Effect of end-group modification on the adsorption of poly(ethylene oxide)-b-poly(butylene oxide) diblock copolymers at the solid–liquid interface

The adsorption of poly(ethylene oxide)-b-poly(butylene oxide) diblock copolymers at the solid–liquid interface was studied using a quartz crystal microbalance with dissipation monitoring (QCM-D). The effect of modifying the end group of the hydrophilic block was investigated by comparing the behaviour of trimethylammonium- and dimethylamino-tipped copolymers, designated as TE _m B _n and DE _m B _n , respectively. For adsorption from aqueous solution onto a gold surface, results for DE₄₉B₂₂ were similar to those of the T-analogue, but for DE₈₀B₃₄ adsorbed amounts were substantially higher, and for DE₂₇B₂₅ enormously higher, than for the T-analogue. It is suggested that very high levels of adsorption are associated with the formation of a multilayer structure.     

Effect of end-group modification,hydrophilic/hydrophobic block ratio and temperature on the surface,associative and thermodynamic behaviour of poly(ethylene oxide)-b-poly(butylene oxide) diblock copolymers in aqueous media

This study describes the surface, micellar, associative and thermodynamic properties of four diblock oxyethylene (E)/oxybutylene (B) copolymers with different hydrophilic block ends and various hydrophilic/hydrophobic ratios in aqueous media. The copolymers were denoted DE₄₀B₁₈, TE₄₀B₁₈, E₅₆B₁₉ and E₅₆B₇. The aqueous polymer solutions at various concentrations and temperatures were investigated by surface tensiometry and dynamic and static laser light scattering. Surface tension measurements were employed to detect the critical micelle concentration (CMC) as well as to calculate the surface-active and thermodynamic parameters of adsorption at the air/water interface. CMC values were also used to calculate the enthalpy of micellization (?H ⁰ _mic), free energy of micellization (?G ⁰ _mic) and entropy of micellization (?S ⁰ _mic). Similarly, various thermodynamic parameters for adsorption at the air/water interface were also deduced. Dynamic light scattering (DLS) was used to obtain the hydrodynamic radii (r _h) and volumes (υ _h) of the micelle at different temperatures, and hence the hydrodynamic expansion parameter (δ _h) was also estimated. Likewise, static light-scattering measurements enabled us to determine various parameters of the copolymer micelles, such as the weight-average molar mass (M _w), association number (N _w), thermodynamic radius (r _t), thermodynamic volume (υ _t), anhydrous volume (υ _a) and the thermodynamic expansion parameter (δ_t). Various thermodynamic and micellar parameters obtained from light scattering show that the micelles formed are spherical in shape and have rather soft interaction potentials at low temperature but become harder at higher temperature. Based on the different experimental results obtained, it can be said that various surface, micellar and thermodynamic parameters are dependent not only on the temperature and solution conditions but also on the hydrophobic/hydrophilic ratio and the end-group composition of the polymer. Modification of the hydrophilic end group of the polymer prominently affects various micellar properties. This effect can be assigned to the difference in polarity and the intermicellar charge effect.     

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     

A Comparative Study on the Aggregation and Thermodynamic Properties of Anionic Sodium Dodecylsulphate and Cationic Cetyltrimethylammonium Bromide in Aqueous Medium: Effect of the Co-solvent N-Methylacetamide

The effect of co‐solvent N‐methylacetamide (NMA) (0.035, 0.046, 0.127, and 0.258 mol kg^?1) on the micellization behaviour of anionic surfactant sodium dodecylsulphate (SDS) (3.21–10.35 mmol kg^?1) and cationic surfactant cetyltrimethylammonium bromide (CTAB) (0.19–3.72 mmol kg^?1) in aqueous solution was explored by employing conductivity measurements at different temperatures (298.15–313.15 K). The critical micelle concentration (CMC) values for SDS and CTAB in aqueous solutions of NMA were determined from the conductivity versus surfactant concentration plots. The variations in the CMC values of SDS with NMA concentration are in striking contrast to those observed in the case of CTAB. The various relevant thermodynamic parameters of micellization, viz. standard enthalpy change, ΔH_m^o, standard entropy change, ΔS_m^o, and standard Gibbs free energy change, ΔG_m^o, were determined using the temperature variation of the CMC values and counterion binding. The results not only relate these thermodynamic parameters to the consequences of intermolecular interactions but are also able to differentiate between SDS–water–NMA and CTAB–water–NMA systems in terms of contributions from head groups as well as alkyl chains of surfactants.     

