Light Scattering from Hydrophobe-Uptake Spherical Micelles near the Critical Micelle Concentration

We have investigated aqueous micellar solutions of mixtures of a surfactant (dodecylpyridinium chloride) and a hydrophobe (1-dodecanol) near the critical micelle concentration (cmc), using simultaneous static and dynamic light scattering measurements. The static light scattering intensity for the aqueous solutions was separated into fast and slow relaxation components using dynamic light scattering results. The slow relaxation component gave us the information about the large scattering component. It turned out from this component that the amount of large colloidal particles of the hydrophobe was very tiny in the solution and hardly affects the association–dissociation equilibrium of the hydrophobe-uptake micelle. The free surfactant molecule and the hydrophobe-uptake spherical micelle in the solutions belong to the fast relaxation component. We have characterized the spherical micelle and also analyzed the association–dissociation equilibrium of the hydrophobe-uptake micelle up to near the cmc, using this scattering component extracted

Complexation of a Globular Protein, β‑Lactoglobulin, with an Anionic Surfactant in Aqueous Solution

The complexation of a globular protein, β-lactoglobulin (BLG), and an anionic surfactant sodium dodecyl sulfate (SDS) in aqueous media was investigated using capillary zone electrophoresis, electrophoretic, static, and dynamic light scattering, and small-angle X-ray scattering in a considerably high protein concentration range (0.27 mM < <i>C</i>_P < 3 mM). On increasing the molar concentration <i>C</i>_R of the surfactant, cooperative binding of SDS to BLG starts at <i>C</i>_R/<i>C</i>_P ≈ 1; the BLG–SDS complex consists mainly of the BLG dimer and approximately 20 SDS molecules, where BLG takes a compact conformation similar to that of the native BLG up to <i>C</i>_R/<i>C</i>_P ≈ 20. At <i>C</i>_R/<i>C</i>_P higher than 30, the BLG dimer in the BLG–SDS complex dissociates into a unimer, but the dissociated BLG unimer still takes a compact conformation at least at 30 < <i>C</i>_R/<i>C</i>_P < 65

Growth Kinetics of Polyelectrolyte Complexes Formed from Oppositely-Charged Homopolymers Studied by Time-Resolved Ultra-Small-Angle X‑ray Scattering

We have monitored the kinetic process of polyelectrolyte complex formation between sodium polyacrylate (SPA) and polyallylamine hydrochrolide (PAH) in aqueous NaCl solution by time-resolved ultra-small-angle X-ray scattering (TR-USAXS) combined with rapid mixing. SPA and PAH with different NaCl concentrations from 0 to 1 M were rapidly mixed in equimolar concentration of the monomer units using a stopped-flow apparatus with a dead time of about 2.5 ms. Within the dead time, percolated aggregate-like structures were observed suggesting that the initially formed small charge neutral aggregates further assembled to form higher order agglomerates. The early stage time evolution of the molar mass of the global structure in the presence of NaCl was found to be comparable to the Brownian-coagulation rate

Structural Analysis of Hydrophobe-Uptake Micelle of an Amphiphilic Alternating Copolymer in Aqueous Solution

We investigated the structure of the hydrophobe-uptake micelle of an alternating amphiphilic copolymer in aqueous solutions, by combining light scattering and small-angle X-ray scattering (SAXS). When the copolymer micelle includes the hydrophobe (1-dodecanol), the unicore flower micelle transforms into the multicore flower necklace, and the flower necklace is slightly stiffer than the hydrophobe-free flower necklace of the same copolymer. Moreover, the hydrophobe is included not in the hydrophobic core region but in the intermingled region of the hydrophobic group and the loop chain of the unit flower micelle. Therefore, the structure of the hydrophobe-uptake micelle of the amphiphilic alternating copolymer is quite different from that of hydrophobe-uptake spherical micelles of low molar mass surfactants and of amphiphilic block copolymers, where the hydrophobe is included in the hydrophobic region of the micelles

Dynamic Segment Size of the Cellulose Chain in an Ionic Liquid

Viscoelasticity and strain-induced birefringence under oscillatory shear flow of cellulose/1-buthyl-3-methylimidazolium chloride (BmimCl) solutions were measured at various temperatures covering a wide frequency zone from the terminal flow to the glassy zone for dilute (2 wt %) and semiconcentrated solution (10 wt %) to clarify the dynamical segment size of the cellulose chain. The estimated dynamical segment size, <i>M</i>_S, obtained from viscoelasticity is much smaller than that from flow birefringence. <i>M</i>_S estimated from dynamic birefringence was 2300 corresponding to 14 repeating glucose residues from 2–10 wt %, showing weak concentration dependence. This value is comparable to the reported value of Kuhn segment size, <i>M</i>_K. This relationship, <i>M</i>_S ≈ <i>M</i>_K, holding even at dilute solution, is in contrast with the large difference (<i>M</i>_S ≈ 5<i>M</i>_K) for polystyrene in dilute solution, indicating that the chain rigidity affects the relationship between <i>M</i>_S and <i>M</i>_K

