The formation of complexes between the cationic surfactant dodecyl trimethylammonium bromide (DTAB) and the comb-type anionic polyelectrolytes poly(sodium acrylate-co-sodium 2-acrylamido-2-methylpropane sulfonate)-g-poly(N,N-dimethylacrylamide) (P(NaA-co-NaAMPS)-g-PDMAMx) was investigated in dilute aqueous solutions by means of turbidimetry, pyrene fluorescence probing, viscometry, z-potential measurements, and dynamic light scattering. The comb-type copolymers consist of an anionic copolymer backbone, P(NaA-co-NaAMPS), containing 84 mol % NaAMPS units, while the weight percentage, x, of the PDMAM side chains varies from x = 12% (w:w) up to x = 58% (w:w). It was found that, contrary to the water-insoluble complexes formed between the linear polyelectrolyte P(NaA-co-NaAMPS) and DTAB, the solubility in water of the complexes formed between the comb-type copolymers and DTAB is significantly improved with increasing x. The complexation process starts at the same critical aggregation concentration (about 2 orders of magnitude lower than the critical micelle concentration of DTAB), regardless of x, and it is accompanied by charge neutralization and appearance of hydrophobic microdomains. Both effects lead to the substantial collapse of the polyelectrolyte chain upon addition of DTAB. However, the complexes of the comb-type copolymers with DTAB are stabilized in water as nanoparticles, and probably consisted of a water-insoluble core (the polyelectrolyte/surfactant complex), protected by a hydrophilic nonionic PDMAM corona. The size of the nanoparticles varies from approximately 35 nm up to approximately 120 nm, depending on x. 相似文献
Comb-type copolymers of poly(acrylic acid) grafted with poly(2-acrylamido-2-methylpropanesulfonic acid) (PAMPSA) side chains form with poly(ethylene glycol), at low pH, water-soluble hydrogen-bonding interpolymer complexes. Turbidimetry, viscometry, and dynamic light scattering measurements suggest that compact, negatively charged, colloidal nanoparticles are formed at pH<3.75. The influence of the structure of the graft copolymers and of the ionic strength of the solution on the size of these nanoparticles was investigated. It was found that their hydrodynamic radius decreases by increasing the molecular mass of the PAMPSA side chains of the graft copolymer and increases with increasing the ionic strength of the solution. 相似文献
We investigated the phase behavior and the microscopic structure of the colloidal complexes constituted from neutral/polyelectrolyte diblock copolymers and oppositely charged surfactant by dynamic light scattering (DLS) and small-angle neutron scattering (SANS). The neutral block is poly(N-isopropylacrylamide) (PNIPAM), and the polyelectrolyte block is negatively charged poly(acrylic acid) (PAA). In aqueous solution with neutral pH, PAA behaves as a weak polyelectrolyte, whereas PNIPAM is neutral and in good-solvent condition at ambient temperature, but in poor-solvent condition above approximately 32 degrees C. This block copolymer, PNIPAM-b-PAA with a narrow polydispersity, is studied in aqueous solution with an anionic surfactant, dodecyltrimethylammonium bromide (DTAB). For a low surfactant-to-polymer charge ratio Z lower than the critical value ZC, the colloidal complexes are single DTAB micelles dressed by a few PNIPAM-b-PAA. Above ZC, the colloidal complexes form a core-shell microstructure. The core of the complex consists of densely packed DTA+ micelles, most likely connected between them by PAA blocks. The intermicellar distance of the DTA+ micelles is approximately 39 A, which is independent of the charge ratio Z as well as the temperature. The corona of the complex is constituted from the thermosensitive PNIPAM. At lower temperature the macroscopic phase separation is hindered by the swollen PNIPAM chains. Above the critical temperature TC, the PNIPAM corona collapses leading to hydrophobic aggregates of the colloidal complexes. 相似文献
