Surface and Aggregation Behavior of Pentablock Copolymer PNIPAM7-F127-PNIPAM7 in Aqueous Solutions

The triblock Pluronic F127 was modified by introducing poly(N-isopropylacrylamide) (PNIPAM) at both the poly(ethylene oxide) ends, and the pentablock copolymer so-prepared was characterized by gel permeation chromatography and (1)H NMR. The degree of polymerization of NIPAM blocks at the two ends was 7. The solution behavior and microstructure of copolymer aggregates in water and aqueous salt solution were examined and compared with F127 by UV-visible absorption spectroscopy, microdifferential scanning calorimetry, dynamic light scattering (DLS), and small-angle neutron scattering (SANS). The behavior of the pentablock copolymer at the air/water interface was determined by Langmuir film balance. Two lower critical solution temperatures were observed for pentablock copolymer, corresponding to poly(propylene oxide) and PNIPAM blocks, respectively. DLS studies show that micelle size increased with increase in temperature and in the presence of salt. SANS measurements provided temperature-dependent structural evolution of copolymer micelles in water and salt solution. The copolymer displays an isotherm with four classical regions (pancake, mushroom, brush, and condensed state). The study has potential applications in controlled drug delivery due to the tunable phase behavior and biocompatibility of the copolymer.

1-Hexanol triggered structural characterization of the worm-like micelle to vesicle transitions in cetyltrimethylammonium tosylate solutions

Incorporation of 1-hexanol close to the palisade layer of CTAT micelles favors transition of worm-like micelles to vesicular structuresviaformation of elongated worm-like micelles.

Solubilization of parabens in aqueous Pluronic solutions: investigating the micellar growth and interaction as a function of paraben composition

The influence of methyl paraben (MP) and butyl paraben (BP) on the aggregation characteristics of Pluronics in an aqueous medium has been investigated by DLS, SANS, viscometry, and fluorescence measurement techniques. Parabens are extensively used as preservatives in cosmetic, pharmaceutical, and food products. In this paper, we show that their influence on the restructuring and growth of Pluronics micelles vary quite significantly with their aqueous solubility and with the composition of Pluronics. In the case of P105 and P104, MP reduces the sphere-to-rod transition temperature down to room temperature, but BP with significantly less aqueous solubility than MP suppresses such micellar transition and leads to the formation of micellar clusters due to the onset of intermicellar attractive interaction. In the case of more hydrophobic Pluronic P103, on the other hand, both MP and BP are able to induce rapid room temperature sphere-to-rod micellar growth, which is not observed in the presence of water structure making salts like NaCl and Na(3)PO(4). These observations have been attributed to modulation of growth and restructuring processes of the Pluronic micelles arising due to different locations of parabens within the micellar corona as determined by their aqueous solubility and the hydrophobicity of the Pluronics.

Interaction between the ionic liquids 1-alkyl-3-methylimidazolium tetrafluoroborate and Pluronic® P103 in aqueous solution: a DLS, SANS and NMR study

The effect of three ionic liquids (ILs) 1-alkyl 3-methyl imidazlolium tetraflouroborates (C(n)mim BF(4)n=4, 6, 8) on micellar solutions of an ethylene oxide-propylene oxide block copolymer (PEO-PPO-PEO), Pluronic® P103 was examined from scattering and NMR techniques. The ILs alter the cloud point and micelle size dependant on their alkyl chain length and the results are discussed in terms of their behavior as cosolvent/cosurfactant. Cloud point data support the hydrogen bonding between the imidazolium cation and P103 while dynamic light scattering (DLS) and small angle neutron scattering (SANS) reveal that presence of ionic liquid is not conducive to the micelle formation of P103. The selective nuclear Overhauser effect (NOESY) indicates that the PPO block of the P103 interacts with the alkyl group of the C(n)mim(+) cation by hydrophobic interaction. Through this kind of interactions, C(n)mim BF(4) and P103 can form mixed micelles. This result indicates that the presence of ILs hinders the micelle formation of P103 in solution and promotes P103 to orient at air/water interface.

Spectral and hydrodynamic studies on p-toluidine induced growth in cationic micelle

The effect of p-toluidine (PTD) on the growth of cationic surfactant micelles in aqueous solutions was examined by viscosity, UV-visible spectroscopy, dynamic light scattering (DLS), (1)H NMR and nuclear Overhauser effect spectroscopy (NOESY). Viscosity and scattering results are used to follow the growth of the aggregates and examine the structural transitions that occur. The reduction of electrostatic repulsions between the surfactant headgroups in combination with the hydrophobicity of the additive caused micellar growth and viscoelasticity at high PTD concentration; the micellar growth was found to be more pronounced in the presence of salt. (1)H NMR chemical shift changes reflect the interaction of PTD molecules with surfactant micelles while 2D NOESY experiments reveal that PTD molecules insert themselves in micelles such that its -CH(3) group is in contact with the core region and the benzene ring resides near the palisade layer of micelle.

Microstructural study of cetyltrimethylammonium bromide / 1-butanol / salt / water system — SANS and 2D-NOESY analysis

Interaction of 1-butanol (BuOH) with a cationic surfactant, cetyltrimethylammonium bromide (CTAB) aggregate, in water and salt solution has been studied by viscometry, small-angle neutron scattering (SANS), and 2D-NMR techniques. The experimental results are interpreted in terms of a possible micellar growth occurring in the presence of added alcohol and salt. It was observed that the addition of BuOH strongly influences the viscosity of the CTAB/salt micellar system, reaching a peak viscosity at about 0.5% w/v of BuOH over a range of salt concentrations. Scattering measurements support the idea of a structural transformation by the observation of a spectral shift (broadening) as the total concentration of surfactant varies, indicating a decrease in the intermicellar distance and narrow size distribution. The chemical shift from 1H NMR measurements gave complementary data on the solubilization of BuOH in CTAB micelles, whereas the expected locus (site) of the additive added to the surfactant including the dynamics of the molecules in micellar aggregates were successfully correlated by significant and positive cross peaks obtained from two-dimensional nuclear Overhauser effect spectroscopy (2D-NOESY).

Influence of a hydrophobic diol on the micellar transitions of Pluronic P85 in aqueous solution

Micellization behavior of an amphiphilic ethylene oxide-propylene oxide-ethylene oxide tri-block copolymer Pluronic P85 [(EO)(26)(PO)(39)-(EO)(26)] in aqueous solution and in the presence of a hydrophobic C(14)diol (also known as Surfynol104) was examined by physico-chemical methods such as viscometry, cloud point (CP) and scattering techniques viz. dynamic light scattering (DLS) and small angle neutron scattering (SANS). The addition of diol decreases the cloud point and gelation temperature of aqueous Pluronic P85 copolymer solution. DLS and SANS measurements of the polymer in aqueous solution indicated micellar growth and sphere to rod transition in the presence of diol. Surfynol 104 is a sparingly water soluble diol surfactant with a solubility of approximately 0.1 wt%. However, up on addition to Pluronic solution, diol gets incorporated in the block copolymer micelles and leads to structural transition of the micelles. An increase in the temperature and the presence of added sodium chloride in the solution further enhances this effect. The addition of hydrophobic C(14)diol increases the hydrodynamic size and aggregation numbers of the micellar system. The micellar parameters for the copolymer in the presence of C(14)diol are reported at different temperatures and added sodium chloride concentrations.