Co-reporter:Biaolan Liu;Jian Wang;Yu Zhang;Shuaishuai Wu;Geying Ru
Soft Matter (2005-Present) 2017 vol. 13(Issue 39) pp:7106-7111
Publication Date(Web):2017/10/11
DOI:10.1039/C7SM01540B
Understanding the morphological transition dynamics related to the hydrophilic–hydrophobic interface has been a challenge due to the lack of an effective evaluation method. Herein, nuclear magnetic resonance spectroscopy was employed to study the morphological transition related chain collapse of poly(N,N′-diethylaminoethylmethacrylate)-b-poly(N-isopropylacrylamide) (PDEAEMA133-b-PNIPA322) and poly(N,N′-dimethylaminoethylmethacrylate)-b-poly(N-isopropylacrylamide) (PDMAEMA95-b-PNIPA228) and was proved to be a powerful technique in morphological transition mechanism studies once combined with dynamic light scattering and transmission electron microscopy. Unlike the cooperative coil collapse of two blocks in the PDMAEMA95-b-PNIPA228 alkaline solution upon heating which induces the assembly of a nanostructure (∼200 nm) with a hydrophobic core containing both collapsed PDMAEMA and PNIPA segments and a hydrophilic surface part consisting of un-shrunk PDMAEMA and PNIPA segments, PDEAEMA133-b-PNIPA322 with a low-temperature core–shell micelle structure showed a micelle–vesicle transition due to temperature-induced inhomogeneous-collapse of PNIPA. The PNIPA segments in the shell sequentially collapse outside (starting at the core–shell interface), accompanied by a gradual decrease in micelle size. Above the critical temperature, the residual hydrophilic PNIPA segments become too short to stabilize the micelle structure, the micelles then transform into vesicles of a slightly larger size, instead of micelle aggregation and precipitation as normally expected.
Co-reporter:Jian Wang;Nian Wang;Biaolan Liu;Jia Bai;Pei Gong;Geying Ru
Physical Chemistry Chemical Physics 2017 vol. 19(Issue 44) pp:30097-30106
Publication Date(Web):2017/11/15
DOI:10.1039/C7CP04384H
Cononsolvency of poly(N-isopropylacrylamide) (PNIPAM) gels in binary mixed solvents (water–acetone and water–DMSO) has been comparatively investigated by 1H HR-MAS NMR spectroscopy. The results demonstrate that, although the addition of both acetone and DMSO gives rise to cononsolvency behavior, PNIPAM preferentially interacts with acetone rather than DMSO in a water-rich regime, regardless of whether the temperature is above or below the volume phase transition temperature (VPTT). It suggests that the preferential adsorption of the additive cannot be deemed as a prerequisite for the cononsolvency in water-rich mixtures. The underlying molecular mechanism of cononsolvency involves a delicate balance between polymer–solvent and solvent–solvent interactions. Moreover, a new NOE-based NMR approach has been proposed to study the preferential adsorption in this work, which can be extensively adopted to study other relevant processes, including protein hydration, ligand binding, enzyme catalysis, etc.
Co-reporter:Jian Wang, Biaolan Liu, Geying Ru, Jia Bai, and Jiwen Feng
Macromolecules 2016 Volume 49(Issue 1) pp:234-243
Publication Date(Web):December 24, 2015
DOI:10.1021/acs.macromol.5b01949
1H MAS NMR spectroscopy has been applied to study the urea effect on phase transition of two similar thermosensitive polymer hydrogels: poly(N-isopropylacrylamide) (PNIPAM) and poly(N,N-diethylacrylamide) (PDEA). It is found that urea influences the phase transition of the hydrogels in opposite ways: lowering the lower critical solution temperature (LCST) of PNIPAM and hence stabilizing its globular structure, whereas raising the LCST of PDEA and destabilizing the globular structure. The self-diffusion coefficient and urea–polymer nuclear Overhauser effect (NOE) measurement reveal that urea has a stronger interaction with PNIPAM than with PDEA. Moreover, the enhanced positive water–PNIPAM NOE suggests that urea not only interacts directly with PNIPAM via hydrogen bond but also intensifies the hydrogen bonding interaction between water and PNIPAM. We suggest that different urea–polymer hydrogen bonding interaction due to the presence or absence of amide hydrogen is correlated with the distinct LCST variation of PNIPAM and PDEA.