Poly(styrene)-block-poly(4-vinylpyridine) (PS-b-P4VP) copolymers and poly(acrylic acid) (PAA) have been mixed in organic solvents. Complexation via hydrogen bonding occurs between the P4VP and PAA blocks. Those insoluble complexes aggregate to form the core of micelles surrounded by a corona of PS chains. Reorganization of these structures occurs upon addition of acidic or basic water, which results in the breaking of the hydrogen bonds between the P4VP and PAA blocks. After transfer of the initial complexes in acidic water, micelles consisting of a PS core and a protonated P4VP corona are observed. In basic water, well-defined nanoparticles formed by the PS-b-P4VP copolymers are obtained. It is demonstrated that these nanoparticles are stabilized by the negatively charged PAA chains. Finally, thermally induced disintegration of the micelles is investigated in organic solvents. 相似文献
The water content-dependent supramolecular structure formation of polystyrene-block-poly(acrylic acid) (PS-b-PAA) copolymer in the presence of a fourth-generation amine-terminated poly(amido amine) dendrimer (PAMAM) is investigated by dynamic light scattering, turbidity measurements, and transmission electron microscopy. The solvent system for this study is a mixture of dioxane/THF and water. A very complex turbidity profile is observed with increasing water content in the system and is explained by the presence of various aggregated structures based on strong interactions between the amine-containing dendrimers and the poly(acrylic acid) blocks of the polymer. The onset of the self-assembly of single chains of PS-b-PAA (primary structure) into single and multiple dendrimer core inverse micelles (secondary structure) is detected as very low water contents of cw < 2% wt (cwc). These micelles consist of dendrimers coated with PAA blocks, which are connected to the corresponding PS chains that form the corona. Further addition of water leads to an association of these micelles into compound multiple dendrimer core inverse micelles (tertiary structure) in the range of cw = approximately 6 to approximately 10% wt. At still higher water content, some of the acrylic acid chains of the block copolymer move from the vicinity of the dendrimer to the outside of the aggregates, resulting in a decrease in the size of the formed structures and the acquisition of progressively increasing hydrophilic character of the aggregates. Multiple dendrimer core inverse onion micelles are formed, which agglomerate into compound multiple dendrimer core inverse onion micelles at cw = approximately 12 to approximately 18% wt. Above this water content, vesicular structures are formed. The complexity is unusual for block copolymer systems and illustrates the importance of strong interactions in structure formation. 相似文献
In aqueous solutions at room temperature, poly( N-methyl-2-vinyl pyridinium iodide)- block-poly(ethylene oxide), P2MVP 38- b-PEO 211 and poly(acrylic acid)- block-poly(isopropyl acrylamide), PAA 55- b-PNIPAAm 88 spontaneously coassemble into micelles, consisting of a mixed P2MVP/PAA polyelectrolyte core and a PEO/PNIPAAm corona. These so-called complex coacervate core micelles (C3Ms), also known as polyion complex (PIC) micelles, block ionomer complexes (BIC), and interpolyelectrolyte complexes (IPEC), respond to changes in solution pH and ionic strength as their micellization is electrostatically driven. Furthermore, the PNIPAAm segments ensure temperature responsiveness as they exhibit lower critical solution temperature (LCST) behavior. Light scattering, two-dimensional 1H NMR nuclear Overhauser effect spectrometry, and cryogenic transmission electron microscopy experiments were carried out to investigate micellar structure and solution behavior at 1 mM NaNO 3, T = 25, and 60 degrees C, that is, below and above the LCST of approximately 32 degrees C. At T = 25 degrees C, C3Ms were observed for 7 < pH < 12 and NaNO 3 concentrations below approximately 105 mM. The PEO and PNIPAAm chains appear to be (randomly) mixed within the micellar corona. At T = 60 degrees C, onion-like complexes are formed, consisting of a PNIPAAm inner core, a mixed P2MVP/PAA complex coacervate shell, and a PEO corona. 相似文献
