Giant reduction in dynamic modulus of kappa-carrageenan magnetic gels

Effects of magnetization on the complex modulus of kappa-carrageenan magnetic gels have been investigated. The magnetic gel was made of a natural polymer, kappa-carrageenan, and a ferrimagnetic particle, barium ferrite. The complex modulus was measured before and after magnetization of the gel by dynamic viscoelastic measurements with a compressional strain. The gels showed a giant reduction in the storage modulus of approximately 10(7) Pa and also in the loss modulus of approximately 10(6) Pa due to magnetization. The reduction increased with increasing volume fraction of ferrite, and it was nearly independent of the frequency. It was also found that the change in the modulus was nearly independent of the magnetization direction and irradiation time of the magnetic fields to the gel. The magnetic gels demonstrating the giant reduction in the dynamic modulus showed a large nonlinear viscoelastic response. It was observed that the magnetic gel was deformed slightly due to magnetization. The observed giant complex modulus reduction could be attributed to the nonlinear viscoelasticity and deformation caused by magnetization. Magnetism, nonlinear viscoelasticity, and effects of magnetization on the morphological and shape changes were discussed.     

Photo-tunable Stationary Phases for Semi-micro HPLC

To develop photo-tunable chromatography, several azobenzene derivatives were immobilized or modified on silica gels or incorporated into polymers. The supports prepared were used as stationary phases in semi-micro HPLC, and the photo-dependence of their retention evaluated. On these stationary phases, the retention measured with 2-propanol in hexane was increased by UV irradiation; in contrast, the retention was decreased when methanol was used as mobile phase. It was assumed that the polarity of the stationary phase increases when the molecular structure of the azobenzene moieties changes from the trans to the cis form. On irradiation of the column with visible light after UV irradiation and with methanol as mobile phase, the change of retention proved to be reversible. However, this reverse change was less dramatic than the initial change. Such retention behavior is attributable to photo-isomerization of the azobenzene moieties. These findings will be exploited in our development of new photo-tunable stationary phases and new photo-controlled separation systems.     

Viscoelastic and photoresponsive properties of microparticle/liquid-crystal composite gels: tunable mechanical strength along with rapid-recovery nature and photochemical surface healing using an azobenzene dopant

We investigated viscoelastic and photoresponsive properties of the microparticle/liquid-crystal (LC) composite gels. The mechanical strength of the colloidal gels can be widely tuned by varying particle concentrations. With increasing particle concentration, a storage modulus of the particle/LC composite gels increased and reached over 10(4) Pa, showing good self-supporting ability. We demonstrated for the first time that the particle/LC composite gels exhibited rapid and repetitive recovery of the mechanical strength after large-amplitude oscillatory breakdown. In addition, photoresponsive properties of the composite gels were investigated by the cis-trans photoisomerization of the azobenzene compound doped into the host LCs. The photochemical gel-sol transition could be repeatedly induced by changing the phase structure of the host LCs between nematic and isotropic, using the photoisomerization. The particle/LC composite gels can be applied to optically healable materials by the site-selective gel-sol transition based on the photochemical modulation of the phase structures of the host LCs.     

Photoinduced swelling control of amphiphilic azoaromatic polymer membrane

To control the swelling of polymer membrane by photoirradiation amphiphilic azoaromatic polymer membranes were prepared and a photoinduced change in the swelling degree of water was investigated. The azobenzene moiety in the side chain of the polymer was isomerized from trans form to cis form by ultraviolet (UV) irradiation and reverse isomerization was found by visible light irradiation. The swelling degree of the polymer membrane for water in the dark was decreased by UV radiation, and when visible light irradiation was carried out in the polymer membrane the degree of swelling recovered to the original level. The swelling degree decreased with an increase in the mole fraction of the azobenzene moiety in the dark and under UV irradiation. The deswelling degree of the polymer membrane by UV irradiation also decreased with an increase in the mole fraction of the azobenzene moiety. This reversible change in the swelling degree was considered to be caused by the photoisomerization of the azobenzene moiety in the polymer membrane.     

How can azobenzene block copolymer vesicles be dissociated and reformed by light?

The underlying mechanism of UV light-induced dissociation and visible light-induced reformation of vesicles formed by an azobenzene diblock copolymer was investigated. These processes were studied in situ by monitoring changes in optical transmittance of the vesicular solution while being exposed to UV or visible light irradiation. The results indicate that the UV-induced dissociation of the vesicles results from their thermodynamic instability due to a shift of the hydrophilic/hydrophobic balance arising from the trans-cis isomerization, while their reaggregation takes place upon visible light irradiation that shifts the hydrophilic/hydrophobic balance in the opposite direction after the reverse cis-trans isomerization. The study suggests a specific design principle for obtaining UV light-dissociable and visible light-recoverable vesicles based on azobenzene block copolymers. On one hand, the structure of azobenzene moiety used in the hydrophobic block should have a small (near zero) dipole moment in the trans form and a significantly higher dipole moment in the cis form, which ensures a significant increase in polarity of the hydrophobic block under UV light irradiation. On the other hand, the hydrophilic block should be weakly hydrophilic. The conjunction of the two conditions can make the light-induced shift of the hydrophilic/hydrophobic balance important enough to lead to the reversible change in vesicular aggregation.     

