Showing papers on "Aggregation number published in 2002"
TL;DR: In this paper, the structure of polyelectrolyte block copolymer micelles in dilute aqueous solution was characterized as a function of pH and ionic strength.
Abstract: We characterize the structures of various polyelectrolyte block copolymer micelles in dilute aqueous solution as a function of pH and ionic strength. The block copolymers carry a common core block, 2-(diethylamino)ethyl methacrylate (DEAEMA), and one of three coronal blocks, 2-(dimethylamino)ethyl methacrylate (DMAEMA), poly(ethylene oxide) (PEO), and DMAEMA, whose side chain amine groups are selectively quaternized with benzyl chloride (Q-DMAEMA). The PEO−DEAEMA, DMAEMA−DEAEMA, and Q-DMAEMA−DEAEMA copolymers form micelles with electrostatically neutral, weakly charged, and highly charged coronae, respectively. We adjust the fractional charge α on the DEAEMA and DMAEMA blocks by adjusting the solution pH. For DMAEMA−DEAEMA micelles increasing the fractional charge α swells the micelle corona while decreasing the aggregation number due to electrostatic repulsions. The decrease in aggregation number is also observed with increasing α for the PEO−DEAEMA and Q-DMAEMA−DEAEMA micelles, due to electrostatic repu...
180 citations
TL;DR: In this paper, the aggregation numbers for DTAB and DTAC were obtained by using time-resolved fluorescence quenching (TRFQ) and electron paramagnetic resonance (EPR) to characterize micelles of dodecyltrimethylammonium bromide and chloride.
Abstract: Time-resolved fluorescence quenching (TRFQ) and electron paramagnetic resonance (EPR) were employed to characterize micelles of dodecyltrimethylammonium bromide and chloride (DTAB and DTAC) as reaction media. For DTAB, the aggregation numbers, N, and the quenching rate constant of pyrene by hexadecylpyridinium chloride, kq, were measured with TRFQ. Both these aggregation numbers for DTAB and those for DTAC taken from the literature depend only on the concentration of counterions in the aqueous phase, Caq, whether these counterions are supplied by the surfactant alone or by surfactant plus added salt. Both surfactants conform to the power law N = N0(Caq/cmc0)γ where N0 is the aggregation number at the critical micelle concentration in the absence of any additives (cmc0). N0 and γ differ for the two surfactants and vary with temperature in DTAB. EPR is employed to investigate the microviscosity and the hydration of the polar shell using a spin probe. The hydration is expressed by the nonempirical polarity p...
160 citations
TL;DR: The results indicated that the location of the OH group at C-7 and its orientation were the most important factors from the viewpoint of chemical structure for the growth of micelles.
147 citations
TL;DR: In this paper, the structure of charged spherical block copolymer micelles in aqueous solution was investigated with static and dynamic light scattering, small-angle neutron scattering, and cryo-electron microscopy as a function of added salt.
Abstract: The structure of charged spherical block copolymer micelles in aqueous solution was investigated with static and dynamic light scattering, small-angle neutron scattering, and cryo-electron microscopy as a function of added salt. At low added salt concentration the polyelectrolyte shell has typical features of an osmotic brush. If the added salt concentration exceeds the intrinsic ionic strength of the polyelectrolyte shell, the micellar aggregation number increases due to screening of the repulsive interaction between polyelectrolyte chains (salted brush). The relation between shell ionic strength and added salt concentration follows a simple Donnan equilibrium. The combination of methods reveals that the polyelectrolyte shell is phase-separated into a dense interior and a dilute outer domain.
136 citations
TL;DR: In this article, the Tergitol 15-S-X (X = 7,9 and 12) was used for modeling polycyclic aromatic hydrocarbons (PAHs) at temperatures below their cloud points.
135 citations
TL;DR: The results indicate that SDS-trypsin aggregates start to form at a surfactant concentration higher than the critical micelle concentration of pure SDS micelle, and the counterion binding decreases in the presence of trypsin.
122 citations
TL;DR: In this paper, a series of gemini surfactants, 12−4(OH)n−12 (n = 0, 1, or 2), with increasing hydroxyl substitution within the spacer group are reported.
