Premicellar Aggregates Research Articles

Exploring Photophysical Properties of Organic Doped Polymeric Aggregates for Detecting Relevant Inorganic Pyrophosphate: A Pathway to Sustainable Development

Pyrophosphate (PPi) is an important environmentally and biologically relevant analyte and its easy and efficient detection is crucial for sustainable development. So, here we designed and synthesized organic-doped polymeric aggregates varying the signaling units (pyrene and anthracene) and examined their photophysical properties. By altering the signaling unit while keeping the polymeric backbone intact, we observed aggregate changes and studied their optical response with inorganic pyrophosphate (PPi). Among these probes, PYR-PEI exhibited a superior turn-off response(~6.1-fold) towards PPi in aqueous media whereas the other two probes ANH-PEI and PYR-PAH showed less response. The distinct response to PPi was primarily determined by electrostatic interaction and aggregate nature. The limit of detection (LOD) for PPi using the PYR-PEI probe was found to be 4.2 ppm, which is below the maximum allowable concentration of phosphate in surface water set by the World Health Organization (WHO) at 5mg/l. The quantification limit (LOQ) for PPi sensing was observed to be 14.27 ppm. Additionally, the PYR-PEI probe showed different fluorogenic responses (ratio-metric change) in the presence of anionic surfactant sodium dodecyl sulfate (SDS), and this resultant adduct was used for the PPi detection. The formation of premicellar aggregates between them drove the difference in the fluorogenic response with PYR-PEI and surfactant. Then the PYR-PEI composite was employed to detect PPi in spiked soil solution. Finally, chemically modified paper strips were prepared for the easy, fast, and on-location detection of PPi present in real-life samples.

Influence of supramolecular self-assembly of oppositely charged Co- and Sn-porphyrins on the their spectral-luminescent properties in aqueous and aqueous micellar media of ionic surfactants

The processes of supramolecular self-assembly of Co(III)-meso-tetra-(4-trimethylammoniophenyl)porphyrin (CoP) and bis-(4-(1-imidazolyl)-phenol)-Sn(IV)-meso-tetra(4-sulfophenyl)porphyrin (SnP) were studied using electronic, steady-state and time-resolved fluorescence, one- and two-dimensional NMR spectroscopy in aqueous media. The main product of such interaction at a 2:1 M ratio of Co and Sn porphyrinates was found to be supramolecular porphyrin trimer CoP–SnP–CoP formed due to donor-acceptor, hydrogen and electrostatic interactions. The distinctive features of the resulting trimer are: significant distortion of the spatial structure of the Co-porphyrin fragments and strong quenching of the Sn-porphyrin macrocycles fluorescence (by 70 %). The distortion of the spatial structure of Co porphyrinates is in good agreement with the quantum chemical calculations as well as with the electronic and NMR spectroscopy data. Adding surfactants – both anionic (Cetyltrimethylammonium bromide - CTAB) and cationic (Sodium dodecyl sulfate - SDS) – even at concentrations below the critical micelle concentration (CMC) leads to the supramolecular trimer destruction. In solutions of ionic surfactants, supramolecular trimer destruction is caused by the interaction of either the peripheral macrocycles of the trimer (CoP) with SDS micelles (premicellar aggregates) or the central macrocycle (SnP) with CTAB micelles (premicellar aggregates). This process is prolonged and the rate of trimer destruction depends on the surfactant concentration. The sizes of the CTAB and SDS micelles solubilized with porphyrin molecules were established by dynamic light scattering. In general, surfactant additions lead to an increase in the SnP fluorescence at least due to the destruction of the supramolecular self-assembly, as well as due to the changes in the state of its microenvironment.

