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1.
Molecules ; 26(16)2021 Aug 19.
Artigo em Inglês | MEDLINE | ID: mdl-34443601

RESUMO

Surfactant aggregates have long been considered as a tool to improve drug delivery and have been widely used in medical products. The pH-responsive aggregation behavior in anionic gemini surfactant 1,3-bis(N-dodecyl-N-propanesulfonate sodium)-propane (C12C3C12(SO3)2) and its mixture with a cationic monomeric surfactant cetyltrimethylammonium bromide (CTAB) have been investigated. The spherical-to-wormlike micelle transition was successfully realized in C12C3C12(SO3)2 through decreasing the pH, while the rheological properties were perfectly enhanced for the formation of wormlike micelles. Especially at 140 mM and pH 6.7, the mixture showed high viscoelasticity, and the maximum of the zero-shear viscosity reached 1530 Pa·s. Acting as a sulfobetaine zwitterionic gemini surfactant, the electrostatic attraction, the hydrogen bond and the short spacer of C12C3C12(SO3)2 molecules were all responsible for the significant micellar growth. Upon adding CTAB, the similar transition could also be realized at a low pH, and the further transformation to branched micelles occurred by adjusting the total concentration. Although the mixtures did not approach the viscosity maximum appearing in the C12C3C12(SO3)2 solution, CTAB addition is more favorable for viscosity enhancement in the wormlike-micelle region. The weakened charges of the headgroups in a catanionic mixed system minimizes the micellar spontaneous curvature and enhances the intermolecular hydrogen-bonding interaction between C12C3C12(SO3)2, facilitating the formation of a viscous solution, which would greatly induce entanglement and even the fusion of wormlike micelles, thus resulting in branched microstructures and a decline of viscosity.


Assuntos
Reologia , Tensoativos/química , Cetrimônio/química , Glutamatos/química , Concentração de Íons de Hidrogênio , Micelas , Viscosidade
2.
Langmuir ; 34(1): 291-301, 2018 01 09.
Artigo em Inglês | MEDLINE | ID: mdl-29228778

RESUMO

Effects of calcium ions (Ca2+) on the solubility, aggregate structure, and rheological behavior of a C22-tailed zwitterionic surfactant, erucyl dimethyl amidopropyl hydroxyl sulfobetaine (EHSB), have been investigated in aqueous solution. In comparison with sodium ions (Na+), Ca2+ ions exhibit a much higher efficiency in decreasing the Krafft temperature (TK) of EHSB. Specifically, contrary to Na+ ions which have no obvious effect on the rheological properties of the EHSB solution, Ca2+ ions increase the viscosity of the EHSB solution at lower EHSB concentration, and enhance its elasticity at higher EHSB concentration. Moreover, Ca2+ ions raise the temperature needed for the elastic-to-viscous transition of the EHSB solution at higher concentration. At lower EHSB concentration, the hydrophobic interaction between the ultralong hydrocarbon chains induces a tighter packing of the hydrophobic chains by forming a more stretched configuration, while at higher EHSB concentration, the electrostatic attraction between Ca2+ ions and the sulfonate groups of EHSB induces a tighter packing of the headgroups by forming Ca2+-mediated bridges among the EHSB headgroups. Besides, the above interactions may strengthen the hydrogen bonding of OH groups and/or of C═O amide groups, which in turn facilitates the compact packing of the surfactant molecules in aggregates and promotes the growth and entanglement of wormlike micelles. Thus, the EHSB solution shows Ca2+-dependent rheological behaviors. The solubility and rheological properties of the ultralong chain surfactant solution can be simultaneously improved with the addition of divalent Ca2+ ions.

3.
Langmuir ; 32(4): 972-81, 2016 Feb 02.
Artigo em Inglês | MEDLINE | ID: mdl-26750978

RESUMO

The aggregation behaviors of the mixtures of cationic gemini surfactant 1,4-bis(dodecyl-N,N-dimethylammonium bromide)-2,3-butanediol (C12C4(OH)2C12Br2) and anionic amino acid surfactant N-dodecanoylglutamic acid (C12Glu) in aqueous solution of pH = 10.0 have been studied. The mixture forms spherical micelles, vesicles, and wormlike micelles at 25 °C by changing mixing ratios and/or total surfactant concentration. Then these aggregates undergo a series of transitions upon increasing the temperature. Smaller spherical micelles transfer into larger vesicles, vesicles transfer into solid spherical aggregates and then into larger irregular aggregates, and entangled wormlike micelles transfer into branched wormlike micelles. Moreover, the larger irregular aggregates and branched micelles finally lead to precipitation and clouding phenomenon, respectively. All these transitions are thermally reversible, and the transition temperatures can be tuned by varying the mixing ratios and/or total concentration. These temperature-dependent aggregate transitions can be elucidated on the basis of the temperature-induced variations in the dehydration, electrostatic interaction, and hydrogen bonds of the headgroup area and in the hydrophobic interaction between the hydrocarbon chains. The results suggest that the surfactants carrying multiple binding sites will greatly improve the regulation ability and temperature sensitivity.


