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Guangzhao Zhang

Publications and source records attributed to Guangzhao Zhang.

12 recordsLinked to original sources
PubMed2007

Hydrogen-bonded dendronized polymers and their self-assembly in solution.

Frechet-type benzyl ether dendrons of second and third generations with a carboxyl group (G2, G3) at the apex site could attach to poly(4-vinylpyridine) (PVP), forming hydrogen-bonded dendronized polymers (HB denpols) in their common solvent, chloroform. The HB denpols show unique self-assembly behavior, forming vesicles in the common solvent under ultrasonic treatment. The structure and morphology of the vesicles were characterized by dynamic light scattering (DLS), static light scattering (SLS), SEM, TEM, and AFM. The size of the vesicles decreases and the thickness of the vascular membrane increases as the molar ratio of Gx/PVP increases. The hydrogen bonding, pi-pi aromatic stacking of the dendrons, and the considerable difference in architecture between the dendron Gx and PVP are the main factors facilitating the assembly of the HB denpols in the common solvent.

Journal Article↗
PubMed2006

Adsorption of polymeric micelles and vesicles on a surface investigated by quartz crystal microbalance.

Polystyrene-b-poly(N-isopropylacrylamide) (PS-b-PNIPAM) diblock copolymers either with or without thiol end groups, depending on the relative length of the two blocks, form micelles or vesicles in water. The adsorption of such micelles or vesicles on a gold surface from aqueous solution was investigated in situ at 20 degrees C by use of a quartz crystal microbalance with dissipation monitoring (QCM-D). The changes in frequency (Deltaf) and dissipation (DeltaD) revealed that the micelles and vesicles without thiol groups were intact with some deformation when they were deposited on the surface. On the other hand, the micelles and vesicles with thiol groups at the end of PNIPAM blocks would transform into trilayers due to the strong interaction between thiols and gold surface.

Journal Article↗
PubMed2006

In2O3 hollow microspheres: synthesis from designed In(OH)3 precursors and applications in gas sensors and photocatalysis.

In this work, well-shaped In(OH)3 hollow microspheres have been successfully prepared via a novel surfactant-free vesicle-template-interface route in the "formamide-resorcinol-water" system, in which spontaneous vesicles were formed under hydrothermal conditions and NH3 from the hydrolysis of formamide acted as the OH- provider. Morphological and structural characterizations indicate that the shells of as-prepared In(OH)3 hollow microspheres were constructed by numerous nanocubes about 80 nm in size. As desired, In2O3 hollow microspheres were obtained from annealing the designed In(OH)3 precursors, and the as-obtained In2O3 hollow microspheres performed well as a gas-sensing material in response to both ethanol and formaldehyde gases and as a photocatalyst for photocatalytic degradation of rhodamine B. The facile preparation method and the improved properties derived from special microstructures are significant in the synthesis and future applications of functional nanomaterials.

Journal Article↗
PubMed2006

Temperature-controlled release of diols from N-isopropylacrylamide-co-acrylamidophenylboronic acid microgels.

N-Isopropylacrylamide-co-acrylamidophenylboronic acid (NIPAM-co-PBA) microgels were prepared by free radical polymerization in water. The release of glucose and Alizarin Red S (ARS) from the microgels as a function of temperature has been investigated by using laser light scattering (LLS) and ultrasensitive differential scanning calorimetry (US-DSC). Such microgels can bind glucose and ARS via boronic acids at a lower temperature. As the temperature increases, the microgels shrink, and the diols are released. The release could be controlled by temperature. The effect of the structure of the microgels on the release is also discussed.

Acrylamides↗
PubMed2006

Nanogels prepared by self-assembly of oppositely charged globular proteins.

Ovalbumin and lysozyme are two main proteins in hen egg white with the isoelectric points of 4.8 and 11, respectively. Herein we report the manufacture of stable, narrowly distributed nanogels (hydrodynamic radius about 100 nm) using a novel and convenient method: ovalbumin and lysozyme solutions were mixed at pH 5.3, the mixture solution was adjusted to pH 10.3, then subsequently stirred and heated. The nanogels were characterized using a combination of techniques. The nanogels have spherical shape and core-shell structure. The core is mainly composed of lysozyme and the shell is mainly composed of ovalbumin. The proteins in the nanogels are in denatured states and they are bound by intermolecular hydrophobic interactions, hydrogen bonds, and disulfide bonds. The charges of the nanogels can be modulated by the pH of the medium. The electrostatic repulsion of ovalbumin molecules on the nanogel surface stabilizes the nanogels in aqueous solution. The formation mechanism of the nanogels is discussed.

Hot Temperature↗
PubMed2006

Microcalorimetric Investigation on the lower critical solution temperature behavior of N-isopropycrylamide-co-acrylic acid copolymer in aqueous solution.

