Aggregation Behavior In Aqueous Solution Research Articles

Dendritic Architectures with Positively Charged Cores and Negatively Charged Shells

AbstractA new family of dipolar ionic dendrimers that consist of a cationic pyridinium core surrounded by a negatively charged shell of carboxylic acids was successfully synthesized and characterized. Both spherical architectures and examples of amphiphiles with a dipolar head group were synthesized. Studies of the aggregation behaviour in aqueous solution by determining the cmc values were performed. This new type of dipolar core–shell dendrons can be considered as molecular architectures that contain a positively charged nucleus covalently incorporated within a negatively charged shell.

Zwitterionic heterogemini surfactants containing ammonium and carboxylate headgroups 2: Aggregation behavior studied by SANS, DLS, and cryo-TEM

The aggregation behavior in aqueous solution of zwitterionic heterogemini surfactants, N,N-dimethyl-N-[2-(N′-alkyl-N′-β-carboxypropanoylamino)ethyl]-1-alkylammonium bromides (2CnAmCa, in which n represents hydrocarbon chain lengths of 8, 10, 12, and 14), with nonidentical headgroups containing ammonium and carboxylate was investigated through small-angle neutron scattering (SANS), dynamic light scattering (DLS), and cryogenic transmission electron microscopy (cryo-TEM) techniques. We found that the aggregation behavior of 2CnAmCa strongly depended on the hydrocarbon chain length and the surfactant concentration. 2C8AmCa forms spherical micelles with radius of approximately 2nm in solution. 2C10AmCa forms rod-like micelles at low concentration in the solution, and the structure changes to vesicles with increasing concentration. The membrane thickness of the vesicle is independent of the surfactant concentration. Aggregation shape transitions were also observed for 2C12AmCa. In addition, it appears that the vesicles of 2C12AmCa coexist with the rod-like micelles at a wide range of surfactant concentrations. Interestingly, 2C14AmCa forms vesicles with averaged membrane thickness of 2.32nm in solution, even at the extremely low concentration of 10 times the cmc. Thus, it was concluded that 2CnAmCa exhibits unique aggregation behavior, such as the formation of spherical micelle→rod-like micelle→rod-like micelle+vesicle (coexistence)→vesicle with increasing hydrocarbon chain length and surfactant concentration. We also found that the membrane structure is an interdigitated bilayer when the vesicles are formed. This formation of interdigitated structures is related to the origins of the effective properties of 2CnAmCa in solution.

Synthesis and Characterization of pH Sensitive Core–Shell–Corona Micelles of Poly(styrene-block-2-vinylpyridine-block-ethylene oxide) ABC Triblock Copolymer in Aqueous Solutions

Abstract The core–shell–corona forming ABC triblock copolymer poly(styrene-block-2-vinylpyridine-block-ethylene oxide), PS–P2VP–PEO, was synthesized using reversible addition fragmentation chain transfer (RAFT) radical polymerization and characterized by NMR and GPC as PS13–P2VP62–PEO47. The aggregation behavior in aqueous solution as a function of pH and temperature was studied. Turbidity measurements were used to monitor the effects associated with change in pH. The pH-sensitive P2VP block (insoluble above pH >5) and resultant protonation/deprotonation phenomenon plays decisive role in the aggregation. We found that spherical micelles of considerably low aggregation number form at pH <5. SANS and DLS characterization indicate the micelles’ size and spherical shape remained virtually constant in the pH range 1 to 5. The size and shape were further confirmed by cryo-TEM.

Synthesis and Properties of Lactobionamide-Based Polysiloxane Surfactant

AbstractA lactobionamide-based polysiloxane surfactant (LBPS) with well-defined structure was prepared via a two-step method. Structure characterization of the LBPS was performed by Fourier Transform Infrared spectroscopy (FT-IR) and proton nuclear magnetic resonance (1H NMR). Surface activity and aggregation behavior in aqueous solution of the LBPS were investigated by surface tension measurements, dynamic light scattering (DLS) and negative-stain transmission electron microscopy (TEM). The results show that the critical micelle concentration (CMC) and surface tension (γCMC) at the CMC in aqueous solution of the LBPS are 7.7 mg · L−1and 27.5 mN · m−1, respectively, and the surfactants can self-assemble into spherical micelles with diameters in the range from 30 to 250 nm.

