Ling-Shu Wan

Mussel-inspired modification of a polymer membrane for ultra-high water permeability and oil-in-water emulsion separation

The surface structures and properties of a membrane largely determine its in-service performance during a filtration process. Here we report a facile hydrophilization method via co-deposition of mussel-inspired polydopamine (PDA) and polyethyleneimine (PEI) on a polypropylene microfiltration membrane. The deposition time is greatly shortened and the surface hydrophilicity is significantly improved compared to those membranes decorated only by PDA. The dopamine/PEI deposition solution can be reused several times with negligible effect on the surface hydrophilicity of membranes. Moreover, the PDA/PEI coating endows the membranes with ultra-high water permeability, allowing microfiltration separation of oil-in-water emulsions under atmospheric pressure.

Ordered microporous membranes templated by breath figures for size-selective separation.

Membranes with highly uniform pore size are important in various fields. Here we report the preparation and performance of ordered membranes, the pore diameter of which is on the micrometer scale. The ordered membranes fabricated at two-phase interfaces enable a high-resolution and energy-saving separation process. Moreover, a possible mechanism for the formation of through-pores has been proposed and experimentally verified.

CuSO4/H2O2‐Induced Rapid Deposition of Polydopamine Coatings with High Uniformity and Enhanced Stability

Mussel-inspired polydopamine (PDA) deposition offers a promising route to fabricate multifunctional coatings for various materials. However, PDA deposition is generally a time-consuming process, and PDA coatings are unstable in acidic and alkaline media, as well as in polar organic solvents. We report a strategy to realize the rapid deposition of PDA by using CuSO4/H2O2 as a trigger. Compared to the conventional processes, our strategy shows the fastest deposition rate reported to date, and the PDA coatings exhibit high uniformity and enhanced stability. Furthermore, the PDA-coated porous membranes have excellent hydrophilicity, anti-oxidant properties, and antibacterial performance. This work demonstrates a useful method for the environmentally friendly, cost-effective, and time-saving fabrication of PDA coatings.

Multiple interfaces in self-assembled breath figures

This feature article describes the multiple interfaces in the breath figure (BF) method toward functional honeycomb films with ordered pores. If a drop of polymer solution in a volatile solvent such as carbon disulphide is placed in a humid environment, evaporative cooling leads to self-assembled arrays of condensed water droplets. After evaporation of the solvent and water, patterned pores can be formed. During this BF process, the interfaces between the solution and the substrate, the solution and water droplets, and the film surface and air play extremely important roles in determining both the structures and functions of the honeycomb films. Progress in the BF method is reviewed by emphasizing the roles of the interfacial interactions. The applications of hierarchical and functional honeycomb films in separation, biocatalysis, biosensing, templating, stimuli-responsive surfaces and adhesive surfaces are also discussed.

Honeycomb-Patterned Film Segregated with Phenylboronic Acid for Glucose Sensing

Phenylboronic acid (PBA)-functionalized materials have attracted considerable attention because of their potential applications in many fields. In this paper, we report a PBA-segregated honeycomb-patterned porous film (HPPF) for glucose sensing. Polystyrene-block-poly(acrylic acid-co-acrylamidophenylboronic acid) with different contents of PBA pendants was synthesized via atom transfer radical polymerization (ATRP) followed by a coupling reaction. PBA-functionalized HPPFs were then fabricated by the breath figure method. Results indicate that the composition of the copolymers and the relative humidity play key roles in pore size and regularity of the films. Using Alizarin Red S (ARS) that does not emit fluorescence itself as a fluorescent probe, it is confirmed that PBA pendants are mainly distributed at the pore wall, instead of at the outer surface of HPPFs. This distribution is caused by the segregation of hydrophilic PBA-blocks toward the condensed water droplets, which act as templates for the pore formation. Quartz crystal microbalance results demonstrate that the PBA-functionalized HPPFs show high sensitivity in glucose sensing, which is owing to the segregation of PBA pendants at the pore wall as well as the large specific surface area of the porous films.

