Ultrathin foam films containing supramolecular structures like micelles in bulk and adsorbed surfactant at the liquid–air interface undergo drainage via stratification. At a fixed surfactant concentration, the stepwise decrease in the average film thickness of a stratifying micellar film yields a characteristic step size that also describes the quantized thickness difference between coexisting thick–thin flat regions. Even though many published studies claim that step size equals intermicellar distance obtained using scattering from bulk solutions, we found no reports of a direct comparison between the two length scales. It is well established that step size is inversely proportional to the cubic root of surfactant concentration but cannot be estimated by adding micelle size to Debye length, as the latter is inversely proportional to the square root of surfactant concentration. In this contribution, we contrast the step size obtained from analysis of nanoscopic thickness variations and transitions in stratifying foam films using Interferometry Digital Imaging Optical Microscopy (IDIOM) protocols, that we developed, with the intermicellar distance obtained using small-angle X-ray scattering. We find that stratification driven by the confinement-induced layering of micelles within the liquid–air interfaces of a foam film provides a sensitive probe of non-DLVO (Derjaguin–Landau–Verwey–Overbeek) supramolecular oscillatory structural forces andmore »
This content will become publicly available on February 1, 2024
Effect of Changing Interfacial Tension on Fragmentation Kinetics of Block Copolymer Micelles
Micelle fragmentation, one of the key mechanisms responsible for equilibration of kinetically trapped micelles, is investigated for block copolymer micelles in ionic liquids. In particular, the role of driving force for micelle fragmentation is studied by altering the solvent quality after micelle preparation, amounting to a jump in interfacial tension γ between solvent and the micelle core. Direct dissolution of a 1,2-polybutadiene-b-poly(ethylene oxide) copolymer (Mn = 17.5 kDa and fPEO = 0.38) in the ionic liquid [C2mim][TFSI] results in large micelles with average size 〖"〈" "R" _"h" "〉" 〗_"∘" " ≈ 68" nm and dispersity "Đ ≈ 1.27" . The solution of the as-prepared micelles is then diluted by the careful addition of a second ionic liquid [C10mim][TFSI] having lower γ with the micelle core, such that the micelles remain unaffected. The γ and hence the quality of the solvent mixture was controlled by the degree of dilution. The choice of the second solvent is based on the measurement of γ for a series of [Cxmim][TFSI] ILs with 1-2-polybutadiene homopolymer, carried out using a pendant drop test. Diluting the micelles by adding another ionic liquid with lower γ tends to decrease the equilibrium micelle size which, in turn, enhances the more »
- Award ID(s):
- 2103630
- Publication Date:
- NSF-PAR ID:
- 10398478
- Journal Name:
- Macromolecules
- ISSN:
- 0024-9297
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
This work establishes a correlation between the selectivity of hydrogen-bonding interactions and the functionality of micelle-containing layer-by-layer (LbL) assemblies. Specifically, we explore LbL films formed by assembly of poly(methacrylic acid) (PMAA) and upper critical solution temperature block copolymer micelles (UCSTMs) composed of poly(acrylamide- co -acrylonitrile) P(AAm- co -AN) cores and polyvinylpyrrolidone (PVP) coronae. UCSTMs had a hydrated diameter of ∼380 nm with a transition temperature between 45 and 50 °C, regardless of solution pH. Importantly, micelles were able to hydrogen-bond with PMAA, with the critical interaction pH being temperature dependent. To better understand the thermodynamic nature of these interactions, in depth studies using isothermal titration calorimetry (ITC) were conducted. ITC reveals opposite signs of enthalpies for binding of PMAA with micellar coronae vs. with the cores. Moreover, ITC indicates that pH directs the interactions of PMAA with micelles, selectively enabling binding with the micellar corona at pH 4 or with both the corona and the core at pH 3. We then explore UCSTM/PMAA LbL assemblies and show that the two distinct modes of PMAA interaction with the micelles ( i.e. whether or not PMAA binds with the core) had significant effects on the film composition, structure, and functionality. Consistent withmore »
-
The self-assembly in aqueous solutions of three quaternary salt-based C 16 -type cationic surfactants with different polar head groups and identical carbon alkyl chain viz. , cetylpyridinium bromide (CPB), cetyltrimethylammonium tosylate (CTAT), and cetyltriphenylphosphonium bromide (CTPPB) in the presence of 1-butanol (BuOH) and 1,4-butanediol (BTD) was investigated using tensiometry, 2D-nuclear Overhauser enhancement spectroscopy (2D-NOESY) and small angle neutron scattering (SANS) techniques. The adsorption parameters and micellar characteristics evaluated at 303.15 K distinctly showed that BuOH promotes the mixed micelle formation while BTD interfered with the micellization phenomenon. The SANS data fitted using an ellipsoid (as derived by Hayter and Penfold using the Ornstein-Zernike equation and the mean spherical approximation) and wormlike micellar models offered an insight into the micelle size/shape and aggregation number ( N agg ) in the examined systems. The evaluated descriptors presented a clear indication of the morphology transition in cationic micelles as induced by the addition of the two alcohols. We also offer an investigation into the acceptable molecular interactions governing the differences in micelle morphologies, using the non-invasive 2D-NOESY technique and molecular modeling. The experimental observations elucidated from computational simulation add novelty to this work. Giving an account to the structural complexity in the threemore »
-
The combination of precision control with wide tunability remains a challenge for the fabrication of porous nanomaterials suitable for studies of nanostructure–behavior relationships. Polymer micelle templates broadly enable porous materials, however micelle equilibration hampers independent pore and wall size control. Persistent micelle templates (PMT) have emerged as a kinetic controlled platform that uniquely decouples the control of pore and wall dimensions. Here, chain exchange is inhibited to preserve a constant template dimension (pore size) despite the shifting equilibrium while materials are added between micelles. Early PMT demonstrations were synthesis intensive with limited 1–1.3× pore size tuning for a given polymer. Here we demonstrate PMT swelling with homopolymer enables 1–3.2× (13.3–41.9 nm) pore size variation while maintaining a monomodal distribution with up to 250 wt% homopolymer, considerably higher than the ∼90 wt% limit found for equilibrating micelles. These swollen PMTs enabled nanomaterial series with constant pore size and precision varied wall-thickness. Kinetic size control here is unexpected since the homopolymer undergoes dynamic exchange between micelles. The solvent selection influenced the time window before homopolymer phase separation, highlighting the importance of considering homopolymer–solvent interactions. This is the first PMT demonstration with wide variation of both the pore and wall dimensions using amore »
-
The use of ionic liquids as solvent for polymers or polymer-grafted nanoparticles provides an exciting feature to explore electrolyte-polymer interaction. 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (HMIm-TFSI) holds specific interactions with the polymer through ion-dipole or hydrogen bonding. For this work, poly(methyl methacrylate)-b-poly(styrene sulfonate) (PMMA-b-PSS) copolymer-grafted Fe3O4 nanoparticles with different sulfonation levels (~4.9-10.9 mol% SS) were synthesized and their concentration dependent ionic conductivities were reported in acetonitrile and HMIm-TFSI/acetonitrile mixture. We found that conductivity enhancement with the particle concentration in acetonitrile was due to the aggregation of grafted particles, hence sulfonic domain connectivity. The ionic conductivity was found to be related to the effective hopping transfer within ionic channels. To the contrary, the conductivity decreased or remained constant with increasing particle concentration in HMIm-TFSI/acetonitrile. This result was attributed to the ion coupling between ionic liquid and copolymer domains.
