단분산 실리카 입자를 제조하여 실리카 분산액이 가지는 광유변학적 거동을 해석하였다.Stober등이 개발한 솔젤법을 이용하여 단분산의 실리카 입자가 제조되었으며 암모늄 수용액의 농도를 변화시키면서 입자의 최종 크기를 조절할 수 있었다. 또,실리카와 같은 굴절률을 가진 에틸렌글리콜과 글리세린의 50:50 혼합물을 분산매로 이용하여 투명한 분산액을 제조할 수 있었다. 실리카 입자의 질량백분율이 30%와 50%인 분산액 모두 비뉴톤거동인 전단담화(shear thinning) 현상을 보였으며 입자의 농도가 증가할수록 이러한 경향은 더욱 뚜렷하였다. 고안된 두 개의 광학배열을 이용하여 유체의 흐름에 의하여 분산계가 가지는 이색도(dichroism)를 측정하였으며 이를 이용하여 이색도와 복굴절(birefringence)을 모두 가지는 시료의 시료의 광유변학적 물성 측정 가능성을 확인하였다. 측정된 이색도는 30% 분산계의 경우 입자의 크기에 커다란 영향없이 비슷한 거동을 나타내었으며 흐름장의 세기가 증가할수록 분산액의 미세구조 변화가 커짐을 확인하였다. 질량백분율 50% 분산액의 경우 미세구조의 변화는 더욱 복잡해져서 전단율의 변화에 따른 이색도 부호의 변화와 함께 복잡한 완화거동을 보여주었다. 이는 분산액 내에서 입자들이 응집체(cluster)와 같은 미세영역을 형성한다는 것을 보여주며 이는 이색도 측정과 흐름상의 정지시에 나타나는 다중산란현상을 통해서 확인되었다.

Rheo-optical behaviors of dispersions of monodispersed silica particles were investigated. Monodispersed silica was prepared by the sol-gel method proposed by Stober et al. and the final particle size was obtained through the control of ammonium hydroxide concentration. Also, the transparent dispersion was prepared by dispersing the silica particles in the index-matching solvent which was composed of 50 : 50 mixture of ethylene glycol and glycerin. All silica dispersions of 30% and 50% by weight exhibited the non-Newtonian behaviors such as shear thinning although they were dispersed in Newtonian medium. Furthermore, the deviation from Newtonian behavior was pronounced when the particle concentration was increased. With two different optical alignments designed in the present study, the flow-induced dichroism was measured. And the simultaneous detection of the dichroism and birefringence was shown to be possible for the sample which possesses both of the rheo-optical properties. The measured dichroisms for 30% dispersions showed that the microstructure evolution was enhanced especially at high shear rates. For 50% dispersion, the microstructural transition becomes more complicated and the sign of dichroism was changed with long relaxation behaviors. This is owing to the formation of micro-domain as cluster in microscale. The result was also checked by dichroism and multiple scattering after flow cessation.

Silica Dispersion Shear Thinning Rheo-Optics Dichroism Microstructure Evolution

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