Abstract: Critical micelle concentration (cmc), degree of micelle ionization (α), headgroup area (a0), mean aggregation number, enthalpy of micellization (ΔHM), and volume of micellization (ΔVφ,M) properties are reported for a series of gemini surfactants, 12−4(OH)n−12 (n = 0, 1, or 2), with increasing hydroxyl substitution within the spacer group. The cmc and mean aggregation numbers are observed to decrease with increased hydroxyl substitution consistent with increasing hydrophilicity of the headgroup. Both a0 and α are unaffected by hydroxyl substitution. ΔHM° is observed to decrease (become more exothermic) with increased substitution of the spacer group, while ΔVφ,M is observed to increase. These observations are rationalized in terms of changes in the solvation and conformation of the spacer group at the micelle−bulk solution interface. Free energies of micellization, ΔGM°, and entropies of micellization, ΔSM°, are calculated from the ΔHM°, cmc, and α values. The results indicate that the micellization proces...
117 citations
TL;DR: In this paper, the effect of various alkali-metal chloride electrolytes on the micellar formation process of Triton X-100 was investigated by using static and dynamic light scattering.
Abstract: The purpose of this paper is to investigate the effect of various alkali-metal chloride electrolytes on the micellar formation process of Triton X-100. We have studied the micellar solutions by using static and dynamic light scattering. A combined analysis of the data obtained from both techniques has been carried out in the context of micellar structure and hydration. To examine the effect of the size and hydration of ions on the micellar growth, experiments with three different electrolytes (LiCl, NaCl, and CsCl) covering a wide range of ionic strength (0−2 M salt added) have been performed. It was found that both the ionic strength and the cation nature have a substantial effect on the micellar growth. The postulated growth mechanism consists of a progressive process involving both an increase in the micellar aggregation number accompanied with a rise of associated water which is nonspecifically bonded with the micelle. However, the amount of water molecules hydrogen bonded was found to decrease with t...
107 citations
TL;DR: Data indicated the formation of micelles with a less ordered structure as the formamide increases in the solvent system, which is attributed to an enhanced solvation in formamide rich solvent mixtures.
101 citations
TL;DR: In this paper, a phenomenological limit mixed micellization line is proposed to define the limit conditions to form mixed mouselles, where the mixing of two cationic surfactants of identical tail but polar heads is considered.
Abstract: Conductivity and steady-state fluorescence measurements have been carried out at 25 °C to study the monomeric and micellar phases of the aqueous solutions of the mixed system constituted by two cationic surfactants, dodecylethyldimethylammonium bromide and dodecyltrimethylammonium bromide. From conductivity data, the total critical mixed micellar concentration, cmc*, and the dissociation degree of the mixed micelle, β, have been obtained, while fluorescence experiments allow for the determination of the total aggregation number, N*, and the micropolarity of the micellar inside. A new experimental method has been designed to determine the partial contribution of each surfactant to the mixed micellization process, through their critical micellar concentrations, cmc1* and cmc2*, and their aggregation numbers, N1* and N2*. A phenomenological limit mixed micellization line is proposed to define the limit conditions to form mixed micelles. The mixing of two cationic surfactants of identical tail but polar heads...
84 citations
TL;DR: In this article, asymmetric poly(ethylenepropylene-b-dimethylsiloxane) diblock copolymer melts have been examined by rheology, smallangle X-ray scattering (SAXS), and small-angle neutron scattering (SANS).
Abstract: Two asymmetric poly(ethylenepropylene-b-dimethylsiloxane) diblock copolymer melts have been examined by rheology, small-angle X-ray scattering (SAXS), and small-angle neutron scattering (SANS). The two copolymers have total molecular weights of 24 400 and 23 900 and PDMS volume fractions of 0.12 and 0.10, respectively. The latter copolymer was obtained by extensive fractionation of the former, the difference in composition arising primarily from the removal of traces of PDMS homopolymer. The order-disorder transition (ODT) is unambiguously identified by rheology and SAXS. Above the ODT the SANS and rheological properties are consistent with the recently proposed disordered micelle regime, whereby the copolymers are associated in micellar aggregates that are not ordered on a lattice. The viscosity of the melt in this regime is greater than that of a poly(ethylenepropylene) homopolymer of the same total molecular weight. The SANS structure factors were analyzed by a generalized inverse Fourier transform and by direct fitting to a model based on the Percus-Yevick structure factor and either a spherical or an ellipsoidal form factor. Both approaches give comparable results, and the average micelle core radius, effective hard-sphere radius, and volume fraction were extracted as a function of temperature. The fitting suggests that as temperature increases the micelles remain relatively unchanged, but their number density and volume fraction decrease steadily. The fractionated copolymer has a significantly smaller micellar core than its precursor and therefore a significantly smaller aggregation number. These differences are attributable to the partitioning of PDMS homopolymer into the micellar cores. For these samples the critical micelle temperature (cmt), where the volume fraction of micelles should become negligible, was not accessed, even 100 deg above the ODT.