Discrimination of structural order and chromophore aggregation as factors effecting the photo-reorientation of azobenzene in copolyglutamate LB films

Photo-reorientation experiments have been performed on LB films of polyglutamates with azobenzene side chains and copolyglutamates with azobenzene moieties and non-photochromic mesogens as side chains. Incorporation of the non-photochromic phenylbenzoate and methyl-substituted biphenyl side chains prevents aggregation of the chromophores, but does not change the LB film structure. Photo-reorientation upon irradiation with polarized light is suppressed by the side-chain structure in the LB film, independent of chromophore aggregation. This structure is disrupted if the amount of side chains which can be photo-isomerized exceeds a critical number. After the structure has been disrupted, photo-reorientation is possible. Not only the chromophores, but also the non-photochromic side chains are reoriented in a cooperative manner.     

Negative Electrorheological Effect of Silicone Gels Containing Barium Titanate

Summary: We observed the negative electrorheological phenomenon on swollen silicone gels containing barium titanate. Contrary, no negative electrorheological effect was observed in unswollen silicone gels containing barium titanate and silicon gels without barium titanate. The change in storage modulus increased with increasing DC electric field strength. The effects of frequency, degree of swelling, and the field strength have been investigated.

Electric‐field dependence of the change in storage modulus at f = 0.1 Hz for swollen silicone/BaTiO₃ gels with varying CAT content; (○): CAT 0.1, (□): CAT 0.2, (⋄): CAT 0.3, (×): SG.     

Photoliquefiable Ionic Crystals: A Phase Crossover Approach for Photon Energy Storage Materials with Functional Multiplicity

Ionic crystals (ICs) of the azobenzene derivatives show photoinduced IC–ionic liquid (IL) phase transition (photoliquefaction) upon UV‐irradiation, and the resulting cis‐azobenzene ILs are reversibly photocrystallized by illumination with visible light. The photoliquefaction of ICs is accompanied by a significant increase in ionic conductivity at ambient temperature. The photoliquefaction also brings the azobenzene ICs further significance as photon energy storage materials. The cis‐IL shows thermally induced crystallization to the trans‐IC phase. This transition is accompanied by exothermic peaks with a total ΔH of 97.1 kJ mol^?1, which is almost double the conformational energy stored in cis‐azobenzene chromophores. Thus, the integration of photoresponsive ILs and self‐assembly pushes the limit of solar thermal batteries.     

含有4,4′-双(甲基丙烯酰胺基)偶氮苯水凝胶的合成及其在结肠位药物释放的动物实验

合成了不同链长的甲基丙烯酸酯、甲基丙烯酰胺及丙烯酸与 4 ,4′ 双 (甲基丙烯酰胺基 )偶氮苯交联共聚的功能凝胶 .三维网络结构通过压缩弹性模量、有效交联密度及聚合物与溶剂间的相互作用参数进行了表征 .主要研究了这类凝胶在pH2 2和pH7 4的缓冲溶液的平衡溶胀特性及其偶氮交联基团在体内的降解行为 ,并讨论了其降解机制 .凝胶在胃部的性能稳定 ,既不发生溶胀 ,亦不发生降解 ;但在盲肠内偶氮交联基因可发生降解 .其降解率与凝胶的平衡溶胀程度有一个很好的关联 :交联程度、疏水基侧链的长度及含量对凝胶溶胀行为的影响结果与这些因素对偶氮交联基团体内降解的影响结果完全一致 .通过调节这些因素不仅可以控制凝胶的溶胀程度 ,而且可以控制偶氮交联基团在体内的降解行为 .     

pH响应性P(MMA-co-MAA-co-HEMA)微凝胶的制备及其性能

利用预乳化乳液法制备了不同单体配比的聚(甲基丙烯酸甲酯-co-甲基丙烯酸-co-甲基丙烯酸羟乙酯)(P(MMA-co-MAA-co-HEMA))微凝胶分散液;采用透射电子显微镜、动态光散射仪研究了微凝胶的微观形态、粒径大小及其溶胀率;利用试管倒转法对微凝胶分散液的凝胶化相转变行为进行了研究,借助椎板流变仪考察了所形成胶态凝胶的储能模量与单体配比、微凝胶分散液浓度和温度的关系.结果表明,所制备的微凝胶的数均粒径为90 nm左右,当MMA与MAA的投料质量不变时,随着HEMA含量的增加,分散液凝胶化所需的临界最小浓度增大,临界最大pH值减小,胶态凝胶的储能模量增加.当保持单体MMA与HEMA的投料质量不变时,随着单体MAA投料质量的增多,微凝胶的数均粒径和溶胀率增大,胶态凝胶的储能模量先升高后降低;当MAA占单体总摩尔数的25%时,浓度为15 wt%的微凝胶分散液在扫描频率为100 rad/s时,胶态凝胶的储能模量最高可达2×104Pa.这类微凝胶分散液在组织工程支架材料方面有潜在的应用价值.     