Assuntos
Butanóis/química , Glutamatos/química , Compostos de Amônio Quaternário/química , Tensoativos/química , Micelas , Soluções , Temperatura de Transição , Água
4.
Langmuir ; 30(27): 7968-76, 2014 Jul 15.
Artigo em Inglês | MEDLINE | ID: mdl-24933418

RESUMO

Cationic quaternary ammonium gemini surfactants C(n)H(2n+1)(CH3)2N(+)CH2CHCHCH2(CH3)2N(+)C(n)H(2n+1)2Br(-) (C(n)C4C(n), n = 12, 8, 6) with alkyl spacers, C(n)H(2n+1)(CH3)2N(+)CH2CHOHCHOHCH2(CH3)2N(+)C(n)H(2n+1)2Br(-) (C(n)C4(OH)2C(n), n = 12, 8, 6, 4) with two hydroxyl groups in alkyl spacers, and cationic ammonium single-chain surfactants C(n)H(2n+1)(CH3)2N(+)Br(-) (C(n)TAB, n = 12, 8, 6) have been chosen to fabricate oppositely charged surfactant mixtures with anionic sulfonate gemini surfactant C12H25N(CH2CH2CH2SO3(-))CH2CH2CH2(CH3)2N(CH2CH2CH2SO3(-))C12H252Na (C12C3C12(SO3)2). Surface tension, electrical conductivity, and isothermal titration microcalorimetry (ITC) were used to study their surface properties, aggregation behaviors, and intermolecular interactions. The mixtures of C12C3C12(SO3)2/C(n)C4(OH)2C(n) (n = 12, 8) and C12C3C12(SO3)2/C12C4C12 show anomalous larger critical micelle concentration (CMC) than C12C3C12(SO3)2, while the mixtures of C12C3C12(SO3)2/C(n)C4(OH)2C(n) (n = 6, 4), C12C3C12(SO3)2/C(n)C4(OH)2C(n) (n = 6, 4), and C12C3C12(SO3)2/C(n)TAB (n = 12, 8, 6) exhibit much lower CMC than C12C3C12(SO3)2. The results indicate that strong hydrophobic interactions between the alkyl chains assisted by strong electrostatic attractions between the headgroups and hydrogen bonds between the spacers lead to the formation of less surface active premicellar aggregates in bulk solution, resulting in the increase of CMC. If these interactions are weakened or inhibited, less surface active premicellar aggregates are no longer formed in the mixtures, and thus the CMC values are reduced. The work reveals that the combination of two surfactants with great self-assembling ability separately may have strong intermolecular binding interactions; however, their mixtures do not always generate superior synergism properties. Only moderate intermolecular interaction can generate the strongest synergism in CMC reduction.

5.
Soft Matter ; 10(11): 1705-13, 2014 Mar 21.
Artigo em Inglês | MEDLINE | ID: mdl-24651935

RESUMO

Coacervation in an aqueous solution of cationic ammonium gemini surfactant hexamethylene-1,6-bis(dodecyldimethylammonium bromide) (C12C6C12Br2) with sodium benzoate (NaBz) has been investigated at 25 °C by turbidity titration, light microscopy, dynamic light scattering, cryogenic temperature transmission electron microscopy (Cryo-TEM), scanning electron microscopy (SEM), isothermal titration calorimetry, ζ potential and (1)H NMR measurements. There is a critical NaBz concentration of 0.10 M, only above which coacervation can take place. However, if the NaBz concentration is too large, coacervation also becomes difficult. Coacervation takes place at a very low concentration of C12C6C12Br2 and exists in a very wide concentration region of C12C6C12Br2. The phase behavior in the NaBz concentration from 0.15 to 0.50 M includes spherical micelles, threadlike micelles, coacervation, and precipitation. With increasing NaBz concentration, the phase boundaries of coacervation shift to higher C12C6C12Br2 concentration. Moreover, the C12C6C12Br2-NaBz aggregates in the coacervate are found to be close to charge neutralized. The Cryo-TEM and SEM images of the coacervate shows a layer-layer stacking structure consisting of a three-dimensional network formed by the assembly of threadlike micelles. Long, dense and almost uncharged threadlike micelles are the precursors of coacervation in the system.