TL;DR: In this article, the micellar formation of a combination of hydrocarbon/fluorocarbon anionic surfactantssodium n-tetradecyl sulfate (STDS) and sodium perfluorononate (SPFN) in water was studied, paying special attention to the interaction between the two surfactants and the aggregation number, N, as a function of composition in the mixture (XSTDS).
Abstract: Micelle formation of a combination of hydrocarbon/fluorocarbon anionic surfactantssodium n-tetradecyl sulfate (STDS) and sodium perfluorononate (SPFN) in waterwas studied, paying special attention to the interaction between the two surfactants and the aggregation number, N, as a function of composition in the mixture (XSTDS). The critical micellization concentration (cmc) at each composition was determined at discrete temperatures by plotting the derivative specific conductance (∂κ/∂C) against the root of molarity (√C) at 40 °C. This plot enabled us to determine the cmc even in solutions with addd salt (NaCl) and thus estimate the degree of counterion binding onto micelles (β) for both single systems from the Corrin−Harkins relation. The micellar composition of STDS (YSTDS) and interaction parameter were estimated on the basis of Rubingh's and our own theoretical equations, and the results obtained from the respective equations were compared. Although Rubingh's and our own equations resulted in differing ...
TL;DR: In this article, a theory describing the self-assembly of diblock copolymers with a weak polyelectrolyte block and a hydrophobic block is developed.
Abstract: A theory describing the self-assembly of diblock copolymers with a weak (annealing) polyelectrolyte block and a hydrophobic block is developed. Copolymers with short hydrophobic and long polyelectrolyte block form starlike micelles in aqueous solution; otherwise, crew-cut micelles are found. We demonstrate that there is strong coupling between copolymer self-assembly and ionization of the polyelectrolyte block. At low pH and/or low salt concentration large quasi-neutral micelles with nondissociated coronae are stable. An increase in salt concentration promotes ionization of coronae and leads to the decrease in aggregation number. The structural rearrangement occurs continuously for crew-cut micelles while for starlike micelles the jump-wise morphological transition is predicted. A subsequent increase in salt concentration results in increasing aggregation number accompanied by weak decrease in the corona span. An increase in pH leads to decreasing aggregation number and increasing span of the corona; this...
TL;DR: In this paper, a steadystate and nanosecond time-resolved study was carried out on the fluorescence quenching of excited pyrene by N, N -dibutylaniline in an aqueous solution of non-ionic micelles of the six Tritons, (oxyethylene) m - p -(1,1,3,3-tetramethylbutyl)phenyl ethers with m ranging from 8 to 70.
Abstract: Steady-state and nanosecond time-resolved studies have been carried out on the fluorescence quenching of excited pyrene by N , N -dibutylaniline in an aqueous solution of non-ionic micelles of the six Tritons, (oxyethylene) m - p -(1,1,3,3-tetramethylbutyl)phenyl ethers with m ranging from 8 to 70. The aggregation numbers and the rate constants of intramicellar quenching have been determined. The critical micelle concentrations of investigated Tritons were determined using the dependence of the fluorescence spectrum of pyrene on the microenvironment. The local polarity was obtained from the intensity ratio of the first to the third peak ( I 1 / I 3 ) in the fluorescence spectrum of pyrene. The microviscosity of the micellar core was estimated to be about 200 cP at ambient temperature on the basis of fluorescence spectra of 1,3-bis(1-pyrene)propane, from the excimer to the monomer emission intensity ratio using the calibration curve determined for a number of solvents of known viscosities.
TL;DR: Aqueous solutions of associative polymers consisting of poly(ethylene glycol) (PEG) (6K or 10k g/mol) terminated at both ends with hydrophobic fluoroalkyl segments, −(CH_2)_2CnF_(2n+1) (n = 6, 8, or 10), exhibit ordering transitions with increasing concentration as mentioned in this paper.