Constructing Gemini‐Like Surfactants with Single‐Chain Surfactant and Dicarboxylic Acid Sodium Salts

Construction of gemini‐like surfactants using the cationic single‐chain surfactant cetyltrimethylammonium bromide C₁₆H₃₃N(CH₃)₃Br₂ (CTAB) and the anionic dicarboxylic acid sodium salt NaOOC(CH₂)_n‐2COONa (C_nNa₂, n = 4, 6, 8, 10, 12) by way of non‐covalent interactions has been investigated by surface tension measurements, hydrogen‐1 nuclear magnetic resonance (¹H NMR) spectroscopy and isothermal titration microcalorimetry (ITC). The critical micelle concentrations (cmc) of the CTAB/C_nNa₂ mixtures are obviously lower than that of CTAB and strongly depend on the mixing ratio. Moreover, the cmc values of the CTAB/C_nNa₂ mixtures decrease gradually with an increasing methylene chain length of C_nNa₂, indicating hydrophobic interaction between the hydrocarbon chains of CTAB and C_nNa₂ facilitates micellization of the mixtures. In particular, the ITC curves and ¹H NMR spectra indicate that the binding ratio of CTAB to C_nNa₂, except C₄Na₂, is around 2:1, i.e., (CTAB)₂C_nNa₂. Additionally, CTAB/C_nNa₂ mixtures are soluble in a whole molar ratio and concentration ranges have been studied, even at the electrical neutralization point. Therefore, these results reveal that highly soluble gemini‐like surfactants are conveniently constructed with oppositely‐charged cationic single‐chain surfactants and dicarboxylic acid sodiums. In an attempt at improving the performance of surfactants this work provides guidance for choosing additives that form gemini‐like surfactants via an uncomplicated synthesis.     

Comparison of micelles formed by amphiphilic poly(ethylene glycol)‐b‐poly(trimethylene carbonate) star block copolymers

In this article, we describe the synthesis and solution properties of PEG‐b‐PTMC star block copolymers via ring‐opening polymerization (ROP) of trimethylene carbonate (TMC) monomer initiated at the hydroxyl end group of the core PEG using HCl Et₂O as a monomer activator. The ROP of TMC was performed to synthesize PEG‐b‐PTMC star block copolymers with one, two, four, and eight arms. The PEG‐b‐PTMC star block copolymers with same ratio of between hydrophobic PTMC and hydrophilic PEG segments were obtained in quantitative yield and exhibited monomodal GPC curves. The amphiphilic PEG‐b‐PTMC star block copolymers formed spherical micelles with a core–shell structure in an aqueous phase. The mean hydrodynamic diameters of the micelles increased from 17 to 194 nm with increasing arm number. As arm number increased, the critical micelle concentration (CMC) of the PEG‐b‐PTMC star block copolymers increased from 3.1 × 10^?3 to 21.1 × 10^?3 mg/mL but the partition equilibrium constant, which is an indicator of the hydrophobicity of the micelles of the PEG‐b‐PTMC star block copolymers in aqueous media, decreased from 4.44 × 10⁴ to 1.34 × 10⁴. In conclusion, we confirmed that the PEG‐b‐PTMC star block copolymers form micelles and, hence, may be potential hydrophobic drug delivery vehicles. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Interactions of a smart cationic polyelectrolyte based on hydroxypropylcellulose with an anionic surfactant

Novel thermosensitive, cationic polyelectrolyte was obtained by grafting N‐vinylformamide onto hydroxypropylcellulose followed by the hydrolysis of the formamide groups to the amine groups. The effect of the ionic strength on the lower critical solution temperature of the polymers was studied. The interactions of the polymers with sodium dodecyl sulfate (SDS) as a model anionic surfactant were studied. It was found by the measurements of the light scattering and fluorescence spectroscopy that the graft copolymers obtained strongly interact with SDS with the formation of polymer‐surfactant complexes. The values of critical association concentration (cac) of these polymer‐surfactant systems were found to be of the order of 10^?5 mol/dm³ at pH = 6.5 and of the order of 10^?6 mol/dm³ at pH = 2.5. The polymer was shown to be potentially useful for the purification of water from anionic surfactants. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Surface behavior and micelle morphology of novel nonionic polyurethane bolaform amphiphilic block copolymers

