Molecular association in solution controlled by photon pressure of a focused laser beam

我们研究了近红外激光聚焦产生的光子压力诱导的一种新现象：纳米胶体粒子如聚合物、超微粒子和胶束被捕获形成单个μ m大小的粒子。这种激光操纵可以扩展到在一种新的光子压力扰动下形成分子组装结构。用激光捕获光谱法研究了各种胶体粒子，得到了以下有趣的结果。聚焦光束的光子压力克服了带电聚合物胶束之间的静电排斥。胶体的最小尺寸可以被捕获的聚焦激光束被确定为12 nm，而分子极化率被证明是一个负责任的参数。化学和光学机制可以很好地解释纳米胶体粒子的聚集和随后形成的微米级粒子。所形成的微粒具有类似橄榄球的形状，在其周围通过水分子中的有效光热转换产生温度梯度。因此，我们提出了一种利用纳秒级紫外激光诱导瞬时熔融将其固定在聚合物基体上的新方法。

We have studied a new phenomenon induced by photon pressure due to a focused near infrared laser beam; a single μm-sized particle is formed by trapping nm colloid particles such as polymer, ultramicroparticle, and micelles. This laser manipulation can be extended to form molecular assembly structure under a novel perturbation of photon pressure. By investigating various colloid particles with laser trapping-spectroscopy methods, the following interesting results have been obtained. Photon pressure of a focused beam overcomes electrostatical repulsion between charged polymer micelles. The minimum size of colloid which can be trapped by the focused laser beam is determined to be 12 nm, while molecular polarizability was demonstrated to be a responsible parameter. Chemical and optical mechanism can explain well gathering of nm colloid particles and the following formation of a μm-sized particle. The formed microparticle has a shape like a rugby ball, around which temperature gradient is produced by efficient photothermal conversion in water molecules. The trapped microparticles disappear when the focused laser beam is switched off, so that we have proposed a new method to fix it on polymer substrate by nanosecond UV-laser induced transient melting.