Abstract: Aqueous solutions of associative polymers consisting of poly(ethylene glycol) (PEG) (6K or 10K g/mol) terminated at both ends with hydrophobic fluoroalkyl segments, −(CH_2)_2CnF_(2n+1) (n = 6, 8, or 10), exhibit ordering transitions with increasing concentration The hydrophobic cores of the micelle-like aggregates order into a body-centered-cubic (bcc) structure, as observed by small-angle neutron scattering The aggregation number of the hydrophobic core N_(ag) is determined by the length of the hydrophobic end group and is insensitive to polymer concentration or temperature Ordering is enhanced by reducing PEG length for a given end group (hence, similar N_(ag)) or by increasing end group length (larger N_(ag)) for a given PEG length This micelle packing effect is manifested in changes in the viscoelastic properties Specifically, the single-relaxation behavior in the dynamic moduli changes upon ordering as a new low-frequency elastic plateau appears, and in creep a linear response changes to yielding behavior
TL;DR: Aggregation in aqueous solutions of sodium methyl 2-acylamido-2-deoxy-6-O-sulfo-d-glucopyranoside surfactants has been studied in this paper.
Abstract: Aggregation in aqueous solutions of sodium methyl 2-acylamido-2-deoxy-6-O-sulfo-d-glucopyranoside surfactants has been studied, where the acyl group is octanoyl, dodecanoyl, or hexadecanoyl. Critical micelle concentration, cmc, minimum area per surfactant at the air/solution interface, σ, degree of counterion dissociation, αmic, and thermodynamic parameters (Gibbs free energy, enthalpy, and entropy) of adsorption and/or micellization were calculated from surface tension and conductance measurements. Static and quasi-elastic light scattering measurements were employed to obtain micellar weight-average molecular weight, aggregation number, Nagg, and hydrodynamic radius. Finally, the fluorescence spectrum of solubilized pyrene was employed for determination of micellar polarity. The similarities between these aminoglucose-based surfactants and simple anionic ones include decrease of cmc and of αmic and increase of Nagg as a function of increasing the chain length of the hydrophobic group. Compared to simple ...
TL;DR: The interdigitation between the surfactant molecules in the micelle will contribute to the unusually long lifetime, in other words, slow surfactants exchange on the NMR time scale.
Abstract: The exchange of a fluorocarbon−hydrocarbon hybrid surfactant between monomer and micelle states in deuterium oxide has been investigated through 19F NMR and 1H NMR experiments. The CF3 group in the surfactant gives two kinds of 19F NMR signals corresponding to the monomer and micelle states, indicating slow surfactant exchange on NMR time scale. The lifetime (τmic) of micelle, estimated by line shape analysis of the signals, is 2.0 ms at cmc, 102 to 103 times longer than that of general surfactant micelles. Pulsed-gradient spin−echo (PGSE) experiments show that the hybrid surfactant forms considerably small micelles with a hydrodynamic radius of 0.6 nm. In contrast, at a higher concentration where no slow surfactant exchange is observed, the micelle radius increases to 1.1 nm. The interdigitation between the surfactant molecules in the micelle will contribute to the unusually long lifetime, in other words, slow surfactant exchange on the NMR time scale.
TL;DR: In this article, the mixed micelles of SDS and tetraoxyethylene dodecyl ether (C12E4 or Brij 30) were studied by surface tension, ζ potential, and fluorescence spectroscopy measurements.
Abstract: The mixed micelles of sodium dodecyl sulfate (SDS) and tetraoxyethylene dodecyl ether (C12E4 or Brij 30) were studied by surface tension, ζ potential, and fluorescence spectroscopy measurements. In the range of 0−0.5 mole fraction (x) of added Brij 30 to a 30 mM SDS solution, the mixed micellar aggregation number (Nagg) changed from 65 to 171, and the ζ potential of the micelles varied from −60 to −15 mV. The change in size was acompanhied by a 2-fold increase in the internal micellar viscosity, indicating that addition of the nonionic surfactant with similar alkyl chain enhances the surfactant packing in the mixed aggregate. The reduction of the electrical surface potential causes a proportional decrease of the binding constant of the cationic dye acridine orange. The change in temperature from 15 to 45 °C of a solution with x = 0.5 results in a decrease in the Nagg from 175 to 128, but the SDS to Brij 30 monomers ratio remains constant. This fact is typical of ionic micelles, opposite to the usual behav...
