Institute of Physical Chemistry, RWTH Aachen University, Landoltweg 2, D-52056 Aachen, Germany.
Langmuir. 2010 Jul 6;26(13):11258-65. doi: 10.1021/la100579b.
Two sets of core-shell microgels composed of temperature-sensitive poly(N-isopropylacrylamide) (PNiPAM) with different spatial distribution of pH-sensitive methacrylic acid (MAA) groups were prepared. The cores consist of either PNiPAM (neutral core; nc) or PNiPAM-co-MAA (charged core; cc). A charged shell existing of PNiPAM-co-MAA was added to the neutral core (yielding neutral core-charged shell; nccs), on the charged core, on the other hand, a neutral shell of PNiPAM was added (charged core-neutral shell; ccns). Complexes of these microgels with positively charged poly(diallyldimethylammonium chloride) (PDADMAC) of different molar masses were prepared. The amount of bound polyelectrolyte was quantified, and the microgel-polyelectrolyte complexes were characterized with respect to electrophoretic mobility and hydrodynamic radius. The penetration of polyelectrolyte into the microgel was also monitored by means of lifetime analysis of a fluorescent dye covalently bound to poly(L-lysine) providing information on the probe's local environment. The architecture of the microgel has a significant influence on the interaction with oppositely charged polyelectrolyte. Complexes with microgel with the charged shell tend to flocculate at charge ratios of 1 and are thus similar to polyelectrolyte complexes with rigid colloidal particles. Complexes with microgels that consist of a charged core and a neutral shell show very different properties: They are still temperature sensitive and reveal an influence of the polyelectrolyte's chain length. Low molecular weight PDADMAC can penetrate through the neutral shell into the charged core, and thus nearly no charge reversal occurs. The high-MW polyelectrolyte does not penetrate fully and leads to charge reversal. The results demonstrate that microgels are able to absorb or adsorb polyelectrolytes depending on the polyelectrolyte's chain length and the microgels architecture. Complexes with different surface properties and different colloidal stability can be prepared, and polyelectrolytes can be encapsulated in the microgel core. Thus, multisensitive core-shell microgels combine permeability and compartmentalization on a nanometer length scale and provide unique opportunities for applications in controlled uptake and release.
两组由温敏性聚（N-异丙基丙烯酰胺）（PNiPAM）组成的核壳微凝胶，其 pH 敏感染料甲基丙烯酸（MAA）的空间分布不同。核由 PNiPAM（中性核；nc）或 PNiPAM-co-MAA（带电核；cc）组成。在中性核上添加了带电荷的壳层，即 PNiPAM-co-MAA（中性核-带电荷壳层；nccs），另一方面，在带电荷核上添加了中性壳层 PNiPAM（带电荷核-中性壳层；ccns）。制备了这些微凝胶与不同摩尔质量的带正电荷的聚二烯丙基二甲基氯化铵（PDADMAC）的复合物。定量了结合的聚电解质的量，并对微凝胶-聚电解质复合物的电泳迁移率和水动力半径进行了表征。通过共价结合到聚（L-赖氨酸）上的荧光染料的寿命分析来监测聚电解质向微凝胶中的渗透，提供了探针局部环境的信息。微凝胶的结构对与带相反电荷的聚电解质的相互作用有显著影响。带有带电壳层的微凝胶的复合物在电荷比为 1 时倾向于絮凝，因此类似于带刚性胶体颗粒的聚电解质复合物。由带电荷核和中性壳组成的微凝胶的复合物表现出非常不同的性质：它们仍然对温度敏感，并显示出聚电解质链长的影响。低分子量 PDADMAC 可以通过中性壳渗透到带电荷的核中，因此几乎不会发生电荷反转。高分子量的聚电解质不能完全穿透，导致电荷反转。结果表明，微凝胶能够根据聚电解质的链长和微凝胶的结构吸收或吸附聚电解质。可以制备具有不同表面性质和不同胶体稳定性的复合物，并可以将聚电解质封装在微凝胶核中。因此，具有多敏感性的核壳微凝胶在纳米尺度上结合了渗透性和分隔性，并为在控制摄取和释放方面的应用提供了独特的机会。
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