A novel series of nonionic bolaamphiphiles—polyurethane amphiphilic block copolymers were synthesized by addition polymerization. Their chemical structures were characterized using FTIR and ¹H-NMR spectra. The critical micelle concentration was determined by surface tensiometer and UV-vis absorption spectra. The surface behaviors of copolymers at air/water interface were also investigated including the effects of concentration, molecular structure, electrolytes, and rest time. The results show that these bolaform polyurethane amphiphilic block copolymers exhibited excellent surface activity: PU₃₄ could attain surface tension as low as 35.6 mN m⁻¹. According to the images of Transmission Electron Microscopy (TEM), the copolymers could self-assemble star-like aggregates comprised of hydrophobic block PPO surrounded by hydrophilic block PEO. Moreover, variation of concentration, the weight fraction of the hydrophilic block (f_phil), and the molecular weight of the copolymers could lead to the transformation of micelle (or premicelle) morphology. This provides a new and simple way to obtain nanoparticles with control over structure on the nanometer scale.     

Synthesis of amphiphilic temperature‐sensitive poly(N‐isopropylacrylamide)‐block‐poly(tetramethylene carbonate) block copolymers and micellar characterization

Amphiphilic thermally sensitive poly(N‐isopropylacrylamide)‐block‐poly(tetramethylene carbonate) block copolymers were synthesized by ring‐opening polymerization of tetramethylene carbonate with hydroxyl‐terminated poly(N‐isopropylacrylamide) (PNiPAAm) as macro‐initiator in the presence of stannous octoate as catalyst. The synthesis involved PNiPAAm bearing a single terminal hydroxyl group prepared by telomerization using 2‐hydroxyethanethiol as a chain‐transfer agent. The copolymers were characterized using ¹H NMR and Fourier transform infrared spectroscopy and gel permeation chromatography. Their solutions show reversible changes in optical properties: transparent below the lower critical solution temperature (LCST) and opaque above the LCST. The LCST depends on the polymer composition and the media. Owing to their amphiphilic characteristics, the block copolymers form micelles in the aqueous phase with critical micelle concentrations (CMCs) in the range 1.11–22.9 mg L^?1. Increasing the hydrophobic segment length or decreasing the hydrophilic segment length in the amphiphilic diblock copolymers produces lower CMCs. A core‐shell structure of the micelles is evident from ¹H NMR analyses of the micelles in D₂O. Transmission electron microscopic analyses of micelle morphology show a spherical structure of both blank and drug‐loaded micelles. The blank and drug‐loaded micelles have an average size of less than 130 nm. Observations show high drug‐entrapment efficiency and drug‐loading content for the drug‐loaded micelles. Copyright © 2010 Society of Chemical Industry     

Effect of cefoperazone sodium on the physicochemical properties of surfactants

The effects of cefoperazone sodium (CS), a pharmaceutical compound, on the critical micelle concentration (CMC) of surfactants with different charges [cetyl trimethylammonium bromide (CTAB), sodium dodecyl sulfate (SDS), and Triton X-100], the cloud point of Triton X-100, and the Krafft temperatures of SDS and CTAB were studied. The interaction of CS with differently charged surfactants was determined by ultraviolet and fluorescence spectrophotometry. The results show that with increasing CS concentration, the Krafft temperature increases and the CMC decreases in the SDS/H₂O system, whereas the opposite results are obtained in the CTAB/H₂O system. Both the cloud point and the CMC of Triton X-100 increase with the addition of CS. The above results are attributed to the different micellar interactions between CS and surfactants with different charges.     

Synthesis and characterization of dual stimuli-responsive block copolymers based on poly(N-isopropylacrylamide)-b-poly(pseudoamino acid)

The current study synthesized amphiphilic thermal/pH-sensitive block copolymers PNiPAAm-b-PHpr by condensation polymerization of trans-4-hydroxy-l-proline (Hpr) initiated from hydroxy-terminated poly(N-isopropylacrylamide) (PNiPAAm) as the macroinitiator in the presence of the catalyst, SnOct₂. ¹H NMR, FTIR, and gel permeation chromatography (GPC) characterized these copolymers. Their solutions showed reversible changes in optical properties: transparent below a lower critical solution temperature (LCST) and opaque above the LCST. The LCST values depended on the polymer composition and the media. With critical micelle concentrations (CMCs) in the range of 1.23-3.73 mg L⁻¹, the block copolymers formed micelles in the aqueous phase owing to their amphiphilic characteristics. Increased hydrophobic segment length or decreased hydrophilic segment length in an amphiphilic diblock copolymer produced lower CMC values. The current work proved the core-shell structure of micelles by ¹H NMR analyses of the micelles in D₂O. Transmission electron microscopy analyzed micelle morphology, showing a spherical core-shell structure. The micelles had an average size in the range of 170˜210 nm (blank), and 195˜280 nm (with drug). Observations showed high drug entrapment efficiency and drug-loading content for the drug micelles.     

