Jinwen Qian

Low-cost high-performance fiber-optic pH sensor based on thin-core fiber modal interferometer

A new fiber-optic pH sensor based on a thin-core fiber modal interferometer with electrostatic self-assembled nanocoating is presented. After inserting a segment of thin-core fiber into a standard single-mode fiber, high-order cladding modes are excited and interfere with the core mode to form an in-fiber modal interferometer. The side surface of the sensor is then deposited with poly(allylamine hydrochloride) and poly(acrylic acid) nanocoating by electrostatic self-assembly technique. A fast and linear response is obtained in either acid or alkali solution (in the pH range 2.5 to 10) with resolution of 0.013 pH unit.

Optical fiber relative humidity sensor based on FBG incorporated thin-core fiber modal interferometer

A new fiber-optic relative humidity (RH) sensor based on a thin-core fiber modal interferometer (TCFMI) with a fiber Bragg grating (FBG) in between is presented. Poly (N-ethyl-4-vinylpyridinium chloride) (P4VP·HCl) and poly (vinylsulfonic acid, sodium salt) (PVS) are layer-by-layer deposited on the side surface of the sensor for RH sensing. The fabrication of the sensing nanocoating is characterized by using UV-vis absorption spectroscopy, quartz crystal microbalance (QCM) and scanning electron microscopy (SEM). The incorporation of FBG in the middle of TCFMI can compensate the cross sensitivity of the sensor to temperature. The proposed sensor can detect the RH with resolution of 0.78% in a large RH range at different temperatures. A linear, fast and reversible response has been experimentally demonstrated.

Facile fabrication of polyelectrolyte complex/carbon nanotube nanocomposites with improved mechanical properties and ultra-high separation performance

Polyelectrolyte–polyelectrolyte complexes/multiwall carbon nanotubes (PECs/MWCNTs) nanocomposites have not been prepared until now because PECs are generally insoluble and infusible. In this work, solution-processable PEC/MWCNT nanocomposites and their membranes were prepared by in situ incorporation of MWCNTs into bulk PECs. The ionic complexation between poly(diallyldimethylammonium chloride) (PDDA) and sodium carboxymethyl cellulose (CMCNa) in the presence of MWCNTs was followed by ζ potential and optical transmittance measurements. Structures of PEC/MWCNT nanocomposites were characterized by FT-IR, thermogravimetric analysis (TGA), transmission electron microscopy (TEM), field emission scanning electron microscopy (FESEM) and atomic force microscopy (AFM). It is found that MWCNTs are encapsulated by a layer of PEC and dispersed in a PEC matrix mainly on a single nanotube level. Mechanical properties of the nanocomposite membrane loaded with 7 wt% MWCNTs are greatly improved, showing 2.6 times higher tensile strength and 1.8 times higher modulus as compared with that of the pristine PEC. PEC/MWCNT nanocomposite membranes also display very high performance in pervaporation dehydration of isopropanol. This high pervaporation performance is reproducible with cycling feed temperatures and stable with increasing operation time up to 20 days.

Studies on structures and ultrahigh permeability of novel polyelectrolyte complex membranes.

This work studies the aggregation structures and free volumes of novel polyelectrolyte complex membranes (PECMs) and correlates the two with their ultrahigh permeability to water. Solution-processable PECs between poly(2-methacryloyloxy ethyl trimethylammonium chloride) (PDMC) and sodium carboxymethyl cellulose (CMCNa) were prepared in a two-step method, i.e., precipitation in HCl and redispersion in NaOH. PECMs were subsequently made in a solution casting method. Chemical and aggregation structures of PECs solids were characterized by FT-IR, element analysis (EA), zeta potential, transmission electron microscopy (TEM), and dynamic light scattering (DLS). Surface and cross-section structures of PECMs were characterized by a field emission scanning microscopy (FESEM) and an atomic force microscopy (AFM). Free volume of PECMs was characterized by positron annihilation lifetime spectroscopy (PALS). The free volume of PECMs is larger than that of component polyelectrolyte and is ascribed to the unique aggregation structures of PECMs. Moreover, PALS shows that a long lifetime component (tau(4)) exists with PECMs, indicating that there are water channels in PECMs. Due to these channels, PECMs showed ultrahigh permeability and selectivity.

