Three dimension Liesegang rings of calcium hydrophosphate in gelatin

Three dimensional Liesegang spherical layers of CaHPO₄ in gelatin ball were performed by employing CaCl₂ and Na₂HPO₄ as the inner and outer electrolyte, respectively. Effects of concentrations of inner and outer electrolyte as well as pH on the morphologies of Liesegang rings (LRs) were investigated. As a result, it was observed that the time law, spacing law and width law found in 1D/2D gel systems were obeyed in this 3D gelatin system. The interaction of Ca²⁺ and HPO₄ ^2? with gelatin matrix played a key role to the formation of LRs due to the existence of carboxylic groups on the gelatin chains. Using Ca²⁺ as the inner electrolyte, LRs were prepared. However, employing HPO₄ ^2? as inner electrolyte, LRs were not obtained. Moreover, pH of gelatin solution greatly impacted on the formation of LRs. The number of LRs increased with the decrease of pH, whereas the width inversely decreased. pH 4.40 was a turn point, from which the spacing coefficient abruptly increased as pH increased. All these results indicated that the network was created by the interaction of Ca²⁺ and –COO^? of gelatin chains, which dominated the formation of CaHPO₄ LRs in gelatin.     

Chitosan–silica nanoparticles catalyst (M@CS–SiO2) for the degradation of 1,1-dimethylhydrazine

Research on Chemical Intermediates - Hybrid materials of chitosan–silica (CS–SiO2) with nonprecious-metallic ions (Cu) immobilized on (Cu–M@CS–SiO2) were developed as green...     

Mechanism of preparing monodispersed poly(acrylamide/methacrylic acid) microspheres in ethanol. II

We previously established a new mechanism of monodispersed poly(acrylamide/methacrylic acid) (PAAm/MAA) microspheres on the basis that the minimonomer droplets of AAm/MAA complexes were formed in ethanol at a polymerization temperature of 60 °C prior to the polymerization. Here, the effects of various factors such as the types and amount of initiators and crosslinking agents on the average diameters and morphologies of PAAm/MAA microspheres were qualitatively discussed on the basis of the new mechanism. The partition of reagents between the minimonomer droplets and the continuous medium was particularly emphasized in discussion because the formation of microspheres occurred in the minimonomer droplets. The new mechanism suggested that the size (number) and morphologies of the microspheres as well as the polymerization kinetics were consequently dependent on the properties and amount of initiators, crosslinking agents, and other monomers. It successfully explained the experimental phenomenon observed thus far in precipitation or dispersion polymerizations that the average diameter of microspheres is increased with the increase of the concentration of initiators, which contradicted the prediction of conventional mechanisms. As an example, the initiator dimethyl 2,2′‐azobisisobutyrate (DMAIB) was dominantly partitioned in ethanol. Thus, the diameter of the PAAm/MAA microspheres was decreased with the increase of the concentration of DMAIB because the formation of microspheres depended on the adsorption of free radicals to the minimonomer droplets. However, the initiator 4,4′‐azobis‐4‐cyanovaleric acid was dominantly partitioned within the minimonomer droplets, thereby increasing the diameter of the microspheres as the concentration of initiator was increased because of the lower efficiency of free radicals. Relative to the initiators, the crosslinking agents showed inverse effects on the diameter and morphology of the microspheres according to the different partitions. The monomer was transferred by the incorporation of minimonomer droplets with growing microspheres. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 2833–2844, 2004     

Characteristics of pH-sensitive hydrogel microsphere of poly(acrylamide-<Emphasis Type="Italic">co</Emphasis>-methacrylic acid) with sharp pH–volume transition

The forming process and characteristics of monodispersed hydrogel microspheres of poly(acrylamide–methacrylic acid) with sharp pH–volume transition were studied. pH-/ion-sensitive and thermosensitive behaviors of microspheres sampled at various stage of polymerization were evaluated by using the dynamic light scattering. It was observed that the sharpness of pH–volume transition increased with the increase in monomer conversion. Both thermo- and ion-sensitive behaviors were affected by pH. At pH 4.3, the hydrodynamic diameter of microspheres monotonically and slightly decreased with the increase in temperature, whereas at pH 3.5 and 3.8, the curves of thermo–volume transition were similar to those of pH–volume transition with a maximum temperature at 25 and 20 °C, respectively. Increasing the [CaCl₂] was to decrease the hydrodynamic diameters of microspheres, irrespective of pH. However, a region at lower [NaCl] was found, where the diameter increased with the increase in [NaCl]. Moreover, the range of diameter increasing extended to higher [NaCl] as pH increased.     