Assuntos
Compostos de Amônio/química , Micelas , Água/química , Brometos/química , Calorimetria , Microscopia Eletrônica de Transmissão , Benzoato de Sódio/química
6.
Langmuir ; 29(39): 12084-92, 2013 Oct 01.
Artigo em Inglês | MEDLINE | ID: mdl-24011133

RESUMO

Anionic single-tail surfactant sodium dodecyl sulfate (SDS) and a molecule with multiple amido and amine groups (Lys-12-Lys) were used as building blocks to fabricate oligomeric surfactants through intermolecular interactions. Their interactions and the resultant complex and aggregate structures were investigated by turbidity titration, isothermal titration microcalorimetry, dynamic light scattering, cryogenic transmission electron microscopy, freeze-fracture transmission electron microscopy, (1)H NMR, and 1D NOE techniques. At pH 11.0, the interaction between SDS and Lys-12-Lys is exothermic and mainly resulted from hydrogen bonding among the amido and amine groups of Lys-12-Lys and the sulfate group of SDS and hydrophobic interaction between the hydrocarbon chains of SDS and Lys-12-Lys. At pH 3.0, each Lys-12-Lys carries four positive charges and two hydrogen bonding sites. Then SDS and Lys-12-Lys form complexes Lys-12-Lys(SDS)6 and Lys-12-Lys(SDS)4 through the head groups by electrostatic attraction and hydrogen bonds assisted by hydrophobic interaction. Moreover, the complexes pack more tightly in their aggregates with the increase of the molar ratio. Especially the Lys-12-Lys(SDS)4 and Lys-12-Lys(SDS)6 complexes behave like oligomeric surfactants taking Lys-12-Lys as a spacer group, exhibiting a series of aggregates transitions with the increase of concentration, i.e., larger vesicles, smaller spherical micelles, and long threadlike micelles. Therefore, oligomeric surfactants Lys-12-Lys(SDS)4 and Lys-12-Lys(SDS)6 have been successfully fabricated by using a single chain surfactant and an oligomeric connecting molecule through noncovalent association.

7.
ACS Appl Mater Interfaces ; 5(12): 5709-16, 2013 Jun 26.
Artigo em Inglês | MEDLINE | ID: mdl-23725038

RESUMO

A novel synthetic approach was developed for creating versatile hollow Au nanostructures by stepwise reductions of Au(III) upon the use of cationic gemini surfactant hexamethylene-1,6-bis(dodecyl dimethylammonium bromide) (C12C6C12Br2) as a template agent. It was observed that the Au(I) ions obtained from the reduction of Au(III) by ascorbic acid can assist the gemini surfactant to form vesicles, capsule-like, and tube-like aggregates that subsequently act as soft templates for hollow Au nanostructures upon further reduction of Au(I) to Au(0) by NaBH4. It was demonstrated that the combination of C12C6C12Br2 and Au(I) plays a key role in regulating the structure of the hollow precursors not only because C12C6C12Br2 has a stronger aggregation ability in comparison with its single chain counterpart but also because the electrostatic repulsion between head groups of C12C6C12Br2 is greatly weakened after Au(III) is converted to Au(I), which is in favor of the construction of vesicles, capsule-like, and tube-like aggregates. Compared with solid Au nanospheres, the resultant hollow nanostructures exhibit enhanced electrocatalytic activities in methanol oxidation, following the order of elongated nanocapsule > nanocapsule > nanosphere. Benefiting from balanced interactions between the gemini surfactant and Au(I), this soft-template method may present a facile and versatile approach for the controlled synthesis of Au nanostructures potentially useful for fuel cells and other Au nanodevices.