Interaction of cationic 5,10,15,20-tetra(N-methylpyridyl)porphyrin and its Co(III) complex with premicellar SDS aggregates: Structure and properties

The study explores the interactions between 5,10,15,20-tetra(N-methylpyridyl)porphyrin (H2P) and sodium dodecyl sulfate (SDS) at concentrations below the critical micelle concentration (CMC) in aqueous solutions employing spectrophotometric and fluorescence methods. The composition and structure of the complexes involved in the association of H2P with premicellar SDS aggregates of varying compositions denoted as [H2P-5·SDS], [H2P-10·SDS] and [H2P-20·SDS] were characterized using mass spectrometry, DOSY, and 1D NOESY techniques. Possible reasons for the decrease in the intensity of absorption and emission of porphyrin in micellar aggregates of SDS compared to porphyrin in an aqueous environment are analyzed.The research has revealed that SDS can act as both a catalyst and an inhibitor, depending on its concentration in the reaction of complexation of H2P with metal cations (Co2+). The spectrophotometric approach examined interaction processes between 5,10,15,20-tetra(N-methylpyridyl)porphyrinate Co(III) and premicellar SDS aggregates, which proceed similarly to the processes with the porphyrin ligand. The study demonstrated the impact of premicellar aggregates on the binding capacity of Co(III) porphyrinate with electron-donating molecules using imidazole as an illustrative example.

Premicellar effects on the reduction of N, N′-phenylenebis(salicylideneiminato)iron(III) by thioglycolic acid: Kinetic study and mechanism

The reduction kinetics of N,N′-phenylenebis(salicylideneiminato)iron(III), [Fe(salphen)]+ by thioglycolic acid (TSH) has been carried out in mixed aqueous medium (DMSO:H2O; 1:4) in pseudo-first order condition at 26 ± 1 °C. A CORNING colorimeter 253 was used to monitor the reaction rates by detecting the absorbance reduction of the reaction at 435 nm. The reaction was acid independent, second order overall and demonstrated zero Brønsted-Debye salt effect. Ions such as Mg2+ and CH3COO- catalyzed the reaction. The thermodynamic parameters indicated an activated complex that is much ordered and a highly solvated transition state. Reaction catalysis was observed in the case of sodium dodecylsulphate (SDS) and cetyltrimethylammonium bromide (CTAB) inclusion. The critical micelle concentrations obtained for SDS were 8.0 × 10−3 and 3.3 × 10−3 mol dm−3 whereas that observed for CTAB were 2.0 × 10−3 and 2.8 × 10−3 mol dm−3 in water and [Fe(salphen)]+ reaction media respectively. Piszkiewicz model was used to analyze the results which indicated the existence of pre-micellar aggregates and significant electrostatic and hydrophobic interactions between the metal complex and the pre-micellar aggregates of the surfactants. The cooperativity index and binding constants obtained were n = 1.22, K = 4.78 × 104 dm3 mol−1, n = 1.27 and K = 4.55 × 104 dm3 mol−1 respectively for SDS and CTAB. A plausible mechanism suggesting an outer-sphere mechanism has been postulated.

Interfacial Structure and Electrostatics Related to Solute Activity in a Model Anionic-Surfactant/Polymer Self-Assembly.

Polymer/surfactant composites are used in industry as an excipient for water-insoluble solutes. Such enhanced dissolution ability of composite media is related to the spontaneous formation of pre-micellar polymer surfactant aggregates (PS) at a magnitude of order lower than the surfactant critical micelle concentration in water. Combining electrochemical and spectroscopic studies, we investigate the microscopic interfacial structure (i.e., interface electrostatics and surface polarity) of PS formed in composite media. We establish that in a composite system, a mere change in the polymer concentration at a fixed surfactant concentration makes possible to regulate the counter-ion binding ability, surface potential, surface charge density, packing and surface polarity of the PS interface. Our study shows that the higher dissolution of water-insoluble nonionic solutes in composite media is driven by the depressing of surface charge density and polarity of the PS interface. A similar modulation of the PS interface acts as a barrier for the passive relocation of water-soluble charged solutes into the PS pseudo-phase. The time-resolved fluorescence anisotropy study allows us to underline the effect of surface charge modulation on the dynamical aspects of solutes at the PS interface.

The surface energy and surface charge of microbubbles generated by frother surfactants

