Mixed micellization between natural and synthetic block copolymers: [small beta]-casein and Lutrol F-127

• Published in: Physical chemistry chemical physics : PCCP 2011-01, Vol.13 (8), p.3153-3160
• Main Authors: Portnaya, Irina, Khalfin, Rafail, Kesselman, Ellina, Ramon, Ory, Cogan, Uri, Danino, Dganit
• Format: Article
• Language: English
• Subjects: Biological; Block copolymers; Cosmetics; Driving; Micelles; Morphology; Proteins; Titration calorimetry
• ISSN: 1463-9076
• DOI: 10.1039/C0CP01321H

Amphiphilic block copolymers and mixtures of amphiphiles find broad applications in numerous technologies, including pharma, food, cosmetic and detergency. Here we report on the interactions between a biological charged diblock copolymer, [small beta]-casein, and a synthetic uncharged triblock copolymer, Lutrol F-127 (EO101PO56EO101), on their mixed micellization characteristics and the micelles' structure and morphology. Isothermal titration calorimetry (ITC) experiments indicate that mixed micelles form when Lutrol is added to monomeric as well as to assembled [small beta]-casein. The main driving force for the mixed micellization is the hydrophobic interactions. Above [small beta]-casein CMC, strong perturbations caused by penetration of the hydrophobic oxypropylene sections of Lutrol into the protein micellar core lead to disintegration of the micelles and reformation of mixed Lutrol/[small beta]-casein micelles. The negative enthalpy of micelle formation ([capital Delta]H) and cooperativity increase with raising [small beta]-casein concentration in solution. [small zeta]-potential measurements show that Lutrol interacts with the protein micelles to form mixed micelles even below its critical micellization temperature (CMT). They further indicate that Lutrol effectively masks the protein charges, probably by forming a coating layer of the ethyleneoxide rich chains. Small-angle X-ray scattering (SAXS) and cryogenic-transmission electron microscopy (cryo-TEM) indicate relatively small changes in the oblate micellar shape, but do show swelling along the small axis of [small beta]-casein micelles in the presence of Lutrol, thereby confirming the formation of mixed micelles.