Synthesis, aggregation behavior and interfacial activity of branched alkylbenzenesulfonate gemini surfactants

Branched alkylbenzenesulfonate gemini surfactants: sodium 6,6′-(propane-1,3-diylbis(oxy))bis(3-(2-propylpentyl)benzenesulfonate) (C8BC3C8B), sodium 6,6′-(propane-1,3-diylbis(oxy))bis(3-(3,5,5-trimethylhexyl)benzenesulfonate) (C9BC3C9B), and sodium 6,6′-(propane-1,3-diylbis(oxy))bis(3-(2,4,4-trimethylpentan-2-yl)benzenesulfonate) (T-C8BC3C8B) have been synthesized. Their interfacial activity and aggregation behavior in aqueous solution were studied by surface/interface tension measurement, electrical conductivity, isothermal titration microcalorimetry, 1H NMR spectroscopy, dynamic light scattering, steady-state fluorescence and cryogenic transmission electron microscopy. The critical aggregation concentration (CAC) and the minimum average surface area/molecule (Amin) decrease with the decrease of the branching factor, i.e., in the order of T-C8BC3C8B, C8BC3C8B and C9BC3C9B. Moreover, alkyl side chain branches generate much more significant increases in CAC and Amin for the gemini surfactants than single-chain surfactants. However, the branching factor does not change the air/water surface tension at CAC regularly. Instead, the air/water surface tension decreases with the increase of the carbon number of the hydrocarbon chains. In addition, it is noted that the branched gemini surfactants display high efficiency in reducing toluene/water interfacial tension. Interestingly, the increase in the branching factor leads to much more endothermic enthalpy of aggregation. All these three surfactants form spherical vesicles in aqueous solution and may present a parallel-displaced structure with a directional arrangement of the benzene ring in the vesicles.

Adsorption and Aggregation Behavior of Tetrasiloxane-Tailed Surfactants Containing Oligo(ethylene oxide) Methyl Ether and a Sugar Moiety

Three novel amphiphilic dicephalic (double-headed) surfactants containing oligo(ethylene-oxide)methyl-ether and a sugar moiety TGA-m (m = 1, 2, and 3) that incorporate a tetrasiloxane at the terminus of a hydrocarbon chain were designed and synthesized. Their surface activity and aggregation behavior in aqueous solution were systematically investigated by surface tension, dynamic light scattering (DLS), and transmission electron microscopy (TEM) techniques at 298 K. The surface tension measurements provided the critical aggregation concentration (CAC) and the surface tension at the CAC (γ(cac)). In addition, with application of the Gibbs adsorption isotherm, the maximum surface excess concentration (Γ(max)) and the minimum surface area/molecule (A(min)) at the air-water interface were estimated. The effect of EO chain length on the surface activity and aggregation behavior was also investigated. It was found that both the γ(cac) and the CAC were lower than those for reported traditional hydrocarbon surfactants. Aggregates of three surfactants, TGA-m (m = 1, 2, and 3), formed in aqueous solutions could be assigned as spherical vesicles as suggested by analysis using DLS and TEM. Moreover the formation of vesicles can be confirmed by the encapsulation of bromophenol blue. These results indicate that these three surfactants have excellent efficiencies of vesicle formation and surface tension reduction in the aqueous phase.