Charges of soluble amphiphiles and particles: random and diblock copolymerizations of MAA/AAm,MAA/St,and MAA/4VP in ethanol

Random and reversible addition-fragmentation chain transfer (RAFT) copolymerizations of methacrylic acid (MAA)/acrylamide (AAm), MAA/styrene (St), and MAA/4-vinyl pyridine (4VP) were carried out in ethanol. (CPDB)-terminated PMAA (PMAA-CPDB) and 2,2′-azobis(2,4-diemthylvaleronitrile) (V-65) was used as the macromolecular chain transfer agent (CTA) and initiator, respectively. Electric conductivity of copolymerization systems was traced throughout the polymerizations, and charges of soluble copolymer and particles were detected. As a result, a considerable increase of conductivity was observed in all of the RAFT polymerization systems, whereas the variation of conductivity in the random copolymerization systems was insignificant. The high conductivity of RAFT polymerization was dominantly contributed by the soluble diblock copolymers in the serum, rather than their particles, except for P(MAA-b-4VP) where only the particles was obtained due to the zwitterionic interactions of PMAA segments and 4VP. In the direct current (DC) field, the behavior of these soluble diblock copolymers, P(MAA-b-AAM) and P(MAA-b-St), indicated that they were positively charged, whereas the particles of (PMAA-b-AAm) and P(MAA-b-4VP) were surprisingly negatively charged, though the composition of MAA was dominant. Soluble random copolymers of P(MAA-co-St) and P(MAA-co-4VP) represented the charge neutrality. These results indicated that the positive charges were contributed by the solvophobic block in the soluble diblock copolymers. Therefore, the diblock copolymers were the macrodipoles boosting the conductivity of solution. Meanwhile, it indicated that the electrostatic interactions of dipoles were possibly the main driving force of their self-assembly. Generally, compared with RAFT polymerization, the particles were hard to be prepared in the random copolymerization. It implies that the electrostatic interactions of diblock copolymers also played an important role in the particle formation.

Mechanism of preparing monodisperse poly(acrylamide/methacrylic acid) microspheres in ethanol. I

The precipitation polymerization of acrylamide/methacrylic acid (AAm/MAA) in ethanol (EtOH) was thoroughly investigated from detecting the homogeneity of the initial solution prior to polymerizations to the final products of the polymerizations. Dynamic light scattering and scanning electron microscopy were employed for the investigations. The solutions of AAm and AAm/acrylic acid (AAm/AA) were homogeneous. However, the solutions of AAm/MAA, AAm/poly(MAA) (PMAA), and AAm/poly(AA) (PAA) were not homogeneous as they are usually considered to be: entities with size distributions of around 150, 40, and 17 nm, respectively, were detected at the polymerization temperature of 60 °C. Accordingly, analogous to the entities that are similar to the structure of micelles formed in the solutions of AAm/PMAA and AAm/PAA because of polymer–AAm interactions, it was suggested that the complexes of AAm/MAA stemming from the molecular interactions, particularly the (lypo‐) hydrophobic interaction, aggregated to form minimonomer droplets at 60 °C. The monodisperse microspheres were prepared only in the AAm/MAA‐EtOH systems, whereas the microspheres were not prepared in the homogeneous AAm‐EtOH systems despite the precipitation of PAAm. The results obtained from various polymerizations showed that the microspheres originated from the polymerization within the minimonomer droplets. A new mechanism was established that describes the processes for the formation of all products possibly generated in the AAm‐MAA‐EtOH polymerization system. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 2823–2832, 2004     

Preparation of pH-sensitive hydrogel microspheres of poly(acrylamide-<Emphasis Type="BoldItalic">co</Emphasis>-methacrylic acid) with sharp pH–volume transition

Monodisperse hydrogel microsphere of polyacrylamide (AAm)-methacrylic acid (MAc) cross-linked by N,N′-methylene-bis(acrylamide) (MB) with sharp pH–volume transition was prepared in ethanol. The dynamic light scattering (DLS) was employed to evaluate the pH sensitivity of these microspheres. The effects of main factors: composition of copolymer, cross-linked degree, and initial total concentration or solid content of comonomers were investigated. Osmotic pressure and deformation of cross-linked polymer network were considered as the two dominant factors influencing the characteristics of pH–volume transition. High content of MAc and cross-linked degree increased the osmotic pressure, thereby moving the onset of pH–volume transition to higher pH. Association/dissociation of poly-MAc segments in the domains contributed to the free energy of hydrogel–solvent mixing. As soon as pH was high enough to overcome the osmotic pressure, the dissociated poly-MAc segments simultaneously decreased the osmotic pressure and free energy of hydrogel–solvent mixing, thereby allowing the sharp and large volume transition. As a result, microspheres were prepared with pH–volume transition of almost 12 times to their original volume within a narrow range of pH variation, ca. 0.5. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.