Kim Jaehoon, Carbonell Ruben G
Department of Chemical and Biomolecular Engineering, North Carolina State University, Raleigh, North Carolina 27606-7905, USA.
Langmuir. 2006 Feb 28;22(5):2117-29. doi: 10.1021/la052625m.
A new coating process is described (deposition from two immiscible supercritical phases, or DISP) in which a solution of supercritical carbon dioxide (scCO2) with a desired solute is displaced by supercritical helium (scHe). After depressurization, the solute is deposited on substrates initially submerged in the coating solvent. Micron-sized particles and thin films of sucrose octaacetate (SOA) were formed on silicon wafer substrate coupons from DISP at relatively low temperatures and pressures (< or = 6500 psi and < or = 60 degrees C). The particle size, film thickness, and morphology of SOA were characterized as a function of coating conditions-solution concentrations, withdrawal velocities, and pressures. Particles in the range of 1-14 microm in diameter were deposited at low solute concentrations (< or = 0.2 wt % at 4500 psi), whereas films in the range of 0.1-0.5 microm in thickness were deposited at higher solute concentrations (> or = 1.5 wt % at 4500 psi). Particle sizes decreased with increasing displacement velocity and increasing pressure. Estimates of characteristic times for diffusion and nucleation indicate that DISP is a diffusion-limited process. Optical microscopy and atomic force microscopy (AFM) were used to characterize film morphology, including defect formations and film roughness. Highly uniform films with low root-mean-square (RMS) roughness (approximately 10 angstroms) were obtained at a low displacement velocity of 0.0035 cm/s, while ring-like defect structures were observed in films deposited at a higher displacement velocity of 0.035 cm/s. The film thickness and morphology of the films deposited from DISP were compared with films from normal dip coating with typical organic solvents (acetone and toluene). Films deposited from scCO2 by DISP were much thicker, more uniform, and exhibited much fewer drying defects and lower RMS roughness compared with films from the organic solvents.
本文描述了一种新的涂层工艺（从两个不混溶的超临界相进行沉积，即DISP），其中含有所需溶质的超临界二氧化碳（scCO2）溶液被超临界氦（scHe）置换。减压后，溶质沉积在最初浸没于涂层溶剂中的基材上。在相对较低的温度和压力（≤6500 psi且≤60℃）下，通过DISP在硅片基材试样上形成了微米级的蔗糖八乙酸酯（SOA）颗粒和薄膜。对SOA的粒径、膜厚和形态进行了表征，作为涂层条件（溶液浓度、提拉速度和压力）的函数。在低溶质浓度（4500 psi下≤0.2 wt%）时沉积的颗粒直径在1 - 14微米范围内，而在较高溶质浓度（4500 psi下≥1.5 wt%）时沉积的膜厚在0.1 - 0.5微米范围内。粒径随置换速度和压力的增加而减小。扩散和成核特征时间的估计表明，DISP是一个扩散受限过程。使用光学显微镜和原子力显微镜（AFM）对膜形态进行表征，包括缺陷形成和膜粗糙度。在0.0035 cm/s的低置换速度下获得了具有低均方根（RMS）粗糙度（约10埃）的高度均匀的膜，而在0.035 cm/s的较高置换速度下沉积的膜中观察到环状缺陷结构。将通过DISP沉积的膜的膜厚和形态与用典型有机溶剂（丙酮和甲苯）进行常规浸涂得到的膜进行了比较。与有机溶剂得到的膜相比，通过DISP从scCO2沉积的膜更厚、更均匀，干燥缺陷更少，RMS粗糙度更低。