Synthesis, surface and aggregation properties of glucosamide-grafted amphiphilic glycopolysiloxanes

Three glucosamide-grafted amphiphilic glycopolysiloxanes (APFPS-GL) were synthesized through a two-step method. First, the aminopropyl functional polysiloxanes (APFPS) were synthesized by equilibrium polymerization; then, gluconolactone was conjugated to the APFPS via ring-opening reaction to give the glycopolysiloxanes APFPS-GL. The final compositions of the amphiphilic glycopolysiloxanes were characterized by FT-IR, 1H NMR and 13C NMR. Surface activities and aggregation behavior in aqueous solution of these three glycopolysiloxanes were investigated by surface tension measurements, dynamic light scattering (DLS) and transmission electron microscopy (TEM). The results show that these three glycopolysiloxanes have much higher surface activity than those of conventional carbon–carbon chain glycopolymers in aqueous solution and they can self-assemble into spherical micelles with average diameters in the range from 200 to 600 nm.

Mesoscopic Simulations on the Aggregation Behavior of Polymeric Surfactants in Aqueous Solutions

Polymeric surfactants are widely used in many fields.Their aggregation behavior is different from that of small molecule surfactants because of complex configurations and large molecular weights.The studies of aggregation behavior at the micro-level can guide applications and therefore,many researchers have focused on theoretical investigations.With the recent advances in computer simulations,the study of surfactant aggregation behavior in aqueous solutions at the micro-or meso-level has been successfully undertaken.Based on our recent work,we review the aggregation behavior of polymeric surfactants by dissipative particle dynamics (DPD) and mesoscopic dynamics (MesoDyn).This paper especially introduces research about the phase behavior of polymeric surfactants as well as their interactions with low molecular weight surfactants.This method can directly provide the process of phase separations and changes in the conformation of the aggregates,which are not observable in macro-experiments.This method has the potential to complement and guide experimental methods.

A SANS investigation of micelles in mixtures of cetyltrimethylammonium bromide (CTAB)/octyl-β- d-glucopyranoside (C 8G 1) in water/glycerol solvent

Mixtures of a classical cationic surfactant (CTAB) with the sugar surfactant octyl-β- d-glucopyranoside (C 8G 1) have been studied with respect to their aggregation behaviour in aqueous solution as well as in D 2O mixtures with glycerol by means of small-angle neutron scattering (SANS). It is observed that the mixtures are governed by weak synergetic interactions and always form mixed micelles that grow with increasing content of CTAB in the mixtures. For the case of the mixed glycerol/water solvent, the size of the mixed micelles decreases with increasing content of glycerol, thereby also changing the shape from prolate to spherical micelles. The observations can be quantitatively interpreted by the expected variation of the head group area of the cationic surfactant that becomes larger due to the decreasing dielectric constant of the solvent with increasing glycerol content.

Femtosecond midinfrared study of aggregation behavior in aqueous solutions of amphiphilic molecules

We study the spectral and orientational dynamics of HDO molecules in aqueous solutions of different concentrations of tertiary butyl alcohol (TBA) and trimethylamine-N-oxide (TMAO). The spectral dynamics is investigated with femtosecond two-dimensional infrared spectroscopy of the O-H stretch vibration of HDO:D(2)O, and the orientational dynamics is studied with femtosecond polarization-resolved pump-probe spectroscopy of the O-D stretch vibration of HDO:H(2)O. Both the spectral and orientational dynamics are observed to show bimodal behavior: part of the water molecules shows spectral and orientational dynamics similar to bulk liquid water and part of the water molecules displays a much slower dynamics. For low solute concentrations, the latter fraction of slow water increases linearly as a function of solute molality, indicating that the slow water is contained in the solvation shells of TBA and TMAO. At higher concentrations, the fraction of slow water saturates. The saturation behavior is much stronger for TBA solutions than for TMAO solutions, indicating the aggregation of the TBA molecules.

Synthesis and Self‐Assembly Behavior of Comb‐Like Surfactant Polymethyl Methacrylate‐g‐Methoxy Polyethylene Glycol

AbstractComb‐like surfactant of polymethyl methacrylate‐g‐methoxy polyethylene glycol (PMMA‐g‐MPEG) with well‐defined structure was synthesized and characterized by FT‐IR, 1H NMR and gel permeation chromatography. Its surface activity and aggregation behavior in aqueous solution were investigated by surface tension measurement, dye encapsulation experiment, transmission electron microscopy (TEM) and dynamic light scattering (DLS). The CMC and surface tension at the CMC of PMMA‐g‐MPEG were 0.2 g/L and 47 mN/m, respectively. DLS and TEM analysis revealed that PMMA‐g‐MPEG could self‐assemble into spherical micelles with the average hydrodynamic diameters in the range from 20 to 300 nm in aqueous solution.

