Department of Chemistry, University of California, Irvine, California 92697-2025, USA.
J Phys Chem B. 2010 Feb 25;114(7):2435-49. doi: 10.1021/jp909661q.
Several complementary experimental and theoretical methodologies were used to explore water uptake on sodium chloride (NaCl) particles containing varying amounts of sodium dodecyl sulfate (SDS) to elucidate the interaction of water with well-defined, environmentally relevant surfaces. Experiments probed the hygroscopic growth of mixed SDS/NaCl nanoparticles that were generated by electrospraying aqueous 2 g/L solutions containing SDS and NaCl with relative NaCl/SDS weight fractions of 0, 5, 11, 23, or 50 wt/wt %. Particles with mobility-equivalent diameters of 14.0(+/-0.2) nm were size selected and their hygroscopic growth was monitored by a tandem nano-differential mobility analyzer as a function of relative humidity (RH). Nanoparticles generated from 0 and 5 wt/wt % solutions deliquesced abruptly at 79.1(+/-1.0)% RH. Both of these nanoparticle compositions had 3.1(+/-0.5) monolayers of adsorbed surface water prior to deliquescing and showed good agreement with the Brunauer-Emmett-Teller and the Frenkel-Halsey-Hill isotherms. Above the deliquescence point, the growth curves could be qualitatively described by Kohler theory after appropriately accounting for the effect of the particle shape on mobility. The SDS/NaCl nanoparticles with larger SDS fractions displayed gradual deliquescence at a RH that was significantly lower than 79.1%. All compositions of SDS/NaCl nanoparticles had monotonically suppressed mobility growth factors (GF(m)) with increasing fractions of SDS in the electrosprayed solutions. The Zdanovskii-Stokes-Robinson model was used to estimate the actual fractions of SDS and NaCl in the nanoparticles; it suggested the nanoparticles were enhanced in SDS relative to their electrospray solution concentrations. X-ray photoelectron spectroscopy (XPS), FTIR, and AFM were consistent with SDS forming first a monolayer and then a crystalline phase around the NaCl core. Molecular dynamics simulations of water vapor interacting with SDS/NaCl slabs showed that SDS kinetically hinders the initial water uptake. Large binding energies of sodium methyl sulfate (SMS)-(NaCl)(4), H(2)O-(NaCl)(4), and SMS-H(2)O-(NaCl)(4) calculated at the MP2/cc-pVDZ level suggested that placing H(2)O in between NaCl and surfactant headgroup is energetically favorable. These results provide a comprehensive description of SDS/NaCl nanoparticles and their properties.
采用了几种互补的实验和理论方法来研究含有不同量十二烷基硫酸钠 (SDS) 的氯化钠 (NaCl) 颗粒对水的吸收，以阐明水与明确定义的、与环境相关的表面的相互作用。实验探测了通过电喷雾法生成的混合 SDS/NaCl 纳米颗粒的吸湿生长，这些纳米颗粒是由含有 SDS 和 NaCl 的 2 g/L 水溶液生成的，其中 NaCl/SDS 重量比为 0、5、11、23 或 50 wt/wt%。具有 14.0(+/-0.2)nm 迁移率等效直径的颗粒被尺寸选择，并通过串联纳米差分迁移率分析仪作为相对湿度 (RH) 的函数来监测其吸湿生长。从 0 和 5 wt/wt%溶液生成的纳米颗粒在 79.1(+/-1.0)%RH 时突然潮解。这两种纳米颗粒成分在潮解前都有 3.1(+/-0.5)个单层吸附表面水，并且与 Brunauer-Emmett-Teller 和 Frenkel-Halsey-Hill 等压吸附等温线吻合良好。在潮解点以上，生长曲线可以通过 Kohler 理论进行定性描述，前提是适当考虑了颗粒形状对迁移率的影响。具有较大 SDS 分数的 SDS/NaCl 纳米颗粒在明显低于 79.1%RH 的 RH 下显示出逐渐潮解。在电喷雾溶液中 SDS 分数增加时，所有 SDS/NaCl 纳米颗粒的迁移率增长因子 (GF(m)) 都呈单调抑制。Zdanovskii-Stokes-Robinson 模型用于估计纳米颗粒中 SDS 和 NaCl 的实际分数；结果表明，与电喷雾溶液浓度相比，纳米颗粒中 SDS 的相对含量增加了。X 射线光电子能谱 (XPS)、傅里叶变换红外光谱 (FTIR) 和原子力显微镜 (AFM) 一致表明 SDS 首先在 NaCl 核周围形成单层，然后形成结晶相。水分子与 SDS/NaCl 片相互作用的分子动力学模拟表明，SDS 在动力学上阻碍了初始水的吸收。在 MP2/cc-pVDZ 水平上计算的甲基硫酸甲酯 (SMS)-(NaCl)(4)、H(2)O-(NaCl)(4)和 SMS-H(2)O-(NaCl)(4)的大结合能表明，将 H(2)O 置于 NaCl 和表面活性剂头基之间在能量上是有利的。这些结果提供了 SDS/NaCl 纳米颗粒及其性质的全面描述。