Controllable Construction of Carbohydrate Microarrays by Site-Directed Grafting on Self-Organized Porous Films

Carbohydrate-protein interactions are critical in many biological processes. However, the interactions between individual carbohydrates and proteins are often of low affinity and difficult to study. Recent development of carbohydrate microarrays provides an effective tool to explore the interaction. In this work, carbohydrate microarrays were controllably constructed by grafting of a carbohydrate-containing monomer on self-organized honeycomb-patterned films. The films were prepared from an amphiphilic block copolymer, poly(styrene-block-(2-hydroxyethyl methacrylate)), by a breath figure method. Three-dimensional fluorescence results demonstrate that the hydroxyl groups aggregate mainly inside the pores, which afford a chance of site-directed surface modification. 2-(2,3,4,6-Tetra-O-acetyl-beta-D-glucosyloxy)ethyl methacrylate was selectively grafted in the pores by a surface-initiated atom transfer radical polymerization. Characterization by attenuated total reflectance Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy, atomic force microscopy, and contact angle measurements confirms the site-directed growth of the glycopolymer chains. Further specific recognition of the carbohydrate microarrays to lectin (concanavalin A) leads to an organized microarray of protein, and hence this approach also opens a new route to fabricating other functional microarrays such as protein-patterned surfaces.

Tunable Assembly of Nanoparticles on Patterned Porous Film

This paper describes an approach to fully selective assembly of nanoparticles on patterned porous surface. Copolymers of polystyrene-block-poly(N,N-dimethylaminoethyl methacrylate) synthesized by atom transfer radical polymerization were used to prepare honeycomb-patterned porous films by the breath figure method. The regularity and pore size of the films can be modulated by changing the polymer composition and casting conditions such as concentration and airflow speed. Positively charged films were fabricated directly from the quaternized copolymers or by surface quaternization. X-ray photoelectron spectroscopy and adsorption of negatively charged fluorescein sodium salt confirmed the quaternization. Then assembly of negatively charged silica nanoparticles from its aqueous dispersion was performed. Results indicate that they assemble on the external surface of patterned porous films that without prewetting. For prewetted films, the nanoparticles assemble both on the external surface and in the pores. Poly(acrylic acid) deposited from its aqueous solution can serve as an effective blocking layer, which directs the selective assembly of nanoparticles into the pores, instead of the external surface of the film. It is concluded that the Cassie-Wenzel transition is the key to the selective assembly on the highly porous films. The well-defined selective assembly forms unique hierarchical structures of nanoparticles and greatly enlarges the diversity of structures of nanoparticle aggregates. This general approach also opens a straightforward route to the selective modification of patterned porous films.

Surface Engineering of Polymer Membranes

Surface Engineering of Polymer Membranes covers the processes that modify membrane surfaces to improve their in-service performance, meaning, to confer surface properties which are different from the bulk properties. Purposes may be to minimize fouling, modulate hydrophilicity/ hydrophobicity, enhance biocompatibility, create diffusion barriers, provide functionalities, mimic biomembranes, fabricate nanostructures, etc. First, the basics of surface engineering of polymer membranes are covered. Then topics such as surface modification by graft polymerization and macromolecule immobilization, biomimetic surfaces, enzyme immobilization, molecular recognition, and nanostructured surfaces are discussed. This book provides a unique synthesis of the knowledge of the role of surface chemistry and physics in membrane science. Dr. Zhikang Xu of the Institute of Polymer Science of Zhejiang University has eight Chinese patents and in 2006 was honored as a Distinguished Young Scholar by the National Natural Science Foundation of China (NNSFC).

Surface engineering of macroporous polypropylene membranes

The surface properties of polymer membranes are crucial to their application. This Review provides concise comments on surface engineering strategies for macroporous polypropylene membranes. The applications of surface engineering concepts in membrane-based bioreactors, bioseparation, biosensing, biosynthesis, environmental analysis, water purification, energy technology, medical devices (artificial lung and liver), and some novel separation processes (intelligent membrane separation) are summarized. The prospect of surface engineered biomimetic polypropylene membrane is also looked at.

Patterned biocatalytic films via one-step self-assembly

Patterned porous films containing enzymes have been facilely prepared via a one-step breath figure process, which is based on the self-assembly of horseradish peroxidase nanoparticles that show good resistance to organic solvents. The patterned biohybrid films possess robust catalytic activity.