TL;DR: In this paper, the structure of a diblock copolymer solution in the vicinity of the transition between micellar liquid and solid phases was investigated using small-angle x-ray scattering (SAXS).
Abstract: The structure of a diblock copolymer solution in the vicinity of the transition between micellar liquid and solid phases was investigated using small-angle x-ray scattering (SAXS). An amphiphilic poly(oxyethylene)–poly(oxybutylene) diblock was studied in water. Static and dynamic light scattering techniques were used to provide an independent measure of micelle dimensions and aggregation number. Dynamic shear rheometry and mobility measurements were used to locate phase transitions. A micellar liquid phase was identified at low concentration and a cubic micellar phase at higher concentration, the transition between the two occurring at higher temperature as the concentration increased. The cubic micellar phase behaves rheologically as a solid and SAXS confirmed a face-centered cubic structure. Intermediate between these two phases, a viscoelastic soft solid was observed, with a finite yield stress but with a much lower dynamic modulus than the crystalline solid. Several distinct suggestions have been put ...
TL;DR: It was found that the monomeric fluorescence intensity ratio (Im3/Im1) of the third to the first vibrational bands of pyrene in the micelles depends on the volume of the hydrophobic core, that is, the alkyl chain length.
Abstract: The locations and numbers of solubilized pyrene molecules in heptaethyleneoxide monoalkyl ether CnE7 (n = 10, 12, 14, and 16) surfactant micelles were studied as functions of the alkyl chain length, micelle concentration, aggregation number, and pyrene concentration by means of steady-state fluorescence spectroscopy. It was found that the monomeric fluorescence intensity ratio (Im3/Im1) of the third to the first vibrational bands of pyrene in the micelles depends on the volume of the hydrophobic core, that is, the alkyl chain length. The ratio of pyrene excimer fluorescence intensity to the intensity of the first vibrational band (Ie/Im1) was found to increase with the CnE7 micelle concentration and to reach a maximum ratio at a particular micellar concentration. The micellar concentration at the maximum value of Ie/Im1 depended on the alkyl chain length and shifted to a lower micellar concentration when the alkyl chain length increased. The number of solubilized pyrene molecules in the unit core volume a...
TL;DR: In this paper, a triblock copolymers of styrene and isoprene with normal tapered, inverse tapered (ITMB), and random (RMB) middle blocks were synthesized by using appropriate anionic polymerization high-vacuum techniques.
Abstract: By using appropriate anionic polymerization high-vacuum techniques, novel triblock copolymers of styrene and isoprene with normal tapered (TMB), inverse tapered (ITMB), and random (RMB) middle blocks were synthesized. In addition, diblock copolymers (SI) as reference materials and normal tapered (TBC) and random (RC) were prepared. All copolymers have practically the same composition (∼50 wt % PS). Their micellization behavior was investigated in dilute solutions in n-decane, a selective solvent for the isoprene part of the macromolecules, by static and dynamic light scattering as well as viscometry. Experiments were directed toward the determination of the micelles fundamental properties (average aggregation number, critical micelle concentration, critical micellization temperature) and compared with those obtained for pure diblock copolymers. No considerable differences, compared to the pure diblock copolymers, were observed for triblocks having a normal tapered middle block (TMB). A considerable decrease in the aggregation number and a corresponding decrease in the critical micellization temperature were found for the triblock copolymers having an inverse tapered middle block (ITMB) with length comparable to the length of the outer pure blocks. A similar decrease in the aggregation number was also observed in the case of a normal tapered copolymer. The differences in behavior are attributed to the different arrangement of the segments, which seems to have a considerable effect on the solubility characteristics of these copolymers.
TL;DR: The micelle formation and micelle structure of an amphiphilic poly(dimethylsiloxane)-graft-polyether copolymer in aqueous solution were investigated with a variety of experimental techniques as mentioned in this paper.
Abstract: The micelle formation and micelle structure of an amphiphilic poly(dimethylsiloxane)-graft-polyether copolymer in aqueous solution were investigated with a variety of experimental techniques. We measured the CMC by three different methodsDPH solubilization, methyl orange hypsochromic shift, and pyrene fluorescence I1/I3 ratio. The microviscosity was evaluated from DPH anisotropy values that were obtained by fluorescence polarization measurements. The microviscosity in the siloxane copolymer micelles was found lower than that in Pluronic block copolyether micelles. The micelle size and structure were obtained from small-angle neutron scattering (SANS) using the hard sphere model. The micelle hydrodynamic radius and the micelle size distribution were monitored by dynamic light scattering (DLS). The degree of hydration was estimated from a combination of DLS and SANS results. The temperature effect on CMC was found to be small; however, a structural transition of micelles from spheres to ellipsoids was obser...
