Microgel suspensions have garnered significant interest in fundamental research due to their phase transition between liquid-like to paste-like behaviors stemming from tunable interparticle and particle–solvent interactions. Particularly, stimuli-responsive microgels undergo faster volume changes in response to external stimuli in comparison to their bulk counterparts, while maintaining their structural integrity. Here, concentrated and diluted suspensions of poly(N-isopropylacrylamide) (PNIPAm) microgels are dispersed to different packing fractions in water for the characterizations of temperature-responsive rheological responses. In the intrinsic volume phase transition (VPT), polymer chains collapse, and microgels shrink to smaller sizes. Additionally, the intermicrogel and microgel–solvent interactions vary in VPT, which results in microgel clusters that significantly affect the linear shear moduli of suspensions. The effect of the temperature ramp rate of PNIPAm microgel suspensions on rheological responses is characterized. Moreover, the effect of the mass fraction of microgels on the relative viscosity of dilute microgel suspensions is investigated. These results shed light on understanding the heating and cooling rate-dependent temperature responsiveness of PNIPAm microgel suspensions, establishing pathways to regulate the rheological characteristics in temperature-responsive microgel-based platforms. Therefore, this work envisions technological advancements in different fields such as drug delivery, tissue engineering, and diagnostic tools.

中文翻译：

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具有温度依赖性流变响应的 3D 打印聚（N-异丙基丙烯酰胺）微凝胶悬浮液

微凝胶悬浮液因其可调节的颗粒间和颗粒-溶剂相互作用而在液体状到糊状行为之间的相变而引起了基础研究的极大兴趣。特别是，与大块对应物相比，刺激响应性微凝胶在响应外部刺激时经历更快的体积变化，同时保持其结构完整性。在此，将聚（N-异丙基丙烯酰胺）（PNIPAm）微凝胶的浓缩和稀释悬浮液分散到水中的不同填充部分，以表征温度响应流变响应。在本征体积相变 (VPT) 中，聚合物链塌陷，微凝胶收缩至更小的尺寸。此外，VPT 中微凝胶间和微凝胶-溶剂相互作用发生变化，这导致微凝胶簇显着影响悬浮液的线性剪切模量。表征了 PNIPAm 微凝胶悬浮液的升温速率对流变响应的影响。此外，还研究了微凝胶的质量分数对稀微凝胶悬浮液相对粘度的影响。这些结果有助于理解 PNIPAm 微凝胶悬浮液的加热和冷却速率依赖性温度响应，建立调节基于温度响应微凝胶的平台的流变特性的途径。因此，这项工作展望了药物输送、组织工程和诊断工具等不同领域的技术进步。