Fabrication of a Thermoresponsive Biohybrid Double Hydrophilic Block Copolymer by a Cofactor Reconstitution Approach

The fabrication of a thermoresponsive biohybrid double hydrophilic block copolymer (DHBC) by a cofactor reconstitution approach is reported. Poly(N-isopropylacrylamide) (PNIPAM) bearing a porphyrin moiety at the chain terminal, PPIXZn-PNIPAM, is synthesized by the combination of ATRP and a click reaction. The subsequent cofactor reconstitution process between apomyoglobin and PPIXZn-PNIPAM affords well-defined myoglobin-b-PNIPAM protein-polymer bioconjugates. Behaving as typical responsive DHBCs, the obtained myoglobin-b-PNIPAM biohybrid diblock copolymer exhibits thermo-induced aggregation behavior in aqueous solution as a result of the presence of the thermoresponsive PNIPAM block, as revealed by temperature-dependent transmittance, dynamic laser light scattering measurements, transmission electron microscopy, and scanning electron microscopy. This work represents the first report of the preparation of responsive biohybrid DHBCs by the cofactor reconstitution process.

ChemInform Abstract: Multifunctional Tetracoordinate Phosphorus Species with High Self-Organizing Ability

Abstract The unique features of the phosphonium salts as functional materials are reviewed, with emphasis being placed on the comparison between the phosphonium salts and the commonly available quaternary ammonium salts, which have the same structure, differing only in the positively-charged heteroatom. The antimicrobial activity of onium salts with different long-chain segments is described with special reference to structure–activity relationships. The unexpected relationship between the antibacterial activity and the aggregation behavior in aqueous solution (i.e. lyotropic liquid-crystalline properties) was revealed through systematic studies on the antibacterial activity of the phosphonium salts as a novel class of cationic biocides. Furthermore, it is shown that the phosphonium salts can act as thermotropic liquid crystals in spite of the fact that they are amphiphiles without a rigid core.

Carbohydrate-Modified Siloxane Surfactants and Their Adsorption and Aggregation Behavior in Aqueous Solution

Four carbohydrate-modified siloxane surfactants, Si(n)N-GA and Si(n)N-LA (n = 3, 4), were designed and synthesized. Their surface activities, adsorption, and aggregation behavior in aqueous solution were investigated by surface tension measurements, dynamic light scattering (DLS) and transmission electron microscopy (TEM). Due to the bulky siloxane moiety at the end of hydrophobic chains, the surfactant solutions displayed low critical aggregation concentration (cac) and low surface tension. Surface tension measurement for all three surfactants are under 22 mN x m(-1), much lower than those of ordinary hydrocarbon surfactants. Due to its poor solubility in water, surface tension of Si(4)N-GA could not be measured. DLS and TEM analysis of Si(3)N-GA, Si(3)N-LA, and Si(4)N-LA aqueous solutions revealed self-assembled spherical vesicles, indicating potential applications as microsphere drug delivery systems and as models of biomembranes.

Amphiphilic Polymer Nanoparticles: Characterization and Assessment as New Drug Carriers

An amino-acid-based hydrophobically modified biocompatible copolymer, poly[(sodium N-acryloyl-L-valinate)-co-(N-octylacrylamide)] was synthesized and characterized. Techniques such as fluorescence probes, DLS, and TEM were used to investigate its aggregation behavior in aqueous solution. The copolymer was observed to form micellar aggregates having diameters in the nanometer range in aqueous solution (pH = 8) through inter-chain hydrophobic association. This behavior was found to be similar to that of poly[(sodium N-acryloyl-L-valinate)-co-(N-dodecylacrylamide)]. The compact micellar nanostructures were observed to be stable with respect to changes of pH and temperature. The encapsulation and release of griseofulvin, a hydrophobic model drug, was studied.

