Double-chain Surfactant Research Articles

Specific ion effects on the self-assembly and interfacial properties of double- and single-chain cationic amphiphiles

Understanding the specific ion effects (SIE) on the self-assembly of ionic amphiphiles is a key unresolved issue in colloid and interface chemistry. We investigated the SIE on interfacial properties, aggregation behaviours, and interfacial molarities of dioctyldimethylammonium (DiC8X) and tetradecyltrimethylammonium (TTAX) (X = Br, Cl, and Ac) surfactants. Our results demonstrate strong SIE on the aggregation behaviours in both single-chain and double-chain surfactants. The aggregation behaviour depends on the net effect of nonspecific interactions and SIE. Vesicle-micelle transitions are observed exclusively in the double-chained surfactants studied in this work, regardless of their tail symmetry, and are absent in the single-chained surfactants examined. These transitions are counterion-dependent, occurring only with bromide, while the surfactants bearing acetate consistently form vesicles. The chemical trapping (CT) results reveal several key insights on interfacial molarities: 1) double-chain surfactants exhibit higher interfacial water molarity compared to single-chain surfactants, with counterion molarity showing an inverse trend; 2) within both TTAX and DiC8X classes, the interfacial water molarity is highest for surfactants with bromide, followed by chloride, and lowest for acetate; 3) for surfactants undergoing vesicle-micelle transitions, both interfacial water and bromide molarity increase with rising surfactant concentration at low concentration ranges, indicating looser interfacial packing with increasing concentration; and 4) the combined CT and molecular dynamic simulations indicate that acetate penetration into interfacial regions significantly increases with surfactant concentration in TTAAc and DiC8Ac aggregates, explaining the consistent vesicle formation of amphiphiles with acetate. Overall, this study provides critical insights into the delicate balance-of-forces controlling the morphologies of aggregates composed of ionic amphiphiles.

Research Progress in Structure Synthesis, Properties, and Applications of Small-Molecule Silicone Surfactants.

Silicone surfactants have garnered significant research attention owing to their superior properties, such as wettability, ductility, and permeability. Small-molecular silicone surfactants with simple molecular structures outperform polymeric silicone surfactants in terms of surface activity, emulsification, wetting, foaming, and other areas. Moreover, silicone surfactants with small molecules exhibit a diverse and rich molecular structure. This review discusses various synthetic routes for the synthesis of different classes of surfactants, including single-chain, "umbrella" structure, double chain, bolaform, Gemini, and stimulus-responsive surfactants. The fundamental surface/interface properties of the synthesized surfactants are also highlighted. Additionally, these surfactants have demonstrated enormous potential in agricultural synergism, drug delivery, mineral flotation, enhanced oil recovery, separation, and extraction, and foam fire-fighting.

Thickening supercritical CO2 at high temperatures with rod-like reverse micelles

Earlier studies demonstrated the ability of some fluorinated surfactants to form rod-like reverse micelles with the ability to thicken water/supercritical CO2 (scCO2) mixtures at temperatures below 45 ºC [Langmuir 26 (2010) 83–88. Soft Matter 8 (2012) 7044–7055. Colloids and Surfaces B, 168 (2018), 201–210.]. Such viscosity enhancement of scCO2 is known to increase sweep efficiency for oil recovery with CO2 flooding. However, temperatures of up to ∼100 ºC in conventional reservoirs are much higher than those employed in laboratory studies, and tend to weaken inter- and intra-molecular interactions between surfactant molecules, discouraging rod-like reverse micelle formation. With the aim of designing surfactants which form rod-like reverse micelles and thicken CO2 at high temperatures, this study examined phase behavior, nanostructures of reverse micelles and thickening ability of double ω-hydroperfluorocarbon-tail anionic surfactants in W/scCO2 mixtures at temperatures of 35 - 75 ºC and pressure of 80 - 400 bar with different water-to-surfactant molar ratios (W0). The measured CO2 viscosity increased by 1.9–2.2 × for double-chain surfactants M(di-HCF6)x (counterion Mx+ = Ni2+ and Co2+) at 40 mM, over the experimental temperature range. On the other hand, the shorter chain H(CF2)4CH2 twin-tail surfactants M(di-HCF4)x and Na(di-HCF6) gave only 1.1–1.5 × viscosity enhancements. The maximum thickening ability of M(di-HCF6)2 was at W0 = 10 in the W0 range of 5–20 75 ºC and 350 bar. High pressure and high temperature small-angle neutron scattering (SANS) was used determine the micellar structure in these systems, and rod micelles of aspect ratios of 4.5–6.5 were found. The results clearly suggest that ω-hydroperfluorohexyl-tails and divalent counterions induce the formation of rod-like reverse micelles in W/CO2 mixtures, even at high temperatures commensurate with in-reservoir conditions.

