Chenglin Yi

Glucose sensors based on electrodeposition of molecularly imprinted polymeric micelles: A novel strategy for MIP sensors

A voltammetric glucose sensor was prepared from novel molecularly imprinted polymeric micelles (MIPMs) through direct electrodeposition. The MIPMs, which were photo-crosslinkable and nano-scaled with high specific surface area, were prepared via macromolecule self-assembly of an amphiphilic photo-crosslinkable copolymer, combined with a molecular imprinting technique using glucose as the template molecule. A MIP film was formed in situ on the electrode surface by electrodeposition of the MIPMs, while photo-crosslinking led to a robust film which showed good solvent resistant to dissolution. With these features, the resulting sensor showed good response and selectivity towards glucose. In particular, the linear response of this glucose sensor ranged from 0.2 mM to 8 mM and its comparatively higher detection limit, about 10 mM, indicated numerous effective recognition sites among the polymer matrix due to the large specific surface area of MIPM. In addition, this MIP sensor also showed good stability and reversibility. The contribution of this work lies in not only the invention of a new type of glucose MIP sensor with good performance, but also the creation of a novel strategy to develop advanced MIP sensors for a wide range of templates in viewing of the versatility of the amphiphilic copolymers and the ease of control and applicability of the electrodeposition process.

Pickering emulsions stabilized by self-assembled colloidal particles of copolymers of P(St-alt-MAn)-co-P(VM-alt-MAn)

A new type of copolymer containing two alternating segments, poly-(styrene-alt-maleic anhydride)-co-poly (7-(4-vinylbenzyloxyl)-4-methylcoumarin-alt-maleic anhydride) P(St-alt-MAn)-co-P(VM-alt-MAn)(PSMVM), was prepared. The copolymer self-assembled into nanoparticles with internal microphase structures in water because the hydrophilicity of segment P(VM-alt-MAn) is higher than that of P(St-alt-MAn). The particle size, morphology, ζ potential and surface properties and their dependence on the pH and slat concentrations were studied with a combination of techniques. The nanoparticles of PSMVM showed surface activity and pH sensitivity for producing Pickering oil-in-water emulsions. The emulsion volume increased and the size of oil/water droplet decreased with increasing salt concentration. Furthermore, cross-linked nanoparticles (CLPs) were obtained by photo-dimerization of the pendent coumarin groups in PSMVM under UV irradiation. The emulsions produced by using the CLPs as emulsifiers showed even better stability upon standing. Solid oil-phase droplets were obtained by preparation of CLPs-stabilized Pickering emulsions with an oil phase of styrene containing the initiator AIBN followed by the polymerization of styrene. Thus, the enrichment and aggregation of the CLPs on the emulsion droplets was visible because the solid droplets remained unchanged during the SEM sample preparation.

Dual-responsive poly(styrene-alt-maleic acid)-graft-poly(N-isopropyl acrylamide) micelles as switchable emulsifiers.

Self-assembled polymeric micelles can be used as efficient particulate emulsifiers. To explore the relationship between micellar structure and emulsification performance, pH- and temperature-responsive self-assembled micelles were prepared and used as emulsifiers, based on a novel grafted polymer poly(styrene-alt-maleic acid)-graft-poly(N-isopropyl acrylamide) (PSMA-g-PNIPAm). Structure of PSMA-g-PNIPAm micelles varies in response to pH and temperature changes and can be classified into four typical states, including shrunken, moderately swollen, extremely swollen, and inverted states, confirmed by a combination of electrophoresis, dynamic light scattering (DLS), transmission electron microscopy (TEM), and (1)H NMR. This structural variation plays a key role in the emulsification performance of PSMA-g-PNIPAm micelles, according to the emulsifying characteristics of the four typical PSMA-g-PNIPAm micelles as well as the micellar morphologies on the surface of oil droplets as observed by SEM. Emulsions stabilised by micelles with moderately swollen structure are especially stable compared with either the shrunken micelles or the extremely swollen micelles, because the moderately swollen micelles combine the advantages of solid particulate emulsifiers and polymeric surfactants.

Influence of photo-cross-linking on emulsifying performance of the self-assemblies of poly(7-(4-vinylbenzyloxyl)-4-methylcoumarin-co-acrylic acid).

Polymeric micelles could be used as model polymeric particulate emulsifiers to elucidate the correlation between the micellar structure and their emulsifying performance. Photo-cross-linkable and pH-responsive micelles were prepared with amphiphilic random copolymers, poly(7-(4-vinylbenzyloxyl)-4-methylcoumarin-co-acrylic acid) (PVMAA), via the self-assembly in selective-solvent DMF/H2O and then used as polymeric particulate emulsifiers to stabilize toluene-in-water emulsions. Primary micelles, based on PVMAA with 12 mol % of hydrophobic composition, were chosen as model to investigate the influence of photo-cross-linking on the emulsifying performance. The larger shrinkage degree by photo-cross-linking (SDC) the micelles have, the lower emulsifying efficiency the micelles exhibit. Furthermore, the structural transitions of micelles with SDC of 0% and 95% in response to pH change were comparatively confirmed by a combination of electrophoresis, dynamic light scattering (DLS), and transmission electron microscopy (TEM). The micelles of various states, manipulated by photo-cross-linking and pH changes, were used as emulsifiers to stabilize toluene-in-water or styrene-in-water emulsions. For the un-cross-linked micelles, polymer chains gradually protrude from micelles with pH increasing, which benefits the increase in the emulsifying efficiency of micelles. However, as pH elevated over 8, the stability of emulsions significantly decreases due to the disintegration of micelles. On the contrary, micelles with SDC of 95% keep their structural integrity and become more rigid as pH increase, leading to lower emulsifying efficiency of micelles and worse stability of the emulsions. This paper provides a new insight into the principles governing the extremely high emulsifying efficiency of polymeric particulate emulsifiers and pH-dependent or pH-responsive properties of the formed emulsions.

