Weijiang Guan

Synthesis and Design of Aggregation-Induced Emission Surfactants: Direct Observation of Micelle Transitions and Microemulsion Droplets

The direct visualization of micelle transitions is a long-standing challenge owing to the intractable aggregation-caused quenching of light emission in the micelle solution. Herein, we report the synthesis of a surfactant with a tetraphenylethene (TPE) core and aggregation-induced emission (AIE) characteristics. The transition processes of surfactant micelles and the microemulsion droplets (MEDs) formed by the surfactant with a TPE core were clearly visualized by a high-contrast fluorescence imaging method. The fluorescence intensity of the MEDs decreased as the size of MEDs increased as a result of weakening of the restriction of intramolecular rotation (RIR). The results of this study deepen our understanding of micelle-transition processes and provide solid evidence in favor of the hypothesis that the AIE phenomenon has its origin in the RIR of fluorophores in the aggregate state.

Fluorescence microscopy as an alternative to electron microscopy for microscale dispersion evaluation of organic-inorganic composites.

Inorganic dispersion is of great importance for actual implementation of advanced properties of organic–inorganic composites. Currently, electron microscopy is the most conventional approach for observing dispersion of inorganic fillers from ultrathin sections of organic–inorganic composites at the nanoscale by professional technicians. However, direct visualization of macrodispersion of inorganic fillers in organic–inorganic composites using high-contrast fluorescent imaging method is hampered. Here we design and synthesize a unique fluorescent surfactant, which combines the properties of the aggregation-induced emission (AIE) and amphiphilicity, to image macrodispersion of montmorillonite and layered double hydroxide fillers in polymer matrix. The proposed fluorescence imaging provides a number of important advantages over electron microscope imaging, and opens a new avenue in the development of direct three-dimensional observation of inorganic filler macrodispersion in organic–inorganic composites.

One-step enrichment and chemiluminescence detection of sodium dodecyl benzene sulfonate in river water using Mg–Al–carbonate layered double hydroxides

In this work, Mg-Al CO3-layered double hydroxides (LDHs) were used as adsorbent materials for sodium dodecyl benzene sulfonate (SDBS) in aqueous solutions, the enriched SDBS can be directly detected by IO4(-)-H2O2 chemiluminescence (CL) system. The commonly existing cations cannot be enriched by Mg-Al CO3-LDHs due to the structurally positively charged layers of LDHs, while other adsorbed anionic interferents had no effect on the IO4(-)-H2O2 CL reaction. The corresponding linear regression equation was established in the range of 0.1-10 μM for SDBS. The detection limit at a signal-to-noise (S/N) ratio of 3 for SDBS was 0.08 μM. The relative standard deviation (RSD) for nine repeated measurements of 0.5 μM SDBS was 2.6%. This proposed method has been successfully applied to the determination of SDBS in river water samples. To the best of our knowledge, we have first time coupled the high enrichment capacity of LDHs towards anions with CL detection for analytes.

Lighting up the interactions between bacteria and surfactants with aggregation-induced emission characteristics

We report a method for imaging and tracking the interactions between bacteria and surfactants by using two ionic surfactants with aggregation-induced emission (AIE) characteristics. The fluorescence of the cationic AIE-active surfactant, tetraphenylethene-dodecyltrimethylammonium bromide (TPE-DTAB), can be turned on in the presence of bacteria, while the anionic AIE-active surfactant, tetraphenylethene-sodium dodecyl sulfonate (TPE-SDS), hardly interacts with bacteria due to electrostatic repulsion. Moreover, TPE-DTAB is applied for imaging its interaction with bacteria. In the fluorescence images, TPE-DTAB with one positively-charged ammonium is firstly attracted to the anionic surfaces of bacteria through electrostatic attraction, and then its long alkyl chain could insert into the bacterial membrane. The disturbing effect of membrane permeability leads to the death of bacteria. Unexpectedly, TPE-DTAB containing a certain amount of TPE-SDS can attain a higher efficiency of killing bacteria. The negative charge of the bacterial membrane has decreased due to the neutralization of TPE-DTAB, making TPE-SDS easier to get close to and react with membrane proteins. The synergistic effect on membrane damage leads to the higher antibacterial efficiency and massive agglomerations of dead bacteria.

Fluorescence visualization of interactions between surfactants and polymers

An aggregation-induced emission (AIE) anionic surfactant, tetraphenylethene–sodium dodecyl sulfonate, is used to image the process of surfactants binding to polymers through the confocal fluorescence microscopy technique. Two inflection points of the interactions between polymers and surfactants are obtained by the change in the fluorescence intensity of the fabricated AIE-active probe. The proposed fluorescence imaging method supports the development of visualization strategies for studying the interactions between surfactants and other polymers.

Cation-π Interaction Triggered-Fluorescence of Clay Fillers in Polymer Composites for Quantification of Three-Dimensional Macrodispersion

It is a considerable challenge to realize 3D fluorescence quantification of macrodispersion of clay fillers in a polymer matrix mainly owing to quenching of light emission in the solid state. Herein, a strong light emission is generated within the interlaminated clay as a result of a cation-π interaction between cationic surfactant and fluorescent polycyclic aromatic hydrocarbon when they are cointercalated into clay. Confocal laser scanning microscopy (CLSM) is applied for 3D imaging of macrodispersion of the fluorescence-labeled clay fillers in a silicone rubber matrix. More importantly, the quantification of macrodispersion of clay fillers in the overall polymer composite is established by a statistical model. The proposed method fills in an important gap in the standard for macrodispersion quantification of inorganic fillers in polymer composites.

Natural montmorillonite nanosheet colloid-catalyzed hydrogen peroxide ultra-weak chemiluminescence

A natural framework in montmorillonite nanosheet colloids is found to enhance hydrogen peroxide ultra-weak chemiluminescence. This work indicates a transformation of nanoparticle-catalyzed chemiluminescence from synthetic to natural.

Surfactant-assisted algal flocculation via aggregation-induced emission with an ultralow critical micelle concentration

Surfactant-assisted algal flocculation has become a significant technique in the algal biodiesel industry. Generally, commercially available surfactants with longer chains are employed for algal flocculation owing to their lower critical micelle concentration (CMC). However, the efficiency of algal flocculation is unsatisfactory even at high concentrations of surfactants. In this work, an aggregation-induced emission surfactant, tetraphenylethene-dodecyltrimethylammonium bromide (TPE-DTAB), was used to flocculate Chlorella vulgaris C4 with high efficiency as a result of its ultralow CMC (24 μM) derived from the hydrophobic and rigid tetraphenylethene moiety. More interestingly, TPE-DTAB could generate fluorescence in its aggregation state in comparison with conventionally nonluminous surfactants. Therefore, the entire flocculation process of TPE-DTAB micelles with algae has been visualized. Our results would be helpful for scientists to design suitable surfactants with ultralow CMC for high-efficiency algal flocculation.