Effect of Surfactants on Catalytic Activity of Diastase α-Amylase

The enzyme amylase is one of the hydrolyzing enzymes used in detergent formulation in order to remove soil based on polysaccharides. The effectiveness of the enzyme depends on its compatibility with other ingredients of the formulation. Among the studied additives, comprising anionic surfactants sodium dodecyl hydrogen sulfate (SDS) and dioctyl sodium sulfosuccinate, the cationic surfactant cetyl trimethyl ammonium bromide (CTAB), nonionic surfactants polyoxyethylene sorbitan monooleate and polyoxyethylene octyl phenyl ether, carboxy methyl cellulose and sodium sulfate, only the anionic surfactant SDS and cationic surfactant CTAB showed catalytic enhancement of α-amylase. The kinetic parameters, K _m and k _cat, showed an increase in catalytic activity in the micellar pseudophase. The decrease in optimum temperature from 55 to 30 °C and the shift in optimum pH from 5.5 to 7 on the addition of SDS and CTAB for the hydrolysis of starch are very favorable to enhance the washing characteristics.     

Physico-Chemical Investigations of Mixed Micelles of Cationic Gemini and Conventional Surfactants: a Conductometric Study

The interaction of cationic gemini and cationic conventional surfactants by conductivity was systematically overviewed, paying attention to synergism observed in micellization. These mixed systems were found to show remarkable synergism in micelle formation. The experimental critical micelle concentration values being lower than the value predicted by ideal solution theory indicate that the mixed micellization is due to attractive interaction between the two components. Gemini/conventional systems form mixed micelle due to attractive interactions (negative β values). The values of micellar mole fraction of constituent 1 (X ₁) in surfactant mixtures are more than in the ideal state (X ₁ ^ideal ), which means that, the mixed micelles are rich in conventional surfactants in comparison to that in the ideal state.     

Synthesis,surface, thermodynamic properties and Biological activity of dimethylaminopropylamine surfactants

The chemical structure of the prepared cationic surfactants which formed through condensation reaction between dimethylaminopropylamine (DMAPA) and butyraldehyde then quaternized by three fatty alkyl bromide was confirmed by FTIR, ¹HNMR and mass spectroscopy. The chemical structure of prepared compounds has an effect on surface properties. By increasing the hydrophobic chain length, the values of CMC and Г_max decrease while A_min value was increased. The Thermodynamic parameters showed that adsorption and micellization processes are spontaneous. It is clear that the prepared cationic surfactants tend to adsorb at surface, then it aggregate to form micelle. The prepared surfactants showed good biological activity against Gram-positive and negative bacteria and fungi. The prepared cationic surfactant showed aggressive effect on the sulfate reducing bacteria growth.     

Synthesis of poly(vinyl alcohol)‐graft‐poly(ε‐caprolactone) and poly(vinyl alcohol)‐graft‐poly(lactide) in melt with magnesium hydride as catalyst

Grafting of poly(ε‐caprolactone) (PCL) and poly(lactide) (PLA) chains on poly(vinyl alcohol) backbone (PVA degree of hydrolysis 99%) was investigated using MgH₂ environmental catalyst and melt‐grown ring‐opening polymerization (ROP) of ε‐caprolactone (CL) and L ‐lactide (LA), that avoiding undesirable toxic catalyst and solvent. The ability of MgH₂ as catalyst as well as yield of reaction were discussed according to various PVA/CL/MgH₂ and PVA/LA/MgH₂ ratio. PVA‐g‐PCL and PVA‐g‐PLA were characterized by ¹H‐ and ¹³C‐NMR, DSC, SEC, IR. For graft copolymers easily soluble in tetrahydrofuran (THF) or chloroform, wettability and surface energy of cast film varied in relation with the length and number of hydrophobic chains. Aqueous solution of micelle‐like particles was realized by dissolution in THF then addition of water. Critical micelle concentration (CMC) decreased with hydrophobic chains. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Association behavior of thermo-responsive block copolymers based on poly(vinyl ethers)

