Yebang Tan

Novel complex gel beads composed of hydrolyzed polyacrylamide and chitosan: an effective adsorbent for the removal of heavy metal from aqueous solution.

A novel kind of complex gel beads containing HPAM (hydrolyzed polyacrylamide) and chitosan components (HPAM-chitosan gel beads) was prepared and applied in the removal of Cu(2+), Pb(2+), and Hg(2+) ions from aqueous solutions. These gel beads exhibited a good performance for heavy metal removal. Moreover, the average diameter of these gel beads was about 1mm, which could be appropriate for use in column system. The removal order was Pb(2+)>Cu(2+)>Hg(2+) under the same conditions. The effects of different experimental parameters, such as adsorbent dosage, initial pH, temperature, and initial metal concentration, on the adsorption capacities were studied. The Freundlich model gave a better fit to the experimental data than the Langmuir model in adsorption isotherm study. Desorption study indicated that the gel beads were easy to be regenerated.

Fabrication and properties of cucurbit[6]uril induced thermo-responsive supramolecular hydrogels

Novel thermo-responsive supramolecular hydrogels consisting of cucurbit[6]uril(CB[6]) and butan-1-aminium 4-methylbenzenesulfonate (BAMB) were prepared, which were based on hydrophobic interaction, π–π stacking interaction and van der Walls interaction. Furthermore, hydrogels were not only sensitive to the thermal stimulation, but also showed an interesting property of the inducing action of CB[6] threaded in [2]pseudorotaxane. In this paper, the external morphology and sol–gel transition process of hydrogels were observed by polarized microscopy observation (PMO) and digital camera. DSC results show that the gel–sol transition temperature rose with increasing the concentration of either BMAB or CB[6]. The characteristics of the xerogels were determined by 1H NMR, FT-IR, SEM and TGA. It was found that the CB[6] was threaded in the butyl amine units of BAMB, and the inducing action of CB[6] threaded in [2]pseudorotaxane was essential for the hydrogel formation. Only when the concentrations of both BAMB and CB[6] reached certain values, hydrogels with three-dimensional network structure could be formed. And the viscosity changes for increasing the temperature of the hydrogel systems with different concentration of either CB[6] or BMAB were determined by the rheometer. A possible model was proposed to explain the driving forcing of the gelation.

Cucurbit[8]uril inducing supramolecular hydrogels by adjusting pH

Novel pH and thermo-responsive supramolecular hydrogels consisting of cucurbit[8]uril (CB[8]) and poly(N-(4-vinylbenzyl)-4,4′-bipyridinium dichloride-co-acrylamide) (P4VBAM) were prepared by adjusting pH to alkalinity. In our supramolecular hydrogels system, the viologen units of P4VBAM and CB[8] could form a 1:2 CB[8]/viologen units binary complex with the addition of NaOH by host–guest interactions leading to forming a three-dimensional network and leading to the formation of hydrogels by the molecular recognition of CB[8] and viologen units. The viscosity of supramolecular hydrogels decreases with increasing shear rate, and these supramolecular hydrogel materials are viscoelastic on account of the dynamic nature of the binary complex with CB[8]. With the molar ratio of CB[8] to viologen units of copolymer increasing, the pore sizes within the xerogels decrease and the gel–sol transition temperature of hydrogels increases.

Controlled gelation kinetics of cucurbit[7]uril-adamantane cross-linked supramolecular hydrogels with competing guest molecules

Gelation kinetics of hydrogels is closely linked to many applications such as the development of injectable and printable hydrogels. However, the control of gelation kinetics without compromising the structure and other properties of the hydrogels, remains a challenge. Here, we demonstrate a method to control the gelation kinetics of cucurbit[7]uril-adamantane (CB[7]-AD) cross-linked supramolecular hydrogels by using competing guest molecules. The association between CB[7] and AD moieties on the polymer backbone was impeded by pre-occupying the CB[7] cavity with competing guest molecules. By using various guest molecules and concentrations, the gelation of the hydrogels could be varied from seconds to hours. The strong interaction of CB[7]-AD pair endue the hydrogels good mechanical properties and stability. Moreover, the binding of functionalized guest molecules of CB[7] moieties offers a facile approach for tailoring of the hydrogels’ scaffold. Combined with hydrogel injection and printing technology, this method offers an approach for the development of hydrogels with advanced temporal and spatial complexity.

Improving Performances of Hydrophobically Modified Polyacrylamide in Mineralized Water by Block Polyether with Branched Structure

The hydrophobically modified polyacrylamide (HMPAM) has been received considerable attention in enhanced oil recovery (EOR) processes. The effect of a block polyether with branched structure polyoxyethylene-polyoxypropylene-polyethylene-polyamine (expressed as polyether or PEO-PPO-PEA) on the rheological performances of HMPAM solutions with 8074 mg · L−1 total salinity were investigated at various time and 65°C in order to satisfy the needs of EOR in high temperature and salinity reservoirs. Results reveal that the addition of a certain amount of PEO-PPO-PEA can improve the viscosity and viscoelasticity of HMPAM solution in mineralized water because of the formation of a strong net-like structure. From the results of the flow characteristic measurement and the core flooding test, it can be concluded that the 1750 mg · L−1 HMPAM system with 25 mg · L−1 PEO-PPO-PEA is applicable to use as a displacement system in polymer flooding process at 65°C and 8074 mg · L−1 total salinity.

