Department of Chemical Engineering and Center for Molecular and Engineering Thermodynamics, University of Delaware, 150 Academy Street, Newark, Delaware 19716, USA.
Nanoscale. 2010 Oct;2(10):2237-43. doi: 10.1039/c0nr00275e. Epub 2010 Aug 12.
Nanostructured thin films are fabricated by directing the assembly of anisotropic titanium dioxide particles from a colloidal suspension by fixed blade flow coating. The titania particles (equatorial radius a = 24 ± 4 nm, polar radius b = 130 ± 31 nm, aspect ratio b/a = 5.4 ± 0.9) undergo an isotropic-nematic (I-N) transition at a volume fraction ϕ* ≈ 0.40. For ϕ > ϕ* the deposited film has three structures depending on the substrate velocity, v. At a blade angle α = 25° and a gap d = 200 μm, nanoparticles orient either isotropically in the direction of the coating flow (v≥ 350 μm s(-1)), exhibit partially oriented "wavy" structures (100 < v < 300 μm s(-1)), or are isotropically oriented (v < 100 μm s(-1)). Below the I-N transition (ϕ < ϕ*), nanoparticles assemble into domains of uniform orientation with dimensions that increase with increasing v. Increasing the blade angle shifts these structural transitions to lower substrate velocities, consistent with an increasing extensional component of the flow. Established scaling relationships describe the film height dependence on ϕ and v. Overall, these results enable nanostructured films to be deposited with desired thickness and structure.
通过固定刀片流涂法引导各向异性二氧化钛粒子从胶体悬浮液中组装，制备了纳米结构薄膜。这些二氧化钛粒子（赤道半径 a = 24 ± 4 nm，极半径 b = 130 ± 31 nm，纵横比 b/a = 5.4 ± 0.9）在体积分数 ϕ*≈0.40 时经历各向同性-向列（I-N）转变。对于 ϕ>ϕ*，沉积的薄膜具有三种结构，这取决于基底速度 v。在叶片角度 α = 25°和间隙 d = 200 μm 时，如果纳米颗粒在涂层流动方向上各向同性排列（v≥350 μm s(-1))，则表现出部分取向的“波浪”结构（100 < v < 300 μm s(-1))，或者各向同性排列（v < 100 μm s(-1))。在 I-N 转变以下（ϕ<ϕ*），纳米颗粒组装成具有均匀取向的畴，其尺寸随 v 的增加而增加。增加叶片角度将这些结构转变转移到较低的基底速度，这与流动的拉伸分量增加一致。已建立的比例关系描述了膜高对 ϕ 和 v 的依赖性。总的来说，这些结果使得可以用所需的厚度和结构来沉积纳米结构薄膜。