TL;DR: By NMR and static and dynamic light scattering, the micelle size, shape, and aggregation number vary during the solubilization of triolein in mixed aqueous solutions of the nonionic surfactant C12En (n = 5 or 6) and nonionic triblock copolymer Synperonic L61 (SL61) as discussed by the authors.
Abstract: By NMR and static and dynamic light scattering we investigated how the micelle size, shape, and aggregation number vary during the solubilization of triolein in mixed aqueous solutions of the nonionic surfactant C12En (n = 5 or 6) and the nonionic triblock copolymer Synperonic L61 (SL61). The latter was found to strongly accelerate the solubilization, although the copolymer alone is unable to solubilize triglycerides. A series of solutions containing different concentrations of surfactant and copolymer has been studied. The light scattering shows that we are dealing with giant micellar aggregates, each of them containing hundreds to thousands of surfactant molecules and dozens of copolymer molecules. Assuming that the micelles have the shape of prolate ellipsoids, we calculated their length and width. The results indicate that the initial, strongly elongated micelles transform into spherical or slightly ellipsoidal ones at the end of solubilization. The micelle aggregation number and hydrodynamic radius d...
TL;DR: In this article, a numerical self-consistent field model was used to analyze the self-assembly of a series of poly(ethylene oxide)-poly(propylene oxide)poly(ethylenes oxide) (PEO-PPO-PEO) surfactants into spherical micelles, where three segment types were identified, CH2, CH3, and O groups.
Abstract: The self-assembly of a series of poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) surfactants into spherical micelles has been analyzed by a numerical self-consistent-field model. A united atom description is used in which three segment types are identified, that is, CH2, CH3, and O groups. The aqueous solution is modeled as water dimers. A thorough parameter study has been performed to investigate the influence of the six Flory-Huggins parameters on the micellization behavior. A thorough thermodynamic analysis leads to the identification of the critical micellization concentration, the critical micellization temperature (CMT), and the cloud point temperature (CPT). The temperature dependence of the system is linked to the variation of the Flory-Huggins parameter for the O-water interactions. With this temperature dependence, good agreement is found between experimental results and theoretical predictions for the CMT and CPT. Calculated results for the structural characteristics of different PEO-PPO-PEO aggregates, such as the aggregation number, the radial density distributions, the core radius, and the headgroup areas, are also discussed.
TL;DR: In this paper, the authors used dynamic light scattering (DLS), time-resolved fluorescence quenching (TRFQ), and isothermal titration microcalorimetry to show that, in dilute solution, low molecular weight poly(ethylene glycol) (PEG, M-w = 12 kDa) interacts with the nonionic surfactant octaethylene gels n-dodecyl monoether, C12E8, to form a complex.
Abstract: Dynamic light scattering (DLS), time-resolved fluorescence quenching (TRFQ), and isothermal titration microcalorimetry have been used to show that, in dilute solution, low molecular weight poly(ethylene glycol) (PEG, M-w = 12 kDa) interacts with the nonionic surfactant octaethylene glycol n-dodecyl monoether, C12E8, to form a complex. Whereas the relaxation time distributions for the binary C12E8/water and PEG/water systems are unimodal, in the ternary mixtures they may be either uni- or bimodal depending on the relative concentrations of the components. At low concentrations of PEG or surfactant, the components of the relaxation time distribution are unresolvable, but the distribution becomes bimodal at higher concentrations of either polymer or surfactant. For the ternary system in excess surfactant, we ascribe, on the basis of the changes in apparent hydrodynamic radii and the scattered intensities, the fast mode to a single micelle, the surface of which is associated with the polymer and the slow mode to a similar complex but containing two or three micelles per PEG chain. Titration microcalorimetry results show that the interaction between C12E8, and PEG is exothermic and about 1 kJ mol(-1) at concentrations higher than the CMC Of C12E8. The aggregation number, obtained by TRFQ, is roughly constant when either the PEG or the C12E8 concentration is increased at a given concentration of the second component, owing to the increasing amount of surfactant micelles inside the complex. (Less)
15 Feb 2002
TL;DR: An increase in the polymer surface favors the binding of SDoD to PEO in aqueous solution, and this conclusion is supported by the results of the viscometric studies of PEO-surfactant solution.