Synthesis and characterization of a series of modified polyacrylamide

We present the synthesis and the characterization of a new class of modified polyacrylamides (MPAM) with the unusual trait of strong emulsification ability, viscosity enhancement capacity, and significant salt tolerance. Besides, the synthesized polymers have the peculiar aggregation behaviors in aqueous solution. The synthesis was carried out by polymerizing the monomers such as acrylamide (AM), acrylic acid (AA), unsaturated amphiphilic functional moieties, and high steric hindrance functional units. Their aggregation behaviors were investigated by using a scanning electron microscope (SEM). The emulsion, formed by 10 ml of MPAM (with the polymer concentration of 1,000 mg/L) and the 10 ml of crude oil, was very stable, which indicates that the synthesized polymers have unique emulsification properties. The strong hydrophobic interaction between molecules and the three-dimensional network formed in aqueous solution were exhibited by the experimental results of steady fluorescence and SEM experiments. It could be concluded that the performance of polymers for enhanced oil recovery (EOR) can be remarkably enhanced by introducing functional monomers to polymer backbone, which allows the new class of modified polymers to have more promising application in enhanced oil recovery.

Synthesis of chiral amphiphilic diblock copolymers via consecutive RAFT polymerizations and their aggregation behavior in aqueous solution

AbstractTwo chiral amphiphilic diblock copolymers with different relative lengths of the hydrophobic and hydrophilic blocks, poly(6‐O‐p‐vinylbenzyl‐1,2:3,4‐Di‐O‐isopropylidene‐D‐galactopyranose)‐b‐poly(N‐isopropylacrylamide) or poly(VBCPG)‐b‐poly(NIPAAM) and poly(20‐(hydroxymethyl)‐pregna‐1,4‐dien‐3‐one methacrylate)‐b‐poly(N‐isopropylacrylamide) or poly(MAC‐HPD)‐b‐poly(NIPAAM) were synthesized via consecutive reversible addition‐fragmentation chain‐transfer polymerizations of VBCPG or MAC‐HPD and NIPAAM. The chemical structures of these diblock copolymers were characterized by 1H nuclear magnetic resonance spectroscopy. These amphiphilic diblock copolymers could self‐assemble into micelles in aqueous solution, and the morphologies of micelles were investigated by transmission electron microscopy. By comparison with the lower critical solution temperatures (LCST) of poly(NIPAAM) homopolymer in deionized water (32 °C), a higher LCST of the chiral amphiphilic diblock copolymer (poly(VBCPG)‐b‐poly(NIPAAM)) was observed and the LCST increased with the relative length of the poly(VBCPG) block in the copolymer from 35 to 47 °C, respectively. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 7690–7701, 2008

Aggregation properties of zwitterionic surfactants with different ionic headgroups, hydrophobic chain length and inter-charge spacers

Three series of zwitterionic surfactants with different ionic headgroups, various hydrophobic chain length, and flexible or rigid inter-charge spacers have been synthesized and their aggregation behaviors in aqueous solution have been studied. Series I and III represent [C n H 2 n+1 (CH 3) 2N +(CH 2) 6N +(CH 3) 2CH 2CH 2CH 2SO 3 −]Br − (C n C 6Tri, n = 12, 14, and 16) and C n H 2 n+1 (CH 3) 2N +CH 2CH 2CH 2SO 3 − ( n = 12, 14, and 16), respectively. Series II are [C 14H 29(CH 3) 2N +C sN +(CH 3) 2CH 2CH 2CH 2SO 3 −]Br – (C 14C sTri, C s = –(CH 2) 2–, –(CH 2) 6–, –(CH 2) 8–, –(CH 2) 10–, p–xylyl), where C s stands for the inter-charge spacer connecting two quaternary ammonium groups. The critical micelle concentrations ( CMC) of the surfactants with two cationic ammonium groups and one anionic sulfonate group (Series I and II) are much larger than those of the corresponding surfactants with one cationic ammonium group and one anionic sulfonate group (Series III). These surfactants exhibit obviously different aggregate morphologies. For Series III, only micelles are observed. For Series I and II, if the surfactants have short or rigid inter-charge spacer (C 14C 2Tri and C 14C pxTri), the aggregates also appear as micelles and have more exothermic micellization enthalpy change. However, even for Series I and II, if the surfactants have longer and flexible inter-charge spacer and longer hydrocarbon chains (C 14C 6Tri, C 16C 6Tri, C 14C 8Tri and C 14C 10Tri), vesicles are observed due to the reduced hydrophilic moiety size and the strong hydrophobic interaction, whereas vesicles cannot be formed if the surfactants have longer and more flexible inter-charge spacer but without enough longer hydrocarbon chain (C 12C 6Tri).