Molecular design on dual stimuli-responsive azobenzene-containing ionic complexes toward self-healing materials under photoirradiation or humid condition at room temperature

Self-healing materials working at room temperature are attractive in the field of materials chemistry. Compared to those requiring one specific external stimulus, one smart material that can launch the self-healing process under multiple stimuli would accommodate more various working conditions. In this work, a double-chain azobenzene-containing surfactant AZO with good molecular flexibility and hydrophilicity is designed for developing self-healing materials with dual responses to light and humidity. By mixing AZO and surfactants containing linear aliphatic chains, the resulted composites gain crystal-to-isotropic liquid phase change ability under the trigger of either light or humidity, thanks to the formation of sufficient free volume for AZO molecules. This leads to the light-/humidity-induced self-healing materials at room temperature. Meanwhile, the composite of AZO and double-chain surfactant has been proved with better responsive sensitivity to light and humidity by forming a homogeneous molecular distribution. This study provides a new designing strategy for gaining dual self-healing materials working via an athermal way, promoting the development of smart materials with multiple stimuli-responsive property.

Synthesis and surface activity of two novel phosphate silicone surfactants

Two phosphate amphoteric surfactants based on silicone were synthesized. Phosphate Gemini surfactant ((C12P2)2Si2) with disiloxane as bridging group and double-chain surfactant (C12P2Si3) with hydrophobic hydrocarbon chain and trisiloxane were prepared by hydrolysis reaction, Kabachnik-Fields reaction, and quaternization reaction. FT-IR, 1H NMR and TGA confirmed the chemical structure and thermal stability of the synthesised (C12P2)2Si2 and C12P2Si3. The physicochemical behavior at the air–liquid interface was investigated. The results showed that the critical micelle concentration (CMC) values of (C12P2)2Si2 and C12P2Si3 are 0.53 and 0.78 mmol/L, respectively. The two new surfactants had surface tension at CMC equal to approximately 28 mN/m and their surface tension varied with temperature and electrolyte (NaCl, CaCl2, and MgCl2) concentration. At high temperatures and with high concentration electrolytes, they exhibited good air–liquid interfacial activity. In addition, the size of the aggregates of the surfactants in aqueous solutions above CMC was determined by the dynamic light scattering (DLS) measurements.

Magnetic Solid-Phase Microextraction Protocol Based on Didodecyldimethylammonium Bromide-Functionalized Nanoparticles for the Quantification of Epirubicin in Biological Matrices.

Due to epirubicin's (EPI) narrow therapeutic index and risk of cardiotoxicity, it is critical to monitor concentrations of this drug when being used to treat cancer patients. In this study, a simple and fast magnetic solid-phase microextraction (MSPME) protocol for the determination of EPI in plasma and urine samples is developed and tested. Experiments were performed using prepared Fe3O4-based nanoparticles coated with silica and a double-chain surfactant-namely, didodecyldimethylammonium bromide (DDAB)-as a magnetic sorbent. All the prepared samples were analyzed via liquid chromatography coupled with fluorescence detection (LC-FL). The validation parameters indicated good linearity in the range of 0.001-1 µg/mL with a correlation coefficient > 0.9996 for plasma samples, and in the range of 0.001-10 µg/mL with a correlation coefficient > 0.9997 for urine samples. The limit of detection (LOD) and limit of quantification (LOQ) for both matrices were estimated at 0.0005 µg/mL and 0.001 µg/mL, respectively. The analyte recovery after sample pretreatment was 80 ± 5% for the plasma samples and 90 ± 3% for the urine samples. The developed method's applicability for monitoring EPI concentrations was evaluated by employing it to analyze real plasma and urine samples collected from a pediatric cancer patient. The obtained results confirmed the proposed MSPME-based method's usefulness, and enabled the determination of the EPI concentration-time profile in the studied patient. The miniaturization of the sampling procedure, along with the significant reduction in pre-treatment steps, make the proposed protocol a promising alternative to routine approaches to monitoring EPI levels in clinical laboratories.