Abstract: The binding of sodium dodecanoate (SDoD) to poly(ethylene oxide) (PEO) in aqueous solution was investigated and compared with the well-known polymer-surfactant complexes formed between PEO and sodium dodecyl sulfate (SDS). Electrical conductivity measurements indicated that the concentration ratio of bound SDoD to PEO (on monomer basis) was greater than that for the system PEO-SDS. However, the aggregation numbers of the micelles supported on the polymer chain are practically constant and similar for both surfactants at concentrations lower than the polymer saturation point. The difference in binding capability is explained in terms of a larger PEO coil expansion upon complexation of SDoD than in the case of SDS. An increase in the polymer surface favors the binding of SDoD to PEO in aqueous solution. This conclusion is supported by the results of the viscometric studies of PEO-surfactant solution.
TL;DR: In this paper, the aggregation number of a nonionic surfactant micelle, Triton X 100 (TX100), in aqueous solution was determined as a function of pressure by using the method of steady-state fluorescence quenching.
Abstract: The aggregation number of a nonionic surfactant micelle, Triton X 100 (TX100), in aqueous solution was determined as a function of pressure by using the method of steady-state fluorescence quenching The method of this work uses the fluorescence quenching of a probe (pyrene) by a quencher (coumarin 153), which are solubilized within a micelle With increasing pressure, the aggregation number of TX100 takes a minimum Namely, it decreases from 250 at atmospheric pressure down to 80 at around 100−150 MPa and then increases up to 230 at 500 MPa, the highest pressure studied This behavior is closely related to the turnover phenomenon of critical micelle concentration (cmc) against pressure By taking the pressure effect on the micellar concentration into account, it is demonstrated that in addition to the equilibrium between dispersed state and micellar state, there are equilibria among different-sized micelles
TL;DR: In this article, two different methods were used (1) homogeneous (water + acetonitrile) and 2) micellar copolymerization, in the presence of sodium dodecyl sulphate (SDS) to solubilize the hydrophobic comonomer, PPO methacrylate (PPOMA).
Abstract: Water soluble associative polymers based on polyacrylamide (PAM) grafted with short poly(propylene oxide) (PPO) chains as pendant groups were synthesized. Two different methods were used (1) homogeneous (water + acetonitrile) (2) micellar copolymerization, in the presence of sodium dodecyl sulphate (SDS) to solubilize the hydrophobic comonomer, PPO methacrylate (PPOMA). As expected from the literature, random or blocky distribution of PPO along the PAM chain, respectively, is obtained by these two methods. This work focuses on the characterization of the micellar reactional medium in order to have a good estimate of the length of the PPO sequences along the main chain. An extensive study of the mixture SDS/PPOMA was performed, by using fluorimetry, light scattering and conductimetry, to characterize the initial mixed micelles (critical micellar concentration and aggregation number). It is shown that the total aggregation number of the micelles and that of SDS decrease when the concentration of PPOMA increases. In addition, preliminary turbidimetry and viscosimetry studies of the thermo-associative properties of the two polymers are given.
TL;DR: In this paper, the interaction of anionic meso-tetrakis(4-sulfonatophenyl)porphyrin (H4TPPS2− and H2TPPS4−) with cationic cyanines, DiOC2(3) and DiOC6(3), was studied.
Abstract: The interaction of anionic meso-tetrakis(4-sulfonatophenyl)porphyrin (H4TPPS2− and H2TPPS4−) with cationic cyanines, DiOC2(3) and DiOC6(3) were studied. The cyanine with the hexyl chain, DiOC6(3) induced aggregation of the porphyrin with new absorption and emission bands. The stoichiometric ratio of porphyrin ∶ cyanine in the aggregate is ∼1 ∶ 4. UV–Vis absorption, fluorescence, fluorescence lifetime, resonance light scattering and dynamic light scattering studies were used for further characterization of the aggregate. The spectroscopic aggregation number for the porphyrin in the aggregate was estimated to be ∼2.5 by comparing the half width of its emission spectrum with that of the monomer. The spontaneous aggregation of porphyrin with DiOC6(3), but not with DiOC2(3),
indicates the role of the chain length of the alkyl group attached to the benzoxazole in the cyanine dye for stabilizing the structure of the aggregate.