Photo-response assisted enantiomer separations on an azobenzene-modified gamma-cyclodextrin stationary phase in micro-HPLC.

The photo-responses of the retention and enantioseparation of several optical isomers were evaluated using an azobenzene-modified gamma-cyclodextrin stationary phase (Az gamma-CDSP) in micro-HPLC. UV light irradiation induced a decrease in the retention and the chiral selectivity for N-(3,5-dinitrobenzoyl)-1-phenylethylamine (DNBPEA) and N-(3,5-dinitrobenzoyl)-1-(1-naphtylethyl)amine (DNBNEA), while an increase was induced for dansylphenylalanine (DnsPhe) using a mixture of methanol and aqueous phosphate buffer as the mobile phase. No changes in the retention and the enantiomer separation of benzoin were observed with UV light irradiation. The retention behaviors were recovered by visible-light irradiation. It was speculated that the main factor of the change in the retention behavior was a change in the pi-pi interaction due to the azobenzene moiety of the stationary phase with photo-irradiation. Comparing the retention behavior before and after UV light irradiation, a suitable condition for obtaining a better resolution and enantiomer separation would be chosen using Az gamma-CDSP.     

Sunlight helps self-healing of liquid-crystalline gels of lignin-graft PMMA doped with GO and azobenzene

ABSTRACT

Self-healing soft matters have attracted much attention because of their extraordinary performance for extending working life of materials. To utilise sunlight to help self-healing of liquid-crystalline gels composed of one low-mass liquid crystal (5CB) and one hyperbranched polymer (lignin-graft-PMMA), a low content of graphene oxide (GO) and one azobenzene compound are doped as photoresponsive additives. Upon irradiation of UV light, the azobenzene can induce gel-sol transition due to the photoinduced molecular cooperative motion, thus surface dents can be repaired. On the other hand, GO functions as the nanoscale heat source because of the photothermal effect under exposure of visible (VIS) or NIR light, heating the gel to undergo gel-sol transition for mending surface cracks. In addition, the mechanical properties of the gels are also improved by addition of GO. This NIR-VIS-UV light responsive liquid-crystalline gel shows highly effective gel-sol transition upon direct solar radiation because of the coexistence of both photochemical and photothermal effect. Furthermore, these sunlight-assistant self-healing gels also show anisotropy and orientation just like other liquid-crystalline materials, enabling them to find various advanced applications with longer service life.     

Effect of gamma irradiation on the thermal and rheological properties of grain amaranth starch

Physical properties of starch from two cultivars of gamma-irradiated grain amaranth with different amylose content were investigated. Pasting viscosities decreased continuously with the increase in dosages of irradiation. Furthermore, different irradiation dosages resulted in modification of the thermal properties and crystallinity of starch. Dynamic oscillation on shear was also employed, temperature and frequency sweeps showed that changes in storage modulus and loss modulus were significant, with Tibet Yellow producing more elastic gels as compared to Hy030 at different irradiation dosages.     

Photoinduced high-quality ultrathin SiO2 film from hybrid nanosheet at room temperature

The paper describes a flexible approach to building up high-quality ultrathin SiO2 films under deep UV light irradiation at room temperature. The ultrathin hybrid nanosheet possessing polyoctahedral silsesquioxane (POSS) has been designed to prepare densely packed ultrathin POSS films by the Langmuir-Blodgett (LB) technique. The LB technique enables POSS to have a multilayered structure with nanoscale precision. The films' hardness and modulus changed considerably from 0.1 and 2.6 GPa to 1.7 and 32.2 GPa, respectively, after deep UV light irradiation. Subsequent FTIR measurements revealed that the organic components were removed completely and that the POSS cage structure turned to an Si-O-Si network structure. X-ray photon spectroscopy also confirmed high-quality SiO2 formation with no suboxides.     

