideality/nonideality of the mixing processes, and activity coefficients (f) were evaluated using Rubingh, Rosen, Motomora, and Sarmoria-Puvvada-Blankschtein models. CMC values significantly deviate from the theroretically calculated values, indicating associative interaction. With increasing mole fraction of AAS (α_AAS), the magnitude of the (β^R/β^σ) values gradually decreased, considered to attributable to hydrophobic interactions. With increasing α_AAS, the micellar mole fraction of HTAB (X₂) decreased insignificantly and X₂ values were higher than those compared to AAS for all combinations, due to the dominance of HTAB in micelles. Micellar mole fraction at the ideal state of AAS () differed from micellar mole fraction of AAS (X₁), indicating nonideality in the mixed micellization process. Gibbs free energy of micellization ( ∆G_m ) values are more negative than the free energy of micellization for ideal mixing (), indicating the micellization process is spontaneous. With increasing α_AAS, the enthalpy of micellization (ΔH_m) and entropy of micellization (ΔS_m) values gradually increased, which indicates micellization is exothermic. The different physicochemical parameters of the mixed micelles are correlated with the variation in the spacer length between the two carboxylate groups of AAS.     

Novel Phospholium-Type Cationic Surfactants: Synthesis,Aggregation Properties and Antimicrobial Activity

A series of novel phospholium amphiphilic compounds with straight alkyl chains with different numbers of carbon atoms (12, 14, 15, 16, 17, 18) were synthesized. The quaternary phosphorus, phosphonium cation, is incorporated into a five-membered heterocyclic ring. Their physicochemical properties were investigated by measurements of surface tension, conductivity and dynamic light scattering. The critical micelle concentration (c _M), the surface tension value at the c _M (γ _cmc), the surface area at the surface saturation per head group (A _cmc), the ionization degree of micelle (α), the free energy of micellization (ΔG° _mic), and hydrodynamic diameter (d _h) were determined. Antimicrobial activity was tested against bacteria and yeast. The structure–activity relationship was determined.     

Synthesis and some studies on fluorinated cationic surfactants: surface and biocidal activities

Three fluorinated cationic surfactants were prepared by condensing N-(2-bromoethyl)perfluoroalkylamides with stoichiometric amounts of pyridine, triethanolamine, and triethylamine to produce three quaternary ammonium salts. The surface and biocidal properties of these surfactants were investigated to find the relation between the structure of the hydrophilic portion of the compounds and their efficiency as biocides. The properties studied included critical micelle concentration (CMC), effectiveness (II_CMC), surface excess concentration (T_max), and area occupied by a molecule (A_min). Free energies of micellization (ΔG _mic ^o) and adsorption (ΔG _ads ^o) of the surfactants in aqueous solution were calculated. The minimal inhibitory concentrations of the prepared compounds were tested against five strains as representative group of microorganisms.     

Synthesis and properties of amphiphilic thermo-sensitive block copolymers

Octadecyl acrylate (ODA) as hydrophobic monomer and N-isopropylacryamide (NIPAAm) as hydrophilic monomer were chosen to synthetize the thermo-sensitive block copolymers PODA_x-PNIPAAm_y-PODA_x (BAB-type) via reversible-addition-fragmentation chain transfer (RAFT) polymerization, the block copolymers could self-assemble to flower-like micelles in aqueous solution with hydrophobic PODA as the inner core and stabilized by hydrophilic PNIPAAm as the outer shell. The characterizations of the micelles such as surfactivity, thermo-sensitivity, micelle hydrodynamic radius (R _h ) and polydispersity index (PdI) were demonstrated by surface tension technique, UV-Vis, and dynamic light scattering (DLS) measurements, respectively. The longer the hydrophilic chain was, the higher the critical micellization concentration (CMC) would be, and the higher content of the PODA was, the lower the lower critical solution temperature (LCST) would be. The average R _h remained at about 100 nm below LCST, but decreased sharply to about 42 nm and kept constant when reaching and above LCST, which meant the non-aggregation of BAB type block copolymers. The micelle was homogeneous with the small PdI within the range of research. B_0.5mA_24mB_0.5m had the largest capacity to encapsulate lipophilic Sudan Red IV model drugs and the drug loading efficiency was 9.76%.     

Influence of end-group modification on interaction of amphiphilic poly(oxyethylene)-<Emphasis Type="Italic">b</Emphasis>-poly(oxybutylene) block copolymers with ionic surfactants

Amphiphilic poly(oxyethylene)-b-poly(oxybutylene) block copolymers having hydrophilic block end-capped with neutral dimethylamino (DE₇₉B₃₄) and cationic trimethyl ammonium (TE₇₉B₃₄) groups, respectively were investigated for their interactions with ionic surfactants, sodium dodecyl sulfate (SDS) and cetyltrimethylammonium bromide (CTAB) using tensiometry, conductometry and dynamic light scattering. The self-assembly of DE₇₉B₃₄ and TE₇₉B₃₄ occur at 0.7 g/dm³ and 0.8 g/dm³, respectively. TE₇₉B₃₄ binds favorably with oppositely charged SDS, causing a substantial change in surface tension compared to other surfactant-polymer systems. In mixed polymer-surfactant systems, the micellization was promoted in the presence of SDS, but it was suppressed with CTAB. Such behavior is expected for cationic block copolymers, since they can engage into ion-pair formation with anionic SDS. For neutral polymers, the behavior is reflective of surfactants’ head group hydrophobicity. The head groups of CTAB are more hydrophobic and their existence in the proximity of hydrophobic segments of polymers induces shape transition to non-spherical morphologies. Gibb’s free energy of adsorption at air – water interface is negative for SDS, CTAB and surfactant-block copolymer systems, indicating that the process is highly spontaneous. The increase in entropy of TE₇₉B₃₄ during micelle formation with temperature is due to disturbance of hydrophobic structure of water molecules, thus hydrophobic parts are removed from bulk solution to the interface and also in the interior of micelle the freedom of hydrophobic part is increased. The dynamic laser light scattering results revealed that due to presence of block copolymers pre-micellar aggregates were favored.     

Polymeric surfactants for enhanced oil recovery. IV—Thermodynamic properties of ethoxylated alkylphenol formaldehyde polymeric surfactants

The thermodynamic properties of some low molecular weight ethoxylated alkylphenol formaldehyde polymeric surfactants have been investigated. Surface tension as a function of concentration of the surfactants in aqueous solutions was measured at 28, 38, 48 and 58°C, using the spinning drop technique. From these measurements, the minimum area per molecule at the aqueous solution/air interface (A_min) was determined. The thermodynamic parameters of micellization (ΔG_mic, ΔH_mic, ΔS_mic) and of adsorption (ΔG_ad, ΔH_ad, ΔS_ad) for these polymeric nonionics were calculated. Micellization is more sensitive to ethylene oxide chain length while adsorption is more dependent on the length of the alkyl chain.