Narrowly distributed core‐shell nano‐particles at relatively high concentration (30 mg/mL) were prepared via in situ polymerization of acrylic acid in an aqueous solution of biocompatible gelatin. These polymeric nano‐particles, in aqueous solution, had cores mainly comprised of an insoluble inter‐polymer complex of poly(acrylic acid, PAA) and gelatin and shells comprised of soluble gelatin (denoted as gelatin/PAA nano‐particles). Dynamic light scattering and electrophoretic light scattering techniques were used to trace the in situ polymerization process. The structure of the gelatin/PAA nano‐particle was further locked‐in via shell crosslinking; i.e., the reaction between glutaraldehyde and gelatin. Scanning force microscopy (SFM) was used to observe the morphologies of the particles before and after cross‐linking. Furthermore, the pH responsive behaviors of the gelatin/PAA nano‐particles before and after shell crosslinking were studied. 相似文献
Summary: Spherical micelles have been formed by mixing, in DMF, a poly(styrene)‐block‐poly(2‐vinylpyridine)‐block‐poly(ethylene oxide) (PS‐block‐P2VP‐block‐PEO) triblock copolymer with either poly(acrylic acid) (PAA) or a tapered triblock copolymer consisting of a PAA central block and PEO macromonomer‐based outer blocks. Noncovalent interactions between PAA and P2VP result in the micellar core while the outer corona contains both PS and PEO chains. Segregation of the coronal chains is observed when the tapered copolymer is used.
Inclusion of comb‐like chains with short PEO teeth in the corona triggers the nanophase segregation of PS and PEO as illustrated here (PS = polystyrene; PEO = poly(ethylene oxide)). 相似文献
Summary: The complexation between polystyrene‐block‐poly(acrylic acid) (PS‐b‐PAA) micelles and poly(ethylene glycol)‐block‐poly(4‐vinyl pyridine) (PEG‐b‐P4VP) is studied, and a facile strategy is proposed to prepare core‐shell‐corona micellar complexes. Micellization of PS‐b‐PAA in ethanol forms spherical core‐shell micelles with PS block as core and PAA block as shell. When PEG‐b‐P4VP is added into the core‐shell micellar solution, the P4VP block is absorbed into the core‐shell micelles to form spherical core‐shell‐corona micellar complexes with the PS block as core, the combined PAA/P4VP blocks as shell and the PEG block as corona. A model is suggested to characterize the core‐shell‐corona micellar complexes.
Schematic formation of core‐shell‐corona (CSC) micellar complexes by adsorption of PEG‐b‐P4VP into core‐shell PS‐b‐PAA micelles. 相似文献
Poly(lactic acid)(PLA)is one of the most important bio-plastics,and chemical modification of the already-polymerized poly(lactic acid)chains may enable optimization of its material properties and expand its application areas.In this study,we demonstrated that poly(lactic acid)can be readily dissolved in acrylic acid at room temperature,and acrylic acid can be graft-polymerized onto poly(lactic acid)chains in solution with the help of photoinitiator benzophenone under 254 nm ultraviolet(UV)irradiation.Similar photo-grafting polymerization of acrylic acid(PAA)has only been studied before in the surface modification of polymer films.The graft ratio could be controlled by various reaction parameters,including irradiation time,benzophenone content,and monomer/polymer ratios.This photo-grafting reaction resulted in high graft ratio(graft ratio PAA/PLA up to 180%)without formation of homopolymers of acrylic acid.When the PAA/PLA graft ratio was higher than 100%,the resulting PLA-g-PAA polymer was found dispersible in water.The pros and cons of the photo-grafting reaction were also discussed. 相似文献