Thermo-sensitive nanosized structures have been prepared in water from poly(methyl vinyl ether)-block-poly(isobutyl vinyl ether) (PMVE-b-PIBVE) block copolymers. The composition and the architecture (diblock and triblock architectures) of the PMVE-b-PIBVE copolymers have been varied. The investigated copolymers had an asymmetric composition with a major PMVE block. While the PIBVE blocks are hydrophobic, the PMVE blocks are hydrophilic at room temperature and become hydrophobic above their demixing temperature (around 36 °C) as a result of the lower critical solution temperature (LCST) behavior. At room temperature, the amphiphilic copolymers aggregate in water above a critical micelle concentration, which has been experimentally measured by hydrophobic dye solubilization. The hydrodynamic diameter of the structures formed above the cmc has been measured by dynamic light scattering (DLS) while their morphology has been studied by transmission electron microscopy (TEM). ¹H NMR measurements in D₂O at room temperature reveal that the aggregates contain PIBVE insoluble regions surrounded by solvated PMVE chains. These investigations have shown that polydisperse spherical micelles are formed for asymmetric PMVE-b-PIBVE copolymers containing at least 9 IBVE units. For copolymers containing less IBVE units, loose aggregates are formed.Finally, the thermo-responsive, reversible properties of these structures have been investigated. Above the cloud point of the copolymers, the loose aggregates precipitate while the micelles form large spherical structures.     

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.     

Synthesis and association properties in water solution of random copolymers of 2‐acrylamido‐2‐methyl‐1‐propane sulfonic acid and isodecyl methacrylate—potential application as surfactants in micellar‐enhanced ultrafiltration processes

Hydrophobically modified water‐soluble polymers have been prepared by copolymerization of 2‐acrylamido‐2‐methylpropane sulfonic acid (AMPS) and isodecyl methacrylate (iDMA) in N,N‐dimethylformamide under nitrogen atmosphere, varying the composition feed. Fluorescence spectroscopy was used to further confirm the copolymers self‐aggregate in water. Critical concentration of the self‐aggregate formation (CAC) decreased by increasing the molar fraction of iDMA in the AMPS_co copolymers and varied between 1.20 and 0.04 g/L depending on the degree of hydrophobic modification. Hence, copolymer composition and charge density allowed tuning the pseudomicellar characteristics of these new amphiphilic copolymers. The addition of a salt or a low‐molecular‐weight surfactant was studied. Binding of CTAB to the AMPS_co copolymers leads to a high decrease of CAC, i.e., 0.006 g/L. Effect of the composition in the viscosimetric behavior of the hydrophobically modified copolymers AMPS_co was investigated. The removal of single metal ions, Cu²⁺, and m‐cresol from aqueous solutions by ultrafiltration with the help of the copolymers was investigated. Equilibrium dialysis experiments demonstrate that the formation of hydrophobic microdomains can be used to control the sequestration of foulants, and thus these novel copolymers have potential application as polymeric surfactants in micellar‐enhanced ultrafiltration processes for water purification. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Mixed Micellar Properties and Related Interaction Parameters of Butanediyl-1,4-bis(dodecyl dimethyl ammonium bromide) Gemini Surfactant with Nonionic Amphiphiles

Mixed micellization of cationic gemini surfactant butanediyl-1,4-bis(dimethyldodecylammonium bromide) with nonionic surfactants (sorbitan esters, alcohols and phenol ethoxylates) and triblock copolymers has been studied tensiometrically. Various physicochemical parameters of the studied systems including ideal CMC values, experimental and ideal micellar compositions, interaction parameters, activity coefficients of the components, etc. have been evaluated by considering theoretical models of Clint, Rubingh, Rosen and Maeda. The experimental critical micelle concentration (CMC) values of the mixed micelles were lower than the CMC values of the individual components and showed a negative deviation from ideal CMC (CMC*) values. The analysis reveals that the mole fractions of gemini are lower compared to the nonionic surfactants/triblock polymers and the values of ΔG _m ^° , ΔG _ad ^° , G _min and ΔG _ex ^m show that the spontaneity of the studied mixed micelles relatively decreases as the content of the gemini in the bulk phase increases.