Effect of Glycols on the Self-Assembly of Amphiphilic Block Copolymers in Water. 2. Glycol Location in the Microstructure

Abstract

The effects of cosolvents on the microstructure of the lyotropic liquid crystals formed by poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) triblock copolymers in water were examined in ternary isothermal systems consisting of a representative PEO-PPO-PEO copolymer (Pluronic P105, (EO)37(PO)58(EO)37), water, and a polar cosolvent (glycerol, propylene glycol, ethanol, or glucose, referred to as "glycols"). The characteristic length scales of the lyotropic liquid crystals were established using small-angle X-ray scattering (SAXS). The SAXS data are analyzed and discussed with respect to (i) influence of the different glycols and the glycol content on the characteristic length scales, (ii) area occupied by one macromolecule at the polar/apolar interface, (iii) location of the different glycols in the microstructure, and (iv) glycol ability to modify the interfacial curvature through swelling the PEO-PPO-PEO macromolecule to different extents. The trends in the glycol effects observed in the ternary phase diagrams ("macroscopic" information) are confirmed and reinforced by the detailed microstructural information obtained here by SAXS. A correlation is found between the glycol effect on the microstructure of the lyotropic liquid crystals (the degree of relative swelling) and the glycol polarity (expressed in terms of octanol/water partition coefficient, dielectric constant or solubility parameter).

Effect of Pharmaceutically Acceptable Glycols on the Stability of the Liquid Crystalline Gels Formed by Poloxamer 407 in Water

“…6). This grouping of glycols is also consistent with the results of our study on the Pluronic P105 self-assembly (48,50).…”

“…The increase of the interfacial area with increasing the propylene glycol or ethanol content can thus be related to a swelling of both PEO and PPO blocks by the glycol. The results obtained here for the role of glycols on the block copolymer selfassembled structure are consistent with our detailed study in the similar Pluronic P105-water-glycol systems (50), and confirm that different glycols, depending on their relative polarities, have preference to locate in different domains of the structure.…”

“…An extensive analysis of the interfacial area in similar PEO-PPO-PEO block copolymer systems and discussion of the assumptions involved can be found in Ref. (50). The interfacial area in the normal hexagonal structure can be calculated from (35,38) …”

“…In addition to the absolute values, also shown in Fig. 5 are the spacing "normalized" with respect the spacing at 0% glycol and the glycol volume fraction "normalized" with respect to the sum of glycol and water volume fractions, as this presentation has been found useful for comparing the glycol effects (50). The trends…”

Adsorption of a Polymeric Siloxane Surfactant on Carbon Black Particles Dispersed in Mixtures of Water with Polar Organic Solvents

“…The solvent quality is a controlling factor in the self-assembly of polymeric surfactants (16,17). In the case of poly(ethylene oxide)-poly(propylene oxide) (PEO-PPO) surfactants, where water is typically used as a solvent (being selective for PEO), the addition to water of solvents such as glycerol, ethanol, or formamide (18)(19)(20)(21)(22)(23) provides extra degrees of freedom in tailoring the solution properties (17,(24)(25)(26)(27). In general, the published information on the effects of polar organic solvents on the self-assembly of polymeric surfactants and on their interactions with colloidal particles is limited.…”