Co-reporter:Pei Gong;Jian Wang;Biaolan Liu;Geying Ru
Cellulose 2016 Volume 23( Issue 3) pp:1705-1711
Publication Date(Web):2016 June
DOI:10.1007/s10570-016-0932-z
Our NMR experiments show that chitin can dissolve well in aqueous KOH through a freeze-thawing process, and the dissolution power of the alkali solvent systems is in the order of KOH > NaOH > LiOH aqueous solution, which is totally contrary to that of cellulose in the alkali aqueous solution (i.e., LiOH > NaOH ≫ KOH). In this work, we systematically study the dissolution process in KOH and KOH/urea aqueous solutions. Chitin has good solubility (solubility ~80 %) in 8.4–25 wt% KOH aqueous solution at −30 °C. The role of urea also has been investigated: unlike aqueous chitin-NaOH solutions, urea indeed enhances the solubility of chitin in KOH aqueous solutions, but the increased degree becomes unobtrusive with decreasing temperature and increasing dissolution time; the DA decline curves of chitin-KOH and chitin-KOH/urea aqueous solutions are nearly overlapping, indicating that the effect of the urea on the degree of acetylation of chitin in KOH aqueous solutions is small, similar to the NaOH/urea solvent.
Co-reporter:Yugui He;Zhen Zhang;Chongyang Huang;Fang Chen
Science China Chemistry 2016 Volume 59( Issue 7) pp:830-835
Publication Date(Web):2016 July
DOI:10.1007/s11426-015-0512-0
Dynamic nuclear polarization (DNP) has become a very important hyperpolarization method because it can dramatically increase the sensitivity of nuclear magnetic resonance (NMR) of various molecules. Liquid-state DNP based on Overhauser effect is capable of directly enhancing polarization of all kinds of nuclei in the system. The combination of simultaneous Overhauser multi-nuclei enhancements with the multi-nuclei parallel acquisitions provides a variety of important applications in both MR spectroscopy (MRS) and image (MRI). Here we present two simple illustrative examples for simultaneously enhanced multi-nuclear spectra and images to demonstrate the principle and superiority. We have observed very large simultaneous DNP enhancements for different nuclei, such as 1H and 23Na, 1H and 31P, 19F and 31P, especially for the first time to report sodium ion enhancement in liquid. We have also obtained the simultaneous images of 19H and 31P, 19F and 31P at low field by solution-state DNP for the first time.
Co-reporter:Xinmiao Liang, Liying Wang, Yangming Jiang, Jian Wang, Huan Luo, Chaoyang Liu, and Jiwen Feng
Chemistry of Materials 2015 Volume 27(Issue 16) pp:5503
Publication Date(Web):July 27, 2015
DOI:10.1021/acs.chemmater.5b01384
Li10GeP2S12 (LGPS) is a new solid electrolyte of the highest Li ionic conductivity reported as of now. An anisotropic 3D Li ionic transport network consisting of an ultrafast Li 1D diffusion tunnel and fast in-plane 2D pathways was previously predicted by molecular dynamics simulations. In this paper, we have studied in detail the Li ion dynamics in LGPS by multiple solid-state NMR methods. Two different Li motion processes, characterized by apparently different activation energies of 0.16 eV and 0.26 eV, were unambiguously probed by both 7Li and 31P solid-state NMR and assigned to Li ion diffusions in the 1D tunnel and in the 2D plane, respectively. 31P spin-locking relaxation measurement further reveals that interstitial position Li(4) is active for in-plane Li migration.
Co-reporter:Geying Ru;Huan Luo;Xinmiao Liang;Liying Wang;Chaoyang Liu
Cellulose 2015 Volume 22( Issue 4) pp:2221-2229
Publication Date(Web):2015 August
DOI:10.1007/s10570-015-0667-2
The low-temperature dissolution mechanism of chitin in NaOH/urea aqueous solution has not been well established yet, especially at a temperature that lowers the crystallization temperature of both NaOH and urea. Using multiple nuclei (1H, 15N and 23Na) nuclear magnetic resonance (NMR) methods, we find that the ternary NaOH/urea/D2O system, different from the fully frozen binary NaOH–D2O system, exhibits solid-liquid phase coexistence below −40 °C, and the residual liquid phase consists of certain concentrations of NaOH (10 wt%), urea (13 wt%) and D2O at −40 °C. Our NMR results further demonstrate that chitin dissolves in the residual liquid phase (containing 5–10 wt% NaOH and 8–12 wt% urea) at low temperatures (−40 and −70 °C). An important role of urea is enhancing the low-temperature stability of NaOH aqueous solutions and then increasing the dissolution temperature range of chitin, thus providing an essential low-temperature liquid environment for chitin dissolution.
