Callejas-Fernández J, Ramos J, Forcada J, Moncho-Jordá A
Grupo de Física de Fluidos y Biocoloides, Departamento de Física Aplicada, Facultad de Ciencias, Universidad de Granada, E-18071 Granada, Spain.
Department of Materials, Department of Bioengineering, and the Institute for Biomedical Engineering, Imperial College London, London SW7 2AZ, United Kingdom; POLYMAT, Bionanoparticles Group, Departamento de Química Aplicada, UFI/56, Facultad de Ciencias Químicas, Universidad del País Vasco UPV/EHU, Apdo. 1072, 20080 Donostia-San Sebastián, Spain.
J Colloid Interface Sci. 2015 Jul 15;450:310-315. doi: 10.1016/j.jcis.2015.03.031. Epub 2015 Mar 20.
This work deals with the scattered light by nanoparticles formed by a temperature sensitive polymer networks, namely nanogel particles. The scattered light is measured as a function of the scattering angle at temperatures below and above the volume phase transition temperature (VPTT) of nanogel particles. Our experimental results indicate that nanogel particles have a core-shell structure, formed by a uniform highly cross-linked core surrounded by a fuzzy shell where the polymer density decays to zero gradually for swollen configurations and sharply for shrunken states. The theoretical fitting of the experimental curves shows that the scattered light at low angle obeys a decreasing power law with the scattering vector, q(-α). The value of exponent α provides information about the radial dependence of the polymer density at the external shell of the particles for swollen nanogels, and about the degree of roughness of the surface for the case of shrunken nanogels. On the one hand, at low temperatures (below the VPPT), the nanogel particle is in the swollen state and the light scattering data show that its shell structure follows a fractal behaviour, with a polymer density that decays as r(α-3), where r is the distance to the particle centre. On the other hand, above the VPPT the results indicate that nanogel collapses into a core of uniform polymer density and a rough shell, with a fractal surface dimension of 2.5.
这项工作研究了由温度敏感聚合物网络形成的纳米颗粒（即纳米凝胶颗粒）产生的散射光。在低于和高于纳米凝胶颗粒的体积相变温度（VPTT）的温度下，测量散射光随散射角的变化。我们的实验结果表明，纳米凝胶颗粒具有核壳结构，由均匀的高度交联的核和模糊的壳组成，在膨胀状态下聚合物密度逐渐衰减至零，在收缩状态下则急剧衰减至零。实验曲线的理论拟合表明，低角度散射光服从散射矢量q（-α）的幂律衰减。指数α的值提供了关于膨胀纳米凝胶颗粒外壳聚合物密度的径向依赖性以及收缩纳米凝胶颗粒表面粗糙度的信息。一方面，在低温（低于VPPT）下，纳米凝胶颗粒处于膨胀状态，光散射数据表明其壳结构呈现分形行为，聚合物密度随r（α-3）衰减，其中r是到颗粒中心的距离。另一方面，在VPPT以上，结果表明纳米凝胶坍缩成聚合物密度均匀的核和粗糙的壳，分形表面维数为2.5。
