Search

The heterogeneous structure of poly (vinyl alcohol)-poly(sodium acrylate) composite hydrogels (PVA-PAA gels), prepared by repeatedly freezing and thawing mixed aqueous solutions of PVA and PAA, has been studied using pulsed NMR. The free induction decay (FID) signals of the transverse magnetization for the PVA-PAA gels were measured by both Carr-Purcell-Meiboom-Gill and solid-echo pulse sequences. The FID signal was decomposed into two or three decaying signals with various spin-spin relaxation times, based upon differences in the molecular mobility that reflected structural heterogeneity. The structural heterogeneity of the PVA-PAA gel is quite different from that of PVA gel free of PAA

Deformation of poly(vinyl alcohol)–poly(sodium acrylate) composite hydrogel (PVA–PAA gel) under sinusoidally varying electric fields was studied in electrolyte solutions. The PVA–PAA gel was prepared by repeatedly freezing and thawing a mixed solution of PVA and polyacrylic acid. A cyclic bending–straightening motion of the PVA–PAA gel rods of about 1 mm in diameter have been observed in Na2CO3 aqueous solutions under the fields. The PVA–PAA gel had a response time of less than several hundreds milliseconds. The bending has also been observed in organic solvents containing an electrolyte when the organic solvent is electrolyzed. It was found that the motion of the gel under electric fields of less than 1 Hz occurred mainly through swelling due to the change of the osmotic pressure based upon the difference of the ion concentration. However, it has not been determined whether the motion at higher frequencies is caused by the osmotic effect. © 1993 John Wiley & Sons, Inc.

ポリ (3-ブチルチオフェン) ゲル (P3BTゲル) の有機溶媒中での外部電場による変形挙動を検討した. P3BTゲルは3-ブチルチオフェンと1, 8-ジ (3-チエニル) オクタンを定電流電解重合し, その生成物をTHFに浸漬することにより得た. P3BTゲルは支持電解質を含むテトラヒドロフラン (THF) 中で1.5V以上の直流電圧の作用で収縮し, また同時にオレンジ色から青色に変化することが明らかになった. これらの変化は電場に対して可逆的であった. 可視スペクトル変化, 化学ドーピングとの比較考察から, 電場による体積と色の変化はP3BTゲル中のポリチオフェン鎖の電気的なドーピングと脱ドーピングによるものと考えられた.

The influence of de electric fields on sodium acrylate—acrylamide copolymer gel near a phase transition point in acetone—water mixtures containing NaOH was studied. In the mixtures free of NaOH, the shrunken-state gel near a phase transition point was not influenced by dc electric fields, while the swollen-state gel near it shrank from its part facing to the positive electrode in dc electric fields. In the presence of NaOH, unprecedented swelling of the shrunken-state gel has been observed. The swollen-state gel showed swelling or shrinking in the field. The type of deformation was determined by the concentration of NaOH. The drift of mobile ions played a role in the deformation. The shrinking occurred through the conformational change of polymer network caused by the drift. The swelling was observed by the change of the osmotic pressure based upon the ion concentration difference between the inside and the outside of a gel.

When an electric field is applied to an ionic gel in a buffer solution, the anode side of the gel shrinks if the gel is contacting with the electrode, while it swells if the gel is placed with sufficient separation from the electrode. The changes of ion concentration profiles under an electric field are calculated, taking account of ion transports and electrochemical reactions. Combining these results with Flory's theory for the swelling of ionic gels, the above phenomena are explained. It is predicted that the swelling behavior is governed by the concentration of the dominant ions and that the swelling speed is proportional to the square of the electric current

Bending of poly(vinyl alcohol) hydrogel mixed with poly(sodium acrylate) chains, PVA–PAA gel, under the influence of dc electric fields was studied. The PVA–PAA gel was prepared by repeatedly freezing and thawing a mixture of PVA and polyacrylic acid aqueous solutions. The PVA–PAA gel was a hydrogel with the PAA chains, which were entangled with the PVA polymer network and were fixed in the gel. The PVA–PAA gel bent toward the negative electrode in electrolyte solutions under dc electric fields as did the polyelectrolyte gel with negatively charged polyions. The PVA gel, free of PAA, was insensitive to dc electric fields. The deflection of the bending and the bending speed were influenced by the filed intensity, the concentration of the polyion in the gel, and the thickness of the gel. The bending of the PVA–PAA gel was qualitatively explained by a bending theory of polyelectrolyte gel, based upon the change of the osmotic pressure due to the ion concentration difference between the inside and the outside of the gel.

微量の水分を吸着した架橋ポリメタクリル酸のナトリウム塩及びコバルト塩をハロゲン化パラフィンに分散してなる電気粘性流体のER効果について粒子鎖モデルによる解析ならびに実験結果との比較を行った. 粒子鎖モデルでは分散粒子は電場により瞬時に分極して質点双極子を形成し, かつ隣接する二つの粒子間のみに双極子間相互作用が働いて電極間で直鎖を形成すると仮定した. ER効果を反映する降伏応力に対する粒子の分散濃度, 粒径及び誘電率, 電場強度の影響を検討したところ, 導電性の低いコバルト塩粒子系流体は定性的かつ定量的にも粒子鎖モデルに従ってほぼ挙動することが明らかにされた. しかし, 導電性の高いナトリウム塩粒子系流体の挙動は粒子鎖モデルでは十分に説明できないことが分かった.

微粒子を分散した高分子ゲルの電場下における粘弾性挙動を検討した. 微粒子には少量の水分を含むポリメタクリル酸コバルト塩の粒子を, 高分子ゲルには二液反応型のシリコーンゲルをそれぞれ用いた. 試料はシリコーンゲルの反応に微粒子を所定量均一に分散させた後, 加熱することにより得た. 微粒子分散高分子ゲルは電場の作用でその粘弾性を可逆的に変化させることが明らかになった. この電気粘弾性効果は分散粒子濃度が高く, 電場印加前に微粒子が互いに接触している状態のときに観測された. 粘弾性変化の大きさは印加電場の強度, せん断ひずみの大きさと周波数などに依存した. 電場下では電流が観測された. 微粒子分散高分子ゲルの示す電気粘弾性効果はマトリックスが絶縁油である懸濁液の示すそれよりも大きいことが明らかにされた.

Transition de phase de spheres de gels ionises de N-isopropylacrylamide avec des diametres compris entre 0,2 et 1 μm