偶氮苯聚合物的光控图案化

将自组装得到的聚苯乙烯胶体晶体,利用反应离子刻蚀和软刻蚀法复形到偶氮苯聚合物膜表面,获得六方非紧密排列的偶氮苯聚合物半球状阵列微图案膜。采用场发射扫描电子显微镜(FESEM)、原子力显微镜(AFM)和接触角测量仪等对膜的微阵列结构和表面润湿性能进行了表征。研究了光照对膜微图案结构和润湿性能的影响。结果表明:基于偶氮苯基团的光致取向特性,偶氮苯聚合物膜的微图案在偏振光照射下,可由初始的半球状阵列微结构形变成纺锤状和椭球状等结构,这种微结构的改变可以改变膜表面润湿性,实现偶氮苯聚合物膜表面不同微图案和润湿性能的光照调控。     

Light-induced water swelling/shrinking recovery of hydrogels based on chemically cross-linked poly (vinyl alcohol)

Photoresponsive hydrogels with high performance are of considerable interest because of their wide application. In this paper, a kind of smart poly (vinyl alcohol) (PVA) hydrogel is obtained using 4, 4′-azodibenzoic acid as cross-link agent. The hydrogels have the ability of swelling and shrinking reversibly under irradiation by ultraviolet or visible light because azobenzene groups show trans–cis isomerization under suitable light wavenumber. Under UV irradiation, azobenzene takes the cis structure which leads to volume decreases; macroscopically, shrinking can be observed. Under visible light irradiation, the volume recovers, and swelling can be observed macroscopically. Hydrogels have excellent swelling/shrinking recovery properties even after 12 cycles. The procedure achieves loop control of the transformation from light energy to mechanical energy.     

Photo-responsive properties of poly(NIPAM-co-AAc) microgel particles with absorbed, hydrophobically modified organic salts

The absorption of two hydrophobically modified organic salts (HMOSs), containing azobenzene units, into poly(N-isopropylacrylamide-co-acrylic acid) microgel particles has been studied at pH 8 and 20 °C. These dispersions were then irradiated with UV light (wavelength 365 nm) for 10 min to observe the effect on the microgel particle properties, such as the adsorbed amount of the HMOS, the particle size, and the electrophoretic mobility. We show that irradiation of these dispersions with UV light can lead to induced, partial desorption of the HMOS molecules, with concomitant changes in the size and electrophoretic mobility of the microgel particles. This is due to a conformational switch (trans-form to cis-form) in the HMOS molecules, which reduces the strength of the hydrophobic interaction between the HMOS molecules and the isopropyl moieties within the microgel network. Moreover, the original absorbed amounts, size, and electrophoretic mobility values can be largely restored after storage in the dark for extended periods.     

Interplay between gelation and phase separation in aqueous solutions of methylcellulose and hydroxypropylmethylcellulose

Thermally induced gelation in aqueous solutions of methylcellulose (MC) and hydroxypropylmethylcellulose (HPMC) has been studied by rheological, optical microscopy, and turbidimetry measurements. The structural and mechanical properties of these hydrogels are dominated by the interplay between phase separation and gelation. In MC solutions, phase separation takes place almost simultaneously with gelation. An increase in the storage modulus is coupled to the appearance of a bicontinuous structure upon heating. However, a thermal gap exists between phase separation and gelation in the case of HPMC solutions. The storage modulus shows a dramatic decrease during phase separation and then rises in the subsequent gelation. A macroporous structure forms in the gels via "viscoelastic phase separation" linked to "double phase separation".     

Photocontrol of supramolecular architecture in azopolymers: Achiral and chiral aggregation

The absorption spectra and circular dichroism responses upon irradiation with 488 nm circularly polarized light (CPL) have been studied on polymeric films processed from two nematic copolymers containing azobenzene chromophores. Influence of the aggregation and orientation of azobenzenes on the photoinduced chiroptical properties has been analyzed. Moreover, polymeric films and 4 μm planar cells filled with the copolymers were studied by polarized optical microscopy (POM) with the aim of investigating the change of macroscopic optical properties and textures of azopolymers upon irradiation with CPL.     

The effects of solvent type and aging on structural development in poly(vinyl chloride) thermoreversible gels

We investigated the effects of solvent type (mono‐ester vs. di‐ester solvent) and aging on the structural development in the poly(vinyl chloride)/butyl benzoate (PVC/BB) and PVC/dibutyl phthalate(DBP) gels, as well as on their viscoelastic and mechanical behaviors. It was found that aged PVC/DBP gels held at RT for 7 days exhibit an improvement of about 100% in storage modulus (G′) compared to fresh gels, with a sudden drop in G′ around 50 °C, whereas the storage moduli of the PVC/BB gels decrease monotonically with temperature, irrespective of the postaging time. These different behaviors of the PVC/BB and PVC/DBP gels arise mainly because of the difference in the network structure produced by the formation of the polymer‐solvent complex between the C?O groups of the solvent and the polarized hydrogen moieties of PVC, as was confirmed with small angle X‐ray scattering and uniaxial tensile experiments. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 263–271, 2008