Intermolecular Interactions and Self-Assembly in Aqueous Solution of a Mixture of Anionic–Neutral and Cationic–Neutral Block Copolymers

Abstract

We have investigated the self-assembly in dilute aqueous solutions of a mixture of an anionic−neutral block copolymer (AP) and a cationic−neutral block copolymer (MP) by changing the added sodium chloride (NaCl) concentration C S or electrostatic interactions among oppositely charged blocks, by direct observation, optical and electron microscopies, and small-angle X-ray scattering. The ratio of the charged to neutral block chain lengths was ca. 10, and the total copolymer concentration and the mixing ratio (the mole fraction of the MP charge unit in the total charge units) of AP and MP were fixed to be 0.005 g/cm 3 and 0.6, respectively. With decreasing C S from 2 to 0 M, we have found reentrant one-phase, two-phase, one-phase transitions in the aqueous solution of the AP−MP mixture. The two-phase to one-phase transition at C S ∼ 0.5 M arises from the competition between the macroscopic phase transition and micellization, which is the first observation in dilute block copolymer solutions. Moreover, we have found a micelle morphology transition from the bilayer vesicle to the cylindrical micelle with further decreasing C S from 0.5 M to lower than 0.05 M.

Conformation of Pullulan in Aqueous Solution Studied by Small-Angle X-ray Scattering

“…If one uses pullulan samples as the standard for SAXS measurements to determine the absolute value of the excess Rayleigh ratio R θ,X for a test polymer solution, contrast factors γ in the optical constant K e for pullulan and the test polymer in solution are necessary-see Equation (1) in the text. The contrast factor γ of a polymer in aqueous NaCl solution is calculated by [38]…”

“…If one uses pullulan samples as the standard for SAXS measurements to determine the absolute value of the excess Rayleigh ratio R θ ,X for a test polymer solution, contrast factors γ in the optical constant K e for pullulan and the test polymer in solution are necessary—see Equation (1) in the text. The contrast factor γ of a polymer in aqueous NaCl solution is calculated by [ 38 ] where the subscript 0 denotes the monomer unit of the polymer (the glucose residue for pullulan), n e, i and M i ( i = 0, H 2 O, and NaCl) are numbers of electrons and molar masses of i , respectively, is the partial specific volume of the polymer, v solv is the specific volume of the solvent, and w NaCl is the weight fraction of NaCl in aqueous NaCl. The value of for pullulan was determined in water by densitometry (=0.649 cm 3 /g), and γ of pullulan in water (or in 0.05 M aqueous NaCl) was calculated to be 0.171 mol/g.…”

Dehydration, Micellization, and Phase Separation of Thermosensitive Polyoxazoline Star Block Copolymers in Aqueous Solution

“…Yield 4.0 g, 80%. 1 The SAXS excess Rayleigh ratio RX, at the scattering angle  and the optical constant Ke of SAXS were calculated by 16,17…”

Gel phase formation in dilute triblock copolyelectrolyte complexes

“…Electrostatic interactions between oppositely charged chains lead to entropy gains from the release of the counterions associated with the chains that drive complexation 5 6 . Conjugation of either or both polyelectrolytes with a neutral polymer block allows for molecular tuning of the microphase separation and results in micelles of diverse shapes 7 8 9 , including spherical 10 11 12 , Janus 13 14 15 , rod-like 16 17 18 and vesicular micelles 19 20 . Substantial water content 21 22 23 and extremely low surface tension against water 24 25 26 of liquid polyelectrolyte complexes facilitate encapsulation of hydrophilic small molecule drugs 27 , nucleic materials 11 28 29 and proteins 30 31 32 in the micelle cores, enabling polyelectrolyte complex (PEC) micelle carriers for targeted, encapsulated delivery of hydrophilic cargos 29 33 34 35 36 37 38 39 40 .…”