Guan Zhecun, Katla Sai Krishna, Dahanayake Vidumin, Bae Jinhye
Department of NanoEngineering, University of California San Diego, La Jolla, California 92093, United States.
Anton Paar USA, Inc., Ashland, Virginia 23005, United States.
ACS Appl Polym Mater. 2024 Mar 21;6(23):14095-14105. doi: 10.1021/acsapm.3c03230. eCollection 2024 Dec 13.
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(-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.
微凝胶悬浮液因其颗粒间和颗粒-溶剂相互作用可调，在从类液体到类糊体行为的相变过程中，在基础研究中引起了极大关注。特别是，与本体材料相比，刺激响应性微凝胶在外部刺激下会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在水中至不同的填充分数，以表征温度响应流变学响应。在固有体积相变（VPT）中，聚合物链坍塌，微凝胶收缩至更小尺寸。此外，在VPT中，微凝胶间和微凝胶-溶剂相互作用会发生变化，这会导致微凝胶簇显著影响悬浮液的线性剪切模量。对PNIPAm微凝胶悬浮液的升温速率对流变学响应的影响进行了表征。此外，还研究了微凝胶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性，为在基于温度响应性微凝胶的平台中调节流变学特性开辟了途径。因此，这项工作展望了药物递送、组织工程和诊断工具等不同领域的技术进步。