Water-Induced Formation of Reverse Micelles from Diblock Copolymer of Styrene and <i>N</i>‑Isopropylacrylamide in 1,2-Dichloroethane

Water-induced formation of reverse micelles from polystyrene-<i>b</i>-poly­(<i>N</i>-isopropylacrylamide) (PS­(<i>x</i>)–PN­(<i>y</i>), where <i>x</i> and <i>y</i> were the degrees of polymerization of PS and PN blocks, respectively) in 1,2-dichloroethane (DCE) was investigated mainly by light scattering. Four PS­(<i>x</i>)–PN­(<i>y</i>) samples with different degrees of polymerization <i>x</i> and <i>y</i> were prepared by the reversible addition–fragmentation chain-transfer (RAFT) radical polymerization technique. While PS­(<i>x</i>)–PN­(<i>y</i>) was molecularly dispersed in DCE, the addition of water remarkably enhanced scattering light intensity from the DCE solutions of all the PS­(<i>x</i>)–PN­(<i>y</i>) samples, indicative of the formation of the reverse micelle having a water pool as the micellar core. Static light scattering (SLS) data for PS­(<i>x</i>)–PN­(<i>y</i>)/water/DCE ternary systems were analyzed using a model of spherical reverse micelle to estimate structural parameters, which were dependent on the hydrophilic–hydrophobic balance, i.e., <i>y</i>/<i>x</i>

Rigid Cyclic Polymer in Solution: Cycloamylose Tris(phenylcarbamate) in 1,4-Dioxane and 2‑Ethoxyethanol

Six cyclic amylose tris­(phenylcarbamate) (ATPC) samples have been prepared from enzymatically synthesized cyclic amylose ranging in the number of repeat units <i>N</i> from 24 to 290. Synchrotron-radiation small-angle X-ray scattering measurements were made for the samples in 1,4-dioxane (DIOX) and 2-ethoxyethanol (2EE) to determine the <i>z</i>-average radius of gyration ⟨<i>S</i>²⟩_<i>z</i> and the particle scattering function <i>P</i>(<i>q</i>). Molar mass dependencies of ⟨<i>S</i>²⟩_<i>z</i> in the two solvents were successfully explained by the current theories for the wormlike ring with the same parameters for linear ATPC in the corresponding solvent, that is, the helix pitch <i>h</i> (or contour length) per residue and the Kuhn segment length λ^–1 (stiffness parameter, twice the persistence length). The latter parameter λ^–1 is 22 and 16 nm in DIOX and 2EE, respectively. Except for the low-<i>q</i> region, <i>P</i>(<i>q</i>) was also explained by the rigid ring having the same contour length <i>Nh</i> as that for linear ATPC. Further, their local conformation estimated from circular dichroism spectra is essentially unaltered from that for linear ATPC at least when <i>N</i> ≥ 24

Effect of Polyelectrolyte Function on Helical Structures of Optically Active Poly(phenylacetylene) Derivatives Bearing Basic or Acidic Functional Pendant Groups

Effect of Polyelectrolyte Function on Helical Structures of Optically Active Poly(phenylacetylene) Derivatives Bearing Basic or Acidic Functional Pendant Group

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

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 <i>C</i>_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/cm³ and 0.6, respectively. With decreasing <i>C</i>_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 <i>C</i>_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 <i>C</i>_S from 0.5 M to lower than 0.05 M

Kinetics of Morphological Transition between Cylindrical and Spherical Micelles in a Mixture of Anionic–Neutral and Cationic–Neutral Block Copolymers Studied by Time-Resolved SAXS and USAXS

This study is concerned with the morphological transition kinetics of polyelectrolyte complex micelles formed from an anionic–neutral block copolymer and a cationic–neutral block copolymer in aqueous NaCl solution. The transformation was induced by changing the mixing ratio of the anionic and cationic monomer units in the copolymers. The kinetics of the morphological transition was directly tracked by time-resolved (ultra) small-angle X-ray scattering coupled with rapid mixing of the block copolymer components by a stopped flow apparatus. The transformation from cylindrical to spherical micelles upon changing the mixing ratio of the copolymers was reversible, and the process occurred via the random scission of the cylindrical micelles along their contours. The reverse transition from spherical to cylindrical micelles was found to be a slow process with high activation energy