Stimuli-responsive materials have attracted great interest in catalysis, sensing, and drug delivery applications and are typically constituted by soft components. We present a one-pot synthetic method for a type of inorganic silica-based shape change material that is responsive to water vapor exposure. After the wetting treatment, the cross-sectional shape of aminated mesoporous silica nanoparticles (MSNs) with hexagonal pore lattice changed from hexagonal to six-angle-star, accompanied by the loss of periodic mesostructural order. Nitrogen sorption measurements suggested that the wetting treatment induced a shrinkage of mesopores resulting in a broad size distribution and decreased mesopore volume. Solid-state ²⁹Si nuclear magnetic resonance (NMR) spectroscopy of samples after wetting treatment displayed a higher degree of silica condensation, indicating that the shape change was associated with the formation of more siloxane bonds within the silica matrix. On the basis of material characterization results, a mechanism for the observed anisotropic shrinkage is suggested based on a buckling deformation induced by capillary forces in the presence of a threshold amount of water vapor available beyond a humidity of about 50%. The work presented here may open a path toward novel stimuli-responsive materials based on inorganic components.

中文翻译：

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刺激响应的变形中孔二氧化硅纳米粒子

刺激响应材料在催化，传感和药物输送应用中引起了极大的兴趣，通常由柔软的成分构成。我们提出一种响应于水蒸气暴露的无机二氧化硅基形状变化材料的一锅法合成方法。润湿处理后，具有六边形孔晶格的胺化介孔二氧化硅纳米颗粒（MSNs）的截面形状从六边形变为六角星形，并伴随着周期性的介观结构顺序的损失。氮吸附测量表明，润湿处理引起中孔收缩，从而导致较宽的尺寸分布和减小的中孔体积。固态²⁹润湿处理后的样品的Si核磁共振（NMR）光谱显示出较高的二氧化硅凝结度，这表明形状变化与二氧化硅基质中更多硅氧烷键的形成有关。根据材料的表征结果，提出了一种观察到的各向异性收缩的机理，该机理是基于在超过50％的湿度下可利用的阈值水蒸气的存在下，由毛细作用力引起的屈曲变形。本文介绍的工作可能会开辟一条通往基于无机成分的新型刺激反应材料的道路。