Effect of a double-chain surfactant on the stabilization of suspensions of silica and titania particles against agglomeration and sedimentation

Dispersions of vesicles of didodecyldimethylammonium bromide (DDAB) were prepared with magnetic stirring of multilamellar liposomes followed by ultrasonication (SS) in order to generate dispersions that contained only unilamellar vesicles, unlike the stirring-only (S) method which also produces many large liposomes. With the SS method, the vesicles had average diameters ranging from 68 to 80 nm, which were much smaller than the diameters generated with the S method. The new vesicle dispersions had nearly infinite viscosities at very low shear stresses at DDAB weight fractions wD from 0.025 to 0.027, even though they were not close-packed, in contrast to the S dispersions. The new SS vesicle dispersions stabilized completely against sedimentation polydisperse nonspherical crystalline titania particles with sizes ranging from ca. 96–156 nm, as well as suspensions of monodisperse spherical amorphous silica particles with diameters of dsed = 454 nm, 691 nm, and 826 nm. These results establish that DDAB vesicle dispersions can stabilize against sedimentation a broad range of particle types and sizes. In addition, at the low values of wD = 0.009 and 0.018, the effective viscosities, ηeff, of the DDAB dispersions, determined from the sedimentation velocities, ranged from 1.35-1.87 cP and 4.34–5.57 cP, respectively. At higher shear stresses, however, these dispersions were highly shear-thinning and still flowable in a capillary under gravity. This behavior is critical for the practical applications of such dispersions for inkjet printing and possibly paints.

Catanionic vesicles and their complexes with hyaluronan – A way how to tailor physicochemical properties via ionic strength

This article offers a comprehensive description of how a change in ionic strength influences the physicochemical properties of dilute solutions of catanionic vesicular systems. Catanionic vesicles are formed from HTMA-DS (hexadecyltrimethylammonium-dodecyl sulphate) ion pair amphiphiles, which were doped by cholesterol and positively charged double-chained surfactant. Due to this positive charge, they can interact with oppositely charged polymers, such as hyaluronan, to form hyaluronan-coated vesicles. Vesicle kinetic stability can be affected by changes in the ionic strength of the environment, which are represented by the addition of sodium chloride. In our study, with the increasing addition of salt, the ζ-potential, as the main parameter of kinetic stability, decreased to zero both for coated and uncoated vesicles. Furthermore, the size of vesicles increased above a concentration of 15 mM NaCl. The membrane rigidity represented by fluorescence anisotropy, of uncoated vesicles decreased rapidly, and slight dehydration of their outer part was observed, which was confirmed by high resolution ultrasonic spectroscopy. Hyaluronan-coated vesicles formed visible aggregates with gradual additions of salt, which were subsequently disintegrated, the degree of disintegration varying for different polymer concentrations. The viscosity of the whole system also decreased significantly with increasing salt concentration.

Effects of Fe3O4 Magnetic Nanoparticle Functionalization with Ionic Liquids and a Double-Chained Surfactant on the Pretreatment of Plasma Samples during Drug Extraction.