Assuntos
Ouro/química , Nanoestruturas/química , Compostos de Amônio Quaternário/química , Tensoativos/química , Alcenos , Ácido Ascórbico/química , Boroidretos/química , Cátions/química , Técnicas Eletroquímicas , Metanol/química , Microscopia Eletrônica de Transmissão , Nanoestruturas/ultraestrutura , Nanotecnologia , Oxirredução
8.
J Phys Chem B ; 117(1): 433-40, 2013 Jan 10.
Artigo em Inglês | MEDLINE | ID: mdl-23205820

RESUMO

Aggregation behaviors in mixtures of an anionic gemini surfactant 1,3-bis(N-dodecyl-N-propanesulfonate sodium)-propane (C(12)C(3)C(12)(SO(3))(2)) and a cationic single-chain surfactant cetyltrimethylammonium bromide (CTAB) have been investigated in aqueous solutions at pH 9.5 by turbidity, rheology, isothermal titration microcalorimetry (ITC), cryogenic transmission electron microscopy, and dynamic light scattering. Reversible aggregate transitions from spherical micelles to wormlike micelles, vesicles, and back to wormlike micelles and spherical micelles are successfully realized through fine regulation over the mixing ratio of surfactants, i.e., the anionic/cationic charge ratio. The five aggregate regions display distinguished phase boundaries so that the aggregate regions can be well controlled. From thermodynamic aspect, the ITC curves clearly reflect all the aggregate transitions and the related interaction mechanism. The self-assembling ability of the C(12)C(3)C(12)(SO(3))(2)/CTAB mixtures are significantly improved compared with both individual surfactants. Micelle growth from spherical to long wormlike micelles takes place at a relative low total concentration, i.e., 2.0 mM. The wormlike micelle solution at 10 mM or higher shows high viscosity and shear thinning property. Moreover, the C(12)C(3)C(12)(SO(3))(2)/CTAB mixtures do not precipitate even at 1:1 charge ratio and relative high concentration. It suggests that applying gemini surfactant should be an effective approach to improve the solubility of anionic/cationic surfactant mixtures and in turn may promote applications of the surfactant mixtures.


Assuntos
Ânions/química , Cátions , Compostos de Amônio Quaternário/química , Ácidos Sulfônicos/química , Calorimetria/métodos , Microscopia Eletrônica de Transmissão , Reologia , Tensoativos/química
9.
Langmuir ; 28(33): 12005-14, 2012 Aug 21.
Artigo em Inglês | MEDLINE | ID: mdl-22827887

RESUMO

Controllable aggregate transitions were realized by mixing two kinds of cationic surfactants, hexylene-1,6-bis(dodecyldimethylammonium bromide) (C(12)C(6)C(12)Br(2)) and didodecyldimethylammonium bromide (DDAB). It was found that two parameters are the main factors determining the aggregation behavior of the mixed system, the total concentration of DDAB and C(12)C(6)C(12)Br(2) (C(T)), and the mole fraction of DDAB in the mixtures of DDAB and C(12)C(6)C(12)Br(2) (X(DDAB)). How these two parameters act on the aggregate transitions was studied in detail by various measurements including surface tension, turbidity, electrical conductivity, ζ potential, isothermal titration microcalorimetry, dynamic light scattering, cryogenic transmission electron microscopy, and (1)H NMR. When C(T) was constant, spontaneous vesicle-to-micelle transitions were found with decreasing X(DDAB) at high C(T). When X(DDAB) was constant, aggregate transitions were generated by gradually increasing C(T), depending on different X(DDAB) ranges. At X(DDAB) < 0.6, small spherical aggregates formed first and then transferred to vesicles, and finally the vesicles transitioned to micelles. At X(DDAB) ≥ 0.6, the progressive increase in C(T) led to aggregate transitions on the order of the arising of vesicles, the continuous growth of vesicles, the disruption of vesicles into micelles, and the final coexistence of vesicles and micelles. The hydrophobic interaction and electrostatic repulsion between DDAB and C(12)C(6)C(12)Br(2) together with the related degree of ionization and hydration of the surfactants were gradually adjusted by changing the ratio and the total concentration of these two surfactants, which should be responsible for the complicated aggregation behavior.


Assuntos
Compostos de Amônio Quaternário/química , Tensoativos/química , Condutividade Elétrica , Modelos Moleculares , Conformação Molecular , Tensão Superficial
10.
J Colloid Interface Sci ; 381(1): 83-8, 2012 Sep 01.
Artigo em Inglês | MEDLINE | ID: mdl-22682325