The interaction of the anionic surfactant sodium dodecyl sulfate (SDS) and the cationic surfactant hexadecyl trimethyl ammonium bromide with poly(N-isopropylacrylamide) (PNIPAAM) microgels with and without poly(acrylic acid) (PAA) was investigated by means of dynamic light scattering (DLS), zeta potential, and turbidimetry measurements. The DLS results show that the PNIPAAM microgels with PAA will contract when an anionic or cationic surfactant is added to the suspension, while the PNIPAAM microgels without PAA expand in the presence of an ionic surfactant. A collapse of the PNIPAAM microgels is observed when the temperature is increased. From the zeta potential measurements, it is observed that the charge density of PNIPAAM microgels in the presence of an ionic surfactant is significantly affected by temperature and the attachment of the negatively charged PAA groups. The turbidity measurements clearly indicate that the interaction between PNIPAAM and SDS is more pronounced than that of the cationic surfactant. 相似文献
Insoluble complexes are formed in acidic aqueous media when poly(acrylic acid) (PAA) and poly-(vinylbenzo-18-crown-6) (P18C6) or polyvinylbenzoglymes are mixed. Complex formation results from hydrogen bonding between carboxyl groups and crown ether- or glyme–oxygen atoms as well as from hydrophobic interactions. The precipitation is pH dependent and was determined as a function of the ratio PAA to P18C6 or to polyglyme at different HCl concentrations in 10?4M solutions of polycrown or polyglyme. Precipitation is nearly quantitative in 0.01N HCl. The compositions of PAA/P18C6 precipitates were determined as a function of the initial PAA/P18C6 ratio in solution. The complexes with P18C6 can be solubilized in acidic media when crown-complexable cations (K+, Cs+, Ba2+) are added, but the charged P18C6 reprecipitates in basic solution as a polysalt complex with the PAA–polyanion. More stable PAA–P18C6 complexes in the form of fibers can be obtained by interfacial complex formation. Poly(methacrylic acid) is less effective as a complex former. 相似文献
The development of technology for on/off switching of enzyme activity is expected to expand the applications of enzyme in a wide range of research fields. We have previously developed a complementary polymer pair system (CPPS) that enables the activity of several enzymes to be controlled by a pair of oppositely charged polymers. However, it failed to control the activity of large and unstable α-amylase because the aggregation of the complex between anionic α-amylase and cationic poly(allylamine) (PAA) induced irreversible denaturation of the enzyme. To address this issue, we herein designed and synthesized a cationic copolymer with a poly(ethylene glycol) backbone, poly(N,N-diethylaminoethyl methacrylate)-block-poly(ethylene glycol) (PEAMA-b-PEG). In contrast to PAA, α-amylase and β-galactosidase were inactivated by PEAMA-b-PEG with the formation of soluble complexes. The enzyme/PEAMA-b-PEG complexes were then successfully recovered from the complex by the addition of anionic poly(acrylic acid) (PAAc). Thus, dispersion of the complex by PEG segment in PEAMA-b-PEG clearly plays a crucial role for regulating the activities of these enzymes, suggesting that PEGylated charged polymer is a new candidate for CPPS for large and unstable enzymes. 相似文献
Simulated graft copolymer of poly(acrylic acid-co-stearyl acylate) [P(AA-co-SA)] and poly(ethylene glycol) (PEG) was synthesized, where acrylic acid, stearyl acylate and PEG was employed as the pH-sensitive, hydrophobic and hydrophilic segment, respectively. Polymeric nanoparticles prepared by the dialysis of simulated graft copolymer solution in dimethylformamide against citrate buffer solution with different pH values were characterized by transmission electron microscopy (TEM), fluorescence technique and laser light scattering (LLS). TEM image revealed the spherical shape of the self-aggregates, which was further confirmed by LLS measurements. The critical aggregation concentration increased markedly (10 to 150 mg/L) with increasing pH (4.6 to 7.0), consistent with the de-protonation of carboxylic groups at higher pH. The hydrodynamic radius of polymeric nanoparticles decreased from 118 nm at pH 3.4 to 90 nm at pH 7.0. The controlled release of indomethacin from those nanoparticles was investigated, and the self-assembled nanoparticles exhibited improved performance in controlled drug release. 相似文献