Heng Jerry Y Y, Thielmann Frank, Williams Daryl R
Department of Chemical Engineering, Imperial College London, South Kensington Campus, London, SW7 2AZ, UK.
Pharm Res. 2006 Aug;23(8):1918-27. doi: 10.1007/s11095-006-9042-1.
The effects of milling and particle size on surface energies of form I paracetamol crystals are reported.
Paracetamol crystals (75-850 microm) were obtained by cooling methanol and acetone saturated solutions. Additionally, macroscopic (>2 cm) single crystals were grown by slow solvent evaporation from saturated solutions, ball milled and sieved into different particle size fractions. Surface properties were characterised using Inverse Gas Chromatography and compared with those calculated from sessile drop contact angle measurements on macroscopic single crystals.
Dispersive surface energies, gamma(d)SV for milled samples increased by 20% with decreasing particle size. With decreasing particle size acceptor numbers, KA values were constant but donor numbers, KB decreased. For unmilled materials KB was comparable to KA but with a significantly lower gamma(d)SV of only 33 mJ/m(2). Milling resulted in fracture along the crystal's lowest attachment energy plane (010), exposing facets of different surface chemistry to that of the native external facets theta for the (010) fracture plane confirmed a higher gamma(d)SV compared to external facets such as (011) of single crystals.
Milling exposes a hydrophobic surface for paracetamol form I crystals which becomes increasingly more dominant with decreasing particle size.
报道研磨和粒径对I型扑热息痛晶体表面能的影响。
通过冷却甲醇和丙酮饱和溶液获得粒径为75 - 850微米的扑热息痛晶体。此外，通过从饱和溶液中缓慢溶剂蒸发法生长出宏观尺寸（>2厘米）的单晶，进行球磨并筛分成不同粒径级分。使用反相气相色谱法表征表面性质，并与通过宏观单晶上的座滴接触角测量计算得到的表面性质进行比较。
研磨样品的色散表面能γ(d)SV随着粒径减小增加了20%。随着粒径减小，受体数KA值保持不变，但给体数KB减小。对于未研磨的材料，KB与KA相当，但γ(d)SV显著更低，仅为33 mJ/m²。研磨导致晶体沿最低附着能平面（010）断裂，使不同表面化学性质的晶面暴露于天然外晶面，对于（010）断裂面，与单晶的（011）等外晶面相比，证实其γ(d)SV更高。
研磨使I型扑热息痛晶体暴露出疏水表面，且随着粒径减小，这种疏水表面变得越来越占主导。