Aggregation behavior of X-shaped branched block copolymers at the air/water interface: effect of block sequence and temperature

The aggregation behaviors of X-shaped block copolymers, Tetronic 1107 and Tetronic 90R4 with a sequential and reverse architecture, at the air/water interface were studied. The effects of block sequence, concentration, and temperature were investigated by equilibrium surface tension, surface dilational viscoelasticity, and surface tension relaxation measurements. The conformations of Tetronic 1107 and Tetronic 90R4 are different at the air/water interface. The possible adsorption model of Tetronic 1107 is “brush” and that of Tetronic 90R4 is invert “umbrella”. With the increase of temperature, the dilational modulus of Tetronic 1107 solutions decreases, while that of Tetronic 90R4 solutions increases. The mechanisms of the temperature which effects on the conformational transition of Tetronic 1107 and Tetronic 90R4 were discussed in detail. Furthermore, the thermodynamic parameters for the micellization of Tetronic 1107 and Tetronic 90R4 were compared at different temperatures.

Solution properties of hydrophobically modified acrylamide-based polysulfobetaines in the presence of surfactants

Polymer–surfactant interactions in aqueous solutions of a acrylamide-based, hydrophobically modified polysulfobetaine (ADS) containing 3-[N-(2-methacryloxylethyl)-N,N-dimethylammonio]-propane sulfonate and stearyl methylacrylate, with sodium dodedyl sulfate (SDS), N-dodecyl-N,N,N-trimethylammonium bromide (DTAB), and Triton X-100 were studied using surface tension, rheology, Rayleigh light scattering, and dynamic laser light scattering techniques. The purpose of this study was to highlight the influences of the surfactant structure and the nature of the surfactant head group on the polymer–surfactant interactions. The results show that the interaction and association between ADS and surfactants are distinctly varied depending on surfactant type and surfactant concentration. SDS produced the strongest interactions with ADS, while DTAB and Triton X-100 interact with ADS to a lesser degree, which is attributed to surfactant structure and the nature of the surfactant head group. For SDS and DTAB, there are two driving forces for the complexation of the polymer and surfactants, resulting from the electrostatic interaction and the hydrophobic association. However, for the nonionic surfactant Triton X-100, only hydrophobic association predominated in the interaction between ADS and the surfactant. The mechanism and reconstruction of the polymer–surfactant complexes have been evaluated and discussed.

Effect of inorganic salts on the aggregation behavior of branched block polyether at air/water and n-heptane/water interfaces

The effect of inorganic salts (CaCl2, MgCl2, NaCl, NaI and NaSCN) on the aggregation behavior of a synthesized polyether with seven poly (ethylene oxide)-b-poly (propylene oxide)-b-poly (ethylene oxide) (PEO-PPO-PEO) arms attached to a tetraethylenepentamine core (simplified AE73) at air/water and n-heptane/water interfaces has been investigated by interfacial tension and oscillating bubble methods. The additions of NaCl, CaCl2, and MgCl2 may facilitate the micellization of AE73 and increase its maximum interfacial excess concentration (Γmax) due to the “salting out” effect, while NaSCN induces opposite effect and NaI exerts little influence. The adsorption kinetics of AE73 is controlled not only by the diffusion between the bulk solution and the interfacial layer but also by the energetic and steric barriers generated by the already adsorbed molecules. The adsorption relaxation time of AE73 is reduced with the addition of salts and this phenomenon is more prominent at the n-heptane/water interface. The “salting in” ions decrease the dilational modulus of AE73 while the “salting out” ions induce an opposite effect. The mechanisms of the interaction between inorganic ions and the polyether were discussed; the difference in aggregation behavior between linear and branched block polyethers were also compared.

A supramolecular switch based on three binding states of a pyrene derivate: a reversible three-state switch with only two stimuli

A fluorescent molecule, N-methyl-pyrenemethylammonium (MPA+), can be encapsulated inside cucurbit[8]urils (CB[8]) cavity to form a binary host–guest complex. And the binary complex can further binds methyl viologen (MV2+), yielding a ternary complex. With only two chemical stimuli, cucurbit[7]uril (CB[7]) and amantadine hydrochloride (AD), the three binding states of MPA+, unbound MPA+, the binary complex and the ternary complex, can transform reversibly and exert three different fluorescence outputs.

Aggregation Behavior of Copolymer Containing Sulfobetaine Structure in Aqueous Solution

Copolymers containing sulfobetaine (P(AM/DMAPS)) were synthesized by aqueous copolymerization of acrylamide with 3-[N-(2-methacroyloylethyl)-N,N- dimethylammonio]-propane sulfonate. Aggregation and disaggregation of P(AM/ DMAPS) copolymer in aqueous solution as a function of copolymer concentration, added salts, and temperature were studied by dynamic laser light scattering. P(AM/DMAPS) copolymers exist as a mixture of individual chains and interchain aggregation in deionized water. At low copolymer concentrations (below 1.0 g L−1), the intrachain aggregation is dominant. With increasing copolymer concentration, the interchain aggregation is enhanced. The addition of a small amount of salts (CNaCl < 0.1 mol L−1; CMgCl2/CaCl2 < 0.05 mol L−1) leads to the disaggregation of the intra- and interchain aggregation. Further addition of salts results in the enhancement of interchain aggregation. The influence of various cations (Na+, Ca2+, Mg2+) on the aggregation behavior increases in the order Na+ < Ca2+ < Mg2+. The increase of temperature from 25°C to 60°C facilitates the breakup of intrachain aggregation and the enhancement of interchain aggregation.