Shuhua Peng

Cationized hydroxyethylcellulose as a novel, adsorbed coating for basic protein separation by capillary electrophoresis.

We present cationized hydroxyethylcellulose (cat‐HEC) synthesized in our laboratory as a novel physically adsorbed coating for CE. This capillary coating is simple and easy to obtain as it only requires flushing the capillary with polymer aqueous solution. A comparative study with and without polymers was performed. The adsorbed cat‐HEC coating exhibited minimal interactions with basic proteins, providing efficient basic protein separations with excellent reproducibility. Under broad pHs, the amine groups are the main charged groups bringing about a global positive charge on the capillary wall. As a consequence, the cat‐HEC coating produced an anodal EOF performance. A comparative study on the use of hydroxyethylcellulose (HEC) and cat‐HEC as physically adsorbed coatings for CE are also presented. The separation efficiency and analysis reproducibility proved that the cat‐HEC polymer was efficient in suppressing the adsorption of basic proteins onto the silica capillary wall. The long‐term stability of the cat‐HEC coating in consecutive protein separation runs has demonstrated the suitability of the coating for high‐throughput electrophoretic protein separations.

Reversible Photorheological Lyotropic Liquid Crystals

We describe novel lyotropic liquid-crystalline (LLC) materials based on photoresponsive amphiphiles that exhibit rapid photoswitchable rheological properties of unprecedented magnitude between solidlike and liquidlike states. This was achieved through the synthesis of a novel azobenzene-containing surfactant (azo-surfactant) that actuates the transition between different LLC forms depending on illumination conditions. Initially, the azo-surfactant/water mixtures formed highly ordered and viscous LLC phases at 20-55 wt % water content. Spectroscopic, microscopic, and rheological analysis confirmed that UV irradiation induced the trans to cis isomerization of the azo-surfactant, leading to the disruption of the ordered LLC phases and a dramatic, rapid decrease in the viscosity and modulus resulting in a 3 orders of magnitude change from a solid (20,000 Pa) to a liquid (50 Pa) at rate of 13,500 Pa/s. Subsequent exposure to visible light reverses the transition, returning the viscosity essentially to its initial state. Such large, rapid, and reversible changes in rheological properties within this LLC system may open a door to new applications for photorheological fluids.

Azobenzene based multistimuli responsive supramolecular hydrogels

Multistimuli responsive supramolecular aqueous gelators (C4-Azo-C5-D230, C4-Azo-C5-D400, C4-Azo-C5-ED900), composed of alkyl chains, an azobenzene unit, and an amine terminated polyether were prepared. We studied their reversible hydrogelation into three-dimensional entangled supramolecular gels upon changes in temperature, light exposure, pH, and shear. Upon irradiation with UV light, the trans isomer of the C4-Azo-C5-D400 photoisomerized to the cis isomer, which goes to a new steady state between both isomers, resulting in disruption of the gel. Rheological measurements of the hydrogel of C4-Azo-C5-D400 suggested that the non-covalent interactions were disrupted. Likewise, high temperature also caused a reversible disruption to the gel. While the binary mixture of C4-Azo-C5-D400 and water formed gels from a solution under neutral and basic conditions, under the acidic conditions the molecules aggregated and precipitated. After intense shaking of the hydrogel, a solution separated from the gel, resulting in a rapid drop in both modulus and complex viscosity. This photoresponsive gelator can also form lyotropic liquid crystal (LLC) mesophases above 70 °C. Through rational design, multistimuli responsive hydrogelators were successful devised, potentially providing an impetus to the ‘design’ of new gelators through the incorporation of other stimuli responsive features.

Hydroxyethylcellulose-graft-poly (N,N-dimethylacrylamide) copolymer as a multifunctional separation medium for CE.