On the Self-Aggregation and Fluorescence Quenching Aptitude of Surfactant Ionic Liquids

The aggregation behavior in aqueous solution of a number of ionic liquids was investigated at ambient conditions by using three techniques: fluorescence, interfacial tension, and (1)H NMR spectroscopy. For the first time, the fluorescence quenching effect has been used for the determination of critical micelle concentrations. This study focuses on the following ionic liquids: [Cnmpy]Cl (1-alkyl-3-methylpyridinium chlorides) with different linear alkyl chain lengths (n=4, 10, 12, 14, 16, or 18), [C12mpip]Br (1-dodecyl-1-methylpiperidinium bromide), [C12mpy]Br (1-dodecyl-3-methylpyridinium bromide), and [C12mpyrr]Br (1-dodecyl-1-methylpyrrolidinium bromide). Both the influence of the alkyl side-chain length and the type of ring in the cation (head) on the CMC were investigated. A comparison of the self-aggregation behavior of ionic liquids based on 1-alkyl-3-methylpyridinium and 1-alkyl-3-methylpyridinium cations is provided. It was observed that 1-alkyl-3-methylpyridinium ionic liquids could be used as quenchers for some fluorescence probes (fluorophores). As a consequence, a simple and convenient method to probe early evidence of aggregate formation was established.

Novel amphiphilic poly(ester‐urethane)s based on poly[(R)‐3‐hydroxyalkanoate]: synthesis, biocompatibility and aggregation in aqueous solution

AbstractBACKGROUND: The aim of this work was to develop polyhydroxyalkanoates (PHAs) for blood contact applications, and to study their self‐assembly behavior in aqueous solution when the PHAs are incorporated with hydrophilic segments. To do this, poly(ester‐urethane) (PU) multiblock copolymers were prepared from hydroxyl‐terminated poly(ethylene glycol) (PEG) and hydroxylated poly[(R)‐3‐hydroxyalkanoate] (PHA‐diol) using 1,6‐hexamethylene diisocyanate as a coupling reagent. The PEG segment functions as a soft, hydrophilic and crystalline portion and the poly[(R)‐3‐hydroxybutyrate] segment behaves as a hard, hydrophobic and crystalline portion. In another series of PU multiblock copolymers, crystalline PEG and completely amorphous poly[((R)‐3‐hydroxybutyrate)‐co‐(4‐hydroxybutyrate)] behaved as hydrophobic and hydrophilic segments, respectively.RESULTS: The formation of a PU series of block copolymers was confirmed by NMR, gel permeation chromatography and infrared analyses. The thermal properties showed enhanced thermal stability with semi‐crystalline morphology via incorporation of PEG. Interestingly, the changes of the hydrophilic/hydrophobic ratio led to different formations in oil‐in‐water emulsion and surface patterning behavior when cast into films. Blood compatibility was also increased with increasing PEG content compared with PHA‐only polymers.CONCLUSION: For the first time, PHA‐based PU block copolymers have been investigated in terms of their blood compatibility and aggregation behavior in aqueous solution. Novel amphiphilic materials with good biocompatibility for possible blood contact applications with hydrogel properties were obtained. Copyright © 2008 Society of Chemical Industry