Effect of hydrogen bonds on gelation by introduction of carboxyl groups in the free‐radical crosslinking copolymerization of butyl methacrylate with 1,6‐hexanediol dimethacrylate

The preliminary study of the effect of physical crosslinking on the gelation in monovinyl/divinyl copolymerizations is described. Thus, mono(2‐methacryloyloxyethyl) succinate was added to the crosslinking copolymerization of butyl methacrylate with 1,6‐hexanediol dimethacrylate and the gelation was explored in terms of the effect of hydrogen bonds formed between carboxyl groups introduced into the primary polymer chain.     

Concerted and sequential Coulomb explosion processes of N2O in intense laser fields by coincidence momentum imaging

The Coulomb explosion dynamics of N2O in intense laser fields (800 nm, 60 fs, approximately 0.16 PWcm2) is studied by the coincidence momentum imaging method. From the momentum correlation maps obtained for the three-body fragmentation pathway, N2O3+-->N++N++O+, the ultrafast structural deformation dynamics of N2O prior to the Coulomb explosion is extracted. It is revealed that the internuclear N-N and N-O distances stretch simultaneously as the bond angle less than approximately N-N-O decreases. In addition, two curved thin distributions are identified in the momentum correlation maps, and are interpreted well as those originating from the sequential dissociation pathway, N2O3+-->N++NO2+-->N++N++O+.     

The effect of various substances on the suppression of the bitterness of quinine-human gustatory sensation,binding, and taste sensor studies

The purpose of this study was to quantify the degree of suppression of the perceived bitterness of quinine by various substances and to examine the mechanism of bitterness suppression. The following compounds were tested for their ability to suppress bitterness: sucrose, a natural sweetener; aspartame, a noncaloric sweetener; sodium chloride (NaCl) as the electrolyte; phosphatidic acid, a commercial bitterness suppression agent; and tannic acid, a component of green tea. These substances were examined in a gustatory sensation test in human volunteers, a binding study, and using an artificial taste sensor. Sucrose, aspartame, and NaCl were effective in suppressing bitterness, although at comparatively high concentrations. An almost 80% inhibition of bitterness (calculated as concentration %) of a 0.1 mM quinine hydrochloride solution required 800 mM of sucrose, 8 mM of aspartame, and 300 mM NaCl. Similar levels of bitterness inhibition by phosphatidic acid and tannic acid (81.7, 61.0%, respectively) were obtained at much lower concentrations (1.0 (w/v)% for phosphatidic acid and 0.05 (w/v)% for tannic acid). The mechanism of the bitterness-depressing effect of phosphatidic acid and tannic acid was investigated in terms of adsorption and masking at the receptor site. With phosphatidic acid, 36.1% of the bitterness-depressing effect was found to be due to adsorption, while 45.6% was due to suppression at the receptor site. In the case of 0.05 (w/v)% tannic acid, the total bitterness-masking effect was 61.0%. The contribution of the adsorption effect was about 27.5% while the residual masking effect at the receptor site was almost 33%. Further addition of tannic acid (0.15 (w/v)%), however, increased the bitterness score of quinine, which probably represents an effect of the astringency of tannic acid itself. Finally, an artificial taste sensor was used to evaluate or predict the bitterness-depressing effect. The sensor output profile was shown to reflect the depressant effect at the receptor site rather well. Therefore, the taste sensor is potentially useful for predicting the effectiveness of bitterness-depressant substances.     

Microrheology of polysaccharide nanogel-integrated system

The viscoelastic behavior of a cholesterol-modified pullulan (CHP) nanogel at various concentrations was measured using passive particle-tracking microrheology. Microrheology measures stress–strain relationships in small volumes of material by monitoring the response of probes embedded in the medium. Although microrheology is a useful way to overcome sample volume limitations, the application of the method to CHP nanogel systems has not been reported. The viscoelastic spectra of the CHP nanogels obtained from the microrheological measurements were in good agreement with the bulk rheological measurements for each sample, demonstrating that microrheological measurement is effective in CHP nanogel systems. The gelation behavior of CHP nanogel dispersions containing pullulans of different molecular weights was also investigated by microrheology. CHP nanogels made from 1.0 or 4.0?×?10⁵ molecular weight pullulans formed a macrogel at around 3.0 wt%, whereas the CHP nanogel consisting of 0.55?×?10⁵ molecular weight pullulan did not form a macrogel. This suggests that the mechanical properties of the system can be controlled by the molecular weight of the pullulan used. These insights into gelation behavior should be useful in predicting the most favorable conditions for developing novel materials.     