RESUMO

Effects of calcium ions on the solubility and aggregation behavior of an anionic sulfonate gemini surfactant 1,3-bis(N-dodecyl-N-propylsulfonate sodium)-propane (12-3-12(SO(3))(2)) have been studied in aqueous solution. Compared with single-chain surfactant sodium dodecylsulfate, 12-3-12(SO(3))(2) shows much better performance to the hardness tolerance with calcium ions. Moreover aggregates of the Ca(2+)/12-3-12(SO(3))(2) complexes in clear solutions influence the morphologies of the precipitates. At 12-3-12(SO(3))(2) concentrations lower than 1.5 mM, the small spherical micelles of Ca(2+)/12-3-12(SO(3))(2) in clear solutions generate precipitates of solid particles owing to complexation of surfactant monomers with Ca(2+). At 12-3-12(SO(3))(2) concentrations higher than 1.5mM, the Ca(2+)/12-3-12(SO(3))(2) complexes transform into large compact spherical aggregates and then into long wormlike micelles. These large aggregates are well dispersed in aqueous solutions and efficiently complex calcium ions. In particular, long wormlike micelles are entangled with each other at 100.0 mM CaCl(2) and 100.0 mM 12-3-12(SO(3))(2) exhibiting viscoelastic properties. In addition, the stacking of long wormlike micelles produces precipitates with ordered fibrillar structures. This work reveals that such anionic sulfonate gemini surfactants are better candidates than single-chain surfactants in applications with high hardness levels, and the ordered aggregate structures may have potential applications in materials science.

11.
J Phys Chem B ; 116(22): 6425-30, 2012 Jun 07.
Artigo em Inglês | MEDLINE | ID: mdl-22612584

RESUMO

Effects of a "gemini-type" organic salt 1,2-bis(2-benzylammoniumethoxy) ethane dichloride (BEO) on the aggregation behavior of sodium dodecylsulfate (SDS) have been investigated by turbidity, surface tension, isothermal titration microcalorimetry, dynamic light scattering, cryogenic transmission electron microscopy, (1)H NMR spectroscopy, and differential scanning microcalorimetry. The aggregation behavior of the SDS/BEO mixed aqueous solution shows strong concentration and ratio dependence. For the SDS/BEO solution with a molar ratio of 5:1, large loose irregular aggregates, vesicles, and long thread-like micelles are formed in succession with the increase of the total SDS and BEO concentration. Because BEO has two positive charges, the SDS/BEO solution may consist of the (SDS)(2)-BEO gemini-type complex, the SDS-BEO complex and extra SDS. The aggregation ability and surface activity of the SDS/BEO mixture exhibit the characteristics of gemini-type surfactants. Along with the results of DSC and (1)H NMR, the (SDS)(2)-BEO gemini-type structure is confirmed to exist in the system. This work provides an approach to construct the surfactant systems with the characteristics of gemini surfactants through intermolecular interaction between a two-charged organic salt and oppositely charged single-chain surfactants.


Assuntos
Compostos de Benzilamônio/química , Dodecilsulfato de Sódio/química , Modelos Moleculares , Estrutura Molecular , Tamanho da Partícula , Transição de Fase , Sais/química , Soluções , Propriedades de Superfície , Água/química
12.
Langmuir ; 27(17): 10570-9, 2011 Sep 06.
Artigo em Inglês | MEDLINE | ID: mdl-21797217

RESUMO

A star-shaped hexameric quaternary ammonium surfactant (PAHB), bearing six hydrophobic chains and six charged hydrophilic headgroups connected by an amide-type spacer group, was synthesized. The self-assembly behavior of the surfactant in aqueous solution was studied by surface tension, electrical conductivity, isothermal titration microcalorimetry, dynamic light scattering, cryogenic transmission electron microscopy, and NMR techniques. The results reveal that there are two critical aggregate concentrations during the process of aggregation, namely C(1) and C(2). The aggregate transitions are proved to be caused by the changes of the surfactant configuration through hydrophobic interaction among the hydrocarbon chains. Below C(1), PAHB may present a star-shaped molecular configuration due to intramolecular electrostatic repulsion among the charged headgroups, and large aggregates with network-like structure are observed. Between C(1) and C(2), the hydrophobic interaction among the hydrophobic chains may become stronger to make the hydrophobic chains of the PAHB molecules curve back and pack more closely, and then the network-like aggregates transfer to large spherical aggregates of ∼100 nm. Beyond C(2), the hydrophobic interaction may become strong enough to cause the PAHB molecular configuration to turn into a pyramid-like shape, resulting in the transition of the spherical large aggregates to spherical micelles of ∼10 nm. Interestingly, the PAHB displays high emulsification ability to linear fatty alkyls even at very low concentration.


Assuntos
Compostos de Amônio Quaternário/síntese química , Tensoativos/síntese química , Modelos Moleculares , Estrutura Molecular , Compostos de Amônio Quaternário/química , Tensoativos/química
13.
J Colloid Interface Sci ; 362(2): 406-14, 2011 Oct 15.
Artigo em Inglês | MEDLINE | ID: mdl-21764066

RESUMO

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, (1)H 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 (A(min)) 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 A(min) 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.

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