Time-dependent mechanical characterization of poly(2-hydroxyethyl methacrylate) hydrogels using nanoindentation and unconfined compression
Time-dependent mechanical characterization of poly(2-hydroxyethyl methacrylate) hydrogels using nanoindentation and unconfined compression
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DOI：
10.1557/jmr.2008.0185
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发表时间：
2008-05-01
影响因子：
2.7
通讯作者：
Klapperich, Catherine M.
中科院分区：
文献类型：
--
作者：
Kaufman, Jessica D.;Miller, Gregory J.;Klapperich, Catherine M.
水凝胶对纳米压痕提出了独特的挑战，包括样品制备，实验参数的控制，以及机械测试仪器和数据分析的限制，这些限制最初用于较硬的材料。已经描述了水合样品在纳米压痕过程中产生的伪影，但是从水合纳米压痕中获得的材料性能尚未与从宏观尺度测试中获得的材料性能相关联。为了评估将软材料的微观和宏观测试结果相关联的最佳方法，对具有一定交联剂浓度的聚2-甲基丙烯酸羟乙酯（pHEMA）水凝胶进行了纳米压痕和无侧限压缩应力松弛试验。采用Oliver-Pharr弹性模型和Maxwell-Wiechert （j = 2）粘弹性模型对纳米压痕数据进行分析。采用Maxwell-Wiechert模型对无侧限压缩数据进行分析。该粘弹性模型能很好地拟合两次试验的应力松弛曲线。纳米压痕和无侧限压缩的时间常数有显著差异，我们认为这些差异是由于微观尺度和宏观尺度实验之间的平衡时间差异以及样品几何形状的差异。Maxwell-Wiechert平衡模量在纳米压痕和无侧限压缩之间提供了最好的一致性。此外，两种纳米压痕分析都表明，随着交联剂浓度的增加，模量也会增加，这证实了纳米压痕可以区分相似的低模量水合样品。
Hydrogels pose unique challenges to nanoindentation including sample preparation, control of experimental parameters, and limitations imposed by mechanical testing instruments and data analysis originally intended for harder materials. The artifacts that occur during nanoindentation of hydrated samples have been described, but the material properties obtained from hydrated nanoindentation have not yet been related to the material properties obtained from macroscale testing. To evaluate the best method for correlating results from microscale and macroscale tests of soft materials, nanoindentation and unconfined compression stress-relaxation tests were performed on poly-2-hydroxyethyl methacrylate (pHEMA) hydrogels with a range of cross-linker concentrations. The nanoindentation data were analyzed with the Oliver-Pharr elastic model and the Maxwell-Wiechert (j = 2) viscoelastic model. The unconfined compression data were analyzed with the Maxwell-Wiechert model. This viscoelastic model provided an excellent fit for the stress-relaxation curves from both tests. The time constants from nanoindentation and unconfined compression were significantly different, and we propose that these differences are due to differences in equilibration time between the microscale and macroscale experiments and in sample geometry. The Maxwell-Wiechert equilibrium modulus provided the best agreement between nanoindentation and unconfined compression. Also, both nanoindentation analyses showed an increase in modulus with each increasing cross-linker concentration, validating that nanoindentation can discriminate between similar, low-modulus, hydrated samples.