Ionic liquids (ILs), also known as "designer solvents," comprise a large group of compounds that can improve overall sample preparation performance due to their unique physical and chemical properties. Some of them have a comparable structure to surfactants, which can be also considered as effective extraction solvents. In this study, nine different ILs and a double-chained surfactant were investigated as potential coating materials for iron oxide-based nanoparticles (NPs) used in the pretreatment of human plasma samples. Various methods of synthesizing and functionalizing NPs were employed in fabricating the magnetic sorbents, with the physicochemical properties of the resultant extraction phases (i.e., naked NPs, NPs coated with silica, and NPs coated with silica and selected IL or surfactant) being characterized via X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, thermogravimetric analysis (TG), and transmission electron microscopy (TEM). The effectiveness of the developed NP-based extraction phases was tested by applying them for the extraction of epirubicin hydrochloride (EPI) from plasma samples, followed by analysis via liquid chromatography with fluorescence detection (LC-FL). The results showed that NPs coated with both silica and IL or silica and surfactant provided significantly higher extraction efficiency compared to naked NPs and NPs coated solely with silica. Additionally, the findings also revealed that the adsorption of analytes depends not only on the coating procedure but also on the type of coating material used to functionalize the NPs. Among the tested structures, didodecyldimethylammonium bromide provided the best performance for the functionalization of NP sorbents previously coated with silica.

‘On and Off’ intercalative binding behaviour of double chain surfactant cobalt(III) complex containing 2, 2′-bipyridyl ligand in β-Cyclodextrin: A detail approach on Host-guest inclusion of surfactant cobalt(III) complex and CT-DNA binding in micro-heterogeneous medium

The binding interaction of surfactant cobalt(III) complex, cis-[Co(bpy)2(HA)2](ClO4)3, in which bpy is 2,2-bipyridine and HA is hexadecylamine or cetylamnine with DNA was through intercalative mode via the long aliphatic chains present in the ligands. The binding was investigated by various techniques, electronic absorption, fluorescence spectroscopy, circular dichroism (CD), cyclic voltametry (CV) and viscosimetry measurements. The spectroscopic studies together with cyclic voltammetry and viscosity experiments support that the surfactant cobalt(III) complex binds to calf thymus DNA by intercalation through the aliphatic chain present in the complex into the base pairs of DNA. The presence of bipyridine ligand with larger π-frame work may also enhance intercalation. UV–vis., spectrum showed 4 nm bathochromic shift of the absorption band at 352 nm along with significant hypochromicity for the absorption band of the complex. The intrinsic binding constants(at below and above CMC are Kb = 2.41 × 105M−1, Kb = 3.12 × 106M−1 respectively) is more in keeping with intercalators and suggests this binding mode. The viscosity measurements showed that the surfactant cobalt(III) complex-DNA interaction can be hydrophobic and confirm intercalation. Moreover, the complex induced detectable changes in the CD spectrum of CT-DNA. Competitive binding study with ethidium bromide (EB) shows that the surfactant complex exhibits the ability to displace the DNA-bound EB indicating that the complex binds to DNA in strong competition with EB for the intercalative binding site. Also, CV results confirm this mode because, with increasing the CT-DNA concentration, shift to higher potential was observed. Besides the effect of binding of surfactant cobalt(III) complex to DNA in presence of β-cyclodextrin has also studied. This binding of the surfactant cobalt(III) complex in presence of β-cyclodextrin medium has been prevented (at below and above CMC are Kb = 5.45 × 104M−1, Kb = 6.92 × 105M−1 respectively) due to the incorporation of the aliphatic chains into the cavity of β-cyclodextrin. In presence of β-cyclodextrin the binding occur through surface and (or) groove binding can be attributed to the inclusion of the long aliphatic chain that is present in one of the ligands into cyclodextrin.

