Franco Silvia, Buratti Elena, Nigro Valentina, Bertoldo Monica, Ruzicka Barbara, Angelini Roberta
Department of Basic and Applied Sciences for Engineering, Sapienza University of Rome, Via Antonio Scarpa 14, 00161 Roma, Italy.
Institute of Complex Systems (ISC-CNR), Sede Sapienza, Piazzale Aldo Moro 2, 00185 Roma, Italy.
Polymers (Basel). 2021 Dec 29;14(1):115. doi: 10.3390/polym14010115.
Stimuli-responsive microgels have recently attracted great attention in fundamental research as their soft particles can be deformed and compressed at high packing fractions resulting in singular phase behaviours. Moreover, they are also well suited for a wide variety of applications such as drug delivery, tissue engineering, organ-on-chip devices, microlenses fabrication and cultural heritage. Here, thermoresponsive and pH-sensitive cross-linked microgels, composed of interpenetrating polymer networks of poly(-isopropylacrylamide) (PNIPAM) and poly(acrylic acid) (PAAc), are synthesized by a precipitation polymerization method in water and investigated through differential scanning calorimetry in a temperature range across the volume phase transition temperature of PNIPAM microgels. The phase behaviour is studied as a function of heating/cooling rate, concentration, pH and PAAc content. At low concentrations and PAAc contents, the network interpenetration does not affect the transition temperature typical of PNIPAM microgel in agreement with previous studies; on the contrary, we show that it induces a marked decrease at higher concentrations. DSC analysis also reveals an increase of the overall calorimetric enthalpy with increasing concentration and a decrease with increasing PAAc content. These findings are discussed and explained as related to emerging aggregation processes that can be finely controlled by properly changing concentration, PAAc content an pH. A deep analysis of the thermodynamic parameters allows to draw a temperature-concentration state diagram in the investigated concentration range.
刺激响应性微凝胶最近在基础研究中备受关注，因为其软颗粒在高填充率下可发生变形和压缩，从而产生奇异的相行为。此外，它们还非常适用于多种应用，如药物递送、组织工程、芯片器官装置、微透镜制造和文化遗产保护。在此，通过在水中的沉淀聚合法合成了由聚（N-异丙基丙烯酰胺）（PNIPAM）和聚丙烯酸（PAAc）的互穿聚合物网络组成的热响应性和pH敏感性交联微凝胶，并通过差示扫描量热法在跨越PNIPAM微凝胶体积相变温度的温度范围内进行了研究。研究了相行为作为加热/冷却速率、浓度、pH值和PAAc含量的函数。在低浓度和PAAc含量下，网络互穿并不影响PNIPAM微凝胶典型的转变温度，这与先前的研究一致；相反，我们表明在较高浓度下它会导致显著降低。DSC分析还表明，随着浓度的增加，总热焓增加，而随着PAAc含量的增加而降低。这些发现被讨论并解释为与新兴的聚集过程有关，这些过程可以通过适当改变浓度、PAAc含量和pH值进行精细控制。对热力学参数的深入分析允许在研究的浓度范围内绘制温度-浓度状态图。
