Boral Shilpi, Gupta Amar Nath, Bohidar H B
Polymer and Biophysics Laboratory, School of Physical Sciences, Jawaharlal Nehru University, New Delhi, India.
Int J Biol Macromol. 2006 Nov 15;39(4-5):240-9. doi: 10.1016/j.ijbiomac.2006.03.028. Epub 2006 Apr 1.
Controlled osmotic swelling and de-swelling measurements have been performed on gelatin, a polyampholyte, hydrogels suspended in water-ethanol marginal solvent at room temperature (20 degrees C) where the alcohol concentration was changed from 0 to 100% (v/v). The change in gel mass was monitored as function of time until osmotic equilibrium was established with the surrounding solvent. It was observed that osmotic pressure of polymer-solvent mixing, pi(m)<<pi(el) (pi(el) being the osmotic pressure due to network elasticity). The osmotic pressure arising from ionic contributions, pi(ion) was found to play a significant role in controlling volume phase transitions. For gelatin hydrogels, total swelling pressure of gel, pi(tot) could be related to gelatin volume fraction phi(2), relaxed volume of network V(0), and crosslink density v(e) as: pi(tot)/RT approximately -(v(e)/V(0))[phi(2)(1/3)-phi(2)/2]+(rho(0)exp(phi(2)/2)) independent of gel pH and swelling time (rho(0) is the reference gelatin charge density at phi(2)=0.01). The entire experimental data generated collapsed onto a single master plot. Asymmetric volume transition was observed about iso-electric pH. Results are compared with those obtained for strong bio-polyelectrolyte gels, and chemically crosslinked gelatin gels.
在室温（20摄氏度）下，对明胶（一种聚两性电解质）水凝胶进行了可控的渗透溶胀和去溶胀测量，该水凝胶悬浮于水 - 乙醇的边缘溶剂中，其中乙醇浓度从0变化到100%（v/v）。监测凝胶质量随时间的变化，直至与周围溶剂建立渗透平衡。观察到聚合物 - 溶剂混合的渗透压π(m) << π(el)（π(el) 是由于网络弹性产生的渗透压）。发现由离子贡献产生的渗透压π(ion) 在控制体积相变中起重要作用。对于明胶水凝胶，凝胶的总溶胀压力π(tot) 可以与明胶体积分数φ(2)、网络的松弛体积V(0) 和交联密度v(e) 相关联，表达式为：π(tot)/RT ≈ -(v(e)/V(0))[φ(2)^(1/3) - φ(2)/2] + (ρ(0)exp(φ(2)/2))，与凝胶pH值和溶胀时间无关（ρ(0) 是φ(2) = 0.01 时的参考明胶电荷密度）。生成的所有实验数据都汇聚到一个单一的主曲线上。在等电pH附近观察到不对称的体积转变。将结果与强生物聚电解质凝胶和化学交联明胶凝胶所获得的结果进行了比较。