The lower critical solution temperature (LCST) behaviors of random and segmented copolymers of N-isopropylacrylamide (NIPAM) and acrylic acid (AA) prepared in dioxane and water have been investigated by using ultrasensitive microcalorimetry (US-DSC). The introduction of AA increases the LCST of the former but slightly affects that of the latter. When the molar fraction of AA is low (approximately 2 mol %), the LCST of the segmented copolymer shifts to a higher temperature with increasing pH, while the LCST of the corresponding random copolymer slightly changes. Below the boiling point of water, the random copolymer and segmented copolymer with the molar fraction of AA about 15 mol % no longer exhibit an LCST at pH > 5. The addition of calcium ions leads the LCST of both the segmented copolymer and random copolymer to decrease. Our results suggest that the LCST behavior of the copolymers is determined by the clustering of poly(N-isopropylacrylamide) segments.

Journal Article↗
PubMed2005

Study of the kinetics of the pancake-to-brush transition of poly(N-isopropylacrylamide) chains.

The chemical grafting of thiol-terminated poly(N-isopropylacrylamide) (HS-PNIPAM) chains to a gold surface from a solution was investigated with a quartz crystal microbalance (QCM) in real time. The frequency and energy dissipation responses revealed that short HS-PNIPAM chains exhibit three-regime kinetics of the grafting. In regimes I and II, the HS-PNIPAM chains form pancake and mushroom structures, respectively. In regime III, the chains form brushes. From regime II to regime III, the mushroom-to-brush transition occurs. For the longer HS-PNIPAM chains, because of the strong segment-surface interaction, the segments cannot desorb from the surface, and the chains do not undergo a pancake-to-brush transition.

Journal Article↗
PubMed2005

Interactions of apo cytochrome C with alternating copolymers of maleic acid and alkene.

Apo cytochrome c (apo cyt c) tends to aggregate at alkali pH. Poly(isobutylene-alt-maleic acid) (PIMA) is soluble molecularly, whereas poly(1-tetradecene-alt-maleic acid) (PTMA) forms particles that tend to dissociate by increasing pH and decreasing concentration. Dynamic light scattering and surface plasmon resonance are used to investigate the interactions of PIMA and PTMA with apo cyt c at different pH values to understand the mechanism of the interactions. When the positive or negative charges are in excess, the copolymer-protein complex particles can be stabilized by the charges on the surface. When the ratio of the positive to negative charges is close to the stoichiometric value, precipitation occurs. At pH 11.8, both PTMA and apo cyt c carry negative charges, but the hydrophobic interaction makes them form complexes. A competition exists between the interaction of the copolymer with apo cyt c and the self-aggregation of PTMA or apo cyt c alone. The interaction of PIMA or PTMA with apo cyt c at neutral and alkali pH destroys the aggregation of PTMA or apo cyt c and forms new complex particles.

Alkenes↗
PubMed2005

Reentrant behavior of poly(N-isopropylacrylamide) brushes in water-methanol mixtures investigated with a quartz crystal microbalance.

The solvent composition induced reentrant behavior of poly(N-isopropylacrylamide) (PNIPAM) chains grafted on a SiO2 surface in water-methanol mixtures was investigated using a quartz crystal microbalance with dissipation monitoring (QCM-D) at 20 degrees C. The frequency and energy dissipation responses showed that the grafted PNIPAM chains sharply collapse when the methanol content (x(m)) reaches approximately 17 mol %. In the range 17-50 mol %, the grafted chains remain in a collapsed state. Further increase of the methanol content leads to an abrupt reswelling of the collapsed chains at x(m) > approximately 50 mol %. The sharp reentrant swelling-to-collapse-to-swelling transition was attributed to the water-methanol complexation instead of the preferential adsorption effect. Our results also suggest that the water-methanol complexation is not induced by hydrophobic interaction but by hydrogen bonding.

Journal Article↗
PubMed2005

Collapse and swelling of thermally sensitive poly(N-isopropylacrylamide) brushes monitored with a quartz crystal microbalance.

Thermally sensitive poly(N-isopropylacrylamide) (PNIPAM) brushes grafted on SiO2-coated quartz crystal surface were prepared with a surface-immobilized initiator. Using quartz crystal microbalance (QCM), we investigated the collapse and swelling of the brushes in water in real time. Both frequency and dissipation of PNIPAM brushes were found to gradually change throughout a temperature range 20-38 degrees C, indicating that PNIPAM brushes undergo a continuous collapse transition in contrast with PNIPAM chains free in dilute solution exhibiting a sharp coil-to-globule transition. This result is in accordance with the previous theoretical prediction. The nonuniformity and stretching of PNIPAM brushes as well as the cooperativity between collapse and dehydration transitions are thought to be responsible for the continuity. On the other hand, a hysteresis was also observed in the cooling process. This is not only due to the intrachain and interchain interactions formed in the collapsed state but also to the nonuniform structure and stretching of the high-density brushes.

Journal Article↗
PubMed2003

Structure of a collapsed polymer chain with stickers: a single- or multiflower?

Using an amphiphilic copolymer with evenly spaced hydrophobic styrene segments (stickers), poly(N-isopropylacrylamide-s-styrene), we recently confirmed a long-standing prediction that such a copolymer chain in a solvent selectively poor for the stickers could self-fold from a random coil to a single-flowerlike core-shell nanostructure. Moreover, we found that the self-folding involves the movement of the sticks to the center and the transition from the random coil to the collapsed globule passes through a proposed ordered coil state.

Journal Article↗