Microscopic diffusion in cationic vesicles across different phases

Understanding the phase behavior and microscopic diffusion mechanism of cationic vesicles is crucial for controlled-release kinetics in gene/DNA transfection. Here, we report our findings on the structure, phase behavior, and microscopic dynamics of a vesicle based on a cationic double-chained surfactant, dihexadecyldimethylammonium bromide (DHDAB), which is a promising candidate for a nonviral gene/DNA carrier. Small-angle neutron-scattering measurements reveal that DHDAB aggregates are in the form of unilamellar vesicles. Calorimetric studies show a strong thermal hysteresis in the heating and cooling cycles following different pathways. Two first-order transitions are observed at 303 and 318 K in the heating cycle. Fourier transform infrared spectroscopy reveals that the first transition (at 303 K) is associated with a polymorphic (solid-solid) transition from coagel to an intermediate crystalline (IC) phase, and subsequently the second transition (at 318 K) is an order-disorder transition from IC to the fluid phase. Interestingly, it is found that in the cooling cycle, the fluid phase directly transforms back into the coagel phase without passing through the IC phase. This is also confirmed by an elastic fixed window scan (EFWS) using incoherent neutron scattering. The phase behavior of DHDAB is in strong contrast to that of its longer-chain counterpart, dioctadecyldimethylammonium bromide (DODAB), where the intermediate gel phase was observed during the cooling cycle. Moreover, no polymorphic transition was observed in the heating cycle of DODAB, in which the coagel phase directly converts to the fluid phase. These sharply contrasting phase behaviors for DHDAB and DODAB suggest the strong dependence of membrane phase behavior to the alkyl chain length. EFWS measurements reveal that the phase transitions observed in the DHDAB membrane are associated with strong changes in the DHDAB dynamics. The changes in conformational entropy of DHDAB molecules estimated from EFWS confirm that the coagel-fluid and IC-fluid phase transitions are accompanied by strong changes in the conformations of the alkyl chains. The microscopic dynamics of DHDAB molecules in each of these phases is investigated by employing quasielastic neutron-scattering (QENS). In the ordered phases (coagel and IC), only localized internal dynamics of the DHDAB is observed in the QENS spectra. However, in the fluid phase, the presence of a long-range lateral diffusion is detected in addition to the localized internal dynamics of the alkyl chain. The lateral motion is found to follow Fickian diffusion. The internal dynamics of DHDAB depends on the phase state of the bilayer. In the ordered phase, the internal dynamics is described by a fractional uniaxial rotational diffusion model. However, in the fluid phase, where alkyl tails are disordered with significant gauche defects, the internal dynamics is described using localized translation within confined spheres. This study highlights the rich phase behavior of the DHDAB membrane and the surfactant dynamics across these phases.

Self-assembly of Symmetric Double Chain Surfactants Derived from Internal Ketone in an Aqueous System

Self-assembly of Symmetric Double Chain Surfactants Derived from Internal Ketone in an Aqueous System

Adsorption and aggregation properties of homogeneous polyoxyethylene alkyl ether- and ester-type nonionic surfactants with multi-branched double chains

Homogeneous polyoxyethylene (EO) alkyl ether- and ester-type nonionic surfactants with multi-branched double chains were newly synthesized. Their adsorption and aggregation properties were investigated through cloud point, surface tension, and small-angle X-ray scattering measurements, and compared to those of homogeneous EO alkyl ether- and ester-type nonionic surfactants with symmetric and asymmetric linear double chains as well as a conventional surfactant with a linear single chain. The surface tension at the critical micelle concentration for the multi-branched double-chain type decreased considerably to 27.9–28.8 mN m−1 despite having a large hydrophilic group of EO12 when multi-branched methyl groups with low surface energy were used as the hydrophobic groups of the surfactants. In the temperature vs. concentration phase diagrams, the regions of lamellar liquid crystals were more extensive for the linear double-chain surfactants because of the small interfacial curvature induced by the steric hindrance of the multi-branched chains.

Gemini Surfactant Mediated Catansomes for Enhanced Singlet Oxygen Generation of Rose Bengal and Their Phototoxicity against Cancer Cells.