Co-reporter:Biaolan Liu, Jian Wang, Geying Ru, Chaoyang Liu, and Jiwen Feng
Macromolecules 2015 Volume 48(Issue 4) pp:1126-1133
Publication Date(Web):February 4, 2015
DOI:10.1021/ma502393z
The phase separation of poly(N,N-diethylacrylamide) (PDEA) gel network in water/alcohol (methanol, ethanol, isopropanol, and n-propanol) mixtures has been systematically investigated by variable-temperature high-resolution 1H MAS NMR. The PDEA gel exhibits the cononsolvency effect and reentrant phase transition in water/isopropanol and water/n-propanol mixtures with larger alcohol hydrophobic groups but not in the water/methanol and water/ethanol bearing smaller alcohol hydrophobic groups, in contrast to the case of poly(N-isopropylacrylamide) where the cononsolvency effect was observed in all water/alcohol solutions. In the present PDEA gel, the phase separation is characterized by dehydration of the hydrophobic alkyl groups of PDEA, resulting in two distinct types of water/alcohol solutions above the lower critical solution temperature: confined binary solvents (3–5 solvent molecules per PDEA repeating unit) inside the gel network and free binary solvents outside the gel. The alcohol concentration in confined mixture solvents is markedly higher than that in free mixture solvents and increases with increasing hydrophobicity of the alcohol moiety. Interestingly, the alcohol enrichment inside the shrunk network does not cause additional dehydration of the PDEA network. Besides, the side chain mobility of shrunk PDEA gel network is enhanced by the appearance of alcohol and increases with the hydrophobicity of alcohol moiety. Our results reveal that there exists a strong interaction between alcohol and gel network.
Co-reporter:Bing Chen, Zhanhai Xiao, Yanhu Li, Lei Yu, Wei Yang and Jiwen Feng
RSC Advances 2014 vol. 4(Issue 91) pp:50027-50034
Publication Date(Web):17 Sep 2014
DOI:10.1039/C4RA06540A
Novel aromatic bipolar host polymers (P1 and P2) containing pyridine as an electron transporting unit and carbazole and fluorene as hole transporting units in the π-conjugation interrupted polymer backbone have been synthesized by a metal-free superacid-catalyzed polyhydroxyalkylation. The present polymers show good thermal stability, with high glass transition temperatures and decomposition temperatures. The conjugation lengths of the polymers are effectively confined into the repeating units due to the δ-C bond interrupted polymer backbone, giving rise to quite high triplet energy (2.79 eV for P1) and a wide band gap of around 3.33 eV, which make them promising hosts for phosphorescent OLEDs. The results suggest that the strategy of incorporating bipolar blocks into the π-conjugation interrupted polymer backbone can be a promising approach to obtain host polymers with high triplet level for green and even blue phosphorescent polymer light-emitting diodes on a simple device structure and using a solution-processed technique.
