Andersson M, Axelsson A, Zacchi G
Department of Chemical Engineering 1, University of Lund, Sweden.
J Control Release. 1998 Jan 2;50(1-3):273-81. doi: 10.1016/s0168-3659(97)00151-x.
In many gel applications the swelling and shrinking kinetics are very important, e.g. in controlled/slow release, where the kinetics determined the rate of out-diffusion of the active component, and in gel extraction where the gel is swollen and shrunk several times. In this study swelling kinetics of poly(N-isopropylacrylamide) gel (NiPAAm gel) was determined by monitoring the swelling process using a stereo microscope and a video camera. The swelling of spherical gel bodies could conveniently be studied after a temperature change. The results obtained were treated according to the approach of Tanaka and Fillmore, in which the swelling and shrinking of a gel is described as a motion of the gel network according to the diffusion equation. This was shown to be valid when the temperature changes are kept below the critical point of the gel. However, the model fails to describe the shrinking process when passing from below to above the critical temperature. The collective diffusion coefficient (D), defined as the osmotic bulk modulus divided by the friction factor, was determined by fitting to the experimental data. D was found to increase with temperature according to the Wilke-Chang relation D = 2.0.10(-11) + 7.6.10(-17).T/mu. The results were used to simulate the swelling/shrinking process. The simulations show the importance of having sufficiently small gel bodies to achieve a short swelling time.
在许多凝胶应用中，溶胀和收缩动力学非常重要，例如在控释/缓释中，动力学决定了活性成分的外扩散速率；在凝胶萃取中，凝胶会经历多次溶胀和收缩。在本研究中，通过使用立体显微镜和摄像机监测聚（N - 异丙基丙烯酰胺）凝胶（NiPAAm凝胶）的溶胀过程来测定其溶胀动力学。温度变化后，可以方便地研究球形凝胶体的溶胀情况。根据田中（Tanaka）和菲尔莫尔（Fillmore）的方法处理所得结果，其中凝胶的溶胀和收缩被描述为凝胶网络根据扩散方程的运动。当温度变化保持在凝胶的临界点以下时，这被证明是有效的。然而，当温度从低于临界温度变为高于临界温度时，该模型无法描述收缩过程。通过拟合实验数据确定了集体扩散系数（D），其定义为渗透压模量除以摩擦系数。发现D根据威尔克 - 张（Wilke - Chang）关系式D = 2.0×10⁻¹¹ + 7.6×10⁻¹⁷·T/μ随温度升高。结果用于模拟溶胀/收缩过程。模拟结果表明，拥有足够小的凝胶体对于实现较短的溶胀时间很重要。
