初探軟顆粒懸浮液流變學：自製流變儀

Abstract

為了研究巨觀軟顆粒懸浮液的流變學性質，將荷重元搭配一個可用程式控制的步進馬達驅動近似雙錐邊界造形的壓克力齒盤，成為一個自製的流變儀，我檢視了儀器在力訊號量測以及馬達在施以材料應變上的的性質與限制。實驗以凝膠球和與其密度匹配的溶液形成不受熱擾動影響，且軟顆粒緊密堆積的懸浮液系統，並且進行實驗量測凝膠球本身的彈性以及體積大小。 初步研究成果包括：在數個不同的體積百分率下，先施以材料一個不為零的剪切速率，接著突然停止外加的剪切速率，觀察材料如何從處於流動的非平衡態，鬆弛到靜止的過程。即使等待數天，軟顆粒材料的應力仍然無法完全歸零，會有殘餘應力留下；同時，觀察在此鬆弛過程中應力隨時間的變化，對照系統在定轉速下的穩態應力，試圖釐清在軟顆粒的懸浮液系統中的時間尺度。

To study the rheology of non-Brownian soft particle suspension system, we construct a rheometer with load cells and a stepping motor. The system drives the material with its double-cone geometry made by acrylic plates. We examined the features of force measurement and the constraints of driving system. Gigantic hydrogel particles with density-matched solution forms the suspension system, where the mechanical properties of hydrogel particles are measured.

After the cessation of flows, material relaxes from non-equilibrium steady state to a quasi-static state. The rheology response of material over few volume fractions is investigated. I observed that the residual stresses are non-zero even after long time waiting. Also, comparing the relaxation process with the non-equilibrium steady state measurements, we try to understand the time scales involved in soft particles suspension.