Co-reporter:Geying Ru
Journal of Polymer Science Part B: Polymer Physics 2011 Volume 49( Issue 10) pp:749-755
Publication Date(Web):
DOI:10.1002/polb.22237
Abstract
Phase transition and mobility of poly(N-isopropylacrylamide) (PNIPA) chains with three different types of end groups (hydroxyl, carbon–carbon double bond, and camphoric sulfonic groups) have been studied by measurements of the normal 1H NMR spectrum, spin–spin relaxation time, and 2D NOESY spectrum. It is found that at room temperature not only the end group parts but also the part of the PNIPA chain with hydroxyl end group have higher mobility than corresponding parts of PNIPA with double bond and camphoric sulfonic end groups. The lower critical solution temperatures (LCST) of PNIPAs modified with hydrophilic hydroxyl and hydrophobic double bond end groups are inversely dependent and directly dependent on the molecular weight of polymer respectively, whereas the LCST of PNIPA with the camphoric sulfonic end group bearing both hydrophobic and hydrophilic structures is independent of the molecular weight. The double bond end groups collapse simultaneously with inner segments of the PNIPA chain, whereas the hydroxyl and camphoric sulfonic end groups still exhibit higher mobility and do not shrink tightly after heating-induced collapsing of inner segments. It is suggested that the hydroxyl and camphoric sulfonic end groups locate on the surface of globules, but the double bond end groups are probably buried inside the globules. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011
Co-reporter:Xiuzhi Gao, Liying Wang, Huan Luo, Qin Zou, Ningdong Feng and Jiwen Feng
Macromolecules 2010 Volume 43(Issue 13) pp:5713-5722
Publication Date(Web):June 10, 2010
DOI:10.1021/ma1000578
The structures and thermal properties of the multiple ordered phases in ethylene−octene and ethylene−butene copolymers have been studied using a combination of solid-state NMR and DSC. Three types of the ordered phases, namely the orthorhombic, monoclinic, and rotator (or ordered mobile phase), have been found to coexist in these two ethylene copolymers. Our experimental results demonstrate that the slow-spinning solid-state CP/MAS 13C NMR provides a convenient method to discern the NMR signals of the three different ordered phases and to measure the 13C chemical shift tensors of orthorhombic and monoclinic phases. The measurements of 13C chemical shift tensors and magnetic relaxation times show that monoclinic and orthorhombic crystal phases have similar chemical shift anisotropy with 180° flip-flop segmental movement. The chemical shift anisotropy and segmental mobility in the rotator phase, on the other hand, are different from those in the orthorhombic and monoclinic phases. DSC results illustrate that a low-melting-point phase forms during room-temperature aging and melts at temperature slightly above the room temperature. The apparent correlation between the low-melting-point phase and the rotator structure is revealed by a combination of variable-temperature solid-state CP/MAS NMR spectra with a slow-spinning rate and DSC measurement. It is thus suggested that the rotator formation induced by room-temperature aging is a common phenomenon for the ethylene copolymers with different sizes of side groups.
Co-reporter:Nian Wang, Geying Ru, Liying Wang and Jiwen Feng
Langmuir 2009 Volume 25(Issue 10) pp:5898-5902
Publication Date(Web):March 31, 2009
DOI:10.1021/la8038363
Preferential interactions of solvents with poly(N-isopropylacrylamide) (PNIPAM) gel networks in binary water/alcohol (water/methanol and water/ethanol) mixtures have been investigated using variable-temperature high-resolution 1H MAS NMR. NMR results for PNIPAM gel in the binary solvents reveal the existence of two distinct types of water/alcohol mixtures above the LCST: confined binary solvents bound inside the gel, and free binary solvents expelled from the gel. It is interesting to find that the alcohol concentration in confined solution is significantly higher than that in free solution. Moreover, of the two alcohols, ethanol is more significantly concentrated in the confined solution. These results demonstrate that the polymer preferentially interacts with alcohol molecules over water and that the alcohol with higher hydrophobicity exhibits higher preferential absorption on PNIPAM. Our results also show that 1H NMR measurements made on two distinct types of solution provide a convenient, direct means of characterizing the preferential adsorption of solvent on polymer.
Co-reporter:Geying Ru, Nian Wang, Shaohua Huang and Jiwen Feng
Macromolecules 2009 Volume 42(Issue 6) pp:2074-2078
Publication Date(Web):February 18, 2009
DOI:10.1021/ma802780d
Phase transition occurring in three different types of poly(N-isopropylacrylamide) gels—normal cross-linked gel, comb-type grafted gel, and comb-type grafted gel with styrene-modified comb chains—has been investigated by variable-temperature measurements of 1H NMR spectra and spin−spin relaxation time. Three different gels exhibit distinct collapse behaviors in response to increasing temperature. For the normal gel, remarkable network shrinking occurs in a relatively narrow temperature range from 32 to 35 °C. For the styrene-modified comb-type gel, overall chain shrinkage appears in a very broad temperature range from 22 to 35 °C in which the styrene-modified comb chains shrink at lower temperatures (22−32 °C) than the backbone networks (32−35 °C). In the comb-type gel without styrene modification, however, the backbone networks shrink first (at 32−35 °C) on heating, followed by collapsing of comb chains (at 35−36 °C). During shrinkage of backbone networks the comb chains are expulsed from the main gel networks which is revealed by abnormal T2 increase of comb chains. T2 measurements also reveal that the styrene-modified comb-type gel in the equilibrium swelling state has more rigid network structure than both conventional gel and comb-type gel without styrene modification.