Microbubbles (MBs) in froth flotation have the important function of facilitating the collision and attachment between air bubbles and hydrophobic materials and subsequently recovering the hydrophobic materials. However, whether MBs can be generated in a flotation cell by adding frother surfactants is unknown. This study was designed to determine whether the two widely used frothers, methyl isobutylcarbinol (MIBC), representing alcohol frothers, and Dowfroth 250 (DF250), representing polyglycol ether frothers, could help generate MBs in a mechanical flotation cell. The underpinning air/water interfacial properties were also studied in the presence of the two frothers. The real time bubble size measurement demonstrated that MBs could be generated in the mechanical flotation cell in the presence of MIBC or DF250, and DF250 produced more and smaller MBs than MIBC. Air/water interfacial tension and microbubble zeta potential measurements indicated that the generation of MBs by MIBC and DF250 was primarily controlled by their ability in reducing surface tension. While DF250 formed premicellar aggregates at air/water interfaces and reduced surface tension significantly, MIBC only formed monolayers at air/water interfaces and reduced surface tension slightly. However, the slower adsorption of DF250 at air/water interfaces inhibited the generation of MBs to some extent. Compared with surface tension, surface charge played a secondary role in generating MBs. The adsorption of MIBC reduced the magnitude of surface charge of MBs, thus inhibiting the generation of MBs, while the adsorption of DF250 increased the magnitude of surface charge of MBs, enhancing the generation of MBs. The different behaviours of MIBC and DF250 in modifying interfacial properties and forming MBs were attributed to their unique structures. DF250 possesses a larger hydrophilic head and a longer hydrophobic chain than MIBC, and thus has a stronger ability to assist with the generation of MBs.

A plausible mechanism in premicellar aggregates for photocurrent generation in photogalvanic cell for simultaneously solar power conversion and storage

Photogalvanic (PG) cells are the only solar cell that can convert and store solar energy simultaneously. The PG cell is based on the diffusion of electrolytes (dye, reductant, alkali/acid and surfactant). We have completed photogalvanic study for the four (BCB-fructose, BCB-AA, MB-fructose and MB-AA) redox systems without and with SDS, CTAB and tween 80 surfactant in our previous research work. The results show that the most efficient system is MB-AA-SDS, in which methylene blue (MB) as a photosensitizer, ascorbic acid (AA) as reductant, and sodium dodecyl sulphate (SDS) as anionic surfactant is used. Since, to make an efficient cell, it is very important to understand the mechanism part. Consequently, the aim of this paper is to provide information about the basic difference of photocurrent generation in PV, DSSC and the PG cell, a plausible mechanism for the generation of electricity in the PG cell having MB, AA and SDS, and also give mechanism for stabilization of MB molecules in premicellar region of SDS on the basis of findings of our previous research work and literature study. For the same, first, made a comparative study for generation of electricity in PV, DSSC and the PG cell, then the most possible mechanism for photocurrent generation in PG cell and lastly mechanism for solubilization and stabilization of the MB molecules by SDS have been given. The comparative study of different solar cells shows that the basic principle for conversion of solar to electrical energy is same for all solar cells. The main difference is in the place of chemical reactions which occur on the surface of the electrode in solar cells while in the PG cells, it occurs inside the electrolytic solution. The AA/ascorbate ion and the base form of the MB are stabilized by premicellar aggregates of SDS, this helps to solubilize the MB molecules by providing an ordered way and enhancing the number of MB molecules for absorption of light in the PG cell. This ultimately enhances the number of leuco forms of MB which leads to an increase in the number of electrons in the external circuit of the PG cell. Thus, by understanding the most plausible mechanism one can make a PG cell in which the compatibility of surfactant is maximum with a dye-reductant system for photocurrent generation and storage, simultaneously. Further, it provides basic ideas about conditions and parameters which are responsible for the better electrical output of the PG cell. This may make the cell practically viable for daily life in the future.

Effects of head-group volume on the thermodynamic parameters and species distribution of ionic liquid-based surfactants in water: 1-(n-hexadecyl)-3-alkylimidazolium bromides and chlorides