Nanohybrids from Direct Chemical Self-Assembly of Poly(styrene-alt-maleic anhydride) as pH-Responsive Particulate Emulsifiers

The nanohybrid particulate emulsifiers based on poly(styrene-alt-maleic anhydride) (SMA) were facilely prepared via the direct chemical self-assembly triggered by the aminolysis of SMA with 3-aminopropyltriethoxysilane (APTES) and the in situ polycondensation of APTES under refluxing in acetone. Transmission electron microscopy and scanning electron microscopy confirmed the spherical-like morphology of the nanohybrids. Dynamic light scattering and electrophoresis revealed the structure transition of the nanohybrids in response to pH change. The emulsification study showed that the nanohybrids were effective particulate emulsifiers when homogenized with various oils including toluene, paraffin oil, silicone oil, isooctyl palmitate, dicaprylyl carbonate, and propylheptyl caprylate. The nanohybrid particulate emulsifiers exhibited pH-sensitivity, and the diameter of paraffin oil droplets remarkably increased with pH of the nanohybrid aqueous dispersion decrease. Also, the reduced dynamic interfacial tension predicted the thermodynamically unstable state of the emulsions prepared at high pH values. Most interesting, the paraffin oil-in-water high internal phase emulsions (HIPEs) with a high oil volume fraction of 83.3% were formed when the nanohybrids were heavily flocculated by adding HCl. The HIPEs were pH-responsive and capable of demulsification with the addition of an alkaline solution showing a potential application in the oil industry.

One-step formation of multiple Pickering emulsions stabilized by self-assembled poly(dodecyl acrylate-co-acrylic acid) nanoparticles.

In this study, a one-step generation of stable multiple Pickering emulsions using pH-responsive polymeric nanoparticles as the only emulsifier was reported. The polymeric nanoparticles were self-assembled from an amphiphilic random copolymer poly(dodecyl acrylate-co-acrylic acid) (PDAA), and the effect of the copolymer content on the size and morphology of PDAA nanoparticles was determined by dynamic light scattering (DLS) and transmission electron microscopy (TEM). The emulsification study of PDAA nanoparticles revealed that multiple Pickering emulsions could be generated through a one-step phase inversion process by using PDAA nanoparticles as the stabilizer. Moreover, the emulsification performance of PDAA nanoparticles at different pH values demonstrated that multiple emulsions with long-time stability could only be stabilized by PDAA nanoparticles at pH 5.5, indicating that the surface wettability of PDAA nanoparticles plays a crucial role in determining the type and stability of the prepared Pickering emulsions. Additionally, the polarity of oil does not affect the emulsification performance of PDAA nanoparticles, and a wide range of oils could be used as the oil phase to prepare multiple emulsions. These results demonstrated that multiple Pickering emulsions could be generated via the one-step emulsification process using self-assembled polymeric nanoparticles as the stabilizer, and the prepared multiple emulsions have promising potential to be applied in the cosmetic, medical, and food industries.

Effect of chain microstructure on self-assembly and emulsification of amphiphilic poly(acrylic acid)-polystyrene copolymers

In this study, a series of random copolymer poly(acrylic acid-co-styrene) (P(AA-co-St)) and block copolymer poly(acrylic acid)-b-polystyrene (PAA-b-PSt) with similar chemical composition but different chain microstructure were synthesized. The self-assembly behavior of random and block copolymers in selective solvent was investigated, and the structural evaluation of random and block copolymers micelles was carried out by transmission electron microscopy (TEM), dynamic light scattering (DLS) measurement, and X-ray photoelectron spectroscopy (XPS). Moreover, together with experimental characterization, the theoretical method dissipative particle dynamics (DPD) approach was applied to investigate the morphological structures of micelles composed from random and block copolymers. Results revealed that the structure of polymeric micelles is significantly affected by the distribution sequence of hydrophilic and hydrophobic monomers in copolymer chains. Furthermore, polymeric micelles based on P(AA-co-St) and PAA-b-PSt with about 50 mol% hydrophilic composition were chosen as the model to investigate the influence of micellar structure on emulsifying performance. For PAA-b-PSt micelles (B48), stable water-in-oil (w/o) emulsions could only obtained when the pH values were lower than 5. As a comparison, the P(AA-co-St) micelles (R49) had an excellent emulsification performance at 4-10 pH, and the pH-induced phase inversion derived from obtained emulsions observed at pH higher than 6. Preliminary results confirm that the micellar structure controlled by chain microstructure plays an important role in the interface behavior of polymer micelles. Compared with PAA-b-PSt micelles, P(AA-co-St) micelles have better interfacial performance and are more tailorable and controllable; thus they can be used as a model for further study of polymeric particulate emulsifiers. This paper provides new insight into the principles governing extremely high emulsifying efficiency of polymeric particulate emulsifiers and pH-responsive properties of the formed emulsions.