Co-reporter:Pengfei Fang;Zhe Chen;Shaoping Zhang;Shaojie Wang;Liying Wang
Polymer International 2006 Volume 55(Issue 3) pp:
Publication Date(Web):30 DEC 2005
DOI:10.1002/pi.1957
Ethylene-(vinyl acetate) copolymer (EVA)/rectorite nanocomposites were prepared by direct melt extrusion of EVA and organo-rectorite. The microstructures and thermal properties of EVA nanocomposites were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), solid-state nuclear magnetic spectroscopy, positron annihilation spectroscopy, thermal gravimetric analysis (TGA) and dynamic mechanical analysis techniques. XRD pattern and SEM images show that the intercalated structure is formed and rectorite is finely dispersed in EVA matrix. When organoclay content of the hybrid increases to 7.5 wt%, or pristine rectorite was used instead of organoclay, the crystallization behavior of EVA nanocomposite changes greatly and the ratio of the monoclinic to orthorhombic crystal increases significantly. The relative fractional free volume of the nanocomposite decreases with the increasing organo-rectorite content, and the values of damping factor (tan δ) for all nanocomposites are lower than that of pure EVA. These facts illuminate that intercalated structure restricts the segment motion and mobilization of polymer chain. TGA results of EVA nanocomposites in air indicate that deacylation of EVA is accelerated because of the catalytic effect and the thermal degradation of the main chain is delayed owing to the barrier effect of silicate layers. Copyright © 2005 Society of Chemical Industry
Co-reporter:Xingzhong Zhao;Liying Wang
Journal of Polymer Science Part B: Polymer Physics 2006 Volume 44(Issue 12) pp:1714-1724
Publication Date(Web):3 MAY 2006
DOI:10.1002/polb.20830
The effects of electron irradiation on the molecular chemical structure, conformation, mobility, and phase transition of vinylidene fluoride (VDF) and trifluoroethylene (TrFE) copolymer have been investigated with variable-temperature, solid-state 19F nuclear magnetic resonance (NMR). It has been found that electron irradiation converts all-trans conformations of both VDF-rich and TrFE-containing segments into dynamically mixed trans–gauche conformations accompanied by a simultaneous ferroelectric-to-paraelectric (or amorphous) transition. The variable-temperature 19F magic-angle-spinning spectra results show that the paraelectric phase melts at much lower temperatures in irradiated films than in an unirradiated sample. Moreover, 19F NMR relaxation data (spin–lattice relaxation times in both the laboratory and rotating frames) reveal that electron irradiation enhances the molecular motion in paraelectric regions, whereas the molecular motion in a high-temperature amorphous melt (>100 °C) is more constrained in irradiated films. Besides these physical changes, electron irradiation also induces the formation of several CF3 groups. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 1714–1724, 2006
Co-reporter:Pengfei Fang;Liying Wang;Chaohui Ye
Journal of Polymer Science Part B: Polymer Physics 2006 Volume 44(Issue 19) pp:2864-2879
Publication Date(Web):29 AUG 2006
DOI:10.1002/polb.20917
Solid-state nuclear magnetic resonance spectroscopy and relaxation measurements, together with DSC, have been used to elucidate the structures and molecular dynamics in poly(ethylene-co-vinyl acetate) (EVA). It has been found that besides immobile orthorhombic and monoclinic crystalline phases, the third mobile crystalline phase (possibly the phase) of a considerable amount (36% of total crystalline phases) appears in the EVA samples, which forms during room-temperature aging as a result of the secondary crystallization and melts at temperature somewhat higher than room temperature. Such a mobile crystalline phase has not only the well-defined chemical shift of its own, but also has different molecular mobility from the orthorhombic phase. The mobile crystalline phase is characterized by the rapid relaxation of the longitudinal magnetization, which is caused by conventional spin-lattice relaxation, while the slow relaxation of the longitudinal magnetization occurring in the orthorhombic phase is originated from the chain diffusion. In addition, the amorphous phase also contains two components: an interfacial amorphous phase and a melt-like amorphous phase. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 2864–2879, 2006
