Department of Chemical Engineering, Massachusetts Institute of Technology, 77 Massachusetts Ave., Cambridge, Massachusetts 02139, USA.
Langmuir. 2011 Sep 6;27(17):10691-8. doi: 10.1021/la201935r. Epub 2011 Aug 16.
The thermodynamics of temperature-responsive polymeric layers was analyzed using a two-state coil to globule model to which the van't Hoff relationship was applied. For soluble homopolymer poly(N-isopropylacrylamide (pNIPAAm), enthalpies of transition, ΔH(vH), were calculated using varations in ultraviolet-visible (UV-vis) spectroscopy with temperature to be 8400 ± 30 and 1652 ± 4 kJ mol-cooperative unit(-1) for standard synthesis and initiated chemical vapor deposition (iCVD), respectively. For the insoluble surface-bound layer of cross-linked iCVD poly(N-isopropylacrylamide-co-di(ethylene glycol) divinyl ether) [p(NIPAAm-co-DEGDVE)], ΔH(vH) was determined to be 810 ± 30 kJ mol-cooperative unit(-1) using quartz crystal microbalance with dissipation monitoring (QCM-D). Microcalorimetry measurements showed the enthalpies per mole NIPAAm monomer to be 5.8 ± 0.2, 3.5 ± 0.6, and 3.1 ± 0.3 kJ mol-NIPAAm(-1), resulting in cooperative unit sizes of 1460 ± 60, 470 ± 80, and 260 ± 30 monomer units for the standard pNIPAAm, iCVD pNIPAAm, and p(NIPAAm-co-DEGDVE) systems, respectively. These values indicate that both per monomer enthalpic contribution as well as cooperative unit size are primary factors contributing to the variations in van't Hoff enthalpies for the three systems studied. Diffusion of bovine serum albumin (BSA) into swollen p(NIPAAm-co-DEGDVE) films below its lower critical solution temperature was elucidated via QCM-D measurements. These data provided a calculated diffusion coefficient of (3.5 ± 0.1) × 10(-14) cm(2) s(-1) of BSA into the swollen hydrogel film with a mesh size of 6.0 ± 0.2 nm (compared to the hydrodynamic radius of BSA, r(H) = 3.36 nm).
使用两态线圈到球粒模型分析了温度响应聚合物层的热力学，该模型应用了范特霍夫关系。对于可溶性均聚物聚（N-异丙基丙烯酰胺）（pNIPAAm），通过紫外-可见（UV-vis）光谱随温度的变化计算了焓变，标准合成和引发化学气相沉积（iCVD）的ΔH（vH）分别为 8400 ± 30 和 1652 ± 4 kJ mol-协同单位（-1）。对于交联 iCVD 聚（N-异丙基丙烯酰胺-共-二（乙二醇）二乙烯基醚）[p（NIPAAm-co-DEGDVE）]的不溶性表面结合层，通过石英晶体微天平耗散监测（QCM-D）确定 ΔH（vH）为 810 ± 30 kJ mol-协同单位（-1）。微量热法测量表明，每摩尔 NIPAAm 单体的焓分别为 5.8 ± 0.2、3.5 ± 0.6 和 3.1 ± 0.3 kJ mol-NIPAAm（-1），导致标准 pNIPAAm、iCVD pNIPAAm 和 p（NIPAAm-co-DEGDVE）系统的协同单位尺寸分别为 1460 ± 60、470 ± 80 和 260 ± 30 个单体单元。这些值表明，对于研究的三个系统，每个单体的焓贡献以及协同单位的大小都是导致范特霍夫焓变化的主要因素。通过 QCM-D 测量阐明了牛血清白蛋白（BSA）在低于其下临界溶液温度扩散到溶胀的 p（NIPAAm-co-DEGDVE）膜中的情况。这些数据提供了 BSA 扩散到溶胀水凝胶膜中的计算扩散系数（3.5 ± 0.1）×10（-14）cm（2）s（-1），该膜的网格尺寸为 6.0 ± 0.2nm（与 BSA 的水动力半径 r（H）= 3.36nm 相比）。