A new multifunctional separation medium, hydroxyethylcellulose‐graft‐poly (N,N‐dimethylacrylamide) copolymer synthesized in our laboratory for application in both basic protein separation and dsDNA separation by CE, is presented in this paper. As a noncovalent coating, this medium showed a powerful capability in resisting basic protein adsorption. Highly efficient and rapid protein separation had been obtained at four different pH values. Meanwhile, the 11 fragments of the dsDNA sample could be baseline separated using this grafted copolymer as sieving matrix at an appropriate concentration.

A new route to nanostructured thermosets with block ionomer complexes

We report a novel approach to prepare nanostructured thermosets using block ionomer complexes. Neither block copolymer polystyrene-block-poly(ethylene-ran-butylene)-block-polystyrene (SEBS) nor block ionomer sulfonated SEBS (SSEBS) is miscible with diglycidyl ether of bisphenol A (DGEBA) type epoxy resin. It is thus surprising that the block ionomer complex of SSEBS with a tertiary amine-terminated poly(e-caprolactone) (PCL), denoted as SSEBS-c-PCL, can be used to prepare nanostructured epoxy thermosets. The block ionomer complex SSEBS-c-PCL is synthesized via neutralization of SSEBS with 3-dimethylamino-propylamine-terminated PCL. Sulfonation of SEBS yields the block ionomer SSEBS which is immiscible with epoxy. But the block ionomer complex SSEBS-c-PCL can be easily mixed with DGEBA. When the curing agent 4,4′-methylenedianiline (MDA) is added and the epoxy cures, the system retains the nanostructure. In cured epoxy thermosets containing up to 30 wt% SSEBS-c-PCL, the exclusion of the poly(ethylene-ran-butylene) (EB) phase forms spherical micro-domains surrounded by separated sulfonated polystyrene phase while the PCL side-chains of SSEBS-c-PCL are dissolved in the cured epoxy matrix. The spherical micro-domains are highly aggregated in the epoxy thermosets containing 40 and 50 wt% SSEBS-c-PCL. The existence of epoxy-miscible PCL side-chains in the block ionomer complex SSEBS-c-PCL avoids macro-phase separation. Hence, the block ionomer complex can act as an efficient modifier to achieve nanostructured epoxy thermosets.

Spontaneous Pattern Formation of Surface Nanodroplets from Competitive Growth

Nanoscale droplets on a substrate are of great interest because of their relevance for droplet-based technologies for light manipulation, lab-on-chip devices, miniaturized reactors, encapsulation, and many others. In this work, we establish a basic principle for symmetrical arrangements of surface nanodroplets during their growth out of oversaturated solution established through solvent exchange, which takes place under simple and controlled flow conditions. In our model system, nanodroplets nucleate at the rim of spherical cap microstructures on a substrate, due to a pulse of oversaturation supplied by a solvent exchange process. We find that, while growing at the rim of the microcap, the nanodroplets self-organize into highly symmetric arrangements, with respect to position, size, and mutual distance. The angle between the neighboring droplets is 4 times the ratio between the base radii of the droplets and the spherical caps. We show and explain how the nanodroplets acquire the symmetrical spatial arrangement during their competitive growth and why and how the competition enhances the overall growth rate of the nucleated nanodroplets. This mechanism behind the nanodroplet self-organization promises a simple approach to control the location of droplets with a volume down to attoliters.

Surfactant-mediated formation of polymeric microlenses from interfacial microdroplets

Nano- and micro-scale lenses have a range of potential applications, such as in antireflective layers in photovoltaic or light emission devices, and in super resolution imaging in the near field modes. One of the protocols to mass produce polymeric microlenses is through the polymerization of microdroplets of a monomer precursor that are produced at solid–liquid interfaces by a solvent exchange technique. In this work, we have advanced this protocol by using surfactants. A cationic surfactant was added to the liquid phase for the control over the formation and morphology of polymerisable microdroplets and their resultant microlenses (i.e. the polymerized microdroplets). The results demonstrate that the surfactant could enable the production of polymerizable microdroplets on hydrophilic substrates by the solvent exchange technique, and eliminate the restriction by the substrate wettability on the microlens fabrication. Furthermore, the size distribution and aspect ratio of microlenses could be tuned by the surfactant concentration.