The following series of ionic liquid-based surfactant halides was studied: 1-(n-hexadecyl)-3-Cm-imidazolium bromides and chlorides (C16CmImBr and C16CmImCl, respectively) where Cm = C1-C4. Using isothermal titration calorimetry, we calculated the enthalpy of micelle formation (ΔH⁰mic) at 25 °C for both halide surfactants, and from 15 to 70 °C for C16CmImCl. Values of ΔH⁰mic were then employed to calculate the entropy of micelle formation (ΔS⁰mic) from the corresponding free energy (ΔG⁰mic); the latter was calculated from the critical micelle concentration (cmc) and the degree of counter-ion dissociation (αmic). Values of ∣ΔG⁰mic∣ increase as a function of increasing Cm, although this increase is smaller than that of the previously studied series CnC1ImCl, where Cn = C10 to C16. This is attributed to the difference in dehydration of the surfactant segments that accompanies micelle formation, which is much larger for the increase in the hydrophobic chain (CnC1ImCl) than for the head-group (C16CmImCl). The calculated enthalpograms (ΔH⁰dilution versus [surfactant]) for C16C4ImBr showed deviation from ideal solution behavior, this was attributed to the formation of premicellar aggregates. The latter conclusion was corroborated by Pulsed Field Gradient (PFG)-NMR experiments of C16CmImCl in D2O. Thus, a model based on the presence of the following species in solution fitted satisfactorily the dependence of the observed surfactant diffusion coefficients on [surfactant]: free surfactant molecules; premicellar aggregates and micellized surfactant. The concentration of the premicellar aggregates increases noticeably as a function of increasing Cm, due to hydrophobic interactions between the Cm groups. The solubilization of (anionic) thymol blue indicator by C16CmImBr was studied using UV–Vis spectroscopy. The solubilization power (=moles of solubilized molecule/mole of micellized surfactant) was calculated, and compared with our previous data on the solubilization of (hydrophobic) Sudan IV dye and (less hydrophobic) drug nitrendipine by C16CmImBr. In all cases, the solubilization power decreases as a function of increasing Cm, albeit to different degrees, due to a combination of steric hindrance by the head-group, and decreased micelle size, both acting in the same direction.

Surfactantes iônicos e não-iônicos: micelas, micelas reversas e sistemas micro heterogêneos

Surfactants are surface-active agents which belong to the category of amphiphilic molecules. Indeed, surfactants are characterized for the presence of polar and apolar domains in the same compound. They can form different types of aggregates, such as those known as micelles, being that the concentration at which they form these micelles is called critical micellar concentration (cmc). The different aggregation states of the surfactant (monomer, pre-micellar aggregate, micelle, and liposomes) can present different properties in terms of capability of chemical interaction. The presence of these different configurations and/or the variation of concentration of each one alters the physicochemical properties of the chemical systems with ionic and non-ionic surfactants. The micro heterogenous systems originated by these surfactants have been widely studied in literature to infer several aspects related to similar media that are encountered in the biological tissues.

Interaction between surfactants and proteins

Several approaches have been focused on the protein-surfactant interaction. Surfactant-protein interactions are very common in the fields of medicine, chemistry, biology etc. Indeed, many aspects of this interaction have been studied, such as the influence of the aggregation state of the surfactant (monomer, pre-micellar aggregate, micelle, and liposomes) on the protein structure, the properties of the surfactant-protein system, the characterization of the interaction sites on the protein surface, the identification of the intermediate protein conformations etc. The interaction of several types of proteins with the different kind of surfactant can furnish various information to the research of biochemical and biophysical systems, such as the structure-activity relationship of proteins as well as the mechanism of interaction between proteins and amphiphilic molecules. In this context, proteins with prosthetic group are very interesting ones, since the presence of the non-amino acid group can furnishes various information through different instrumental techniques of analysis, acting as a label of all polypeptide chains. The present work analyzes this topic and the potential of these studies.

Thioglycolic acid oxidation by N, N′-phenylenebis(salicylideneiminato)manganese(III) in DMSO/H2O: Effects of sodium dodecylsulfate and cetyltrimethylammonium bromide

Thioglycolic acid (TSH) oxidation by N,N’-phenylenebis(salicylideneiminato)manganese(III), [Mn(salphen)]+ was carried out in DMSO:H2O (1:4) at 32 ± 1 °C. The reaction displayed first order kinetics in each reactant, acid invariant and zero Brønsted-Debye salt effect. Activation data were computed such as ΔHǂ = +40.58 kJ mol−1, ΔSǂ = −164.40 J mol−1 K−1, ΔGǂ = +90.72 kJ mol−1, Ea = +43.12 kJ mol−1. The critical micelle concentrations of sodium dodecylsulfate (SDS) and cetyltrimethylammonium bromide (CTAB) were obtained in water and [Mn(salphen)]+ reaction media as 8.0 × 10−3 and 2.8 × 10−4 mol dm−3, 2.0 × 10−3 and 4.0 × 10−4 mol dm−3 respectively. The reaction was catalyzed by SDS and CTAB and an application of Piszkiewicz model evaluated the data by specifying the presence of pre-micellar aggregates with strong electrostatic and hydrophobic connections between [Mn(salphen)]+ and the pre-micellar aggregates of the surfactants.