Pervaporation Recovery of Acetone-Butanol from Aqueous Solution and Fermentation Broth Using HTPB-Based Polyurethaneurea Membranes

In this paper, hydroxyterminated polybutadiene-based polyurethaneurea (HTPB-PU) pervaporation membranes were prepared by phase inversion and used for recovering acetone and n-butanol from dilute aqueous solutions. The effects of the operation temperature and feed composition on the pervaporation performance were investigated. The differences of the separation performance between the ternary mixture and binary mixture were also studied through evaluating the permeability coefficient, the swelling degree of the membrane, and the activity coefficient. The results indicated that a complex “coupling effect” occurred in the ternary mixture. The pervaporation performance for the ternary mixture was superior to that for the binary mixture because of the permeant-permeant and permeant-membrane interactions. A high selectivity towards acetone and n-butanol was obtained. Acetone and butanol were condensed from 1.5 to 11.9 wt% and 3.0 to 43.5 wt% at 40°C for the ternary mixtures, respectively. Furthermore, potential of the membrane for separation of organics from fermentation was also studied by testing the pervaporaton performance, and acetone and butanol were condensed from 0.5 to 8.7 wt% and 1.1 to 16.4 wt% at 45°C, respectively.

A novel method for estimating unperturbed dimension [η]θ of polymer from the measurement of its [η] in a non-theta solvent

Abstract A novel method based on the Einstein’s viscosity equation modified by Guth–Simha–Gold and the model on concentration dependence of polymer chain dimension proposed in our previous study has been developed to estimate the unperturbed dimension, [η]θ, of a polymer (i.e., the intrinsic viscosity at theta conditions) from the measurement of the intrinsic viscosity, [η], at non-theta conditions only. The [η]θ values obtained in present method for polystyrene, poly(oxyethylene), poly(methyl methacrylate), poly(vinyl chloride) and poly(isobutene) are good consistent with their experimental values at theta conditions or with their calculated values according to Mark–Houwink–Sakurada equation at theta conditions by the aid of their Kθ and molecular weight.

Speedy fabrication of free-standing layer-by-layer multilayer films by using polyelectrolyte complex particles as building blocks

A novel method for speedy fabrication of free-standing layer-by-layer (LbL) multilayer films in salt free media, and without the need for a sacrificial sublayer is described by using two different polyelectrolyte complex (PEC) nanoparticles as LbL self-assembly building blocks. Negatively charged polyelectrolyte complex particles (PEC−) consisting of poly(diallyldimethylammonium chloride)/sodium carboxymethyl cellulose (PDDA/CMCNa), and positively charged polyelectrolyte complex particles (PEC+) consisting of PDDA/poly(sodium-p-styrenesulfonate) (PDDA/PSSNa) were prepared and characterized by FT-IR, zeta-potential (ζ potential) and transmission electron microscopy (TEM). The LbL self-assembly of PEC+/PEC− and PDDA/PEC− was followed by quartz crystal microbalance (QCM), optical transmittance, UV-vis absorption spectroscopy and atomic force microscopy (AFM). QCM results show that the thickness growth rate of the PEC+/PEC− pair is 9 times faster than that of the PDDA/PEC− pair and this result is also supported by optical transmittance and UV-vis absorption. A robust free-standing multilayer film of (PEC+/PEC−)25 can be easily peeled off from the substrate after being cross-linked in 3.5 wt% glutaraldehyde (GA) (80 °C, 50mins). Field emission electron scanning microscopy (FESEM) indicates that both the surface and cross-section of the multilayer film display layered structures. Furthermore, multiwall carbon nanotubes (MWCNTs) can also be uniformly incorporated into the free-standing LbL multilayer film by pre-incorporating MWCNTs into PEC− particles. The experimental results show that using oppositely charged PEC particles as LbL assembly components is a speedy and convenient method to fabricate free-standing LbL multilayer films either with or without nanofillers.