Revisiting structure of silica gels from water glass: an 1H and 29Si MAS and CP-MAS NMR study

The silica gels, derived from water glass solution with pH adjusted at 3.0 and 9.9, were revisited to investigate their constitution, although water glass has been studied for last tens of decades on gelation. Solid-state nuclear magnetic resonance spectroscopy was applied to the nuclei ¹H and ²⁹Si, by the use of magic angle spinning (MAS), ¹H → ²⁹Si CP-MAS (CP: cross-polarization), and modern techniques such as 2D HETCOR (two dimensional heteronuclear correlation), and variable-contact time CP techniques. Gelation time (t_gel) showed U-letter shape dependence on pH. All gels consisted of Qⁿ groups (n: 2, 3, and 4), where Qⁿ stands for a silicate unite [(O_1/2)_nSi (–O^?)_4?n] (n: 0–4). The analysis of the ¹H → ²⁹Si CP kinetics and ¹H-²⁹Si HETCOR spectra elucidated the presence of four kinds of ¹H nuclei, i.e., those giving a peak at 6.9 ppm in chemical shift δ: ¹H–OSi hydrogen bonded to H₂O molecules; one at 4.3 ppm: ¹H of adsorbed water molecules, hydrogen-bonded to the silanol groups; one at 1.7 ppm: ¹H–OSi confined in the gel lattice, including that forming aggregations like Si–O^H/_NaO–Si; and one at 4.2 ppm: ¹H of water molecules on the outermost hydration layer.     

Morphological study on diffusion‐limited aggregates of poly(ethylene oxide) on alkali halides

When poly(ethylene oxide) was crystallized on a fresh cleavage surface of alkali halides from solution in isoamyl acetate, diffusion‐limited‐aggregate dendrites were formed. Their patterns varied, depending on the kind of substrate on which the poly(ethylene oxide) crystallized: On a KCl substrate, rather ordered dendrites grew with fibrillar crystallites aligning roughly in the 〈110〉_KCl direction, and coarse dendritic clusters formed on NaCl and KBr during the initial stage of their growth. The dendrites grew and matured to sheet the whole surface of alkali halides with a uniform thickness, and subsequently, tetragonal lamellae formed on it through the spiral growth mechanism or the primary nucleation process. Tetragonal lamellar crystals grew with their diagonals parallel to fibrillar crystallites of dendrites. Their orientation did not result from direct, epitaxial contact with the alkali halide substrate but depended on the fibrillar orientation of the underlying sheeted layer. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 2421–2430, 2002     

Effect of hydrogen bonds on intermolecular crosslinking reaction by introduction of carboxyl groups in free-radical crosslinking monomethacrylate/dimethacrylate copolymerizations

The effect of physical interaction through hydrogen bonds on the intermolecular crosslinking reaction leading to the promoted gelation in free-radical crosslinking monovinyl/divinyl copolymerizations was discussed from the standpoint of the control of network formation. The solution copolymerizations of benzyl methacrylate (BzMA) with 2 mol% of 1,6-hexanediol dimethacrylate in t-butylbenzene were conducted in the absence and presence of different amounts of mono(2-methacryloyloxyethyl) succinate (MMOES). Gelation was promoted by the addition of MMOES and the ratio of the actual gel point to the theoretical one became smaller; this would be related to the formation of hydrogen bonds between carboxyl groups introduced into prepolymer and growing polymer radical. As an extension of the above discussion, we treated the effect of hydrogen bonds on the gelation in the crosslinking BzMA/triicosaethylene glycol dimethacrylate copolymerization. The addition of MMOES obviously promoted the gelation. The ratio of the actual gel point to the theoretical one calculated according to Stockmayer's equation [J. Chem. Phys. 12 (1944) 125] was obtained as 1.9, very close to unity.     

Salt effect on the heat-induced association behavior of gold nanoparticles coated with poly(N-isopropylacrylamide) prepared via reversible addition-fragmentation chain transfer (RAFT) radical polymerization

Poly(N-isopropylacrylamide) (PNIPAM) with a narrow molecular weight distribution was prepared by reversible addition-fragmentation chain transfer (RAFT) radical polymerization. A dithioester group at the chain end of PNIPAM thus prepared was cleaved by treating with 2-ethanolamine to provide thiol-terminated PNIPAM with which gold nanoparticles were coated via reactions of the terminal thiol with gold. The thermoresponsive nature of the maximum wavelength of the surface plasmon band and hydrodynamic radius (Rh) for the PNIPAM-coated gold nanoparticles were found to be sensitively affected by added salt. In pure water, Rh for the PNIPAM-coated gold nanoparticles at 40 degrees C (>lower critical solution temperature (LCST)) was smaller than that at 25 degrees C (相似文献