Surfactant aggregate size distributions above and below the critical micelle concentration.

Aggregate size distributions in an aqueous solution containing either charged or neutral surfactants are investigated using Raman multivariate curve resolution (Raman-MCR) spectroscopy and analyzed with the aid of a multi-aggregation chemical potential surface (MCPS) modeling strategy. Total least squares decompositions of the concentration-dependent Raman-MCR spectra are used to quantify the free and micelle surfactant populations, and the surfactant's C-H stretch frequency is used as a measure of its average aggregation state. MCPS predictions relate the experimental measurements to the underlying surfactant aggregate size distribution by fitting either the component concentrations or the average C-H frequency to MCPS predictions, and thus determine the critical micelle concentration (CMC) and estimate the corresponding micelle size and polydispersity. The Raman-MCR spectra of aqueous 1,2-hexanediol, sodium octanoate, and sodium dodecyl sulfate, measured both below and above CMC, provide critical tests of the assumed functional form of the MCPS and the presence of low-order premicellar aggregates. Our results indicate that the low-order aggregate population gradually emerges as the CMC is approached and then remains nearly concentration-independent after the appearance of micelles.

Effect of Surfactant Tail Length on the Hydroxypropyl Cellulose-Mediated Premicellar Aggregation of Sodium n-Alkyl Sulfate Surfactants.

Polymer/surfactant composites have emerged as a subject of interest for their diverse applications. The improved solution properties in polymer/surfactant composites have been correlated to the formation of premicellar surfactant aggregate-polymer complexes (PS) at a surfactant concentration well below their critical micelle concentrations. Using different physicochemical and spectroscopic techniques here we have studied PS formed by hydroxypropyl cellulose, a nonionic-biocompatible polymer, and alkyl sulfate surfactants of different tail lengths. Our study shows that an increase in surfactant tail length eases PS formation and enhances PS-induced polymer cross-linking and, correspondingly, solution viscosity. PS consisting of shorter tail surfactants and those with longer tail surfactants differ microscopically as the former offers more polar interior than the later as evidenced from fluorescence measurements. Our study establishes that shorter tail surfactants intend to stay loosely packed inside PS and allow larger water penetration, which creates a relatively polar hydrophobic core compared to the PS with longer tail surfactants. The stronger packing of PS with longer tail surfactants is an outcome of favorable interaction between polymer polar groups and surfactant headgroups, which further creates strongly hydrogen-bonded water in their hydration shell.

The effect of gold nanoparticle capping agents on 1O2 detection by singlet oxygen sensor green

Singlet Oxygen Sensor Green (SOSG) is the most widely used fluorescent probe for detecting singlet oxygen (1O2). 1O2 can be efficiently produced by exciting the surface plasmon of gold nanoparticles with laser pulses. However, gold nanoparticles are usually embedded in a chemical stabilizer that can interact with SOSG, leading to erroneous detection of 1O2. This article shows that the emission properties of SOSG strongly depend on the concentration of cetyltrimethylammonium bromide (CTAB), a capping agent widely used for nanoparticles synthesis and stabilization. The sensitivity of SOSG to 1O2 is also drastically affected by the presence of CTAB. This effect is due to the fluorescent probe's aggregation in CTAB premicellar aggregates and micelles, and the emergence of fluorescent conformers of the probe in the micelles. Furthermore, the behavior of SOSG in the presence of two other widely-used capping agents, i.e., citrate and Polyethylene Glycol (PEG), is investigated to determine the right nanoparticle stabilizer to use with SOSG probe.

