Authors: Andre Thompson
Source: Deep Blue (University of Michigan) (article, 2018-01-01)
Field: Chemistry — Organic Chemistry

Effect of Ternary Additives on the Evolution of Structure Formation in Aqueous PEO-PPO-PEO Micelles Amphiphilic solutions and dispersions represent a key way that low solubility additives can be mixed within aqueous systems. While the phase behavior and gel structure of neat micelle solutions have been well studied, less is known about the effects of ternary constituents like a low solubility additive on micelle structure. In this dissertation, we probe the link between amphiphile micelle gels housing other hydrophilic or hydrophobic molecules and the effect on permeability and flame retardancy. Differential scanning calorimetry was performed on solutions of poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) (L101, 10% PEO; P104, 40% PEO; P105, 50% PEO; and F108, 80% PEO) amphiphiles (0-2% mass/v) to resolve their critical micelle concentrations (0.4-3.0% mass/v). Work was done from 2-10% mass/v copolymer concentrations and co-formulated methylparaben and cisplatin (0-0.1% mass/v) to resolve any deviation in the enthalpy of micelle formation (250-360 kJ/mol). Enthalpy-entropy compensation plots revealed combinations of both drug influenced and drug invariant interaction with forming micelle structures. P104 was most sensitive with cisplatin over all other amphiphiles, noted as a decrease from 302K to 289K when containing up to 0.1% cisplatin. The statistical significance of this cisplatin-induced perturbation was a linear regression from the enthalpy-entropy plots and it was significant at a 95% confidence interval. Other cisplatin-amphiphile combinations were more statistically insignificant. Small-angle x-ray scattering determined temperature dependent colloidal crystal formation in 31% amphiphile solutions both neat and co-formulated with cisplatin (up to 0.1% mass/v). Focusing on P104, we noted a ~4.0% rise in crystal expansion over the 25oC temperature sweep. Adding cisplatin results in a 4-5% reduction in the unit cell dimensions, which is attributed to decreased water content in the hydrophilic corona by adding cisplatin. Upon heating, added drug changed the nucleation behavior within the sample from a homogenous process to a more heterogeneous distribution of nucleated species. Dynamic diffusion experiments were performed on 20% mass/v micelle gels (F127, 70% PEO) mixed with indicator dyes and cisplatin (0.1% mass/v) by UV-visible spectroscopy. Each additive was tested neat at room temperature and 40oC, and formulated with F127 at room temperature and 40oC. The behavior of the added drug was complicated as the first 5 hours of permeation resulted in a burst delivery (6% total release with cisplatin-F127-RT compared to 4% cisplatin-RT). The higher fluence at elevated temperature is attributed to coalescing the amphiphiles that blocked transport on the tube walls as they formed colloidal gels. There is likely a separate factor at higher temperature and higher permeability if the membrane pores also expand with temperature. Lastly, micelle gels (F127) were used for fire retardants for cotton. Vertical flame tests, thermogravimetric analysis (TGA), micro-scale combustion calorimetry (MCC), and microscopy were used to assess flammability and coating quality of fire retardant-encapsulated micelle gels. After coating, the cotton fabrics were more ignition resistant and, if ignition occurred, the coatings self-extinguished. Coated cotton was found to decompose at higher temperatures (150oC vs 75oC cotton control). Coating thicknesses resulted in a >200% mass gain which still requires further optimization. But the combination of flame-retardants packaged in an amphiphilic matrix retarded cotton flame ignition. Overall, polyether based amphiphiles have shown as schemes for both cisplatin and combinations of flame retardants both of which either have low solubility with flame retardants or high systemic toxicity in vivo like cisplatin. Micelle ; Ternary operation ; Aqueous solution ; Chemical engineering ; Materials science ; Chemistry ; Polymer chemistry ; Organic chemistry ; Computer science Surfactants and Colloidal Systems ; Conducting polymers and applications ; Spectroscopy and Chemometric Analyses