Novel quasi-interpenetrating network/functionalized multi-walled carbon nanotubes double-network composite matrices for DNA sequencing by CE.

Poly(N, N‐dimethylacrylamide) (PDMA)‐functionalized multi‐walled carbon nanotubes (MWNT‐PDMA) were prepared via atom transfer radical polymerization and then added into quasi‐interpenetrating network (quasi‐IPN) composed of linear polyacrylamide (3.3 MDa) and PDMA to form polymer/nanotube double‐network composite sieving matrices for DNA sequencing by CE. The CE results show that, compared with quasi‐IPN, the novel composite matrices can improve ssDNA sequencing performances due to the formation of a double‐network consisting of a flexible quasi‐IPN polymer network and a rigid MWNT network based on a unique tubular structure, which makes the total sieving networks more restricted and stable and increases the apparent molecular weight of the matrices. The effects of MWNT‐PDMA concentration in matrices and molecular weight of PDMA side chains in MWNT‐PDMA on ssDNA sequencing performances were studied in detail. Furthermore, these double‐network composite matrices were also compared with other matrices and the results indicate that they are promising ones for DNA sequencing. The separation provided with high resolution, speediness, excellent reproducibility and easy loading owing to the addition of MWNT‐PDMA is likely to achieve full automation, especially for capillary array electrophoresis and microchip electrophoresis.

Microwetting of Supported Graphene on Hydrophobic Surfaces Revealed by Polymerized Interfacial Femtodroplets

Understanding the wettability of graphene is the crucial step toward the design and control of graphene-based surface in contact with liquids. In this work, the static microwettability of a supported single layer graphene (SLG) immersed in water or alcoholic aqueous solutions is revealed by the morphological characterization of the polymerized interfacial femtoliter droplets. As expected, the contact angle of the femtoliter droplets on the SLG in water is in between that on the underlying silanized silicon and that on graphite (HOPG). However, the wettability of femtoliter droplets on the SLG demonstrates a unique dependence on the compositions of the surrounding liquid medium: Their contact angle on SLG becomes much larger than that on both graphite and on silanized silicon, once short-chain alcohol molecules are present in the surrounding medium. To account for this finding, we hypothesize two scenarios to rationalize the effect of alcohol on the microwettability on SLG. The understanding elucidated in this study may allow for improved control of the interaction between graphene and the surrounding liquid environment and facilitate applications in which graphene is in contact with liquids, such as in microfluidics and in lab-on-chip systems.

Azobenzene moiety variation directing self-assembly and photoresponsive behavior of azo-surfactants

The effect of varying the position of the azobenzene group within two comparable photoresponsive amphiphiles on their capability to form lyotropic liquid crystals (LLCs) was investigated in detail in this study. Two photoresponsive amphiphiles having comparable structures were designed and synthesized consisting of hydrophilic oligooxyethylene units, a hydrophobic alkyl chain and a light-sensitive azobenzene moiety. When the azobenzene group was located in the middle of the hydrophobic alkyl chain, multiple LLC phases were observed at various water contents in the azo-surfactant–water binary system. In contrast, when the azobenzene group was directly attached to the hydrophilic domain, the azo-surfactant–water binary system exhibited only lamellar phases. The temperature dependence of these self-organised nanostructures was also investigated by the combination of small angle X-ray scattering (SAXS), differential scanning calorimetry (DSC), and rheology. Under alternating UV and visible light irradiation, reversible trans–cis photoisomerization of the azobenzene group occurred efficiently in dilute solution for both azo-surfactants. However, only photoisomerization of the surfactant possessing the azobenzene group localized in the middle of the alkyl chain induced significant changes in the self-assembled structure and its bulk properties. This study demonstrates that self-assembly and photoresponsive behaviour of photosensitive amphiphiles is extremely sensitive to the position of the photoactive moiety within the surfactant molecular architecture.