Corrigendum to “Investigation on the gelatin-surfactant interaction and physiochemical characteristics of the mixture” [Journal of Molecular Liquids, 224 (2016) 900–908/MOLLIQ_2015_362

Abstract The effect of gelatin, a denatured protein on the micellization of a series of polyoxyethylated hexadecyl ethers (BC-X) were investigated through several physicochemical techniques such as surface tensiometry, contact angle measurement, fluorimetry, cyclic voltametry, zeta potential measurement, dynamic light scattering studies. The critical micellar concentrations (cmc) of BC-X increased with increase in gelatin concentration in the mixture which was also corroborated by other techniques performed. This increase in cmc was attributed to the decrease of monomeric surfactant concentration as a result of the formation of gelatin-BC-X complex. The surface excess concentration, minimum area per molecule, and surface pressure at the cmc were estimated from surface tension data. The free energies of adsorption and micellization indicated the micellization and adsorption at air/water interface to be spontaneous phenomena. Micropolarity and the aggregation numbers of the mixed systems were determined using the fluorescence behaviour of pyrene. The slanting nature of curve of polarity parameters-surfactant concentration in conjunction with appearance of pyrene excimer peak at the lower BC-X concentrations supported the stepwise growth of the micelles through the formation of pre-micellar aggregates. The entwining of the protruded chains of the surfactants around the gelatin moiety through polar and hydrophobic interactions was endorsed to be the main reason behind the formation of small sized mixed micelles. The zeta potential studies envisaged the surface of both gelatin and BC-X to have negative electrostatic potential independently. The decrease in the zeta potential of the gelatin-surfactant mixtures was attributed to the removal of fraction of the negatively charged BC-X surface as a result of casing by the hydrophobic and neutral segments of gelatin.

Interaction of alkyl chain containing pyrene derivatives with different micellar media: Synthesis and photophysical study.

The present work describes the synthesis and photophysical studies of four newly synthesized alkyl chain containing pyrene derivatives and their applications in micellization process of different types of surfactants e.g. CTAB and SDS. The fluorescent properties of these pyrene derivatives were utilized to understand the micellization process of CTAB and SDS. The length of alkyl chain affects the hydrophobicity of pyrene fluorophore which also affects the sensitivity of fluorophore towards the micellization of CTAB and SDS surfactants. The longest alkyl tail containing, PBBU showed more sensitivity whereas moderate alkyl chain containing, PABU and PBME showed moderate sensitivity and finally PAME contained smallest alkyl tail, showed no sensitivity towards the micellization of CTAB and SDS. The alkyl tail of fluorophore make it more hydrophobic and it could easily bind with the hydrophobic inner core of micelles. In both surfactants, PBBU showed LE emission at ~400 nm and aggregate emission at ~470 nm, whereas, PABU and PBME showed LE emission band at ~400 nm. Before CMC, the aggregates band of PBBU increased with increasing the surfactant concentrations, but after CMC the individual PBBU present into the water medium could binds with the inner core of micelles. Thus PBBU senses the formation of premicellar aggregates of CTAB and SDS. The LE emission of the fluorophore gradually increases while increasing the CTAB and SDS concentrations. The change in fluorescence emission of PABU, PBME and PBBU with increasing concentration of CTAB and SDS were used to calculate the CMC of CTAB and SDS surfactants.

Thermodynamics of Mixing of TEHDGA with Isodecanol in Dodecane: Effect of Equilibration with Aqueous Nitric Acid

The use of any new extractant requires the study of its tendency to form third phases. To understand the phase separation process it is important to have knowledge of the molecular scale phenomena present in the system. This includes the mixing of the substances and the behavior and nature of the aggregates. Here we report the mixing properties of N,N,N′,N′-tetra-(2-ethyl hexyl) diglycolamide (TEHDGA)–dodecane–isodecanol (in the absence and presence of micellar aggregates) which is recognized as a promising system for the separation of minor actinides through the conventional solvent extraction route. The nature of interactions between TEHDGA and isodecanol was investigated using several techniques, including density and speed of sound measurements, ultraviolet absorption spectroscopy and computational studies. The TEHDGA–isodecanol interaction was found to be favored over the inter-isodecanol interaction. On equilibrating the organic phase with nitric acid, some indication of pre-micellar aggregation was obtained. Increase of micellar aggregate size on addition of isodecanol was indicated.