Influences of Solution Property and Charge Density on the Self-Assembly Behavior of Water-Insoluble Polyelectrolyte Sulfonated Poly(sulphone) Sodium Salts

Two sulfonated poly(sulphone) sodium salts (SPSF) with different molecular weights and ionic exchange capacities in a N,N-dimethyl formamide/water (DMF-H2O) mixed solvent with various DMF contents were selected as a model system for investigating the influences of solvent composition, solution properties, and charge density of polyelectrolytes on the layer-by-layer (LbL) self-assembly of water-insoluble polyelectrolytes. Poly(dimethyldiallylammonium chloride) (PDDA) in aqueous solution was used as the counterpart. The PDDA/SPSF multilayer films grew nearly linearly with the layer numbers regardless of the volume fraction of DMF, phiDMF, in the SPSF solutions. The total absorption amount of the PDDA/SPSF multilayer films was strongly dependent on the charge density of the SPSF molecules and the phiDMF value of the SPSF solutions. Minimum values of absorption amount were observed at phiDMF = 0.6 to approximately 0.7. The surface hydrophobicity and roughness of the multilayer films can be tuned by varying phiDMF. These observations were rationalized in terms of the chain dimension and the ionization degree of the SPSF molecules as a function of phiDMF, which was characterized by the intrinsic viscosity ([eta]SPSF) and conductivity (LSPSF) of the SPSF solutions. The results indicate that the molecular structures of the DMF-H2O mixed solvent strongly affect the solution properties of SPSF, which in turn determine the growth behavior and physical properties of the PDDA/SPSF multilayer films.

Fabrication of free-standing polyelectrolyte multilayer films: a method using polysulfobetaine-containing films as sacrificial layers.

A new pH-dependent sacrificial system based on zwitterionic polysulfobetaine was proposed for the fabrication of free-standing polyelectrolyte multilayer films. The zwitterionic polysulfobetaine, poly(4-vinylpyridine propylsulfobetaine) (P4VPPS), was synthesized and its layer-by-layer (LbL) self-assembly behavior with poly(diallyldimethylammonium) (PDDA) as counterpart was investigated by using UV-vis absorption spectroscopy, quartz crystal microbalance (QCM) and atomic force microscopy (AFM). The LbL multilayer films of PDDA/P4VPPS were successfully constructed in acid aqueous solution at pH 2 with 0.5 M NaCl. The resultant PDDA/P4VPPS multilayer films were pH-dependent and could be disintegrated in alkali aqueous solutions, especially with pH > or = 12. This disintegration property rendered such multilayer film as a sacrificial layer for further preparing free-standing polyelectrolyte multilayer films. The PDDA/poly(sodium 4-styrenesulfonate) (PSS) multilayer films deposited on the PDDA/P4VPPS sacrificial layer were confirmed to be successfully released after treated successively by alkali aqueous solution at pH 12 and ethanol. The obtained PDDA/PSS free-standing multilayer films had thicknesses of ca. 847 nm.

Layer-by-layer self-assembly, controllable disintegration of polycarboxybetaine multilayers and preparation of free-standing films at physiological conditions

The self-assembly and disintegration behavior of polyzwitterion, poly(4-vinylpyridiniomethanecarboxylate) (PVPMC), and negatively charged polyelectrolyte, poly(acrylic acid) (PAA), layer-by-layer (LbL) multilayer films were investigated in detail by using UV-vis absorption spectroscopy, quartz crystal microbalance (QCM) and atomic force microscopy (AFM). The results indicated that the PVPMC/PAA multilayer films grew linearly with increasing bilayer number. The disintegration rate of PVPMC/PAA multilayers could be well controlled by varying the concentration of salt in aqueous solution. It was found that PVPMC/PAA multilayer films could be completely disintegrated in 0.9% normal saline solution within 15 min. Such controllable disintegration behavior rendered the PVPMC/PAA multilayer as an excellent sacrificial sublayer for fabricating free-standing LbL multilayer films. Free-standing multilayer films were then successfully fabricated by LbL self-assembly of positively charged polyelectrolyte complex (PEC), made from poly(diallyldimethylammonium) (PDDA) and poly(sodium 4-styrenesulfonate) (PSS), and negatively charged PSS with PVPMC/PAA as a sacrificial sublayer, which was disintegrated in 0.9% normal saline solution. The obtained free-standing films had good mechanical properties with 24.1 MPa tensile strength at break and 0.56 GPa Youngs modulus.