Photodynamic therapy (PDT) is an innovative technique for cancer treatment with minimal side effects, based on the use of a photosensitizer, oxygen, and light. Photosensitizers (PSs) have several limitations, that may limit their clinical use, like poor solubilization, self-aggregation, and lack of specific targeting, which can be addressed with the use of nanomaterials. Herein, a unique type of catansomes (CaSs) was prepared using a gemini imidazolium-based surfactant (1,3-bis[(3-octadecyl-1-imidazolio)methyl]benzene dibromide (GBIB) and a double chain surfactant, diaoctyl sodium sulfosuccinate or Aerosol OT (AOT). The formation of CaS GBIB/AOT was optimized in various ethanol/water (E/W) solvent ratios by employing a facile, quick, and most reliable solution-solution mixing method. The CaS was characterized by dynamic light scattering (DLS) and field emission gun scanning electron microscopy (FEG-SEM) techniques. The experimental results reveal that stable CaSs with a spherical shape were obtained at lower concentration (100 μM). Rose Bengal (RB), a PS of the xanthene family, was incorporated into these prepared CaSs, as proven by fluorescence spectroscopy, UV-visible absorption spectroscopy, and confocal laser scanning microscopy. Singlet oxygen (1O2) generation studies revealed the relevant role of the E/W solvent ratio as there was a 4-fold boost in the 1O2 production for GBIB/AOT in E/W = 50:50 and around 3-fold in E/W = 30:70. Also, the GBIB-rich 80:20 fraction was more efficient in increasing the 1O2 generation as compared to the AOT rich fraction (20:80). Further, their phototoxicity was tested in a water-rich solvent ratio (E/W = 30:70) against MCF-7 cells. Upon irradiation with a 532 nm laser (50 mW) for 5 min, RB@GBIB/AOT(20:80) fraction caused 50% decrease in the metabolic activity of MCF-7 cells, and RB@GBIB/AOT(80:20) fraction produced a maximum 85% decrease in cell viability. Furthermore, the enhancement in intracellular 1O2 generation by RB@GBIB/AOT, as compared to pure RB, was confirmed with singlet oxygen sensor green (SOSG). This new type of CaS based on gemini surfactants exhibiting a large amount of 1O2 generation, holds great interest for several applications, such as use in photomedicine in future.

Mixed Micellization, Thermodynamic and Adsorption Behavior of Tetracaine Hydrochloride in the Presence of Cationic Gemini/Conventional Surfactants.

In this approach, tensiometry and UV-visible techniques are used to determine the effect of cationic gemini and conventional surfactants on tetracaine hydrochloride (TCH), an anesthetic drug. We have estimated micellar, interfacial, and energetic constraints. To gain a deep understanding of their mixed association behavior, the outputs were examined using different theoretical models. The critical micelle concentration for single and mixed amphiphiles was estimated. The cmc values of mixed amphiphiles were found between the individual amphiphiles due to strong attractive interaction (synergism) between the components after mixing. The non-ideal behavior of mixtures was confirmed by the larger values of ideal cmc than the experimental cmc values. The negative values of interaction parameter (β) and values of activity coefficients less than unity indicate strong synergistic interaction between drug and surfactant. The stability of the mixed systems is demonstrated by the negative Gibbs free energy of micellization and excess free energy of micellization. In contrast to a single chain surfactant, a double chain surfactant (gemini) exhibits better interactions with the drug. Spectral measurements (UV-visible spectra) were used to monitor the binding of the drug with surfactant (conventional as well as gemini). Studying these mixed aggregates could help to optimize their compositions and find synergistic properties between TCH monomers and surfactants.

Advanced Eco-Friendly Formulations of Guar Biopolymer-Based Textile Conditioners.

Fabric conditioners are household products used to impart softness and fragrance to textiles. They are colloidal dispersions of cationic double chain surfactants that self-assemble in vesicles. These surfactants are primarily derived from palm oil chemical modification. Reducing the content of these surfactants allows to obtain products with lower environmental impact. Such a reduction, without adverse effects on the characteristics of the softener and its performance, can be achieved by adding hydrophilic biopolymers. Here, we review the role of guar biopolymers modified with cationic or hydroxyl-propyl groups, on the physicochemical properties of the formulation. Electronic and optical microscopy, dynamic light scattering, X-ray scattering and rheology of vesicles dispersion in the absence and presence of guar biopolymers are analyzed. Finally, the deposition of the new formulation on cotton fabrics is examined through scanning electron microscopy and a new protocol based on fluorescent microscopy. With this methodology, it is possible to quantify the deposition of surfactants on cotton fibers. The results show that the approach followed here can facilitate the design of sustainable home-care products.

