刺激响应性微凝胶最近在基础研究中引起了极大的关注,因为它们的软颗粒可以在高填充分数下变形和压缩,从而导致奇异相行为。此外,它们也非常适合各种应用,如药物输送,组织工程,器官芯片设备,微透镜制造和文化遗产。这里,热响应和pH敏感的交联微凝胶,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,通过沉淀聚合法在水中合成,并通过差示扫描量热法在PNIPAM微凝胶的体积相变温度范围内进行研究。研究了相行为与加热/冷却速率的关系,浓度,pH和PAAc含量。在低浓度和PAAc含量下,与以前的研究一致,网络互穿不会影响PNIPAM微凝胶的典型转变温度;相反,我们表明,它诱导在较高浓度下显著下降。DSC分析还揭示了总热焓随浓度增加而增加,随PAAc含量增加而降低。这些发现被讨论和解释为与新兴的聚集过程有关,这些聚集过程可以通过适当改变浓度来进行精细控制。PAAc含量和pH。对热力学参数的深入分析可以在所研究的浓度范围内绘制温度-浓度状态图。
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(N-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.