Surface properties and premicellar aggregation behavior of cationic gemini surfactants with mono- and di-(2-hydroxypropyl)ammonium head groups

Novel cationic gemini surfactants - pentanediyl-1,5-bis[mono(2-hydroxypropyl) alkylammonium] dibromide and pentanediyl-1,5-bis[di(2-hydroxypropyl) alkylammonium] dibromide {in the abbreviation form - CnC5Cn[iso-Pr(OH)] and CnC5Cn[iso-Pr(OH)]2; alkyl - CnH2n+1 with n = 8, 9, 12 and 16} were synthesized. Surface tension, electroconductivity and dynamic light scattering methods were applied to study aggregation properties of these surfactants in aqueous medium. By tensiometric method it was established that, at two studied concentrations in water, the synthesized gemini surfactants form aggregates. This occurs well below the critical micelle concentrations (CMC) of these surfactants. The influence of the length of the surfactants alkyl chain and the number of the 2-hydroxypropyl fragments in the head group on the surface activity parameters and binding degree of the counterion has been studied. By dynamic light scattering method, the impact of the number of the 2-hydroxypropyl groups in the gemini surfactants with C12–chain on the micelles sizes at the concentrations higher than CMC has been investigated. It was revealed that the synthesized surfactants possess an antimicrobial property.

Mechanisms of anionic surfactant penetration into human skin: Investigating monomer, micelle and submicellar aggregate penetration theories.

Once penetrated into the stratum corneum, anionic surfactants bind to and denature stratum corneum proteins as well as intercalate into and extract intercellular lipids. With repeated exposures, this leads to skin dryness and irritation, compromising barrier function and skin health. The mechanisms of anionic surfactant penetration into the skin, however, are still widely debated. The objective of this study was to evaluate current theories of surfactant penetration into human skin. A test set comprising 15 anionic surfactant systems and one non-ionic surfactant, all having either dodecyl or lauryl alkyl chains, was tested for surfactant penetration into split-thickness human cadaver skin invitro using radiolabelled sodium dodecyl sulphate (14 C-SDS). Select physical properties of these formulations thought to be associated with skin penetration including critical micelle concentration, micelle diameter, filtrate concentration and zeta potential were also measured. 14 C-SDS penetration into human cadaver skin from surfactant systems invitro was found to correlate well with CMC (R2 =0.34, P<0.05), filtrate concentration (R2 =0.36, P<0.05) and zeta potential (R2 =0.76, P<0.001), but poorly with micelle diameter (R2 =0.12). Furthermore, the latter measure correlated inversely with penetration compared to what would be expected based on the micelle penetration theory. Neither monomer nor micelle penetration theories are sufficient to explain anionic surfactant penetration into human skin. Submicellar (or premicellar) aggregate penetration theory is difficult to defend at relevant surfactant concentrations. We propose a new hypothesis for this mechanism in which short-term penetration is based on monomer concentration and longer term penetration is based on surfactant-induced damage to the skin barrier.

Evidence of pre-micellar aggregates in aqueous solution of amphiphilic PDMS-PEO block copolymer.

The self-assembly process in a water solution of an amphiphilic polydimethylsiloxane-b-polyethyleneoxide (PDMS-PEO) diblock copolymer was investigated by means of small-angle X-ray scattering (SAXS) experiments in the concentration region below (and near) the critical micellar concentration (c.m.c. = 0.007 g cm-3). In the highly diluted region, at the copolymer concentration of c = 0.002 g cm-3, the early stage of the self-assembly process was characterized by the formation of small (primary) micellar units (with a radius of R = 2.7 nm) with core-shell morphology, which coexisted with larger supramolecular aggregates of entangled micelles (with an average radius of R = 9.5 nm). The increase in the copolymer concentration (to c = 0.005 and c = 0.01 g cm-3) caused increase in the sizes of both the small micelles and supra-micellar aggregates. Interestingly, at the concentration of c = 0.005 g cm-3, both the size and micelle aggregation number (Nagg) were found to increase on increasing the temperature in the range of 10 ≤ T ≤ 55 °C. This phenomenon was characterised by the dehydration process of the ethylene oxide (EO) segments, as evidenced by the calculation of excess water in the hydrophilic shell of the micelles. The more compact (less hydrated) structure of the hydrophilic PEO chains, which strongly influenced the spontaneous curvature of the amphiphile hydrophilic region, turned out to be the driving factor that favoured the increase in the micelle aggregation number with the increase in temperature. The obtained results evidence that the self-assembly process of PDMS-PEO copolymer amphiphiles is a gradual process that is already present at the very low concentration region (far below the macroscopically determined c.m.c.); moreover, it is characterised by a multi-stage organization process, where the primary building blocks self-assemble into more complex secondary structures that encompass multiple length scales.