Molecular Packing in a Triphenylene‐Surfactant Complex Monolayer: Unambiguous Determination of Electrostatically Driven Molecular Packing in a Triphenylene–Surfactant Complex Monolayer (Adv. Mater. Interfaces 13/2021)

Self-assembly is a technique of choice for the bottom-up fabrication of molecular devices. In article number 2100187, Snehasis Daschakraborty, Alpana Nayak, and co-workers report intricate details of the self-assembly processes and resultant ordered structures of a technologically useful molecular system comprising of discotic liquid crystal and double chain surfactant.

Effects of the Method of Preparation and Dispersion Media on the Optical Properties and Particle Sizes of Aqueous Dispersions of a Double-Chain Cationic Surfactant.

As inferred from visual observations and turbidity measurements, the average radius of the unilamellar vesicles formed in water from the cationic double-chain surfactant didodecyldimethylammonium bromide (DDAB) varies with the method of preparation, being ∼24 nm after sonication (SS method) and ∼74 nm after extrusion/ultrafiltration (SE method). The radii were larger when the vesicles were produced in 10 mM NaBr, ∼65 nm for the SS method and ∼280 nm for the SE method. The specific turbidity, or turbidity per unit path length divided by the surfactant weight fraction, w, of these vesicular dispersions increased with decreasing w until a constant value was reached at w*, which depends on the preparation method and the dispersion medium. The constant specific turbidities are indicative of single and independent scattering and were used to estimate vesicle radii by solving the specific turbidity equations derived for the Rayleigh-Debye-Gans (RDG) regime. Two turbidity equations were used, one accounting for absorbance errors due to some scattered light reaching the detector and another with no correction. Estimates of the average distances between the vesicles and their corresponding Debye lengths were obtained for evaluating the importance of intervesicle electrostatic interactions, which could lead to dependent scattering at higher weight fractions.

Powerful tailoring effects of counterions of ammonium surfactants on the phase transitions of solvent-free DNA thermotropic liquid crystals

Solvent-free DNA-surfactant thermotropic liquid crystals (TLCs) are new developed soft biomaterials in recent years. The phase transition behaviors of these DNA TLCs could be regulated by the chain lengths of used double chain surfactants. While, the impact of counterions of ammonium surfactants on the phase transitions of DNA TLCs is still not clear. Herein, a series of ammonium surfactants with different counterions were prepared and put into use of fabrication of DNA TLCs. With inorganic counterions, the resulted DNA materials exhibit distinct decrease on the thermodynamic stability of LC states along with the size increase of counterions, while, the use of planar p-toluenesulfonate as counterion leads to remarkable increased LC thermostability for the resulted DNA material, due to the different interaction between counterions and surfactant layers. These observations indicate that the LC property of DNA-surfactant complexes could be conveniently tailored by using surfactants with designed counterions, providing a new strategy for designing advanced solvent-free biomaterials.

Photoresponsive supramolecular strategy for controlled assembly in light-inert double-chain surfactant system

HypothesisOne of the main advances in double-chain surfactant systems has been their progress from the construction of assemblies to the transformation application in medicine and material science, especially to the drug delivery systems. Thus, it is critical to develop stimuli-responsive assemblies based on double-chain surfactants. We predicted that reversible assembly switching can be achieved by manipulation of the ternary host-guest competitive complexation among β-cyclodextrin (β-CD), surfactants, and designed azobenzene (Azo). ExperimentsIn this work, Azo was introduced into vesicles using supramolecular assembly strategy. Vesicles are formed only when Azo moieties are in trans-form. UV switching of Azo groups led to fast disruption of the Azo@β-CD complexes and relatively slow disintegration of the vesicles. With the alterative irradiation of UV and Vis light, the photoisomerization of azo group provokes the reversible disassembly and reassembly of vesicles. FindingsThis photo-responsive supramolecular strategy offered a controllable way to prepare responsive vesicles assembled from complex double-chain surfactants, such as phospholipids, which could be further used in drug delivery systems. This new perspective is instructive for the design and functional use of complex surfactants assembly. Importantly, the study results paved the way for the development of novel light-responsive assembly materials operating in aqueous media and biological field.