Light Scattering - Hikarisanran

[ I ] Light is scattered by particles. This method uses the phenomenon of light scattering to measure the molecular weight (particle amount), size, shape, etc. of polymer or colloid particles. In a solution, the presence of solute molecules causes density fluctuations, i.e., fluctuations in the refractive index, and the incident light is scattered. If the refractive index of the solution is n and the concentration is c , the molecular weight can generally be determined by measuring dn / dc and the scattered light intensity when the value of c is changed. The second Virial coefficient, which indicates the degree of interaction between solute molecules in a solution, can also be determined. This method has the advantage of being able to simultaneously measure the molecular weight, molecular size (mean square radius), and intermolecular interactions in a single method, making it an effective tool in the research of polymers and colloidal solutions. [ II ] This method uses light scattering by suspended particles in the air to measure their amount. Air containing suspended particles is introduced into a dark box, a light beam is irradiated onto it, and the intensity of the scattered light is measured. In this case, the scattered light is weak, so instead of directly amplifying the current generated in the photomultiplier tube, it is pulsed and measured as the number of pulses generated per unit time. Measuring devices that use this method are commercially available under the name of digital dust meters. The basic method of measuring suspended particulate matter in the air is to measure the weight of particulate matter collected by filtration from the air, but as this is a complicated process, this light scattering method is widely used for automatic measurement of air pollution.

Source: Morikita Publishing "Chemical Dictionary (2nd Edition)" Information about the Chemical Dictionary 2nd Edition

【Ⅰ】光は粒子によって散乱を受ける．その光散乱の現象を利用して，高分子あるいはコロイド粒子の分子量(粒子量)，大きさ，形などを測定する方法である．溶液中では溶質分子が存在することによって密度のゆらぎ，すなわち屈折率のゆらぎが起こり，入射光は散乱される．溶液の屈折率をn，濃度をcとし，dn/dcの測定とcの値をいろいろ変えた場合の散乱光強度の測定から，一般に分子量が求められる．また，溶液中における溶質分子間の相互作用の程度を表す第二ビリヤル係数も求めることができる．この方法は分子量，分子の大きさ(平均二乗半径)，分子間の相互作用を一つの方法で同時に測定できる利点があり，高分子やコロイド溶液の研究において有効な手段となっている．【Ⅱ】大気中の浮遊粒子による光散乱を利用して，その量を測定する方法．浮遊粒子を含む大気を暗箱内に導入，これに光のビームを照射し，散乱された光の強さを測定する．この場合，散乱光は微弱であるので，光電子増倍管に生じた電流を直接増幅するのではなく，これをパルス化し，単位時間に生じるパルスの数として計測する．この方法による測定器はデジタル粉じん計という名で市販されている．大気中の浮遊粒子状物質の測定は，大気から濾過捕集したものの重量測定が基本となるが，操作が煩雑なので，この光散乱法が大気汚染の自動測定に広く利用されている．

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